HD148937: a multiwavelength study of the third Galactic member of the Of?p class

TL;DR

This study provides the first detailed optical and X-ray analysis of the rare Galactic Of?p star HD148937, revealing its spectral variability, physical parameters, and X-ray properties, contributing to understanding this unique stellar class.

Contribution

It offers the first comprehensive multiwavelength characterization of HD148937, expanding knowledge of Of?p stars and their magnetic and X-ray phenomena.

Findings

Spectroscopic monitoring shows low-level variability and possible 7-day periodicity.

Model fits indicate T_eff=41000K, log(g)=4.0, nitrogen overabundance.

X-ray spectrum is thermal, cool, broad-lined, and overluminuous compared to normal O stars.

Abstract

Three Galactic O-type stars belong to the rare class of Of?p objects: HD108, HD191612, and HD148937. The first two stars show a wealth of phenomena, including magnetic fields and strong X-ray emission, light variability, and dramatic periodic spectral variability. We present here the first detailed optical and X-ray study of the third Galactic Of?p star, HD148937. Spectroscopic monitoring has revealed low-level variability in the Balmer and HeII4686 lines, but constancy at HeI and CIII4650. The Ha line exhibits profile variations at a possible periodicity of ~7d. Model atmosphere fits yield T_{eff}=41000+-2000K, log(g)=4.0+-0.1, Mdot_{sph}<~ 10^{-7}Msol/yr and a surabondance of nitrogen by a factor of four. At X-ray wavelengths, HD148937 resembles HD108 and HD191612 in having a thermal spectrum dominated by a relatively cool component (kT=0.2keV), broad lines (>1700km/s), and an order-of-magnitude overluminosity compared to normal O stars (log [L_X^unabs/L_BOL] ~ -6).