Automatic Parameterization and Analysis of Stellar Atmospheres: a Study of the DA White Dwarfs

A method for automatically calculating the atmospheric parameters (T(,eff) and log g) of hydrogen-rich degenerate stars from low resolution spectra is advanced and then applied to the spectra of 53 DA white dwarfs. All data were taken using the Mark II spectro- graph on the McGraw -Hill 1.3 m telescope and cover the spectral range (lamda)(lamda)4100 -7000 at a resolution of eight Angstroms. The model grid was generated at Dartmouth using the atmosphere code LUCIFER; it contained over 275 synthetic spectra extending from 6,000-100,000 K in effective temperature and 7.4-9.3 in log g. A new value for the width of the DA mass distribution of (sigma)(,M(,o)) (LESSTHEQ) (+OR-)0.10 is achieved using the techniques presented here. Accuracies in the atmospheric parameters greater than twice those previously published are obtained, resulting in a mass resolution of (DELTA)M(,o) (TURN) (+OR-)0.05. The data indicate the distribution is asymmetrically skewed to low masses; however, there is also evidence of a high mass non-Gaussian tail. These results place strict constraints on the magni- tude of mass-loss in stars in the red-giant phase, as well as in the mechanisms responsible for the loss. Analysis of the parallax sub- set provides compelling evidence for the existence of a single, well defined, DA cooling sequence about an average radius of <log(,10)R/R(,o)> = -1.896. This work was supported in part by the National Science Foun- dation through grants AST82-19474 and AST85 -15219 as well as by the National Aeronautics and Space Administration through grant NAG5-287.