Vega: A rapidly rotating pole-on star

Abstract

High-dispersion (2.4 A/mm), ultrahigh signal-to-noise ratio (3000:1) Reticon spectra of Vega revealed two distinct types of profiles. The strong lines exhibit classical rotational profiles with enhanced wings, but the weak lines have distinctly different, flat-bottomed profiles. Using ATLAS9 model atmopheres and SYNTHE synthetic spectra, Vega has been modeled as a rapidly rotating, pole-on star with a gradient in temperature and gravity over the photosphere. By fitting to the flat-bottomed line profiles of Fe 1 lambda 4528 and Ti 2 lambda 4529, we find least-squares fit values of V sin i = 21.8 plus or minus 0.2 km/sec polar T(sub eff) = 9695 plus or minus 25 K, polar log(base 10)g = 3.75 plus or minus 0.02 dex, V(sub eq) = 245 plus or minus 15 km/sec, and inclination 5 deg .1 plus or minus 0 deg .3. The variations in T(sub eff) and log(base 10)g over the photosphere total 390 K and 0.08 dex, respectively. Assuming V sin i = 21.8 km/sec, an independent fit to the observed continuous flux from 1200 to 10,500 A produced a similar set of values with polar T(sub eff) = 9595 plus or minus 20 K, polar log(base 10)g = 3.80 plus or minus 0.03 dex, and inclination 6 deg .0 plus or minus 0 deg .7.