scholarly journals Radio Observations of Be Stars: (Review Paper)

1976 ◽  
Vol 70 ◽  
pp. 157-164 ◽  
Author(s):  
C. R. Purton
Keyword(s):  
Radio Emission ◽  
Radio Astronomy ◽  
Review Paper ◽  
Be Stars ◽  
Radio Observations ◽  
The Past ◽  
Be Star ◽  
Radio Stars

During the past few years the search for radio stars has been both intensive and extensive, and Be stars are among the various types of objects which have been examined. A large number of Be stars have not been detected, and to date no classical Be star has been found to emit detectable amounts of radio emission. However, following the tradition of radio astronomy to emphasise the abnormal or extreme cases, radio emission has been observed which is associated with a few peculiar Be stars.

scholarly journals X-Ray Observations of B-Emission Stars (Review Paper)

1987 ◽  
Vol 92 ◽  
pp. 291-308 ◽  
Author(s):  
E.P.J. van den Heuvel ◽  
S. Rappaport
Keyword(s):  
Review Paper ◽  
Circumstellar Disks ◽  
Close Binaries ◽  
Be Stars ◽  
X Ray ◽  
Blue Stragglers ◽  
Galactic Clusters ◽  
Be Star ◽  
Emission Stars ◽  
X Ray Binaries

Most evidence on X-ray emission from the vicinity of Be stars concerns the Be/X-ray binaries. Presently some 20 of these systems are known, making them the most numerous class of massive X-ray binaries. Evidence for the binary nature of these systems comes from (i) Doppler modulation of X-ray pulse periods, (ii) periodic X-ray flaring behavior, and (iii) correlated optical and X-ray variability. The correlation between X-ray pulse period and orbital period found by Corbet (1984) can potentially provide important information on the densities and velocities in the circumstellar disks of Be stars.Evolutionary models indicate that the Be/X-ray binaries represent a later stage in the evolution of normal close binaries with initial primary masses predominantly in the the range 8 to 15 M⊙ . These models indicate that also a class of slightly less massive Be star binaries should exist in which the compact companions are white dwarfs. Be-type blue stragglers in galactic clusters may be such systems.

scholarly journals Magnetic Fields in Be Stars? (Review Paper)

1987 ◽  
Vol 92 ◽  
pp. 38-48
Author(s):  
Paul K. Barker
Keyword(s):  
Magnetic Fields ◽  
Field Strength ◽  
Review Paper ◽  
Stellar Winds ◽  
Be Stars ◽  
Circumstellar Envelopes ◽  
Star Models ◽  
Upper Limits ◽  
Be Star

AbstractNo mean longitudinal or toroidal magnetic fields have yet been detected on any classical Be star. Models of stellar winds and circumstellar envelopes around magnetic Be stars are not appreciably constrained by present observed upper limits on field strength. A few magnetic Be stars do exist among the helium strong stars, but these objects show spectral phenomenology which is unmistakably distinct from that shown by every other object known as a Be star.

scholarly journals Models for the Circumstellar Envelopes of Be Stars: (Review Paper)

1976 ◽  
Vol 70 ◽  
pp. 335-370 ◽  
Author(s):  
J. M. Marlborough
Keyword(s):  
Ad Hoc ◽  
Review Paper ◽  
Circumstellar Matter ◽  
Be Stars ◽  
Circumstellar Envelopes ◽  
Structure And Dynamics ◽  
Restricted Problems ◽  
Be Star ◽  
Physical Phenomena

A survey is presented of the theoretical attempts to determine the structure of the circumstellar matter around Be stars. The general equations describing the structure and dynamics of Be star envelopes are given. The complications introduced by various physical phenomena are briefly discussed and initial attempts to solve restricted problems are considered. The various ad hoc models proposed for Be stars are discussed and comparisons of the observations with predictions of these models are illustrated. The strengths and weaknesses of these models are evaluated and areas where progress is being or should be made are considered.

scholarly journals Radio Stars of the SKA

Universe ◽  
2021 ◽  
Vol 7 (5) ◽  
pp. 119
Author(s):  
Bin Yu ◽  
Albert Zijlstra ◽  
Biwei Jiang
Keyword(s):  
Radio Emission ◽  
Milky Way ◽  
Galactic Plane ◽  
High Sensitivity ◽  
Hii Regions ◽  
Be Stars ◽  
M Dwarfs ◽  
Ob Stars ◽  
5 Ghz ◽  
Radio Stars

Radio emission from stars can be used, for example, to study ionized winds or stellar flares. The radio emission is faint and studies have been limited to few objects. The Square Kilometer Array (SKA) brings a survey ability to the topic of radio stars. In this paper we investigate what the SKA can detect, and what sensitivity will be required for deep surveys of the stellar Milky Way. We focus on the radio emission from OB stars, Be stars, flares from M dwarfs, and Ultra Compact HII regions. The stellar distribution in the Milky Way is simulated using the Besançon model, and various relations are used to predict their radio flux. We find that the full SKA will easily detect all UltraCompact HII regions. At the limit of 10 nJy at 5 GHz, the SKA can detect 1500 Be stars and 50 OB stars per square degree, out to several kpc. It can also detect flares from 4500 M dwarfs per square degree. At 100 nJy, the numbers become about 8 times smaller. SKA surveys of the Galactic plane should be designed for high sensitivity. Deep imaging should consider the significant number of faint flares in the field, even outside the plane of the Milky Way.

scholarly journals Radio observations of the comet Arend-Roland

1959 ◽  
Vol 9 ◽  
pp. 56-57
Author(s):  
G. R. Whitfield ◽  
J. Högbom
Keyword(s):  
Radio Emission ◽  
Solar Corona ◽  
Electron Density ◽  
Radio Observations ◽  
Radio Stars

Observations were made at Cambridge between 1957 March 12 and May 13 in an attempt to detect radio emission from the comet at 3.7- and 7.9-m wavelengths by observing radio stars through its tails, to derive information on the electron density in the manner used by Hewish [1] in investigating the outermost layers of the solar corona.

scholarly journals Radio astronomy and the origin of cosmic rays

1959 ◽  
Vol 9 ◽  
pp. 589-594 ◽  
Author(s):  
V. L. Ginzburg
Keyword(s):  
Cosmic Rays ◽  
Radio Emission ◽  
Radio Astronomy ◽  
Cosmic Ray ◽  
Cosmic Radio ◽  
Cosmic Radio Emission ◽  
Galactic Radio Emission ◽  
Radio Stars ◽  
Galactic Radio

A paper [1] sent to the Manchester Symposium on Radio Astronomy in 1955 described the views developed earlier [2] concerning a magnetobremsstrahlung (synchrotron) origin of nonthermal cosmic radio emission. Unfortunately, for unknown reasons, it was not included in the Symposium volume [3]. At the same time the paper by Unsöld was published [3] (see also [4]), in which the nonthermal galactic radio emission is connected with radiation of a great number of cold dwarfs (radio stars). At the same time, Unsöld criticizes the theory of cosmic-ray origin, according to which the main sources of these rays are envelopes of supernovae and, perhaps, novae [2, 5, 6, 7, 8]. Therefore, we begin with some critical remarks.

scholarly journals Rotationally-Enhanced Stellar Winds (Review Paper)

1987 ◽  
Vol 92 ◽  
pp. 316-338
Author(s):  
J. M. Marlborough
Keyword(s):  
Mass Transfer ◽  
Stellar Wind ◽  
Review Paper ◽  
Current Status ◽  
Stellar Winds ◽  
Be Stars ◽  
Stellar Rotation ◽  
Circumstellar Envelopes ◽  
Wind Model ◽  
Be Star

The rotationally-enhanced stellar wind model for Be stars represents one attempt to understand many of the phenomena related to Be stars in terms of a stellar wind distorted and perhaps also enhanced by rapid stellar rotation. This review will concentrate exclusively on this particular approach; the current status of other attempts to model the circumstellar envelopes (CE) of Be stars are described in other reviews in this volume. It is assumed that Be stars are single stars; if a member of a multiple system, the separation of all components from the Be star is assumed to be sufficiently large that interactions due to mass transfer from any companion to the Be star are negligible.

scholarly journals Spectroscopic Observations of Be Stars in the Photographic and Visual Regions

1982 ◽  
Vol 98 ◽  
pp. 109-124 ◽  
Author(s):  
Arne Slettebak
Keyword(s):  
Main Sequence ◽  
Review Paper ◽  
Planetary Nebulae ◽  
Be Stars ◽  
Early Type ◽  
Spectroscopic Observations ◽  
Be Star ◽  
Hα Emission

The term “Be star” has been used at times to describe classes of objects which are physically rather different from one another. While it could include early-type supergiant stars with Hα emission, early-type pre-main sequence nebular variables, or quasi-planetary nebulae like MWC 349, I will limit this review paper to a discussion of the “classical” Be stars. These are defined as stars of luminosity classes III to V, usually rapid rotators, which show normal B-type spectra with superposed Balmer (and sometimes Fe II) emission. Included also, however, will be the Oe stars and the A-type shell stars, which seem to represent extensions of the classical Be phenomenon to higher and lower temperatures, respectively.

scholarly journals Be Stars as Nonradial Pulsators (Review Paper)

1987 ◽  
Vol 92 ◽  
pp. 361-383 ◽  
Author(s):  
Dietrich Baade
Keyword(s):  
Review Paper ◽  
Be Stars ◽  
Density Maximum ◽  
Rapid Variability ◽  
Theoretical Predictions ◽  
Be Star ◽  
Observational Status ◽  
The Difference ◽  
Low Order

AbstractThe observational status of the ubiquitous rapid variability of Be stars is summarized. The most comprehensive interpretation is obtained with a traveling velocity field and associated temperature variations. But neither the available observations nor theoretical predictions presently allow an unambiguous mode determination of these nonradial pulsations. In addition to rapid rotation, an NRP mode of low azimuthal order, m ≈ 2, seems another prerequisite for a B star becoming a Be star. The amplitudes of these modes are variable and have been observed to decrease with some delay after an outburst. For low-order sectorial modes, NRP's therefore have the potential of explaining the three oldest unsolved problems of Be stars: the difference between Be and Bn stars (the latter do not usually have a low-order mode), the episodic component of the mass loss from Be stars, and the equatorial density maximum of their winds. Mechanisms for the transfer of energy to the atmosphere and its transformation into the kinetic energy of an outburst are discussed.

scholarly journals Radio Emission Of The Nuclei Of Barred Spiral Galaxies

1966 ◽  
Vol 19 (6) ◽  
pp. 883 ◽  
Keyword(s):  
Radio Emission ◽  
Radio Telescope ◽  
Radio Astronomy ◽  
Spiral Galaxies ◽  
Astronomy Observatory ◽  
Radio Observations ◽  
Barred Galaxies ◽  
Radio Astronomy Observatory ◽  
Barred Spiral Galaxies

The results of radio observations of 98 barred galaxies at 11, 21, and 75 cm are presented. The observations were carried out with the 210 ft radio telescope of the Australian National Radio Astronomy Observatory and with the Mills Cross of the Sydney Uni

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