Modeling the near-infrared lines of O-type stars

¹ Astronomical Institute “Anton Pannekoek", Kruislaan 403, 1098 SJ Amsterdam, The Netherlands
² Institut für Astronomie und Astrophysik, Universitätssternwarte, Scheinerstr. 1, 81679 München, Germany

Corresponding author: A. Lenorzer, lenorzer@astro.uva.nl

Received: 30 January 2004
Accepted: 30 March 2004

Abstract

We use a grid of 30 line-blanketed unified stellar photosphere and wind models for O-type stars; computed with the code cmfgen in order to evaluate its potential in the near-infrared spectral domain. The grid includes dwarfs, giants and supergiants. We analyse the equivalent width behaviour of the 20 strongest lines of hydrogen and helium in spectral windows that can be observed using ground-based instrumentation and compare the results with observations. Our main findings are that: i) / line ratios in the J, H and K bands correlate well with the optical ratio employed in spectral classification, and can therefore be used to determine the spectral type; ii) in supergiant stars the transition from the stellar photosphere to the wind follows a shallower density gradient than the standard approach followed in our models, which can be mimicked by adopting a lower gravity in our prescription of the density stratification; iii) the Brγ line poses a number of peculiar problems which might partly be related to wind clumping; and iv) the Brα line is an excellent mass-loss indicator. For the first and last item we provide quantitative calibrations.