Comparison of White Dwarf Models with STIS Spectrophotometry

Abstract

Computed Ñux distributions for four white dwarf (WD) stars with nearly pure hydrogen atmospheres are tied to the Vega Ñux scale with V-band Landolt photometry. With broadband photometric precision in the range 0.2%È0.4%, Space Telescope Imaging Spectrograph (STIS) low-dispersion spectrophotom-etry tightly constrains the relative continuum Ñuxes of the various model atmosphere computations. The set of non-LTE (NLTE) model continua has residuals that are slightly less than the residuals with respect to LTE models or with respect to a NLTE set that includes a metal lineÈblanketed model for G191B2B. The LTE models have Balmer line proÐles that are matched to ground-based observations, while a consistent NLTE Balmer line analysis has not been published for all four stars. Residuals with respect to the LTE model continua are less than D1% from 2000 to 9000 Total uncertainties in the A Ž. adopted absolute Ñux distributions for the four WD standard stars decrease from 4% at 1300 to 2% A Ž at 5000È10000 and include estimates for all systematic e †ects. The STIS sensitivity in the broad hydro-A Ž gen lines is uncertain with respect to the adjacent continuum by 2%È3% in the wings and by up to 5% in the line cores, because the Ñux in the wings di †ers among the various models and because the observed cores are contaminated by out-of-band light in the wide 52A ] 2A calibration slit.