Abstract
We present a review of UV observations of massive stars and their analysis. We discuss O stars, luminous blue variables, and Wolf–Rayet stars. Because of their effective temperature, the UV (912−3200 Å) provides invaluable diagnostics not available at other wavebands. Enormous progress has been made in interpreting and analysing UV data, but much work remains. To facilitate the review, we provide a brief discussion on the structure of stellar winds, and on the different techniques used to model and interpret UV spectra. We discuss several important results that have arisen from UV studies including weak-wind stars and the importance of clumping and porosity. We also discuss errors in determining wind terminal velocities and mass-loss rates.
Highlights
According to Wien’s Law, the peak of a star’s energy distribution occurs in the UV for a star whose temperature exceeds 10,000 K
Analysis of X-ray profiles indicates that they originate in the stellar wind (e.g., [75]), and that the implied mass-loss rate is lower than that derived using density-squared diagnostics at other wavelengths (e.g., [76])
In many massive stars much of the flux is emitted in the extreme ultraviolet (EUV) shortward of This region is responsible for supplying much of the momentum used to the Lyman limit at 911Å
Summary
According to Wien’s Law, the peak of a star’s energy distribution occurs in the UV for a star whose temperature exceeds 10,000 K. ∼2000 km s−1 , signifying that the giants and supergiants were losing mass in a stellar wind [2] Spectral lines exhibiting both emission and blueshifted absorption are classified as P Cgyni profiles ([3] and Figure 1). WNh stars may still be core hydrogen burning (e.g., [16,17]) These massive stars show strong emission lines in their optical spectra because of their high luminosities. These include: the importance of the UV for mass-loss determinations (Section 5.1), observations of the extreme ultraviolet (Section 5.2), weak winds (Section 5.3), superions (Section 5.4), non Galactic/Magellanic studies (Section 5.5), and the iron forest (Section 5.6). We discuss accuracies in V∞ (Section 7.1) and mass-loss rates measured from UV spectra (Section 7.2)
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