Catálogo de publicaciones - revistas

<jats:p> <jats:bold>American Astronomy.</jats:bold> Community, Careers, and Power, 1859-1940. JOHN LANKFORD, with Ricky L. Slavings. University of Chicago Press, Chicago, 1997. xxvi, 447 pp., illus. $65 or £51.95. ISBN 0-226-46886-0. </jats:p>

<jats:p> <jats:bold>Shadow of a Star.</jats:bold> The Neutrino Story of Supernova 1987A. ALFRED K. MANN. Freeman, New York, 1997. xiv, 210 pp., illus., + plates. $22.95. ISBN 0-7167-3097-9. </jats:p>

<jats:p>Brown dwarfs are objects with masses between that of stars and planets. Postulated some three decades ago, they remained elusive until recently. Unlike stars, these objects have no sustained energy source and cool as they age. One such cool brown dwarf has been discovered as a companion to a nearby star. The spectrum of this object is similar to that of Jupiter. Single brown dwarfs have been detected in stellar nurseries. Ongoing and planned efforts, from both ground and space, will enable astronomers to decisively determine the population of these elusive and dim objects.</jats:p>

<jats:p>As stars are created by the gravitational contraction of knots in giant interstellar clouds, they shed angular momentum and magnetic and gravitational energy in an interplay of complex circumstellar structures: swirling disks, fast collimated jets, and shock waves in the surrounding cloud. Many of these structures were inferred a decade ago from ground-based telescope observations. The high resolution of the Hubble Space Telescope and other instruments has now revealed these circumstellar regions in great detail, showing features never before imagined. In the Orion Nebula alone, examples of all types of interactions between young stars and their environment can be seen simultaneously, highlighting circumstellar dynamics in sharp relief in one of astronomy’s most famous objects.</jats:p>

<jats:p>The development of new observational, experimental, and computational technologies is changing our understanding of the origins of the elements by thermonuclear burning in stars. Gamma-ray lines from newly made radioactive nuclei have been identified using instruments onboard low-Earth orbiting satellites. Grains in meteorites have isotopic anomalies which suggest that the grains were put together in a stellar explosion such as a supernova. Computer simulations allow such anomalies to be used to probe how these events happen. The simulations are being independently tested by experiments with high-energy density lasers. These developments are beginning to provide a quantitative diagnostic of galactic evolution, and of the epoch of formation of the first stars and galaxies.</jats:p>

<jats:p>To investigate the formation and early evolution of stars, astronomers study the x-ray emission of T Tauri stars, which are young, solar-mass stars called pre–main sequence stars. Two Earth-orbiting x-ray satellites, the Röntgen X-ray Satellite (ROSAT) and the Advanced Satellite for Cosmology and Astrophysics (ASCA), have discovered x-ray emission from young protostars, called Class I objects. Many T Tauri stars were detected as x-ray sources by ROSAT. X-ray luminosity functions and correlations with other stellar parameters can be studied and used to investigate the x-ray emission mechanism. From the ROSAT data hundreds of T Tauri stars have been discovered, some of which are located outside regions of ongoing star formation. Stellar x-rays also irradiate circumstellar disks, regions where planets may form, so x-ray emission data from T Tauri stars may also be used to investigate the formation of planets.</jats:p>

<jats:p>Globular clusters form homogeneous populations of stars. On the one hand, because initial conditions are homogeneous within one cluster but vary from cluster to cluster, their study can shed light on stellar evolution processes. On the other hand, globular clusters contain the oldest known stellar population in galaxies. The study of the characteristics of globular cluster systems is one way to understand parent galaxy formation and early evolution. Unfortunately, a direct observation of the time when globular clusters and galaxies formed is still out of reach for today’s telescopes, but this remains a major goal.</jats:p>