This long-awaited graduate textbook, written by two pioneers of the field, is the first to provide a comprehensive introduction to the observations, theories and consequences of stellar winds. The rates of mass loss and the wind velocities are explained from basic physical principles. This book also includes chapters clearly explaining the formation and evolution of interstellar bubbles, and the effects of mass loss on the evolution of high- and low-mass stars. Each topic is introduced simply to explain the basic processes and then developed to provide a solid foundation for understanding current research. This authoritative textbook is designed for advanced undergraduate and graduate students and researchers seeking an understanding of stellar winds and, more generally, supersonic flows from astrophysical objects. It is based on courses taught in Europe and the US over the past twenty years and includes seventy problems (with answers) for coursework or self-study.

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We report on a 67 ks High-Energy Transmission Grating observation of the optically brightest early O star z Puppis (O4 f). Many resolved X-ray lines are seen in the spectra over a wavelength range of 5-25 Å . Chandra has sufficient spectral resolution to study the velocity structure of isolated X-ray line profiles and to distinguish the individual forbidden, intercombination, and resonance (fir) emission lines in several He-like ions, even where the individual components are strongly Doppler-broadened. In contrast to X-ray line profiles in other hot stars, z Pup shows blueshifted and skewed line profiles, providing the clearest and most direct evidence that the Xray sources are embedded in the stellar wind. The broader the line, the greater the blueward centroid shift tends to be. The N vii line at 24.78 Å is a special case, showing a flat-topped profile. This indicates that it is formed in regions beyond most of the wind attenuation. The sensitivity of the He-like ion fir lines to a strong UV radiation field is used to derive the radial distances at which lines of S xv, Si xiii, Mg xi, Ne ix, and O vii originate. The formation radii correspond well with a continuum optical depth of unity at the wavelength of each line complex, indicating that the X-ray line emission is distributed throughout the stellar wind. However, the S xv emission lines form deeper in the wind than expected from standard wind-shock models.

We present X-ray grating spectra of the recurrent nova RS Ophiuchi during its 2006 outburst, obtained with XMMNewton and Chandra. For the first month after optical maximum, the X-ray spectrum was hard and dominated by emission lines of H-like and He-like ions. The X-ray luminosity was 2:4 ; 10 36 ergs s À1 in the 0.33Y10 keV range. The spectra indicate a collisionally dominated plasma with a broad range of temperatures and an energy-dependent velocity structure. During an observation obtained in week 4, a soft X-ray flare occurred in which a new system of soft, higher velocity emission lines appeared in the spectrum. Then, during weeks 6Y10, the supersoft continuum of the hot white dwarf atmosphere was the dominant emission component. The X-ray luminosity reached at least 9 ; 10 37 ergs s À1 in the 0.2Y1 keV range, while the intrinsic nebular absorption decreased by a factor of 5 since the first observation. Preliminary model fitting indicates a white dwarf temperature of $800,000 K, and a mass of at least 1.2 M . Therefore, RS Oph may be an important Type Ia supernova progenitor. We show that the data are consistent with mass loss ending before day 54 of the outburst, and nuclear burning ending around day 69. A rapid decay in X-ray luminosity followed after week 10. The X-ray luminosity 5, 7, and 8 months after optical maximum dropped by more than 2 orders of magnitude. The spectra do not appear to be consistent with emission from an accretion disk.

We present a comprehensive study of X-ray emission and wind properties of massive magnetic early B-type stars. Dedicated XMM-Newton observations were obtained for three stars xi1 CMa, V2052 Oph, and zeta Cas. We report the first detection of X-ray emission from V2052 Oph and zeta Cas. The observations show that the X-ray spectra of our program stars are quite soft. We compile the complete sample of early B-type stars with detected magnetic fields to date and existing X-ray measurements, in order to study whether the X-ray emission can be used as a general proxy for stellar magnetism. We find that hard and strong X-ray emission does not necessarily correlate with the presence of a magnetic field. We analyze the UV spectra of five non-supergiant B stars with magnetic fields by means of non-LTE iron-blanketed model atmospheres. The latter are calculated with the PoWR code, which treats the photosphere as well as the the wind, and also accounts for X-rays. Our models accurately fit the stellar photospheric spectra in the optical and the UV. The parameters of X-ray emission, temperature and flux are included in the model in accordance with observations. We confirm the earlier findings that the filling factors of X-ray emitting material are very high. Our analysis reveals that the magnetic early type B stars studied here have weak winds. The mass-loss rates are significantly lower than predicted by hydrodynamically consistent models. We find that, although the X-rays strongly affect the ionization structure of the wind, this effect is not sufficient in reducing the total radiative acceleration. When the X-rays are accounted for at the intensity and temperatures observed, there is still sufficient radiative acceleration to drive stronger mass-loss than we empirically infer from the UV spectral lines. (abridged)Comment: 20 pages, accepted by MNRA

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The Chandra spectrum of Ori A shows emission lines from hydrogen-and helium-like states of Si, Mg, Ne, and O, along with N vii Ly and lines from ions in the range Fe xvii-Fe xxi. In contrast to the broad lines seen in Pup and Ori (850 AE 40 and 1000 AE 240 km s À1 half-width at half-maximum [HWHM], respectively), these lines are broadened to only 430 AE 60 km s À1 HWHM. This is much lower than the measured wind terminal velocity of 2000 km s À1. The forbidden, intercombination, and resonance (fir) lines from He-like ions indicate that the majority of the X-ray line emission does not originate at the base of the wind, in agreement with the standard wind shock models for these objects. However, in that model the X-ray emission is distributed throughout an expanding, X-ray-absorbing wind, and it is therefore surprising that the emission lines appear relatively narrow, unshifted, and symmetric. We compare the observed line profiles to recent detailed models for X-ray line profile generation in hot stars, but none of them offers a fully satisfactory explanation for the observed line profiles.