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NAIC Celebrates 40th Anniversary

=D2What we celebrate today is the scale of achievements that are =
possible=20
when creative people, nurturing institutions, governments and=20
supportive citizens work together in common purpose.=D3 These words of=20=

the NAIC Director, Robert Brown captured the sentiment of the 40th=20
anniversary celebration of the Arecibo Obsevatory.

On Saturday, November 1, 2003 a 4-day event kicked off with the=20
attendance of many people closely associated with the founding,=20
building, and shaping of what is still the world's largest and most=20
sensitive radio telescope. In addition, visitors from local and state=20=

government and from the Cornell Club of Puerto Rico joined the=20
observatory scientific staff for the festivities. The visitors toured=20=

the site, visiting the edge of the dish and witnessing a pulsar=20
observation in the control room, accompanied by entertaining=20
descriptions by their tour guides. Following the tours, and during a=20
heavy rainstorm, the attendees gathered in the Angel Ramos Visitor=20
Center for the anniversary ceremony. Later, with the telescope=20
shrouded in mist, they assembled on the viewing platform for a cocktail=20=

party.

The culmination of the ceremony was the keynote address by Arecibo=20
Observatory founder Dr. William E. Gordon, entitled "The Arecibo=20
Story."

Gordon=D5s imposing figure approached the podium as the 135 invitees in=20=

the audience expressed their appreciation. He began by remarking =D2I do=20=

not know how we ever built it.=D3 Indeed, forty years later it still is=20=

an engineering marvel, recognized officially as such by the American=20
Society of Mechanical Engineers and the Institute for Electrical and=20
Electronics Engineers.

Gordon showed photos from the time of construction, which took an=20
amazingly short time from conception to inauguration. He mentioned that=20=

it had been Ward Low at ARPA who thought that a parabolic design as=20
initially suggested, was a serious limitation, and who suggested to=20
Gordon that he should get in touch with the Air Force Cambridge=20
Research Laboratory, where spherical reflectors and line feeds were=20
being designed.

The instrument was designed to have a ten-year lifetime. Forty years=20
later Gordon expressed the thought that Arecibo will be around for=20
another forty years. =D2One of the most exciting few days of the=20
construction was the lift of the triangle=D3 (a reminder to many of us =
of=20
the more recent lift of the Gregorian dome). =D2A big cheer went up =
when=20
it was completed,=D3 Gordon said.

Gordon admitted that at the dedication in November of 1963, with=20
congressmen, generals and the governor of Puerto Rico, the honorable=20
Luis Mu=96oz Mar=92n present, he had a person ready at the platform to=20=

manually activate the switches in case the control room hardware=20
failed. Gordon did not need him.

The observatory held a staff party on Sunday, and a 2-day workshop=20
highlighting historical achievements of the observatory and charting=20
its future directions. The workshop included the second annual Gordon=20=

Lecture, given by Tor Hagfors, entitled =D2Arecibo and the Spawning of=20=

New Science and New Observatories.=D3 Summaries of the workshop=20
presentations form the major part of this issue of the NAIC Newsletter.


----------
Herb Carlson: Some Early Arecibo Discoveries and Where They Stand Now

Herb Carlson discussed three major ionospheric discoveries made at the=20=

Arecibo Observatory, and for each spoke of where they stand today.

The first example was from 1965 and involves the pre-dawn electron=20
temperature enhancement observed in the F-region ionosphere. This=20
temperature enhancement is observed in the winter hemisphere before the=20=

sun is actually illuminating the region in question. The solution to=20
this problem involved electrons travelling up the earth's magnetic=20
field lines from the conjugate position in the southern hemisphere. =20
These electrons are excited by the earlier sunrise in the summer=20
hemisphere, which heats the electrons. These hot electrons arrive in=20
the ionosphere over Arecibo well before dawn and heat the electron gas.=20=

An equivalent phenomenon is seen post-sunset, as the ionosphere=20
remains hot after falling into the earth's shadow, as long as the=20
conjugate position in the south is sunlit.

Herb also raised the prediction, soon confirmed by observation, that=20
the hot electrons from the conjugate position should cause enhanced=20
emission of the O(1D) airglow line at 6300 =81. He showed a result from=20=

1966 comparing the 6300 and 5577 =81 lines from oxygen with emissions =
for=20
Na at 5893 =81 and N2 at 5300 =81. The other lines are all from the =
lower=20
thermosphere, where collisions prevent a similar phenomenon from=20
occurring, while the 6300 =81 emission clearly demonstrates the expected=20=

transience. As further confirmation of the theory, the seasonal=20
behavior of the F-region electron temperature and 6300 =81 emission was=20=

that expected if caused by conjugate electrons.

More recently, measurements by Lancaster et al. (1996) of the oxygen=20
emission at 8446 =81 were made. This should be a more direct =
measurement=20
of oxygen abundances. Though the results fit closely to the theory at=20=

sunset, there was a time difference at sunrise, where the 8446 =81=20
brightness led the expected enhancement by several minutes. This=20
problem is yet unresolved. An additional unsolved problem is that of=20
the electron gas thermal balance, in which the observed cooling rate is=20=

two times slower than physical models predict.

Herb's second example was the 1964 discovery that ion composition could=20=

be determined from the Doppler broadening of the ion line. One=20
memorable point was that "even in 1964 we knew there was much more He=20
than predicted, a fact only recently universally accepted."

Now the Arecibo Observatory can make precise tests of incoherent=20
scatter theory and show, for example, how T_He and T_O are different. =20=

As for the He abundance, work at Arecibo has confirmed that the=20
predictions of Sir James Jeans were wrong, the reasons are understood,=20=

and this knowledge can be applied to the study of planetary=20
atmospheres.

Herb's final example was ionospheric heating, which first took place in=20=

1970-71. The initial HF antenna was designed and built by Merle=20
LaLonde, and it hung above the dish, much like the next generation=20
design (see section below on Sulzer/Breakall presentation). Initial=20
work included: the generation of an artificial lens in the ionosphere,=20=

driving plasma instability, and localized temperature enhancements of=20
1000s of K.

Today, there is the question of what "turns on" the nonlinear response=20=

to the HF wave, a consuming question that has seen over $100 million=20
spent on it study over 30 years. Another question of modern interest=20
is how the plasma interacts with the AC electric field. This has=20
important implications for nuclear fusion, as in the fusion environment=20=

we cannot study this interaction, but we can in the ionosphere.

Finally Herb discussed some of the history that led the NSF to build=20
and support the chain of ionospheric radars, in particular, the=20
coupling of the high to low latitude ionosphere via gravity waves. In=20=

the future, Arecibo will make important contributions to measuring the=20=

global distribution of atomic oxygen in the ionosphere.
--end Herb Carlson--

Gordon Pettengill
Gordon Pettengill, who was an early site director, talked about the=20
early development of the Observatory from a tobacco farm in 1960 to the=20=

discoveries in the late 1960s in planetary radar. It was Gordon who=20
chose digital over analog equipment for pointing the telescope, giving=20=

1 arcmin accuracy (now a few arcsecs). Arecibo improved the accuracy=20
of the Astronomical Unit from a few thousand km to about 1 km, measured=20=

the rotation of Venus, discovered that the rotation and revolution of=20
Mercury were not synchronous, but that the rotation was tidally locked=20=

in 3:2 ratio to the orbital revolution. The telescope was also used to=20=

measure the retardation of the radar signal as it skimmed the sun on=20
its way to a planet beyond, thus providing an early confirmation of=20
General Relativity. Gordon told how one of the first maps of Venus was=20=

made by Don Campbell using a second dish to get interferometric fringes=20=

which resolved the north/south ambiguity of the radar echoes. =20
Radar-bright features were seen on the surface, which is covered by=20
clouds in the optical view.
--end Gordon Pettengill-- Alice

--Marshall Cohen--Tapasi
--Joanna Rankin-- Desh


Dr. Richard Behnke
Ionospheric Techniques and Discoveries
During his talk at the 40th anniversary workshop, Richard Behnke took=20
us back to the 1970s and early 80s as he described the atmospheric=20
science achievements and discoveries from those years. During that=20
decade, experimenters with new ideas took advantage of the upgraded=20
primary surface and new line feed to produce a new array of results in=20=

the lower (D & E-region), middle (F region) and topside of the=20
ionosphere. One of the most significant experiments developed at that=20=

time was the beam-swinging technique to measure F region 3 dimensional=20=

ion velocities (thus taking advantage of the spherical dish and=20
linefeed mentioned by Gordon). With that technique, it became possible=20=

to study electric fields (from velocities perpendicular to the local=20
magnetic field), the influence of neutral winds (from the ion motion=20
along the field line) and the propagation of traveling ionospheric=20
disturbances.

Great progress was also achieved in the E-region with the introduction=20=

of coded and multiple pulse schemes. Coded pulses, like Barker codes,=20=

make it possible to have good height resolution with good=20
signal-to-noise, which is crucial to study what goes on in the thin=20
sporadic E layers and descending layers. The multiple pulse technique=20=

improved greatly the correlation measurements in the E-region, where=20
the correlation times are long and the scale heights are short, so good=20=

height resolution is needed while making an efficient use of the=20
transmitter power.

More breakthroughs in ionospheric experiments took place with the use=20
of the special purpose correlator designed by Jon Hagen. With this=20
machine it was possible to perform computations faster, which in turn=20
lead to improvements in the precision of the measurements. The use of=20=

the correlator also made possible new measurements, like the electron=20
portion of the incoherent scatter spectrum, the so-called electron=20
line, which in recent times has become an interesting topic of=20
investigation, as the predictions of the traditional incoherent scatter=20=

theory do not match the Arecibo observations. Other measurements that=20=

were performed with the correlator, included topside measurements of=20
light ions and counter streaming ion velocities.

The 1970s also brought the first heating facility to Arecibo. And this=20=

is particularly interesting because the first heating facility used an=20=

arrangement of a log periodic antenna hanging at some distance below=20
the platform, which is a similar concept to what has been proposed for=20=

the third Arecibo HF facility, hopefully coming in the near future. =20
The heating experiments in the 1970s looked at the thermal balance, the=20=

enhanced plasma lines and the generation of plasma instabilities.

Using the words of Behnke, the 1970s were =D2a time of unequalled=20
progress at the Arecibo Observatory=D3.

--end behnke--

Don Campbell, a past site director, continued where Gordon Pettengill=20
left off, by describing the 1973 upgrade, which replaced the surface of=20=

the dish and introduced the 2.4 GHz radar with 420 kW power for=20
planetary work. The second upgrade doubled the power and again=20
improved the surface. He showed a rising sensitivity over the years of=20=

32 dB, about 1 dB/year. The improvements came from the Love feed, the=20=

upgrades and the recent surface tune-up. Don gave credit for this to=20
the many scientists, students, engineers, and Observatory employees who=20=

supported this project. The scientific achievments of this period were,=20=

for Mars: warning the Viking lander team of surface roughness; for=20
Venus: mapping the surface through the clouds before the Magellan=20
spacecraft arrived with 10 times the resolution, dating the Venus=20
surface by crater counts, and investigating surface polarization by=20
receiving the echo at the GBT; for the Galilean satellites of Jupiter: =20=

finding icy surfaces by the strange polarization effects of the echoes;=20=

for Mercury and the Moon: finding ice in permanently shadowed craters=20=

on Mercury and not on the Moon. Comets, asteroids, and the particles=20
of Saturn's rings have been detected and their sizes and dynamics=20
illuminated. Saturn's Titan recently showed indications of surface=20
lakes, and Saturn's Iapetus with its optically bright/dark hemispheres=20=

showed uniform radar echoes, which imply that the optical effect is a=20
surface deposit and not structural.

--end Don Campbell-- Alice
--
Extra Galactic HI =D0 Martha Haynes.

-Arecibo as a redshift machine
-environmental influences on galaxy evolution
-Search for hidden galaxies
-appliaction of the TF relation
-peculiar velocities (low z)
=13Galaxy evolution (high z)


Arecibo as a redshift machine:
=46rom an HI measurement, 3 parameters are immediately available:
The systemic Velocity
The rotational Velocity
The HI mass

=46rom the rotational velocity, it is possible to use the TF relation =
to=20
estimate the baryonic mass.
Over the last 20 years, Arecibo has been used to observe and measure=20
~11 000 galaxy redshifts in the perseus-pisces supercluster (PPS).=20
These observations revealed the filamentary structure of the cluster.


Galaxy evolution:
EG. The Arecibo observations at HI of the Leo triplet (I can get a=20
contour image of this if you wish). Shows a tidal outflow feature (and=20=

an outflow feature which she didn't mention!).

Observations of galaxy clusters have shown that the galaxies in the=20
centres of the groups are relatively HI poor, and have shrunken disks.=20=

(Giovanelli + Haynes).


Dark halos:
Theoretical models suggest a significant amount of matter should be=20
detectable in small dwarf halos nearby to larger, cannibalising halos.=20=

It is often extremly difficult to detect these, since they are not=20
optically obvious, they are typically serendipitous detections. One=20
such detection, found in the 'OFF' pointing for some observations is an=20=

HI cloud 1225+1 (Gio & Haynes, 1989)

TF reln.
The fact that Large scale structure exists implys that peculiar=20
velocities exist.
The Tully fisher relation can be used to estimate peculiar velocities.
Conclusion: The universe is a bowl of spagetti.
Beginnings of mega maser research =D0 Willem Baan

--end haynes--

OH Megamasers - Willem Baan
History re-hash:
OH megamaser emission was first detected from Arp 220 (IC 4553) =
in=20
1982, (Baan et al)


OH outflows used as a diagnostic for ULIRG population

Outflows have linewidths of 1300-2200 km/s scan up to z. (1300MHz)

many bright IR galaxies are also found to host megamasers

MRK 231
OH emission region straddles nuclear region
model of torus about a black hole 7.2 x107 Mo
MRK 273
OH emission reion straddles nuclear region.
Model of torus about a black hoel 3.5x108 Mo

Formaldehyde.
1993 detections with mini gregorian (during measurements of standing=20
waves):
2MJy lines (ARP 220) emission on two nuclei

also CH emission detected =D0 ongoing AO researc

--end Willem Baan--

--Carmen Pantoja-- Carmen


- M.C. Kelley
Michael Kelly dedicated his discussion to a description of highlights=20
of the successes at the Observatory in research and education. He=20
touched on the topics of:
- New technologies developed and applied at the Observatory
- The Arecibo Observatory as a national center, hosting both US and=20
international scientists
- Maintaining the Arecibo Observatory as a CEDAR class 1 facility by=20
the routine addition of new instrumentation and development of new=20
techniques
- The contribution of the Arecibo Observatory in its participation in=20
the development of new facilities such as the AMISR (Advanced Modular=20
Incoherent Scatter Radar). He went on to explain in detail the design=20=

and purpose of AMISR.
- The contribution of the Arecibo Observatory in the education Ph.D.=20
students, in particular of Hispanic origin, including Arecibo Site=20
Director Sixto Gonz=87lez and staff member N=8Estor Aponte, C=8Esar =
LaHoz and=20
Francisco Garc=92a.
- The participation of Arecibo in campaigns. In Coqui II 3 NASA=20
fellowships were granted to PR students, << into the direction to get even more students>>>.
- The science issues he discussed included a summary of gravity waves=20
showing how we can be visualize their structures using an all-sky=20
camera to image the airglow, and the observation of plumes shooting up=20=

as seen by Arecibo and Jicamarca radars. (ask Sixto or Mike for the=20
details)
--end kelley--

Nearly four decades of optical measurements at Arecibo
Craig A. Tepley (Shikha)
Craig Tepley gave the highlights of optical developments at Arecibo=20
starting from 1963. He divided his talk chronologically over the four=20=

decades and discussed the important achievements during each period.

The first decade (1963 =D0 1973) was the era when photometry evolved.=20
This happened when Colin Hines forwarded a proposal from Keith Cole to=20=

measure the effects of conjugate electrons that cause enhancement of=20
630 nm airglow emission in the early morning hours due to bombardment=20
of oxygen with photoelectrons. In July 1965, Gordon gave permission to=20=

Herb Carlson to purchase the required instrumentation and a photometer=20=

that could measure airglow emissions at 6300, 5577, 5893, 5300 =81 was=20=

acquired. In 1968, Carlson reported observations of the excited=20
nitrogen emission at 3914 A, which illustrated the influence of high=20
energy photo electrons on the local ionosphere. Later on, Nelson and=20
Cogger (1971) used the airglow line at 6300 A to show the association=20
between its enhanced emission and the descent of F-layer ionosphere,=20
which is generally referred to as the post midnight descent of F-layer.=20=

Cogger et al. (1970) measured linewidths of 6300 =81 and inferred =
airglow=20
temperatures that were used to validate satellite and incoherent=20
scatter radar temperatures.

The decade (1973 =D0 1983) was the period of spectroscopy that Craig=20
referred to as =D4Meriwether Years=D5. During this period, measurements =
of=20
7320 =81 twilight emissions were made. Afterwards, the mapping of=20
meridional intensity gradients (MIG=D5s) by Herrero and Meriwether were=20=

made in 1981, and imagers were first installed by visitors at the=20
observatory.

The third decade (1983 - 1993) was marked with the development of=20
interferometery. Roger Burnside used the 6300 A emission to measure=20
thermospheric winds using this technique. A few examples were shown=20
illustrating the coupling between ions drifts and neutral winds.=20
Recently, 23 years of wind data from the observatory were analyzed by=20
Robles et al. (2002). They showed a gradual eastward rotation of the=20
wind vector. In 1986, Kerr and his colleagues made observations of the=20=

Ha line that originates from the geocorona. This work was followed by=20
Kerr and Tepley (1988) inferring hydrogen concentrations in the=20
exosphere.

The last decade (1993=D02003) marks the era when lidar techniques=20
flourished at the observatory. The work started in 1989 when the=20
University of Illinois brought their laser to participate in the AIDA=20
campaign. This was followed by the development of Doppler Rayleigh=20
lidar in 1990 at the observatory. In 1995, an Alexandrite laser was=20
purchased to enhance the lidar program. During the Coqui campaign in=20
1998, several simultaneous measurements using Na lidar and Incoherent=20
Scatter Radar were made for studying sudden Na layers and their=20
coupling with sporadic E. Seasonal variations of K, Fe and mesospheric=20=

temperatures have been studied using Arecibo=D5s resonance lidars.

In summary, Craig presented a rich history of accomplishment in 40=20
years and how this will continue into the next decades.
--end tepley--

Exosphere/Plasmasphere Studies, Long Term Trends
Bob Kerr Monday 3 November, 2003 2:20pm

Bob Kerr began his presentation by acknowledging the valuable=20
contributions of Ra=9Cl Garc=92a, Craig Tepley and Roger Burnside over =
the=20
years. He then described how use of the "forbidden" emission at 6300 =81=20=

has provided a method for measuring F-region neutral winds for nearly=20
40 years.

He went on to show how Arecibo explored the possibility of determining=20=

O concentration by reconciliation of the OI 8446 =81 emission. There=20
were two candidates for excitation of O that produces this emission. =20
These are Bowen Fluorescence and photoelectron impact. Using the=20
Arecibo Fabry Perot Interferometer, the 8446 =81 triplet members were=20
isolated from each other and from bright OH contamination. As a=20
result, electron impact was confirmed as dominant source of this=20
emission. The excess of 8446 =81 emission at midnight and in the =
morning=20
sector relative to =D4Glow=D5 indicates possibly a plasmaspheric source.

Kerr went on to look to the future of airglow observations at Arecibo. =20=

With John Noto (Scientific Solutions), Kerr developed a photometer that=20=

was temporarily based at Arecibo and has since been installed at Cerro=20=

Tolodo in Chile.
<<>>

Future observations will use nested instrumentation at Arecibo and at=20
its conjugate location in the southern hemisphere to constrain=20
photoelectron models and measure thermospheric O concentrations from=20
the ground.

Measurements of vertical winds <<>>
Kerr discussed observations of the metastable helium emission at 10830=20=

=81 that is caused by electron impact. Arecibo accomplished the first=20=

measurements of metastable helium in the mid-90s using a Fabry-Perot=20
interferometer and infrared detector. The full potential of the 10830=20=

=81 wind and temperature diagnostic will be realised by slightly higher=20=

spectral resolution and with the use of IR array detection.

OH 7320 A =D4Hot O=D5

Arecibo followed the work of John Meriwether, mentioned by Craig=20
Tepley, of 30 years ago, by making improved measurements by use of a=20
narrow-band interference filter (? Not sure about this part, he speeded=20=

up and I couldn=D5t keep up)
Kerr showed some raw 7320 =81 emission profiles from May 2003, which=20
showed no broadening of the 7320 =81 line profile that would suggest hot=20=

oxygen. New instrumentation will be used later this year to test these=20=

observations

Finally, Kerr discussed his twenty years of work on hydrogen escape=20
flux, which at mid-latitudes is preferentially supplied during solar=20
maximum at winter solstice. The Ha 6563 =81 emission is observed for=20
these studies. The 2+ solar cycle trend shows some evidence of secular=20=

change, with increased H in upper thermosphere and exosphere, although=20=

the results are as yet inconclusive.
--end kerr--

John Mathews

John Mathews dedicated his timeto a discussion of the meteor=20
observations that have been going on since 1994 at Arecibo. He gave an=20=

update of how the Penn State group deals with the analysis of data. He=20=

presented results of the present state of that analysis, showing=20
altitude and velocity distributions as well as some orbital results of=20=

detected interplanetary and interstellar dust.
--end mathews--

******Extra Galactic HI - Riccardo Giovanelli

LSS from small scale perturbations -WMAP
density fluctuation: 1 part in 1 million.
Density contrast increases with age
Baryonic mass is 15% of total mass

Elliptical galaxies:
Galaxies form through multiple (major) mergers.
Kinetic energy of random motions barely exceeds that of large scale=20
orderly motions, such as rotation.
Spiral:
=46rom from less crowded environments
accrete at a slower pace (un affected by major mergers)

Lambda CDM model is successful in describing the presences of large=20
scale structure, but it predicts many more small mass halos/galaxies=20
than is observed.

Low mass objects are very few. i.e. Very nearby
distance and mass is uncertain, and affected by peculiar velocites.

Solutions: either
1.The LCDM model is wrong.
2.Galaxies have NO baryonic matter (Baryonic blow out)
3.DM does exist, but it does not form stars =D0 is it detectable in HI?=20=

<- this is where arecibo fits in.


Survey simulations:
Objectives:
investigate the faint end of the HI mass function (HIMF)
determine local density dependecies of the HIMF.
Estimate the time needed to detetect a given object, with mass MHI and=20=

velocity width Wkms:

T=3D1/4 f-2_(MHI/106M_)2(DMpc)4(Wkms/100)-2_

where f _ is the beam dilution, gamma=3D-3/4 for W<100, or gamma =3D-1 =
for=20
W >100

i.e. The depth of the survey increases as t1/4

The sensitivity of Arecibo is superior to any existing telescope at HI,=20=

it is the ideal tool to search for small, faint HI galaxies and and=20
around the local cluster.
--end giovannelli--

--Don Backer-- Desh
--Alex Wolszczsan-- Desh
--Tim Hankns-- Desh
----
OH megamasers =D0 J darling
Formed in Galaxy mergers (multiple mergers?)
rare, approx 100 known, 50% have been detected with the AO.
z> 0.1

First discovered in 1982 (W. Baan et al)
Study now needs sup arcsec resolution
OHMM emission traces galaxy merges (i.e. ULIRGS), Starformation and=20
massive black holes.

Empirical reln exists: L1.2IR ~ LOH


Take three examples (Martha, Riccardo, Bob)
Martha Riccardo
IRAS 02524+2046 IRAS 12032+1707
Z =3D 0.182 Z=3D0.217

These have very broad velocity width: of order of a 1000km/s

But.. Variability found in these objects by 10-14% -> therefore the=20
masing regions are compact.

Martha:
-has intra-day variability.
-Multiple narrow variable components
-1665 line varies often, but not always identically to the 1667 =
line.
(therefore, the masing regions are spatially nearby and compact)
-Flaring events occur for both transitions
-components can shift a few km/s
-variable features are narrower in velocity than average, =
structure on=20
< pc scale
-1667:1665 ~20% (vs. the theoretical 30% for a point source)

Riccardo:
narrow features vary, structure ~25 pc.
Broader structures are ~120pc
use VLBA to observe these features.

OH observations can probe variation in Fine structure constant:
=C6_ (_1665-_--1665)=3D 2(=C6+-=C6-)_4 (how cool is that??)
But..
bright enough OH and CH at high Z are rare, so it is difficult to check=20=

this properly, so this is what arecibo is good at.

--end darling--

-- Emmanuel Momjian -- Tapasi

40th Anniversary Workshop
"Magenetic Fields - Zeeman Effect" by Carl Heiles
-------------------------------------------------

Carl Heiles spoke about the experiment he and Tom Troland have been=20
performing using the Zeeman Effect to directly measure the interstellar=20=

magnetic field in HI clouds seen as absorption features against=20
extragalactic radio sources. He noted that this has used some 800 hr=20
of telescope time. A typical strong detection would yield values for=20
the magnetic field such as 5.6 $\pm$ 2.0 $\mu$G!!

Carl and Tom have also decomposed each of their absorption spectra into=20=

a number of Gaussian components which yield column density, spin=20
temperature, turbulence velocity, and magnetic field. It had previously=20=

been thought that to be thermally stable, the spin temperature of the=20
gas should be near either 80 or 8000 K. However, they find that much of=20=

the gas lies at excluded values near 2000 K.

In the Cold Neutral Medium, the turbulent velocities give a broad=20
spread of turbulent Mach numbers. The typical value is 3, suggesting=20
strong shocks which would be dissipatory, and hence short-lived. Thus a=20=

source of energy input is needed. Typical column densities are N$_{H}=20
\sim 3 \times 10^{19} cm^{-2}$. Much of this phase seems to exist in=20
very thin sheets having aspect ratios of $\sim$200:1, and a depth of=20
about 0.1 pc along the line of sight. This aspect ratio is about that=20
of a sheet of paper! If these sheets are oriented randomly, there will=20=

be a large number seen at low N$_{H}$, and only a few at high N$_{H}$.

Magnetic fields have been detected in 20 sources, though there are more=20=

yielding upper limits. The distribution of magnetic fields (including=20
upper limits) is consistent with $\Phi(B) =3D \Beta^{2} e^{-\Beta^{2}}$,=20=

where $\Beta =3D B/2.2$\mu$G. The width of this fitted curve is twice=20=

that which can be explained by the uncertainties, implying a spread in=20=

the distribution of fields. The median field is $\sim$5.4 $\mu$G. They=20=

compute a ratio of thermal to magnetic pressure of 0.3, with the=20
turbulent and magnetic energies being roughly in equipartition.

Carl & Tom are currently performing a detailed statistical analysis of=20=

the magnetic field results to firm up these statistical statements,=20
which should be regarded as preliminary and tentative at the present=20
time.

--end heiles--
..................
HI Self-Absorption: A Peculiar Puzzle and Potential Probe Predating
the Arecibo Telescope

Paul F. Goldsmith

The 21cm line was discovered in emission from the interstellar medium=20
of our galaxy by H. Ewen (last year's Gordon Lecturer) and E. Purcell=20
in 1951. But only 4 years later, D. Heeschen published HI spectra with=20=

"dips", and it was already suspected that they might be due to cold HI.=20=

1960 saw the first appearance of the term "Self-Absorption", but the=20
location of the material responsible was unclear. In 1969, C. Heiles=20
surveying dark clouds (visual extinction greater than a few mag.) found=20=

in very few a self-absorption signature that agreed in velocity with=20
that of the OH emission. This, and an extensive comparison of H2CO and=20=

OH, with HI absorption in Taurus (Heiles & Gordon 1975) confirmed that=20=

the narrow HI self-absorption is associated with molecular emission. =20
Di Li (then a graduate student at Cornell, now at CFA) and I have been=20=

pursuing this topic. The Arecibo Gregorian allows observing HI and OH=20=

simultaneously, with better sensitivity and angular resolution than=20
previously available. In a paper published in 2003 (ApJ 585, 823) we=20
found that about 80% of clouds in Taurus which we surveyed showed HI=20
narrow self absorption, which we gave the acronym "HINSA". We found=20
that the emission has non thermal line width similar to that of 13CO,=20
and that the HI is very cold, as low as ~10K, as would be expected if=20
it were from the cold central portions of dark clouds.

Continuing this work, we have mapped HI, OH, 13CO and C18O in four=20
clouds and found that the HINSA is centrally concentrated and that its=20=

distribution agrees with that of the molecular emission. What is the=20
origin of this atomic gas in what are asserted to be molecular regions?=20=

We find that the volume density is generally larger than that expected=20=

from steady state production by cosmic ray destruction of H2 molecules.=20=

The best explanation is that most of the cold HI is actually residual=20=

gas from the period when the cloud was largely atomic. The time scale=20=

for conversion of HI to H2 is on the order of 1 million years, and thus=20=

this HI is a chronometer for the evolutionary history of the gas in=20
terms of possible shocks and compression which increased the visual=20
extinction and initiated the HI to H2 transition. To exploit this=20
further, we are proposing a survey of the entire Taurus region using=20
the ALFA focal plane array. This project, called "ALFA-TAU" will give=20=

us new insight into the evolution of a molecular cloud complex, and=20
tracing the early stages of the process which ultimately produces new=20
solar-type stars.
--end Paul Goldsmith-- Mayra

John Harmon, who until recently served as Assistant Site Director,=20
showed the spectacular radar maps of Mercury that extend our knowledge=20=

of the surface beyond the images taken by the only Mercury mission,=20
Mariner 10 in 1975. The polar ice patches are probably water ice, and=20=

have helped in refining the pole position. Mars has not been in the=20
Arecibo sky since the upgrade (it will be in 2005), but in the past we=20=

learned a great deal about the surface using the non-repeating long=20
code technique to overcome the frequency folding due to Mars's rapid=20
rotation. Small-scale roughness is seen as are lava flows. Since=20
Comet Encke in 1980, nine comets have been detected, some with both=20
nucleus and coma (cm-sized grains). Density and mass loss are the=20
goals, but comets are not often close enough to be radar targets=20
becouse of radar's 4th-power dependence on distance.
--end John Harmon-- Alice

Steve Ostro, who was at Arecibo as a graduate student in the 1970s,=20
completed the planetary astronomy story by summing up the asteroid=20
work, now the most frequent use of the radar. This work has focused=20
primarily on Near Earth Asteroids, but some Main Belt Asteroids have=20
been observed as well. Many give strong enough echoes to be imaged in=20=

delay-Doppler and to give a good polarization ratio. Bulk density,=20
proportion of rock/regolith on the surface, shape, spin state, average=20=

slopes, and metallic/rocky composition can be determined for some=20
objects. The radar detection improves our knowledge of the orbit,=20
which we need for dynamical models and for impact prediction. Recently=20=

the long-term effect of radiation on a rotating body (the Yarkovsky=20
effect) was measured for the first time at Arecibo.
--end Steve Ostro-- Alice

--Steve Torchinsky-- steve

----
Sulzer/Breakall Talks

Title: HF Facility Upgrade/New HF Feed for Arecibo Observatory

The description of the proposed plans for the new ionospheric=20
modification HF (High Frequency) facility was given in a joint effort=20
between Mike Sulzer and Jim Breakall. During the first part, Mike=20
stated the reasons for bringing back the Arecibo HF facility and the=20
main scientific goals for the new instrument. It is important to note=20=

that even though there are other HF facilities in operation, none of=20
them can provide the combination of a relatively quiet ionospheric=20
background with the world's most sensitive diagnostic tool to probe=20
ionospheric plasma. Furthermore, the Arecibo Observatory now has=20
greater capabilities to make measurements of the neutral atmosphere=20
with its optical instruments.

The new HF facility is a very important project for Arecibo. With this=20=

new facility, it is expected to bring a broader user base, with=20
interests beyond traditional aeronomy. After Hurricane Georges=20
destroyed the Islote HF facility, Arecibo lost the capability to=20
perform experiments to study the interactions between powerful HF waves=20=

and the ionospheric plasma. This type of experiment turns the=20
ionosphere over Arecibo into a natural plasma physics laboratory, and=20
already the scientific community has identified several specific=20
problems that the new HF facility can address uniquely.

The proposed new HF facility will be a much improved version from=20
previous Arecibo HF systems. First of all, the transmitter will be a=20
500 kHz AM transmitter capable of putting about 620 KW average power=20
and up to 2 MW of peak power. Since this new transmitter can be=20
modulated, it is also possible to use this system as an HF radar=20
itself. This feature will no doubt make possible other applications=20
for the system. In its initial stage, the HF system will operate at=20
frequencies of 5 and 8.175 Mhz, with plans to add a lower frequency of=20=

3 Mhz at a later date.

As Jim Breakall took his turn to describe the details about the new HF=20=

feed, he started by putting things into perspective, as he showed=20
viewgraphs from the original onsite HF facility back in the 70s, and=20
then the second generation located at Islote. He then went on to=20
describe the new cross dipole feeds and the supporting mechanism, which=20=

consist of cables supported by the towers, not the platform, so it=20
won=D5t add any weight to the already loaded platform. =46rom this =
point=20
on, Jim concentrated on the results of very accurate computer=20
simulations to determine the performance of the new feeds when they are=20=

embedded in a realistic background comprised of the main reflector and=20=

the platform, including the suspended line feed along with the=20
Gregorian dome. The presentation of the expected performance and=20
general description of the system, generated a lively discussion at the=20=

end of the talk regarding parameters, possible uses of the system and=20
concerns on the impact of the HF feed for radio astronomy measurements.

--end sulzer/breakall--

The Sun Earth Connection
T. Bastian (covered by Chris Wilford & Chris Salter)

This talk mainly focused on frequency agile solar radio telescope=20
(FASR) for studying various astrophysical issues as sun offers access=20
to such parameters. Such studies are important to understand magnetic=20
dynamo, magnetic energy release, space weather etc. It is known that=20
sun=D5s output vary dramatically resulting in sudden outburst of energy=20=

that can have many implications on earth=D5s ionosphere, astronaut=20
safety, satellites and many other things. One example of such event=20
occurred on 28 October 2003 when a series of solar flares were=20
observed. This event resulted in enormous proton output and caused=20
auroral display at higher latitudes.

The decadal review of NRC (Astronomy and Astrophysical Survey=20
Committee) recommended an integrated suite of 3 instruments: (a)=20
Advanced Technology Solar Telescope, (b) FASR, and (c) Solar dynamic=20
observatory. Apart from this, NRC (Solar and Space Physics Survey=20
Committee) considered promoting solar heliospheric and ionospheric=20
physics. This resulted in the development of a solar probe, which was=20
the first in-situ instrument that went close to 0.3 AU, the innermost=20
region of the heliosphere.

Coming to ground based instruments, Nobeyama radioheliograph would=20
employ interferometric methods for studying small scale perturbations.=20=

Bastian compared FASR specifications with the Japanese instrument that=20=

has 64 antennas while FASR will have 100 of them (5000 baselines). FASR=20=

frequency range will vary from 0.1 =D0 30 GHz with resolution varying=20
between 0.1 =D0 3 GHz. The field of view will be about 0.5=A1, so that =
it=20
can image all of the sun. To satisfy all the constraints, simulations=20
have shown that array configuration should be arranged in a=20
=D4self-similar log spiral way=D5.

This instrument can shed light on some of the major scientific areas=20
like:
- Nature and evolution of coronal magnetic fields
- Temporal and spatial evolution of fields
- Flares (energy release, plasma heating, origin of storms)
- Birth and acceleration of Coronal Mass Ejections (CMEs)
- Prominence eruptions Space weather (Build up and initiation of CMEs)
- Origin of Solar Energetic Particles
- Thermal solar atmosphere (solar wind)
- Radiative inputs to the upper atmosphere
- Flare Statistics (Relationship between CMEs and Flares)
-
To summarize, FASR will perform broadband imaging spectroscopy of the=20
sun that can address number of scientific issues. Combined with other=20
instruments, FASR will provide an integrated picture.
--
"FASR -- The Sun-Earth Connection" by Tim Bastian (NRAO) (Chris S.)
--------------------------------------------------------

Tim Bastian described the proposed Frequency-Agile Solar Radiotelescope
(FASR) project. He noted that this was relevant to the interests of all
three scientific specialities at Arecibo - solar system studies, space
and atmospheric physics, and passive radio astronomy. FASR will give
access to an astrophysical environment where we can study;

. Magnetic dynamo

. Magnetic energy release

. The physics of partially and fully ionized media

. Particle acceleration and transport

. Shocks

The Sun's output stirs up the interplanetary medium (IPM) and impacts
the near-earth environment. The details are encapsulated by the
catch-all term -- Space Weather.

The past 15 years have seen a growth of space-based solar physics
investigations (e.g. SMM, CGRO, Yokoh, WIND, Ulysses, SOHO, ACE, TRACE,
RHESSI). Within the next 24 months, Solar B and STEREO will follow.

The Decadal Review of the NRC Astronomy and Astrophysics Survey
Committee recommended the construction of three very complimentary
instruments, 2 ground-based and 1 space-based. These were;

. The Advanced Technology Solar Telescope (ATST -- Optical/IR)

. The Solar Dynamics Observatory (SDO -- Optical/UV/EUV)

. FASR (Radio)

Since, the NRC Solar & Space Physics Review (SSPS Survey Committee),
and the Space Studies Board have recommended the following proposals as
their priorities;

. At > $400M, The Solar Probe

. At $250M -- 400M, The Magnetospheric Multiscale Mission (MMS)

. At < $250M, FASR

FASR would employ an interferometric approach. In practice, the Sun
varies so rapidly that normal Earth-rotation synthesis is not possible,
and many dishes are required to give good instantaneous
spatial-frequency coverage. This is especially needed as the Sun is
both large and complex! FASR proposes using 3 different arrays to cover
the complete radio frequency range of 0.1 - 30 GHz, as follows;

---------------------------------------------------------
Freq Range Antenna Elements Freq Resn $\Delta\Tau$
(GHz) (msec)
---------------------------------------------------------
0.1 - 3.0 Log-Periodics 1% 100
3.0 - 18.0 6-m dishes 0.1% 10
18.0 - 30.0 2-m dishes 1% 100
---------------------------------------------------------

Some 100 antenna elements (about 5,000 baselines) would record
data, and provide an angular resolution of ~20/$\nu$(GHz)
arcsec over a Field of View of ~0.5 deg or larger, i.e. sufficient
for full-disk imaging over most of the proposed frequency range.
The array configuration will likely be "self-similar"; e.g., a=20
logarithmic
spiral, this having excellent imaging properties, even at the "dirty
map" stage.

The key science that FASR would address includes;

. The nature and evolution of coronal magnetic fields, such as
measurement of these magnetic fields, the temporal and spatial
evolution of the fields, the role of electric currents in the
corona, and coronal seismology.

. The study of solar flares, including energy release, plasma
heating, and electron acceleration and transport, and the origin
of solar energetic particles (SEPs).

. The drivers of space weather, such as the birth and acceleration
of CMEs, prominence eruptions, again the origin of SEPs, and the
fast solar wind.

. The thermal solar atmosphere, e.g. coronal heating and nanoflares,
thermodynamic structure and dynamics, and the formation and
structure of filaments.

. The solar wind, as exemplified by its birth in networks, coronal
holes, fast/slow streams, and turbulence and waves.

. Synoptic studies, including radiative inputs to the upper
atmosphere, the global magnetic field/dynamo, and flare
statistics.

--end bastian--

**************BREAKOUT SESSIONS************

"The SKA -- The Technical Development Project" by Jim Cordes (Cornell)
----------------------------------------------------------------------

Jim Cordes talked about the Square Kilometer Array (SKA) which is=20
planned to be the paramount international radio telescope facility for=20=

the next generation of astronomers.

Why is the SKA needed when individual instruments can already provide=20
milliarcsecond angular resolution, immense bandwidths, fine spectral=20
resolution, and nanosecond time resolution? The answer is that one=20
would like to have all of these, coupled with a huge sensitivity=20
improvement over existing instruments, and preferably with a wide-field=20=

survey capability.

The Arecibo telescope is currently the most sensitive single telescope=20=

in the World, and is expected to continue to be so until the SKA enters=20=

service. To give an example of the expectations for the SKA, the=20
Arecibo ALFA surveys planned for the coming years expect to discover=20
some 1,000 new pulsars. With similar integration times, it is expected=20=

that the SKA would reveal an order of magnitude more such discoveries!

Despite some plateaus, the cumulative collecting areas of optical and=20
IR telescopes have risen steadily over the years. For radio telescopes,=20=

there was a big step forward in collecting area available during the=20
1970's. However, since then the only new telescope of large area has=20
been the GMRT. Instead, much work has gone into algorithm development=20=

to get the very best out of what exists.

The development history of the SKA concept began in the early 1990s=20
with the idea of a collecting area of 1 km$^{2}$, working at=20
frequencies suitable for HI studies. In the late 1990s, as the USA=20
prepared for its "millennium" decadal survey, ideas became more=20
ambitious, and in 1999 the United States Square Kilometer Array=20
Consortium (US SKA) was constituted. This currently consists of=20
representatives from 12 different institutions.

Internationally, 7 design proposals exist for the SKA;
. "Large-N, Small-D" (LNSD), the US concept
. The Canadian "Aerostat" dish
. The Chinese "KARST" concept
. The Australian array of "Molonglo cylinders"
. The Australian array of Luneberg lenses
. The Dutch "Aperture Array"
. The Indian array of Preloaded Parabolic Dishs

Scientifically, the chosen design would be expected to provide=20
break-through studies from our Solar System to the early Universe. The=20=

key-science goals include;
. The cosmological evolution of HI
. Probing dark energy
. The origin of cosmic magnetic fields
. Imaging the "cradles of life": (proto)planetary disks
. Gravity and Pulsars: Did Einstein have the last word?

The "baseline" SKA design goals can be found at=20
http://www.skatelescope.org.
The timeline for the SKA is presently;
2002.5 The concept white papers
2003.5 Site Proposals
2004.5 Updated concept and site white papers
2006 Site selection
2007 Design concept selection
2009 Preparations for construction proposals

The US LNSD concept would use a large number (N) of small diameter (D)=20=

parabolic dishes. Large-N is chosen to give large collecting area, high=20=

dynamic range, good "dirty image" characteristics in "snapshot mode",=20
self-calibration considerations, and fault tolerance. Small-D is chosen=20=

to give a wide field of view of $\sim$1 deg at L-band, and to minimize=20=

costs. 4400 $\times$ 12-m paraboloids are currently projected, with=20
feeds covering 0.15 to at least 23 GHz. This design will meet the=20
Science Compliance Matrix issued by the International Science Advisory=20=

Committee (ISAC) in Sept. 2003.

Funding has been made available to the US SKA Consortium by the NSF to=20=

explore technical elements of LNSD. There is a lot to do in terms of=20
reducing costs to a minimum. The method for transporting signals from=20
the antennas to the control center is being investigated, as are RFI=20
mitigation, post-processing, and operations and maintenance.

The SKA Technical Development Project (TDP) will have 7 main work=20
areas. For this, the Allen Telescope Array (ATA) will serve as a=20
test-bed for a number of the aspects to be studied. There is also an=20
extensive outreach element being undertaken.

The TDP will include the participation of all US SKA Consortium=20
members, but is to be managed by NAIC. A project office for this is=20
being set up in Ithaca. The Project Director is Jim Cordes. The=20
implications for NAIC and the Arecibo Observatory are that they will=20
contribute to the management of the US project, participate in the=20
design and optimization of the antenna optics, have access to broadband=20=

low-noise amplifiers, work on RFI mitigation, develop science goals,=20
make pilot observations to gain experience (e.g. the EoR Catwalk=20
experiment), and indulge in outreach work.

--end cordes--

"The Catwalk EoR Experiment" by John Dickey (U. Minnesota)
----------------------------------------------------------

John Dickey addressed the Symposium concerning the possibility of=20
detecting HI emission from before the "Era of Reionization" (EoR). This=20=

planned Arecibo "catwalk" experiment will serve both as a pilot project=20=

for the Square Kilometer Array (SKA), and as an exciting scientific=20
investigation of cosmology and fundamental physics in its own right.

Reionization of the intergalactic HI is thought to have happened=20
shortly after the first galaxies formed. Its epoch of occurrence is=20
believed to have been at a redshift within the range, 6.5 < z < 25,=20
corresponding to HI emission being observed between about 200 and 50=20
MHz respectively. There is indeed some evidence for increased opacity=20
of the intergalactic medium at redshifts near the lower end of the=20
range given above. However, results from the polarimeter aboard WMAP=20
suggest that reionization occurred at 11 < z < 30, which would imply=20
reaching very low frequencies to detect the signature of the EoR. It=20
has even been suggested that there were two EoR's, firstly at=20
z$\sim$15, and again at z$\sim$6. The HI spin temperature prior to=20
reionization would have been equal to that of the Cosmic Microwave=20
Background (CMB) at that epoch.

The Arecibo telescope catwalk runs from the ground to the platform, to=20=

which it provides access. At one point near its top, it passes through=20=

the paraxial surface of the telescope and a feed placed here can=20
receive "focussed" radiation collected by the telescope's primary=20
surface. The pointing declination of such a set up is close to that of=20=

the Orion Nebula. An earlier attempt at detecting HI emission near 240=20=

MHz from the Arecibo catwalk was undertaken in the 1990s by Bernie=20
Burke, Jonathan Weintroub and Ian (Max) Avruch, who were interested in=20=

detecting massive proto-cluster clouds at $z \sim 5$. They illuminated=20=

a 150-m diameter area of the primary surface using a point (helical)=20
feed mounted below the catwalk.

In practice, it is possible to "multi-beam" from the catwalk, and a=20
4-feed system is now being proposed for the new EoR HI experiment. To=20
be successful with observations at such low frequencies, it has also to=20=

be possible to efficiently excise radio frequency interference (RFI).=20=

Frank Briggs has shown that using an independent reference signal and=20
closure relations it should be possible to get at least 25 dB of RFI=20
rejection.

If Arecibo can indeed defeat the problem of RFI, this essentially=20
dedicated commensal project could obtain an integration time on the=20
305-m dish of (say) a year or so over the next three years. It would=20
then have a fair chance of detecting the spectral-line signature of the=20=

EoR. This would be the critical first step toward using this method to=20=

do cosmic tomography (i.e. three dimensional mapping of the=20
pre-ionization medium).

--end dickey--
VLBI with Arecibo, Jim Ulvestad
Carmen Pantoja

Jim Ulvestad, NRAO High Sensitivity VLBI with Arecibo (20min): briefly=20=

talked about VLBI with Arecibo. Gave a review of frontiers of VLBI:=20
from the 1960's to 1970's studies regarding Superluminal Motion during=20=

the 1980's Space VLBI during the 1990's VLBA, miliarcsecond scales,=20
studies of megamasers, disks,jets during the 2000's MARK5 More=20
resolution? requires larger baselines. higher frequencies? now about 86=20=

GHz, but its difficult to go higher The new frontier is Sensitivity,=20
which makes Arecibo Observatory very attractive because of its large=20
collecting area. With more sensitivity can study how stars and=20
supermassive black holes form. Did they have mergers? Can we detect=20
small separations, binary blackholes in galaxy mergers? VLBA at 5GHz=20
Tsys 312 Jy Arecibo 5GHz Tsys=3D4 - 8 Jy fringe detection 4mJy with=20
Arecibo gets you into high sensitivity VLBI total collecting area=20
increase by factor of 10. noise level in a few hours reduced by a=20
factor of 5 Observe routinely with Arecibo with VLBA VLBI cover < 5 -=20
10 mJy below fringe detection threshold look at gamma ray burst, pulsar=20=

astrometry at 5 - 8 GHz, high redshift galaxies and quasars, water=20
vapor radiometry, GPS troposphere calibration.

VLBA identify AGN's in wide fields NOAO wide Deep Field merger galaxies=20=

Arp 220, Arp 299 young star formation, 2.3 GHz, 5 GHz, higher frequency=20=

is better for star formation very young supernova remnants (some years)=20=

can be studied with high sensitivity. What has been seen with VLBA=20
young SN a few light years of an AGN Conclusion new science new targets=20=

Atmospheric calibration is difficult JPL claims it can work 2/3 of the=20=

time depending on how much liquid water is in the atmosphere millimeter=20=

people are working on it VLBA + Arecibo 5 Gbits a second phase ref on 1=20=

mJy source would be a possibility instead of atmospheric calibration

--end Ulvestad--

--Baan -- Tapasi
--Backer--

"The Arecibo Astrometric/Timing Array" by Robert Brown (NAIC)=20
-------------------------------------------------------------

Bob Brown described the projected Arecibo Astrometric/Timing Array.=20
Presently, this is conceived as an L-band system.

With the 305-m telescope alone, an rms noise in 1 sec of about 0.13=20
mJy/beam is expected with the present receivers. However, the L-band=20
confusion limit lies much higher at a few mJy/beam. A solution to this=20=

impasse would be an interferometer array, thereby increasing the=20
angular resolution, and hence lowering the confusion level, while=20
having the 305-m dish as an array element would still yield high=20
sensitivity performance.

An out-station antenna of some 30-m diameter would result in an rms=20
noise of $\sim$0.57 mJy/beam/baseline with the 305-m telescope. Bearing=20=

the confusion limit in mind, this is already better than would be=20
achieved with the single-dish by itself

If 4 $\times$ out-station antennas could be provided, considering only=20=

baselines to the 305-m telescope, an rms continuum noise of $\sim$0.3=20
mJy/beam/sec should result, or $\sim$5 $\mu$J$/beam in an hour. If the=20=

dishes were spread over the island of Puerto Rico, then the resulting=20
resolution would be about 0.5" $\times$ 1.0". It would be possible to=20
connect the out-stations to Arecibo using optical-fiber links. The=20
L-band front ends would have bandwidths of 300 MHz, and the beam=20
pattern of a 30-m antenna would encompass all 7 beams of the ALFA=20
front-end on the 305-m telescope. With a 300-MHz bandwidth, bandwidth=20
synthesis could be used to enhance the spatial-frequency coverage.

In respect of the science that could be achieved with the array;

. A deep continuum survey could be undertaken.

. HI emission/absorption studies could be undertaken for 0 < z $\lapp$=20=

0.14, with a detection level of $\tau$(HI) < 0.1 for HI absorption=20
against continuum sources of $\sim$2 mJy for integration times of less=20=

than 1 hr.

. Studies of the transient sky. The challenge would be to distinguish=20
transient emission from radio frequency interference (RFI). The 7=20
$\times$ 2 channels of data acquired via the ALFA front-end, each=20
correlated with signals from the 4 out-stations, would produce 4=20
$\times$ 7 $\times$ 2 data streams for Stokes I data. RFI should not=20
correlate between the 305-m telescope and the out-stations. Further, a=20=

real signal would only appear in one set (4 $\times$ 2) of the=20
correlations between the 305-m and the out-stations, i.e. those=20
involving data from a single ALFA beam.

This project has great relevance to partnership with the University of=20=

Puerto Rico "recintos" at Arecibo, Humucao, Mayaguez, Ponce and Rio=20
Piedras. Out-station dishes could be used as teaching instruments when=20=

not involved in array activities.

--end Brown--

In the part of the Workshop dealing with Future Instrumentation, Don=20
Campbell posed the question: Where is the next increase in sensitivity=20=

to come from? He discussed using the SKA for planetary radar; adding a=20=

transmitter station could give a factor of 20 in sensitivity but would=20=

cost about $100 million to build. Other ways are to change the Arecibo=20=

transmitter from S-band to X-band frequency, for $4 million, giving a=20
factor of 2 or 3, or to use the Canadian LAR telescope, or transmit=20
with Arecibo and receive with the VLA or VLBA. The science drivers are=20=

solar system dynamics, small bodies, location of water, and solar=20
system formation.
--end Campbell--

--Wertheimer--

Faraday Tomography by A. Deshpande (NAIC)
-----------------------------------------

Avinash Deshpande (NAIC) addressed the symposium on the topic of=20
"Faraday Tomography". He pointed out that measurements of Faraday=20
Rotation (FR) against galactic and extragalactic radio sources can=20
yield a determination of the magnetoionic properties of the intervening=20=

medium. However, the background sources against which FR can be studied=20=

are not limited to discrete objects, but also include the extended=20
synchrotron emission from the entire Galaxy.

Several extensive surveys have mapped the band-averaged polarized=20
intensity from the "galactic background" at various frequencies using=20
both single dishes and synthesis imaging. Images of the net=20
polarization, position angles and the "apparent" Rotation Measures=20
(RMs) reveal rich structure over the whole range of angular scales=20
studied. FR-induced structures are seen at both high and low radio=20
frequencies at different galactic latitudes.

As expected, the net background polarization percentage decreases with=20=

frequency, while the apparent RMs are rather small compared with those=20=

against compact sources. However, to date, such studies have derived=20
just a single RM value per image pixel, this corresponding closely to=20
the RM of the foreground, which is the dominant contributor to the=20
polarized emission recorded. Nevertheless, we expect the extended=20
polarized emission to be well spread in depth along a given line of=20
sight. Thus, for each image pixel, different regions (or slabs) of=20
polarized emission at different depths contribute with their respective=20=

foreground FR signatures. What is this signature? It is contained in=20
the spectral modulation of the Stokes Q & U signals.

Desh argued that with an appropriate combination of observing=20
frequency, bandwidth and spectral resolution (unavailable from existing=20=

surveys), it should be possible to perform "Faraday Tomography" for=20
each pixel by transforming the spectral modulations to a set of=20
linearly polarized (complex) intensities as a function of Faraday Depth=20=

(i.e. RM). In this way, polarized intensity data cubes (analogous to=20
spectral-line cubes) could be formed with the axes (l, b, RM). The RM=20
axis here is closely related to the "delay" or lag axis in the context=20=

of (say) cross-correlation between orthogonal circularly polarized=20
signals. The usual Fourier inverse relationships apply between, a) the=20=

spectral resolution and the (unaliased) RM range, and b) the full=20
spectral bandwidth and the resolution in RM. Both of these properties=20
share a common, rather steep ($\propto f^{3}$) dependence on the center=20=

frequency, f. The angular beam size and the RM resolution define the=20
volume over which depolarization is unavoidable.

Arecibo offers attractive possibilities for such studies. At 327 MHz,=20
with 25-MHz bandwidth and 1024 spectral channels, one would get an RM=20
resolution of $\Delta$RM $\approx 15 rad m^{-2}$, and an (unaliased) RM=20=

range of $\approx 10^{4} rad m^{-2}$. If L-band data, with a 400-MHz=20
bandwidth and 128 spectral channels, can be used in combination with=20
327-MHz data, $\Delta$RM \approx 5 rad m^{-2}$. (Of course, the raw=20
beam sizes for the two bands differ, and the higher frequency data=20
would need to be mapped and angularly smoothed before combination.)=20
Together, the 7$ \times$ ALFA beams would sped up and match the=20
coverage. Naturally, "beam depolarization" could be large following the=20=

smoothing. However, a recent spatial spectral analysis by Tucci et al.=20=

(2002, ApJ, 579, 607) of the continuum polarized emission shows an=20
increase in Stokes Q & U intensity variations with increasing spatial=20
scale size. Hence, we expect to see a substantial fraction of the=20
polarization structure in the extended component, and missing details=20
at arcminute resolutions may not hurt so much. Further, Arecibo is a=20
single dish and samples the crucial low spatial frequencies that are=20
missed in existing synthesis surveys.