Contributed Talk - Splinter HotStars
Spectroscopic Evidence for Weaker Clumping and X-ray Emission Cool B-Supergiants
Bernini-Peron M., Sander A. A. C., Marcolino W. L. F., Bouret J-.,C.
After starting their lives as O dwarfs, massive stars quickly evolve off the main sequence towards cooler temperatures. Connecting hot evolutionary stages with the cold supergiants, we find the B supergiants (BSGs), which lie at the cool end of the line-driven wind regime. Studying them is paramount to improve our knowledge about the physics of hot stellar winds and high-mass stellar evolution. In my talk, I will present new analyses of BSGs with temperatures below the so-called Bi-Stability jump (Teff < 21 kK, cooler than B1). These objects are much less studied and understood than their hotter counterparts. We modeled their atmospheres and spectra using the stellar atmosphere codes CMFGEN and PoWR. By including clumping and X-rays in the wind, we overcome previous problems in the spectral modeling of these stars (especially in the UV). Besides obtaining the stellar parameters, our results indicate that both clumping and X-rays need to be taken into account for cooler BSGs, even though on different levels than what is usually assumed for O and early BSGs. For our targets, we derive X-ray luminosities lower than the usually assumed ratio of 10^-7 between L_x and L_bol in galactic OB stars. Our findings are in line with present upper limits for X-rays in cooler BSGs, but they also show that X-rays cannot be neglected for these objects. The obtained clumping parameters further reveal significantly smoother winds in our targets than obtained for hotter OB stars. This confirms recent predictions from hydrodynamical simulations. We finish by discussing the potential consequences of our study for high-mass stellar evolution.