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Scientific paper
Jul 2008
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2008hst..prop11515b&link_type=abstract
HST Proposal ID #11515. Cycle 17
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Scientific paper
This proposal is based on SMOV Activity COS-37 {SMOV4 Light Leak test}. This activity consists of a set of external exposures designed to determine whether a particular science instrument {SI} is susceptible to light leaks resulting from photons escaping from the calibration system of another SI. For the identified combination of SIs {see list below}, the SI assumed to be the light source will carry out a calibration activity while, in parallel, the other SI will perform an external exposure. The test is designed to detect gross light leaks that may affect science data during typical calibration lamp exposure sequences. The test will provide an initial estimate of the amount of contamination present. Follow-up observations for cases where light is detected may be warranted. The most likely cases for light leaking out of an instrument will be configurations with COS as prime when it is in TAGFLASH mode, with another SI exposing on the sky in parallel. In TAGFLASH mode, the COS external shutter is open and a PtNe wavelength calibration lamp is flashed periodically for short intervals {5-30 seconds} during the science exposure. We use CVZ targeting of regions of sky near the orbit north pole position in order to minimize the number of orbits required and the impact to the existing SMOV4 timeline. All COS external exposures will be centered with the COS primary science aperture on a blank region of sky. However, bright object checks will need to be performed by the COS team after selection of the final target positions, which depend upon time of execution. This test is based on the following guidelines: 1} Check new instruments as source and sink {WFC3 & COS}. Check both WFC3/UVIS and WFC3/IR. Check COS/FUV only if a problem is seen for COS/NUV imaging mode. COS FUV is not currently part of this proposal. 2} Check known issues {e.g., WFPC2->ACS/WFC and NICMOS->WFPC2, with the obvious substitution of WFC3 for WFPC2}. 3} STIS and ACS/SBC will not be used in parallel with COS externals, and therefore will not require testing as light sinks. They will not be checked as sources either in this proposal. 4} STIS and ACS/SBC are not likely to be used often with COS internals and therefore are not tested in this proposal. 5} Check ACS/SBC later only if a problem is seen for ACS/HRC {no problem seen previously for WFPC2 -> ACS/HRC}. 6} NICMOS is not likely to be used often with COS externals or COS internals, and therefore requires testing only with WFC3. However, the experimental design allows NICMOS to be tested as a source with COS as sink. 7} There are no known problems for axial bay to axial bay cross contamination {ACS <-> STIS or ACS <-> NICMOS or STIS <-> NICMOS}, so no problems are expected for NICMOS <-> COS. The specific combinations of SIs to be tested for light leakage and unwanted light detection are as follows: 1. With the COS External {PtNe TAGFLASH} and Internal {PtNe} calibration lamp as the potential source, check for potential detections by: - ACS/WFC, ACS/HRC, WFC3/UVIS, and WFC3/IR 2. With the WFC3 Internal {Tungsten} calibration lamp as a potential source, check for potential detections by: - ACS/WFC, ACS/HRC, and COS/NUV 3. With the ACS Internal {Tungsten} calibration lamp as a potential source, check for potential detections by: - WFC3/UVIS, WFC3/IR, and COS/NUV 4. With the NICMOS {Quartz Halogen} calibration lamp as the potential source, check for potential detections by: - WFC3/UVIS, WFC3/IR, and COS/NUV Pre-requisite proposals that must be executed prior to this proposal include: COS-06 NUV Detector Functional ACS-20 UV Sensitivity, Geometric Distortion & Flat-field Uniformity ACS-11 HRC Sensitivity, Geometric Distortion & Flat-field Stability NIC-04 NICMOS Filter Wheel Test WFC3-33 UVIS Dark, Read Noise, and Background WFC3-34 IR Dark, Read Noise, and Background;
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