Popper 9415653 As our theoretical understanding of the structure and evolution of stars advances, greater and greater demands are made on the reliability and accuracy of the fundamental properties of stars -- their masses, radii, and temperatures. This proposal will advance our empirical knowledge of these properties into the relatively unexplored realm (because of strong selection effects) of stars less massive than the Sun down to about 0.6 solar masses. The only source of information on fundamental properties of normal stars accurate enough to test modern theories of stellar structure and evolution is detached eclipsing binaries. Several factors provide the wherewithal to overcome the difficulties posed by the selection effects, which result from the low luminosities and small sizes of the less massive stars. First is the availability of the Hamilton eschelle-CCD spectrometer at the Lick Observatory, which is unsurpassed for the effective observation of spectra of double-lined eclipsing binaries down to about the 12th magnitude. Second is the availability of efficient computer programs (IRAF programs in this case) for obtaining reliable radial velocities of both components in the spectrum. Even though the lines in the crowded spectra are washed out by axial rotation and badly blended, cross-correlation of the binary star spectrum with one from a star of known velocity does the trick. Third is the availability of computing equipment (now routine) for rapid application of the programs. The resulting masses in the new realm, obtained from analysis of the binary star orbits, will be essential in a wide variety of problems in stellar astronomy. ***
