The spectral energy distribution and mass-loss rate of the A-type supergiant Deneb

A stellar wind module has been developed for the PHOENIX stellar atmosphere code for the purpose of computing non-LTE, line-blanketed, expanding atmospheric structures and detailed synthetic spectra of hot luminous stars with winds. We apply the code to observations of Deneb, for which we report the first positive detections of millimeter and centimeter emission ( obtained using the Submillimeter Common-User Bolometric Array and the Very Large Array) as well a strong upper limit on the 870 mum flux (using the Heinrich Hertz Telescope). The slope of the radio spectrum shows that the stellar wind is partially ionized. We report a uniform-disk angular diameter measurement theta(UD) = 2.40 +/- 0.06 mas from the Navy Prototype Optical Interferometer (NPOI). The measured bolometric flux and corrected NPOI angular diameter yield an effective temperature of 8600 +/- 500 K. Least-squares comparisons of synthetic spectral energy distributions from 1220 Angstrom to 3.6 cm with the observations provide estimates for the effective temperature and the mass-loss rate of similar or equal to8400 +/- 100 K and (8+/-3) 10(-7) M-. yr(-1), respectively. This range of mass-loss rates is consistent with that derived from high-dispersion UV spectra when non-LTE metal-line blanketing is considered. We are unable achieve a reasonable fit to a typical Halpha P Cygni profile with any model parameters over a reasonable range. This is troubling because the Halpha profile is the observational basis for the wind momentum luminosity relationship.