Axi-symmetric models of B[e] supergiants

I. The effective temperature and mass-loss dependence of the hydrogen and helium ionization structure

¹ Dept. of Physics and Astronomy, University of Pittsburgh, 3941 O'Hara St., Pittsburgh, PA 15260, USA e-mail: jzsargo@astro.phyast.pitt.edu
² Instituto de Astronomia, Universidad Nacional Autonoma de Mexico (UNAM), CD. Universitaria, Apartado Postal 70-264, 04510, México DF, México

Received: 17 July 2007
Accepted: 21 November 2007

Abstract

Aims.We calculate the hydrogen and helium ionization in B[e] envelopes and explore their dependence on mass-loss and effective temperature. We also present simulated observations of the Hα emission line and the  1550 doublet, and study their behavior. This paper reports our first results in an ongoing study of B[e] supergiants, and provides a glimpse on the ionization of the most important elements in self-consistent numerical simulations.

Methods.Our newly developed 2D stellar atmosphere code, ASTAROTH, was used for the numerical simulations. The code self-consistently solves for the continuum radiation, non-LTE level populations, and electron temperature in axi-symmetric stellar envelopes. Observed profiles were calculated by an auxiliary program developed separately from ASTAROTH.

Results.In all but one of our models, H remained fully ionized – only for  > 10 yr^-1 and T_eff ≤ 18 000 K did we obtain a neutral H disk, and then only for radii beyond . Due to ionizations from excited states it is much more difficult to get a H neutral disk than indicated by previous analytical calculations. Near the poles, the ionization is high in all models, while helium recombined in the equatorial regions for all but our lowest mass-loss rate (10 yr^-1). Although the model parameters were not adjusted to provide fits to any particular star, the theoretical profiles show some features seen in the profiles of R126. These include the partially resolved double peaked profile of Hα, and the weak emission associated with the UV C iv resonance line.