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Space Telescope Imaging Spectrograph
STAN - February 1998

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STScI                        .  . __..___.                       Number 7 
Analysis                     |__|(__   |                         February 1998
Newsletter                   |  |.__)  |   
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               G H R S     ( S | T | I | S )      F O  S  
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CONTENTS:
 
       - STIS CALIBRATION NEWS 
	 + Check Out New Calibration Related Instrument Science Reports.
         + First Order Mode Sensitivity Calibration Completed!!!!
         + Slit Width and Spectral Purity of STIS Data; a reminder.
	 + Flux stability of long pointing small slit observations good.
         + Target acquisition FSW Upgrade Completed.
	 + Monitoring Accuracies; Acquisitions, MSM Repeatability, Focus. 
	 + Missing CCD Darks.
	 + Buckets of Calibration Data in Archive.	

	- STIS PIPELINE AND SOFTWARE NEWS
	 + Major Improvements to CALSTIS!!!!
	 + Recalibration recommended.
	 + Echplot updated.
	 + Script for creating daily darks available.
         + Special IRAF task to correct observed time in timetag for aberration.

	- STIS PHASE 2 NEWS
	 + New Version of RPS2 Released; must be used for future submissions.

        - NEW STIS DOCUMENTATION 
         + STIS ISRs (Instrument Science Reports), FAQs, and Advisories.

        - HST DATA HANDBOOK 
	 + HST Data Handbook for Heritage Instruments (FOS+GHRS) available.
	 + HST Data Handbook Errata; where to look for STIS, FOS, and GHRS!

        - GHRS NEWS
	 + New GHRS FAQ on Scattered Light.
	 + Two Addenda to Data Handbook Posted.	

        - FOS NEWS     
	 + Closeout Calibration Files Delivered.
	 + Wavelength Calibration Uncertainties Identified.
	 + FOS Polarimetry Calibration.	
	 + FOS Scattered Light Modeling Software.
	 + FOS WWW Page Updates.	
	 + Some FOS Starview Reports Misleading.
	 + FOS WWW Advisories.
 
        - DATA ANALYST POSITIONS AVAILABLE AT STScI
      
        - APPENDIX: HST Spectroscopy Contacts

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


STIS Calibration News   
--------------------------
+  Check out new Calibration related ISRs on:
	Absolute Flux Calibration for STIS First-Order, Low-Resolution Modes, 
	GO Added Near-IR Fringe Flats,  
	STIS Near-IR Fringing: Basics and Use of Contemporaneous Flats..
	Diffuse Source Absolute Sensitivity and Point Source Relative 
            Sensitivity 
	Spectroscopic Mode Image Quality of STIS I. First Order Modes
	Doppler Compensation in Calstis
	                                                   

+  First Order L Mode Sensitivity Calibration Complete 

The initial calibration of the first order low resolution mode (G750L,
G430L, G230LB, G230L, G140L) sensitivities is now complete and new
photometry tables have been delivered to the pipeline, synphot, and the ETC
along with revised calstis spectroscopic reduction software (see Pipeline
News below). These modes collectively span a wavelength range 
from 1140 to 10320 Angstroms. The curves were determined by comparing wide 
slit (52" x 2") observations of the spectrophotometric standard star GD153 
to a pure hydrogen white dwarf model. Except for G140L, there is no good 
evidence for changes in the sensitivity beyond ~1% through the end of 1997.  
Except for the G140L, where there may be systematic changes in sensitivity
as a function of time at the ~5% per year level and the long wavelength part 
of G750L where the fluxes are difficult to determine accurately due to
the fringing and broad PSF wings, the absolute flux calibration is accurate 
for observations in 1997 to 3-sigma=4% for stars centered in the 52x2" slit.
Preliminary results on the vignetting analysis for the first order modes suggest
that the smooth changes in sensitivity as a function of distance along the slit
are less than +/-2 % for all first order modes, except for the extremities of
G140L, where 5% differences in detector QE are observed. While the 52x2" slit is
ideal for photometric continuum determinations, a narrower slit should be used
for line profile measurements in order to minimize the contamination from the
impure light in the wings of the PSF.  For the narrower slits, local
inhomogeneities in the slit width can cause a variable throughput along 
the slit (see the STIS Foibles page on the STIS Instrument WWW pages), and
for observations at slit center photometric accuracy will typically be limited 
by OTA breathing and its affect on slit throughput. Two new ISRS (STIS 97-14
and STIS 98-01) describe the first order mode sensitivity calibration

+ Slit Width and Spectral Purity of STIS data; a reminder.

Observers who wish to perform high-precision line-profiles studies should
take into account that, as with all spectrographs, STIS spectra suffer 
from spectral impurity if taken through large entrance apertures. 
The optical performance is degraded due to a less than perfect OTA, and 
scattering on the detector and on the gratings.  Most of these effects can 
be minimized if the observations are taken using small slit widths. A full 
test series to address these issues will be performed later this year. 
Preliminary results suggest the following recommendations:

The maximum spectral purity for first-order gratings is achieved with entrance 
slits of 0.2" width or smaller. 

Echelle observations taken through the 0.2" x 0.2" or larger apertures are still
somewhat affected by spectral impurity; use of the two pixel wide slits will
increase the spectral purity. More generally, the combination of interorder 
scatter, the cross-dispersion profile and the detector PSF can make it
difficult to accurately determine and subtract the inter-order background
and we encourage GOs to experiment with the use of different size extraction
and background boxes in the reduction of their echelle data. Smaller 
extraction boxes generally increase the spectra purity of the data, at the
expense of the accuracy of the absolute flux calibration.

More details on spectral purity can be found off the Data Foibles page of 
the STIS WWW pages at 
     http://www.stsci.edu/ftp/instrument_news/STIS/foibles/specpur.html.

+ Flux Stability of Long Pointing Small Slit Observations

We have been monitoring all long (multi-orbit) exposures in a given 
configuration to check the stability of HST in keeping a target in the 
STIS slits.  Initial results shows that the pointing is quite stable, with 
the typical variation in  the target flux (over several orbits) of 1-2%.
To date we have monitored observations taken in the following
configurations: E140M + 0.2X0.06, G140L + 52X0.2, G140M + 52X0.2, G750M + 
52X0.2, and G750M + 52X0.1. Updates will be posted to the STIS On 
Orbit Performance Pages.

+ Target Acquisition FSW Upgrade Completed and Accuracy Rechecked

An update to the STIS Target Acquisition flight software was recently
uplinked to perform a 3-pixel dither between the images in both the
coarse and fine locate phases of an ACQ observation.  This revision
was needed to allow for a more robust handling of hot pixels on the
CCD in the target acquisition subarray.  On-orbit testing has revealed
that the dithering technique is working well, and we have released the
new software for general use.  No changes are required to the
specification of your ACQ exposure, although the overhead for an ACQ
has increased slightly (32 seconds to account for the small slews).

+ Monitoring Accuracies; target acquisitions, MSM repeatability, and focus.

As always, we have been performing regular (monthly) monitors of 
We find that the target acquisition (ACQ) accuracy is 0.005" (even
better than what was reported during SMOV), and the peakup accuracy is 5% 
of the slit width.  The Focus monitor shows that STIS has return to nominal 
focus after the NIC3 campaign.  The Mode Selection Mechanism appears 
repeatable to 0.5-1.5 pixels.  The HITM and Tungsten calibration lamps show 
no sign of decreased throughput since launch, while the LINE lamp shows
inconsistent results.  For long exposures, we see no significant
degradation (variations are less than 3%) in the flux stability 
during long pointing observations (see also above). We will continue
to monitor the performance of STIS and will be posting our results
on the STIS On Orbit Performance pages on the STIS Instrument WWW pages.
        
+ Missing CCD darks: 

Due to an unfortunate oversight, the regular weekly darks for 
the STIS CCD were not taken from December 5 to February 16.
The effect on the quality of the pipeline reference file is
expected to be minor, because darks were obtained in the
CCD annealing program and the CCD performance monitoring, and
daily darks have been taken continuously (at gain 4).
 
* Calibration data available in the archive:

Quite a lot of calibration data have come in over the last
few months. It will take some time to analyze it all, and in
the meantime observers may wish to take a look for themselves.
Some proposals that have recently executed are as follows:
 
Calibration Programs With Observations in December 1997

   ID   Title
  ----  -------------------
  7600 CCD Performance Monitor                       
  7601 CCD Darks and Biases Monitor                  
  7604 MAMA Dark Monitor                             
  7634 CCD Flat Fielding Monitor                     
  7635 CCD Hot Pixel Annealing                       
  7636 CCD Spectroscopic Internal Flats              
  7639 CCD Contamination/Sensitivity over Full Field 
  7646 CCD Scattered Light Near Earth Limb...        
  7649 Missed Dispersion Solutions, MAMA             
  7666 CCD Linearity and Shutter Stability Test      
  7673 Contamination/Sensitivity/Focus Monitor, MAMA 
  7674 IR Standards                                  
  7711 STIS CCD G750L Fringing Flats                 
  7723 Grating scatter                               
  7783 CCD External Flats, Sky parallels             
  7802 Daily Darks part II                          

Calibration Programs With Observations in January, 1998

  7604 MAMA Dark Monitor
  7635 CCD Hot Pixel Annealing
  7634 CCD Flat Fielding Monitor                    
  7636 CCD Spectroscopic Internal Flat
  7653 LSF Measure, MAMA Spectroscopic Mode         
  7657 Spectroscopic and Imaging Sensitivity, MAMA  
  7660 STIS to FGS Alignment - Cycle 7 Check (CCD)  
  7672 Contamination/Sensitivity Monitor, CCD       
  7673 Contamination/Sensitivity/Focus Monitor, MAMA
  7674 IR Standards                                 
  7711 STIS CCD G750L Fringing Flats                
  7783 CCD External Flats, Sky parallels            
  7802 Daily Darks part II                          


Calibration Programs With Observations Scheduled Through March 1, 1998

  7604 MAMA Dark Monitor                              
  7602 Missing CCD Flats                              
  7634 CCD Flat Fielding Monitor                      
  7635 CCD Hot Pixel Annealing                        
  7636 CCD Spectroscopic Internal Flats               
  7639 CCD Contamination/Sensitivity over Full Field  
  7650 Yearly Dispersion Solution Check, CCD          
  7651 Yearly Dispersion Solution Check, MAMA         
  7654 Slitless Spectroscopy,CCD                      
  7660 STIS to FGS Alignment - Cycle 7 Check (CCD)    
  7665 Geometric Distortion, CCD                      
  7672 Contamination/Sensitivity Monitor, CCD         
  7673 Contamination/Sensitivity/Focus Monitor, MAMA  
  7674 IR Standards                                   
  7711 STIS CCD G750L Fringing Flats                  
  7803 Daily Darks part III                           
  7905 CCD Acq Checkout for FSW Hot Pix Fix           
  7926 CCD Dark and Bias Monitor, Continued           
  7928 CCD Spectroscopic Flatfielding, Continued    

Newly Approved Calibration Proposals

  7943 Transmission of Filtered Echelle Slits
  7945 MAMA Ramp-up Check -retry


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

STIS Pipeline News.
--------------------------
!!Note: the changes described below are used now in the pipeline and
will be available externally in the next release of STSDAS (2.0.1)
which should be available by early March for downloading.!!

+ New and Very Improved Calstis in the Pipeline    

Highlights of changes include:

	- ONE-DIMENSIONAL SPECTRAL EXTRACTION as part of the pipeline 
	calibration has been enabled for first-order and echelle modes in 
	calstis v1.6, which was installed in the pipeline on 2 February 1998.  

	- Sky background will now be accounted for in COSMIC RAY REJECTION. 
	The sky background is subtracted off before cosmic ray rejection takes
	place, and is added back into the final output image.

	- The PHOTOMETRIC CALIBRATION KEYWORDS (PHOTFLAM, etc.) were incorrectly
	populated for filtered imaging modes because the filter throughput was
	not being taken into account.  This problem has been corrected. 

	-FLUXCORR, the CONVERSION TO ABSOLUTE FLUX in calstis6 (x1d), previously
	did not take into account the fact that a finite height extraction
	aperture was used when generating the throughput reference tables
	(PHOTTAB - _pht.fits).  Beginning with calstis v1.7, the throughputs in
	the PHOTTAB reference file will be for an "infinite" extraction
	region.  The factor to correct from a finite extraction region to an
	"infinite" region is contained in a new reference table with header
	keyword PCTAB, and calstis6 now applies the correction from this table
	to the flux conversion.  


	- The stand-alone iraf calibration tasks (calstis, basic2d, x1d, x2d,
	ocrreject, wavecal) now take wildcard file name input.

	- To solve some problems associated with identification of the best
	reference files for recalibration, combined with the fact that when
	using the starview Reference screen to retrieve the latest reference
	files only the science portion of an associated data set is used in the
	screen, calstis now compares reference file names in the science header
	and wavecal header.  If there are any differences, a warning is
	printed, and the file name from the science header is used for
	calibrating both files. 

	- A number of additional enhancements and minor problem fixes have been
	made.

FOR MORE DETAILS ON THESE CHANGES TO CALSTIS, SEE THE STIS "PIPELINE
SOFTWARE HISTORY" PAGE ON THE WWW.

+ Recalibration recommended, particularly for First Order Mode Observers

The Calstis software changes have been quite significant, particularly
for first order mode observers. In addition, the Calstis changes described 
above have been accompanied by new throughput reference Files (PHOTTAB) 
for all first order low resolution modes (G140L, G230L, G230LB, G430L, G750L)
(see above in this STAN and the new ISRs).

Anyone with first order mode data taken prior to installation of calstis 
v1.7 in the pipeline is strongly advised to recalibrate their data to get 
the most up to date in-flight calibration.

+ Echplot has been improved and updated.

+ New CCD DARK REFERENCE FILES for January were delivered on 9 February 1998.  

A script for creating daily darks has been put on the web under
Calibration Resources, along with an explanation on how to use it.

+ Special IRAF task to correct for observed times in time-tag data 
    
The time-tag mode of STIS is capable of a temporal resolution of  
150 microseconds.  So the effects on the observed times
of both the orbital motions of the Earth and the telescope may need
to be corrected using times to the solar-system barycenter.  
A special task 'odelaytime' is developed for this purpose, which is
available under the 'stis' package. The task reads the input time-tag 
file (a table) and creates a new output column with the times  
corrected for light delay from three sources: (1) general relativistic 
effects (up to 2 milliseconds), (2) displacement of the telescope  
from the center of the Earth (up to 20 milliseconds), and
(3) displacement of the Earth from the solar-system barycenter (up to 
500 seconds). Time accuracy is preserved by using double precision  
data in the output column. 


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

STIS Phase 2 News
------------------

+ A new version of RPS2, Version 7.3, has been released. 

We recommend that any GO/GTO that needs to revise/resubmit their STIS
program obtain the new version of the RPS2 to properly process their
observations.  Besides the enhanced capabilities (such as the CCDFLAT
target for fringe flats), there are timing changes (particularly for
target acquisition and the autowavecals) that will impact the orbit
structure. Additionally, the settings of the autowavecals are improved;
specifically (i) to decrease the duration of the autowavecal exposures, where
possible by a more optimal selection of lamp settings, (ii) to improve the 
signal-to-noise in the autowavecals for specific settings where the
previous settings were not optimal and (iii) to assure autowavecals
are always taken with slits less than 0.5'' in width as the narrower
slit wavecals produce significantly better zeropoint accuracies. Note
that all STIS proposals were retransed in house, so that all observations
taken after Feb 6, 1998 will used the improved acquisitions and
wavecals; you do NOT need to resubmit your phase 2.

============================================================================
 
                           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)...
-----------------------------------------

97-14  Absolute Flux Calibration for STIS
       First-Order, Low-Resolution Modes, Ralph Bohlin, et. al.

97-15  GO Added Near-IR Fringe Flats, S. Baum, et al.

97-16  STIS Near-IR Fringing: Basics and Use of Contemporaneous Flats for 
       Extended Sources

98-01  Diffuse Source Absolute Sensitivity and Point Source Relative
       Sensitivity as a Function of Extraction Slit Height for STIS First-Order
       Modes, Ralph Bohlin, 1998.

98-02  Cycle-7 MAMA Pulse Height Distribution  H. Ferguson et al. (coming soon)
        stability: Fold Analysis Measurement            
 
98-03  MAMA Anomalous Recovery Procedures   H. Ferguson et al. (coming soon)

98-04  Spectroscopic Mode Image Quality of STIS I. First Order Modes
				K. Sahu et al.

98-05  Doppler Compensation in Calstis.  K. Sahu et al.                                         


STIS FAQs (Frequently Asked Questions)...
-----------------------------------------

Phase II FAQs:  

  How do I insert a NIR-flat into my program?

  Does a miscentering of my target impact the wavelength scale?  If so,
  what can I do about it?


Data Analysis FAQs:  

  How good is the pipeline reduction at removing hot pixels?
  How can I improve on this?

  What does target miscentering do to my wavelength calibration?


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

  Problems with pipeline processing of STIS data.

  Using Starview/Bestref to retrieve reference files to recalibrate data. 
 
 
Other STIS (Updates, Technical Memos, etc.)...
-----------------------------------------
 
Information about the HST Archival Pure Parallels, and how to retrieve
the data, is now online, at: http://archive.stsci.edu/hst/parallels/.
Check it out! Lots of new information provided.

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

HST Data Handbook

+ HST Data Handbook for Heritage Instruments

Volume II of the third edition of the HST Data Handbook was
released in January.  This volume presents updated and expanded
calibration and analysis information for all of the instruments that
have been retired from HST, namely FOS, GHRS, HSP, and WF/PC-1.
Electronic copies are available via the FOS and GHRS WWW pages.
Printed copies may be obtained by contacting help@stsci.edu.

+ HST Data Handbook Errata Pages Now On-Line; Updates Planned

The following Web page has been established to guide users to errata and 
addenda to the HST Data Handbook (DHB): 

	http://www.stsci.edu/documents/dhb/Errata.html

Links from there will list all the changes by instrument/major section.  
Links have also been placed on the DHB core page, at the URL below, 
informing users of the availability of the corrected matter: 

	http://www.stsci.edu/documents/data-handbook.html

In general, errata and small addenda will appear very soon after they are 
documented.  If you know of or suspect errors in the STIS, FOS, or GHRS 
chapters of the DHB, please contact the Help Desk. 

By mid-March the first update to the DHB (Version 3.1) will be available 
on the Web.  These updates will appear as often as quarterly, and will 
take the form of revised PDF files for each chapter.  The table of contents 
and index will also be revised, if necessary, to reflect the changes.  The 
affected chapters (both hardcopy and Web versions) will contain a special 
indication of the version number and release date, so that users will know 
whether or not they need to update their document.  

At a minimum, the errata posted by the time each update is prepared 
will be incorporated into the DHB, although more extensive changes and 
additions may also be incorporated at that time.  

 
==============================================================================
 
                              GHRS NEWS
			      ---------


One new GHRS FAQ and two New GHRS Data Handbook Addenda were posted to the
WWW page:

  FAQ: 
	Are GHRS spectra background subtracted?
  Addenda:
	Addendum to Incident Angle Correction information in Table 37.6
	Addendum to Discussion of the LSA-SSA Differential LSF. and
		corrected Table 38.1 with the LSFs.
	
 
==============================================================================
 
                                FOS NEWS
				--------

+ FOS Closeout Calibration Reference Files Available

A variety of FOS closeout calibration reference files are now
available.  The post-COSTAR sensitivity calibration has been updated
and now is based upon standard star observations from the entire
post-COSTAR period as opposed to only the 1994-95 observations used in
the previous calibration.  All post-COSTAR sensitivity observations
have now been reduced with flatfields from the actual epoch of
observation.  Additionally, aperture throughputs are now available for
barred and 0.1-PAIR apertures.

Pre-COSTAR aperture throughputs are also available for barred
and 0.1-PAIR apertures.  No adjustments have been made to pre-COSTAR
sensitivities at this time.

A complete set of SINGLE aperture flatfield reference files
for all available post-COSTAR observing epochs is now available.
These new reference files, which replace average flatfields that were
based only upon 1994-95 observations, allow more accurate tracking of
variable flatfield features.  All of these flats are derived with the
FOS superflat/superflux method and replace all previous post-COSTAR
FOS flatfields.  An equivalent set of post-COSTAR flatfields for PAIR
apertures will be available shortly.  No updates to pre-COSTAR
flatfields have been made at this time.

A complete discussion of the accuracies and characteristics of
the FOS closeout flatfield and sensitivity calibrations is included in
Chapter 32 of Volume II of the HST Data Handbook version 3.

+ Changes in Zero-Points of FOS Wavelength Scale

Michael Rosa (ECF) has performed an analysis of the
characteristics of the FOS wavelength scale and has found a gradual
drift in the zero-point of FOS/BL WAVECAL exposures of roughly 7
pixels (full amplitude) from launch through the end of cycle 6 and a
large dispersion in the zero-points of the FOS/RD wavelength scale (7
pixels) over the entire period.

The current pipeline FOS wavelength scale, for both pre- and
post-COSTAR cases, is defined by a single set of observations for each
disperser.  As detailed in Chapter 32 of Volume II of the HST Data
Handbook version 3, when the effects of FOS filter-grating wheel (FGW)
positional uncertainty are considered, this leads to potential
uncertainties of the order described above.

The detailed examination of all FOS WAVECAL exposures reveals:

1.  for FOS/BL: 

	- at any given epoch, the peak-to-peak scatter of zero-point
shifts about a derived mean trend is +/- 1 quarter-stepped pixel with
measurement error of +/- 0.1 pixels for the high resolution
gratings.

	- the trend amounts to an average shift of 0.5 pixel / year
with respect to the zero-point of the pipeline wavelength scale for
each grating.  An observation in cycle 6, therefore, may be off by as
much as 6 pixels from nominal zero velocity (before the effects of FGW
positional uncertainty are even considered).

	- motion of the FGW injects an additional uncertainty of +/- 1
pixel into any wavelength scale obtained from a previous observation.

	- changing apertures without changing gratings between
exposures does not have any effect on scales larger than 0.1 pixel.

2.  for FOS/RD:

	- at any given epoch, the peak-to-peak scatter of the zero
point shifts about a mean by +/- 3.5 pixels with a measurement error
of 0.1 pixel for the high resolution gratings.

	- there is currently no immediately obvious trend with epoch,
but further analysis continues.

Source of error and trending: The initial analysis suggests
that it is very likely these effects are related to the magnetic
shielding properties of the FOS Digicons, i.e., associated with the
GIM motion.  The overall characteristics of this x-coordinate trending
are very similar to those of previously reported y-coordinate (Y-BASE)
changes.

FOS/BL magnetic shielding material may have become magnetized
over time causing systematic shifts of spectrum position on the diode
array.  The FOS/RD had a much poorer shield which produced substantial
image motions (and wavelength shifts) depending on the position and
orientation of HST in the geomagnetic field at the time of the
observation.  The FOS/BL wavelength shifts can be removed via the
re-delivery to CDBS of the FOS dispersion solutions as a function of
time. As noted above, further analysis is required to determine the
utility of any FOS/RD correction algorithm.  Once the analysis is
finalized, an announcement will be posted on the FOS WWW pages and in
an upcoming STAN.


+ Additional FOS Wavelength Calibration Concern for FOS/RD G570H

The residuals for FOS dispersion solutions are typically < 0.1
diodes, however, there appears to be a significant systematic
difference of approximately 60 km/sec (0.25 diodes) between
high-precision target velocities determined for H-alpha and H-beta
with the FOS/RD G570H disperser.  Velocities determined from lines at
the blue end of this spectral region should be considered more
suspect.  At present it is not possible to determine whether this is
due to less well-constrained fits to arc-lamp lines at the blue end of
the wavelength region or due to a wavelength-dependent offset between
the internal calibration beam and the external target light path for
this disperser.
 
+ FOS Polarimetry Calibration

Potential archive proposers who wish to use FOS polarimetry
data should be aware that ALL FOS polarimetry data currently in the
HST Archive MUST be re-calibrated.

	- Post-COSTAR data: The current version of CALFOS will not
correct for the influence of the COSTAR optics on FOS polarimetry
observations.  A new version of CALFOS, currently in preparation, will
properly calibrate post-COSTAR data.  The new software is anticipated
to be available in mid-spring 1998 and will be announced on the FOS
WWW page.  Please contact help@stsci.edu for further information.

	- Pre-COSTAR data: Obtain currently recommended reference
files.  Data may be properly re-calibrated with routine usage of the
current CALFOS package.

Please refer to Chapter 32 of Volume II of the HST Data
Handbook version 3 for detailed information concerning the accuracies
of pre- and post-COSTAR polarimetry.

We expect to recalibrate and rearchive all FOS polarimetry
data by early summer.

+ FOS Scattered Light Modeling Software

The software tools necessary for modeling FOS grating-scatter,
BSPEC and COUNTSPEC, will be available in the HST_CALIB.FOS package of
the next STSDAS release (version 2.0.1).  These routines, based upon
code authored by Michael Rosa at ECF and described in FOS ISR 127, are
identical to the modeling software that has been available previously
through help@stsci.edu.  Prospective users are strongly cautioned to
read all task help information and to refer to FOS ISR 127.


+ FOS WWW Page Updated

The FOS WWW pages have been thoroughly updated to incorporate
the results of the FOS closeout calibration and recent news.  These
pages will continue to be updated to present all important FOS news
and advisories in a timely fashion.


+ Some FOS Starview Reports May be Slightly Misleading

The STARVIEW screen which reports a comparison of the `Used' vs
currently `Recommended' Calibrations available for any given FOS
dataset is misleading in certain cases. When reporting on a dataset
which was archived before the Average Inverse Sensitivity (AIS) flux
calibration method was available, this tool correctly reports that
none of the associated calibration files were `used' and also
correctly lists the files needed to perform this calibration. However,
the STARVIEW screen incorrectly qualifies the `Level of Change' of
these calibrations as `N/A'. The AIS corrections are ALWAYS
RECOMMENDED. This notice applies as well to data archived before
implementation of the default Scattered Light Correction (.cy9
reference file).

+ FOS WWW Advisories (Data Analysis):

  Improved algorithm for accumulator "wrap-around" correction.

============================================================================
 
		Data Analyst Position Available at STScI
		----------------------------------------
 
The Space Telescope Science Institute currently has openings for
Data Analysts. Data Analysts in the Science Support Division help General
Observers and Archive Researchers analyze HST data, work with Instrument
Scientists in calibrating the HST instruments, and work with STScI staff
on grant-supported research projects. These research projects span a range
of size scales from comets and planets to the large scale structure of
the universe and a range of wavelengths from radio to X-ray astronomy.
 
Applicants should possess a B.S. degree (M.S. degree a plus) in astronomy
or physics, or equivalent; experience with astronomical research; familiarity
with scientific computing; expertise in data analysis; knowledge of IRAF, IDL
or other software packages for astronomical data analysis; and programming
ability. Additional mathematical, statistical, and computer skills are
desirable. Candidates should have the ability to work with a minimum of
direction, enjoy research, and possess skills to develop excellent working
relationships. Candidates should send a cover letter with current curriculum
vitae and the names of three references to:
 
Human Resources Manager
Space Telescope Science Institute
3700 San Martin Dr.
Baltimore, MD 21218
 
Women and minorities are strongly urged to apply. AAE/EOE.
 
===========================================================================
 
                 APPENDIX: HST Spectroscopy 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
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