Constraining the X-Ray Luminosities of Asymptotic Giant Branch Stars: TX Camelopardalis and T Cassiopeia
© 2004 The American Astronomical Society.
Also archived in: arXiv: astro-ph/0403063 v1 2 Mar 2004
The authors thank John Houck and the anonymous referee for helpful suggestions concerning this paper. We acknowledge support for this research provided by NASA/GSFC XMM-Newton General Observer grant NAG5–13158 to RIT. N.S. acknowledges support from the Israel Science Foundation.
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To probe the magnetic activity levels of asymptotic giant branch (AGB) stars, we used XMM-Newton to search for X-ray emission from two well-studied objects, TX Cam and T Cas. The former star displays polarized maser emission, indicating magnetic field strengths of B ~ 5 G, and the latter is one of the nearest known AGB stars. Neither star was detected by XMM-Newton. We use the upper limits on EPIC (CCD detector) count rates to constrain the X-ray luminosities of these stars and derive Lx< 10^31 ergs s^-1 (< 103^0 ergs s^-1) for an assumed X-ray emission temperature Tx= 3 x10^6 K (10^7 K). These limits represent < ~10% (< ~1%) of the X-ray luminosity expected under models in which AGB magnetic fields are global and potentially play an important role in collimating and/or launching AGB winds. We suggest, instead, that the B field strengths inferred from maser observations are representative of localized magnetic clouds (Refer to PDF file for exact formulas).