16932

PurposedoublePoint Observe final two JWST calibration stars to obtain STIS spectra to complete the optical-UV observations of the JWST calibration sample. Stellar model atmosphere are fit to these data and the resulting best fit model provides the flux density predictions at all JWST wavelengths. Both the STIS SEDs amd the model SEDs will be delivered to CALSPEC. DescriptiondoublePoint The JWST absolute flux program has been designed with the core goal of ensuring robust flux calibration internal to and between all the JWST science instruments for both point and extended source science. This program is based on a sample of calibration stars that have been extensively vetted based mainly on Hubble Space Telescope comma Spitzer Space Telescope comma and Transiting Exoplanet Survey Satellite observations. The program uses multiple stars of three different comma well understood types (hot comma A dwarf comma and solar analog stars) to allow for the statistical (within a type) and systematic (between types) uncertainties to be quantified. The Hubble-STIS observations are core to providing an accurate flux calibration as STIS is the only instrument that can directly transfer the laboratory calibrated observations of Vega and Sirius to stars that are faint enough to be observed with JWST. In addition comma the STIS spectra provide the needed data to precisely determine the stellar atmosphere parameters comma which are required to extrapolate the models to all JWST wavelengths. These final 2 stars were added to the JWST program in the last year to provide a full set of targets at bright (HR 7018 comma esp. for MIRI) and faint (NGC2506-G31 comma esp. for NIRCam-NIRISS) flux densities.