WFC3 IR Fowler Sampling Will Not Be Calibrated During Cycle 17
The Fowler sample sequences for the IR detector (MIF600, MIF900 MIF1200, and MIF1500)
were utilized by only 6% of Cycle 17 programs. Most observers chose to use the SPARS,
or STEP sample sequence of comparable exposure time. Due to the small number of requests
for the Fowler sample sequences and in view of the high demand for calibration resources
in the first observing cycle after the installation of WFC3 onboard HST, STScI has
decided not to calibrate the MIF sample sequences in Cycle 17. Contact Scientists
have worked with the Principal Investigators of all of the affected Cycle 17 WFC3
programs to change their exposures to SPARS, or STEP sample sequences. The decision
not to calibrate MIF sample sequence exposures could also affect other Cycle 17 programs
such as the NICMOS programs that have converted to WFC3, or Director's Discretionary programs.
At this time, STScI plans to continue in Cycle 18 the "Available but Unsupported" status of
the MIF sample sequences.
Fowler sample sequences are intended to be used with the full number of 15 samples. The exposure time for those MIF600, MIF900, MIF1200, and MIF1500 sample sequences are 600 - 1500 seconds, respectively. Exposures of comparable exposure time and number of samples can be obtained with SPARS50 (13 samples, 603 sec), SPARS100 (10 samples, 903 sec), SPARS100 (14 samples, 1203 sec), SPARS100 (15 samples, 1403 sec), SPARS200 (9 samples, 1603 sec), STEP50 (15 samples, 500 sec), STEP100 (15 samples, 900 sec), STEP200, (15 samples, 1600 sec). Note that the SPARS and STEP sample sequences provide superior rejection of cosmic rays to that enabled by Fowler sequences.
If you were considering to use Fowler sample sequences and would like further information about the alternative SPARS and STEP sample sequences, or about designing user-supplied calibration of MIF sample sequences, please contact your Contact Scientist, or the Help Desk.