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| GGGGGGG HH HH RRRRR SSS |
STScI | GG HH HH RR R SS | STAN - GHRS
Analysis | GG GGG HHHHHH RRRRR SS | Number 15
News | GG GG HH HH RR R SS | August 1996
| GGGGGGG HH HH RR R SSS |
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CONTENTS:
- GHRS NEWS
+ Throughput Changes
+ Background and Dark Measurements
+ Paper Products
- NEW GHRS DOCUMENTATION
+ ISR-076: G140L Flat Fields
- RECENT PREPRINTS
- APPENDIX: GHRS CONTACTS
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Throughput Changes
------------------
We remind observers that we have seen changes in the absolute throughput
of the GHRS since the 1993 Servicing Mission. Above Lyman-alpha these
changes have reached about 4% net over two years, which is less than the
uncertainty in absolute fluxes. However, below Lyman-alpha the decline
is more significant, and amounts to 30 to 40% at the shortest wavelengths.
If your observations include wavelengths below Lyman-alpha, and absolute
fluxes at those wavelengths are important for your science, please contact
your Contact Scientist or help@stsci.edu so that we can determine an
appropriate flux correction for when your data were taken. A detailed
analysis is in progress so that GOs and ARs can make these corrections
themselves.
Background and Dark Measures
----------------------------
Your GHRS observations normally include measurements of the background
seen at the time of observation. This is done with either the science
diodes or the corner diodes, depending on the STEP-PATT chosen (see the
Instrument Handbook for details). For short (see Table 1 below)
observations, the count rate seen is so low that the statistical
accuracy of the dark determination is poor. Corner diodes are usually
worse than science diodes for measuring backgrounds but are preferable
when scattered light contaminates the interorders, such as for certain
echelle observations. However, CALHRS currently interpolates between
the means of the right and left corner diodes instead of averaging all
4 together to get a constant. Therefore, we now recommend that users
ignore the background calculated by CALHRS for STEPPATTs 1-3, 8, 9, 14,
and 15.
As an alternative to these 2 situations, for observations which do not
pass through the SAA, we will implement a model for the background
counts developed by Don Lindler that predicts the dark rate from the
geomagnetic position at the time of the observation, and will advise
when that is available. In the mean time, that model is described on
p. 216 of Calibrating Hubble Space Telescope: Post Servicing Mission.
If you have questions about dark/background measurements, please
contact help@stsci.edu.
Table 1: Stepping
Quarter Half
STEPPATTs: (Odd**) (Even)
Detector 1 less than 16 min less than 8 min
Detector 2 less than 30 min less than 16 min
** except STEPPATT=1 which has NO sub-stepping.
Paper Products
--------------
The GHRS Group has just begun to review standard paper products that will
be included with all GO observations. We anticipate that GOs will start
receiving these paper products for observations made after September 1.
These sheets provide a quick summary of vital statistics of the observation
and some useful graphical information.
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NEW GHRS DOCUMENTATION
----------------------
G140L Flat Fields
-----------------
An Instrument Science Report is now available about flat fields for
exposures made with grating G140L. To request the full report, send email
to help@stsci.edu requesting GHRS-ISR-076.
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RECENT PREPRINTS
----------------
We draw your attention to these papers, based on GHRS 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.
COWAN, J.J.; SNEDEN, C.; TRURAN, J.W.; BURRIS, D.L.;
MCWILLIAM, A.; PRESTON, G.W. "R- and S-process signatures
in metal-poor halo stars" Nucl. Phys. A accepted
LEITHERER, C. "Spectral synthesis analysis of hot-star
populations" Liege Colloq. 33
PISKUNOV, N.; WOOD, B.E.; LINSKY, J.L.; DEMPSEY, R.C.;
AYRES, T.R. "Local interstellar medium properties and
deuterium abundances for the lines of sight toward HR 1099,
31 Comae, beta Ceti, and beta Cassiopeiae" ApJ accepted
WOLVEN, B.C.; FELDMAN, P.D.; STROBEL, D.F.; MCGRATH, M.A.
"Lyman-alpha induced fluorescence of H2 and CO in HST
spectra of a comet Shoemaker-Levy 9 impact site on Jupiter"
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APPENDIX: GHRS 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.
Analysis, STSDAS or any other questions can also be addressed to help@stsci.edu.
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