Measurement of Parallaxes and Proper Motions

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Dr. Arthur Upgren will continue a program of measuring parallaxes and proper motions of stars with the 61-cm telescope of the Van Vleck Observatory. He will obtain high precision parallaxes and photometry of stars of the lower main sequence as well as of subdwarf stars. These stars are among the oldest in our Galaxy, but their parallaxes and distances are not well known. It is expected that Dr. Upgren's observations will allow calibration of the distance scale of these old stars with much greater precision than is now available. Graduate and undergraduate students will be involved in all aspects of the program. Trigonometric parallaxes of nearby stars are fewer in number and lower in precision than is generally perceived. Beyond the Solar System, the distances to even the nearest stars are surprisingly poorly known. All but a few percent of published parallaxes are of stars so distant that the parallax method is inapplicable. Most parallax determinations are more than twenty years old and thus have errors much larger than those possible in recent years, even with conventional equipment. Dr. Upgren's program has made use of the increases made possible in precision in obtaining parallaxes and proper motions since 1967. His is one of the two most extensive such programs now active.