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W. Herbst (Wesleyan U.), A. Francis (Hamilton College), S. Dhital (Swarthmore College), N. Tresser (Wesleyan U.), L. Lin (CfA), E. Williams (Wesleyan U.)
The young cluster NGC 1333 has been photometrically monitored at Wesleyan University for five years beginning in October of 2000. A number of periodic variables have been discovered, among them HBC 338 (Herbig & Bell 1995; VizieR On-line Catalog: V/73A.) What distinguishes this star from the hundreds of other periodic variables found by this program in various young clusters, is that its period has changed substantially with time. During the first three years of observation, from October 2000 through March 2003 the star had a significant periodicity at 5.58, 5.57 and 5.52 days, which is a common scatter of periods, commensurate with the expected error in the period determination. In other words, the period was stable within our detection capability. Remarkably, in the 2003/2004 observing season the star was again detected as significantly periodic, but with a period of 4.47 days. This dramatic change was confirmed in the 2004/2005 season, when the star's period was found to be 4.46 days. We reiterate that no other star in our sample of more than a thousand, monitored over as much as fifteen years has ever behaved this way. As Cohen, Herbst & Williams (2004 AJ 127, 1602) discuss, the typical difference in periods from year-to-year is 1%, with no example of a clearly significant period change. There is also no definitive example in the literature of a T Tauri star changing its period significantly. This star, appears to be such a case: the period change is about 20%, which is highly significant. We discuss the possible causes of this unexpected result and suggest that it indicates the presence of substantial differential rotation on the star, in the sense that the poles rotate more slowly than the equator. Both Alice Francis and Suarav Dhital were undergraduate summer students at Wesleyan, supported by the Keck Northeast Astronomy Consortium. We gratefully acknowledge the support of the NSF through an REU grant (AST-0353997) that supports the program.
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Bulletin of the American Astronomical Society, 37 #4
© 2005. The American Astronomical Soceity.