scholarly journals Vibrational instability of Population III very massive main-sequence stars due to the -mechanism

2012 ◽  
Vol 421 (1) ◽  
pp. L34-L38 ◽  
Author(s):  
Takafumi Sonoi ◽  
Hideyuki Umeda
Keyword(s):  
Nuclear Energy ◽  
Main Sequence ◽  
Early Stage ◽  
Cooling Process ◽  
Main Sequence Stars ◽  
Hydrogen Burning ◽  
Cno Cycle ◽  
The Universe ◽  
Vibrational Instability ◽  
Population Iii

ABSTRACT Very massive stars are thought to be formed in the early Universe because of a lack of cooling process by heavy elements, and might have been responsible for the later evolution of the Universe. We had an interest in the vibrational stability of their evolution and have carried out a linear non-adiabatic analysis of radial and non-radial oscillations for Population III very massive main-sequence stars with . We found that only the radial fundamental mode becomes unstable due to the -mechanism for these stars. The instability appears just after the CNO cycle is activated and the nuclear energy generation rate becomes large enough to stop the pre-main-sequence contraction, and continues during the early stage of core hydrogen burning. Also, we have roughly estimated the amount of mass loss due to the instability to evaluate its significance.

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 Magnetic main sequence stars as progenitors of blue supergiants

2014 ◽  
Vol 9 (S307) ◽  
pp. 391-392
Author(s):  
I. Petermann ◽  
N. Castro ◽  
N. Langer
Keyword(s):  
Magnetic Fields ◽  
Large Scale ◽  
Main Sequence ◽  
Mass Range ◽  
Main Sequence Stars ◽  
Core Mass ◽  
Hydrogen Burning ◽  
Sequence Band ◽  
Convective Core ◽  
The Right

AbstractBlue supergiants (BSGs) to the right the main sequence band in the HR diagram can not be reproduced by standard stellar evolution calculations. We investigate whether a reduced convective core mass due to strong internal magnetic fields during the main sequence might be able to recover this population of stars. We perform calculations with a reduced mass of the hydrogen burning convective core of stars in the mass range 3–30 M⊙ in a parametric way, which indeed lead to BSGs. It is expected that these BSGs would still show large scale magnetic fields in the order of 10 G.

scholarly journals Lithium Abundance, Diffusion and Turbulence

1995 ◽  
Vol 10 ◽  
pp. 459-460
Author(s):  
G. Michaud ◽  
G. Beaudet
Keyword(s):  
Main Sequence ◽  
Normal Values ◽  
Present Theory ◽  
Constant Mass ◽  
Physical Processes ◽  
Main Sequence Stars ◽  
Hydrogen Burning ◽  
Lithium Abundance ◽  
Calculated Curve ◽  
Fully Coupled

Richer & Michaud (1993) calculated a series of envelopes fully coupled to non-rotating, constant mass, stellar evolution models of hydrogen burning stars with masses in the range of 1.2 to 2.2 M⊙, typical of A and F main sequence stars. They included He settling. The location of the theoretically predicted gap of the Hyades agrees quite well with the observed one, a result obtained without the introduction of any free parameter. At temperatures above the gap, while the observed lithium abundances are within a factor of 2-3 of normal values, the theoretical calculated curve drops to very low values. Diffusion velocities being fairly small, any other physical process with larger or similar velocities can reduce the effect of diffusion and produce the observed results. Mass loss is one such process. Another difficulty with the present theory is the width of the gap. Observations show that the observed gap is wider than the calculated one in the Hyades. This also suggests that other physical processes play an important role.

Structure and Appearance of Envelopes around Protostars

1977 ◽  
Vol 42 ◽  
pp. 38-64
Author(s):  
Harold W. Yorke
Keyword(s):  
Star Formation ◽  
Main Sequence ◽  
Interstellar Matter ◽  
Main Sequence Stars ◽  
Hydrogen Burning ◽  
Final Answer

The existence of material in the immediate vicinity of young main sequence stars or even younger objects, protostars, still contracting and evolving towards the main sequence, is related closely to the details of star formation. Although a number of individual idealized problems related to star formation have been well studied, our overall understanding of how interstellar matter evolves into full fledged hydrogen-burning stars can be deemed qualitative at best. The emerging picture is neither complete nor should it be considered the final answer as to how stars form. Let us summarize this picture by a list of “axioms”, valid for star formation (SF) in the plane of our Galaxy.

scholarly journals Distances of Planetary Nebulae

1993 ◽  
Vol 155 ◽  
pp. 109-121 ◽  
Author(s):  
Yervant Terzian
Keyword(s):  
Physical Parameter ◽  
Main Sequence ◽  
Planetary Nebulae ◽  
Variable Stars ◽  
Stellar Systems ◽  
The Sun ◽  
Stellar Clusters ◽  
Main Sequence Stars ◽  
The Universe ◽  
Fundamental Physical

One of the most fundamental physical parameter in astronomy is the distance to the objects we detect in the universe. For many classes of astronomical objects, accurate and proven methods have been developed to determine their distances. Such classes of objects include stars within ∼100 pc from the sun, binary stellar systems, variable stars, stellar clusters, main sequence stars, and other galaxies. It has been, however, more difficult to develop satisfactory methods to determine accurate distances to the more than 1000 planetary nebulae that have been discovered in our galaxy.

scholarly journals VINCI/VLTI Observations of Main Sequence Stars

2004 ◽  
Vol 219 ◽  
pp. 80-84
Author(s):  
Pierre Kervella ◽  
Frédéric Thévenin ◽  
Pierre Morel ◽  
Janine Provost ◽  
Gabrielle Berthomieu ◽  
...  
Keyword(s):  
Main Sequence ◽  
Extrasolar Planets ◽  
Physical Processes ◽  
Main Sequence Stars ◽  
M Dwarfs ◽  
The Past ◽  
Wide Range ◽  
Solar Type ◽  
The Universe ◽  
Angular Diameters

Main Sequence (MS) stars are by far the most numerous class in the Universe. They are often somewhat neglected as they are relatively quiet objects (but exceptions exist), though they bear testimony of the past and future of our Sun. An important characteristic of the MS stars, particularly the solar-type ones, is that they host the large majority of the known extrasolar planets. Moreover, at the bottom of the MS, the red M dwarfs pave the way to understanding the physics of brown dwarfs and giant planets. We have measured very precise angular diameters from recent VINCI/VLTI interferometric observations of a number of MS stars in the K band, with spectral types between A1V and M5.5V. They already cover a wide range of effective temperatures and radii. Combined with precise Hipparcos parallaxes, photometry, spectroscopy as well as the asteroseismic information available for some of these stars, the angular diameters put strong constraints on the detailed models of these stars, and therefore on the physical processes at play.

Survival of Population III stars

2018 ◽  
Vol 14 (S342) ◽  
pp. 266-267
Author(s):  
Jayanta Dutta ◽  
Sharanya Sur ◽  
Athena Stacy ◽  
Jasjeet Singh Bagla
Keyword(s):  
Main Sequence ◽  
Milky Way ◽  
Core Collapse ◽  
Escape Velocity ◽  
First Stars ◽  
Present Epoch ◽  
Final Mass ◽  
Population Iii Stars ◽  
The Universe ◽  
Population Iii

AbstractIn our earlier studyDutta (2016a), it has been shown that a number of primordial protostars (the ‘first stars’ in the Universe, also known as Population III or Pop III stars) are being ejected from the cluster of their origin with the velocity exceeding their escape velocity. Hence there is possibility that some of these protostars can enter main sequence and survive till present epoch, even in Milky Way. We ask the question if the protostars can avoid core collapse, and stop accreting before being ejected from the cluster, with the final mass of stars as 0.8 Mȯ.

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