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 The Eclipsing Triple System U Ophiuchi Revisited

2006 ◽  
Vol 2 (S240) ◽  
pp. 109-110
Author(s):  
Luiz Paulo R. Vaz ◽  
Johannes Andersen ◽  
Antônio Claret
Keyword(s):  
Radial Velocity ◽  
Triple System ◽  
Heavy Element ◽  
Main Sequence ◽  
Element Abundance ◽  
Apsidal Motion ◽  
Eclipsing Binary ◽  
The Third ◽  
Sequence Band ◽  
Nearby Stars

AbstractWe have redetermined the absolute dimensions of the mid B-type eclipsing binary U Oph from new light and radial-velocity curves, accounting for both the apsidal motion and the light-time orbit around the third star. The stars in U Oph have masses of 5.27 and 4.74 M⊙(±1.5%) and are located in the middle of the main-sequence band for an an age of ∼50 Myr. U Oph and three other systems (V760 Sco, MU, Cas and DI Her) all have components within 10% of 5M⊙ and ages below 100 Myr; we find significant heavy-element abundance differences between these young nearby stars.

scholarly journals Discussion D: Observational problems with Li, Be and B

2009 ◽  
Vol 5 (S268) ◽  
pp. 493-497
Author(s):  
Poul Erik Nissen
Keyword(s):  
Globular Clusters ◽  
Heavy Element ◽  
Main Sequence ◽  
Downward Trend ◽  
Element Abundance ◽  
Theoretical Studies ◽  
Dwarf Stars ◽  
Giant Stars ◽  
Halo Stars ◽  
Solar Type

AbstractIn Discussion D the following problems were addressed: Has 6Li really been detected in the atmospheres of metal-poor halo stars? Is there a downward trend or increased scatter of Li abundances in stars on the ‘Li-plateau’ at metallicities [Fe/H] ≲ −2.5? Are there significant differences of Li abundances in main-sequence, turn-off, and sub-giant stars in globular clusters? Is the Li abundance in solar-type stars related to the presence of planets? How does the Be abundance in dwarf stars increase with the heavy-element abundance, and is there a cosmic scatter in Be at a given [Fe/H]? The discussion of these problems is summarized and some suggestions for future observational and theoretical studies are mentioned.

scholarly journals On the Star Formation in Early Stage of Galactic Evolution

1981 ◽  
Vol 93 ◽  
pp. 68-69
Author(s):  
Y. Yoshii ◽  
Y. Sabano
Keyword(s):  
Molecular Hydrogen ◽  
Thermal Instability ◽  
Heavy Element ◽  
Hydrogen Gas ◽  
Initial Mass Function ◽  
Element Abundance ◽  
Subsequent Stage ◽  
Pure Hydrogen ◽  
Wide Range ◽  
Gas Cloud

Evolution and fragmentation of a gas cloud are investigated for the primordial chemical composition which is the same as the products of the Big Bang. A pure-hydrogen gas cloud collapses isothermally at 500–1000 K when a low fraction of molecular hydrogen works as a coolant, and breaks into small subcondensations with mass less than 10 M⊙ due to thermal instability associated with molecular dissociation. On the other hand a pure-hydrogen gas cloud which contains no molecular hydrogen collapses isothermally at 6000–8000 K in a thermally stable condition, and enters the region where thermal energy exceeds radiation energy when thermal equilibrium between matter and radiation is achieved in the cloud. Consideration of energetics in the subsequent stage of the cloud evolution leads to the mass range of 0.1–20 M⊙ for the stable nuclear-burning protostars of the first generation. The thermal behavior of a gas cloud in the regime of z (the ratio of heavy element abundance to solar one) less than 10−4 is essentially similar to that in the case of no heavy element, and the heavy element cooling brings about thermal instability in a wide range of parameters in the regime of z greater than 10−3. Linear perturbation analysis gives growth time of the instability much shorter than the free-fall time, and suggests the efficient excitation of density fluctuation driven by thermal instability. Thus the possibility of the initial mass function relatively enhanced in massive star at early times is denied, and the slow rate of metal enrichment in the interstellar medium is suggested.

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 Understanding Jupiter’s deep interior: the effect of a dilute core

2019 ◽  
Vol 632 ◽  
pp. A76
Author(s):  
Dongdong Ni
Keyword(s):  
Heavy Element ◽  
Equations Of State ◽  
Layer Structure ◽  
Core Region ◽  
Element Abundance ◽  
Interior Structure ◽  
Core Mass ◽  
The Core ◽  
Two Envelopes ◽  
Structure Calculations

Context. The Juno spacecraft has significantly improved the accuracy of low-order even gravitational harmonics. It has been demonstrated that a dilute core is helpful to interpret Juno’s gravity measurements. However, introducing a dilute core adds a new degree of freedom to Jupiter’s interior models in addition to the uncertainties in the equations of state for hydrogen and helium. Aims. We present four-layer structure models for Jupiter where a dilute core region is added above a central compact core of rocks. The effect of the dilute core on the structure and composition of Jupiter is investigated in detail. Combined with current knowledge of Jupiter’s composition and thermal state, we aim to obtain information on the dilute core. Also, we investigate the effect of equations of state for hydrogen and helium on the predictions of the core mass and heavy element abundance. Methods. In the four-layer structure model, the heavy element abundances in the outer two envelopes and the mass of the compact core were adjusted to reproduce Jupiter’s equatorial radius as well as Juno’s gravity observations. Different dilute core configurations were constructed in terms of its size and composition and different equations of state for hydrogen and helium were used in interior structure calculations. Optimized calculations were then performed to investigate the effect of dilute cores and equations of state on Jupiter’s internal structure and composition. Results. It is found that the absolute values of J6 and J8 tend to decrease as helium becomes more depleted in the dilute core region. Most interior structure calculations seem to prefer an inward decrease of the helium mass fraction from the metallic envelope to the dilute core region. We also show that the core mass and heavy element abundance in Jupiter are dependent upon the rock-to-ice ratio in the dilute core region, the temperature jump from the molecular to metallic envelope, and the equations of state for hydrogen and helium. The resulting heavy-element mass in the core is generally larger than the three-layer structure models owing to the heavy elements dissolved in the dilute core region, and the global heavy-element abundance is in good agreement with the available dilute-core predictions.

scholarly journals Evolution of massive stars: main sequence and close to it

1993 ◽  
Vol 137 ◽  
pp. 426-436
Author(s):  
Norbert Langer
Keyword(s):  
Main Sequence ◽  
Massive Stars ◽  
Nuclear Data ◽  
Mass Range ◽  
Sequence Evolution ◽  
Mixing Processes ◽  
Convective Mixing ◽  
Internal Mixing ◽  
The Status ◽  
Standard Models

AbstractWe discuss the status of current models for the early evolutionary stages of stars in the initial mass range 10-40 M⊙. Effects of the pre-main sequence evolution, mass loss, internal mixing, and changes in atomic and nuclear data are outlined and confronted with several basic observational facts, which are unexplained by standard models. We conclude that especially internal mixing processes deserve much more attention in future investigations, and we show why convective mixing may be less efficient than generally assumed, but more mixing should be present in the radiative zones of at least a fraction of all massive stars.

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.

The Infancy of Solar-Type Stars and its Relevance for the Origin of Life

1997 ◽  
Vol 161 ◽  
pp. 267-282 ◽  
Author(s):  
Thierry Montmerle
Keyword(s):  
Main Sequence ◽  
Solar Nebula ◽  
Circumstellar Disks ◽  
T Tauri Stars ◽  
Necessary Condition ◽  
Sequence Evolution ◽  
T Tauri ◽  
Solar Type ◽  
Optical Domain ◽  
The Origin Of Life

AbstractFor life to develop, planets are a necessary condition. Likewise, for planets to form, stars must be surrounded by circumstellar disks, at least some time during their pre-main sequence evolution. Much progress has been made recently in the study of young solar-like stars. In the optical domain, these stars are known as «T Tauri stars». A significant number show IR excess, and other phenomena indirectly suggesting the presence of circumstellar disks. The current wisdom is that there is an evolutionary sequence from protostars to T Tauri stars. This sequence is characterized by the initial presence of disks, with lifetimes ~ 1-10 Myr after the intial collapse of a dense envelope having given birth to a star. While they are present, about 30% of the disks have masses larger than the minimum solar nebula. Their disappearance may correspond to the growth of dust grains, followed by planetesimal and planet formation, but this is not yet demonstrated.

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