10621( 3) - 07/26/05 14:38 - [ 1] HUBBLE SPACE TELESCOPE OBSERVING PROGRAM 10621 Version: 3 Check-in Time: 26-Jul-2005 18:38:03 Title ACS Zero Point Verification ------------------------------------------------------------------------------------ Type Cycle Parallel Pointing Tolerance GO 14 ------------------------------------------------------------------------------------ Investigators Contact? PI: Dr. Andrew Dolphin University of Arizona ------------------------------------------------------------------------------------ Abstract The uncertainties in the photometric zero points create a fundamental limit to the accuracy of photometry. The current state of the ACS calibration is surprisingly poor, with zero point uncertainties of 0.03 magnitudes. The reason for this is that the ACS calibrations are based primarily on semi-emprical synthetic zero points and observations of fields too crowded for accurate ground-based photometry. I propose to remedy this problem by obtaining ACS images of the omega Cen standard field with all nine broadband ACS/WFC filters. This will permit the direct determination of the ACS zero points by comparison with excellent ground-based photometry, and should reduce their uncertainties to less than 0.01 magnitudes. A second benefit is that it will facilitate the comparison of the WFPC2 and ACS photometric systems, which will be important as WFPC2 is phased out and ACS becomes HST's primary imager. Finally, three of the filters will be repeated from my Cycle 12 observations, allowing for a measurement of any change in sensitivity. ------------------------------------------------------------------------------------ 10621( 3) - 07/26/05 14:38 - [ 2] Observations Description ------------------------ The goal of the proposed observations is to obtain accurate photometry of the omega Cen standard stars in the WFC in all nine broadband filters. For the optimal comparisons with WFPC2 observations, the exposure times will be 25 seconds, which is the median exposure time of the WFPC2 omega Cen observations. (This will also ensure signal-to-noise exceeding that of the ground-based standard data.) Based on my Cycle 12 observations of this field, I do not expect cosmic rays to be a significant problem. Thus I will again be obtaining two images per filter, one with the field centered on each chip. The resulting 18 exposures will fit into the three orbit allocation. Real Time Justification ----------------------- Calibration Justification ------------------------- Additional Comments ------------------- ------------------------------------------------------------------------------------ 10621( 3) - 07/26/05 14:38 - [ 3] TARGET LIST Fixed Targets ------------------------------------------------------------------------------------------------------------------------------------ Tar| Target | Target | Target |Coord | Radial | Flux data No | Name | Description | Position |Eqnx | Vel. | ------------------------------------------------------------------------------------------------------------------------------------ 1 OMEGA-CEN STELLAR CLUSTER, RA=13H25M37.0000S +/- 0.1", J2000 V = 4.0 GLOBULAR CLUSTER DEC=-47D35'38.00" +/- 0.1" Coordinate Source: HST_IMAGE 10621( 3) - 07/26/05 14:38 - [ 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 OMEGA-CEN ACS/WFC ACCUM WFC1 F435W GAIN=2,CR-SPLIT=NO 1 25 S ------------------------------------------------------------------------------------------------------------------------------------ 2 OMEGA-CEN ACS/WFC ACCUM WFC1 F475W GAIN=2,CR-SPLIT=NO 1 25 S ------------------------------------------------------------------------------------------------------------------------------------ 3 OMEGA-CEN ACS/WFC ACCUM WFC1 F550M GAIN=2,CR-SPLIT=NO 1 25 S ------------------------------------------------------------------------------------------------------------------------------------ 4 OMEGA-CEN ACS/WFC ACCUM WFC1 F555W GAIN=2,CR-SPLIT=NO 1 25 S ------------------------------------------------------------------------------------------------------------------------------------ 5 OMEGA-CEN ACS/WFC ACCUM WFC1 F606W GAIN=2,CR-SPLIT=NO 1 25 S ------------------------------------------------------------------------------------------------------------------------------------ 6 OMEGA-CEN ACS/WFC ACCUM WFC1 F625W GAIN=2,CR-SPLIT=NO 1 25 S ------------------------------------------------------------------------------------------------------------------------------------ 7 OMEGA-CEN ACS/WFC ACCUM WFC1 F775W GAIN=2,CR-SPLIT=NO 1 25 S ------------------------------------------------------------------------------------------------------------------------------------ 8 OMEGA-CEN ACS/WFC ACCUM WFC1 F814W GAIN=2,CR-SPLIT=NO 1 25 S ------------------------------------------------------------------------------------------------------------------------------------ 9 OMEGA-CEN ACS/WFC ACCUM WFC1 F850LP GAIN=2,CR-SPLIT=NO 1 25 S ------------------------------------------------------------------------------------------------------------------------------------ 10 OMEGA-CEN ACS/WFC ACCUM WFC2 F435W GAIN=2,CR-SPLIT=NO 1 25 S ------------------------------------------------------------------------------------------------------------------------------------ 11 OMEGA-CEN ACS/WFC ACCUM WFC2 F475W GAIN=2,CR-SPLIT=NO 1 25 S ------------------------------------------------------------------------------------------------------------------------------------ 12 OMEGA-CEN ACS/WFC ACCUM WFC2 F550M GAIN=2,CR-SPLIT=NO 1 25 S ------------------------------------------------------------------------------------------------------------------------------------ 13 OMEGA-CEN ACS/WFC ACCUM WFC2 F555W GAIN=2,CR-SPLIT=NO 1 25 S ------------------------------------------------------------------------------------------------------------------------------------ 14 OMEGA-CEN ACS/WFC ACCUM WFC2 F606W GAIN=2,CR-SPLIT=NO 1 25 S ------------------------------------------------------------------------------------------------------------------------------------ 15 OMEGA-CEN ACS/WFC ACCUM WFC2 F625W GAIN=2,CR-SPLIT=NO 1 25 S ------------------------------------------------------------------------------------------------------------------------------------ 16 OMEGA-CEN ACS/WFC ACCUM WFC2 F775W GAIN=2,CR-SPLIT=NO 1 25 S ------------------------------------------------------------------------------------------------------------------------------------ 17 OMEGA-CEN ACS/WFC ACCUM WFC2 F814W GAIN=2,CR-SPLIT=NO 1 25 S ------------------------------------------------------------------------------------------------------------------------------------ 18 OMEGA-CEN ACS/WFC ACCUM WFC2 F850LP GAIN=2,CR-SPLIT=NO 1 25 S ------------------------------------------------------------------------------------------------------------------------------------ 10621( 3) - 07/26/05 14:38 - [ 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 | ------------------------------------------------------------------------------------------------------------------------------------ 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 | ------------------------------------------------------------------------------------------------------------------------------------ OMEGA-CEN 1 ACS/WFC ACCUM WFC1 F435W none none none none 1 N/A OMEGA-CEN 2 ACS/WFC ACCUM WFC1 F475W none none none none 1 N/A OMEGA-CEN 3 ACS/WFC ACCUM WFC1 F550M none none none none 1 N/A OMEGA-CEN 4 ACS/WFC ACCUM WFC1 F555W none none none none 1 N/A OMEGA-CEN 5 ACS/WFC ACCUM WFC1 F606W none none none none 1 N/A OMEGA-CEN 6 ACS/WFC ACCUM WFC1 F625W none none none none 1 N/A OMEGA-CEN 7 ACS/WFC ACCUM WFC1 F775W none none none none 2 N/A OMEGA-CEN 8 ACS/WFC ACCUM WFC1 F814W none none none none 2 N/A OMEGA-CEN 9 ACS/WFC ACCUM WFC1 F850LP none none none none 2 N/A OMEGA-CEN 10 ACS/WFC ACCUM WFC2 F435W none none none none 2 N/A OMEGA-CEN 11 ACS/WFC ACCUM WFC2 F475W none none none none 2 N/A OMEGA-CEN 12 ACS/WFC ACCUM WFC2 F550M none none none none 2 N/A OMEGA-CEN 13 ACS/WFC ACCUM WFC2 F555W none none none none 3 N/A OMEGA-CEN 14 ACS/WFC ACCUM WFC2 F606W none none none none 3 N/A OMEGA-CEN 15 ACS/WFC ACCUM WFC2 F625W none none none none 3 N/A OMEGA-CEN 16 ACS/WFC ACCUM WFC2 F775W none none none none 3 N/A OMEGA-CEN 17 ACS/WFC ACCUM WFC2 F814W none none none none 3 N/A OMEGA-CEN 18 ACS/WFC ACCUM WFC2 F850LP none none none none 3 N/A 10621( 3) - 07/26/05 14:38 - [ 6] Summary Form for Proposal 10621 Item Used in this proposal ------------------------------------------------------------------------------------------------------------------------------------ Apertures WFC1 WFC2 ------------------------------------------------------------------------------------------------------------------------------------ Configurations ACS/WFC ------------------------------------------------------------------------------------------------------------------------------------ Opmodes ACCUM ------------------------------------------------------------------------------------------------------------------------------------ Optional Parameters GAIN=2 CR-SPLIT=NO ------------------------------------------------------------------------------------------------------------------------------------ Proposal Category GO ------------------------------------------------------------------------------------------------------------------------------------ Spectral Elements F435W F475W F550M F555W F606W F625W F775W F814W F850LP ------------------------------------------------------------------------------------------------------------------------------------ Target Names OMEGA-CEN ------------------------------------------------------------------------------------------------------------------------------------