Astronomy and Astrophysics – Astronomy
Scientific paper
Mar 1995
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1995a%26a...295...75k&link_type=abstract
Astronomy and Astrophysics (ISSN 0004-6361), vol. 295, no. 1, p. 75-100
Astronomy and Astrophysics
Astronomy
58
Magellanic Clouds, Metallicity, Stellar Evolution, Stellar Mass Ejection, Wolf-Rayet Stars, Abundance, Emission Spectra, Iue, Line Spectra, Spectrum Analysis, Stellar Magnitude, Stellar Spectrophotometry, Ultraviolet Astronomy
Scientific paper
We present optical spectrophotometry for five WO Wolf-Rayet stars, three of them in our own Galaxy and one in each of the Small Magellanic Cloud (SMC) and Large Magellanic Cloud (LMC). IUE ultraviolet spectrophotometry has also been obtained for the two Magellanic Cloud WO stars, including a high resolution spectrum for one of them. Quantitative spectral typing criteria are defined for WO subtypes spanning WO1 to WO5 and, for the case of the two WO stars in spectroscopic binaries, spectral types for the O-type primaries are derived. From our spectrophotometry we derive reddenings and magnitudes for each star. Absolute visual magnitudes of -2.5 and -1.8 are derived for a WO4 star and for a WO2 star, respectively, each star lying at a known distance. Wind terminal velocities ranging from 4200 km/s to 5500 km/s are derived from the black absorption edge of an ultraviolet P Cygni profile and from the full width at zero intensity (FWZI) of strong optical emission lines. The relative abundances of helium, carbon and oxygen in the winds of each of the WO stars are derived using a recombination theory analysis of selected ultraviolet and optical emission lines to determine the ionic abundances of He(2+), C(4+), O(4+), O(5+), and O(6+). The derived abundance ratios show relatively narrow ranges. C/He number ratios of 0.51 - 0.52 are derived for two Galactic WO stars and one LMC WO star, with their C/O ratios ranging between 4.6 and 5.2, and their (C+O)/He ratios equal to 0.62. The one SMC WO star has a C/He ratio of 0.81, a C/O ratio of 2.7 and a (C+O)/He number ratio of 1.10. These abundance ratios are broadly consistent with evolutionary models for the advanced stages of massive stars, and promising agreement as a function of initial metallicity is found with the most recent evolutionary models.
Barlow Michael J.
Kingsburgh Robin L.
Storey Peter J.
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