WFPC2 Instrument Handbook for Cycle 11

Future Calibrations, Calibration by Observers, and Calibration Outsourcing

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The Cycle 11 calibration program will be defined a few months after the Phase II deadline for approved programs. It is expected that the same calibrations outlined here for recent cycles and the current Cycle 10 plan will be maintained for Cycle 11. However, it is possible that as the number WFPC2 users decreases with the availability of ACS, some WFPC2 calibrations maybe curtailed. For example, monitoring observations may become less frequent, and special modes (e.g. ramp filters) may not receive further calibration. It is the intention of STScI to develop a calibration program that effectively balances the needs of the community for obtaining excellent science results from the instrument with the limited resources available (e.g., a nominal limit of 10% time available for calibration). As always, frequently used modes of the instrument will be fully calibrated.

In special situations it is possible that observers may find the STScI calibration programs do not meet their needs. For example, they may require an accuracy better than outlined in Table 8.11, or may require calibration of some unique mode or observation strategy. In these cases observers may propose to obtain their own calibration data. Such observations may be proposed in one of two ways.

The first type of special calibration would be to simply request additional orbits within a GO program for the purpose of calibrating the proposed science data (see section 4.3 of the CP). In this case the extra calibration would only need to be justified on the basis of the expected science return of the GO's program.

The second type of special calibration would be performed as a general service to the community via Calibration Proposals (section 3.7 of CP, sometimes called "Calibration Outsourcing"). These proposals are to obtain calibration data and/or support analysis of data (including archival data) for the purpose of improving calibrations. New observations obtained for calibration programs will generally be flagged as non-proprietary, and will be immediately released to the community. These proposals will generally be judged on their value to the scientific community and scientific impact they are likely to make (see the Call for Proposals for details). These programs, if approved, will usually carry a requirement to provide separately negotiated deliverables (e.g. results, reference files, documentation) so as to support other members of the community.

Proposers interested in obtaining either type of special calibration should consult with Instrument Scientists from the WFPC2 Group via the Help Desk at least 14 days before the proposal deadline in order to ascertain if the proposed calibrations would be done at STScI in the default program.

During Cycles 9 and 10, two WFPC2 Calibration Outsource programs were awarded. The first (Karkoshka, PI) seeks to improve the signal-to-noise ratio of the UV flatfields. While the standard UV flats provided by STScI are adequate for most observers, people with bright targets (e.g. planets) have sometimes found their signal-to-noise ratio was limited by the calibration flats rather than photon noise. We anticipate this program will provide new flatfields in the UV which reduce noise in certain observations by up to a factor ~3. The second program (Saha, PI) tests for a position independent component of CTE by comparing ground-based and WFPC2 observations of several fields containing faint standard stars. This program could potentially improve the photometric accuracy for faint targets, and impact scientifically important problems such as the extragalactic distance scale. Results of both programs will be disseminated via the WFPC2 WWW site, as results become available.