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The last few decades have seen significant progress in our understanding of the occurrence of magnetic fields in stars with radiative envelopes, in particular in massive stars and in intermediate mass stars at early evolutionary stages. This book provides a comprehensive review of the most recent achievements in the measurements of stellar magnetic fields in O, B and A stars. These include the archetypes of stellar magnetism, the chemically peculiar Ap and Bp stars, O- and early B-type stars with their magnetospheres, accreting Herbig Ae/Be stars, Wolf-Rayet stars and high-mass X-ray binaries, among others. It provides an overview of the underlying physics for the interpretation of the data and identifies the requirements, both observational and theoretical, for improving our understanding of the origin of the magnetic fields in early-type stars. It aims to educate scientists working on stars, who are not yet experts in magnetic field studies, assuming that the reader is already familiar with basic terms and concepts of stellar astrophysics. Key Features Provides a comprehensive review of the field for researchers and students Gives an overview of the underlying physics for the interpretation of data Identifies requirements for understanding the origin of magnetic fields in early-type stars First research-level book on the topic Written by experts in the field of stellar magnetism
Laboratory astrophysics is the Rosetta Stone that enables astronomers to understand and interpret the distant cosmos. It provides the tools to interpret and guide astronomical observations and delivers the numbers needed to quantitatively model the processes taking place in space, providing a bridge between observers and modelers. IAU Symposium 350 was organized by the International Astronomical Union's Laboratory Astrophysics Commission (B5), and was the first topical symposium on laboratory astrophysics sponsored by the IAU. Active researchers in observational astronomy, space missions, experimental and theoretical laboratory astrophysics, and astrochemistry discuss the topics and challenges facing astronomy today. Five major topics are covered, spanning from star- and planet-formation through stellar populations to extragalactic chemistry and dark matter. Within each topic, the main themes of laboratory studies, astronomical observations, and theoretical modeling are explored, demonstrating the breadth and the plurality of disciplines engaged in the growing field of laboratory astrophysics.
This volume contains papers presented at IAU Colloquium No. 90. at the Crimean Astrophysical Observatory in May of 1985. A few additional contributions are included from authors who for various reasons were unable to attend the meeting. Four years have passed since the last major international conference on chemically peculiar stars of the upper main sequence was held in Liege. Belgium in 1981. Previous conferences were held in 1975 (Vienna. Austria) and in 1965 (Greenbelt. Maryland. USA). As the proceedings of this Colloquium show. the recent availability of ultraviolet spectra of large numbers of normal and chemically peculiar A and B stars is having a major impact on the way we study these objects. and has led to many new. exciting and unanticipated results. Simultaneously. the more traditional study of optical spectra has been advanced through the increasing use of very high spectral resolution with high signal-to-noise detectors. The chemically peculiar (CP) stars on the upper main sequence belong in the standard framework within which we understand stellar evolution and the history of matter. Recent work has made it clear that the unusual chemistry and magnetic structure of these objects is of relevance across the broad domain of stellar astronomy. from the upper main sequence to horizontal branch stars and white dwarfs. Metal poor (J>. Boo) as well as metal rich (Ap. Am) stars are an integral part of the picture.
To gain insight into the chemical and magnetic evolution of upper-main sequence stars, we have undertaken a study of magnetic Ap stars in nearby northern open clusters with well-determined ages. Using the MuSiCoS spectropolarimeter on the 2 m Bernard Lyot telescope at Pic du Midi observatory, high-resolution (R = 35,000), moderate to high S/N (50--700) circular polarisation spectra have been obtained for 11 Ap stars (HD 19805, HD 21699, HD 23387, HD 23408, HD 23850, HD 28319, HD 171586, HD 171782, HD 205116, HD 205117, HD 205073) proposed as members of 5 open clusters (M39, IC 4756, the Pleiades, alpha Per and the Hyades). We determined chemical abundances using spectral line synthesis, with each elemental abundance determined based on multiple spectral lines, with the typical abundance uncertainty being 0.2 dex. Longitudinal magnetic field strengtl-1s were determined using Least Squares Deconvolved Stokes V profiles; with a typical uncertainty of about 100 gauss. Finally, projected rotational velocities were determined for each star, with a typical precision of 2 km/s. During the course of this study it became apparent that many of the stars studied are not in fact magnetic chemically peculiar stars. Some stars appear to be chemically normal, others appear to be other classes of non-magnetic chemically peculiar stars. Ultimately, it was concluded that only two of the observed stars are in fact magnetic chemically peculiar stars. Is this interesting and surprising finding purely a result of misclassification in the archival data, or does this say something important about the occurrences of magnetic chemically peculiar stars in open clusters? We present the results of this study, discussing the implications and providing suggestions for future research.