Документ взят из кэша поисковой машины. Адрес оригинального документа : http://www.stsci.edu/ftp/instrument_news/FOS/stans/fos_stan15 Дата изменения: Sat May 31 00:44:07 1997 Дата индексирования: Sun Dec 23 01:27:09 2007 Кодировка: Поисковые слова: reflection nebula

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| FFFFFF OOOOOO SSS |
STScI | FF OO OO SS | STAN - FOS
Analysis | FFFF OO OO SS | Number 15
News | FF OO OO SS | January 1997
| FF OOOOOO SSS |
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CONTENTS:

- FOS NEWS
+ Important FOS/BL G130H Sensitivity Changes
+ Observed FOS PSFs and LSFs, ISR-148, is Undergoing Revision

- New Version of the Data Handbook is Planned

- RECENT PREPRINTS

- APPENDIX: FOS CONTACTS

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Important FOS/BL G130H Sensitivity Changes
--------------------------------------
by Tony Keyes

Following are two important items pertaining to FOS/BL G130H
sensitivity changes and methods of analysis.

1) FOS/BL G130H sensitivity measured with the 4.3 aperture appears to have
increased in the wavelength range 1250-1600 by approximately 5% between
July 1995 and late December, 1996. A possible decrease in sensitivity of
several percent also seems to have occurred for the region 1150-1180 Angstroms.

The 25 April 1996 sensitivity measurements for FOS/BL G130H indicated
that instrumental sensitivity remained consistent with the mean sensitivity
derived from all prior pre-COSTAR measures within 3% though at certain
wavelengths these measures were near one 3% extremum. No changes to the
pipeline FOS sensitivity reference file were deemed necessary after the
April 1996 observations.

No additional successful sensitivity measurements were obtained
until 23 December 1996. These (and two more recent) sensitivity measures
indicate a 5% increase in the wavelength region 1250-1600 Angstroms relative to
the pipeline sensitivity, which is virtually identical with July, 1995
sensitivity. Naturally, these changes can be very important for analyses
requiring precise absolute or relative spectrophotometry with G130H.

Possible explanations for the observed changes include image motion on
the photocathode and migration of the photosensitive bialkali materials in the
photocathode.

As part of FOS close-out activities we will provide new and more
detailed time-dependent sensitivity corrections including a more precise
discussion of color uncertainties in this spectral range. At the present time,
we suggest an interim correction of 0.25% per month INCREASE in instrumental
sensitivity SINCE 1 July 1995 be applied to the FOS/BL 1250-1600 Angstrom range.
NOTE: the sense of this correction means that corrected FOS fluxes
will be SMALLER than pipeline calibrated values in this region. Essentially no
correction seems required at 1200 A. A linear ramp between 1200 and 1250
can be applied.

2) We wish to remind observers that FOS instrumental sensitivity is a very
steep function of wavelength shortward of 1200 Anstroms. Although instrumental
sensitivity is determined to 3% accuracy in this region, this steep sensitivity
gradient requires accurate knowledge of observed wavelengths to insure accurate
flux calibration. Common instrumental uncertainties can produce important
systematic errors in pipeline processing.

Both telescope pointing uncertainties and FOS filter-grating wheel (FGW)
position uncertainties can affect observed FOS wavelengths. An error of
0.5 Angstroms, or 2 pixels, produces little effect longward of 1200 A., but
yields systematic photometric errors of 2% at 1180 A. and 4% at 1150 A. Larger
miscenterings will yield proportionately larger systematic errors in this
region. Target centering inaccuracies of only 0.15 arcsec or filter-grating
wheel misalignment of 0.5 diodes will yield such 2 pixel offsets. Note that
ACQ/BINARY alone is not sufficient to avoid pointing errors of this magnitude.
The target acquisition strategies recommended in the FOS Handbook version 6
for programs requiring accurate photometry and/or wavelengths yield pointing
accuracies of 0.04 arcsec (~0.5 pixels). Three-sigma FGW uncertainties are of
the order of 1.2 pixels.

Observers with a need for accurate absolute or relative flux
calibration in the 1150-1200 A. region should examine fiducials in the G130H
spectral range, such as Lyman alpha absorption, to determine the degree of
miscentering along dispersion. Since the pixel-positions of flat field
features are not affected by target centering, any re-calibration should
proceed normally through flat field correction (.c5 output products), next
the spectrum should be shifted by the appropriate amount, and then flux
calibrated.


Observed FOS PSFs and LSFs, ISR-148, is Undergoing Revision.
------------------------------------------------------------
by Ed Smith

The post-COSTAR, FOS/RED, observed PSF provided in CAL/FOS
ISR-148 includes artifacts. The image was created by co-addition
of 30 separate data sets. Several of these data sets have been found
to contain possible reflection and diffraction effects due to the target's
proximity to the edge of the aperture. Therefore the FOS/RED PSF, in
particular, should not be used. It is being reproduced without the artifacts
and all other PSFs and LSFs provided in ISR-148 are being reviewed. This
review will result in a new ISR. The revision will include PSFs appropriate
for data taken in standard ACCUM mode as well as reproducing ISR-148's IMAGE
mode PSFs.

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New Version of the Data Handbook is Planned
--------------------------------------------
by M. Voit

A revised version of the HST Data Handbook, including new chapters
on NICMOS and STIS, is being planned for this fall. To aid in our
planning, we would like your comments on the current version
(Version 2, December 1995). How can we improve it? What features
do you find helpful or unhelpful? Does the current structure
quickly lead you to what you need to know? What issues should
be covered in greater depth? Is there any material you have
found particularly confusing or unclear?

Please send all comments to Mark Voit at voit@stsci.edu.

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RECENT PREPRINTS
----------------

We draw your attention to these papers, based on FOS data, that will appear in
the next few months. This list includes all preprints received by the STScI
Library not yet published in the journals. Please remember to include our
Library in your preprint distribution list.

KORMENDY, J.; BENDER, R.; AJHAR, E.A.; DRESSLER, A.; FABER,
S.M.; GEBHARDT, K.; GRILLMAIR, C.; LAUER, T.R.; RICHSTONE,
D.; TREMAINE, S. "Hubble Space Telescope spectroscopic
evidence for a 1 x 10 (9)-M black hole in NGC 4594" ApJ
12-20-96 www.ifa.hawaii.edu/~kormendy

BIANCHI, L.; VASSILIADIS, E.; DOPITA, M. "Hot evolved
objects in different parent galaxies: the stellar winds of
three planetary nebula nuclei in the Large Magellanic
Cloud" ApJ accepted

SCHULTZ, A.B.; HART, H.M.; HAMILTON, F.C.; KOCHTE, M.;
BRUHWEILER, F.C.; BENEDICT, G.F.; CALDWELL, J.; CUNNINGHAM,
C.C.; FRANZ, O.G.; KEYES, C.D.; BRANDT, J.C. "Lessons
learned from an HST faint companion search program"
Planets Beyond the Solar System

HAMILTON, A.J.S.; FESEN, R.A.; WU, C.-C.; CRENSHAW, D.M.;
SARAZIN, C.L. "Interpretation of UV absorption lines in
SN1006" ApJ accepted

WU, C.-C.; CRENSHAW, D.M.; HAMILTON, A.J.S.; FESEN, R.A.;
LEVENTHAL, M.; SARAZIN, C.L. "Far-UV absorption lines in
the remnant of SN 1006" ApJ 3-1-97

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APPENDIX: FOS contacts
-----------------------

Any questions about the scheduling of your observations should be addressed to
your Program coordinator. Post-Observation questions can be addressed to your
Contact Scientist. If you do not know who these persons are, you can find the
information on the WWW at http://www.stsci.edu/public/propinfo.html.

Analysis, STSDAS or any other questions can also be addressed to help@stsci.edu
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