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).
Department, Program, or Center
Chester F. Carlson Center for Imaging Science (COS)
Astrophys.J. 608 (2004) 978-982
RIT – Main Campus