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 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 On the stellar gravity and effective temperature dependence of the ratio of terminal to escape velocities in stellar winds

1981 ◽  
Vol 59 ◽  
pp. 75-78
Author(s):  
Luis Carrasco
Keyword(s):  
Temperature Dependence ◽  
Effective Temperature ◽  
Main Sequence ◽  
Stellar Winds ◽  
Early Type ◽  
Main Sequence Stars ◽  
Velocity Information ◽  
Early Type Stars ◽  
Fitting Parameters

Contrary to the results of some investigators, the ratio of terminal to escape velocities (V∞/Vesc) observed for the winds in early-type stars is found to be linearly correlated with log Γ - Γ being the ratio of stellar to Eddington's luminosities.Although the determination of terminal velocities for O-type main sequence stars from edge velocity information may be somewhat questionable (Lamers, 1980). The determined values for the β and γ fitting parameters for the observed profiles by Conti and Garmany (1980) are tipically on the order of one for these stars. Hence, from the grid of profiles by Castor and Lamers (1979), we estimate that at most a 10% error is introduced by adopting the edge velocities as representative values of the terminal velocities of main sequence O-type stars.

scholarly journals C IV resonance line profiles in O stars

1979 ◽  
Vol 83 ◽  
pp. 95-98
Author(s):  
S. B. Parsons ◽  
J. D. Wray ◽  
K. G. Henize ◽  
G. F. Benedict
Keyword(s):  
Resonance Line ◽  
Main Sequence ◽  
Uv Spectra ◽  
Line Profiles ◽  
Early Type ◽  
Main Sequence Stars ◽  
Objective Prism ◽  
Early Type Stars

The S-019 experiment on Skylab (cf. Henize et al. 1975; “Paper I”) recorded far UV spectra in about 160 4° x 5° fields, covering 10% of the sky, on 101 film with a 15 cm aperture objective-prism telescope. Several hundred early-type stars were observed in the vicinity of 1550 Å with a resolution between 3 and 4 Å, as well as thousands of stars at longer wavelengths and correspondingly lower resolution. An atlas of spectra for types 04 to B5 is illustrated in Paper I. That figure shows that the P Cygni profile is a characteristic of all supergiants earlier than B3 and main sequence stars earlier than 08.

scholarly journals Singly-Ionized Iron Emission Lines in the Spectra of Early Type Stars

1976 ◽  
Vol 70 ◽  
pp. 99-103
Author(s):  
R. Viotti ◽  
P. Koubský
Keyword(s):  
Spectroscopic Investigation ◽  
Emission Lines ◽  
Be Stars ◽  
Early Type ◽  
Atomic Processes ◽  
Early Type Stars ◽  
Stellar Envelopes ◽  
Two Parameter

The appearance of singly ionized iron emission lines in the spectra of early type stars is studied, and the results of a spectroscopic investigation of EW Lac and other Be stars are given. We also discuss the atomic processes of excitation of Fe ii in the stellar envelopes using a two-parameter diagram W, NeT−1/2e.

scholarly journals Photospheric and “Chromospheric” CIV Lines in B-Main-Sequence Stars

1986 ◽  
Vol 116 ◽  
pp. 113-116
Author(s):  
Fiorella Castelli ◽  
Carlo Morossi ◽  
Roberto Stalio
Keyword(s):  
High Temperature ◽  
Stellar Wind ◽  
High Velocity ◽  
Main Sequence ◽  
Stellar Atmosphere ◽  
Uv Spectra ◽  
Spectral Lines ◽  
Early Type ◽  
Main Sequence Stars ◽  
Early Type Stars

The presence in the far-UV spectra of early-type stars of spectral lines of superionized atoms is argument of controversial debate among astronomers. Presently there is agreement on the non-radiative origin of these ions but not on the proposed mechanisms for their production nor on the proposed locations in the stellar atmosphere where they are abundant. Cassinelli et al. (1978) suggest that the Auger mechanism is operative in a cool wind blowing above a narrow corona to produce these ions; Lucy and White (1980) introduce radiative instabilities growing into hot blobs distributed across the stellar wind; Doazan and Thomas (1982) make these ions to be formed in both pre- and post-coronal, high temperature regions at low and high velocity respectively.

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 A Search for Coronal Emission Lines from Early-Type Stars

1988 ◽  
Vol 132 ◽  
pp. 123-125
Author(s):  
D. Baade ◽  
L. B. Lucy
Keyword(s):  
Stellar Wind ◽  
Controversial Issue ◽  
Emission Lines ◽  
Stellar Winds ◽  
Early Type ◽  
Wind Model ◽  
Coronal Emission ◽  
Early Type Stars ◽  
Hot Corona

For more than ten years now, a controversial issue in studies of stellar winds has concerned the existence or not of a coronal zone (T ∼ 106 K) at the base of the cool winds (T ∼ Teff) of early-type stars. The latest revival of interest in this possibility is due to Wolfire et al. (1985) who showed that Waldron's (1984) recombination stellar wind (RSW) version of the hot corona – cool wind model (Hearn 1975; Cassinelli et al. 1978) yields models for ξ Puppis (O4 If) that are consistent with both IRAS and Einstein IPC data, thus refuting an earlier claim (Lamers et al. 1984) to have excluded the existence of a coronal zone.

Fossil magnetic fields and rotation of early-type stars

1994 ◽  
Vol 162 ◽  
pp. 184-185
Author(s):  
A.E. Dudorov
Keyword(s):  
Magnetic Field ◽  
Star Formation ◽  
Magnetic Fields ◽  
Molecular Clouds ◽  
Main Sequence ◽  
Early Type ◽  
Main Sequence Stars ◽  
Early Type Stars ◽  
Quadrupole Magnetic Field ◽  
Interstellar Molecular Clouds

Observational data of the last 10 years allow two main conclusions:a) Main sequence stars can be separated in two classes: - magnetic (Bp) stars with surface strengths of a dipole or quadrupole magnetic field of Bs ≈ n · (102 − 103) G, n = 2,3,4…7, and - normal main sequence stars (F-O) with magnetic fields Bs ≈ 1 − 100 G (< 300 G);b) Typical star formation takes place in interstellar molecular clouds with magnetic field strengths B ≈ 10-5 G (See Dudorov 1990).

scholarly journals Search for Rotational Modulation in Pre-Main Sequence Herbig Ae/Be Stars

1988 ◽  
Vol 132 ◽  
pp. 105-108
Author(s):  
C. Catala ◽  
J. Czarny ◽  
P. Felenbok
Keyword(s):  
Main Sequence ◽  
Stellar Winds ◽  
Be Stars ◽  
Main Sequence Stars ◽  
Intermediate Mass ◽  
The Past ◽  
Rotational Modulation

The Herbig Ae/Be stars (Herbig, 1960; Finkenzeller and Hundt, 1984) are widely believed to be intermediate mass (2-5 M⊙) pre-main sequence stars. In the past few years, a big effort has been made to model their outer layers, and it has been shown that they possess stellar winds and extended chromospheres (Catala et al., 1984; Catala et al., 1986a; Catala and Kunasz, 1987).

scholarly journals High-Energy Phenomena in Be Stars (Review Paper)

1987 ◽  
Vol 92 ◽  
pp. 250-262 ◽  
Author(s):  
Theodore P. Snow
Keyword(s):  
General Property ◽  
Review Paper ◽  
High Energy ◽  
Early Years ◽  
Stellar Winds ◽  
Be Stars ◽  
Early Type ◽  
Ob Stars ◽  
Early Type Stars

It was discovered in the early years of the Copernicus satellite operations that the stellar winds in early-type stars are often characterized by degrees of ionization inconsistent with the spectral types of the stars. The most notable early example was the discovery of strong OVI lines in the form of P Cygni profiles in stars too cool to have this ion in their photospheres, such as τ SCO (BOV; Rogerson and Lamers 1975). Systematic studies showed that excess ionization is a general property of the winds in OB stars (e.g. Lamers and Snow 1978).

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