Issue |
A&A
Volume 435, Number 2, May IV 2005
|
|
---|---|---|
Page(s) | 669 - 698 | |
Section | Stellar atmospheres | |
DOI | https://doi.org/10.1051/0004-6361:20042365 | |
Published online | 29 April 2005 |
Atmospheric NLTE-models for the spectroscopic analysis of blue stars with winds
II. Line-blanketed models
1
Universitäts-Sternwarte München, Scheinerstrasse 1, 81679 München, Germany e-mail: uh101aw@usm.uni-muenchen.de
2
Institute for Astronomy, University of Hawaii at Manoa, 2680 Woodlawn Drive, Honolulu, Hawaii 96822, USA e-mail: urbaneja@ifa.hawaii.edu
3
Facultad de Ciencias Astronómicas y Geofísicas, Universidad Nacional de La Plata, Paseo del Bosque s/n, B1900FWA La Plata, Argentina e-mail: roberto@fcaglp.unlp.edu.ar
4
BT (Germany) GmbH & Co. oHG, Barthstr. 22, 80339 München, Germany e-mail: uwe@springmann.net
5
Astronomical Institute “Anton Pannekoek”, Kruislaan 403, 1098 SJ Amsterdam, The Netherlands e-mail: mokiem@science.uva.nl
Received:
15
November
2004
Accepted:
6
February
2005
We present new or improved methods for calculating NLTE, line-blanketed
model atmospheres for hot stars with winds (spectral types A to O), with
particular emphasis on fast performance. These
methods have been implemented into a previous, more simple version of the
model atmosphere code Fastwind (Santolaya-Rey et al. 1997) and allow us to
spectroscopically analyze large samples of massive stars in a
reasonable time-scale, using state-of-the-art physics. Although this updated
version of the code has already been used in a number of recent
investigations, the corresponding methods have not been explained in detail
so far, and no rigorous comparison with results from alternative codes has
been performed. This paper intends to address both topics.
In particular, we describe our (partly approximate) approach to solve the
equations of statistical equilibrium for those elements that are primarily
responsible for line-blocking and blanketing, as well as an approximate
treatment of the line-blocking itself, which is based on a simple statistical
approach using suitable means of line opacities and emissivities. Both
methods are validated by specific tests. Furthermore, we comment on our
implementation of a consistent temperature structure.
In the second part, we concentrate on a detailed comparison with results
from two codes used in alternative spectroscopical investigations, namely
cmfgen (Hillier & Miller 1998) and wm-Basic (Pauldrach et al. 2001). All
three codes predict almost identical temperature structures and fluxes for
400 Å, whereas at lower wavelengths a number of discrepancies
are found. Particularly in the Heii continua, where fluxes and
corresponding numbers of ionizing photons react extremely sensitively to
subtle differences in the models, we consider any uncritical use of these
quantities (e.g., in the context of nebula diagnostics) as unreliable.
Optical H/He lines as synthesized by fastwind are compared with
results from cmfgen, obtaining a remarkable coincidence, except for
the Hei singlets in the temperature range between 36 000 to 41 000 K for
dwarfs and between 31 000 to 35 000 K for supergiants, where cmfgen
predicts much weaker lines. Consequences of these discrepancies are
discussed.
Finally, suggestions are presented as to adequately parameterize
model-grids for hot stars with winds, with only one additional
parameter compared to standard grids from plane-parallel, hydrostatic models.
Key words: methods: numerical / line: formation / stars: atmospheres / stars: early-type / stars: mass-loss
© ESO, 2005
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