2014•Proceedings of SPIE, the International Society for Optical Engineering/Proceedings of SPIERequires access
HST/WFC3 flux calibration ladder: Vega
Susana E. Deustua, R. C. Bohlin, Nor Pirzkal, John MacKenty
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Abstract
Vega is one of only a few stars calibrated against an SI-traceable blackbody, and is the historical flux standard. Photometric zeropoints of the Hubble Space Telescope’s instruments rely on Vega, through the transfer of its calibration via stellar atmosphere models to the suite of standard stars. HST’s recently implemented scan mode has enabled us to develop a path to an absolute SI traceable calibration for HST IR observations. To fill in the crucial gap between 0.9 and 1.7 micron in the absolute calibration, we acquired -1st order spectra of Vega with the two WFC3 infrared grisms. At the same time, we have improved the calibration of the -1st orders of both WFC3 IR grisms, as well as extended the dynamic range of WFC3 science observations by a factor of 10000. We describe our progress to date on the WFC3 ‘flux calibration ladder’ project to provide currently needed accurate zeropoint measurements in the IR