10622( 3) - 07/25/05 08:00 - [ 1] HUBBLE SPACE TELESCOPE OBSERVING PROGRAM 10622 Version: 3 Check-in Time: 25-Jul-2005 11:59:38 Title ACS Photometric Calibration from Faint Standards ------------------------------------------------------------------------------------ Type Cycle Parallel Pointing Tolerance GO 14 ------------------------------------------------------------------------------------ Investigators Contact? PI: Dr. Andrew Dolphin University of Arizona CoI: Dr. Abhijit Saha National Optical Astronomy Observatories, N AURA ------------------------------------------------------------------------------------ Abstract When calibrating photometry, the typical approach is to use short exposures of bright standard stars to calibrate long exposures of faint scientific targets. This is fine for most ground-based telescopes, whose detectors are linear, but presents difficulties when calibrating HST. The resulting HST calibrations are thus extremely sensitive to the accuracy of linearity corrections such as that for CTE loss. We propose a more robust calibration of ACS/WFC using our photometric sequences in Pal 4 and Pal 14 (Saha et al. 2005). These sequences include stars with 10% photometry down to V=24.2 and I=23.4, a brightness comparable to that of many HST science targets. We believe these data will allow us to determine a complete set of transformations accurate to 1% and relatively insensitive to errors in the CTE correction. ------------------------------------------------------------------------------------ 10622( 3) - 07/25/05 08:00 - [ 2] Observations Description ------------------------ Our observing plan is to obtain CR-split images in all broadband filters using ACS/WFC, with the appropriate exposure times such that our faintest standards (V=24.5, typical S/N of 7-8 in our ground-based photometry) have S/N=10. (In practice, this should give S/N~15, as PSF-fitting photometric uncertainties in uncrowded fields are generally closer to the optimal S/N than to the regular calculation.) For F850LP, the total exposure time had to be shortened from 500s to 380s so that our brightest stars in Pal 14 (I=16.3) would not saturate. As our calibrated fields are approximately 9x9 arcmin, we require only a single pointing per filter to get sufficient numbers of standards on both chips. Between the two pointings, several hundred of our standard stars will be observed. Looking at how many orbits to request, we have three options. The most appealing one is to sqeeze all of our observations into three orbits per cluster. This would require eliminating the CR-split in two or three filters. Because of the number of cosmic rays, we believe this would compromise our results and be unacceptable. An alternative is to obtain a full set of WFC and HRC images, which would require five orbits per target. While we feel this could be productive exercise, we are not confident that there is a 29x26 arcsec region with enough standards to obtain an accurate calibration. We are thus left with a four-orbit observing strategy. This allows us to add F550M to the program and place our five shortest-exposure filters into two orbits and the other four filters into the other two orbits. Real Time Justification ----------------------- Calibration Justification ------------------------- Additional Comments ------------------- ------------------------------------------------------------------------------------ 10622( 3) - 07/25/05 08:00 - [ 3] TARGET LIST Fixed Targets ------------------------------------------------------------------------------------------------------------------------------------ Tar| Target | Target | Target |Coord | Radial | Flux data No | Name | Description | Position |Eqnx | Vel. | ------------------------------------------------------------------------------------------------------------------------------------ 1 PAL-4 STELLAR CLUSTER, RA=11H29M14.0000S +/- 0.1", J2000 V = 20.0 GLOBULAR CLUSTER DEC=+28D57'30.00" +/- 0.1" Coordinate Source: Other_Source: SIMBAD 2 PAL-14 STELLAR CLUSTER, RA=16H10M59.0000S +/- 0.1", J2000 V = 20.0 GLOBULAR CLUSTER DEC=+14D57'42.00" +/- 0.1" Coordinate Source: Other_Source: SIMBAD 10622( 3) - 07/25/05 08:00 - [ 4] Visit: 01 Visit Priority: Visit Requirements: On Hold Comments: Additional Comments: Exposures ------------------------------------------------------------------------------------------------------------------------------------ Exp | Target | Instr | Oper. | Aper |Spectral|Central| Optional |Num| Time | Special Num | Name | Config | Mode | or FOV |Element |Waveln.| Parameters |Exp| | Requirements ------------------------------------------------------------------------------------------------------------------------------------ 1 PAL-4 ACS/WFC ACCUM WFC F555W CR-SPLIT=2,GAIN=2 1 250 S ------------------------------------------------------------------------------------------------------------------------------------ 2 PAL-4 ACS/WFC ACCUM WFC F550M GAIN=2,CR-SPLIT=2 1 500 S ------------------------------------------------------------------------------------------------------------------------------------ 3 PAL-4 ACS/WFC ACCUM WFC F850LP GAIN=2,CR-SPLIT=2 1 380 S ------------------------------------------------------------------------------------------------------------------------------------ 4 PAL-4 ACS/WFC ACCUM WFC F435W GAIN=2,CR-SPLIT=2 1 430 S ------------------------------------------------------------------------------------------------------------------------------------ 5 PAL-4 ACS/WFC ACCUM WFC F625W GAIN=2,CR-SPLIT=2 1 180 S ------------------------------------------------------------------------------------------------------------------------------------ 6 PAL-4 ACS/WFC ACCUM WFC F775W GAIN=2,CR-SPLIT=2 1 210 S ------------------------------------------------------------------------------------------------------------------------------------ 7 PAL-4 ACS/WFC ACCUM WFC F606W GAIN=2,CR-SPLIT=2 1 120 S ------------------------------------------------------------------------------------------------------------------------------------ 8 PAL-4 ACS/WFC ACCUM WFC F814W GAIN=2,CR-SPLIT=2 1 160 S ------------------------------------------------------------------------------------------------------------------------------------ 9 PAL-4 ACS/WFC ACCUM WFC F475W GAIN=2,CR-SPLIT=2 1 230 S ------------------------------------------------------------------------------------------------------------------------------------ Sub Exposures ------------------------------------------------------------------------------------------------------------------------------------ Target | Exp |Instr | Oper. | Aper |Spectral|Cent.|Primary |Secondary |Iteration |CR-SPLIT |Orbit |Duration Name | Num |Config | Mode | or FOV |Element |Wave.|Pattern Pos |Pattern Pos |Num |Num |Number | ------------------------------------------------------------------------------------------------------------------------------------ PAL-4 1 ACS/WFC ACCUM WFC F555W none none none 1 1 N/A PAL-4 1 ACS/WFC ACCUM WFC F555W none none none 2 1 N/A PAL-4 2 ACS/WFC ACCUM WFC F550M none none none 1 1 N/A PAL-4 2 ACS/WFC ACCUM WFC F550M none none none 2 1 N/A PAL-4 3 ACS/WFC ACCUM WFC F850LP none none none 1 2 N/A PAL-4 3 ACS/WFC ACCUM WFC F850LP none none none 2 2 N/A PAL-4 4 ACS/WFC ACCUM WFC F435W none none none 1 2 N/A PAL-4 4 ACS/WFC ACCUM WFC F435W none none none 2 2 N/A PAL-4 5 ACS/WFC ACCUM WFC F625W none none none 1 3 N/A PAL-4 5 ACS/WFC ACCUM WFC F625W none none none 2 3 N/A PAL-4 6 ACS/WFC ACCUM WFC F775W none none none 1 3 N/A PAL-4 6 ACS/WFC ACCUM WFC F775W none none none 2 3 N/A PAL-4 7 ACS/WFC ACCUM WFC F606W none none none 1 3 N/A PAL-4 7 ACS/WFC ACCUM WFC F606W none none none 2 4 N/A PAL-4 8 ACS/WFC ACCUM WFC F814W none none none 1 4 N/A PAL-4 8 ACS/WFC ACCUM WFC F814W none none none 2 4 N/A PAL-4 9 ACS/WFC ACCUM WFC F475W none none none 1 4 N/A 10622( 3) - 07/25/05 08:00 - [ 5] Sub Exposures ------------------------------------------------------------------------------------------------------------------------------------ Target | Exp |Instr | Oper. | Aper |Spectral|Cent.|Primary |Secondary |Iteration |CR-SPLIT |Orbit |Duration Name | Num |Config | Mode | or FOV |Element |Wave.|Pattern Pos |Pattern Pos |Num |Num |Number | ------------------------------------------------------------------------------------------------------------------------------------ PAL-4 9 ACS/WFC ACCUM WFC F475W none none none 2 4 N/A 10622( 3) - 07/25/05 08:00 - [ 6] Visit: 02 Visit Priority: Visit Requirements: On Hold Comments: Additional Comments: Exposures ------------------------------------------------------------------------------------------------------------------------------------ Exp | Target | Instr | Oper. | Aper |Spectral|Central| Optional |Num| Time | Special Num | Name | Config | Mode | or FOV |Element |Waveln.| Parameters |Exp| | Requirements ------------------------------------------------------------------------------------------------------------------------------------ 1 PAL-14 ACS/WFC ACCUM WFC F555W GAIN=2,CR-SPLIT=2 1 250 S ------------------------------------------------------------------------------------------------------------------------------------ 2 PAL-14 ACS/WFC ACCUM WFC F550M GAIN=2,CR-SPLIT=2 1 500 S ------------------------------------------------------------------------------------------------------------------------------------ 3 PAL-14 ACS/WFC ACCUM WFC F850LP GAIN=2,CR-SPLIT=2 1 380 S ------------------------------------------------------------------------------------------------------------------------------------ 4 PAL-14 ACS/WFC ACCUM WFC F435W GAIN=2,CR-SPLIT=2 1 430 S ------------------------------------------------------------------------------------------------------------------------------------ 5 PAL-14 ACS/WFC ACCUM WFC F625W GAIN=2,CR-SPLIT=2 1 180 S ------------------------------------------------------------------------------------------------------------------------------------ 6 PAL-14 ACS/WFC ACCUM WFC F775W GAIN=2,CR-SPLIT=2 1 210 S ------------------------------------------------------------------------------------------------------------------------------------ 7 PAL-14 ACS/WFC ACCUM WFC F606W GAIN=2,CR-SPLIT=2 1 120 S ------------------------------------------------------------------------------------------------------------------------------------ 8 PAL-14 ACS/WFC ACCUM WFC F814W GAIN=2,CR-SPLIT=2 1 160 S ------------------------------------------------------------------------------------------------------------------------------------ 9 PAL-14 ACS/WFC ACCUM WFC F475W GAIN=2,CR-SPLIT=2 1 230 S ------------------------------------------------------------------------------------------------------------------------------------ Sub Exposures ------------------------------------------------------------------------------------------------------------------------------------ Target | Exp |Instr | Oper. | Aper |Spectral|Cent.|Primary |Secondary |Iteration |CR-SPLIT |Orbit |Duration Name | Num |Config | Mode | or FOV |Element |Wave.|Pattern Pos |Pattern Pos |Num |Num |Number | ------------------------------------------------------------------------------------------------------------------------------------ PAL-14 1 ACS/WFC ACCUM WFC F555W none none none 1 1 N/A PAL-14 1 ACS/WFC ACCUM WFC F555W none none none 2 1 N/A PAL-14 2 ACS/WFC ACCUM WFC F550M none none none 1 1 N/A PAL-14 2 ACS/WFC ACCUM WFC F550M none none none 2 1 N/A PAL-14 3 ACS/WFC ACCUM WFC F850LP none none none 1 2 N/A PAL-14 3 ACS/WFC ACCUM WFC F850LP none none none 2 2 N/A PAL-14 4 ACS/WFC ACCUM WFC F435W none none none 1 2 N/A PAL-14 4 ACS/WFC ACCUM WFC F435W none none none 2 2 N/A PAL-14 5 ACS/WFC ACCUM WFC F625W none none none 1 3 N/A PAL-14 5 ACS/WFC ACCUM WFC F625W none none none 2 3 N/A PAL-14 6 ACS/WFC ACCUM WFC F775W none none none 1 3 N/A PAL-14 6 ACS/WFC ACCUM WFC F775W none none none 2 3 N/A PAL-14 7 ACS/WFC ACCUM WFC F606W none none none 1 3 N/A PAL-14 7 ACS/WFC ACCUM WFC F606W none none none 2 4 N/A PAL-14 8 ACS/WFC ACCUM WFC F814W none none none 1 4 N/A PAL-14 8 ACS/WFC ACCUM WFC F814W none none none 2 4 N/A PAL-14 9 ACS/WFC ACCUM WFC F475W none none none 1 4 N/A 10622( 3) - 07/25/05 08:00 - [ 7] Sub Exposures ------------------------------------------------------------------------------------------------------------------------------------ Target | Exp |Instr | Oper. | Aper |Spectral|Cent.|Primary |Secondary |Iteration |CR-SPLIT |Orbit |Duration Name | Num |Config | Mode | or FOV |Element |Wave.|Pattern Pos |Pattern Pos |Num |Num |Number | ------------------------------------------------------------------------------------------------------------------------------------ PAL-14 9 ACS/WFC ACCUM WFC F475W none none none 2 4 N/A 10622( 3) - 07/25/05 08:00 - [ 8] Summary Form for Proposal 10622 Item Used in this proposal ------------------------------------------------------------------------------------------------------------------------------------ Apertures WFC ------------------------------------------------------------------------------------------------------------------------------------ Configurations ACS/WFC ------------------------------------------------------------------------------------------------------------------------------------ Opmodes ACCUM ------------------------------------------------------------------------------------------------------------------------------------ Optional Parameters CR-SPLIT=2 GAIN=2 ------------------------------------------------------------------------------------------------------------------------------------ Proposal Category GO ------------------------------------------------------------------------------------------------------------------------------------ Spectral Elements F555W F550M F850LP F435W F625W F775W F606W F814W F475W ------------------------------------------------------------------------------------------------------------------------------------ Target Names PAL-4 PAL-14 ------------------------------------------------------------------------------------------------------------------------------------