STScI Logo

Hubble Space Telescope

S T A N / W F P C 2 - Number 9, September 1995



by Stefano Casertano

Harry Ferguson and Massimo Stiavelli have joined the WFPC2 group as Instrument Scientists. Harry will work initially on the CTE problem , while Massimo will be working on flat fields and related products.

Some users have reported to us that in a few cases, observations of the same field but with different exposure times (e.g., 30 and 900 seconds) may have magnitude zero points differing by up to 0.05 mag. We are currently investigating this phenomenon and would appreciate any report of similar or contradictory observations. Please send any information you might have to Stefano Casertano (, 410-338-4752) or to Brad Whitmore (, 410-338-4743)

As we are now in the process of updating the Phase II preparation instructions for Cycle 6, if you have suggestions or comments on how to improve our documentation, please send them to Sylvia Baggett (, 410-338-5054).


by John Biretta and Michael S. Wiggs

We would like to solicit comments regarding the new on-line WFPC2 Exposure Time Calculator (ETC) tool. The ETC tool has been available now for several weeks, and has been used approximately 12,000 times.

If you have used the program, what are your general impressions? Have you experienced any problems with it? Are there any features or changes you would like to see added before the Phase II proposal deadline? Please send comments to


The proceedings of "Calibrating Hubble Space Telescope: Post Servicing Mission" workshop (Anuradha Koratkar and Claus Leitherer, editors) were published. All participants of the workshop, cycle 4 and cycle 5 GOs and GTOs were mailed a copy. A very limited number of extra copies are available.If you are interested in receiving one, please send a message to An electronic version of the proceedings will be posted to our Documents page.


by Olivia Lupie and Bruce Toth

The Observation Logs contain a specialized set of pointing and engineering data associated with each science exposure (including the jitter information). They have the same first 8 characters as the rootname of the science exposure to which they pertain, and at present, are composed of a header (with extension CMH) and two fits tables (extensions CMJ and CMI). These files are now also included in the tape mailed to GOs.

Currently, to accurately define the jitter function, the very large CMJ file to produce a jitter image is used. Due to the excessive size of it and because the primary information of interest to an observer is the jitter distribution, it was decided to replace it with an image of the jitter. This image is appreciably smaller (64pix x 64pix; 0.002"/pix) and contains all the information from the high time resolution file which the user needs to deconvolve their image.

The coordinate system is the detector coordinate orientation for all Science Instruments. An empty file is produced for moving targets, internal exposures and Earth calibrations. Jitter images for moving targets will be produced in a future release.

Since this is a major change to the Observation Logs, the file extensions were changed. The Observation Log header file now has an extension of JIH. This file contains all the original contents of the CMH file plus the keywords needed to describe the jitter image. The table, which averages each parameter over a 3 second interval, now has an extension of JIT. The contents of this table remain exactly the same as the old CMI file.

We would like to emphasize the importance of understanding the origin of the parameters and their errors before interpreting the results. For example, the absolute pointing provided in the Log is reconstructed from the guide star data and the guide star absolute coordinates whose catalog errors are of order several tenths of arcseconds. When the tracking mode uses the gyros only, the absolute pointing is reconstructed from the gyro data which has time-dependent errors due to gyro drift.

Documentation describing the details and accuracy of the Observation Logs is available on line under the Observer page, in the Documentation section. Please note that the documentation is still undergoing revision.


We draw your attention to these papers, based on WF/PC and WFPC2 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.

"The apparently normal galaxy hosts for two luminous 
quasars" Bahcall, J.N.; Kirhakos, S.; Schneider, D.P. 
- ApJ accepted 

"HST and MERLIN observations of the jet in 3C 273"  
Bahcall, J.N.; Kirhakos, S.; Schneider, D.P.; Davis, 
R.J.; Muxlow, T.W.B.; Garrington, S.T.; Conway, R.G. 
- ApJ accepted

"Globular clusters in Coma galaxy NGC 4881"  
Baum, W.A.; Hammergren, M.; Groth, E.J.; Ajhar, 
E.A.; Lauer, T.R.; O'Neil, E.J.Jr.; Lynds, C.R.; 
Faber, S.M.; Grillmair, C.J.; Holtzman, J.A.; Light, R.M.
AJ December

"Hubble Space Telescope observations of the very-low-mass 
companion to Gliese 105A"  ApJ Golimowski, D.A.; Fastie, W.G.; 
Schroeder, D.J.; Uomoto, A. - ApJ accepted

"The HST medium deep survey: progression towards resolution 
of the faint blue galaxy problem"  Griffiths, R.E.; Ratnatunga, 
K.U.; Casertano, S.; Im, M.; Neuschaefer, L.W.; Ostrander, E.J.; 
Ellis, R.S.; Glazebrook, K.; Santiago, B.; Windhorst, R.A.; 
Driver, S.P.; Mutz, S.B.; Green, R.F.; Sarajedini, V.; Huchra, 
J.P.; Tyson, J.A.Ap. Lett. Comm. 

"An HST survey of cores of early-type galaxies" 
Kormendy, J.; Byun, Y.-I.; Ajhar, E.A.; Lauer, T.R.; 
Dressler, A.; Faber, S.M.; Grillmair, C.; Gebhardt, K.; 
Richstone, D.; Tremaine, S.  - IAU Symp 171

"New `Einstein Cross' gravitational lens candidates in 
HST WFPC2 survey images" Ratnatunga, K.U.; Ostrander, E.J.; 
Griffiths, R.E.; Im, M. - ApJ accepted

"Titan's surface, revealed by HST imaging"  
Smith, P.H.; Lemmon, M.T.; Lorenz, R.D.; Sromovsky, L.A.;
Caldwell, J.J.; Allison, M.D. - Icarus, accepted 


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 in

Analysis, STSDAS or any other questions can also be addressed to

Comments, questions, requests for issues, additions or deletions to the mailing list, etc. can be e-mailed to

The Space Telescope Science Institute is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS 5-26555.