Studies in Stellar Evolution. VIII. The Time Scale for the Diffusion of Energy in the Stellar Interior

1969 ◽  
Vol 156 ◽  
pp. 549 ◽  
Author(s):  
Louis Henyey ◽  
J. L'Ecuyer
Keyword(s):  
Stellar Evolution ◽  
Time Scale ◽  
Stellar Interior

scholarly journals Observations of evolutionary changes in the pulsation period of cepheids

1984 ◽  
Vol 105 ◽  
pp. 445-448
Author(s):  
L. Szabados
Keyword(s):  
Detailed Analysis ◽  
Stellar Evolution ◽  
Time Scale ◽  
Theoretical Work ◽  
Pulsation Period ◽  
First Approximation ◽  
Evolutionary Changes ◽  
Classical Cepheids ◽  
Cepheid Variables

In spite of the fact that Cepheid variables pulsate quite regularly their pulsation period remains constant only in the first approximation. The pulsation period is subject to variations because of stellar evolution. The calculations made by Hofmeister (1965) predicted that the evolutionary period changes of classical Cepheids should be observed on a time scale of several decades or longer. No detailed analysis of the observed period changes has been made since Hofmeister's fundamental theoretical work.

scholarly journals On monolithic supermassive stars

2020 ◽  
Vol 494 (2) ◽  
pp. 2236-2243 ◽  
Author(s):  
Tyrone E Woods ◽  
Alexander Heger ◽  
Lionel Haemmerlé
Keyword(s):  
Early Universe ◽  
Stellar Evolution ◽  
Time Scale ◽  
Main Sequence ◽  
Massive Stars ◽  
Rotating Stars ◽  
One Dimensional ◽  
General Relativistic ◽  
The One ◽  
Limiting Case

ABSTRACT Supermassive stars have been proposed as the progenitors of the massive ($\sim \!10^{9}\, \mathrm{M}_{\odot }$) quasars observed at z ∼ 7. Prospects for directly detecting supermassive stars with next-generation facilities depend critically on their intrinsic lifetimes, as well as their formation rates. We use the one-dimensional stellar evolution code kepler to explore the theoretical limiting case of zero-metallicity non-rotating stars, formed monolithically with initial masses between $10$ and $190\, \mathrm{kM}_{\odot }$. We find that stars born with masses between $\sim\! 60$ and $\sim\! 150\, \mathrm{kM}_{\odot }$ collapse at the end of the main sequence, burning stably for $\sim\! 1.5\, \mathrm{Myr}$. More massive stars collapse directly through the general relativistic instability after only a thermal time-scale of $\sim\! 3$–$4\, \mathrm{kyr}$. The expected difficulty in producing such massive thermally relaxed objects, together with recent results for currently preferred rapidly accreting formation models, suggests that such ‘truly direct’ or ‘dark’ collapses may not be typical for supermassive objects in the early Universe. We close by discussing the evolution of supermassive stars in the broader context of massive primordial stellar evolution and the possibility of supermassive stellar explosions.

scholarly journals On Magnetic Mixing and Rotation in Stellar Evolution

1978 ◽  
Vol 80 ◽  
pp. 323-331
Author(s):  
Peter G. Gross
Keyword(s):  
Magnetic Fields ◽  
Stellar Evolution ◽  
Evolutionary Status ◽  
Relevant Parameter ◽  
Stellar Rotation ◽  
Convective Turbulence ◽  
Stellar Interior ◽  
Magnetic Mixing ◽  
Ap Stars

In this paper some thoughts and problems are presented from the viewpoint that the evolution of stars may play a key role in generating magnetic fields which, in turn, may affect the mixing of nuclearly processed elements from the stellar interior to the surface. The relevant parameter is stellar rotation which, upon interaction with convective turbulence driven by thermal instabilities, leads to the generation of magnetic fields. A possible connection to Bidelman's hypothesis on the evolutionary status of Ap stars is also discussed in the context of a post-core-helium-flash hypothesis.

scholarly journals About the Luminous Blue Variable He3-519

2010 ◽  
Vol 6 (S272) ◽  
pp. 87-88
Author(s):  
Anthony Hervé ◽  
Jean-Claude Bouret
Keyword(s):  
Stellar Evolution ◽  
Time Scale ◽  
Massive Stars ◽  
Model Atmosphere ◽  
Transition Phase ◽  
Evolutionary Status ◽  
Stellar Winds ◽  
Luminous Blue Variables ◽  
Luminous Blue Variable

AbstractLuminous Blue Variables (LBVs) are massive stars, in a transition phase, from being O-type stars and rapidly becoming Wolf-Rayet objects. LBVs possess powerful stellar winds, high luminosities and show photometric and spectroscopic variability. We present the stellar and wind parameters of He3-519 obtained by the modeling of UVES observations with the model atmosphere code CMFGEN. We compare our results to previous studies in order to find mid-time scale variability of the stellar parameters and finally, we use stellar evolution models to determine the evolutionary status of this star.

scholarly journals Coulomb Corrections and Globular Cluster Stellar Evolution

1993 ◽  
Vol 137 ◽  
pp. 451-453 ◽  
Author(s):  
Charles R. Proffitt
Keyword(s):  
Equation Of State ◽  
Stellar Evolution ◽  
Globular Cluster ◽  
Globular Clusters ◽  
Main Sequence ◽  
Stellar Interior ◽  
Coulomb Effects

AbstractThe effects of Coulomb corrections on the evolution of globular clusters stars are discussed. Coulomb corrections alter the equation of state by about 1% in most of the stellar interior, and for stars of fixed initial parameters, this results in an 8% increase in the ZAMS luminosity and an 8% decrease in the age at the main sequence turnoff. Ages for globular clusters measured by comparing to the turnoff luminosity of theoretical isochrones are lowered by ≈ 4% when Coulomb effects are included.

Observational Evidence for Atmospheric Physical Characteristics Relevant to Stellar Evolution

1977 ◽  
Vol 4 (2) ◽  
pp. 105-114
Author(s):  
R. and G. Cayrel
Keyword(s):  
Mass Loss ◽  
Nuclear Fuel ◽  
Stellar Evolution ◽  
Effective Temperature ◽  
Time Scale ◽  
Loss Rate ◽  
Mass Loss Rate ◽  
Observational Evidence ◽  
High Luminosity ◽  
Very High

As a star burns its nuclear fuel, its radius R and its luminosity L are modified. Its mass may as well be affected if the mass loss rate has a time scale comparable to the nuclear time scale; this is likely to occur for stars of very high luminosity. Currently, the change in radius R and luminosity L of an evolving star is described in the socalled theoretical Herzsprung-Russel diagramme with in abscissa the logarithm of the effective temperature defined by:

Fossil fields in early stellar evolution

2008 ◽  
Vol 4 (S259) ◽  
pp. 443-444
Author(s):  
Rainer Arlt
Keyword(s):  
Magnetic Fields ◽  
Stellar Evolution ◽  
Time Scale ◽  
Convection Zone ◽  
Evolutionary Time ◽  
Evolutionary Time Scale ◽  
Zone Depth

AbstractFavored explanations for the presence of magnetic fields on CP stars and the presence of the solar tachocline below the convection zone both imply fossil magnetic fields in the radiative zones. The initial, convective evolution of magnetic fields in a proto-star is studied by numerical, global simulations. The computations are to be extended by a change of the convection zone depth on an evolutionary time-scale.

General calibration problems

1966 ◽  
Vol 24 ◽  
pp. 303
Author(s):  
R. M. Petrie
Keyword(s):  
Stellar Evolution ◽  
Absolute Magnitude ◽  
Stellar Atmosphere ◽  
Stellar Structure ◽  
Surface Gravity ◽  
Central Problem ◽  
Spectral Parameters ◽  
Stellar Interior ◽  
Radiation Passing

During this symposium we have already heard papers which have dealt with the calibration of certain spectral parameters. In this session we turn to the matter of calibrating luminosity criteria in terms of absolute magnitude. This is a central problem in studies of our Galaxy and it finds in this topic its widest application. At the same time we remind ourselves that the determination of absolute magnitude is necessary in studies of stellar structure and stellar evolution since this information tells us about the radiation passing through the stellar interior and the stellar atmosphere and of the amount of energy generated by the star. The luminosity also allows us to calculate the size of a star and to estimate its surface gravity.

scholarly journals Sakurai's object – stellar evolution in real time

1999 ◽  
Vol 191 ◽  
pp. 481-486
Author(s):  
Martin Asplund
Keyword(s):  
Chemical Composition ◽  
Real Time ◽  
Stellar Evolution ◽  
White Dwarf ◽  
Time Scale ◽  
Surface Cooling ◽  
Born Again

The born-again giant Sakurai's object is currently experiencing its second stage as an AGB-star. Furthermore, Sakurai's object has shown an unprecedented rapid stellar evolution since discovery in 1996, both in terms of a continued cooling of the photosphere and spectacular changes in chemical composition on a time-scale of a mere few months. The surface cooling and abundance alterations of H, Li and the s-elements are the direct consequences of the expansion, mixing and nucleosynthesis which has ensued as a result of a final He-shell flash occurring while the star was descending the white dwarf cooling track. Sakurai's object shows striking similarities with the R CrB stars in both chemical composition and visual variability.

The Evolution of the Nuclei of Planetary Nebulae

1972 ◽  
Vol 2 (2) ◽  
pp. 72-78
Author(s):  
D. J. Faulkner
Keyword(s):  
Stellar Evolution ◽  
Time Scale ◽  
Planetary Nebulae ◽  
Considerable Importance ◽  
Stellar Objects ◽  
The Past ◽  
Low Mass

In the past decade, planetary nebulae have assumed considerable importance in elucidating our understanding of the final stages of stellar evolution at low mass. This began with the work of Shklovsky, O’Dell and Seaton, who showed not only that the nuclei of these nebulae were among the hottest stellar objects, but also that they evolved on a track in the Hertzsprung-Russell diagram (the Harman-Seaton sequence) on a time scale very rapid by stellar evolutionary standards (~ 20,000 years).

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