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Observations of the short period Magnetic Chemically Peculiar (MCP) star CU Vir have been made since 1990 in the Stromgren four-color system on the Four College automatic telescope (CAPT) on Mt. Hopkins. The purpose of this program is to search for year-to-year changes in the shapes of the light curves caused by possible free body precession due to a distortion in the shape of the star by the magnetic field. CU Vir was chosen since it has the shortest known period of the MCP stars, 0.52 days. For stars with periods of less than one day, the precession periods would be expected to be about 5 to 10 years. The data for CU Vir may show subtle changes in the light curves from year to year; previous data obtained with the Phoenix 10 automatic telescope show these results best. Similar changes for the 0.73-day periodic MCP have also been found by Adelman. Unexpectedly, comparisons with previous photometric studies (O-C) going back to 1958, shows evidence of a period change in this star that may have occurred in about 1985. Previous to 1983, data can be represented by a period of 0.5206778 days; since 1987, the period seems to have increased to 0.5207020 days. Since the star is not a member of a binary system, mass transfer cannot be the cause of such a change. Light, spectrum and magnetic variations in an MCP star is believed to be due to "rigid" rotation of an inhomogeneous atmosphere with a large magnetic field. Due to this rigid rotation, the proposed precession would be expected to change the shape of the light curves but not the period. Further monitoring of this star will be necessary in order to clarify these results.
This research has been supported in part by NSF Grant AST-9115114.
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