High-resolution X-Ray Spectroscopy of the Magnetic Of?p Star HD 148937

Naze, Y.; Zhekov, S. A.; Walborn, N. R.
The Astrophysical Journal, Volume 746, Issue 2, article id. 142, 8 pp. (2012).


High-resolution data of the peculiar magnetic massive star HD 148937 were obtained with Chandra-HETGS, and are presented here in combination with a re-analysis of the older XMM-RGS data. The lines of the high-Z elements (Mg, Si, S) were found to be unshifted and relatively narrow (FWHM of about 800 km s-1), i.e., narrower than the O line recorded by RGS, which possibly indicates that the hot plasma is multi-thermal and has several origins. These data further indicate a main plasma temperature of about 0.6 keV and a formation of the X-ray emission at about one stellar radius above the photosphere. From the spectral fits and the H-to-He line ratios, the presence of very hot plasma is, however, confirmed, though with a smaller relative strength than for the prototype magnetic oblique rotator θ1 Ori C. Both stars thus share many similarities, but HD 148937 appears less extreme than θ1 Ori C despite also having a large magnetic confinement parameter.