High-resolution X-ray spectroscopy of the magnetic Of?p star HD148937

TL;DR

This study presents high-resolution X-ray spectra of the magnetic star HD148937, revealing details about its plasma temperature, origin, and magnetic confinement, and compares it with similar stars to understand magnetic effects on stellar X-ray emission.

Contribution

First high-resolution X-ray spectral analysis of HD148937 combining Chandra and XMM data, revealing plasma properties and magnetic influence on X-ray emission.

Findings

Hot plasma is multi-thermal with several origins.

X-ray emission forms about one stellar radius above the photosphere.

HD148937 is less extreme than the prototype magnetic star θ¹ Ori C.

Abstract

High-resolution data of the peculiar magnetic massive star HD148937 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 800km/s), 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 0.6keV 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 $\theta^1$\,Ori\,C. Both stars thus share many similarities, but HD148937 appears less extreme than $\theta^1$\,Ori\,C despite having also a large magnetic confinement parameter.