Spectral analyses of 19 Wolf-Rayet (WN) stars in the LMC.
Abstract
The helium spectra of 19 Wolf-Rayet stars in the Large Magellanic Cloud are analyzed, and their luminosities, radii, temperatures and mass-loss rates are determined. The sample covers different subtypes of the nitrogen (WN) sequence. The analyses are based on multi-level non-LTE model calculations for the spectrum formation in spherically expanding stellar atmospheres, composed of pure helium. The results are compared with a Galactic sample analyzed previously with the same methods. The stellar temperatures obtained for the LMC stars are similar to those of Galactic stars. The "late" subtypes (WNL) form a homogeneous group with T about 30 kK, while the temperatures of WNE-s stars ("early" subtypes with strong lines) range from 50 kK to 90 kK. The LMC stars tend to lower luminosities (10^4.8^ to 10^5.6^ L_sun_) than our Galactic sample, which might be a real trend irrespective of selection effects. Terminal wind velocities and mass-loss rates do not show systematic differences between LMC and Galaxy when stars of same subtypes are compared. Such differences, however, would be expected as an effect of the different metallicities if the winds were driven by radiation pressure. The mechanical momentum in the winds exceeds the single- scattering limit by a large factor (up to 50). The evolutionary status of the WR stars is discussed by comparing their positions in the HR diagram with the theoretically predicted tracks for post-red-supergiant evolution. Although recent calculations now show some general agreement, the predicted luminosities are still higher than observed, especially for the LMC stars.
- Publication:
-
Astronomy and Astrophysics
- Pub Date:
- August 1991
- Bibcode:
- 1991A&A...248..166K
- Keywords:
-
- Astronomical Spectroscopy;
- Magellanic Clouds;
- Spectrum Analysis;
- Stellar Spectra;
- Wolf-Rayet Stars;
- Helium;
- Hertzsprung-Russell Diagram;
- Stellar Atmospheres;
- Stellar Evolution;
- Stellar Models;
- Astrophysics