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The systematic, spectroscopic two-dimensional classification of the HD stars by N. H. is approximately threequarters complete. Over 161,000 stars have been classified visually using 10 objective-prism plates (2 8 resolution) taken at CTIO with the Michigan Curtis Schmidt telescope. The published portion of this large, homogeneous database, taken from volumes 1Y5 of the Michigan Spectral Catalogue (declination À90 to +5 ), has been used to create an H-R diagram. The Hipparcos parallax measurements provide a large homogenous database, too. H-R diagrams of the HD stars found in both catalogs are produced for distances to 20, 50, 100, and 200 pc.

Our differential BV photometric observations, acquired with an automated telescope at Fairborn Observatory, show that HD 71636 is an eclipsing binary. From follow-up red-wavelength spectroscopic observations we classify the primary and secondary as an F2 dwarf and an F5 dwarf, respectively. The system has a period of 5.01329 days and a circular orbit. We used the Wilson-Devinney program to simultaneously solve our BV light curves and radial velocities and determined a number of fundamental properties of the system. Comparison with evolutionary tracks indicates that both stars are well ensconced on the main sequence. The age of the system is about 1.2 billion years.

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