Äîêóìåíò âçÿò èç êýøà ïîèñêîâîé ìàøèíû. Àäðåñ îðèãèíàëüíîãî äîêóìåíòà : http://www.naic.edu/~newslet/no34/NAICNo34.pdf Äàòà èçìåíåíèÿ: Wed Mar 20 16:55:28 2002 Äàòà èíäåêñèðîâàíèÿ: Tue Oct 2 04:36:05 2012 Êîäèðîâêà: Ïîèñêîâûå ñëîâà: comet holmes

N AT I O N A L A ST

R

Y AND IO NO OM ON S

ENTER EC ER PH

AR EC RY IB O TO O B S E R VA

March 2002, Number 34
Photo: David Parker, 1997/Science Photo Library

Gravitational-Lens VLBI using the Arecibo Telescope Richard Porcas, MPIfR, Bonn

I

am a lucky man! On 25th January, I received a DAT tape from the VLBA correlator in Socorro containing 1.95 Gbytes of "Global" VLBI data. The observations in question -- project GP030A -- consist of an 18-station VLBI run on the gravitational lens system 2016+112, made at 5 GHz in November 2001. The project was initiated in February 2000, when Michael Garrett, Alok Patnaik, Sunita Nair and I decided that the time was ripe for a
50 40 30 20 10 0 MilliJanskys SC - AR ( 9 - 10 )

"definitive" high-resolution study of this interesting system using the soon-to-beoperational Arecibo VLBA4 recording terminal. Alas, we had to weather delays in its delivery (actually, we had to resubmit the proposal in June 2001 because it had gone "stale"!) before scheduling last November became possible. This gravitational lens system has always been something of a puzzle. There are 3 image "regions" (A,B,C) spread over an area of 4 arcseconds. Previous VLBI observations (see, e.g., Garrett et al., 1996, MNRAS, 279, L7) reveal that A and B are both images of a single radio source, produced by bending and delay

of the ray paths as they traverse the intense gravitational field of a massive galaxy a few arcseconds to the south. Region C breaks up into at least 4 distinct components, aligned along a gently curving arc of length 200 milliarcsec. It is presumed that this region contains the "merging images" of (almost) another 2 images of the same source, making this system a (nearly) 4-image "quad" system. Howeve r, the details of the relationship between

INDEX
Gravitational-Lens VLBI ................ Pre-Doctoral Program ..................... IEEE/ASME Recognition ................ Primary Adjustments Update ......... Astronomy Highlights ...................... Solar System Studies ........................ Space and Atmospheric Sciences .... Computer Department News ......... Wolszczan on new Polish Stamp ..... Service & Queue Observing ........... Telescope Operations ....................... Astronomy Job Opening .................. New North VSQs .............................. Employee of the Year ....................... Comings & Goings ........................... Alert for 1176 MHz Observers .... X-Band HC3N Detection! ................ Recent Colloquia .............................. Proposal Deadline ............................ Notes to Observers ........................... Hot News!.......................................... 1 2 3 5 6 1 2 2 2 2 2 2 2 2 2 2 2 2 3 3 3

20 00

30

21 00 TIME (HOURS)

30

22 00

Figure 1: (Upper) The 6-cm fringe amplitude for 2016+112 on the Arecibo-VLBA_Saint Croix baseline. The bandwidth is 16 MHz, the integration time per point is 1 min, and the two circular polarizations are averaged. Note the beating between the three image regions. (Lower) A very preliminary 5-GHz Global VLBI map of 2016+112, region C. (Courtesy: Richard Porcas)

8 0 3 4 4 5 5 5 6 7 8 9 9 0 0 0

The NAIC is operated by Cornell University under a Cooperative Agreement with the National Science Foundation.


images A and B, and their partial counterparts in region C remain unclear; we hope these VLBI observations (another observation at 1.6 GHz was made on February 25th) will shed some light on the matter. It is very gratifying to report that all 18 stations (VLBA, phased-VLA, Arecibo and 6 stations of the EVN) worked successfully during the November observations. The calibration source shows fringes on all 152 baselines (you might think there should be 153, but there was no common scan between VLBA_MK, Hawaii, and Torun, Poland!), including all 17 baselines to Arecibo for the 2.25 hr for which the source was trackable there (Fig 1, upper pane). There are fringes on the gravitational lens source(s) too, but these are harder to see for two reasons. Firstly, the total source flux is around 10 times weaker than the calibrator -- about 70 mJy. But secondly, this is distributed amongst the 3 image regions, which causes very rapid beating in the visibility function on the long, transatlantic baselines -- and bandwidth smearing too if you average across the 16-MHz bandwidth used. Thus, to preserve the total 4 arcsecond field of view for the mapping process, the data must be kept unaveraged in time (1-s samples) and bandwidth (500-kHz samples) -- and this is not so easily viewed!

Because we expect only a very weak signal on long baselines (even those to the highly-sensitive Arecibo), we observed in "phase-reference" mode, so that the instrumental "residuals" (clock errors, phase errors, etc.) could be determined from frequent observations of the calibrator, 2029+121. We used a duty cycle of 6 or 7 minutes -- a compromise which ensured that Arecibo did not spend most of the cycle driving between the program source and the calibrator, whilst hopefully fast enough to track the wandering instrumental phase throughout the observation. Examination of these residuals revealed a surprising result -- the position used at the VLBA correlator for Arecibo was way off! In a world where geodetic VLBI observations are used to measure radio telescope positions to sub-cm accuracy on a routine basis, it is indeed strange to find that the largest radio telescope on Earth was unlocated at the ... 70-m level! My MPI colleague Dave Graham soon derive d a set of X,Y,Z corrections from my data and some other scraps he got hold of -- not quite geodetic standard but probably good at the meter level. In fact, it is very important for these observations since the phase-referencing method fails with bad antenna positions. (Ed. note: We at Arecibo had also become aware of this inaccuracy in the position used for Arecibo in VLBI correlation. Almost simultaneous determinations by Mike Nolan -- via GPS measurements

-- and by Slava Slysh -- from S2 VLBI measurements -- are consistent within the errors with Dave Graham's derived values for X,Y,Z.) So, now begins the up-hill journey of data analysis! Not so easy, as many who have made global VLBI observations can testify. There is amplitude calibration data to be collated and adjusted (for VLBI at milliarcsec resolution we cannot generally rely on "unresolved" calibration sources to calibrate baselines -- so we deduce it from the properties of the individual antennas instead); and there is editing out the data when the telescopes were driving between sources. And plenty of phase and amplitude corrections to worry about. Is there anything to show at this stage? I must confess to having made a crude milliarcsec-resolution image of the gravitational lens from unedited, not-properly-calibrated, blindphase-referenced data. It is the start of a more laborious process of calibration and editing refinement. The map in Fig. 1, lower pane, is a v ery crude representation of region C. Of course, at this stage I cannot identify any specific region in this map which depends on the presence of Arecibo in the VLBI observing network, but one CAN see the 4 distinct components of region C -- a thin band of emission, stretched by the strong gravitational field of the galaxy lens.

Support for Pre-Doctoral Research at the Arecibo Observatory

T

he National Astronomy and Ionosphere Center (NAIC) announces support for doctoral students from any U.S. institution pursuing Ph.D. degrees in the fields of astronomy, planetary science, and space and atmospheric science. This program enables students to pursue their thesis research in residence at Arecibo Observatory. It is a joint effort of NAIC and universities who seek to broaden their academic research program by providing thesis students with a concentrated exposure to research in the above fields and/or the associated instrumentation, and computational techniques. Under this program, and with the consent of their academic departments, the students carry out thesis research in residence at the Arecibo Observatory, under the joint supervision of the student's advisor and an NAIC staff scientist. While in residence at Arecibo Observatory, the students are paid a monthly stipend and are eligible for the Cornell University health and life insurance programs available to NAIC staff in Puerto Rico. There are no application deadlines for the NAIC pre-doctoral research program, applications being accepted throughout the year. On selection, a student may start at his/her convenience, and the duration of the appointment may be from six to twenty-four months, according to the student's needs. Research students in astronomy, planetary science, and space and atmospheric science are encouraged to apply. Further information on this program, can be found at http://www.naic.edu/~astro/predoc.shtml

March 2002, Number 34

2

NAIC/AO N ewsletter


A specially commissioned serigraphy of the Arecibo telescope

Arecibo Observatory Recognized by IEEE, ASME
Daniel R. Altschuler and Jon Hagen n a joint ceremony that took place on November 3, 2001, The Institute of Electrical and Electronics Engineers (IEEE) and the American Society of Mechanical Engineers (ASME) made a special award to the Arecibo Observatory. The Arecibo Radio Telescope was declared an IEEE Milestone in Electrical Engineering, and an ASME Landmark in Mechanical Engineering. This makes the Arecibo Observatory the eighth recipient of these prestigious joint awards. Other similar designations include the Stanford Linear Accelerator and the Mill Creek Hydroelectric Plant. This award was requested by the Puerto Rico & Caribbean Section of the IEEE, and the elegant ceremony was organized and funded by them with support from the Puerto Rico Tourism Company, Abbott Laboratories and the Instituto de Ingenieros Electricistas. Brief presentations were made by the Honorable Ferdinand Mercado, Secretary of State of the Commonwealth of Puerto Rico, Juan RamÑn FalcÑn, chairman of the IEEE Puerto Rico, Caribbean Section, William A Weiblen, president of the American Society of Mechanical Engineers, and Joel Snyder, President of the Institute of Electrical and Electronics Engineers. Bill Gordon, Distinguished Professor Emeritus, Rice University, presented some reminiscences from the time of construction of the Observatory, Joseph Bordogna, Deputy Director of the NSF, Paul F. Goldsmith, Director of NAIC and Daniel R. Altschuler, Director of the Observatory also delivered greetings. (Joseph Bordogna's remarks ar eincluded below.) The ceremony was preceded by an invocation by Domingo Albino, who for many years worked as transmitter engineer at the Observatory. The Arecibo Observatory, home of the world's largest radio telescope, was dedicated in 1963. Its unique design was based on the efforts of professor William Gordon, then a member of the engineering faculty at Cornell University. Gordon's motivation was to build an instrument that could be used to study the higher layers in the atmosphere, and objects in the solar system using radar. William E. Gordon William E. Gordon was born in Paterson, New Jersey on June 8, 1918. He served in the Air Force during World War II, and earned a Ph.D. at Cornell University in 1953. He married Elva Freile in 1941 and with whom he had a son and a daughter. During the first half of his academic career (1948-66) at Cornell he conceived, supervised the design and construction, and directed the early operation of the Arecibo Observatory with its 300 meter spherical antenna. At Rice University (1966-86) he served as a Professor of Space Science and Electrical Engineering, as Dean of Sciences and Engineering, as Provost and Vice President, and is currently Distinguished Professor Emeritus. He is a member and Foreign Secretary (1986-90) of the National Academy of Sciences, a member of the National Academy of Engineering, a Foreign Associate of the Engineering Academy of Japan, a Fellow of the American Academy of

I

From left to right: Donald B. Campbell, William E. Gordon, Paul F. Goldsmith and Daniel R. Altschuler .

March 2002, Number 34

3

NAIC/AO N ewsletter


Arts and Sciences, and the American Association for the Advancement of Science, the American Geophysical Union, and the Institute of Electrical and Electronics Engineers. He was the Vice President of the International Council of Scientific Unions (1988-93) and is an Honorary President of the International Union of Radio Science. He received the Balth van der Pol Gold Medal in 1966, the Arctowski Gold Medal in 1984, a USSR Academy of Sciences Medal in 1985 for distinguished contributions in international geophysical programs and the Centennial Medal of the University of Sofia in 1988. He is currently a consultant for Northwest Research Associates on large radar facilities, an advisor to the Air Force and Navy on the HAARP facility in Alaska, a member of the Advisory Committee for the 2001 Asia-Pacific Radio Science Conference and a speaker at the Inauguration of the Indonesia/Japan radar facility on the equator at the source of El Nißo/La Nißa. The IEEE and Puerto Rico The Institute of Electrical and Electronics Engineers, IEEE ("eye-triple-E"), is a non-profit, technical professional association of more than 350,000 individual members in 150 countries. Through its members, the IEEE is the leading authority in technical areas ranging from computer engineering, biomedical technology and telecommunications, to electric power, aerospace and consumer electronics, among others. The IEEE World is geographically divided among 10 regions which are the sponsors to the basic local entity called the IEEE section. The Region that houses Puerto Rico is Region 9 known as the "IEEE Latin America Region". There are more than 300 IEEE sections around the globe for member networking and information sharing. In the Caribbean area we have two of these sections: the IEEE Puerto Rico and Caribbean and the Western Puerto Rico sections. These sections groups contain more than 1,200 individual IEEE members including 6 student branches and 7 technical Society chapters. The IEEE presence in Puerto Rico dates back to the 1920's in the form of the oldest student Branch in Region 9, the University of Puerto Rico MayagÝez Campus IEEE Student Branch. The professional section was formed in the 1960 and is known as the Puerto Rico and Caribbean Section.

Remarks made by Dr. Joseph Bordogna, Deputy Director, Chief Operating Officer, NATIONAL SCIENCE FOUNDATION at the IEEE Milestone Ceremony

G

ood afternoon. I'm delighted to be a part of this celebration honoring engineers and scientists and their achievements, and I bring you warm and hearty greetings from the National Science Foundation.

I want to thank the Honorable Ferdinand Mercado for distinguishing these proceedings with his personal presence and rank, Engineer William Gordon, creator of the observatory we recognize today, as well as the many others who have worked so hard to make this facility a success. The Arecibo Observatory represents a strong and unique alliance in research and education that exists between NSF, Cornell University, the University of Puerto Rico and many other institutions. This honor bestowed by IEEE and ASME acknowledges one of the finest and most powerful radar instruments ever built, not to mention the largest stationary radar telescope in the world. The award recognizes an awesome legacy. Built in 1963 with support from the National Science Foundation, Arecibo allowed us to determine for the first time, the rotation rate of the planet Mercury, as well as giving us the first discovery of planets outside our solar system. Now we know of almost 80 extra solar planets. Just imagine, after 4.5 billion years of Earth's formation, it is at Arecibo that humankind has first seen planets around stars other than our own. The observatory not only assists scientists and engineers in making discoveries, Arecibo became a star/luminary in its own right, co-starring alongside actress Jody Foster in "Contact" and the legendary James Bond in "Goldeneye." Who knows what will come next. (Though I hear contract negotiations are on the horizon.) In all seriousness, exploring and understanding our universe has required a breathtaking pace of technological innovation, engineering infrastructure building, and scientific discovery. For example, a $27-million upgrade in 1997, made Arecibo capable of "hearing" signals from greater distances and further back in time than before. The telescope undoubtedly has contributed to launching astronomy to even greater heights. Something we at the National Science Foundation always envision.

March 2002, Number 34

4

NAIC/AO N ewsletter


NSF is committed to such large facility projects. They are a splendid example of U.S. science and engineering. They are the starting points for countless journeys to the frontiers of discovery and learning. Throughout its 51-year history, NSF has enjoyed an extraordinarily successful track record in providing state-of-the-art facilities for science and engineering research and education. Currently, NSF invests over $1 billion annually in facilities and other infrastructure projects. With emerging cross-boundary science and engineering opportunities, large facility projects are becoming increasingly necessary and more complex, more exotic, for progress at the frontier. At NSF, our motto is "build right those facilities that are the right ones to build." We are depending on the engineering community to help us construct these new facilities as the foundation of future scientific and engineering discoveries. Facilities like Arecibo have opened up vast new research vistas and enabled us to pursue the most imaginative and creative ideas. The Arecibo Observatory has certainly been built right, and it was the right thing to build. We should all be proud of ourselves. Together we can do "The Right Stuff" and continue to make history happen for astronomy. The selection of this observatory as an IEEE milestone and an ASME landmark was the right decision, as was NSF's support of this facility for the last four decades. Thank you for inviting NSF, and me, to join you in this wonderful celebration.
Ed. Note: This article was reprinted from the following source: http://www.nsf.gov/od/lpa/forum/bordogna/jb011103ieee.htm

The commemorative plaque

Update on Primary Reflector Adjustment and Operation at High Frequencies Paul F. Goldsmith

T

his primary reflector a d justment project w a s discussed in some detail in the March 2001 Newsletter. Work has continued during the past year, with significant improvements in performance already realized. Lynn Baker (NAIC) has been leading the effort based on optical photogrammetry. In this technique, an optical target on

each panel of the surface (38,700 total) is measured by multiple photographs taken from the top of the three towers by Felipe Soberal (NAIC). Using the technique of photogrammetry, Felipe Soberal and Lynn Baker measured the position of an optical target on each of the 38,700 panels which make up the primary surface. Following several iterations on the approximately 2000 tie back cables which define the large-scale shape of the spherical reflector, the residuals from a best-fit sphere were approximately 5 mm rms. The measurement precision is about 0.7 mm rms (the exact value depends on

the number of "pictures" in which the target is included). JosÈ Maldonado (NAIC) organized crews of workers to use the special carts, which travel on cables under the reflector surface, to adjust the surface panels and eliminate these errors. This is a non-trivial operation, but had been made easier by extensive preparatory work in terms of cleaning corrosion from the adjustment bolts and replacing several thousand of them which had deteriorated past the point of usability. This effort extended through the summer

March 2002, Number 34

5

NAIC/AO N ewsletter


definitely moving forward. The very first measurements of the beam show that there is some significant coma, which may be a result of the receiver or the dome alignment. We need to do a lot more measurements and anticipate an effort to align the dome elevation rails before Fall 2002. This should finally get the telescope system ready for operation up to 10 GHz! We are accepting proposals for using the 8-10 GHz receiver on a "shared risk" basis for the 1 June 2002 proposal deadline. (see article entitled: Proposal Deadline on page 30).
Figure 2: The spectrum of H2CO 6-cm absorption against the CMB for the dark cloud L1512. The histogram shows the Arecibo data obtained in Dec 2001. The smooth curve is a best fit, including relative intensities of hyperfine components, and a peak optical depth of 1.4. The extremely narrow line width (~0.3km s-1) allows impressive resolution of the hyperfine structure and ultimately accurate determination of the column density and its distribution within this cloud. This data was obtained using total-power ON-SOURCE integration only (no switching) and indicates the impressive baselines obtainable with the Arecibo system. (Courtesy: Neal Evans )

Radio Astronomy Highlights Compiled by Chris Salter VLBI of the Luminous IR Galaxy, NGC 7674 mmanuel Momjian (U. Kentucky/ NRAO), Jon Romney, Chris Carilli (NRAO) & Tom Troland (U. Kentucky) have used Arecibo in their VLBA+phased-VLA observation of the Luminous Infrared Galaxy, NGC 7674. This took place during the commissioning phase of the VLBA4 recorder, and despite initial calibration errors, fringes were detected between Arecibo and the other telescopes. The nodding-style phase-referencing technique was used successfully in this observation.

of 2001, and in the late fall, Felipe and Lynn took another set of photographs to assess the results. Unfortunately, the "measuring machine", which Tony Acevedo (NAIC) operates to measure the large film photographs of the surface targets, developed a malfunction after measuring less than 1/8 of the total surface. For this subset of the entire surface, the rms is somewhat over 2 mm, a significant improvement compared to the 5mm previously found! But there are clearly (as is always the case in this type of effort) "outlier" targets that may have been misadjusted or missed entirely, and we expect that when we make another pass the rms should be below the 2mm level. We are expecting to have the measuring machine back online in a few weeks, and complete measurement of the films and do final surface adjustment by the end of Spring 2002. The benefit of all this work is already apparent in the measured antenna efficiencies. Phil Perillat and other NAIC staff members have been obtaining data over a range of frequencies, and we see a dramatic improvement, to about 7 K/Jy at 5 GHz, and to over 10 K/Jy at 1.4 GHz. These numbers are so good that they require careful checking in

terms of the source fluxes, and also our noise diode calibration, but the evidence is clear that we are set for efficient operation at 5 GHz, and that it is time to try at higher frequencies. As one indication of what can be achieved at 5 GHz, Figure 2 shows a spectrum of the 6 cm formaldehyde line in absorption in the dark cloud L1512 against the cosmic microwave background. These data were obtained by K. Mueller and N. Evans (University of Texas), and P. Goldsmith (NAIC) as part of an observing proposal searching for cold, dense pre-protostellar condensations. Resolving the hyperfine structure this clearly is exceptional, and should allow accurate determination of the optical depth and thus column density, and its distrib ution. This molecular transition, observed with the good angular resolution -- 1 arcmin -- and superb spectral baselines now available at Arecibo, should be an extremely important tracer of dense molecular material at low temperatures. This is just one of the many exciting potential uses of Arecibo at 6 cm and shorter wavelengths. An 8-10 GHz cryogenic dual-polarization receiver was installed towards the end of 2001. There have been the usual issues getting this system integrated with the IF/LO system, but things are

E

The first results from the project are shown in Fig. 3, where the HST optical image of the galaxy is shown at the top left hand corner. The other images in the figure show the 21-cm radio continuum maps made from the observation, and represent the central part of NGC 7674. Two regions can be seen in the large scale radio image (top right), a core-jet structure (shown enlarged at the bottom right) and a hot spot at a distance of 0.5 arcsec from the core. The resolution of these images is 12â6 milliarcsec, while the rms noise is 0.25 mJy/beam. The spectrum presented at the bottom left shows the neutral hydrogen (HI) absorption spectrum on the Arecibo-VLBASt.Croix baseline. One major goal for this study is to determine the distribution

March 2002, Number 34

6

NAIC/AO N ewsletter


DECLINATION (J2000)

08 46 44.40 Cont Peak Flux = 1.4057E-02 Jy/Beam Levs=1.406R-04 * (10,20,30,40,50,60,70, 44.35 80,90,100) 44.30 44.25 44.20 44.15 44.10 23 27 56.71 56.70 56.69 RIGHT ASCENSION (J2000) 56.68

Search for a Pulsar in SNR IC433 Bryan Jacoby, Stuart Anderson (Caltech), Dale Frail (NRAO), & Jonathan Keohane (NCSSM) have searched for radio pulsations from the supernova remnant (SNR), IC443. Their search targeted the soft X-ray point seen with Chandra (Olbert et al. 2001, ApJ, 554, L205), which is surrounded by diffuse radio emission that appears to be a pulsar wind nebula. This point source is not at the center of the SNR where previous pulsar searches have focused. To date, analysis of Arecibo observations at 430 MHz with the PSPM and at 1.4 and 2.4 GHz with BACSPIN show no sign of radio pulsations. Similarly, less-deep VLA observations at 1.4 GHz reveal no radio point source, pulsed or unpulsed. The team concludes that the X-ray point source is most likely a pulsar which is unobservable because its radio beams do not intersect the earth. Determination of the Binary Orbit of PSR J0407+16 Dunc Lorimer (Jodrell Bank), Kiriaki Xilouris (UVA), Andy Fruchter (STScI), Ingrid Stairs (NRAO), àngel VÀzquez & J o Ann Eder (NAIC) have begun regular timing observations of PSR J0407+16: a 25.7-ms pulsar discovered as part of the Arecibo upgrade 430-MHz drift scan searches. Earlier observations revealed the pulsar to be a member of a binary system with a 680-day orbital period (see Fig. 4) and a 0.003 M mass function. These data imply that the orbiting companion has a mass of ~0.2 M and, based on what is known from other binary millisecond pulsars, is most likely a low-mass white dwarf star. The orbital period of J0407+16 is by far the longest known for a millisecond (<30 ms) pulsar and second only to PSR B0820+02 for low-mass binary pulsar systems. Due to the sparsity of the earlier data, a phase-connected timing solution has so far not been possible. The goal of the new observations is to obtain

41 40 39 Sc-Ar 38 37 36 35 34 33 9200 9000 8800 8600 8400 8200 velocity (km/s) (HELIO)

Levs=1.406E-4(10,20,30,40,50,60,70,80,90,100) 08 46 44.16 44.15 44.14 44.13 43.12 44.11 23 27 56.712 56.711 56.710 56.709 56.708
Cont peak flux = 1.4057e 2 Jy/beam Levs = 1.406e 4 x (10, 20, 30, 40, 50, 60, 70, 80, 90, 100)

Stokes I (mJy)

Cont peak flux 1.4057E-2 Jy/Beam

RIGHT ASCENSION (J2000)

Figure 3: VLBI imaging of NGC 7674. The optical HST image of the galaxy is shown at the top left of the collage. The 21-cm "wide-field" VLBI continuum image of the central region is at the top right (resolution 12 â 6 milliarcsec), with the core-jet structure of the nucleus enlarged at the bottom right. The HI absorption spectrum on the Arecibo-St. Croix baseline is presented at the bottom left. (Courtesy: Emmanuel Momjian)

and kinematics of neutral gas leading to an estimate of the gravitational mass at the center of the galaxy powering the nuclear starburst and/or the AGN phenomena. The impact of having the Arecibo Telescope join with the VLBA is a boost in sensitivity by a factor of 4.1. Having both Arecibo and the phased-VLA with the VLBA can provide very sensitive short and long baselines, and improve the sensitivity of the VLBA by a factor of 6.2. This increase in sensitivity will play a very important role in studying fa int compact emission regions and weak spectral lines at very high resolutions. VLBI of Long Period Variable Star Maser Emission VLBI and VLBA maps of OH emission from long-period variable stars have shown numerous weak, highly polarized components spread over regions 100's
March 2002, Number 34

of milliarcsecs across. Because the components are weak, signal to noise limitations have prevented many kinds of analyses. Maps at different frequencies and at different epochs are difficult to compare because they have not had a common phase reference. To overcome these limitations, John Fix (U. Alabama, Huntsville) & Robert Mutel (U. Iowa) have carried out a pilot program to observ e six long-period variable OH masers using the VLBA plus Arecibo and the phased-VLA. The large collecting areas of Arecibo and the phased-VLA will result in high angular resolution polarization maps with high dynamic range and sensitivity. From this pilot project, Fix & Mutel hope to identify one or two stars for a long-term synoptic study of the changes in the relationship of structure at the three OH frequencies, as well as models for maser pumping and polarization. They also hope to determine the parallaxes of the masers with mas accuracy.

7

NAIC/AO N ewsletter


member of a binary system. While there are not yet enough data to determine the orbital parameters, the data indicate that the system is probably a member of the quickly growing class of compact binary pulsars with v ery lo w-mass companions. The orbital period is most likely between 2 and 5 hr and, given the size of the resulting orbit, the minimum companion mass is probably only a few hundredths of a solar mass. Additional observations will be necessary before any more details emerge. The isolated 3.7-ms pulsar M13C was detected in each of 5 observations of M13, although its flux density changed drastically on the timescale of tens of minutes due to scintillation. This pulsar was also detected in a complementary 8-hour observation of M13 taken with the new GBT. The 3.1-ms binary pulsar M13D was detected twice (with high confidence) in 10 min sections of data from observations taken on different days. During each detection, the measured accelerations were very different (-4.9 and 4.5 ms -2), indicating that the pulsar is a member of a binary system. Follow-up observations should allow determination of the orbital parameters and the nature of the companion.
2 Pulses of Best Profile

Figure 4: The variation of pulse period of J0407+16 due to orbital motion. Inset: The 430-MHz template pulse profile used in the timing analysis. (Courtesy: Dunc Lorimer)

Fraction of Observation

Fraction of Observation

Fraction of Observation 0.5

Time(s)

Time(s)

Time(s)

a phase-connected solution over the coming year. This should enable the previous data stretching back o v e r the last 3 yr to be included. The resulting ephemeris should then substantially improve upon the existing orbital parameters and determine the pulsar's position, spindown rate and possibly also proper motion. One of the many parameters measurable with these data will be the orbital eccentricity which, on theoretical grounds, is expected to be strongly correlated with the orbital period. For PSR J0407+16, the predicted value is about e = 1 0 -3. A c o mplete knowledge of the orbit, spin and kinematics of this unique binary system should improve our knowledge on the origin and evolution of long-period binary pulsars. The team hopes to report many of these facts to Newsletter readers in the coming year. The WAPP finds its First Pulsars Vicky Kaspi, Scott Ransom (McGill), Ingrid Stairs (NRAO), Jason Hessels (McGill) & Dunc Lorimer (Jodrell Bank) have begun processing the 1.5 TB of Wideband Arecibo Pulsar Processor (WAPP) pulsar search data taken on 10 globular clusters this past summer. After completing analysis of the 5 clusters M5, M13, M15, M53, and NGC6760,

all containing previously known pulsars, they are delighted to report the discovery of 3 additional millisecond pulsars, a binary pulsar in M5 and two pulsars (one isolated, one binary) in M13 (Fig. 5). Prior to this search effort, M5 and M13 were each known to contain an isolated and a binary pulsar. The new 2.4-ms pulsar M5C has been detected six different times for ~10 min each in 4 out of 5 observations of M5. Variations in the measured periods and accelerations indicate that this pulsar is a
2 Pulses of Best Profile

2 Pulses of Best Profile

M5C

M13C

M13D

1.0

1000

1000

1.0

0.8

1000

0.6

0.8

500

500

0.6

0.4

500

0.2

0.4

0

0.2

0

0

0

0.5

1 1.5 3 2 1 0 Phase Reduced 2

0

0.5

1 1.5 3 2 1 0 Phase Reduced 2

0

0

0

1 1.5 3 2 1 0 Phase Reduced 2

Figure 5: The average 1.4-GHz pulse profiles for the new globular cluster millisecond pulsars, M5C, M13C, and M13D. The greyscale below the average pulse profile shows the consistency of the pulsed emission (as well as some effects due to RFI, and scintillation). These data were obtained in June 2001 with the WAPP. (Courtesy: Scott Ransom)

March 2002, Number 34

8

NAIC/AO N ewsletter

0

0.2

0.4

0.6

0.8

1.0


PSR B1849+00

FREQ (MHz) 0 1663 800 1664 600 1665 1666 1667 0 1668

400 200 V (km/s) lsr 1667 0 200 (km/s) lsr 1665

400

200

V

400

Figure 6: 1665- and 1667-MHz absorption lines towards PSR B1849+00 obtained with the Arecibo telescope. (Courtesy: Joel Weisberg)

ing temporal va riations seen in some absorption spectra, Snezana Stanimirovic (NAIC), Joel Weisberg (Carleton), John Dickey (U. Minnesota), Stuart Anderson (Caltech), plus Carleton undergraduates Abby Hedden, Katie Devine, Anton de la Fuente & Tyler Green, have searched several pulsars with known HI absorption for detectable lines at 1665 & 1667 MHz using the Arecibo telescope. They struck lucky with PSR B1849+00, which shows a deep, narrow absorption line at vLSR = +105 km s -1 at both 1665 & 1667 MHz (Fig. 6). These absorption lines correspond to an interstellar cloud directly in front of the pulsar itself. In addition, two other sets of OH absorption lines, one at vLSR = +105 km/s, the other at vLSR = +10 km/s, were detected in the pulse-off spectrum and most likely arise against the nearby SNR, G33.6+0.1. The same features were seen in the HI absorption spectrum against G33.6+0.1 by Frail & Clifton (1989). Hence, their observations reve al two different clouds in front of the SNR G33.6+0.1, one of these being also seen against B1849+00, with both HI and OH absorption lines along the same line-ofsight. These are perfect candidates for a comparative study of properties of atomic and molecular gas. While further analyses are underway, these authors hope to search for OH absorption towards other pulsars, as well as to investigate the potential presence of temporal variations in the absorption spectrum of PSR B1849+00. The Crab Nebula Pulsar at many Wavelengths The Crab-Nebula Pulsar, noted for its sporadic emission of giant pulses and the highly unusual frequency-dependent behavior of its pulse profile, has been studied at wave lengths ranging from radio to -rays. The atypical nature of the pulse profile, and its frequency dependence, makes it difficult to interpret the observational data in terms of the canonical picture whereby the radio emission arises from a simple dipole field geometry. Tim Hankins (NMT),

The pulsar group at McGill University has recently completed construction of a 100+ processor Beowulf cluster dedicated to pulsar research. Using the cluster's 52 compute nodes (with 1 GB of RAM and 100+ GB of disk) and two 0.6-TB fileservers, the very computeintensive searches of the clusters with unkno wn dispersion measures will be finished within the next couple of months. More millisecond pulsars will almost certainly appear in the highquality data. The First-ever Detection of OH Absorption against a Pulsar Emission-absorption studies have been very successful at probing the properties of the ISM towa rds both strong background continuum sources and pulsars. The great advantage that pulsars offer for such studies is that they turn on and off, allowing the absorption and emission spectra to be measured without moving the telescope. This eliminates errors introduced into the absorption spectrum by small scale variations in the emission. While the HI absorption against pulsars has been commonly detected, the only search for OH absorption, by Galt (1974) with the 25.6-m Onsala dish, was unsuccessful. Motivated by the great potential that OH absorption would have for a comparative study of neutral atomic and molecular gas along the same sight lines, as well as for understand-

Jim Cordes (Cornell), Jeff Kern (NMT), Ramesh Bhat (NAIC) & Maura McLaughlin (Jodrell Bank) have undertaken an Arecibo study, with the goal of investigating the frequency evolution of the various components of this pulsar and its polarization properties, particularly at above 1 GHz, in order to help refine the interpretation of the Crab in terms of the inner and outer gap models of pulsar emission. In the first phase of this project, observations were made in early 2002 in multiple frequency bands accessible to Arecibo's 430-MHz, L-, S- and C-band receivers. Data were taken using the WAPP, with all four Stokes parameters being recorded. The wide bandwidths and high time resolutions (~20-100 µs) available with the WAPP will also enable a much better polarization study than has been previously possible. The observational goals are twofold: (a) To achieve much finer sampling in frequency of the average pulse profile in order to e xamine how the pulse components appear and disappear. The observations capitalize on the large bandwidths feasible with the Gregorian receivers to achieve excellent frequency sampling from 1 to 6 GHz. The choice of frequency bands was largely based on the VLA results of Moffett & Hankins (1996, ApJ, 468, 779). (b) To obtain new statistics for the giant pulses, and in particular to compare the giant pulse polarization with the average polarization in order to investigate from where the giant pulses originate. Data from observations made so far will enable this team to form Stokes parameter profiles for 7 different frequency bands from 0.4 to 4.2 GHz. Observations were also attempted at higher frequency bands, and the lack of successful detections at 5.0 and 5.9 GHz can plausibly be accounted for by the long scintillation times (approximately man y hours) expected for this pulsar at high frequencies. Recent work in close consultation with Malvin Ruderman (Columbia) suggests that the giant pulses are produced

1.0

March 2002, Number 34

0.5

I/I0

9

NAIC/AO N ewsletter


330 MHz (VLA)

430 MHz (Arecibo)

giant pulses at bandwidths of up to 500 MHz for ~2ns time resolution, and continuous or gated sampling of up to 200 MHz with full polarimetry at two frequency bands simultaneously. HI Narrow Line Absorption (HINLA) and Molecular Clouds 2001 marked the 50th anniversary of the discovery of the 21-cm line. In this somewhat "old", yet fruitful field, the study of 21-cm absorption in the Galaxy is gaining more and more attention. Such absorption is studied in two ways. One is against continuum background radiation (e.g. Dickey 1997, ApJ, 488, 258). The other is to study the so-called HI self-absorption (HISA) features in HI emission spectra (e.g. Wilson & Minn 1977, A&A, 54, 933). Based on both methods, a consensus has emerged from recent studies that there exists cold (<20 K) HI in the Galaxy (Heiles 2001, ApJL, 551, L105; Knee & Brunt 2001, Nature, 412, 308; Li & Goldsmith 1999, BAAS, 195, 7208). The correlation between HISA and molecular clouds is inconclusive. In the recent Canadian Galactic Plane Survey, HISA features are present both with and without CO counterparts (Gibson et al. 2000, ApJ, 540, 851). In Arecibo observ ations (Feb 2001), ho we v e r, Di Li (Cornell) & P aul Goldsmith (NAIC/Cornell) found a good correlation between narrow HI absorption and OH emission. A sample of 32 nearby dark clouds was surveyed and HI narrow line absorption (HINLA) was found in the majority (77-90%) with corresponding OH emission. The peak velocity and line width of HINLA and OH are similar. These nearby dark clouds have also been mapped in CO isotopologues at FCRAO, and the maps smoothed to the Arecibo L-band beam size. Spectra of the atomic carbon line at 492 GHz have also been obtained using the Submillimeter Wave Astronomy Satellite (SWAS). The SWAS 4-arcmin beam size is well suited for comparison

606 MHz (VLA)

812 MHz (VLA)
LFC

1180 MHz (Arecibo)

1418 MHz (VLA)

1475 MHz (Arecibo)
IP

2150 MHz (Arecibo)

2330 MHz (Arecibo) 2695 MHz (VLA) 2850 MHz (Arecibo) 4150 MHz (Arecibo)
HFC1 HFC2 IP'

4700 MHz (VLA)

4888 MHz (VLA)

8400 MHz (VLA)

Figure 7: The average total intensity profiles of the Crab Nebula Pulsar at many wavelengths; the composite plot consolidates data from observations with the VLA (Moffett & Hankins 1996) and recent Arecibo observations. Arecibo data were recorded with the WAPP over bandwidths of 100 MHz, except at 0.43 GHz where the bandwidth was 12.5 MHz. Profiles at 0.43 and 4.15 GHz have integration times of 500 and 1800 s respectively, and that for the other Arecibo bands is 3600 s. Locations of interpulse (IP and IP'), the low frequency component (LFC) at L-band, and two high frequency components (HFC1 and HFC2) appearing at and above C-band are also marked. (Courtesy: Ramesh Bhat)

by a maser amplification mechanism in the outer-gap beams. Further, processing of radio emission within the magnetosphere is thought to be the key to understanding the nature and frequenc y evolution of the va rious pulse components. The data from these observations will help test these ideas. Fig. 7 shows the average total-intensity profiles at many frequencies obtained from observations at various frequen-

cies. These data confirm a new component (LFC) seen at 1.4 GHz and two additional components (HFC1 and HFC2) that appear above 4 GHz. Further, the interpulse (IP) seems to disappear near 2.9 GHz, and it (or a new component) reappears at an earlier phase at higher frequencies. Future observations will also make use of the new pulsar backend from New Mexico Tech. This is designed for direct voltage sampling of individual

March 2002, Number 34

10

NAIC/AO N ewsletter


turbulence. The outstanding question regarding HINLA is not cooling, but rather, its location and quantity of cold HI, which must, in some cases, be at temperatures below 20 K. The standard H2 formation model (Hollenbach & Salpeter 1971, ApJ, 163, 155) dictates the atomic hydrogen density to be about 1 cm-3 regardless of the H2 density of molecular clouds. However, recent experimental results (Caselli et al. 1998, ApJ, 495, 309; Pirronello et al. 1999, A&A, 344, 681) and simulations by Li & Goldsmith reveal a slowdown of H2 formation in dark clouds, and thus raise the steady state value of n(HI) to about 100 cm-3. To test the validity of new models, both the column density of cold HI from HINLA and its spatial extent are needed. These issues can and will be addressed in further analysis of the Arecibo survey of nearby dark clouds.
Figure 8: Composite spectra of Lynds cloud, L1574. The HINLA (21 cm) and OH (1667 MHz) data are from Arecibo, with the CO, 13CO and C18O data from FCRAO. The CI data are from SWAS. (Courtesy: Di Li)

with Arecibo observations. All these molecular-cloud tracers show remarkable correlation with HINLA (Fig. 8). Preliminary mapping of HINLA was carried out at Arecibo in Jan 2002, and in both spatial extent and the morphology of the intensity variations, the positive correlation between HINLA and OH was confirmed (Fig. 9).

clouds. Since this type of HI absorption involves separate background HI emission and foreground molecular clouds, it is better termed HI Narrow Line Absorption (HINLA). HINLA reveals a steady state population of HI inside molecular clouds maintained by cosmic ray dissociation of H2 (possibly in combination with some other processes). Compared with general HISA, they have narrower line widths (v ~ 1 km/s), which are a result of both confinement in space and reduction in
L1544 HI 21cm

Based on this observational evidence, the following statements are postulated as a first step in a comprehensive understanding of cold atomic hydrogen in the Galaxy. There are two types of HISA. The first reflects the temperature fluctuations in the cold neutral medium (CNM). It is w o rth noting that the 10 dissociation of such cold HI clouds from molecular clouds poses a critical challenge to the standard ISM model 5 (McKee & Ostriker 1977, ApJ, 218, 148). How can a HI cloud be cooled to 0 such low temperatures without molecular coolants and also remain stable? Further investigation is certainly needed. -5 The second kind of HISA, studied by the 10 Arecibo 21-cm survey of dark clouds, is definitely associated with molecular Figure 9:
March 2002, Number 34

The positive correlation between HINLA and molecular tracers make HINLA a very interesting tool -- an atomic tracer of molecular clouds. First, the structures of HINLA at sub-arcmin scales will be studied by the VLA. These high resolution data can be compared directly with millimeter data in order to study details of cloud chemistry. Second, the narrowness and strength of HINLA make it an ideal Zeeman tracer. Compared to OH emission, the primary (if not the only) Zeeman tracer of dark clouds, HINLA is usually 10

L1544 OH 1667 MHz

10 5


0 -5

5

0



-5

-10

10

5

0



-5

-10

HINLA and OH maps from Arecibo observations carried out in Jan 2002. (Courtesy: Di Li)

11

NAIC/AO N ewsletter


Figure 10: A sample 21-cm HI spectrum for IC443. The dashed line is the Stokes-I ON-OFF spectrum, while the solid line is 100x Stokes-V. Koo et al. derive an upper limit about 100 µG for the strength of magnetic field in the shocked atomic gas. (Courtesy: Bon-Chul Koo)

times stronger. The promise of HINLA in measuring magnetic fields will be explored in Arecibo observations scheduled for this August. HI and OH in Old Supernova Remnants Magnetic fields have major effects on the dynamical evolution of old SNRs. It is generally believed that they dominate the pressure and limit the final compression in the radiative shell. However, the 21-cm HI line emission from such shocked gas is generally too weak for Zeeman observations, and it is believed that no HI Zeeman observations have been made toward old SNRs. Bon-Chul Koo (Seoul), Carl Heiles (Berkeley), Snezana Stanimirovic (NAIC) & Tom Troland (U. Kentucky) have attempted to measure the magnetic field strength in two SNRs, IC443 and W51C. Among SNRs with high-velocity shocked atomic gas, these are the only two with 21-cm HI emission lines strong enough for a Zeeman observation. Fig. 10 shows a sample spectrum for IC443, where the dashed line is the Stokes-I ON-OFF spectrum, and the solid line is 100x Stok es-V. The broad line between vLSR= ­100 and ­20 km/s is the emisMarch 2002, Number 34

sion from the shocked gas. The leastsquares fit to the magnetic field within the dotted lines yields B = 60±43 µG. However, the quoted error is too small because, as always for least-squares fits, this assumes Gaussian noise. The uncertainty in the V spectrum is dominated by systematics and a "realistic upper limit" would be ~100 µG. They observed 3-4 points in each SNR, and obtained similar results for each. For IC443, Koo et al. also mapped the distribution of the shocked HI gas. This is a classical SNR interacting with

a molecular cloud, and has been studied in detail using various molecular lines. Its HI was observed at Arecibo at 21 cm by Giovanelli & Haynes (1979), but their coverage was incomplete and the sampling irregular. Considering the uniqueness of the source in the study of molecular cloud-SNR interaction, a fully-sampled Arecibo map is highly desirable. The data are presently being reduced and analyzed. They simultaneously observed the 1612-, 1665+1667-, and 1720-MHz lines of OH using the remaining subcorrelators. The OH lines provide important information about the physical conditions of the shock e d gas. In particular, the 1720-MHz line has been detected to w a rd SNRs as maser emission and is considered to be evidence for slow, non-dissociating shocks propagating through molecular clouds. However, at Arecibo the 1720-MHz band is heavily affected by strong interference (RFI), and observations at this frequency are usually thought to be of little value. Since the RFI is sporadic, it was possible to confirm the steadiness of celestial emission by repeating the observation several times. Fig. 11 shows the detection of the OH maser in IC443 using this technique, plus its spectrum. This maser was originally discovered by DeNoyer in 1979. No new maser emission is detected. This team now plan a sensitive 1720-MHz OH line survey toward SNRs using the Arecibo telescope.

23 DEC. (J2000)

0

T(K) 70 60 50

22

0

16h 16m 18m R.A. (J2000) R.A. (J2000)

0

-5 v (km/s)

-10

Figure 11: (left) The integrated intensity map at 1720 MHz of SNR IC443. The bright spot in the field center is the OH maser; (right) the line spectrum of the OH maser. (Courtesy: Bon-Chul Koo)

12

NAIC/AO N ewsletter


2MASS Galaxies

of optically-selected dw arf galaxy candidates reaching luminosities and surface brightnesses approaching those of the faintest Local Group dwarfs (Flint et al. 2001, ApJS, 134, 53). The Leo I sample provides an opportunity to probe the faint-end of the galaxy luminosity function, testing cosmological models which significantly o v erpredict the number of dwarfs observed in LocalGroup-like groups (e.g. Klypin et al. 1999, ApJ, 522, 82).
Pisces-Perseus Supercluster

Great Attractor Region

Figure 12: This shows the distribution of relatively bright (K-band magnitude <11.5) 2MASS galaxy candidates identified by automatic algorithms. The map is an Aitoff projection in Galactic coordinates centered on the Anticenter direction. The bold curved lines show the Arecibo northern and southern observing limits. (Courtesy: Carmen Pantoja)

Galaxies in the Zone of Avoidance Steve Schneider (UMass), John Huchra (CfA), & Carmen Pantoja (UPR) have initiated a program to obtain 21-cm HI line spectra for low Galactic latitude galaxy candidates identified from 2MASS. This near-infrared survey minimizes the effects of obscuration from the Milky Way, allowing galaxy identification deep into the Zone of Avoidance where optical galaxy catalogs are incomplete. The map in Fig. 12 shows the distribution of relatively bright (K-band magnitude < 11.5) 2MASS galaxy candidates identified by automatic algorithms. The galaxy candidates were inspected on the J-, H- and K-band images before making Arecibo observations. By selecting extended sources with fairly large
20.537+32.93 0.06

sizes and J-K colors in the range of normal galaxies, it is possible to produce a sample of sources to within a few degrees of the Galactic plane that have about a 30% probability of HI detection in a 3-min ON-OFF observation (the total velocity coverage of the observations spanned from ­442 to 17498 km/s). Near infrared colors and morphology do not show much difference between gas-rich and gas-poor galaxies, bu t it appears that by selecting 2MASS sources with lower central surface brightnesses, the probability of an HI detection grows to better than 50%. Some 200 candidates have been observed in sessions during 2001 toward both the Galactic center and the Anticenter regions accessible from Arecibo. A typical profile for a detected galaxy 4.0° from the Galactic plane is shown in Fig. 13. This project is currently in progress, with further data gathering and analysis still required. The Dwarf Galaxy Population of the Leo I Group As part of an on-going program to characterize the dwarf galaxy membership in the Leo I group, Katy Flint (DTM) & Chris Impey (U Arizona) obtained HI spectral line data for a large sample of group candidates in Jan 2002. At a distance of 10 Mpc, Leo I is a poor group of galaxies containing a new sample

0.04

0.02

0 3900 4100 4300 4500 4700 4900 5100

Heliocentric velocity (km/s)

Figure 13: The HI profile for galaxy, 20.537+32.93, which lies 4.0° from the Galactic plane. (Courtesy: Carmen Pantoja)

The primary challenge of measuring the luminosity function to these limits is determining group membership for each galaxy candidate. Fainter dwarfs have increasingly lower surface brightness, which mak es optical, spectroscopic redshifts and direct distance measurements very difficult. However, fainter dwarfs also appear to have larger neutral gas fraction, making Arecibo HI-line observations the perfect complement to optical spectra at brighter luminosities. Preliminary results from 40 hr of targeted observations in Jan 2002 with the L-narrow receive r have doubled the number of confirmed dwarf galaxy members in Leo I. These opticallyselected dwarf members probe HI gas masses as low as 5â106 M , which is comparable to the lowest mass dwarf irregulars in the Local Group. The R-band surface brightness and absolute magnitude of these dwarf galaxies are plotted in Fig. 14 ( filled symbols), compared to Local Group dwarfs (stars). Leo I dwarfs are coded by HI mass, with triangles for MHI < 107 M , and squares for MHI 107M . Furthermore, a number of their optically selected dwarf candidates are coincident with HI detections around the edges of a large, quiescent HI cloud in the group center, which was previously reported to be primordial with no indication of associated star formation (Schneider et al. 1989, AJ, 97, 666). These objects require more follow-up work to understand their relationship to the larger cloud. Yet, the abundance of low-mass dwarfs predicted by Local Group models and observed in higher density galaxy clusters is not seen in the Leo I group.

Flux (Jy)

March 2002, Number 34

13

NAIC/AO N ewsletter


Areibo and 600 at NanÃay. About 30% of the objects were detected. So far, the data have shown lots of quite gasrich objects, but none with the record high MHI/LB ratios found for some red cluster LSBs. Search for Zeeman Splitting in the 700-MHz Lines of CH In June 2001, Alyssa Goodman (CfA) & Carl Heiles (Berkeley) made the first known attempt to detect the Zeeman effect in the 700 MHz lines of CH. If the Zeeman effect were to be detectable in these, such measurements would offer the best non-maser probe yet of magnetic fields in dense (n~106 cm-3) molecular gas. Goodman & Heiles had waited nearly a decade to make these observations, first for the upgrade to be completed, and then for an appropriate receiving system at these frequencies to be constructed (thanks go to Edgar Castro and his team at NAIC for that one!). The primary challenge to making these observations was isolating signal from RFI at these low frequencies; beepers, cell phones and, most importantly, TV stations, abound in Puerto Rico. After a great deal of detective work, much of it inside the Gregorian enclosure (thanks go especially to Lisa Wray), Goodman & Heiles found that the worst TV station was not just adding an unwanted signal to their observations, but was saturating the front-end electronics, making observing at the CH frequencies impossible. After a workaround was found to this problem, RFI was limited to signals that could be (mostly) removed in data-reduction software. After nearly 100 hr of observations, and heroic data reduction efforts (using Heiles' new cross-correlation techniques) the CH lines were clearly detected, in absorption against H II regions, in several massive star-forming regions (Fig. 15). As for the Zeeman effect, as of now there are some intriguing 2-type "measurements" of the magnetic fields, which Goodman & Heiles prefer to think of as upper limits. A paper describing the

CH Zeeman Observations of W49 at Arecibo (~4 hours on-source; 2P3/2, J=3/2, F=2-2; n=701.679 MHz) Goodman & Heiles, June 2001 4

2 OFF 0 ON-OFF -2 -4 STOKES I, with Gaussian fit -40 -20 0 20 4 OFF, Stokes V 2

40

60

Figure 14: R-band surface brightness and absolute magnitude of dwarf galaxies in the Leo I group (filled symbols), compared to Local Group dwarfs (stars). Leo I dwarfs are coded by HI mass, with triangles for MHI<107M , and squares for MHI 107 M . (Courtesy: Katy Flint)

0 ON, Stokes V, with Zeeman fit superimposed -2

HI in 2MASS LSB Galaxies Low surface brightness (LSB) galaxies still remain a fascinating class of objects about which much remains to be learned. Often, being gas-rich, they are obvious targets for HI line observations. Most of the objects studied are blue, and the red cluster LSBs studied at Arecibo by O'Neil et al. (2000) showed truly extreme properties: MHI/LB ratios of 20M /L (or more!), and/or rotation velocities which appear to lie outside the standard Tully-Fisher relation. In an effort to learn more about these objects, a group of French and US astronomers have used the Arecibo and NanÃay radio telescopes to observe a sample of LSB galaxies detected in the near-infrared all-sky 2MASS survey. The observing strategy combines the greater sensitivity of the Arecibo telescope with the sky coverage between declinations of +90° and ­39° of the 100-m class NanÃay instrument. These data are complemented by optical CCD imaging and theoretical modeling of their star formation history. Delphine Monnier Ragaigne, Wim van Driel & Chantal Balkowski (Paris Observatory, France), Steve Schneider (UMASS), Tom Jarrett (IPAC) & Karen O'Neil (NAIC) are finishing the collection of HI data on 1000 2MASS LSB objects, of which 400 were observed at

-4 -40

-20

0

20

40

60

Figure 15: The lowest trace in the top panel shows the Stokes-I spectrum, which is approximately equal to the usual TA*2. If a Zeeman signal were present, the lowest trace in the bottom panel (Stokes-V) would show an "S-curve," proportional to the derivative of Stokes-I. The darker solid curve in the lowest trace of the bottom panel shows the "best fit" Zeeman field (650±270 mG), which Goodman & Heiles will claim as a 3- upper limit of 810 mG for the magnetic field toward W49. (Courtesy: Alyssa Goodman)

limits, and their implications -- both for magnetic fields in molecular clouds, and for future CH Zeeman experiments -- will be submitted to the ApJ. Probing Low Temperature and High Density Clouds via 6-cm Formaldehyde Absorption of the CBR How do you study very cold molecular condensations which may be "preprotostellar clouds" (or PPCs) -- the sites of incipient collapse to form a new star or stars? This is a difficult challenge. Most density tracers employed by astronomers involve a pair of rotational transitions of a linear molecule (e.g. CO, CS, HC3N). Since the different transitions have different spontaneous decay rates, they require different collision rates to bring their populations into thermal equilibrium. At a specific density, their relative populations reflect the collision rate and thus allow determining the hydrogen density.

March 2002, Number 34

14

NAIC/AO N ewsletter


This can work well, but there is an important caveat: the different rotational levels generally lie at significantly different levels above the ground state, given approximately by the rigid-rotor formula E(J) = hB0J(J + 1). For C18O, J = 1 is at 5.3 K, J = 2 is at 15.8 K, J = 3 at 31.6 K, etc. When we are dealing with a very cold cloud (T 10 K) or, in fact, a cloud whose temperature structure is uncertain, there is a very significant uncertainty introduced. The collisional ex citation rates themselves, as well as the LTE level populations, depend sensitively on the kinetic temperature of the gas. The lack of detailed temperature information means that the density determined becomes mixed up with the temperature. It is extremely difficult to disentangle the two, especially for cold dark clouds which may have warm edges heated by the interstellar radiation field. For this very interesting class of objects, the PPCs, the heated edge can dominate the excitation effects and only with quite elaborate models could we become confident that we have properly separated the temperature and the density structure. The latter is of critical importance to assess whether the cloud appears to be in equilibrium, or whether it may be beginning a process of collapse. Clearly, a better probe of density is needed for studying cold, dark clouds. Fo rtunately, one is a v ailable. The lowest transition of ortho-formaldehyde (H2CO) is seen in absorption against the cosmic background radiation (CBR) in molecular clouds. The reason for this peculiar behavior is that the excitation temperature of these levels is lowered by collisional pumping. As the density rises, however, the level populations are forced toward equilibrium at the kinetic temperature, and the line goes into emission. Since these levels lie very low in energy, they provide a probe of high density material with very little sensitivity to temperature in the range of interest. The discovery of absorption against the CBR by the lowest transition of

H 2CO at 6-cm wavelength wa s quite surprising as it is impossible for any two-level system to have an excitation temperature below that of the CBR. Townes & Cheung (1969, ApJL, 157, L10) proposed a collisional pumping scheme to lower the excitation temperature; this scheme employed collisions to higher levels and radiative decay. The propensity of collisions to favo r lower levels in each excited K-doublet transition led, via radiative decay and selection rules, to an overpopulation of the lower level of the J=1 K-doublet. This pumping scheme works over a range of densities up to about 105 cm-3, at which point collisions begin to dominate and drive the excitation temperature toward the kinetic temperature. Thus, there is a range of densities with neither emission nor absorption. At sufficiently high densities (n>10 6 cm -3), the line goes into emission. As the 6-cm line does not require high temperatures but goes into emission solely as a result of high density, it is a unique tracer of cold, dense gas. The transition between the levels of the lowest K doublet of H2CO (the JK-1K1 of l11 and l10 levels) occurs at 6 cm. Previous observations of this transition were done mostly with very large beams (~6'), with the exception of a few VLA observations. In a VLA study of B335 (Zhou et al. 1990, ApJ, 363, 168), a dark cloud in the early phases of forming a low mass star, a ring of absorption was found surrounding the center of the object. It was proposed that the absence of absorption toward the center was caused by elevated densities in the center. This was verified by observations of mm-lines with the IRAM 30-m telescope, which in turn led to the identification of B335 as a collapsing protostar (Zhou et al. 1993, ApJ, 404, 232). A quantitative interpretation depends on the detailed behavior of collapse, and very different collapse scenarios are in competition at present (for a review, see Myers et al. 2000, Protostars & Planets IV, eds. Mannings, Boss, Russell; Univ. Arizona, p. 217). In particular, the collapse depends on the initial conditions: collapse from

a singular isothermal sphere produces a constant mass accretion rate (Shu 1977, ApJ, 214, 488), while collapse from a density distribution like a Bonnor-Ebert sphere produces an initial phase of very rapid collapse, relaxing toward the Shu solution at later times. Neal Evans, Kaisa Mueller (U. Texas) & Paul Goldsmith (NAIC/ Cornell) made Arecibo H2CO observations in Dec 2001. The first challenge wa s to dev elop an appropriate data taking strategy. The standard Arecibo position-switching routine, with OFF position designed to track the illumination across the same section of the primary reflector, wa s p r oblematic here, as the sources are embedded in much larger, low density clouds, and absorption in the OFF position could "contaminate" the data, producing fake emission. Switching to a fixed reference position was a quickly-developed option, but would have negative implications for data reduction. Fortunately, taking simple total power "ON SOURCE" spectra revealed that the receiver and autocorrelator (with digital bandpass filters) gave a baseline that was limited only by fluctuations expected from the radiometer equation. This method also doubles the sensitivity compared to position switching, and should be of general value for observation of narrow spectral lines. The absorption spectrum obtained at the central position of the PPC L1512 is shown in Fig. 2 (pg. 6). The line width is ex tremely narrow and they have what is perhaps the best astronomical resolution to date of the hyperfine components of the transition. This is likely a result in part of the relativ ely small (1') Arecibo beam at 6 cm. The hyperfine structure is an additional tool to determine the optical depth and thus the distribution of formaldehyde in the cloud. Evans et al. observed 7 positions for each of 3 PPCs: the center, 2 positions 1' from the center on the long axis of the source, 2 positions 1' off-axis (perpendicular to the axis), 2 positions 2' away off-axis. For L1544 and L1498

March 2002, Number 34

15

NAIC/AO N ewsletter


Figure 16: A map of H2CO 6-cm absorption against the CMB for the dark cloud L1544. The F= 1-0 hyperfine component is clearly visible as the weaker dip at higher velocity, and there appear to be small line-profile changes as a function of position. (Courtesy: Neal Evans)

the axis runs NW-SE, while for L1512 the axis runs N-S. After 4 nights they had an integration time of about 100 min (20-25 â 5-min scans) for each central position and an average rms of 0.015 K. The line was about 0.5 K at each central position and hyperfine components were clearly visible. Integrations were about 30 min on each of the other positions, with resultant rms of about 0.025-0.030 K. A map of five positions observed in L1544 is shown Fig. 16. The observed sources are all considerably more extended than the map coverages; this is somewhat unexpected, and may be indicati v e of an increase in the abundance of H 2 CO aw ay from the cloud centers. This would be a surprise in terms of the cloud chemistry. This team now propose to complete the maps of these 3 clouds. They hope to combine this data with other cm- and mm-wave data to determine accurate densities for the clouds and will be in a position to model the density as a function of position. Note that Arecibo's high angular resolution is essential for this to separate the small, dense source from the ex tended cloud. They also wish to observe additional sources, to determine whether these clouds are sufficiently dense to exhibit H2CO 6-cm emission. This would immediately be an interesting result in terms of accurate modeling of the dynamical state of such a core.

Detection of OH in IRC+10°216 Saavik Ford, David Neufeld (Johns Hopkins) & Paul Goldsmith (Cornell/NAIC) have used the Arecibo telescope to obtain the first detection of OH molecules in the circumstellar envelope of the extreme carbon star IRC+10°216 (CW Leonis), providing additional evidence for the presence of icy bodies in orbit around that star. The OH detected at Arecibo is believed to arise from the photodissociation of circumstellar water vapor by interstellar ultraviolet radiation; the new result thereby provides an important confirmation of a previous direct detection of water vapor around IRC+10°216 by the Submillimeter Wave Astronomy Satellite (SWAS), removing any doubt as to the identification of the single spectral line that SWAS observ ed. (The new Arecibo observations also demonstrate the fruitful synergy that can be obtained by combining observations from the largest and the smallest radiotelescopes in the world!) The discovery of water vapor in the outflow of this extreme carbon star -- announced at a press conference at NASA Headquarters last July -- is surprising because the water abundance inferred from either the SWAS water detection or the Arecibo OH detection is five orders of magnitude larger than that expected within the outflow from a star as carbonrich as IRC+10°216. Melnick et al. (2001, Nature) have argued that the only plausible explanation for the observed water vapor abundance is that a population of orbiting icy objects is being vaporized as the star ascends the Asymptotic Giant Branch (AGB) and stellar luminosity increases dramatically. Thus the SWAS and Arecibo observations provide the first evidence for the presence of orbiting water ice in a solar system other than our own. Detailed calculations (Ford and Neufeld, 2001, ApJL) indicate that 10­100 Earth masses of orbiting ice are required at a distance of 75­300 AU from the star in order to supply the observed amounts of water and OH throughout the AGB phase; this is comparable to the amount of ice originally believed to have

Figure 17: (Upper panel) The spectral profile of the 1667-MHz OH line for IRC+10°216 obtained at Arecibo in 30 hr. (Lower panel) The 557-GHz line of water vapor detected in 392 hr using SWAS. (Courtesy: Paul Goldsmith)

been present in our own solar system's Kuiper belt. Fig. 17 (upper panel) shows the Arecibo spectral line profile o f t h e 1667-MHz OH line, obtained with a total integration time of 30 hr. The blue feature is significant at the 5- level. Its 1665-MHz counterpart is detected at the 3- level, with a line strength that is consistent with excitation in local thermodynamic equilibrium. The lower panel shows the 557-GHz line of water vapor detected in a 392 hr observation using SWAS. The obvious difference between the line profiles reflects the fact that the water line is optically thick and originates within a region much smaller than the SWAS beam whereas the OH lines are optically thin and spatially more extended. Additional observations are under way at Arecibo to improve the signalto-noise ratio in the OH spectra and to allow the line profiles to be better constrained. A careful study of the OH-line profiles promises to provide important clues about the spatial distribution of the OH molecules and of the

March 2002, Number 34

16

NAIC/AO N ewsletter


parent water molecules that gave rise to them. A C-Band Spectral-Line Survey of IRC+10°216 In Dec 2001 and Jan 2002, a team lead by Esteban Araya & Peter Hofner (UPR-RP) conducted an Arecibo C-Band (4-6 GHz) spectral scan towards IRC+10°216 (CW Leo). This is a latetype carbon-rich star with extensive mass loss. It is also the strongest source of circumstellar mm-wave spectral lines due to the large number of carbon-based molecules in its envelope and its relative proximity to the Solar System (290 pc). More than 45 different molecules have been identified in the extended atmosphere of this AGB star, 15 of which have only been detected towards this source. Systematic spectral-line surveys of IRC+10°216 have been published in recent decades, principally at mm and sub-mm wavelengths. The procedure used for these observations was the standard ON-OFF + noise-diode. Observations of calibrator point sources were conducted to obtain the telescope gain. Sources with declinations similar to that of IRC+10°216 were used, so that the gain curves obtained correspond to similar tracks on the sky to that followed by CW Leo itself. Fig. 18 shows the spread of the measured gain for different frequencies. The vertical spread at each frequency is due mainly to the different positions on the sky where the calibrators were measured.

Velocity (km/s)

Velocity (km/s)

Figure 20: Spectra of the total-power and Stokes-Q emission of the 1665-MHz line from OH maser IRAS06446+0029 (Courtesy: Slava Slysh)

The four boards a v ailable in the Arecibo correlator were centered at different frequencies with bandwidths of 25 MHz each. This setup gave around 85 MHz of useful spectral coverage per scan. Thus, a total of 25 scans were needed to co v e r the entire Arecibo C-Band frequency range. An average of 35 min on-source were spent on each of the 25 scans, resulting in a rms noise level of ~3 mK. The strongest line detected corresponds to the rotational transition J = 2­1 of the HC5N molecule (Fig. 19). Nine additional spectral line candidates were also detected, which will need confirmation. As part of the results of this project, the team will estimate the column density of HC5N, as well of other detected molecules, and establish constraints on abundances of non-detected molecules. They will also prepare an Arecibo Technical Memo on the RFI encountered during the observations. A Polarization Survey of OH Masers Most Galactic Plane OH masers accessible from Arecibo are being measured in all Stokes parameters for the four OH

ground state transitions by Slava Slysh (NAIC). The goal of the survey is to find linearly polarized spectral features which can be used in future VLBI observations for simultaneous phase calibration of both LCP, and RCP channels. The first part of the survey in the Anticenter region has been completed, with several new linearly polarized masers found. As an e xample, Fig. 20 shows spectra of the total-power and Stokes-Q emission of the 1665MHz line from OH maser IRAS 06446+0029. The Death of OH/IR Stars OH/IR stars evolve into "dead OH/IR stars" when they are no longer expected to exhibit detectable 1612-MHz masers. The discovery of the prototype, IRAS18455+0448, was made by Arecibo summer students during the initial tests after the Gregorian upgrade. By 1998 its masers had weakened over 10 yr from 2.1 Jy to ~100 mJy, and were seen thereafter to decay exponentially. 18455+0448 has not been detectable since Dec 2000; moreover its red IR colors and the lack of any variability in its mainline masers suggest that it has indeed become a proto planetary nebula. The identification of more dead stars has been a prime objective of the summer project for REU students run by Murray Lewis (NAIC) over the past 3 yr, and wherein new 1612-MHz spectra are obtained for the set of OH/IR stars detected at Arecibo during 1985-88. Spectra for ~75% of this set, including all 328 with a peak first-epoch I (1612 MHz) > 100 mJy, are now to hand. These have provided 3 more dead

Figure 18: Measured Gain versus Frequency. The vertical spread at each frequency is mainly due to different positions on the sky where the calibration sources were observed. (Courtesy: Esteban Araya)

Frequency (MHz)
Figure 19: The rotational transition line (J = 2­1) of the HC5N molecule in the circumstellar envelope of IRC+10°216. (Courtesy: Esteban Araya)

March 2002, Number 34

17

NAIC/AO N ewsletter


stars, while a fourth, FV Boo, is in the process of dying, having exponentially decaying masers that should disappear within 2-4 yr. However, the blue IR colors of the newly-identified "dead" stars, together with their H2O & SiO masers, and the 315-day period of FV Boo suggest that these objects are still AGB stars, rather than proto planetary nebulae. So most dead stars cycle back through a Mira variable phase, before evolving into OH/IR stars again after an interlude of many thousands of years. This scenario thus expects AGB stars to pass through the OH/IR star phase more than once. The positions of the dead OH/IR stars on first-epoch plots of I(1612 MHz) against S(25µ), and on plots of the ratio of these quantities against the IR color, are entirely normal. However, all of the dead stars have small, <12 km s-1, expansion velocities, and all but one have blue IR colors. When these criteria are used to delimit the sample further, the 5 dead stars in a sample of 112 imply a mean 1612-MHz emission life of 112â14/5 ~ 314 yr. The short duration of this emission phase is readily understood if oxygen-rich AGB stars toward the end of the AGB pass through a brief OH/IR star phase after a thermal pulse, when, as often happens, they are not bright enough to support heavy mass-loss on the luminosity ascent to a thermal pulse. Copious AGB mass-loss is thus frequently triggered by events following after a thermal pulse. Solar System Studies Don Campbell

Figure 21. Moon over 2002 BM26: A delay-Doppler image of the binary near earth asteroid 2002 BM26 made on February 14, 2002 with the Arecibo 13 cm radar system. Time delay (distance from Arecibo) increases from the top down with each pixel corresponding to 15 m (50 ft). The horizontal axis is Doppler shift or relative velocity between different parts of the rotating bodies in the system. At the time this image was made the small secondary body was almost directly in line between the earth and the larger primary body. The primary looks much larger than three times the secondary because its 2.7 hr rotation period is much smaller than that of the secondary so its Doppler broadening is much larger.

F

or Arecibo's Planetary Radar program the past few months have been a period of considerable success in the observational programs coupled with great concern about the future funding of the program. NASA funded the installation of the first 13 cm wavelength transmitter at Arecibo in the mid-1970s and the current, higher powered, one as part of the recent NSF and NASA-funded upgrading of the telescope and radar system. Along with
March 2002, Number 34

the capital costs NASA has also provided yearly operating funds, most recently under the Near Earth Object Observing (NEOO) program. These funds cover the incremental costs of the operation and maintenance of the transmitter and data acquisition with the NSF covering the normal telescope operations costs. In late 2001 NASA indicated that they would no longer be able to support the program starting in 2002 due to the limited funds in the NEOO program and the need to concentrate on the search for NEOs. Following strong, and greatly appreciated, expressions of community support for the Arecibo program NASA restored about 75% of the requested 2002 funding with future funding dependent on discussions with the National Science Foundation and a review of the program. At this time funding for 2003 and beyond is still uncertain. Observationally, late 2001 and early 2002 have seen very heavy use of the radar system for studies of near and mainbelt asteroids, of the rings, Titan and Iapetus in the Saturn system, and of Io, the volcanic Galilean satellite of Jupiter. All of these program s have benefited greatly from the increase in sensitivity due to the resetting of the panels of the primary reflector. As a result of the

resetting the telescope's gain at 13 cm went from about 7 K/Jy to 10 K/Jy. Since the sensitivity of the radar system is dependent on the square of the gain this represents a doubling of the radar's sensitivity. This has had a tremendous impact on the quality of the observations of asteroids, Titan and the rings of Saturn and enabled the first detection of a radar echo from Iapetus. Binary NEAs A fifth binary near-Earth asteroid was discovered by M. Nolan, E. Howell (NAIC), C. Magri and B. Beeney (U. Maine), using the Arecibo 13 cm radar. 2002 BM26 w a s found on January 26, 2002 by the MIT/Lincoln Laboratory LINEAR near earth object search program. Its estimated diameter was 410 m and close approach to the earth was in mid-February at a distance of 0.06 AU . Since BM26's transit time at Arecibo coincided with the time of a program of radar observations of mainbelt asteroids being conducted by C. Magri, M. Nolan and collaborators, a "quick look" observation of BM26 was made on February 9. The delayDoppler image showed two components at roughly the same distance from Arecibo but separated in Doppler shift

18

NAIC/AO N ewsletter


by an amount corresponding to a velocity difference of about 0.1 m/sec (4 inches/sec) along the line-of-sight to Arecibo. Subsequent observations on Feb 10, 12, 13 and 14 clearly showed the binary nature of BM26 with the last three observations having high sensitivity as they were made near the date of closest approach of BM26 to the earth (Fig. 21). The range extent of BM26 gives a size estimate between 700 m and 800 m, considerably larger than predicted from the optical observations indicating that it has a much darker surface than most asteroids. The "moon" is about one third the diameter of the primary body and is rotating about the primary at a distance of about 1.2 km with an orbital period close to 24 hrs. The Arecibo and Goldstone planetary radar systems have now discovered five binary NEAs in the last 18 months. Given the number of NEAs that have been observed with the radar systems it appears that 10% to 20% of NEAs may be binaries. This is in agreement with the inferred percentage from optical brightness changes that are interpreted as being due to occultations or eclipses in binary systems and the number of paired impact craters on the earth. How these systems are formed is still a considerable puzzle. However, one important result of the discovery of these systems is that their mass can be obtained from the binary orbits allowing for the first time estimates of the densities of NEAs, a major indicator of their internal structure and composition. Rings of Saturn P. Nicholson (Cornell), D. Campbell (Cornell/NAIC), R. French (Wellesley), M. Nolan (NAIC) and J-L. Mar got (Caltech) used the radar system to image the rings of Saturn in December, 2001 (Fig. 22). This w a s the third set of observations made ove r three years with the primary objective of studying azimuthal asymmetries, variations in the radar echo power with azimuth in the A or B rings, as a function of the tilt of the ring plane to the line-of-sight

1000 December 2001

Delay (msec)

500

0

­500

­1000 ­400

­200

0 Doppler (kHz)

200

400

Figure 22: Delay-Doppler radar image of Saturn's rings at a frequency of 2380 MHz acquired at Arecibo in December 2001. Time delay increases from bottom to top (±1 second relative to Saturn's center of mass), while Doppler shift increases from left to right. The near side of the outer or A ring appears at a smaller delay than the inner or B ring, but the Keplerian velocity gradient in the rings means that the B ring appears at a larger Doppler shift (both positive and negative). The four bright "crossover" regions correspond to longitudes approximately 35 deg on either side of each ring ansa, where signal from both the A and B rings falls into the same delay-Doppler cells. The azimuthal asymmetry is most visible in these regions, with the rings being brighter in the far quadrant on the receding (negative Doppler) ansa and in the near quadrant of the approaching (positive Doppler) ansa. In agreement with the earlier Arecibo results, the echo from the C ring is too weak to detect. The farthest portion of the B ring is blocked by Saturn. The planet itself does not reflect radar waves, and is invisible. (Courtesy: P. Nicholson and R. French)

from the earth. This work parallels an effort lead by R. French to study the asymmetries at optical wavelengths using the Hubble Space Telescope. Looking at Figure 22 the rings are noticeably brighter in the far quadrant on the receding (negative Doppler) ansa and in the near quadrant of the approaching ansa. Fits of models to the data show that the asymmetry is concentrated in the outer, or A, ring, where its amplitude is 25% of the average reflectivity. A similar asymmetry has long been seen in optical images of the A ring, b u t the radar amplitude is 2 to 3 times larger. The most widely-accepted ex planation of this phenomenon involves gravitational "wakes" generated by individual large ring particles, which are distorted by Keplerian shear into elongated structures trailing at angles of approximately 70 deg from the radial direction. Such wakes are indicative of incipient gravitational instability and are e x pected to ha v e characteristic length scales of 30­100 m. The rings appear brighter when the wakes are seen sidew ays, and f ainter when they are viewed end-on. Surprisingly,

there also appears to be a much weaker azimuthal asymmetry in the B ring, with the same phase as that in the A ring. This was seen first in the 1999 radar images, and then confirmed in near-simultaneous HST images and the subsequent radar data. By continuing to image the rings as their opening (tilt) angle slowly decreases over the next few years, valuable information will be obtained on both the small-scale wake structures and on the vertical thickness of the rings, which is thought to be as little as a few tens of meters. This can tell us, in turn, something about the mechanics of interparticle collisions in the rings and the size of the largest ring particles. Iapetus One result of the increase in the sensitivity of the radar system due to the resetting of the telescope's primary reflector was the first detection of Iapetus, the third largest satellite of Saturn after Titan and Rhea, by G. Black (NRAO), D. Campbell, L. Carter (Cornell), M.

March 2002, Number 34

19

NAIC/AO N ewsletter


Nolan (NAIC), and S. Ostro (JPL). An unsuccessful attempt was made to detect Iapetus in late 2000 before the telescope's reflector surface was fully reset. The observations concentrated on the bright (trailing) face of Iapetus and showed that this hemisphere has relatively "normal" radar reflection properties, very unlike those of the icy Galilean satellites of Jupiter. Since the bright face of Iapetus is an icy surface this is a puzzle. The dark "leading" hemisphere of Iapetus is about 10 times less bright than the trailing hemisphere. Whether this is due to a thin surficial layer of dark material or to a thick layer of, possibly, hydrocarbons is not known. Radar observations of the dark hemisphere planned for late 2002 may answer this question. Space and Atmospheric Sciences Sixto A. GonzÀlez Studies of lightning and lightning induced ionospheric effects at Arecibo Observatory n August-September 2001 an experimental campaign was conducted in Puerto Rico to perform correlative studies of lightning and lightning-induced ionospheric effects using the Arecibo Observatory 430 MHz UHF radar, a VHF radio interferometer and broadband electric field plate antenna of New Mexico Tech, broadband and narrowband VLF receivers of Stanford University, and a low light video camera. Also GOES 8 weather imagery was continuously acquired and archive d during the duration of the campaign.

effects of thunderstorms, studies of VHFquiet positive leaders, and studies of large-scale optical phenomena above ocean thunderstorms in the tropics. In order to thoroughly study the atmosphere/ionosphere and the lightning at lower altitudes, the Arecibo Observatory 430 MHz UHF radar operated in two modes: (1) The ionospheric mode (pulse length 104 microseconds -- 13 baud Barker code, IPP 10 ms, range 22-500 km); and (2) The leader mode (pulse 2 microseconds, IPP 1 ms, range 6-60 km). In addition, lightning properties, location and time of occurrence (with 1 microsecond resolution) were measured using the 274 MHz New Mexico Tech interferometer system deployed in Barrio Dominguito, Arecibo. A flat plate antenna, allowing detection of the electrostatic field change and polarity of cloud to ground lightning strikes, complemented the interferometer system. Stanford University deplo yed a VLF receiver on Vieques Island to perform broadband recordings of lightning sferics --"sferics" is an abbreviation of "radio atmospherics", which are electromagnetic signals in the ELF/VLF frequency ranges that are launched into the Earthionosphere waveguide by lightning discharges -- and narrowband recordings of a sub-ionospherically propagating 40.75 kHz VLF signal from a NAU transmitter (Aguada, Puerto Rico) in order to monitor lightning-associated lower ionospheric

disturbances. The observational program was complemented by video recordings of lightning and large-scale luminous phenomena above thunderstorms (i.e., sprites and jets) using a SONY CCD video camera equipped with GEN III intensifier. All instruments planned for this program were successfully deployed and collected unique data sets, analysis of which is currently ongoing. The interesting results that have been uncovered to date include: (1) The discovery of sprites above Haiti/Dominican Republic thunderstorms on September 3, 2001; (2) The successful detection in the sidelobes of UHF returns from lightning dischar ges, which dev eloped in the vicinity of the Arecibo Observatory on September 5, 2001. These returns have been successfully correlated with the VHF interferometer data; and (3) The discovery of a new luminous phenomenon, which represents an electrical discharge from a thundercloud top to the lower ionosphere, on September 15, 2001. The new luminous discharge results were accepted for publication in Nature. There will be a separate web page with all the electronic materials related to our Nature paper available for ev eryone. The link to the web page will be available directly from http://www.nature . com . Copies of all materials will also be available at http://pasko.ee.psu.edu/Nature. (Editors

I

The team of visiting scientists at Arecibo Observatory included Victor Pasko and John Mathews (CSSL Laboratory, The Pennsylvania State University), Mark Stanley (Department of Physics, New Mexico Tech; currently at Los Alamos National Laboratory), and Tr oy Wood (STAR Laboratory, Stanford University).--see photo. The scientific goals of the campaign included studies of the ionospheric
The lightning studies team, from left to right: Victor Pasko, Mark Stanley, John Mathews, and Troy Wood.

March 2002, Number 34

20

NAIC/AO N ewsletter


note: please see the image on page 30 of the "Blue Jet" from the Nature article.)

This program was supported by a Small Grant for Exploratory Research of the National Science Foundation to the Pennsylvania State University. The GEN III intensifier wa s provided by ITT Night Vision Industries. We are grateful to Jim Ducharme for help with deployment and operation of the VLF system on Vieques Island. In addition to the support the team received from the SAS staff they especially acknowledge special efforts by Eva Robles, Arun Venkataraman, and Edgar Castro (all NAIC). Topside ionosphere and exosphere Robert Kerr (Scientific Solutions, Inc.), and RaÇl GarcÌa and Sixto GonzÀlez (NAIC) performed topside observations during the October 2001 and January 2002 new moon periods. The Optical Laboratory operated Fa bryPerot interferometers at 630 nm, 656.3 nm, and in the infrared at 1083.0 nm, measuring F2 -re gion O, e xospheric H, and He in the upper thermosphere respectively. James Wey of Analog Devices Inc. assisted with the infrared Fa bry-Perot data-taking during the January campaign. Two photometers also operated during these observation periods, at 844.6 nm and 656.3 nm. The 844.6 nm photometer pro vides information on the photoelectron flux and constrains atomic O density above the F2 peak. The October period was a weather washout for the optics, as Kerr garnered only 3 hours ove r a 6-day period of clear sky data. The ISR detected very strong He+ layers (of over 50%) during that period and also during a 24-hour POLITE World Day observation that same week. The January period, on the other hand, was excellent weatherwise, and we obtained six consecutive nights of optical data; unfortunately the performance of the 430 MHz transmitter was poor, barely achieving 1 MW of power. Consequently the quality of the radar data was not up to what we are
March 2002, Number 34

accustomed. Preliminary analysis shows the layers were not as strong as in the equinox campaign. The He airglow data from that period were of the highest spectral resolution yet obtained, and will provide exobase neutral He temperature with unprecedented precision. Also during the month of January we hosted a visit from Chris Holmes from Williams College in Massachusetts. He spent four weeks working with GonzÀlez and using the topside data we ha v e acquired over the last few years to do a study on the behavior of the nighttime O+ and H+ fluxes in the lower topside ionosphere. Electron and Gyro-lines Very powerful and sensitive incoherent scatter radars, such as Arecibo and Jicamarca, sometimes surprise their users with unexpected results. Such mysteries should be followed up because the y might lead to new discoveries or the resolution of nagging problems in novel ways. Recently, we have been improving our data-taking system in order to do our ISR measurements over much wider bandwidths than were tractable before. Efforts by Mike Sulzer (NAIC) and Sixto GonzÀlez to measure the entire incoherent scatter spectrum, so as to include the gyroline, electron line and low density plasma line, have resulted in spectral measurements that do not agree with our theoretical calculations, and this is a mystery still under investigation. These parts of the incoherent scatter spectrum are difficult to measure because the spectra cover a wide frequency range and are very weak. We did not realize this when we made the first measurements in July of 2000, but we were elated to find that we could measure the nearly Gaussian shape expected for the electron component when the density is very low and the electrostatic interaction is very weak. We were very lucky that our measurements corresponded to the Bastille Day storm, which depleted the ionosphere, and thus gave us the low densities we required at

a lower height (better signal to noise ratio) than normal. Our elation wa s soon gone when we found that the spectra from higher density regions did not agree with our expectations. The first mistake we found wa s that we had not been properly accounting for the magnetic field effects in our calculations. There are very few published spectra with the full calculation; it is neither easy nor terribly useful, since it is generally not needed (for example, for least squares fitting of the ion line the effect is negligible), as one would expect if the spectra under study do not test this part of the theory. We did get the calculations correct, duplicating results from a twenty-five year old paper that used a very different method. The agreement actually verifies both methods of calculation. There are various reasons why the measurements might not agree with the theory, and it is only after eliminating many that one begins to suspect the theory. First, could there be something special about the storm night spectra? We cannot think of anything, but in any case we made more measurements, and they were the same. Could there be something wrong with the data collection and processing. This experiment requires the collection of large amounts of raw data and off-line computing. In order to store as little as possible we kept samples of two bits only. This should be fine, but in order to verify it we collected more data with a new system. The data were the same. To check the effect of the two-bit approximation we collected eight-bit data. The the amount of data w a s somewhat overwhelming, but, except for the fact that with the eight bit data we can go to lower altitudes where the signal is stronger and thus begins to exceed the noise level, the results were the same as with two-bit data-taking. Now we have a measurement showing the plasma line very much as the theory predicts in the lower topside. At higher heights the disagreement with the theory becomes large and then decreases at still

21

NAIC/AO N ewsletter


2200 km

ne = 2676cm -3

Measured (24 Oct 01) and Theoretical Spectra
Scales of individual plots adjusted for good visibility 6171

10772 Te = 1200K 1300 km 18803

32821

coded-long-pulse gives less RMS error than the double pulse technique. Also in October, Wes Swartz et al. (Cornell) had three nights of observations using the Arecibo ISR in dual beam mode together with a coherent 50 MHz radar (CUPRI) stationed at Isabela. They encountered strong sporadic- E ( E s) during all three nights. On two of the nights they noticed range changes with time as the echoing layer moved south and AO data indicated a decrease in height of the observed layer. On the third night, the echoes had QP characteristics. Jonathan Friedman (NAIC) and Jonas Hedin (LuleÅ University of Technology, Sweden) carried out observations of the mesospheric potassium layer throughout the fall period. Temperature profiles of the mesopause-region (80-105 km) can now be measured on a regular basis and data were recorded during October, November, and February. These observations will contribute to the study of mesopause-region climatology. Strong mesospheric inversion layers have been observed frequently, and on November 13 in the pre-dawn hours a very strong inversion layer occurred. The temperature increased from about 200°K to near 250°K in a five-hour period! These and other temperature data are presently being analyzed in greater depth. On the night of November 17, Friedman and Hedin, along with Craig Tepley and Shikha Raizada (NAIC) operated K and Fe lidars in meteor mode -- short integrations and small range bins -- during the Leonids meteor shower peak period. It was a spectacular night to spend at the lab, as we sat outside watching a meteor show that reached near-storm proportions. Just after 0500 local time we were counting over 10 meteors per minute! The lidar data has not yet been fully analyzed, but we hope to present our results at a future Leonids meteor shower workshop. In February, the alexandrite laser received a much needed service call that included upgrades to the cavity

57290 Bottom three heights amplified to show weak gyro feature 1e+05

410 km

2.5 MHz

Frequency

2.5 MHz

Figure 23: Observed electron line spectra on October 24, 2001 (left panel). The horizontal axis is frequency in MHz (Only half of the spectrum is shown) and each subpanel in the vertical direction is for a different range increasing in altitude from 410 to 2200 km. The right panel shows what ISR theory predicts for similar temperature, density and magnetic field conditions. It is clear that there is some agreement for the plasma line (the outermost feature in the plots near 2.5 MHz that moves towards the center with increasing height/decreasing density). However the gyroline (the inner feature that is close to 1 MHz) shows disagreement in the shape, location and variation with respect to density/height. (Courtesy Mike Sulzer and Sixto GonzÀlez)

higher heights, as shown in Figure 23. It is very hard to find fault with these measurements! In order to check the eight-bit system we made one more measurement involving weak and strong spectral features in the same spectrum. This was a gyro line measurement in the E-region. This succeeded once years ago with much inferior equipment and seemed worth doing for its own sake. As usual when one does a novel experiment the results can be surprising! The gyro line was detected, and its frequency varies with field angle changes in the direction predicted by theory, although the absolute frequency is off a bit. The surprising thing is that there is a second "gyro line" at a higher frequency that changes in the opposite direction with field angle variation. If real, it must be the result of photoelectrons, since it is far outside the thermal distribution.

Mesospheric and E-region studies In September we conducted the first dual beam LTCS campaign. By taking advantage of the newly available computing power, we were able to sample at 300 m height resolution whereas before the upgrade the height resolution was limited to 1.2 km. The dual beam capability allows the direct observations of vertical and horizontal drifts simultaneously, and thus provides a good opportunity to better understand the ionization layer formation process. The improved capability will allow us to provide better quality data to the CEDAR community and is especially significant for upcoming CEDARTIMED campaigns. In October, Dennis Riggin (Colorado Research Associates, Inc.) and Qihou Zhou (NAIC) used the ISR dual-beam to measure the E-region winds. The objective of the experiment was to compare va rious methods to determine which one gives the best velocity estimates. Preliminary analysis shows that the

March 2002, Number 34

22

NAIC/AO N ewsletter


stabilization electronics, the Q-switch driver, and the addition of a new and more stable seed laser. It got its first test during a 4-day and 5-night run that included Rayleigh lidar and the ISR to observe tidal motions in the MLT region. From February 13-18, 2002, Zhou, Tepley, Raizada, Hedin, and Friedman carried out thesee optical/radar observations, which included E-region airglow observations as well. The objective of the experiment was to combine the radar and lidar measurements to obtain ion-neutral collision or ion composition within Es layers. By combining the radar daytime and lidar nighttime measurements, they hope to characterize the tides much more accurately. Finally, Raizada and Tepley were recently able to detect neutral calcium in the upper atmosphere using resonance fluorescence lidar. This was done by configuring the Arecibo frequencyagile dye laser to tune to the resonance line of Ca at 422.7 nm. Lidar backscatter signal strength wa s found to be relatively weak, however, the emission wa s detectable in a few minutes of integration. Figure 24 shows the distribution of Ca as a function of altitude for the morning of 22 February 2002, for a 100-minute average (22 profiles). The altitude distribution, roughly between 80 and 100 km, is similar to what we have observed for other metals like Na, K, and Fe, but the abundance is lower than expected for this initial measurement.
Calcium Distribution at Arecibo 22 Feb 2002, 04:06-05:47 AST 110
Ca (422.7 nm)

Observations of calcium (compared with other metallic species) are important because not all metals behave the same in terms of their chemistry. For example, in typical meteors, Ca is twice as abundant as sodium, and its backscatter crosssection is 2.5 times larger as well. Based on this, and what we have observed in the past for Na, one would expect to see at least 1000 atoms/cm3 for Ca, not a factor of 100 times less that we observed, as shown in the figure. We suspect that calcium does not ablate completely from meteors to its atomic form where it can be detected by resonance lidar, but instead breaks off in the form of larger, multiatom clusters. We need to carry-out these studies further to determine if our first detection was a typical or an anomalous night, because such observations have a direct bearing on understanding the chemistry of va rious metals and the problems of meteor ablation. Other news The 2-day Wide-Latitude World Day Study in November went well, however a substantial amount of time was lost during the December World Day because of both receiver and transmitter problems. Also, Diego Janches (Penn State/NAIC) has been continuing his work on micrometeors using the 430 MHz radar as well as the Na, Fe and K lidar facilities. As part of his CEDAR/NSF fellowship work, Diego has been observing one or two nights a month using both the ISR and lidar facilities. So far he has done this in December January and February and will try to continue a series of monthly observations for the remainder of the current year. The proposal to reestablish our HF capabilities here on site is coming along well. Mike Sulzer is awaiting a few cost estimates in order to complete the budget. These are expected shortly, and then we will have a document that can be circulated for comments. We expect to have the proposal submitted later this spring. The data-taking situation is also continually improving and we expect to

gradually add power and flexibility to our system over the coming year. Computer Department News Arun Venkataraman Internet 2 and remote access he AO's connection to the Abilene/ Qwest high-speed research network backbone ("Internet 2") was made in early November 2001 via a dedicated OC3c fiber link to the PRISANET gigaPOP located at the University of Puerto Rico's High Performance Computing Facility (http://www.hpcf.upr.edu). The mainland connection is via a 45Mbps link to the South Florida gigaPOP provided by the AMPATH Project (http:/ /www.ampath.fiu.edu ). Initial tests have yielded unoptimized single-stream transfer rates of up to 500KBytes/s. Typical unoptimized aggregate transfer rate (using multiple streams) is 1-2MBytes/s.

T

Routing to the Internet 2 backbone is currently transparent to internal hosts: the AO border router will automatically select the Internet 2 access path for connections to I2 institutions, sending other traffi c via the T1 commodity Internet link. Remote access from external I2 sites is allowed using Secure Shell to the host "remote2.naic.edu". WAPP upgrade An upgraded version of the Wideband Arecibo Pulsar Processor (WAPP) is under development by Bill Sisk and Jeff Hagen, using a dual 1GHz Intel Pentium III processor board. Off-theshelf I/O interfaces are used to acquire data from the WAPP's 100MHz, 16-chip correlator board at up to 50MBytes/s. Output rate is currently limited by the single disk I/O rate of 30MBytes/s. Four such machines will be initially built for an aggregate maximum observing bandwidth of 400MHz. An expanded version of this machine will serve as a backend for the multibeam system.

Altitude (km)

100

90

80

70

0

5

10 Concentration (cm-3)

15

20

Figure 24: First lidar observations of neutral calcium at Arecibo. The range resolution for these data was 150 m and the transmitted power at 422.7 nm was 0.8 W. (courtesy C. Tepley and S. Raizada).

March 2002, Number 34

23

NAIC/AO N ewsletter


Alex Wolszczan Receives the Stamp of Approval from Poland
C. Salter leksander (Alex) Wolszczan, planet-discoverer extraordinaire and pulsar aficionado, is an old friend at Arecibo, and an ex-colleague of many of us here. Although Alex left Arecibo after 8 years on the staff in 1992, his visits back to the island have been sufficiently frequent that we almost feel as if he never left! Indeed, he is presently here in residence at the Observatory on an extended sabbatical visit. In 1992, Alex moved to Penn State University, where he is the Evan Pugh Professor of Astronomy & Astrophysics. Subsequently, in 1994, in parallel to his duties at Penn State, he became a professor of Nicolaus Copernicus University, Torun, in his native Poland, and the Director of Torun Centre for Astronomy. He was also elected a member of Polish Academy of Sciences. Alex is no stranger to global recognition of his achievements starting from the Polish Astronomical Society Award for Young Astronomers in 1976. More recently, in 1996, the American Astronomical Society honored him with its prestigious Beatrice M. Tinsley Prize, citing his "creative and innovative analysis of binary and relativistic pulsars culminating in the discovery of a system of planets outside our solar system"; these were the first extra-solar planets known. He was also awarded the 1996 Casimir Funk Natural Sciences Award for natural sciences of the Polish Institute of Arts and Sciences of America. These were soon followed by the Commander Cross of the Order of Merit Award from the President of Poland in 1997, the Gold Medal Award of the American Institute of Polish Culture in 2000, and the Marian Smoluchowski Medal in 2001 - the highest prize awarded by the Polish Physical Society. Now, Poland has recognized him in a unique manner, by placing him on one of their most recent postage stamps. The honor came just 10 years after the announcement of the pulsar planets discovery. The stamp is one of a set of sixteen, each costing Zloty.PLN 1.00, and entitled "The Polish Millennium". The series was released in November 2001, and summarize 1000 years of history, culture, and science in Poland from the perspective of the 21st century. Each is devoted to a different field of life, based on the concept of comparing and associating events and personalities from recent history with times past. The topics covered include Christianity, the theatre, the Polish army, education, art, music, literature and, of course, astronomy. The stamp featuring Alex (born 1946) places stamp,while from the left side we are looked out at by Copernicus forms part of the background. In Lech Walesa, composers Krzysztof Penderecki --Wislawa Szymborska, King Jan III Sobieski, own first day cover? Observing software The AO (graphical) User Interf ace (http://www.naic.edu/~aoui) has been e xtensiv ely e x e rcised o v e r the past sev eral months, and receiv e d man y helpful comments -- a big "thank you" to our user community! Plans for the interface include a dedicated realtime data display screen and a more ergonomically efficient arrangement of the Control Room display screens. The reflective memory monitoring network (using Systran Corp's SCRAMNET Plus architecture) is being expanded to him in august company. He faces us from the right hand side of the by Nicolaus Copernicus (1473­1543). A fragment of "De revolutionibus" addition, Alex shares the rest of the stamp set with ex-Polish President and Fryderyk Chopin, poet--and 1996 Nobel Laureate in Literature and Pope John Paul II. We trust that Alex remembered to order his

A

provide easier access for visitor-owned equipment. Onsite network access A common question encountered from visitors these days is: "How may I connect my laptop to your network?" The problem is easily and automatically solved by enabling DHCP (Dynamic Host Control Protocol) on the laptop (available on most Windows and Linux and Macintosh systems) to obtain all necessary information from our DHCP server. Visitor offices and V SQs are

equipped with 10/100 network switches which accept RJ-45 (twisted pair) drop cables. Just plug in! Service and Queue observing at AO Daniel R. Altschuler

W

ith the position of Service Observing Specialist (SOS) now occupied by HÈctor HernÀndez we are able to offer the new option of service and queue observing, in addition to remote observing. Although we welcome and prefer that observers visit the Arecibo Observatory for their

March 2002, Number 34

24

NAIC/AO N ewsletter


observations we recognize may not always be possible sometimes be inefficient, as tine monitoring programs observations.

that this and may with rouor short

The SOS will also undertake queue observing of approved proposals, using small pieces of unassigned time on the telescope schedule. Observers that get approval for Service Observing for their projects will have to provide the SOS (well in advance) with detailed and clear procedural instructions and relevant information. We define observing programs as remote when the conduct of the program remains with the proposers from a remote site via electronic access. The remote observer is responsible for data quality and efficient telescope use. This option provides for the use of Arecibo in standardized monitoring and search programs, and in standardized investigations of large source lists, where most on-the-spot help is provided by telescope operators. The sanctioning of a remote program obligates its PI to contact telescope operations at least three working days before the program reaches the telescope, in order to finalize all program details. Some programs will only be run as remote, with the proviso that a PI or a collaborator is present at Arecibo for its start, both to ensure that an appropriate protocol is established and to ensure that the quality of data is acceptable. The telescope operator always retains final control and responsibility for the security of the telescope. Remote observers should provide for circumstances that

cannot be foreseen (e.g. communications dropout) so as to insure a successful completion of the observing session. Telescope Operations News JosÈ Cruz roject Phoenix is back again for several weeks. Actual testing and preparations are now in progress by John Ross and Peter Backus. They will start observing on the 4th of March and end on the 23th of March. The Operator's Home Page will soon get upgraded. All information pertaining to operations, receivers, equipment etc.will be given as quickly as possible. The complete URL for telescope operations is: http://www.naic.edu/~operator/ New North Visiting Scientist Quarters (VSQ) Daniel R. Altschuler

Therefore, there is now the option of requesting service observing on the proposal cover sheet in addition to the remote option. The Arecibo Scheduling Advisory Committee (ASAC) will determine whether the project qualifies for the requested service based on: 1. the availability of the SOS, 2. appropriateness of the proposed work to be done as service or remote observing, and 3. the justification for the request. The Service Observing option is intended to provide greater operational flexibility with respect to selected projects for visiting scientists who either cannot travel to the AO facility to carry out their observations at the scheduled periods, or cannot stay at the AO site to complete long observing sessions. The SOS will support a variety of observing projects which do not require the presence of the principal investigator at the Observatory. The SOS will initiate observing runs, monitor data quality, communicate with investigators as necessary, seek advice from NA IC scientific and technical staff, and ship data to observers.

P

A

s you can see from the photographs (next page), construction of the the new North VSQ is proceeding at a rapid pace. This comfortable two-story twelve room unit is located outside our gate at an easy ten minute walk from the control room. Rooms will be equipped with desks and workstations as well as satellite TV. With this unit we will be able to accommodate participants of multi-investigator projects who will not be forced to find

Astronomy Research Associate Position

T

he National Astronomy and Ionosphere Center (NAIC) has an opening for a radio astronomer at the Arecibo Observatory. The vacancy can be filled at the level of staff Senior Research Associate, Research Associate, or Post-Doctoral Research Associate, depending upon the qualifications an d experience of the successful applicant.

A stimulating research environment is provided by approximately 25 resident staff scientists, postdoctoral fellows and senior engineers, as well as over 200 visiting scientists per year. In addition, physics and engineering faculty and students of the University of Puerto Rico have a cooperative research and educational association with the Observatory. Applicants whose research interests include any field of radio astronomy that can be exploited with the Arecibo telescope will be considered for the position. Besides conducting an independent research program, on-site staff scientists are expected to advise visiting scientists in all aspects of their observations, and to help define and implement improvements in equipment, observing procedures and data reduction. A PhD in astronomy or a related field is required. Further details, including application instructions, can be found at http://www.naic.edu.

March 2002, Number 34

25

NAIC/AO N ewsletter


Rooms have a balcony (back of image), bathroom (behind cristal wall) and a small place for a desk (to the right before balcony)

workshops will also benefit from the ability to house the teachers on site. Finally the AUSAC and NAIC-VC who come each year to Arecibo will be housed on site, instead of being placed in expensive hotels at over one hour drive from the Observatory. This will result in improved interaction of committee members with Observatory staff, a better use of available time, and result in significant savings. It would also be possible to shorten the meetings from the current five days to four.

General view of the new North VSQ.

housing outside the Observatory, as was sometimes the case in the past. In addition we will be able to house our REU summer students on site instead of in rented houses at some distance from the observatory . It will be easier for them to adjust their working hours to best use the computing facilities and adjust for observing. It will also improve their interaction with the staff and visiting scientists, and

make their visit more stimulating and rewarding. With the recent completion of the new conference center we have a very nice venue to hold small (of order 30 participants) sc ientific and technical workshops and the North VSQ when added to our current facilities will allow us to house participants on site. Our very successful summer science teacher

Empleado del Aßo
Daniel Altschuler

O

rlando RodrÌguez came to the Arecibo Observatory in 1983 and originally toiled at the now defunct heating facility in Caßo Tiburones. In 1992 he moved onto the main site as a utility maintenance worker. In January 2000 Orlando was promoted to Platform Mechanic, a position he holds to this day. Orlando is a hard worker and very much respected by both his colleagues and his supervisors. He understands the mission of the observatory and the fact that without the hard work of the guys in the trenches, we clean-handed scientists would not have this marvelous facility in which to carry out our invesigations. He is always willing to go the extra mile; he never says no. We are happy to announce that Orlando was nominated by his co-workers and chosen by the Comite del Empleado del Aßo to be the recipient of the 2001 Employee of the Year Award. Congratulations Orlando!

Orlando RodrÌguez receives the 2001 Employee of the Year award from Daniel Altschuler.

March 2002, Number 34

26

NAIC/AO N ewsletter


Comings and Goings Bienvenido Slava Slysh Chris Salter rofessor Slava Slysh, Deputy Director of the Astro Space Center (ASC) of the Lebedev Physical Institute in Moscow, and Chief of the Space Astronomy Division and Science Program Manager for the Raidioastron Space VLBI Project, stands very high among the ranks of the world's radio astronomers. His contributions to the fields of molecular spectroscopy, high-energy radio astrophysics, and space VLBI, to name bu t three, have been enormous. His extensive studies of methanol masers made over recent years were honored in 1997 when the Russian Academy of Sciences presented Slava with their award for outstanding results in astronomy ­ the Bredikhin Prize. Those of us who have had the good fortune to meet Slava over the years, and to number him among our friends, know also of his personal charm, infectious humor and unrivaled enthusiasm.

P

scans. He has also been gracious enough to take on the role of "Friend of the C-band Receiver" for the duration of his stay, and has provided useful input towards improving the optics of our telescope. Slava's stay in Arecibo had a "rocky start" when he was laid low by a potentially serious illness near the end of 2001. Howeve r, he bounced back in amazing fashion, and was soon back in his office working away as if nothing had happened. It was particularly touching during this worrying time to experience the concern of all members of his group in the ASC, as expressed through daily (almost hourly at times) e-mail enquiries, and numerous "get well soon" messages. Fortunately, Slava is now once again in fine form, back to his usual self, and recently attended the IAU Colloquium No. 187 on "Exotic Stars" in Miami. We wish him and Elvira the pleasantest of stays for the rest of their time here with us in Arecibo.

(and hopefully profiting from) their year in the Hatillo Montessori school. Yash is a well known pulsar astronomer, as well as having been intimately involved in the deve lopment of the correlators, pulsar backends and other important aspects of the Giant Metrewave Radio Telescope (GMRT) recently completed, commissioned and operated by the NCRA. On arrival at Arecibo, he soon became active in making observations for pulsar scintillation and singlepulse studies, and showing interest in the development of pulsar instrumentation here. Yash is no stranger to this side of the world, having completed his Ph.D. at the University of San Diego in 1990. He then returned to India and NCRA, where he is an Associate Professor. One of the bonuses of spending a year in Arecibo has been that Yash can continue his working relationship with Ramesh Bhat, now a Research Associate with NAIC but who performed much of his ow n doctoral w o rk in collaboration with, and under the supervision of, Yash. We trust that Yash and his family will have a fruitful, enjoyable time here over the coming months. We also thank him for his contributions to the Observatory, plus his infectious enthusiasm and friendship, during the whole stay.

Bearing all this in mind, Arecibo Observatory has been extraordinarily fortunate in having Slava join us for a year as a visiting Senior Research Associate. Sla v a arri v e d in Puerto Rico at the beginning of October 2001, accompanied by his wife, Elvira. He has been active in developing spectralline polarization measurements with the 305-m telescope, working on OHmaser Space -VLBI data which includes Arecibo and HALCA baselines, and participating in Arecibo C-band spectral

Yashvant Gupta

Bienvenido Yashvant Gupta Chris Salter Arecibo Observatory are in the happy situation of hosting Professor Yashwant Gupta of the National Centre for Radio Astrophysics (NCRA), Pune, India, while he is on sabbatical year. Yash joined us in September 2001 and will be here until August 2002, accompanied in his stay in Puerto Rico by his wife, Richa, and his daughters, Vishakha and Kritika. Over the past months, the Gupta family have become valued members of our local community, the girls enjoying

Bienvenido de Nuevo a NÈstor Aponte Sixto GonzÀlez and Craig Tepley NÈstor rejoined SAS as a Research Associate on the regular staff in January 2002. When his original postdoctoral appointment ran out in September 2001 he choose to take a break and we are delighted to have him back. NÈstor graduated from Cornell where he completed his Ph.D., under the tutelage of Don Farley, developing new analysis techniques to improve estimates of F-region electron and ion temperatures. NÈstor applied these techniques to address two classic problems of the equatorial ionosphere: the energy balance and the midnight

Slava Slysh

March 2002, Number 34

27

NAIC/AO N ewsletter


Adios a Orlando Gil Orlando Gil retired from the Arecibo Observatory on February 28, 2002 after 34 years of service. Orlando joined the Observatory staff in 1968 as an Office Stock Clerk in the warehouse. In 1978 he was promoted to Supply Supervisor. Later, in 1993, he shifted to the Purchasing Department where he worked as a Purchasing Aide for John Pappas. We wish Orlando all the best in his retirement, which he plans to spend in Orlando (FL).

NÈstor Aponte

temperature maximum. He did most of his observational work at Jicamarca before coming to Arecibo in September 1998 as a Cornell Post-Doc. Prior to that time, he was a REU summer student at Arecibo working with Qihou Zhou. Bienvenido Diego Janches Diego Janches comes to us from the Swedish Institute for Space Physics in Kiruna, where he recently completed a term as a Visiting Research Fellow. Diego received his Ph.D. in Electrical Engineering from Penn State University working under Prof. John Mathews in

Diego Janches

2000. His thesis was entitled: Physical and Orbital Properties of Micrometeors Observed using the 430 MHz Arecibo Observatory Radar. Diego plans to continue his study of micrometeors here at the Arecibo Observatory and at Penn State for the next two years, while being supported by a NSF/CEDAR Post-Doctoral Fellowship. Diego hails from Argentina and is a rabid soccer fan. His presence here during the coming World Cup will be welcome.

An Alert for High-z HI and OH Observers

T

his short note is to acquaint Arecibo users with a potential RFI threat for certain L-band observations. This involves a new broadband civil GPS system, GPS L5, planned for the band 1176.45 ± 12 MHz (1164 - 1188 MHz). Recent information slates this system for a first launch in 2004, with a full satellite constellation in 2011. It is proposed that the signals of GPS L5 be 6 dB stronger than those of the current GPS L1. The "HI redshift space" that may well be lost on an essentially permanent basis will be at least 0.195 < z < 0.220. Assuming this system is implemented as described above, there is also likely to be a severe effect on high-redshift searches for galaxies containing OH megamasers (OHMs) at z ~ 0.42. Galaxies have been detected from Arecibo in "the GPS L5 band" both in HI emission and absorption. However, detection of HI (and OHM) emission requires particularly long integrations at these redshifts, even with the 305-m telescope. In addition, 1125 ­ 1225 MHz is a band that Arecibo pulsar astronomers now use regularly, and find to be relatively clean. In view of the above, NAIC now appeals to potential users of the above frequency band to consider at a high priority the submission of Arecibo proposals that absolutely need to observe within the proposed GPS L5 frequency band. This appeal is seen as the astronomical equivalent of an archeological "rescue dig" of a site about to be destroyed by land developers! For completeness, we mention that a new coded GPS signal is planned for 1227.6 MHz, this being co-frequency with the existing GPS L2 transmissions. This is also perhaps an appropriate place to mention the planned installation later this year on the 305-m telescope of a new single-pixel, L-band receiver with improved performance over the existing "L-wide" system. An all-up system temperature of about 25K is being aimed for, with a frequency coverage of about 1125 ­ 1730 MHz. System gain should be at least as good as the 10 K/Jy of the present "L-wide". All future Arecibo proposals should adopt these parameters for their L-band technical justifications.

March 2002, Number 34

28

NAIC/AO N ewsletter


deg [K]

Late Breaking News ­ First Spectral Line Detection with X-Band Receiver Paul Goldsmith and Phil Perillat

06 Mar '02 HC3N, HC7N in TMC1
2.0 1.0 0.0 9096.95
deg [K]

HC3N 1­0 F=1­1 (9097.0346 MHz)

O

n Wednesday march 6, the X-band receiver was used in test observations of the Taurus Molecular Cloud (TMC­1). This v e ry dense, wellshielded molecular region is one of the richest sources of molecular emission in the Galaxy, and serves as one of the fiducial points against which models of cloud structure, chemistry, and evolution are tested. We chose to observe the J = 1­0 transition of cyanoacetylene (HC3N) at about 9.1 GHz. There are three components due to h y p e r fi n e structure (HFS): the F = 2­1, F = 1­1, and F = 0­1 components, with separations of 1 to 2 MHz. Consequently, with the very high resolution necessary to resolve emission in very quiescent dark clouds (line widths less than 0.5 km/s) a separate correlator is needed for each HFS component. Since we have four correlators, we placed the remaining one on the 9.024 GHz HC7N line. We integrated in standard ON+OFF position switched mode with 5 minute on-source integrations, and total integration time of 40 minutes. The resulting spectra are shown in the accompanying figure. There are clear detections of all lines, and you can immediately verify that the HC3N components are in the ratio 5:3:1 expected for optically thin emission in local thermodynamic equilibrium. The high resolution reveals the two distinct velocity characteristic of TMC­1, but even higher resolution and signal to noise ratio could be helpful for a detailed study of the structure of this region. Recent Colloquia 26 February 2002 John Mathews, Penn State Univ ersity ­ "Radio Science Issues Surrounding HF/VHF/UHF Radar Meteor Studies" 21 February 2002, Avinash Deshpande, Raman Research Institute ­ "The Small-

9097.00

9097.05

9097.10

2.0 1.0 0.0

HC3N 1­0 F=2­1 (9098.3321 MHz)

9098.25
deg [K]

9098.30

9098.35

9098.40

2.0 1.0 0.0

HC3N 1­0 F=0­1 (9100.2727 MHz)

9100.20 0.2
deg [K]

9100.25

9100.30

9100.35

HC7N 8­7 0.1 (9024.004 MHz) 0.0 9023.6 9023.8 9024.0 9024.2 9024.4

-0.1

Rest Freq [MHz] (for 5.5 km/s LSR)
Antenna Temperature as a rest frequency for J = 1­0 transition of HC3N and J = 8­7 transition of HC7N. The last plot of HC7N has been smoothed by 11 channels in frequency and velocity. The temperature scale was arrived at by using 45K for Tsys. (Courtesy: Phil Perillat)

scale Structure in Interstellar HI: A Puzzle Resolved?" 19 February 2002, Neil Comins, University of Maine ­ "Heavenly Errors: Exploring Misconceptions About the Cosmos" 31 January 2002, Shami Chatterjee, Cornell Uni v ersity ­ "Neutron Star Kinematics: Pulsar VLBI and its Applications"

28 January 2002, Di Li, Cornell University ­ "HI Narrow Line Absorption--Molecular or Not?" 17 January 2002, Mike Sulzer, Arecibo Observatory ­ "Measuring F region ion and electron temperatures at Jicamarca using incoherent scatter radar: results and theory including the effects of Coulomb collisions"

March 2002, Number 34

29

NAIC/AO N ewsletter


3 January 2002, Robert Mutel, University of Iow a ­ "The Agon y and the Ecstasy: The Rise and Fall of the Small Comet Theory" 14 December 2001, Yashwant Gupta, TIFR Pune University ­ "Cones vs. Patches : Understanding the Geometry of Radio Pulsar Emission Regions" 5 December 2001, Mary Putman, Univ. of Colorado, Boulder ­ "Tracing Galaxy Assembly with High-Velocity Clouds" 29 No v ember 2001, Karen O'Neil, Arecibo Observatory ­ "Crouching Giants? The Properties and Stellar History of Low Surf ace Brightness Galaxies" 15 November 2001, Diego Janches, Arecibo Observatory ­ "Radar meteor studies with Arecibo and EISCAT" 7 November 2001, Bon-Chul Koo, Seoul National University ­ "Shocked HI Gas in Old SNRs" 25 October 2001, Mike Nolan, Arecibo Observatory ­ "Arecibo Radar Observations of Asteroids" 17 October 2001, Paulo Freire, Arecibo Observatory ­ "The millisecond pulsars in 47 Tucanae"

Proposal Deadline
he next deadline for proposal submission will be 01 June, 20002 (although proposals may be submitted at any time). Submission for a given deadline implies that the observations are requested to be initially scheduled during the four month period which starts four months after that deadline. Proposals have a validity of two 4-month cycles. If a proposal has not been scheduled after this second period, it will not be considered further unless it is re-submitted. A complete list of available receivers available for this deadline can be seen at http://www.naic.edu/~astro/RXstatus. Use of the Arecibo Observatory is available on an equal, competitive basis to all scientists from throughout the world to pursue research in radio astronomy, radar astronomy and atmospheric sciences. Observing time is granted on the basis of the most promising research. Potential users of the telescope should submit a proposal to the Observatory Director at Arecibo describing their desired observations and the scientific justification for these. The procedures for submitting proposals, the mechanics of evaluation and the life-cycle of these proposals, are outlined at http://www.naic.edu/~astro/proposals.

T

Notes to Observers 1. We would like to remind our readers that when you publish a paper using observations made with the Arecibo Observatory, please provide us with a reprint of your article. You can send reprints to: Librarian, NAIC Arecibo Observatory, HC3 Box 53995, Arecibo, PR 00612.
2. Additionally, any publication that make s use of Arecibo data should include the following acknowledgement: "The Arecibo Observatory is part of the National Astronomy and Ionosphere Center, which is operated by Cornell University under a cooperative agreement with the National Science Foundation."

Hot News! Editors Note: The adjacent photo arrived just before press time, and we felt it too important to leave out. he adjacent photo is an image of a blue jet propagating upwards from a thundercloud top to an altitude of about 70 km, taken from Arecibo Observatory, Puerto Rico on the late evening of September 14, 2001. The original monochrome image from [Pasko et al., Nature, 416, 152, 2002] is reproduced in false color. (See article on Space and Atmospheric Sciences, page 20.)

T

The NAIC/AO Newsletter is published three times a year by the NAIC. The NAIC is run by Cornell University under a cooperative agreement with the National Science Foundation. Karen O'Neil and Jonathan Friedman, editors. Contact: koneil@naic.edu or jonathan@naic.edu; http:www.naic.edu

March 2002, Number 34

30

NAIC/AO N ewsletter