STScI Logo

Hubble Space Telescope
WFPC2 STAN

S T A N / W F P C 2 - Number 50, January 2002

CONTENTS:

Dither Advisory:

If STSDAS V2.3 has been recently installed, then we recommend that users of the "dither" package should first run the task "dunlearn", just a single time, before using tasks in the "dither" package. This resets all the parameters of the dither tasks to their default values. If this is not done, then some of the tasks may crash with error messages about "parameters not found", which is due to the fact that some of the parameters of the tasks have been changed since the previous release of STSDAS.

Phase II Advisory: WFPC2 Clocks-ON Close Out (ISR 02-01):

by A.B. Schultz, S. Baggett, J. Biretta

About 6% of all WFPC2 observations have been obtained with the serial clocks ON. This operational mode is used for two purposes: (1) to minimize impact of charge bleeding on severely saturated images, and (2) to reduce the overhead time on exposures > 180 sec. The standard star GRW+70D5824 (HIC 66578; V=12.77; B-V=-0.09) was observed with the serial clocks ON (proposal ID: 9252). The comparison between count rates of the standard star for different filters obtained with clocks ON and OFF indicates that the normal WFPC2 photometric calibration with clocks OFF is sufficient for data obtained with clocks ON and OFF. The count rates are generally within 2% (0.02 mag) peak to peak of each other with the associated errors quite small.

Analysis of 1800 sec (commanded) darks (serial clocks ON and OFF) indicate that the count levels for the clocks ON darks are similar to those for the clocks OFF darks. When the 1 minute difference in exposure time between an 1800 second clocks ON and OFF dark is taken into account, the clocks ON dark current is found to be a few % higher than the clocks OFF dark current. Since the pipeline dark reference files for clocks ON mode have always been generated from clocks OFF darks (minimizing the number of calibration observations required), the difference in dark current may affect the calibration of some clocks ON observations. It will not be a problem in the majority of clocks ON exposures.

The normal default operational mode is to have the serial clocks OFF during an exposure. In order to read out an exposure taken with the serial clocks OFF, an extra minute of overhead is required to enable the serial clocks. WFPC2 observations obtained with the serial clocks ON execute with one minute less of overhead. It now appears that there are no major artifacts, induced noise, or cross talk, when obtaining data with the serial clocks ON. However, we cannot guarantee that there are no minor artifacts for very faint targets. If you decide to use the clocks ON option to save the one minute of overhead, simply use the CLOCK=YES optional parameter on the Phase II proposal form.

Pipeline (OTFR) Software Version 13.3 and LRF Photometry Keywords:

by M. McMaster and S. Baggett

The latest version of the pipeline software, 13.3, was installed on January 7 and with it, an improvement in the way the photometry keywords (PHOTFLAM, PHOTPLAM, and PHOTBW) are calculated for linear ramp filter data.

When the keyword DOPHOTOM is set to 'yes' in the raw (.d0h) header file, calwp2 calls the bandpar task within SYNPHOT to calculate the photometry keywords mentioned above, using the information given in the keyword PHOTMODE.

Generally, PHOTMODE for WFPC2 data consists of the instrument, chip, gain, filter, and whether or not the data have been calibrated (bias subtracted, flat fielded, etc.). For example, PHOTMODE for a calibrated image on WF2 taken at gain 7 with the F555W filter would be: WFPC2,2,A2D7,F555W,,CAL Where 'CAL' signifies that the data have been flatfielded and the space after F555W would be used for an observation with crossed filters.

When bandpar is run, the central wavelength for the filter, along with the other components of PHOTMODE, is used in determining PHOTFLAM, PHOTPLAM, and PHOTBW. However, due to the nature of the Linear Ramp Filters, there is no single central wavelength (e.g. FR533N and its associated rotated configurations has a wavelength range of 4746 to 6007 Angstroms) and previous versions of the pipeline software would produce values for the photometry keywords that were not usable. In this case, observers were asked to run bandpar themselves and to substitute the value of the header keyword LRFWAVE for the filter in the 'obsmode' parameter (while keeping the values for instrument, chip, gain, and calibration from the PHOTMODE keyword).

For Linear Ramp Filter exposures, the latest version of the pipeline software now uses the value of LRFWAVE rather than the name of the filter in determining the value of the photometry keywords. For example, consider an observer who has calibrated exposures taken at a wavelength of 6344 Angstroms on WF3 at a gain of 7. The PHOTMODE keyword generated by previous versions of the pipeline software would be WFPC2,3,A2D7,FR680N,,CAL; with the resulting photometry keywords: PHOTFLAM = 8.5558E-19, PHOTPLAM = 5783.6 and PHOTBW = 2063.4. For the same set of observations using version 13.3 of the pipeline software, PHOTMODE is WFPC2,3,A2D7,LRF#6344.0,,CAL and the photometry keywords have the values: PHOTFLAM = 5.6191E-17, PHOTPLAM = 6343.9, and PHOTBW = 31.168.

RECENT PREPRINTS:

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.

BARTHOLOMEW, L.J.; ROSE, J.A.; GABA, A.E.;
CALDWELL, N. "Radial Color Gradients in K + A
Galaxies in Distant Clusters of Galaxies" AJ 122:
2913-2922, 2001

GRILLMAIR, C.J.; SMITH, G.H. "The Main-Sequence
Luminosity Function of Palomar 5 from the Hubble
Space Telescope" AJ 122: 3231-3238, 2001

HARBECK, D.; GREBEL, E.K.; HOLTZMAN, J.;
GUHATHAKURTA, P.; BRANDNER, W.; GEISLER, D.;
SARAJEDINI, A.; DOLPHIN, A.; HURLEY-KELLER, D.;
MATEO, M. "Population Gradients in Local Group
Dwarf Spheroidal Galaxies" AJ 122: 3092-3105, 2001

HARRIS, J.; CALZETTI, D.; GALLAGHER, J.S. III;
CONSELICE, C.J.; SMITH, D.A. "Young Clusters in the
Nuclear Starburst of M83" AJ 122: 3046-3064, 2001

RUIZ, J.R.; CRENSHAW, D.M.; KRAEMER, S.B.; BOWER,
G.A.; GULL, T.R.; HUTCHINGS, J.B.; KAISER, M.E.;
WEISTROP, D. "Kinematics of the Narrow-Line Region
in the Seyfert 2 Galaxy Markarian 3" AJ 122:
2961-2968, 2001

SCOVILLE, N.Z.; POLLETTA, M.; EWALD, S.; STOLVOVY,
S.R.; THOMPSON, R.; RIEKE, M. "High-Mass, OB Star
Formation in M51: Hubble Space Telescope H alpha
and Pa alpha Imaging" AJ 122: 3017-2045, 2001

SULENTIC, J.W.; ROSADO, M.; DULTZIN-HACYAN, D.;
VERDES-MONTENEGRO, L.; TRINCHIERI, G.; XU, C.;
PIETSCH, W. "A Multiwavelength Study of Stephan's
Quintet" AJ 122: 2993-3016, 2001

APPENDIX: WFPC2 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: www.stsci.edu/public/propinfo.html.

Analysis, STSDAS or any other 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 wfpc_news YOUR NAME

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