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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 10
News | GG GG HH HH RR R SS | February 1996
| GGGGGGG HH HH RR R SSS |
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CONTENTS:
- GHRS NEWS
- Error in Delivering GO Data
- New Dead Diode Identified
- Use of Attenuated Mirrors in Cycle 6
- GHRS Sensitivity
- RECENT GHRS PREPRINTS
- APPENDIX: GHRS CONTACTS
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Error in Delivering GO Data
---------------------------------
Some GHRS observations in the past month were not delivered to GOs as
expeditiously as is usually the case. An error in a computer file
resulted in GHRS observations being diverted from pipeline processing.
All the data were put into the archive properly and none were lost. By
the time you read this all affected PIs will have been notified and the
data sent.
New Dead Diode Identified
---------------------------------
A new dead diode in the Side 2 Digicon has been identified: number 51.
Future observations will automatically be corrected for the presence of
this now nonoperational diode, and we believe we have identified recent
affected observations. Nevertheless, recent observers may wish to check
for anomalously low counts at or near this diode. Remember that:
1) COMB addition, which averages over either 2 or 4 adjacent
diodes, will result in propagating the effect of an uncorrected
dead diode to the same number of pixels (2 or 4) in the RAW data.
2) When the new dead diode control table is enabled on-board, CALHRS will
be able to correct for the effect of the new dead diode. Before
that, however, an uncorrected dead diode will likely have a
width of 16 pixels in calibrated, merged, normally substepped data.
Specifically, for calibrated data with MER_CORR=COMPLETE, a dead diode
will have the width of (combaddition * nsteps), where the value of
'combaddition' is as discussed in 1) above, and 'nsteps' is the number
of science bins in the substep pattern (four for quarter-stepped
(default) data and two for half-stepped).
Use of Attenuated Mirrors in Cycle 6
-----------------------------------------
We remind observers preparing Phase II proposals for Cycle 6 that the
attenuated mirrors (A2 and A1) are best for acquiring very bright stars
because the "normal" mirrors (N2 and N1) lead to heavily saturated count
rates. The attenuated mirrors also require significant
overheads for internal calibrations, leading to long acquisition times.
This is unfortunate but unavoidable if a good acquisition is to occur.
Bear in mind that the GHRS is only available during the first half of
Cycle 6. That means that if an observation fails, for whatever reason,
it will probably be impossible to repeat it. Conservative observing
strategies are called for. Acquisition count rates may be calculated
from information in the GHRS Instrument Handbook.
GHRS Sensitivity
----------------------------------------------
A recent repetition of our sensitivity monitoring shows that the GHRS
continues to decline in response with time. The change for wavelengths
above Lyman-alpha is no more than about 2%, which is well within nominal
10% accuracies on absolute fluxes. Significantly larger changes are seen
below Lyman-alpha, but the overall response at those wavelengths is low
and few observers work there. If you have questions about GHRS sensitivity,
please contact your Contact Scientist or help@stsci.edu.
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RECENT GHRS 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.
LECKRONE, D.S.; JOHANSSON, S.; KALUS, G.; WAHLGREN, G.M.;
BRAGE, T.; PROFFITT, C.R. "Abundance and isotopic
anomalies of thallium in the atmosphere of the HgMn star,
chi Lupi" ApJ accepted
LINSKY, J.L.; WOOD, B.E. "The alpha Centauri line of
sight: D/H ratio, physical properties of local interstellar
gas, and measurement of heated hydrogen near the
heliopause" ApJ accepted
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APPENDIX: GHRS contacts
-----------------------
Any questions about the scheduling of your observations should be addressed to
your PRESTO contact.
Analysis, STSDAS or any other questions can also be addressed to help@stsci.edu.
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Note: All new Cycle 6 GOs and ARs have been subscribed to the GHRS STAN
listserver.
To subscribe or unsubscribe send a message to listserv@stsci.edu with
the Subject: line blank and the following in the body:
[un]subscribe ghrs_news YOUR NAME
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The Space Telescope Science Institute is operated by the Association of
Universities for Research in Astronomy, Inc., under NASA contract NAS5-26555.
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