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

Y. Naze (1), N.R. Walborn (2), G. Rauw (1), F. Martins (3), A.M.T. Pollock (4), H.E. Bond (2)

1=IAGL, ULg, 2=STScI, 3=GRAAL, 4=ESA

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).

Reference: accepted by AJ
Status: Manuscript has been accepted

Weblink: http://arxiv.org/abs/0803.0605


Email: naze@astro.ulg.ac.be