Bibcode
Puls, J.; Kudritzki, R.-P.; Herrero, A.; Pauldrach, A. W. A.; Haser, S. M.; Lennon, D. J.; Gabler, R.; Voels, S. A.; Vilchez, J. M.; Wachter, S.; Feldmeier, A.
Referencia bibliográfica
Astronomy and Astrophysics, v.305, p.171
Advertised on:
1
1996
Revista
Número de citas
503
Número de citas referidas
409
Descripción
A new, very fast approximate method is presented to determine mass-loss
rates of O-stars from Halpha_ line profiles. The method uses
H and HeII departure coefficients from unified model atmospheres
parametrized in a simple way as function of wind velocity together with
photospheric NLTE line profiles as the inner boundary condition for a
numerically exact radiative transfer solution to derive a wind
contaminated Halpha_-profile. The method is also applied to
Hgamma_ to determine stellar gravities corrected for wind
emission. A detailed analytical discussion of Halpha_ line
formation in O-star winds is given and it is demonstrated that former
very simple approaches considering only optically thin wind emission
lead to significant systematic errors. Scaling relations and generalized
curves of growth are presented that connect mass-loss rate, terminal
velocity, stellar parameters and Halpha_ equivalent width.
The method is applied to samples of O-stars in the Galaxy, LMC and SMC
and mass-loss rates are derived from Halpha_ in combination
with terminal velocities measured from IUE and HST spectra. The results
reveal that a tight empirical relation exists between the radius
modified stellar wind momentum rate
˙(M)vinfinity_R_*_^0.5^ and the stellar luminosity. The
variations of this relationship between the Galaxy, LMC and SMC are
explained in terms of different abundances. Furthermore, for almost all
objects with dense winds (mostly supergiants), the commonly used
velocity field exponent β could be derived, indicating a typical
value of β=~1. A comparison with the improved theory of radiation
driven winds (as presented recently by Pauldrach et al. 1994) shows that
the observed wind momentum-luminosity relationship can be understood
qualitatively in terms of the theory. However, there exist significant
systematic discrepancies as a function of effective temperature,
luminosity class and wind performance number
η=˙(M)vinfinity_c/L. We stress that these
discrepancies would not have been detected with previous simplified
Halpha_ -approaches. The deficiencies of the theory are
discussed and suggestions for future improvements are made.