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 NGC 6611 601: A hot pre-main sequence spectroscopic binary containing a centrifugal magnetosphere host star

2021 ◽  
Author(s):  
M E Shultz ◽  
E Alecian ◽  
V Petit ◽  
S Bagnulo ◽  
T Böhm ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Main Sequence ◽  
Magnetic Star ◽  
Be Stars ◽  
Strong Emission ◽  
Surface Magnetic Field ◽  
Spectroscopic Binary ◽  
Be Star ◽  
Hα Emission ◽  
Strong Surface

Abstract W 601 (NGC 6611 601) is one of the handful of known magnetic Herbig Ae/Be stars. We report the analysis of a large dataset of high-resolution spectropolarimetry. The star is a previously unreported spectroscopic binary, consisting of 2 B2 stars with a mass ratio of 1.8, masses of 12 M⊙ and 6.2 M⊙, in an eccentric 110-day orbit. The magnetic field belongs to the secondary, W 601 B. The Hα emission is consistent with an origin in W 601 B’s centrifugal magnetosphere; the star is therefore not a classical Herbig Be star in the sense that its emission is not formed in an accretion disk. However, the low value of log g = 3.8 determined via spectroscopic analysis, and the star’s membership in the young NGC 6611 cluster, are most consistent with it being on the pre-main sequence. The rotational period inferred from the variability of the Hα line and the longitudinal magnetic field 〈Bz〉 is 1.13 d. Modelling of Stokes V and 〈Bz〉 indicates a surface dipolar magnetic field Bd between 6 and 11 kG. With its strong emission, rapid rotation, and strong surface magnetic field, W 601 B is likely a precursor to Hα-bright magnetic B-type stars such as σ Ori E. By contrast, the primary is an apparently non-magnetic (Bd < 300 G) pre-main sequence early B-type star. In accordance with expectations from magnetic braking, the non-magnetic primary is apparently more rapidly rotating than the magnetic star.

scholarly journals The Possible Role of Radiative Acceleration in Supporting Extended Atmospheres in Be Stars

1976 ◽  
Vol 70 ◽  
pp. 377-382 ◽  
Author(s):  
R. L. Kurucz ◽  
R. E. Schild
Keyword(s):  
Effective Temperature ◽  
Detailed Calculation ◽  
Be Stars ◽  
Be Star ◽  
Hα Emission ◽  
Two Peaks ◽  
Radiative Acceleration ◽  
Emission Strength ◽  
Peaked Function

A detailed calculation of the radiative acceleration in B-type stars shows it to be a double-peaked function of effective temperature at small optical depths. The two peaks are shown to coincide approximately with peaks in the distribution of mean Hα emission strength as a function of B - V color in Be stars. These facts suggest that radiation may play an important role in the support of the Be star extended atmosphere.

scholarly journals The Connection with B[e] stars

2000 ◽  
Vol 175 ◽  
pp. 26-36 ◽  
Author(s):  
Franz-Josef Zickgraf
Keyword(s):  
Common Property ◽  
Main Sequence ◽  
Emission Lines ◽  
Circumstellar Dust ◽  
Evolutionary Status ◽  
Be Stars ◽  
Early Type ◽  
Circumstellar Envelopes ◽  
Early Type Stars ◽  
Uniform Group

AbstractThe characteristics of the various types of B[e] stars are discussed and compared with those of classical Be stars. Both groups of stars are characterized by the presence of emission lines in their spectra, in particular of hydrogen. However, there are also significant differences between these classes. Classical Be stars lack hot circumstellar dust and strong forbidden low-excitation emission lines, which are typical characteristics produced by B[e]-type stars. While classical Be stars are a rather uniform group of early-type stars, B[e]-type stars form a quite heterogeneous group, very often of poorly known evolutionary status, comprising such diverse types of objects as near main-sequence objects, evolved lowmass proto-planetray nebulae and massive evolved hot supergiants. Even pre-main sequence Herbig Ae/Be stars sometimes find their way into the group of B[e] stars. However, despite these dissimilarities classical Be stars and B[e]-type stars, share a common property, namely the nonsphericity of their circumstellar envelopes.

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 Be Phenomena in Young Early-type Stars: Various Forms of Interaction between the Star and the Circumstellar Gaseous Envelope

2000 ◽  
Vol 175 ◽  
pp. 344-347
Author(s):  
M. Pogodin
Keyword(s):  
High Resolution ◽  
Stellar Wind ◽  
Main Sequence ◽  
Stellar Surface ◽  
High Resolution Spectroscopy ◽  
Evolutionary Status ◽  
Be Stars ◽  
Early Type ◽  
Early Type Stars ◽  
Gaseous Envelope

AbstractNew results of high-resolution spectroscopy of four pre-main sequence Ae/Be stars are presented. An analysis of parameters of lines originating in different regions of the circumstellar (CS) envelope (Hα, Hβ, He I 5876, DNal) allows to reconstruct a picture of the interaction between the star and the CS environment which can be displayed in different forms. At least two separate processes seem to impact the structural and kinematical properties of the envelope: the stellar wind from the stellar surface and the matter infall onto the star from the CS media. A possible relation between these two phenomena is discussed in the framework of different models. Some similarity between observational phenomena in Herbig Ae/Be and classical Be stars is noted in spite of their difference in evolutionary status.

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 Observations of stellar winds in early type stars

1981 ◽  
Vol 59 ◽  
pp. 1-18
Author(s):  
Peter S. Conti
Keyword(s):  
Resonance Line ◽  
Optical Spectrum ◽  
Main Sequence ◽  
Emission Lines ◽  
Stellar Winds ◽  
Be Stars ◽  
Early Type ◽  
Main Sequence Stars ◽  
Early Type Stars ◽  
Line P

I have been asked to review the “observations” of winds in “early-type” stars. This normally means stars of spectral type OB and those of the Wolf-Rayet (WR) class. In this paper I will concentrate on the massive population I stars of these types, and primarily the O and WR classes on which most of the recent work has been done. The early B type supergiants share many of the wind properties of the O stars but the later supergiant types, Be stars, and main sequence stars may not. Stellar winds are a ubiquitous phenomenon among these early type stars (Snow and Morton 1976). We see evidence of their winds in the resonance line P Cygni profiles in the UV region, in the emission lines of Hα and λ4686 He II in the optical spectrum, and in the free-free emission from the ionized plasma as observed in the IR and radio regions of the spectrum.

scholarly journals Be Star Surveys in Open Clusters with Balmer-line Photometry

2000 ◽  
Vol 175 ◽  
pp. 63-66
Author(s):  
Gemma Capilla ◽  
Juan Fabregat ◽  
Deborah Baines
Keyword(s):  
Emission Line ◽  
Main Sequence ◽  
Open Clusters ◽  
Balmer Line ◽  
Be Stars ◽  
Late Type ◽  
Efficient Tool ◽  
Be Star ◽  
Almost All ◽  
Evolutionary Interpretation

AbstractWe present CCD Hα and Hβ photometry of young open clusters. We show that the comparison of the α and β photometric indices provides an efficient tool for identifying emission line stars. We report on the discovery of several new Be stars.The preliminary results of our survey are the following: i. the younger clusters (age < 10 Myr) are almost lacking of Be stars, ii. clusters in the age interval 10–30 Myr are rich in Be stars. Almost all of them are of spectral types earlier than B5, while late-type Be stars are scarce. These results point towards an evolutionary interpretation of the Be phenomenon, in the sense that Be stars are close to the end of their main sequence lifetime.

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