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S T A N / W F P C 2 - Number 14, April 1996


Pipeline Headers for WFPC2 Scan Data:

by J. Baum, C. Ritchie, S. Baggett

As of April 18, 1996, WFPC2 headers from dithered data processed through the HST pipeline will correctly reflect the pointing at the time of each observation. This fix affects data taken with the dither-type=line or box options as well as any spatial scan data. Previously, due to the relatively small number of scans being performed, the pipeline provided only minimal support for WFPC2 dwell scans: only the initial dwell point position was used for the target pointing, so each exposure had the same CRVAL data, resulting in slightly incorrect metric results on all but the initial scan image. Note: the fix was only necessary for scan data; manually dithered images, e.g. using the POS-TARG option, had headers which properly reflected the pointing.

Just a reminder: brief summaries about this and other changes affecting WFPC2 data (e.g., decontamination dates, focus changes, pipeline upgrades, and more) are kept in the frequently updated WFPC2 WWW "History" file, accessible via the WFPC2 Document.

Note on PHOTFLAM values for WFPC2:

by K. Rudloff and B. Whitmore

WFPC2 images contain a keyword named PHOTFLAM in their header that can be used to determine the photometric zeropoint. The flatfields for the gain=14 setup are normalized so that all 4 chips have the same value of PHOTFLAM. However, Holtzman et al. (1995, PASP, 107, 1070) found that the zeropoints were slightly different for each chip when the gain=7 setup, used for most science observations, was employed. Values of PHOTFLAM should be divided by 0.9905 (PC1), 0.9985 (WF2), 1.000 (WF3), and 0.9746 (WF4), in order to normalize the values to WF3 which is standard. The easiest way to obtain this information is to use the IMHEADER command. For example,

imheader u3040106t.c0h[2]   

lists keywords in image u3040106t. PHOTFLAM is roughly 40 lines from the top. Remember to include the group number (e.g. [2] gives the header information for WF2).

Alternatively, you can simply add -0.010 mag (PC1), -0.002 mag (WF2), 0.000 mag (WF3), or -0.028 mag (WF4) to your photometric zeropoint to correct for the difference in the 4 chips.

The main reason for including this article in STAN is to point out an error in the article "Photometry with the WFPC2" by Brad Whitmore, which appears in "Calibrating HST: Post Servicing Mission". On pg. 272 of the proceedings, the footnote to Table 41.1 reads: "Values are for WF3 using the gain=7 setup.For the other chips >multiply< PHOTFLAM by ...". This should read "For the other chips >divide< PHOTFLAM by ...".

Note that the same table appears on pg.510 of the HST Data Handbook, V2.0. The values of PHOTFLAM and Zeropoints in this table also refer to WF3 using the gain=7 setup. We apologize for any confusion that this error may have caused. Please see the HST Data Handbook, the Whitmore article, or the Holtzman article referenced above for more details.

Scientific Programmer Positions Available at STScI:

The Space Telescope Science Institute has two openings for the position of Scientific Programmer in the Science Software Branch. The programmers are responsible for design, coding, testing, and maintenance of the software used by the international astronomical community for the calibration and analysis of data from the Hubble Space Telescope. Programmers within the group work closely with astronomers on the ST ScI staff in developing software requirements and algorithms for instrument-specific tasks (including data analysis pipelines for new HST instruments). They also participate in larger development projects, often in collaboration with programming staff at other astronomical institutions, to enhance the system-level environment.

Proficiency in C and Fortran and a working knowledge of the Unix and VMS operating systems are required. Experience with object-oriented languages such as C++ is desirable, as is experience with the IRAF data analysis system. A background in research data analysis and algorithm development for image or spectral data is required; an astronomical background is highly desirable. Excellent verbal and written communications skills are necessary.

A Bachelor's Degree in Astronomy, Physics, Computer Science, or related field is required; an advanced degree is preferred. The successful candidate will have a minimum of two years experience in scientific software development. Substitution of additional relevant education or experience for stated qualifications may be considered. Females and minorities are encouraged to apply. These positions will remain open until suitable candidates have been found. Send a curriculum vitae, letter of application, and samples of C or Fortran code to:

	Human Resources Manager
	Space Telescope Science Institute
	3700 San Martin Drive
	Baltimore, MD 21218


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.

ELSON, R.A.W.; SANTIAGO, B.X.; GILMORE, G.F.  "Halo stars,
starbursts, and distant globular clusters: a survey of
unresolved objects in the Hubble Deep Field"  New Astron.

observations of the unusual blue compact dwarf galaxy
Markarian 996"  ApJ 5-20-96

L.D.; SAHA, A.; SHARA, M.M.  "Stellar variability in the
central populations of 47 Tucanae from WF/PC observations
with the Hubble Space Telescope. II. Binary systems"  ApJ

SAHA, A.; MACCHETTO, F.D.; PANAGIA, N.  "Ho from HST"  Sci.
with the HST 2


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