The first X-ray survey of Galactic luminous blue variables

Abstract

Aims: The X-ray emission of massive stars has been studied when these objects are in their main-sequence phase, as well as when they are in their Wolf-Rayet phase. However, the X-ray properties of the transitional luminous blue variable (LBV) phase remain unknown.
Methods: Using a dedicated but limited XMM-Newton survey and archival XMM-Newton and Chandra observations, we performed the first X-ray survey of LBVs: about half of the known LBVs or candidate LBVs were studied.
Results: Apart from the well known X-ray sources eta Car and Cyg OB2 #12, four additional LBVs are detected in this survey, though some doubt remains on the association with the X-ray source for two of these. For the other LBVs, upper limits on the flux were derived, down to log [L_X/L_BOL] - 9.4 for P Cyg. This variety in the strength of the X-ray emission is discussed, with particular emphasis on the potential influence of binarity.

Based on observations collected with XMM-Newton, an ESA Science Mission with instruments and contributions directly funded by ESA Member States and the USA (NASA), and with Chandra.