X‐Rays from the Mira AB Binary System

We present the results of XMM-Newton X-ray observations of the Mira AB binarysystem, which consists of a pulsating, asymptotic giant branch primary andnearby (~0.6'' separation) secondary of uncertain nature. The EPIC CCD (MOS andpn) X-ray spectra of Mira AB are relatively soft, peaking at ~1 keV, with onlyvery weak emission at energies > 3 keV; lines of Ne IX, Ne X, and O VIII areapparent. Spectral modeling indicates a characteristic temperature T_X ~ 10^7 Kand intrinsic luminosity L_X ~ 5x10^29 erg s^{-1}, and suggests enhancedabundances of O and, possibly, Ne and Si in the X-ray-emitting plasma. Overall,the X-ray spectrum and luminosity of the Mira AB system more closely resemblethose of late-type, pre-main sequence stars or late-type, magnetically activemain sequence stars than those of accreting white dwarfs. We conclude that MiraB is most likely a late-type, magnetically active, main-sequence dwarf, andthat X-rays from the Mira AB system arise either from magnetospheric accretionof wind material from Mira A onto Mira B, or from coronal activity associatedwith Mira B itself, as a consequence of accretion-driven spin-up. One (or both)of these mechanisms also could be responsible for the recently discovered,point-like X-ray sources within planetary nebulae.Comment: 14 pages, 3 figures; to appear in the Astrophysical Journa