Showing papers in "Annual Review of Astronomy and Astrophysics in 2000"
TL;DR: In this article, calibrated light curves of type Ia supernovae have become a major tool to determine the local expansion rate of the universe and also its geometrical structure, considerable atte
Abstract: ▪ Abstract Because calibrated light curves of type Ia supernovae have become a major tool to determine the local expansion rate of the universe and also its geometrical structure, considerable atte...
1,203 citations
TL;DR: Our understanding of the evolution of organic molecules and their voyage from molecular clouds to the early solar system and Earth has changed dramatically as discussed by the authors, and our understanding of molecular evolution has been changed dramatically.
Abstract: ▪ Abstract Our understanding of the evolution of organic molecules, and their voyage from molecular clouds to the early solar system and Earth, has changed dramatically. Incorporating recent observ...
877 citations
TL;DR: In this paper, the main physical effects to be considered in the building of evolutionary models of rotating stars on the Upper Main Sequence (MS) were reviewed, and the internal rotation of the stars was discussed.
Abstract: ▪ Abstract In this article we first review the main physical effects to be considered in the building of evolutionary models of rotating stars on the Upper Main-Sequence (MS). The internal rotation...
832 citations
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TL;DR: In this paper, a review of the analysis of stellar winds from O-stars, B-supergiants, and Central Stars of Planetary Nebulae with O-type spectra is presented.
Abstract: ▪ Abstract This review deals with the winds from “normal” hot stars such as O-stars, B- and A-supergiants, and Central Stars of Planetary Nebulae with O-type spectra. The advanced diagnostic methods of stellar winds, including an assessment of the accuracy of the determinations of global stellar wind parameters (terminal velocities, mass-loss rates, wind momenta, and energies), are introduced and scaling relations as a function of stellar parameters are provided. Observational results are interpreted in the framework of the stationary, one-dimensional (1-D) theory of line-driven winds. Systematic effects caused by nonhomogeneous structures, time dependence, and deviations from spherical symmetry are discussed. The review finishes with a brief description of the role of stellar winds as extragalactic distance indicators and as tracers of the chemical composition of galaxies at high redshift.
744 citations
TL;DR: The field of low-mass stars and substellar objects has progressed considerably, both from theoretic and experimental perspectives as mentioned in this paper, since the discovery of the first bona-fide brown dwarfs and extra-solar planets in 1995.
Abstract: ▪ Abstract Since the discovery of the first bona-fide brown dwarfs and extra-solar planets in 1995, the field of low-mass stars and substellar objects has progressed considerably, both from theoret...
580 citations
TL;DR: The end of at least one cable is connected to a float and the other end exerts a tractive effort on one or a number of collecting vehicles which land on the bottom at predetermined points with respect to the point of landing of the ballast.
Abstract: ▪ Abstract The first millisecond X-ray variability phenomena from accreting compact objects have recently been discovered with the Rossi X-ray Timing Explorer. Three new phenomena are observed from low-mass X-ray binaries containing low-magnetic-field neutron stars: millisecond pulsations, burst oscillations, and kilohertz quasi-periodic oscillations. Models for these new phenomena involve the neutron star spin and orbital motion close around the neutron star, and rely explicitly on our understanding of strong gravity and dense matter. I review the observations of these new neutron-star phenomena and some possibly related phenomena in black-hole candidates, and describe the attempts to use these observations to perform measurements of fundamental physical interest in these systems.
576 citations
TL;DR: In this paper, the authors identify fundamental differences between the profiles of radio-quiet and radio-loud sources as well as differences between high and low ionization lines, especially in the radioquiet majority of AGNs.
Abstract: ▪ Abstract Broad emission lines hold fundamental clues about the kinematics and structure of the central regions in AGN. In this article we review the most robust line profile properties and correlations emerging from the best data available. We identify fundamental differences between the profiles of radio-quiet and radio-loud sources as well as differences between the high- and low-ionization lines, especially in the radio-quiet majority of AGN. An Eigenvector 1 correlation space involving FWHM Hβ, W(FeIIopt)/W(Hβ), and the soft X-ray spectral index provides optimal discrimination between all principal AGN types (from narrow-line Seyfert 1 to radio galaxies). Both optical and radio continuum luminosities appear to be uncorrelated with the E1 parameters. We identify two populations of radio-quiet AGN: Population A sources (with FWHM(Hβ) 4000 km s−1, generally strong FeII emission and a soft X-ray excess) show almost no parameter space overlap with radio-loud sources. Population B shows optical properties...
465 citations
TL;DR: The discovery of counterparts in X-ray and optical to radio wavelengths has revolutionized the study of γ-ray bursts, until recently the most enigmatic of astrophysical phenomena as discussed by the authors.
Abstract: ▪ Abstract The discovery of counterparts in X-ray and optical to radio wavelengths has revolutionized the study of γ-ray bursts, until recently the most enigmatic of astrophysical phenomena. We now...
340 citations
TL;DR: In this paper, a combination of thermal bremsstrahlung and line emission was found to be the most likely mechanism for the X-ray emission in groups of galaxies, where the entire volume of groups was filled with a hot, low-density gas known as the intragroup medium.
Abstract: ▪ Abstract ROSAT observations indicate that approximately half of all nearby groups of galaxies contain spatially extended X-ray emission. The radial extent of the X-ray emission is typically 50–500 h−1100 kpc or approximately 10–50% of the virial radius of the group. Diffuse X-ray emission is generally restricted to groups that contain at least one early-type galaxy. X-ray spectroscopy suggests the emission mechanism is most likely a combination of thermal bremsstrahlung and line emission. This interpretation requires that the entire volume of groups be filled with a hot, low-density gas known as the intragroup medium. ROSAT and ASCA observations indicate that the temperature of the diffuse gas in groups ranges from approximately 0.3 keV to 2 keV. Higher temperature groups tend to follow the correlations found for rich clusters between X-ray luminosity, temperature, and velocity dispersion. However, groups with temperatures below approximately 1 keV appear to fall off the cluster LX-T relationship (and p...
312 citations
TL;DR: In this article, the authors explore the infrared emission of distant, high-redshift galaxies using the Infrared Space Observatory (ISO) satellite for the first time and reveal a wealth of detail about the nature of the energy source(s) and the physical conditions in galaxies.
Abstract: ▪ Abstract More than a decade ago the IRAS satellite opened the realm of external galaxies for studies in the 10 to 100 μm band and discovered emission from tens of thousands of normal and active galaxies With the 1995–1998 mission of the Infrared Space Observatory1, the next major steps in extragalactic infrared astronomy became possible: detailed imaging, spectroscopy, and spectrophotometry of many galaxies detected by IRAS, as well as deep surveys in the mid- and far-IR The spectroscopic data reveal a wealth of detail about the nature of the energy source(s) and about the physical conditions in galaxies ISO's surveys for the first time explore the infrared emission of distant, high-redshift galaxies ISO's main theme in extragalactic astronomy is the role of star formation in the activity and evolution of galaxies
310 citations
TL;DR: In this paper, the common envelope phase of binary star evolution plays an essential role in the formation of short period systems containing a compact object, and significant mass and angular mass of a binary star can play an important role in this process.
Abstract: ▪ Abstract The common envelope phase of binary star evolution plays an essential role in the formation of short period systems containing a compact object. In this process, significant mass and ang...
TL;DR: In this article, a review emphasizes the mass loss processes that affect the fates of single stars with initial masses between one and nine solar masses and finds that empirical relationships between mass loss rates and stellar parameters are determined mostly by selection effects and tell us which stars are losing mass rather than how stars lose mass.
Abstract: ▪ Abstract This review emphasizes the mass loss processes that affect the fates of single stars with initial masses between one and nine solar masses. Just one epoch of mass loss has been clearly demonstrated to be important for these stars; that is the episode that ends their evolution up the asymptotic giant branch. Quite a clear picture of this evolutionary stage is emerging from current studies. Mass loss rates increase precipitously as stars evolve toward greater luminosity and radius and decreased effective temperature. As a result, empirical relationships between mass loss rates and stellar parameters are determined mostly by selection effects and tell us which stars are losing mass rather than how stars lose mass. After detailed theoretical models are found to match observational constraints, the models may be used to extrapolate to populations not available for study nearby, such as young stars with low metallicity. The fates of stars are found to depend on both their initial masses and their ini...
TL;DR: The first confirmed brown dwarfs were announced in 1995 as discussed by the authors, due to a combination of increased sensitivity, better search strategies, and new means of distinguishing substellar from stellar objects.
Abstract: ▪ Abstract The brown dwarfs occupy the gap between the least massive star and the most massive planet. They begin as dimly stellar in appearance and experience fusion (of at least deuterium) in their interiors. But they are never able to stabilize their luminosity or temperature and grow ever fainter and cooler with time. For that reason, they can be viewed as a constituent of baryonic “dark matter.” Indeed, we currently have a hard time directly seeing an old brown dwarf beyond 100 pc. After 20 years of searching and false starts, the first confirmed brown dwarfs were announced in 1995. This was due to a combination of increased sensitivity, better search strategies, and new means of distinguishing substellar from stellar objects. Since then, a great deal of progress has been made on the observational front. We are now in a position to say a substantial amount about actual brown dwarfs. We have a rough idea of how many of them occur as solitary objects and how many are found in binary systems. We have ob...
TL;DR: The Hubble Space Telescope observations of the northern Hubble deep field, and more recently its counterpart in the south, provide detections and photometry for stars and field galaxies as discussed by the authors, which is the basis for our work.
Abstract: ▪ Abstract The Hubble space telescope observations of the northern Hubble deep field, and more recently its counterpart in the south, provide detections and photometry for stars and field galaxies ...
TL;DR: The understanding of fine features of the structure and evolution of stars has become possible as a result of enormous progress made in the acquisition of high-quality high-qu....
Abstract: ▪ Abstract During the last decade, the understanding of fine features of the structure and evolution of stars has become possible as a result of enormous progress made in the acquisition of high-qu...
TL;DR: A very fortunate career in astronomy, benefiting greatly from numerous accidents of fate, can be found in this paper, where the authors describe their experiences in the field of astronomy and astrophysics.
Abstract: ▪ Abstract I have had a very fortunate career in astronomy, benefiting greatly from numerous accidents of fate. I grew up in Cincinnati, Ohio, served in the US Army Air Force in World War II, and had all my further education at the University of Chicago, from PhB in the College to PhD in astronomy and astrophysics. There, as a postdoc at Princeton University, and as a young faculty member at Caltech and Mount Wilson and Palomar Observatories, I had excellent teachers and mentors. I have done research primarily on gaseous nebulae and active galactic nuclei, but also made a few early contributions on stellar interiors and the heating in the outer layers of the Sun. The major part of my scientific career was at the University of Wisconsin and Lick Observatory, but I also had three productive years at the Institute for Advanced Study.
TL;DR: Using state-of-the-art spectrographs, photometers, spectrometers and infrared detectors, the Palomar astronomers investigated the spectra of stars, interstellar matter, AGNs and quasars in great detail as discussed by the authors.
Abstract: ▪ Abstract We review the research on a wide variety of topics using data obtained with the 200-inch Hale telescope. Using state-of-the-art spectrographs, photometers, spectrometers and infrared detectors, the Palomar astronomers investigated the spectra of stars, interstellar matter, AGNs and quasars in great detail. Spectral resolutions ranged from 1000 A for broad-band photometry to 0.04 A using interferometric techniques.