We present the results of XMM-Newton X-ray observations of the Mira AB binary system , which consists of a pulsating , asymptotic giant branch primary and nearby ( \sim 0.6 ^ { \prime \prime } separation ) secondary of uncertain nature .
The EPIC CCD ( MOS and pn ) X-ray spectra of Mira AB are relatively soft , peaking at \sim 1 keV , with only very weak emission at energies > 3 keV ; lines of Ne ix , Ne x , and O viii are apparent .
Spectral modeling indicates a characteristic temperature T _ { X } \sim 10 ^ { 7 } K and intrinsic luminosity L _ { X } \sim 5 \times 10 ^ { 29 } erg s ^ { -1 } , and suggests enhanced abundances 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 resemble those of late-type , pre-main sequence stars or late-type , magnetically active main sequence stars than those of accreting white dwarfs .
We conclude that Mira B is most likely a late-type , magnetically active , main-sequence dwarf , and that X-rays from the Mira AB system arise either from magnetospheric accretion of wind material from Mira A onto Mira B , or from coronal activity associated with 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 .