scholarly journals Powerful explosions atZ= 0?

2008 ◽  
Vol 4 (S255) ◽  
pp. 194-198
Author(s):  
Sylvia Ekström ◽  
Georges Meynet ◽  
Raphael Hirschi ◽  
André Maeder
Keyword(s):  
Black Holes ◽  
Total Mass ◽  
Main Sequence ◽  
Explosion Energy ◽  
Stellar Winds ◽  
Sequence Evolution ◽  
Constant Mass ◽  
Core Mass ◽  
Metal Free ◽  
The Core

AbstractMetal-free stars are assumed to evolve at constant mass because of the very low stellar winds. This leads to large CO-core mass at the end of the evolution, so primordial stars with an initial mass between 25 and 85M⊙are expected to end as direct black holes, the explosion energy being too weak to remove the full envelope.We show that when rotation enters into play, some mass is lost because the stars are prone to reach the critical velocity during the main sequence evolution. Contrary to what happens in the case of very low- but non zero-metallicity stars, the enrichment of the envelope by rotational mixing is very small and the total mass lost remains modest. The compactness of the primordial stars lead to a very inefficient transport of the angular momentum inside the star, so the profile of Ω(r) is close to Ωr2= const. As the core contracts, the rotation rate increases, and the star ends its life with a fast spinning core. Such a configuration has been shown to modify substantially the dynamics of the explosion. Where one expected a weak explosion or none at all, rotation might boost the explosion energy and drive a robust supernova. This will have important consequences in the way primordial stars enriched the early Universe.

scholarly journals The Origin of the RS CVn Binaries

1976 ◽  
Vol 73 ◽  
pp. 381-387 ◽  
Author(s):  
P. Biermann ◽  
D. S. Hall
Keyword(s):  
Angular Momentum ◽  
Star Formation ◽  
Total Mass ◽  
Total Angular Momentum ◽  
Main Sequence ◽  
Be Stars ◽  
Large Space ◽  
Single Star ◽  
The Core ◽  
Thermal Phase

We consider six possible origins for the RS CVn binaries based on the following possibilities. RS CVn binaries might now be either pre-main-sequence or post-main-sequence. A pre-main-sequence binary might not always have been a binary but might have resulted from fission of a rapidly rotating single pre-main-sequence star. The main-sequence counterparts might be either single stars or binaries.To decide which of the six origins is possible, we consider the following observed data for the RS CVn binaries: total mass, total angular momentum, lack of observed connection with regions of star formation, large space density, kinematical age, and the visual companion of WW Dra. In addition we consider lifetimes and space densities of single stars and other types of binaries.The only origin possible is that the RS CVn binaries are in a thermal phase following fission of a main-sequence single star. In this explanation the single star had a rapidly rotating core which became unstable due to the core contraction which made it begin to evolve off the main sequence. The present Be stars might be examples of such parent single stars.

The Main Sequence Evolution of Inhomogeneous Stars

1982 ◽  
Vol 4 (4) ◽  
pp. 396-400 ◽  
Author(s):  
J. Lattanzio
Keyword(s):  
Gravitational Collapse ◽  
Heavy Element ◽  
Main Sequence ◽  
Element Abundance ◽  
Sequence Evolution ◽  
Interstellar Gas ◽  
Convective Mixing ◽  
The Core ◽  
Gas Cloud

Duley (1974) has shown that, at the temperatures usually associated with interstellar gas clouds, we would expect CNO grains to be present. During gravitational collapse these grains migrate to the centre of the gas cloud, leading to an enhancement of the heavy-element abundance in the core (Prentice 1976, 1978). It was Krautschneider (1977) who verified such a scenario, by considering the dynamical collapse of gas and grain clouds. If such an initial radial abundance inhomogeneity existed, Prentice (1976a) showed that this configuration may well survive the later convective mixing phase and thus approach the zero-age main-sequence (ZAMS) with a small (-v 3% by mass) metal enhanced core.

scholarly journals Effects of rotation on the main sequence evolution of a 5M⊙ star

1994 ◽  
Vol 162 ◽  
pp. 147-148
Author(s):  
J. Fliegner ◽  
N. Langer
Keyword(s):  
Angular Momentum ◽  
Main Sequence ◽  
Chemical Elements ◽  
Sequence Evolution ◽  
Early Type ◽  
Mixing Processes ◽  
Core Mass ◽  
Convective Core ◽  
Early Type Stars ◽  
Effects Of Rotation

The way rotation influences the main sequence evolution of early type stars depends strongly on their internal angular momentum distribution. Their convective core mass is not always decreased as a consequence of a reduced “effective mass” due to rotation, since rotation laws close to uniform specific angular momentum may increase Δrad and thereby the convective core mass (Clement). In addition, rotationally induced mixing processes may redistribute angular momentum and chemical elements inside the stars (e.g. Endal & Sofia 1978).

scholarly journals Models of Type II Supernova Explosions

1986 ◽  
Vol 7 ◽  
pp. 629-633
Author(s):  
Wolfgang Hillebrandt
Keyword(s):  
Main Sequence ◽  
Critical Mass ◽  
Iron Core ◽  
Heavy Nuclei ◽  
Core Mass ◽  
The Core ◽  
Supernova Explosions ◽  
M Stars ◽  
Chandrasekhar Limit ◽  
Carbon Burning

Present stellar evolution codes predict that stars with He-core masses above approximately 2 M⊙, corresponding to main sequence masses of at least 8 M⊙ burn carbon non-violently. After hydrostatic core carbon burning all those stars contain O-Ne-Mg cores but their further evolution is strongly dependent on the stellar entropy and thus on the main sequence and the core mass. If the He-core mass is below 3 M⊙ the O-Ne-Mg core grows due to carbon-burning in a shell and the crucial question is, whether or not it grows beyond the critical mass for Neignition (≅1.37 M⊙). Stars with He-cores less massive than about 2.4 M⊙ will never ignite Ne, but due to electron-captures, mainly on Ne and Mg, their cores will contract until O-burning begins. Since the matter of the O-Ne-Mg core is weakly degenerate O-burning propagates as a (subsonic) deflagration front and incinerates a certain fraction of the core into a nuclear statistical equilibrium (NSE) composition of iron-group elements (Nomoto, 1984). If, on the other hand, the mass of the O-Ne-Mg core is slightly larger than 1.37 M⊙ Ne and O burn in a shell from about 0.6 M⊙ to 1.4 M⊙, but again the outcome is a NSE-composition (Wilson et al., 1985). In both cases the core-mass finally exceeds the Chandrasekhar limit because electron captures on free protons and heavy nuclei lower the electron concentration and consequently also the effective Chandrasekhar mass. The cores, therefore, continue to contract and finally collapse to neutron star densities with iron-core masses between 0.7 and 1.4 M⊙.

scholarly journals The Distribution of Planetary Nebula Nuclei in the log L-log T Plane: Inferences from Theory

1989 ◽  
Vol 131 ◽  
pp. 473-480
Author(s):  
R. A. Shaw
Keyword(s):  
Planetary Nebula ◽  
Main Sequence ◽  
Galactic Disk ◽  
Mass Function ◽  
Initial Mass Function ◽  
Sequence Evolution ◽  
Selection Effects ◽  
Core Mass ◽  
Star Forming ◽  
History Of

The expected distribution of planetary nebula nuclei (PNNs) on the log L-log T plane is calculated based upon modern stellar evolutionary theory, the initial mass function (IMF), and various assumptions concerning mass loss during post-main sequence evolution. The distribution is found to be insensitive to the assumed range of main-sequence progenitor mass, and to reasonable variations in the age and the star forming history of the galactic disk. Rather, the distribution is determined primarily by the heavy dependence of the evolution rate upon core mass, and secondarily upon the steepness of the IMF and other factors. The distribution is rather different than any found from observations, and probably reveals strong observational selection effects.

scholarly journals Isochrone-cloud fitting of the extended main-sequence turn-off of young clusters

2019 ◽  
Vol 632 ◽  
pp. A74 ◽  
Author(s):  
C. Johnston ◽  
C. Aerts ◽  
M. G. Pedersen ◽  
N. Bastian
Keyword(s):  
Main Sequence ◽  
Theoretical Interpretation ◽  
Individual Member ◽  
Stellar Rotation ◽  
Core Mass ◽  
The Core ◽  
Core Boundary ◽  
Young Clusters ◽  
The One ◽  
The Individual

Context. Extended main-sequence turn-offs (eMSTOs) are a commonly observed property of young clusters. A global theoretical interpretation for eMSTOs is still lacking, but stellar rotation is considered a necessary ingredient to explain eMSTOs. Aims. We aim to assess the importance of core-boundary and envelope mixing in stellar interiors for the interpretation of eMSTOs in terms of one coeval population. Methods. We constructed isochrone-clouds based on interior mixing profiles of stars with a convective core calibrated from asteroseismology of isolated galactic field stars. We fitted these isochrone-clouds to the measured eMSTO to estimate the age and core mass of the stars in the two young clusters NGC 1850 and NGC 884, assuming one coeval population and by fixing the metallicity to the one measured from spectroscopy. We assessed the correlations between the interior mixing properties of the cluster members and their rotational and pulsational properties. Results. We find that stellar models based on asteroseismically-calibrated interior mixing profiles lead to enhanced core masses of eMSTO stars. Additionally, these models can explain a significant fraction of the observed eMSTOs of the two considered clusters in terms of one coeval population of stars, which have similar ages to those in the literature, given the large uncertainties. The rotational and pulsational properties of the stars in NGC 884 are not sufficiently well known to perform asteroseismic modelling as it is achieved for field stars from space photometry. The stars in NGC 884 for which we have v sin i and a few pulsation frequencies show no correlation between these properties and the core masses of the stars that set the cluster age. Conclusions. Future cluster space asteroseismology may allow for the interpretation of the core masses in terms of the physical processes that cause them, based on the modelling of the interior mixing profiles for the individual member stars with suitable identified modes.

scholarly journals Evolution of zero-metallicity massive stars

2003 ◽  
Vol 212 ◽  
pp. 334-340
Author(s):  
Paola Marigo ◽  
Cesare Chiosi ◽  
Léo Girardi ◽  
Rolf-Peter Kudritzki
Keyword(s):  
Mass Loss ◽  
Large Range ◽  
Massive Stars ◽  
Stellar Winds ◽  
Constant Mass ◽  
Helium Burning ◽  
Free Gas ◽  
Metal Free ◽  
Massive Models ◽  
Carbon Burning

We discuss the evolutionary properties of primordial massive and very massive stars, supposed to have formed from metal-free gas. Stellar models are presented over a large range of initial masses (8 M⊙ ≲ Mi ≲ 1000 M⊙), covering the hydrogen- and helium-burning phases up to the onset of carbon burning. In most cases the evolution is followed at constant mass. To estimate the possible effect of mass loss via stellar winds, recent analytic formalisms for the mass-loss rates are applied to the very massive models (Mi ≥ 120 M⊙).

scholarly journals Stellar Winds and Spindown — Observations

1983 ◽  
Vol 102 ◽  
pp. 417-438
Author(s):  
L. Hartmann
Keyword(s):  
Magnetic Field ◽  
Angular Momentum ◽  
Magnetic Fields ◽  
Main Sequence ◽  
Mechanical Energy ◽  
Stellar Winds ◽  
Sequence Evolution ◽  
Angular Momentum Loss ◽  
Solar Type ◽  
Radiative Losses

Stars with masses ≲ 1 M⊙ are observed to rotate more slowly as they age. The angular momentum loss is undoubtedly caused by the coupling of the stellar magnetic field to the escaping wind (Schatzman 1962). Chromospheric and coronal radiative losses depend upon rotation (Wilson 1966a, b; Kraft 1967; Skumanich 1972; Hall 1976; Bopp 1980; Walter and Bowyer 1981; Walter 1981; Vaiana et al. 1981). It is therefore likely that both magnetic fields (Skumanich 1972) and the mechanical energy fluxes required to drive mass loss also depend upon rotation as well. This complicated feedback between magnetic fields, winds, and rotation must control the variation of solar-type activity over much of the HR diagram, and may have very important effects on pre-main sequence evolution.

scholarly journals Blue Stragglers as Long-Lived Stars

1981 ◽  
Vol 93 ◽  
pp. 187-189
Author(s):  
J. Craig Wheeler ◽  
Michel Breger
Keyword(s):  
Main Sequence ◽  
Narrow Range ◽  
Core Region ◽  
Open Clusters ◽  
Apparent Mass ◽  
Core Mass ◽  
Hydrogen Burning ◽  
Blue Stragglers ◽  
The Core ◽  
Chandrasekhar Limit

The existence of blue stragglers in old open clusters with apparent mass more than twice the mass of the turnoff argues against simple binary mass transfer as the mechanism of their origin. The excess of blue stragglers to the red of the termination of the core hydrogen burning main sequence suggests that blue stragglers are not evolving normally. Stellar evolution models invoking mixing in an extended core region can account for the distribution of blue stragglers in the H-R diagram. Such models live longer, brightening and evolving further to the red before core hydrogen exhaustion than do normal stars. The distribution of blue stragglers in NGC 7789 is consistent with a range of mixed core mass fraction ~30–90 per cent and a narrow range in mass ~1.7–2.1 M⊙. Such evolution will result in a class of helium rich stars which have lived longer than normal and whose total mass exceeds the Chandrasekhar limit.

scholarly journals Interaction Beyond the Main Sequence: One Recipe?

1992 ◽  
Vol 151 ◽  
pp. 41-50
Author(s):  
Jean-Pierre De Greve
Keyword(s):  
Mass Transfer ◽  
Phase Space ◽  
Main Sequence ◽  
Mass Range ◽  
Sequence Evolution ◽  
Helium Burning ◽  
The Core ◽  
Simple Concept ◽  
Homogeneous Set ◽  
Mass Ratios

We investigate the different aspects that govern the interaction of post-main-sequence evolution of binaries, using a new, homogeneous set of computations. The set describes the evolution of both components through the phase of mass transfer, till the end of the core helium burning of the primary. The mass range is 9 to 40 Mo, the mass ratios are 0.9 and 0.6 (and introducing 0.99 as a newcomer). Both for small and large masses we discuss the consequences of non-conservative mass transfer. Using a simple concept for the fraction β of transferred matter, we look to its value at the onset of mass transfer for various mass ratios and periods. Exploration of the phase space of interacting binaries reveals the influence of the various parameters on the dimensions of the resulting systems after mass transfer. Special attention is given to binaries with mass ratios very close to one. Their secondaries evolve directly into yellow supergiants such as observed in the LMC.

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