scholarly journals Winds

1993 ◽  
Vol 137 ◽  
pp. 620-633
Author(s):  
K.B. MacGregor
Keyword(s):  
Mass Loss ◽  
Internal Structure ◽  
Physical State ◽  
Main Sequence ◽  
Stellar Atmosphere ◽  
Present Review ◽  
Main Sequence Stars ◽  
Dynamical State ◽  
Stellar Interiors

AbstractIt is by now well known that most main sequence stars continuously lose mass as a consequence of the winds they emit. In addition to affecting the thermal and dynamical state of the stellar atmosphere, such mass loss can also induce changes in the interiors of stars. In the present review, we consider a few of the ways in which sustained, wind-like mass loss can alter the physical state of main sequence stellar interiors by examining the differences in internal structure, composition, and rotation between mass-losing and conservatively evolving stars.

scholarly journals The CNO-Cycle Elements in Atmospheres of B-Type Main Sequence Stars

1991 ◽  
Vol 145 ◽  
pp. 125-135
Author(s):  
L.S. Lyubimkov
Keyword(s):  
Main Sequence ◽  
Short Review ◽  
Stellar Atmospheres ◽  
Main Sequence Stars ◽  
Oxygen Abundance ◽  
Cno Cycle ◽  
C And N ◽  
Stellar Interiors ◽  
Principle Source

The aim of this short review is to pay attention to some problems connected with the He, C and N abundances in atmospheres of B-type main sequence stars. These elements participate in CNO-cycle which is the principle source of energy in such stars. As known, the He, C and N abundances in stellar interiors are considerably changed owing to CNO-cycle (oxygen abundance alter insignificantly). There are some variations of the He, C and N abundances in stellar atmospheres, too, and our task is to discuss probable causes of such variations. It is necessary to emphasize that only normal B-type stars are considered (not He-rich or He-weak, for example).

scholarly journals Small and Intermediate Mass Stellar Evolution - Main Sequence and Close to It

1993 ◽  
Vol 137 ◽  
pp. 410-425 ◽  
Author(s):  
A. Noels ◽  
N. Grevesse
Keyword(s):  
Mass Loss ◽  
Stellar Evolution ◽  
Turbulent Diffusion ◽  
Main Sequence ◽  
Main Sequence Stars ◽  
Intermediate Mass ◽  
Physical Mechanisms ◽  
Standard Models

AbstractWe present the standard models for small and intermediate main sequence stars and we discuss some of the problems arising with semiconvection and overshooting. The surface abundance of Li serves as a test for other physical mechanisms, including microscopic and turbulent diffusion, rotation and mass loss.

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 Mass-Losing Peculiar Red Giants: The Comparison Between Theory and Observations

1989 ◽  
Vol 106 ◽  
pp. 339-347
Author(s):  
M. Jura
Keyword(s):  
Mass Loss ◽  
Loss Rate ◽  
Main Sequence ◽  
Mass Loss Rate ◽  
Solar Neighborhood ◽  
Asymptotic Giant Branch ◽  
Red Giants ◽  
Main Sequence Stars ◽  
Dwarf Stars ◽  
White Dwarf Stars

AbstractThe mass loss from evolved red giants is considered. It seems that red giants on the Asymptotic Giant Branch (AGB) are losing between 3 and 6 10-4 MΘ kpc-2 yr-1 in the solar neighborhood. If all the main sequence stars between 1 and 5 MΘ ultimately evolve into white dwarfs with masses of 0.7 MΘ the predicted mass loss rate in the solar neighborhood from these stars is 8 10-4 MΘ kpc-2 yr-1. Although there are still uncertainties, it appears that there is no strong disagreement between theory and observation. However, it could also be that we have not yet identified much of the source of the mass-loss from pre-white dwarf stars.

scholarly journals The Effects of Main-Sequence Mass Loss on Surface C/N Abundance Ratios During the Ascent of the First Giant Branch

1989 ◽  
Vol 106 ◽  
pp. 228-228
Author(s):  
J. A. Guzik ◽  
T. E. Beach
Keyword(s):  
Mass Loss ◽  
Stellar Evolution ◽  
Mass Fraction ◽  
Main Sequence ◽  
High Mass ◽  
Core Material ◽  
Main Sequence Stars ◽  
Rapid Rotation ◽  
Final Mass ◽  
Evolution Modeling

The surface C/N abundance ratios of many cluster and field G and K giants following the 1st dredge-up phase are much lower than predicted from standard stellar evolution modeling. The occurrence of substantial mass loss, either during or immediately after the main-sequence phase would both reduce the mass fraction of the unprocessed envelope necessary to contaminate with CN-cycle products, as well as allow CN-processing of a greater amount of core material during the earlier high-mass phase. Willson, Bowen and Struck-Marcell (1987) have proposed that a combination of pulsation and rapid rotation could drive substantial mass loss in main-sequence stars of initial mass 1-3 MΘ. We evolved a grid of 16 mass-losing models from the zero-age main sequence through 1st dredge-up. The models have initial masses of 1.25, 1.5, 1.75 and 2.0 MΘ, and exponentially decreasing mass-loss rates with e-folding times 0.2, 0.4, 1.0 and 2.0 Gyr; all models evolve toward a final mass of 1.0 M". Since the mass-loss epoch is short-lived, most of the models reach 1.0 M0 rapidly, and follow the evolutionary track of a standard 1 MΘ model redward away from the main sequence and up the 1st giant branch. The convecuve envelope deepens during 1st dredge-up to homogenize the outer 3/4 of the star's final mass.

scholarly journals NLTE spectroscopic analysis of the 3He anomaly in subluminous B-type stars

2018 ◽  
Vol 618 ◽  
pp. A86 ◽  
Author(s):  
D. Schneider ◽  
A. Irrgang ◽  
U. Heber ◽  
M. F. Nieva ◽  
N. Przybilla
Keyword(s):  
Main Sequence ◽  
Spectroscopic Analysis ◽  
Stellar Atmosphere ◽  
Atomic Diffusion ◽  
Horizontal Branch ◽  
Line Profiles ◽  
Main Sequence Stars ◽  
Sdb Stars ◽  
Non Local ◽  
First Time

Several B-type main-sequence stars show chemical peculiarities. A particularly striking class are the 3He stars, which exhibit a remarkable enrichment of 3He with respect to 4He. This isotopic anomaly has also been found in blue horizontal branch (BHB) and subdwarf B (sdB) stars, which are helium-core burning stars of the extreme horizontal branch. Recent surveys uncovered 11 3He sdBs. The 3He anomaly is not due to thermonuclear processes, but caused by atomic diffusion in the stellar atmosphere. Using a hybrid local/non-local thermodynamic equilibrium (LTE/NLTE) approach for B-type stars, we analyzed high-quality spectra of two known 3He BHBs and nine known 3He sdBs to determine their isotopic helium abundances and 4He/3He abundance ratios. We redetermined their atmospheric parameters and analyzed selected He I lines, including λ4922 Å and λ6678 Å, which are very sensitive to 4He/3He. Most of the 3He sdBs cluster in a narrow temperature strip between 26000 K and 30000 K and are helium deficient in accordance with previous LTE analyses. BD+48° 2721 is reclassified as a BHB star because of its low temperature (Teff = 20700 K). Whereas 4He is almost absent (4He/3He < 0.25) in most of the known 3He stars, other sample stars show abundance ratios up to 4He/3He ∼2.51. A search for 3He stars among 26 candidate sdBs from the ESO SPY survey led to the discovery of two new 3He sdB stars (HE 0929–0424 and HE 1047–0436). The observed helium line profiles of all BHBs and of three sdBs are not matched by chemically homogeneous atmospheres, but hint at vertical helium stratification. This phenomenon has been seen in other peculiar B-type stars, but is found for the first time for sdBs. We estimate helium to increase from the outer to the inner atmosphere by factors ranging from 1.4 (SB 290) up to 8.0 (BD+48° 2721).

Temperatures and radii of O stars

1979 ◽  
Vol 83 ◽  
pp. 103-108
Author(s):  
A. B. Underhill ◽  
L. Divan ◽  
V. Doazan ◽  
M.L. Prévot-Burnichon
Keyword(s):  
Main Sequence ◽  
Near Infrared ◽  
Stellar Atmosphere ◽  
Class Iii ◽  
Main Sequence Stars ◽  
Class V ◽  
Intermediate Band ◽  
B Stars ◽  
Luminosity Class ◽  
Effective Temperatures

Angular diameters have been estimated for 18 O and 142 B stars using absolute intermediate-band photometry in the near infrared and they have been combined with integrated fluxes to yield effective temperatures. The effective temperatures of the O stars lie in the range 30000 K to about 47000 K. For a given subtype, the luminosity class I stars have lower effective temperatures than the main-sequence stars by about 1000 K. The absorption-line spectral types of the supergiants of types O and B reflect electron temperatures which are higher than can be maintained by the integrated flux which flows through the stellar atmosphere. Distances have been estimated for all the stars and linear diameters found. The average radius for an 08 to 09.5 supergiant is about 23.3 R⊙; the radii for luminosity class III and Class V O stars lie in the range 6.8 to 10.7⊙ R.

scholarly journals On the nature of massive helium star winds and Wolf–Rayet-type mass-loss

2020 ◽  
Vol 499 (1) ◽  
pp. 873-892
Author(s):  
Andreas A C Sander ◽  
Jorick S Vink
Keyword(s):  
Mass Loss ◽  
Main Sequence ◽  
Terminal Velocity ◽  
Stellar Atmosphere ◽  
Major Step ◽  
Theoretical Understanding ◽  
Star Evolution ◽  
Helium Stars ◽  
Low Metallicity ◽  
Helium Star

ABSTRACT The mass-loss rates of massive helium stars are one of the major uncertainties in modern astrophysics. Regardless of whether they were stripped by a binary companion or managed to peel off their outer layers by themselves, the influence and final fate of helium stars – in particular the resulting black hole mass – highly depends on their wind mass-loss as stripped-envelope objects. While empirical mass-loss constraints for massive helium stars have improved over the last decades, the resulting recipes are limited to metallicities with the observational ability to sufficiently resolve individual stars. Yet, theoretical efforts have been hampered by the complexity of Wolf–Rayet (WR) winds arising from the more massive helium stars. In an unprecedented effort, we calculate next-generation stellar atmosphere models resembling massive helium main-sequence stars with Fe-bump driven winds up to $500\, \mathrm{M}_\odot$ over a wide metallicity range between 2.0 and $0.02\, \mathrm{Z}_\odot$. We uncover a complex Γe-dependency of WR-type winds and their metallicity-dependent breakdown. The latter can be related to the onset of multiple scattering, requiring higher L/M-ratios at lower metallicity. Based on our findings, we derive the first ever theoretically motivated mass-loss recipe for massive helium stars. We also provide estimates for Lyman continuum and $\rm{He\,{\small II}}$ ionizing fluxes, finding stripped helium stars to contribute considerably at low metallicity. In sharp contrast to OB-star winds, the mass-loss for helium stars scales with the terminal velocity. While limited to the helium main sequence, our study marks a major step towards a better theoretical understanding of helium star evolution.

Sign in / Sign up

Export Citation Format

Share Document