S T A N / W F P C 2 - Number 19, September 1996
- WFPC2 NEWS:
- Update on WFPC2 Polarization Calibration
- RECENT PREPRINTS
- APPENDIX: WFPC2 CONTACTS
Update on WFPC2 Polarization Calibration:
by John Biretta and Matt McMaster
We have developed a model for the WFPC2 polarization characteristics based on Mueller matrix calculus. In this formalism the usual throughput of each optical element is replaced by a 4x4 matrix containing its full polarization properties. Complicating factors, such as the instrumental polarization (~3%) and linear phase retardance (up to ~27 degrees) induced by the 47 degree pick-off mirror, and the crossed-hand leakage in the polarizer, are included in the model. Comparisons between the model and limited on-orbit data suggest the calibration is accurate to about 1% of the total intensity (i.e. 1% in fractional polarization) in F555W and F675W, and about 2% in F336W and F410M, for the unrotated polarizer in apertures PC1, WF2, WF3, and WF4. For reasons which are unclear, the accuracy in the rotated filter positions (POLQN33 and POLQP15) is only 2% to 5% of the total intensity, but this may merely reflect some inadequacy in the model, and we are actively studying this.
A WWW page has been created which describes this model, and it will be updated as our understanding of the calibration evolves. There is also a WWW tool which can be used to calibrate polarization observations with the above model. The present tool is somewhat labor intensive to use; a better version is being developed. Polarizer flat fields are also available through the page. The polarization calibration page is accessible through the WFPC2 WWW pages.
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.
DE MARCHI, G.; PARESCE, F.; STRATTA, M.G.; GILLILAND, R.L.; BOHLIN, R.C. "The density profile of 47 Tucanae" ApJ 468: L51-L54, 1996 LAVERY, R.J. "An extremely thin gravitational arc formed by the distant cluster CL 0016+1609: lensing of a compact HDF-type object?" AJ 11-96 MENDEZ, R.A.; MINNITI, D.; DE MARCHI, G.; BAKER, A.; COUCH, W.J. "Starcounts in the Hubble Deep Field: constraining galactic structure models" MNRAS accepted REID, I.N.; YAN, L.; MAJEWSKI, S.; THOMPSON, I.; SMAIL, I. "Starcounts redivivus II: Deep starcounts with Keck and HST and the luminosity function of the galactic halo" AJ accepted FORBES, D.A.; BRODIE, J.; HUCHRA, J. "Globular cluster luminosity functions and the Hubble constant from WFPC2 imaging: the dominant group elliptical NGC 5846" AJ ODEWAHN, S.C.; WINDHORST, R.A.; DRIVER, S.P.; KEEL, W.C. "Automated morphological classification in deep HST UBVI fields: rapidly and passively evolving faint galaxy populations" ApJ 11-10-96 PASCARELLE, S.M.; WINDHORST, R.A.; ODEWAHN, S.C.; KEEL, W.C. "Sub-galactic clumps at a redshift of 2.39 and implications for galaxy formation" Nature 383: 45-50, 1996 THUAN, T.X.; IZOTOV, Y.I.; LIPOVETSKY, V.A. "HST observations of the blue compact dwarf SBS 0335-052: a probable young galaxy" ApJ
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 http://www.stsci.edu/public/propinfo.html.
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