AAS 203rd Meeting, January 2004
Session 85 Stellar Structure, Evolution and Abundances
Poster, Wednesday, January 7, 2004, 9:20am-6:30pm, Grand Hall

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[85.03] The Onset of Magnetic Dynamo Activity in A-Type Stars

D. E. Turner-Bey (Rockhurst University), V. Kashyap, N. Evans, A. Mossman (Harvard-Smithsonian Center for Astrophysics), ChaMP Collaboration

A solar type magnetic dynamo is believed to come into operation in late-A stars causing high-temperature coronae to form that may be detected in X-rays. No X-ray emission has been conclusively detected in early-type A stars, and because these stars represent a transition state in the type of their atmospheres, constraining the point of onset of the dynamo is of significant theoretical importance. Here we present the preliminary results of a survey we have undertaken to detect X-ray emission from late-B and A type stars using data from the Chandra Extended Stellar Survey (ChESS), a part of the Chandra Multiwavelength Project (ChaMP). In this survey, we matched the X-ray detections from ChaMP with point sources in the Guide Star Catalog (GSC2.2) and selected candidate sources that may be A type stars based on their V-R color. These candidates were further pruned by matching with the SIMBAD database to eliminate QSOs and other nonstellar objects and setting a threshold of X-ray to optical ratio of < 10-3; this leaves us with a sample of approximately 20 candidates that are likely A stars with X-ray emission. Here we present the X-ray properties of this sample of A star candidates. We find that the data are consistent with main sequence stars becoming X-ray emitters (and hence magnetically active) at V-R ~ 0.15, corresponding with the range A6-A9.

This work was supported in part by the SAO intern program under NSF grant AST-9731923.

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Bulletin of the American Astronomical Society, 35#5
© 2003. The American Astronomical Soceity.