Standard external CTE monitoring part for timely scheduling. Special external calibration visits (10-13) added. ----- Attempting Submission 1 (Fri Oct 07 01:46:23 GMT 2011) ----- ----- Attempting Submission 2 (Wed May 02 02:58:34 GMT 2012) ----- POS TARGs out of field of view warnings can be ignored, these large offsets are intentional. UVIS CTE Monitor: Star Clusters This program extends the Cycle 17 and 18 external CTE calibration (CAL/WFC3 IDs 11924, 12379) program for WFC3/UVIS over Cycle 19. Targets are (i) the sparse cluster NGC 6791 observed in Cycle 17, to continue a consistent set of observations that allows to isolate the time evolution of the CTE, and (ii) two denser fields in 47 Tuc (NGC 104). The latter will provide data to measure the dependence of the CTE on field crowding. It will also provide a consistent comparison between the CTE evolution of WFC3/UVIS and that of ACS/WFC at the same time into the flight (3 years), because ACS/WFC CTE data were based on 47 Tuc observations. Additional observations of 47 Tuc over a range of sky backgrounds will provide a wide range of background levels to measure the background dependence of the UVIS CTE. Goals are (i) the continued monitoring of the time evolution of the WFC3/UVIS CTE, (ii) establishing the detector X,Y dependence of the CTE, (iii) CTE dependence on the source flux and the background level and (iv) an improved CTE correction model based on these measurements. These goals include CTE effects on both photometry and astrometry. Standard CTE Monitoring: -------------------- We observe three star fields of different densities, the open cluster NGC 6791 and 2 fields in 47 Tuc (NGC 104) in order to investigate the effects of crowding, differing background levels, detector position and count rates on the WFC3/UVIS channel detectors' Charge Transfer Efficiency (CTE). Sets of 3 visits, one for each target, are observed 3 times during cycle 19, spaced approximately 3-4 months apart. Exposure times are set to maximize the signal to noise over a brightness range of X-Y magnitudes. An additional observation of 47 Tuc (Visit 010) will provide a wide range of background levels to test the background dependence of the CTE. These data will be used to measure the CTE, and compare these values to the CTE measurements obtained during Cycle 17,18, SMOV and ground testing. We will also compare the rate of change in the WFC3 CCDs' CTE with those of the ACS CCDs. We expect to measure the CTE to a precision of 1% in point source photometry and 5% in point source centroid shift (astrometry). For NGC 6791 (Visits 01, 04, 07), observations will be similar to those in Cycle 17,18 / CAL/WFC3 Proposals 11924,12379, with equal exposure times, coordinates, filters, but a reduced dither pattern (2 pointings, one dithered approx. 2000 pixel in detector Y, omitting the 2000 pxl X dither). The long and short exposures, and the measurements of the same stars on both detectors, provide data to establish a CTE model as a function of various parameters. For 47 Tuc (Visits 02,03,05,06,08,09), we will only use a detector Y direction dither to measure the main CTE component's dependence on field crowding, as well as its comparison between ACS/WFC3 and WFC3/UVIS. Both NGC 6791 and 47 Tuc are observed in the F606W and F502N filters to increase the range of background levels useful to establish a UVIS CTE model. Non-standard CTE monitoring: ------------------------- 1) Visits 10 and 11 observe the open cluster NGC 6583. This target lies on the ecliptic and allows HST to observe it at ORIENTs of 140 degrees and 320 degrees, 180 degrees rotated, within 2 days. Observing a target twice, 180 degrees rotated, on each UVIS detector, allows to measure the absolute CTE of each detector individually. The standard monitoring approach measures the CTE averaged between both UVIS detectors. At each of the 180 degrees rotated ORIENTs, we take for each detector 2 long exposures in F502N, separated by a 10 pixel detector X offset, and one short exposure in F502N. To fill the orbit, we add one long exposure in F606W on UVIS1 for each ORIENT. 2) We also step the cluster 47 Tuc across the field of view of each individual detector, in 7 equal - spaced steps on each detector, 293 pixels in detector Y direction. These observations will provide another individual measurement of the CTE for each detector. Scheduling: ---------------- 1) The CTE long-term monitoring observations (Visits 01 to 09) will be taken at 3 epochs in Cycle 19, the first epoch as soon as possible in Oct/Nov 2011, the following two epochs spaced evenly throughout the cycle. We ask that pairs of NGC 6791 and 47 Tuc observations (Visits 01-03, Visits 04-06, Visits 07-09) are taken within 7 days from each other, to sample the CTE at similar epochs. We have set visit-level timing requirements for visit groups accordingly. 2) The 180 degree rotated observations of NGC 6583, Visits 10 and 11, will need to be scheduled on June 25/26, within a day of each other. Scheduling requirements are set accordingly. 3) The observations that step 47 Tuc across the field of view in detector Y direction, Visits 12 and 13, should be scheduled close in time to the third epoch of the standard CTE monitoring program (Visits 07-09); 12 and 13 should also be scheduled very close in time (back to back) and at the same orientation. Scheduling requirements are set accordingly. These data will be used to determine the rate of change of the CTE with time, and with position on the detector. Results will be compared to CY 17 and 18 CTE measurements for WFC3/UVIS CCDs, as well as to ACS/CCDs, and where possible to CTE measurements of first and second generation HST instruments. The analysis of the data will be used to obtain a model of CTE-induced losses in both FLT and DRZ UVIS images, with a precision of better than 1% for stellar photometry and less than 5% for astrometric effects from CTE-induced source centroid shifts. Methodology and results will be described in instrument science reports (ISR), and in the WFC3 instrument and data handbooks. 12 false 0.0 0.0 false false false false RESTRICTED STELLAR CLUSTER GLOBULAR CLUSTER This object was generated by the targetselector and retrieved from the SIMBAD database. 47-TUC J2000 J2000 STELLAR CLUSTER OPEN CLUSTER This object was generated by the targetselector and retrieved from the SIMBAD database. J2000 J2000 STELLAR CLUSTER GLOBULAR CLUSTER 47-TUC J2000 STELLAR CLUSTER OPEN CLUSTER This object was generated by the targetselector and retrieved from the SIMBAD database. Coordinates updated from Carraro, Mendez & Costa 2005, MNRAS, 356, 647 J2000 Timing link suitability includes constraints ([Group (01 02) Within 7.0 days] [Group (01 03) Within 7.0 days]) The scheduling data was generated by CASM 20.0. 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