----- Submission 1 (Thu May 05 19:11:13 GMT 2005) ----- Phase II Proposal 10622 (pal414) successfully submitted. ----- Submission 2 (Wed Jul 20 23:25:50 GMT 2005) ----- Assigned ID: 529 ----- Submission 1 (Fri Jan 21 23:26:29 GMT 2005) ----- Phase I Proposal 529 (pal414) successfully submitted. ACS Photometric Calibration from Faint Standards 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.
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. STELLAR POPULATIONS 0 true 0.0 false false false false false SUPPORTED STELLAR CLUSTER GLOBULAR CLUSTER J2000 11 29 14.0000 +28 57 30.00 J2000 STELLAR CLUSTER GLOBULAR CLUSTER J2000 16 11 4.9000 +14 57 29.00 J2000 ACS/WFC Imaging No No F435W ACS/WFC Imaging No No F475W ACS/WFC Imaging No No F550M ACS/WFC Imaging No No F555W ACS/WFC Imaging No No F606W ACS/WFC Imaging No No F625W ACS/WFC Imaging No No F775W ACS/WFC Imaging No No F814W ACS/WFC Imaging No No F850LP ACS/WFC Imaging No No F435W ACS/WFC Imaging No No F475W ACS/WFC Imaging No No F550M ACS/WFC Imaging No No F555W ACS/WFC Imaging No No F606W ACS/WFC Imaging No No F625W ACS/WFC Imaging No No F775W ACS/WFC Imaging No No F814W ACS/WFC Imaging No No F850LP /private/tmp/OPVisit49519.xml (Tic-Visit :proposal-id 10622 :visit-id "01" :proposal-version -1 :trans-version "20050323" :date "20-Jul-2005 17:25:36.0" :trans-errors '(:WARNINGS 0 :ERRORS 0 :HEALTH-AND-SAFETY 0 :FATAL-ERRORS 0 :CONTINUABLE-FATALS 0) :number-of-orbits 4 :saa-model "27" :si-bright-earth-limb-angle 20.0 :data-volume 5116032 :tdrss-contact-duration 0 :coron NIL ) (Tic-Obset :proposal-id 10622 :visit-id "01" :obset-id "01" :pcs-mode "FGS" ) (Tic-Orbit :proposal-id 10622 :visit-id "01" :orbit-number 1 :pcs-time 367 :si-vis-utilization 2457 :al-overhead-at-end 0 :internal-dur-at-end 349 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3267 :pcs-gap 0 ) (Tic-Orbit :proposal-id 10622 :visit-id "01" :orbit-number 2 :pcs-time 367 :si-vis-utilization 2489 :al-overhead-at-end 0 :internal-dur-at-end 349 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3267 :pcs-gap 0 ) (Tic-Orbit :proposal-id 10622 :visit-id "01" :orbit-number 3 :pcs-time 367 :si-vis-utilization 2661 :al-overhead-at-end 0 :internal-dur-at-end 349 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3267 :pcs-gap 0 ) (Tic-Orbit :proposal-id 10622 :visit-id "01" :orbit-number 4 :pcs-time 367 :si-vis-utilization 2641 :al-overhead-at-end 0 :internal-dur-at-end 349 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3267 :pcs-gap 0 ) true 4 0 /Users/andy/HST_C14/pal414/OP-cache/pal414-v01.xml /Users/andy/HST_C14/pal414/OP-cache/pal414-v02.xml (Tic-Visit :proposal-id 10622 :visit-id "02" :proposal-version -1 :trans-version "20050323" :date "02-May-2005 12:50:34.0" :trans-errors '(:WARNINGS 0 :ERRORS 0 :HEALTH-AND-SAFETY 0 :FATAL-ERRORS 0 :CONTINUABLE-FATALS 0) :number-of-orbits 4 :saa-model "27" :si-bright-earth-limb-angle 20.0 :data-volume 5116032 :tdrss-contact-duration 0 :coron NIL ) (Tic-Obset :proposal-id 10622 :visit-id "02" :obset-id "02" :pcs-mode "FGS" ) (Tic-Orbit :proposal-id 10622 :visit-id "02" :orbit-number 1 :pcs-time 367 :si-vis-utilization 2457 :al-overhead-at-end 0 :internal-dur-at-end 349 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3251 :pcs-gap 0 ) (Tic-Orbit :proposal-id 10622 :visit-id "02" :orbit-number 2 :pcs-time 367 :si-vis-utilization 2489 :al-overhead-at-end 0 :internal-dur-at-end 349 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3251 :pcs-gap 0 ) (Tic-Orbit :proposal-id 10622 :visit-id "02" :orbit-number 3 :pcs-time 367 :si-vis-utilization 2661 :al-overhead-at-end 0 :internal-dur-at-end 349 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3251 :pcs-gap 0 ) (Tic-Orbit :proposal-id 10622 :visit-id "02" :orbit-number 4 :pcs-time 367 :si-vis-utilization 2641 :al-overhead-at-end 0 :internal-dur-at-end 349 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3251 :pcs-gap 0 ) true 4 0 /Users/andy/HST_C14/pal414/OP-cache/pal414-v02.xml