Slow hydrodynamic regime to model the wind of B supergiant stars

VENERO, R.; HAUCKE, M.; CURÉ, M.; CIDALE, L.

San Juan

Congreso; 59º Reunión Anual de la Asociación Argentina de Astronomía; 2016

Icate - Conicet - UNSJ

In the spectra of B supergiants (Bsg) there are clear evidences of a widediversity of winds, which show notable dierences even in stars with thesame eective temperatures. These winds are driven by the transfer of ra-diation momentum in metal line transitions, a phenomenon which was rstmodelled by Castor et al. (1975) in the so-called CAK theory. The hydrody-namic solution they found, known as the fast solution, is obtained by solvingthe momentum equations for a parameterization of the line-force (Abbott,1982) with three parameters: k, Alpha and Delta. These parameters represent theeective number of lines driving the wind, the opacity of the lines and theionization stratication, respectively. Cure (2004) and Cure et al. (2011) discovered two new solution in 1-D models conned to the equatorial plane of a rotating star. These are the Omega-slow solution (for stars with high values of Omega, i.e. the quotient between the rotational speed and the critical velocity) and the Delta-slow solution (for high values of parameter Delta, i.e., high ionization rates), which exists even in a non-rotating case. Both slow solutions lead to slower winds, with higher, similar, or even lower mass-loss rate (M) than in the fast solution case.Recently Venero et al (2016) explored the domains of these solution regimesand found a clear boundary between the fast and the slow regimes. Thisboundary consists in a well-defined gap in parameter space, where nostationary solution is found. Venero et al. (2016) tested models inside the gap with the code Zeus-3D (Clarke, 2010), and found a non-stationary solution with the form of a blend between both adjacent regimes. The location and width, in a Delta scale, of the gap strongly depend on the rotation rate.In this work we compute hydrogen line proles for the slow regime, in orderto check the ability of this kind of solution to represent the wind of Bsupergiants. The synthetic line proles are calculated by mean of the well-known NLTE model atmosphere code FASTWIND (Puls et al., 2005, andreferences therein). With this analysis we expect to obtain new insights onthe physical conditions of the wind of early supergiants.