STScI Logo

Space Telescope Imaging Spectrograph
STAN - May 1997

-------------+--------------------------------------------+-----------------
             |        SSS  TTTTTTT  IIIIIII    SSS        |
STScI        |       SS       T        I      SS          | STAN - STIS
Analysis     |        SS      T        I       SS         | Number 3
News         |         SS     T        I        SS        | May 1997
             |       SSS      T     IIIIIII   SSS         |
-------------+--------------------------------------------+-----------------

CONTENTS:

       - STIS NEWS 
         + Phase II Processing Underway
         + Cycle-7 Calibration Plan
         + Calibration Reference Files
         + STIS at the AAS:  Winston-Salem, NC.; June 1997
         + SMOV Progress

	- PARALLELS -- COMING SOON TO AN ARCHIVE NEAR YOU

       - NEW STIS DOCUMENTATION 
         + STIS ISRs (Instrument Science Reports)...
         + STIS FAQs (Frequently Asked Questions)...
         + STIS Advisories...
         + STIS Related RPS2 Advisories...

       - APPENDIX: STIS CONTACTS

============================================================================

Phase II Processing Underway
----------------------------

With the passing of the Phase II deadlines for submission of STIS
proposal ingestion, processing of the proposals is now in full swing.
We would like to thank everyone for their timely submissions.  A lot of
good questions from PIs were posed during the preparation of proposals,
many of which were very helpful in clarifying various issues.  As
processing continues, we will be coordinating with you the Phase B
review of all proposals in preparation for scheduling.  This process
begins 6-10 weeks prior to planned execution.  We will be continually
updating the status of STIS and its capabilities throughout via the
STAN, the STIS Web site, and other documentation to reflect our
improved understanding of the instrument.  There will be no need,
however, for you to submit revised Phase II proposals until the Phase B
processing, unless changes such as ORIENTs which affect the LRP (Long
Range Plan) are involved.

As part of the Institute's continuing effort to improve the overall
submission process, we would encourage you to jot down any favorable,
or negative, comments while they are still fresh in your mind regarding
your experience with RPS2, etc. and send them to the Help Desk
(help@stsci.edu).  We will see that they are presented for
consideration for improvements or enhancements in support of future
cycles.


Cycle-7 Calibration Plan
------------------------

Detailed plans for calibrating STIS are firming up rapidly.  The STScI
STIS instrument group has now completed Phase 2 proposals for CCD
calibration proposals and is working toward a mid-June deadline for
submitting calibration proposals for the MAMA detectors.  There are a
lot of different aspects of the instrument that need to be calibrated,
and as might be expected there have been many difficult decisions
regarding the timing and thoroughness of different calibrations.  We
would greatly value input from observers on the plan as it now stands.
In particular, we urge you to review the calibration plan posted on the
web with an eye toward whether it will satisfy your needs for your own
observations.  Please let us know if you think there is something
missing, either from the calibration plans, or from our descriptions of
them.  Suggestions for new calibrations will, of course, have to be
weighed against competing time demands on the telescope, but we would
rather consciously choose not to calibrate something, than simply
overlook it!  Comments should be e-mailed to help@stsci.edu, with a
clear title, such as "Comments on STIS cycle-7 calibration plan."

The calibration plan will be posted to the STIS Calibration Resources
web page link.

Calibration Reference Files
---------------------------

New STIS reference files have recently been delivered to the
calibration pipeline and are now accessible from the Hubble Data
Archive (via starview). They include:

- 2 final ground based pixel-to-pixel flatfield images for the NUV-MAMA
  based work described in ISR 97-07.
- 1 incidence angle correction table for the CCD that corrects for the
  different plate scales in the cross dispersion direction which occurs
  for the scanned modes due to the angle in and angle out being
  dissimilar in the spectral direction.

- 2 'dummy' low-order flatfield images to replace the low order ground
  flats that show inconsistent results (better to apply no flat rather
  than a potentially incorrect one which was currently in ground
  system)
- 5 inflight CCD superbias image reference files created from SMOV 7061
  data.
- 1 inflight CCD superdark image reference file created from SMOV 7092
  data, available for all gains and offsets, but for amplifier D only


 
STIS at the AAS:  Winston-Salem, NC.; June 1997
-----------------------------------------------

Two sessions at the AAS meeting in Winston-Salem will focus on initial
in-flight performance and science returns of STIS. On Tuesday, 10 June,
an extra session entitled "Preliminary Results from the New Instruments
on HST" will include a presentation of first results from STIS by STIS
principal investigator, Bruce Woodgate.  On Wednesday, a STIS poster
session will present details on the in-flight detector and optical
performance of STIS and the STScI calibration pipeline.

For detailed information on the program check out the AAS web page at
http://www.aas.org/meetings/aas190/program/  --otherwise, we'll see you
there.



SMOV Progress 
-------------

STIS is now entering the final phase of SMOV. Over the course of the
past month since the last STAN substantial progress has been made, with
the most important new results coming in the areas of the functioning
of the MAMA detectors and in the commissioning of target acquisitions.
New results on the optical quality in the spectroscopic CCD modes are
also available.


The MAMA detectors:

MAMA SMOV began May 19. Both the NUV-MAMA and the FUV-MAMA are healthy
and both have already seen first light. Over the course of the next 2
months the MAMAs will go through a series of basic characterization
activities.

Full sensitivities have not yet been measured in all modes on an
external target, but indications from initial tests indicate that both
the FUV-MAMA and the NUV-MAMA throughputs are within 25% of the values
advertised in the STIS Handbook with mean throughputs across modes
better than those advertised in the Handbook.

The final focusing of STIS to optimize the PSF at the slit plane in the
UV has been impeded by a rounding error in the NSSC-1 flight software,
which leads to inaccurate slews at the 1.5 milliarcsec level.
Ordinarily this small an error would be undetectable, but the errors
accumulated during the pattern of slews used to peak up on targets in a
very small STIS aperture can be significant.  The problem will be
fixed, so that the advertised peakup accuracy will be achieved, even in
the smallest echelle slits.  The fine alignment of the STIS correctors
will be re-performed in roughly 1 month, in time for the start of Cycle
7.  Already, however, the optical quality of the images on axis in the
MAMAs looks reasonably good, with encircled energies in the central 2x2
pixels in each band within about 10% of the pre-launch projections.

The major anomaly uncovered in the activation of the UV detectors was a
high dark current in the NUV-MAMA. The value expected pre-launch was
130 counts/s over the whole detector (or 1.25 x 10^-4
counts/sec/pixel).  The values observed since turn-on have ranged from
300 counts/s to 5000 counts/s, with a strong dependence on temperature
and distance from the South Atlantic Anomaly.  The increased dark count
comes from cosmic-ray induced phosphorescence in the faceplate window.
The MgF2 (magnesium fluoride) MAMA windows were screened before launch
to avoid this problem, but an error in the screening process allowed
this window to slip through. The phosphorescence has now been confirmed
on the ground in a flight-spare window cut from the adjacent segment of
the same ingot.  Measurements are planned both in the laboratory and on
orbit to characterize the variation in dark current.  We anticipate
that these tests will reveal ways to help manage the observations and
the temperature control of the detector to minimize the background.
However, it is expected that the NUV-detector background will be
significantly higher than advertised.  GOs with NUV-MAMA observations
will be contacted once the dark current of the NUV-MAMA has been more
fully characterized.

The good news is that the FUV-MAMA dark current appears very low ~7-10
counts/s across the whole detector (1x10^-5 counts/sec/pixel); roughly
a factor of 7-9 below the handbook value,  consistent with measurements
during thermal vacuum testing before launch.  This consistency
indicates that the MAMA electronics are successfully rejecting the
cosmic-ray induced Cerenkov radiation that was the major source of
background in the GHRS.

Finally, we note that activation of the echelle modes of STIS for
science must await a flight software fix to the Doppler application
code.  This problem was uncovered in the final stages of Ground Testing
of STIS at GSFC in November of 1996, but at that time it was thought
that the problem only occurred when observing at very high count
rates.  Recently, however, with ongoing work by the GSFC 512 HST Flight
Software Group, Ball Aerospace and the STIS IDT, the nature of the
problem and its implications have been understood.  In a nutshell, STIS
can suspend (all STIS observations be brought to a halt) when
application of Doppler correction during MAMA observations causes
misaddressing of an incoming photon.  Such misaddressing occurs
sporadically.  We are hopeful that the software update can be completed
by the summer's end, allowing STIS MAMA echelle science to commence at
that time, still quite early on in Cycle 7.


STIS Acquisitions:

The SMOV series of target acquisition and acquisition/peakup tests is
nearing completion, with very promising results for the accuracies
which will be routinely achieved.  The testing has also revealed some
problems with the target acquisition flight software code, which need
to be fixed to assure the robustness of the acquisitions and to allow
routine activation of science using acquisition peakups.  We expect
those fixes to be in by late summer; in the meantime science using the
larger slits can proceed on course.

The really important and good news is that SMOV testing has shown that
the acquisition positional accuracy looks to be appreciably higher than
advertised!  Testing of point source acquisitions in SMOV have shown
typical accuracies of 0.025 arcseconds or better (as compared to the
0.1 arcsecond advertised in the Handbook and current Target Acquisition
Cookbook).  Similarly, for diffuse source acquisitions, the accuracy
returned is ~0.05 arcseconds.  Thus peakups should not generally be
needed for science utilizing the 0.2 arcsecond wide/high slits,
considerably reducing overheads and leaving more time for science!Similarly, once the flight software fix for the acq/peakup is in, the
accuracy of the peakups should be roughly +-5% of the slit width
(instead of the +- 15% previously advertised).  Again, this will give
higher accuracy with less overhead.

============================================================================

PARALLELS -- COMING SOON TO AN ARCHIVE NEAR YOU
-----------------------------------------------

The capability of HST to obtain parallel observations has been vastly
expanded with the addition of NICMOS, STIS and the Solid State
Recorder.  Likewise with three imaging instruments all of which can
operate in parallel with each other, and each of which provides unique
capabilities for parallel science studies the value of pure parallels
is very high.  The Cycle 7 Telescope Allocation Committee recognized
the expanded capability of HST for pure parallel science, and
recommended that STScI take on the task of managing large, archival
pure-parallel programs as a community service.  Data to be obtained in
such programs will be made available immediately to the full community
via the HST archive.

Pure-parallel, archival observations with STIS and NICMOS have
commenced as of 2 June 1997.  These initial parallels are implemented
with very simple single orbit exposure sets that are simply replicated
onto as many opportunities as possible in a given week.  As the ground
system is developed further this summer, we anticipate that a new set
of pure parallels will be implemented that more fully utilize the
existing capability by using information on sky position and
characteristics of the primary observing window to craft the individual
parallel observations.  A committee including TAC members and
astronomers with interests in parallel science opportunities will
provide recommendations on the appropriate science to address and the
parallel observations needed to carry this out.

The current parallel observation units are: for STIS a short image with
the CCD followed by a long G750L slitless spectroscopy exposure at the
longest wavelength setting ( coverage from 6460-11490A), for NICMOS the
F110W, F160W and F222M filters are cycled through with NIC2 in focus
using the SPARS256 MULTI-ACCUM sequence, F110W and F160W on NIC1 and
F160W plus a grism, G141 exposure on NIC3 using the same sequence.
Given the lack of parfocality of NIC3 with the other two cameras
operated simultaneously, the grism observations are not expected to be
scientifically useful.  They will give useful technical data on the
NICMOS background characteristics, however.

The proposal numbers for these community support programs are 7675 and
7676 for STIS and NICMOS respectively, and 7700 and 7701 for shorter
visit versions of the same that can fit in smaller opportunities.  In
the first two weeks the ~40 minute parallel units for both STIS and
NICMOS schedule about 15 times for one orbit pointings of the prime, 6
times for 2 orbits, 6 for 3-4 orbits, and 6 for 5-10 orbits.  The
shorter ~20 minute parallel units receive a comparable number of
"hits".  As an illustration, a 6 orbit prime window results in total
exposure times of 1800s STIS/CCD clear image, 10,800s for the G750L
slitless spectroscopy, and 4608s (F110W), 6144s (F160W), and 4608s
(F222M) on NIC2.  The STIS and NICMOS exposure time calculators may be
used to determine how deep such exposures will go for your favorite
objects -- the limiting magnitudes are impressive for multi-orbit
cases.  For NICMOS the high quality diffraction limited infra-red
imaging, coupled with a lower than anticipated thermal background allow
exceedingly faint limiting magnitudes particularly in the H band.

A web page, http://archive.stsci.edu/pure_parallels.html, has been set
up to quickly show users what observations have been done in these
programs, with the most recently archived datasets listed first.
Extensions of these programs, which may entail additional proposal IDs
will be incorporated in this web page in a transparent fashion.
Registered archive users will then be able to retrieve the data through
this page.

The priorities for WFPC2 are to finish the approved Cycle 6 GO
parallels before phasing in an appropriate archival, pure-parallel
program.  The Cycle 7 approved GO parallel programs will have high
priority for execution beginning this fall when the more robust ground
system implementation for parallels becomes available.

There is no proprietary period for the community service pure
parallels, so these data will be the first STIS and NICMOS observations
broadly available to HST users and may be used not only for science,
but also to obtain a measure of how well the new instruments perform.


============================================================================

                           NEW STIS DOCUMENTATION
                           ----------------------

All new STIS related documentation noted here, along with previous
items, may be found on the "Documentation" link off the STIS Home
Page.

STIS ISRs (Instrument Science Reports)...
-----------------------------------------

During the past month 3 new ISRs were released and one updated.
These include

New:
97-10   STIS Results from SMOV: CCD Baseline Performance
97-09   The STScI STIS Pipeline: Bias Level Correction 
97-08   The Spectrum Splicer Task
97-07   Pre-Launch NUV MAMA Flats

Updated:
97-03B  A User's Guide to Target Acquisition With STIS (Revision B) 



STIS FAQs (Frequently Asked Questions)...
-----------------------------------------
 
Supported Wavelengths:  
     Are all central wavelengths (prime and secondary) supported? 

Data Buffer Storage Units:  
     Does the STIS data buffer store Analog-to-Digital Units (ADUs,
     sometimes also referred to as DN or Data Numbers) or electrons in
     case of CCD observations?

Parallel Observations vs Different Apertures:  
     I am attaching parallel observations to my STIS exposures, and
     RPS2 is warning me against grouping primary observations together
     that have different apertures.  While I am using different STIS
     apertures, there were no errors before I added the parallels.  Why
     do I now get a error?


STIS Advisories...
------------------

09 May 97:  Most Recent Pre-launch STIS Slit Throughputs 
02 May 97:  New Operating Procedures for MAMAs; Impact to GOs
01 May 97:  STIS Filter Red Leaks
01 May 97:  Exposure Time Calculator Updates



STIS Related RPS2 Advisories...
-------------------------------
 
No new STIS related advisories with RPS2 7.1 have been posted since the
April STIS STAN (30 April 1997).  However, you should frequently check
the RPS2 Advisory link off the STIS Proposal Resources web page for up
to date information on any new problems identified with the most recent
software release.  Previously existing problems are noted in the list
of known RPS2 7.1 problems as well as general RPS2 issues.


============================================================================

                          APPENDIX: STIS 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 HST-related questions can also be
addressed to help@stsci.edu
============================================================================
To subscribe or unsubscribe send a message to listserv@stsci.edu with
the Subject: line blank and the following in the body:

                     [un]subscribe stis_news YOUR NAME

===========================================================================
Comments, questions, suggestions, etc. can be e-mailed to help@stsci.edu.
===========================================================================
The Space Telescope Science Institute is operated by the Association of
Universities for Research in Astronomy, Inc., under NASA contract
NAS5-26555.
===========================================================================