X-Ray and UV Observations of the Contact Binary KIC 9832227

We investigate the X-ray and UV emission from the contact binary star KIC 9832227, which was observed with XMM-Newton for one orbital cycle. The binary is detected with an average X-ray luminosity of 3.4 × 10³⁰ erg s^-1. The X-ray emission is restricted to energies below 3 keV and originates from a multitemperature plasma with temperatures up to 1 keV. The X-ray spectrum has at least two distinct components, a cooler, mostly steady component, and a hotter component exhibiting significant variability. The variable X-ray emission appears to originate from a compact flare near the contact region between the two stars that is being eclipsed by the secondary. We analyze the eclipse profile to constrain the location, size, and density of the flaring region. The remaining X-ray emission is not eclipsed and could originate from the polar region on the primary star or an extended corona. The UV emission exhibits the same nearly sinusoidal modulation at half the orbital period that is observed at longer wavelengths. The primary and secondary eclipses have slightly different depths, which is generally attributed to starspot activity. Using simulations of the UV light curve with stellar atmosphere models, we deduce the presence of a starspot near the polar region of the primary, and we determine the time of primary eclipse.