HD 148937: A MULTIWAVELENGTH STUDY OF THE THIRD GALACTIC MEMBER OF THE Of?p CLASS

Three Galactic O-type stars belong to the rare class of Of?p objects: HD 108, HD 191612, and HD 148937. The first two stars show a wealth of phenomena, including 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, HD 148937. Spectroscopic monitoring has revealed low-level variability in the Balmer and He ii λ4686 lines, but constancy at He i and C iii λ4650. The Hα line exhibits profile variations at a possible periodicity of ∼7 days. Model atmosphere fits yield T eff = 41000 ± 2000 K, log( g ) = 4.0 ± 0.1, M ☉ yr −1 , and an overabundance of nitrogen by a factor of 4. At X-ray wavelengths, HD 148937 resembles HD 108 and HD 191612 in having a thermal spectrum dominated by a relatively cool component ( kT = 0.2 keV), broad lines (⩾1700 km s −1 ), and an order-of-magnitude overluminosity compared to normal O stars (log[ L unabs X / L BOL ] ∼ −6).