《#8226;Stellar Astrophysics With SIM》.pdf

SIM Science Studies: Stellar Astrophysics with SIM Calibration and Characterisation across the HR diagram Brad Hansen (UCLA) eporting on studies by PIs Wei-Chun Jao (Georgia State) Stephen Ridgway (NOAO) Jay Holberg (Arizona) William Hartcopf (USNO) The Space Interferometry Mission offers the opportunity to obtain astrometric accuracies at the level of a few microarcseconds. This will make it possible to obtain trigonometric parallaxes across the entire Galaxy #8: A Novel SIM-based technique for the precise determination of absolute stellar fluxes (Holberg Bergeron) The goal of this study is to calibrate the absolute spectrophotometry of well-understood white dwarfs, using accurate parallaxes, to better than 1% Motivation includes the idiosyncratic nature of Vega, the need to extend accurate flux standards to the near-IR to enable high-redshift work, and the need for a stable, accurate, all-sky flux standard for pan-chromatic, wide- field surveys (e.g. LSST) A flux standard based on DA white dwarfs has the advantage that such stars are numerous, nearby (unreddened), chemically homogeneous and accurately reproduced by theoretical models Photometric parallax is based on broad band photometry and atmosphere models The addition of SIM parallaxes promises to take this calibration to well below a level of 1%. However, this can expose other systematics that this SIM study proposes to address. One of these is the accuracy of the spectroscopic gravity used to determine the radius - at high temperatures it can be affected by radiative levitation, and at low temperatures by convective d