"Spectral Classification of Hot Subdwarfs" AST-9819835
A system for classifying the spectra of rare but astrophysically important hot stars called subdwarfs has been developed. Such luminous stars are important clues to stellar evolution and provide valuable distance and age indices for studies of star clusters in the Galaxy. It has been found that three parameters are necessary to uniquely classify such stars: temperature, luminosity and "helium abundance." This project will refine and complete the basic system of classification. Particular attention will be paid to what appears to be two "parallel spectral sequences" that depend upon whether a star exhibits strong lines of carbon (CII, CIII or CIV), that are thought to be an index for He abundance. A calibration of the new spectral types with effective temperature, surface gravity, luminosity, photometric color and helium abundance will be derived and an attempt will be made to draw connections between these spectral types and the groups of hot subdwarfs identified during the Palomar-Green survey.