Hot stars observed by XMM-Newton - I. The catalog and the properties of OB stars

摘要

Aims. Following the advent of increasingly sensitive X-rayobservatories, deep observations of early-type stars became possible.However, the results for only a few objects or clusters have until nowbeen reported and there has been no large survey comparable to thatbased upon the ROSAT All-Sky Survey (RASS). Methods. A limited survey of X-ray sources, consisting of all public XMM-Newtonobservations (2XMMi) and slew survey data (XMMSL1), is now available.The X-ray counterparts to hot, massive stars have been searched for inthese catalogs. Results. About 300 OB stars were detected with XMM-Newton.Half of them were bright enough for a spectral analysis to be possible,and we make available the detailed spectral properties that werederived. The X-ray spectra of O stars are represented well by low(<1keV) temperature components and seem to indicate that anabsorption column is present in addition to the interstellarcontribution. The X-ray fluxes are well correlated with the bolometricfluxes, with a scatter comparable to that of the RASS studies and thuslarger than found previously with XMM-Newton for some individual clusters. These results contrast with those of B stars that exhibit a large scatter in the relation, no additional absorption being found, and the fits indicate aplasma at higher temperatures. Variability (either within one exposureor between multiple exposures) was also investigated whenever possible:short-term variations are far more rare than long-term ones (the formeraffects a few percent of the sample, while the latter concerns betweenone third and two thirds of the sources). Conclusions. This paper presents the results of the firsthigh-sensitivity investigation of the overall high-energy properties ofa sizable sample of hot stars. Key words: X-rays: stars - stars: early-type - catalogs