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WFPC2 UPDATE

TIPS : August 15, 2002 L.M. Lubin. WFPC2 UPDATE. New WFPC2 Documentation. Cycle 12 Instrument Handbook (V7.0, Biretta et al.) Updated information on the CLOCKS=YES mode. Status of anomalous rotational offset for WFPC2 filters. Presentation of most up-to-date correction formula for CTE .

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WFPC2 UPDATE

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  1. TIPS : August 15, 2002 L.M. Lubin WFPC2 UPDATE New WFPC2 Documentation • Cycle 12 Instrument Handbook (V7.0, Biretta et al.) • Updated information on the CLOCKS=YES mode. • Status of anomalous rotational offset for WFPC2 filters. • Presentation of most up-to-date correction formula for CTE . • Discussion of latest conclusions on apparent “Long vs. Short” anomaly. • Description of the new options available in the on-line ETC. • Description of latest flat-field files and improved accuracy. • A summary of the Cycle 11 calibration plan.

  2. TIPS : August 15, 2002 L.M. Lubin WFPC2 UPDATE New WFPC2 Documentation • 2. Data Analysis Tutorial (V3.0, Gonzaga et al.) • Written for novice WFPC2 users. • Being used as part of new DA training. • Major revisions include : • overview on retrieving WFPC2 data from the archive using StarView • updated examples of useful WFPC2-related IRAF/STSDAS tasks • example of aperture photometry on NGC 2100 using PHOT (including aperture correction, Dolphin’s CTE correction, and conversion from WFPC2 flight to standard magnitudes)

  3. TIPS : August 15, 2002 L.M. Lubin WFPC2 UPDATE Charge Transfer Efficiency for Very Faint Objects and a Reexamination of the Long-vs-Short Problem Whitmore & Heyer WFPC2 ISR 2002-03 • Whitmore, Heyer & Casertano (1999) formula does reasonable job correcting for CTE loss down to extremely low count levels. • Comparison between WHC99 and Dolphin (2000) formula shows reasonable agreement, with D00 giving better results.

  4. TIPS : August 15, 2002 L.M. Lubin WFPC2 UPDATE CTE and Long-vs-Short : WFPC2 ISR 2002-03 Dolphin (2000) Dolphin (2002)

  5. TIPS : August 15, 2002 L.M. Lubin WFPC2 UPDATE CTE and Long-vs-Short : WFPC2 ISR 2002-03 • Long-vs-short effect is very small (a few %) or non-existent for uncrowded fields (<1000 stars/chip), but for crowded fields (~10,000 stars/chip), apparent non-linearities of tens of % are possible, most likely due to an overestimate of the sky measurement in the short exposure.

  6. TIPS : August 15, 2002 L.M. Lubin WFPC2 UPDATE CTE and Long-vs-Short : WFPC2 ISR 2002-03 UNCROWDED FIELD CROWDED FIELD

  7. TIPS : August 15, 2002 L.M. Lubin WFPC2 UPDATE CTE and Long-vs-Short : WFPC2 ISR 2002-03 • Preflashing is useful method of reducing effect of CTE for some observations (i.e. bright objects on faint background), but added noise and longer overheads limit its effectiveness. • Detection thresholds for broad band observations reduced by 0.1-0.2 mag in the ~7 years since WFPC2 was launched, with the worst-case (F336W) being ~ 0.4 mag.

  8. TIPS : August 15, 2002 L.M. Lubin WFPC2 UPDATE New Contamination Rates (McMaster et al.) F160BW, F170W, F218W, F255W, F336W, F439W Comparison between ’97-’98 and ’01-’02 • Slight increase in clean count for UV filters • Decrease of clean count for F255W and redwards • Slowing of rate for filters up to F439W F170W

  9. TIPS : August 15, 2002 L.M. Lubin WFPC2 UPDATE New Contamination Rates (McMaster et al.) F160BW, F170W, F218W, F255W, F336W, F439W SM2 & SM3a F170W

  10. TIPS : August 15, 2002 L.M. Lubin WFPC2 UPDATE New Contamination Rates (McMaster et al.) F160BW, F170W, F218W, F255W, F336W, F439W F439W

  11. TIPS : August 15, 2002 L.M. Lubin WFPC2 UPDATE Dither Working Group Report - MultiDrizzle & PyDrizzle Automatic Registering, Cleaning & Combining of Dithered Images (Koekemoer et al.) • MultiDrizzle is a single, integrated "wrapper" script which uses PyDrizzle, along with other tasks in the dither package, to provide a single integrated approach to cleaning and drizzling dithered images. • Carries out the following steps: • Create bad-pixel masks • Perform sky subtraction • Optionally carry out single-image CR rejection • Drizzle images onto separate output frames • Create a median image from the drizzled images • "Blot" the median back to the frame of each input image • Compare the median and original to identify CR's • Drizzle a final, combined image using the CR masks

  12. TIPS : August 15, 2002 L.M. Lubin WFPC2 UPDATE Dither Working Group Report - MultiDrizzle & PyDrizzle • Refinement of Shifts : • Can refine shifts using catalogs (from Sextractor/DAO-Find) • Automatically creates new cosmic ray masks using improved shifts • Testing currently in progress : • CR rejection • Shift refinement • Median-image creation • Variety of WFPC2 & ACS datasets • STIS & NICMOS to be added next • Prototype version already currently available within Dither Working • Group; will be publicly released as soon as it is stabilized after • testing (approximately in the Fall).

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