AAS 200th meeting, Albuquerque, NM, June 2002
Session 70. Angular Momentum Evolution and Young Stars
Display, Thursday, June 6, 2002, 9:20am-4:00pm, SW Exhibit Hall

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[70.06] Chandra observations of a young embedded magnetic B star

K. Hamaguchi (NASA/GSFC), Kyoto University, Cosmic Ray Group Collaboration, NASA/GSFC/LHEA Collaboration

We report the analyses of the young magnetic B star \rho Oph S1 (hereafter S1) observed twice with the Chandra X-ray observatory for about 100 ksec each. \rho Oph S1 is a highly embedded young star with the magnetosphere, associated with the \rho Ophiuchi cloud core A, and a candidate of young magnetic chemically peculiar(CP) stars. It may fill the gap between pre-main-sequence(PMS) stars and main-sequence(MS) stars and is thus important for studying the evolution of stellar X-ray activity.

With Chandra, the X-ray emission is detected in both observations. The average flux is almost the same between the observations, but, in each observation, it shows significant time variations by a factor of two. Each spectrum is reproduced with an absorbed power law model or thin-thermal plasma model of ~ 2keV with extreme low metal abundance (less than 0.1 solar). The spectrum in the first observation seems to have an excess above 6 keV, which might correspond to highly ionized iron, whereas the spectrum in the second observation shows an anomalous absorption edge at ~ 4 keV.

If the X-ray emission is thermal, the log LX/Lbol ratio or the plasma temperature is similar to magnetic CP stars (He strong stars) and intermediate mass PMSs. This supports S1 as a young magnetic CP star. In this case, however, S1 might need to have a mechanism to select elements in the atmosphere, which is generally seen on CP stars. If it is nonthermal, the X-rays might originate from nonthermal bremsstrahlung emission like solar hard X-ray flares, produced by the collision of infalling materials on the surface. A plausible structure of the emitting region is also discussed, including the interpretation of the edge like feature.

Acknowledgement: This research is supported by the National Space Developmen Agency of Japan and the National Research Council.

The author(s) of this abstract have provided an email address for comments about the abstract: kenji@milkyway.gsfc.nasa.gov

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Bulletin of the American Astronomical Society, 34
© 2002. The American Astronomical Soceity.