Other
Scientific paper
Jul 2003
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2003hst..prop10014b&link_type=abstract
HST Proposal ID #10014
Other
Hst Proposal Id #10014
Scientific paper
Faint spectrophotometric standard stars required for COS and the SBC channel on ACS have been established via the STIS FASTEX program that has executed over the last three cycles. Cycle 12 is an especially opportune time to establish companion faint IR standards for WFC3, because the NICMOS proposal 9998 includes observations in cycle 12 of all 6 of the primary standard stars in order to establish the absolute flux calibration of the three grism modes to 1%. In addition to WFC3, these new faint secondary IR standards will be a significant step towards establishing flux standards for JWST, as well as for SNAP, SIRTF, and SOFIA. The 6 primary standards included in Propid=9998 are in the range of V=11-13 and include three hot pure hydrogen WDs and 3 solar analogs. We propose to establish new IR faint standards in the 15-17 mag range. Appropriate spectral types for faint IR standards are solar analogs and hotter WDs. Many M type and cooler stars are variable, so that long term monitoring is required before committing HST time to such cool stars. A few G type and WD faint stars will provide a set of faint IR standards with minimal sky and color coverage. Existing HST images of any candidates can provide verification that there are no contaminating stars above the 1% level within 2-3arcsec. However, the ACS calibration field in 47 Tuc is too crowded for linking to ground based observations. If the other candidates are selected from SDSS or other ground based data, then the NICMOS and STIS acquisition images can provide this verification, as well as correction factors for arbitrary photometric size apertures. The SNAP team is providing the northern faint stars using unreleased SDSS data. In addition, the extreme coolest types such as L and T stars have proven essential to sorting out the long wavelength QE of ACS; both the ACS and eventually WFC3 calibrations could be improved with knowledge of L and T SEDs in the region beyond 0.95 microns. In addition to the primary purpose of ACS QE vs. wavelength and broad band F814W and F850LP calibrations, these three stars in C.} below are at the flux level required for WFC3 grism calibration. The brighter M, L, and T standard stars will each require a NICMOS orbit, while each faint standard requires two Nicmos orbits and one STIS orbit for complete wavelength coverage. The STIS spectra of the M and L stars are done as ACS calibrations in cycles 12 and 11, respectively. An additional faint WD has already been proposed for 2 Nicmos and 4 STIS orbits in their cycle 12 programs already. See Table 1 for a summary of the 18 orbit allocation for this program 10014. Bright stars in the V=0-6 mag range would be useful for direct comparisons to NIST calibrated lamps. This comparison would offer the opportunity to compare two fundamentally different realms of physics: pure hydrogen stellar models and laboratory black body physics. Unfortunately, the Nicmos bright limit is V=~8 for a solar analog and a 1s exposure without defocussing the OTA. The primary Sloan standard BD+17d4708 at V=9.9 is safely fainter than this Nicmos limit.
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