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Hubble Space Telescope

S T A N / W F P C 2 - Number 5, March 1995




by Michael S. Wiggs and Brad Whitmore

In an effort to provide observers with easier access to WFPC2 information we recently redesigned the WFPC2 homepage available via the Wide World Web (WWW). Some of the improvements are a clearer format for seeing what is available and a more direct route to actually view the material, including a redesigned and expanded Frequently Asked Questions (FAQ) section, a guide to all available WFPC2 documents, as well as a User Support section.

Since we are anxious to have WFPC2 users routinely make use of this powerful new communications technology, we offer a few answers to common questions to help people get started. The most common way to access the WWW is via Mosaic, hence these tips are primarily for Mosaic users.

  Q: How do I download a PostScript file since when I 
     click on it I get put directly into ghostview ?
  A: Go up to the "Options" button on Mosaic and select "Load
     to local disk" before selecting the PostScript file

  Q: Is it possible to print or save selected pages from 
     a document?
  A: Yes. When viewing the document with ghostview, select 
     the page(s) of interest by dragging the mouse (with 
     the left button pressed) over the list of pages on the 
     left of the ghostview window. Once highlighted, hit the 
     "m" key. The pages are then "marked" and can then be 
     printed or saved to your local disk.

  Q: How do I stop the transfer of an extremely large file 
     when it becomes obvious that it will take too long.
  A: Click on the world symbol in the upper right corner.

  Q: How do I speed up the downloading of pages that have 
     images on them?
  A: Go up to the "Options" button on Mosaic and select 
     "Delay image loading". 

Give it a try! If you have any problems with our homepage, please let us know by sending E-mail to


by Stefano Casertano

In a typical observation, the CCDs in WFPC2 have a significant number of pixels with an elevated dark current. These "hot" pixels are probably generated by cosmic ray hits, at a rate of approximately 60 per CCD per day - the exact number depends on the threshold. The majority of these pixels return to a normal state after the camera is warmed during monthly decontaminations. Since "hot" pixels are transient, a static mask is not appropriate to identify and reject/correct them.

In order to facilitate rejection and/or correction of these hot pixels for any given observation, we have produced monthly lists of hot pixels, which include their location and intensity. The lists are provided in the form of UNIX-compressed ASCII files, and are available through the WFPC2 Webpage.

Currently, lists through the end of February are available; it is intended that the lists be kept current, with a one-month delay in order to complete each decontamination.

There are four files, one for each CCD, for each period between decontaminations. The files have names such as:

       		^      ^   ^
       		|      |   |
       		|      |   Chip no. (1=PC, 2=WF2 etc)
       		|     End date (yymmdd)
      		Start date (yymmdd)

Before reading the file you need to run the "uncompress" UNIX command on it.

If you do not have access to a UNIX system, please contact an instrument scientist, and we will provide uncompressed lists as necessary.

We have plans to produce a new STSDAS task that will be capable of flagging and/or correcting the hot pixels in an automated way.


by Stefano Casertano

Faint Object Camera observations taken on Day 58 (February 27) appear blurred. A possible cause of the blurring is a defocus and/or decenter of the secondary mirror, potentially related to the unusual thermal environment of the telescope - which had been pointed very close to the anti-sun direction for several days (ie., most of the telescope structure is in the shadow caused by the wider instrument compartment at the "bottom" of the telescope). WFPC2 observations taken shortly before and during the blurred FOC observations have been inspected for degradation of the PSF. These observations contain very few well-exposed stars in the PC, and therefore our assessment of the PSF properties in WFPC2 is necessarily limited. However, it appears that any degradation in the light distribution is very minor, and the FWHM of the observed stars is close to normal - the measured increase of less than 10% (to 1.8-1.9 PC pixels in F814W) is within the errors of the measurement. The PSF monitoring carried out on March 4 shows nominal results.

However, the _shape_ of the PSF in the WFPC2 observations may be consistent with a defocusing of the secondary mirror of order of 10 micron, the value suggested by the FOC data. Such a defocusing could affect photometry based on small apertures or PSF fitting at the 5-10% level; scientific programs that depend on accurate knowledge of the PSF itself, such as observations of faint objects in the vicinity of bright point sources, would also need to take the possible defocusing into account. On the other hand, morphology and surface photometry of extended sources would be largely unaffected. If your observation was taken between February 23 and March 3 and the scientific results might be sensitive to the shape of the PSF, please contact us.


                      May 15 - 17, 1995
                     Baltimore, Maryland 


This is the second announcement for a workshop on calibrating Hubble Space Telescope Data after the servicing mission. The workshop will be held at the Space Telescope Science Institute in Baltimore from May 15th to May 17th 1995.

I. Rationale:

The rationale behind this workshop is to bring together the HST community and the STScI instrument scientists and other STScI staff so they can exchange ideas on calibration of HST data and its analysis. It has been nearly a year since the servicing mission launched the WFPC2, and changed the characteristics of the FOC, FOS and GHRS. Hence, it is time to assemble the collected wisdom of the HST community to summarize our current understanding of HST and the science instruments onboard.

II. Workshop Schedule:

An outline of the schedule for the meeting is given below. At this time we have firm commitments from all invited speakers. Their names are included in the agenda. No assignments for contribute talks have yet been made. These will be selected from the abstracts we receive after this announcement.

Monday, May 15, 1995:

09:00 - 11:00 WFPC2 Overview:

  WFPC2 Calibration Status Report - John MacKenty
  CCD Idiosyncrasies 		  - John Trauger
  Flat Fields, Polarization 	  - John Biretta
  PSF and Scattered Light         - John Krist
  Photometry                      - Brad Whitmore

11:00 - 11:30 Coffee and Posters

11:30 - 12:30 FOC Overview:

  FOC Calibration Status Report	- Antonella Nota
  Image Quality and PSF		- Robert Jedrzejewski

13:30 - 15:00 GHRS Overview:

  GHRS Calibration Status Report -  Claus Leitherer
  Side-1 Capabilities		 -  Dennis Ebbets
  High S/N Observations		 -  Jason Cardelli
  PSF and Aperture Throughput	 -  Robinson
  R136: Imaging & Target Acquisition - Eliot Malumuth

15:00 - 15:30 Tea and Posters

15:30 - 17:00 FGS Overview and STSDAS Overview:

  FGS Calibration Status Report  - Mario Lattanzi
  STSDAS Status Report	         - Rick White
  New Analysis Tools in Development - tba

Tuesday, May 16, 1995:

09:00 - 11:00 FOS Overview:

  FOS Calibration Status Report	- Anuradha Koratkar
  FOS Flat Fields	        - Tony Keyes
  Absolute Photometry and Standard Stars - Ralph Bohlin

11:00 - 11:30 Coffee and Posters

11:30 - 12:30 Archive Overview:

  Archive Status Report		- Kirk Borne
  How to Work with Archive Data	- Michael Rosa

12:30 - 13:30 Lunch

13:30 - 15:00 WFPC2 and FOS Working Groups (Contributed 
papers invited)

	Tentative Topics for WFPC2:

Main-Sequence Photometry and Ages for the Outermost Halo Clusters
WFPC2 and FOC Photometric Methods, with Emphasis on Globular
Cluster CMD, Luminosity Functions, and Density Distributions
Methods for Combining "Dithered" WFPC2 Images
Calibration for HST Medium Deep Survey

	Tentative Topics for FOS:

Location of FOS Spectra
Target Acquisition Nuances
LSF/PSF issues
FOS Wavelength Calibration
Dark Issues
FOS Polarimetry

15:00 - 15:30 Tea and Posters

15:30 - 17:00 WFPC2 and FOS Working Groups: (Contributed 
papers invited)

Wednesday, May 17, 1995:

09:00 - 11:00 FOC and GHRS Working Groups: (Contributed 
papers invited)

	Tentative Topics for FOC:

FOC Photometry
Extended Source Photometry
Comparison of FOC with WFPC2

	Tentative Topics for GHRS (Contributed papers 

Calibration close-out before the removal of the GHRS
Far-UV campaign with Costar mirrors removed

11:00 - 11:30 Coffee and Posters

11:30 - 12:30 FOC and GHRS Working Groups

12:30 - 13:30 Lunch

13:30 - 15:00 Overview of STIS and NICMOS:

  STIS Status Report	- Mark Clampin
  NICMOS Status Report	- Dave Axon

III. Proceedings:

In addition to the above talks, contributed papers or posters are invited from all participants. The deadline date is 1st May 1995, so that we can arrange the working sessions.

The proceedings of the workshop will be published as part of the STSCI publication series. Each registered participant will be mailed a personal copy of the volume. In order to achieve this fast turn around, we request that we receive the camera-ready manuscripts by July 31, 1995. Instructions on the style and on how to obtain sample Latex files will be given during the conference. Ample space will be provided for the reviews and for the poster and oral contributions.

IV. Organizing Committee:

Anuradha Koratkar (Chair),,  410-338-4470
Chris Blades (New Instruments),,    410-338-4805
Tony Keyes (FOS),     ,     410-338-4975
Mario Lattanzi (FGS),    410-338-4866
Claus Leitherer (GHRS),, 410-338-4425
John MacKenty (WFPC2),,  410-338-4559
Antonella Nota (FOC), ,      410-338-4520
Michael Rosa (ST-ECF),,        49-893-2006
Brad Whitmore (Analysis),,  410-338-4743

V. Location:

The workshop will take place at the Space Telescope Science Institute in Baltimore, Maryland. Maps to the area and other logistics will be mailed after we receive your registration form.

VI. Accommodation:

We will make arrangements for most participants to stay in a nearby hotel within walking distance of the institute. The hotel is 'The Colonnade Inn' and the accommodation charges are $109/night. Please indicate in the registration form below, your arrival and departure dates.

VII. Registration:

Registration forms are attached to this letter below. We request that you send the completed registration form to Although there is no registration fee, your registration and room reservation will be effective only after we have received the e-mail form. An electronic acknowledgment will be sent to you. The completed registration form should be returned to us as soon as possible.



Please register me for the workshop 
in May 1995.







I will probably want to give a presentation:

Title if available:

The break away groups that I plan on attending:

I would like hotel (single/double room) accommodations for ----- days,

from ---------May, 1995 to --------- May, 1995.


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 morphology of the narrow line region of Mrk 3"
Capetti, A.; Macchetto, F.; Axon, D.J.; Sparks, W.B.; 
Boksenberg, A. ApJ 8-1-95

"Ellipticals with kinematically-distinct cores: WFPC1 
imaging of nearby ellipticals"  
Forbes, D.A.; Franx, M.; Illingworth, G.D.; AJ accepted 

"HST images of the eclipsing pulsar B1957+20"  
Fruchter, A.S.; Bookbinder, J.; Bailyn, C.D.  
ApJ 4-10-95

"Imaging of low redshift QSOs with WFPC2"  AJ accepted
Hutchings, J.B.; Morris, S.C.  

"Unusual comets (?) as observed from the Hubble Space 
Telescope" Meech, K.J.; Weaver, H.A.; Small Bodies in 
the Solar System


Any questions about the scheduling of your observations should be addressed to your PRESTO contact. If you do not know who this person is, PRESTO's page ( contains that information.

Post-Observation questions should be addressed to the WFPC2 Team, or

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.