New mass-loss rates of B supergiants from global wind models Jiri Krticka$^1$, Jiri Kubat$^2$, Iva Krtickova$^1$ 1 - Masaryk University, Brno, Czech Republic 2 - Astronomical Institute, Ondrejov, Czech Republic Massive stars lose a significant fraction of mass during their evolution. However, the corresponding mass-loss rates are rather uncertain, especially for evolved stars. To improve this, we calculated global line-driven wind models for Galactic B supergiants. Our models predict radial wind structure and particularly the mass-loss rates and terminal velocities directly from basic stellar parameters. The hydrodynamic structure of the flow is consistently determined from the photosphere in nearly hydrostatic equilibrium to supersonically expanding wind. The radiative force is derived from the solution of the radiative transfer equation in the comoving frame. We provide a simple formula that predicts theoretical mass-loss rates as a function of stellar luminosity and effective temperature. The mass-loss rate of B supergiants slightly decreases with temperature down to about 22.5 kK, where the region of recombination of Fe IV to Fe III starts to appear. In this region, which is about 5 kK wide, the mass-loss rate gradually increases by a factor of about 6. The increase of the mass-loss rate is associated with a gradual decrease of terminal velocities by a factor of about 2. We compared the predicted wind parameters with observations. While the observed wind terminal velocities are reasonably reproduced by the models, the situation with mass-loss rates is less clear. The mass-loss rates derived from observations that are uncorrected for clumping are by a factor of 3 to 9 higher than our predictions on cool and hot sides of the studied sample, respectively. These observations can be reconciled with theory assuming a temperature-dependent clumping factor that is decreasing toward lower effective temperatures. On the other hand, the mass-loss rate estimates that are not sensitive to clumping agree with our predictions much better. Our predictions are by a factor of about 10 lower than the values currently used in evolutionary models appealing for reconsideration of the role of winds in the stellar evolution. Reference: Astronomy & Astrophysics, in press Status: Manuscript has been accepted Weblink: https://arxiv.org/abs/2101.04973 Comments: Email: krticka@physics.muni.cz --- Submitted on Thu Jan 14 2:45:48 CST 2021------------------------- Particle acceleration and non-thermal emission in colliding-wind binary systems J. M. Pittard$^1$, G. E. Romero$^2$, G. S. Vila$^2$ 1 - School of Physics and Astronomy, The University of Leeds, UK 2 - Instituto Argentino de Radioastronomia, La Plata, Argentina We present a model for the creation of non-thermal particles via diffusive shock acceleration in a colliding-wind binary. Our model accounts for the oblique nature of the global shocks bounding the wind-wind collision region and the finite velocity of the scattering centres to the gas. It also includes magnetic field amplification by the cosmic ray induced streaming instability and the dynamical back reaction of the amplified field. We assume that the injection of the ions and electrons is independent of the shock obliquity and that the scattering centres move relative to the fluid at the Alfven velocity (resulting in steeper non-thermal particle distributions). We find that the Mach number, Alfvenic Mach number, and transverse field strength vary strongly along and between the shocks, resulting in significant and non-linear variations in the particle acceleration efficiency and shock nature (turbulent vs. non-turbulent). We find much reduced compression ratios at the oblique shocks in most of our models compared to our earlier work, though total gas compression ratios that exceed 20 can still be obtained in certain situations. We also investigate the dependence of the non-thermal emission on the stellar separation and determine when emission from secondary electrons becomes important. We finish by applying our model to WR 146, one of the brightest colliding wind binaries in the radio band. We are able to match the observed radio emission and find that roughly 30 per cent of the wind power at the shocks is channelled into non-thermal particles. Reference: MNRAS, in press Status: Manuscript has been accepted Weblink: https://arxiv.org/abs/2104.07399 Comments: Email: j.m.pittard@leeds.ac.uk --- Submitted on Mon Apr 19 4:13:09 CDT 2021-------------------------