scholarly journals Testing convective mixing in massive stars

2003 ◽  
Vol 212 ◽  
pp. 291-295
Author(s):  
Mounib F. El Eid ◽  
Philip J. Flower
Keyword(s):  
Molecular Weight ◽  
Stellar Evolution ◽  
Massive Stars ◽  
Mass Range ◽  
Star Cluster ◽  
Helium Abundance ◽  
Small Magellanic Cloud ◽  
Average Composition ◽  
Convective Mixing

Stellar evolution sequences are presented for stars in the mass range 5-21 M⊙ with initial metallicity Z = 0.002 and initial helium abundance Y = 0.25 resembling average composition of the Small Magellanic Cloud. The stellar models are calculated with different treatment of convective mixing in regions of varying molecular weight gradient. The stellar sequences are used to study the morphology of the well-observed star cluster NGC 330 in the SMC. We argue that convective mixing should be inhibited in inhomogeneous stellar regions in order to understand the morphology of NGC 330. In other words, our contribution emphasizes the important role of semi-convection in the evolution of massive stars.

scholarly journals Populations of OB-type stars in galaxies

2010 ◽  
Vol 6 (S272) ◽  
pp. 233-241
Author(s):  
Christopher J. Evans
Keyword(s):  
Stellar Evolution ◽  
Massive Stars ◽  
Spectral Synthesis ◽  
High Redshift ◽  
Young Star ◽  
Magellanic Clouds ◽  
Star Forming ◽  
The Galaxy ◽  
External Galaxies

AbstractOne of the challenges for stellar astrophysics is to reach the point at which we can undertake reliable spectral synthesis of unresolved populations in young, star-forming galaxies at high redshift. Here I summarise recent studies of massive stars in the Galaxy and Magellanic Clouds, which span a range of metallicities commensurate with those in high-redshift systems, thus providing an excellent laboratory in which to study the role of environment on stellar evolution. I also give an overview of observations of luminous supergiants in external galaxies out to a remarkable 6.7 Mpc, in which we can exploit our understanding of stellar evolution to study the chemistry and dynamics of the host systems.

scholarly journals Stellar models and isochrones from low-mass to massive stars including pre-main sequence phase with accretion

2019 ◽  
Vol 624 ◽  
pp. A137 ◽  
Author(s):  
L. Haemmerlé ◽  
P. Eggenberger ◽  
S. Ekström ◽  
C. Georgy ◽  
G. Meynet ◽  
...  
Keyword(s):  
Star Formation ◽  
Stellar Evolution ◽  
Main Sequence ◽  
Massive Stars ◽  
Mass Range ◽  
Stellar Clusters ◽  
Solar Metallicity ◽  
Low Mass ◽  
Stellar Models ◽  
Young Clusters

Grids of stellar models are useful tools to derive the properties of stellar clusters, in particular young clusters hosting massive stars, and to provide information on the star formation process in various mass ranges. Because of their short evolutionary timescale, massive stars end their life while their low-mass siblings are still on the pre-main sequence (pre-MS) phase. Thus the study of young clusters requires consistent consideration of all the phases of stellar evolution. But despite the large number of grids that are available in the literature, a grid accounting for the evolution from the pre-MS accretion phase to the post-MS phase in the whole stellar mass range is still lacking. We build a grid of stellar models at solar metallicity with masses from 0.8 M⊙ to 120 M⊙, including pre-MS phase with accretion. We use the GENEC code to run stellar models on this mass range. The accretion law is chosen to match the observations of pre-MS objects on the Hertzsprung-Russell diagram. We describe the evolutionary tracks and isochrones of our models. The grid is connected to previous MS and post-MS grids computed with the same numerical method and physical assumptions, which provides the widest grid in mass and age to date.

scholarly journals Fate of most massive stars

2011 ◽  
Vol 7 (S279) ◽  
pp. 431-432
Author(s):  
Norhasliza Yusof ◽  
Raphael Hirschi ◽  
Hasan Abu Kassim
Keyword(s):  
Mass Loss ◽  
Stellar Evolution ◽  
Crucial Role ◽  
Milky Way ◽  
Massive Stars ◽  
Mass Range ◽  
Pair Creation ◽  
High Mass ◽  
Chemical Signature

AbstractThe first generations of stars are thought to have been more massive than Pop I stars and therefore some of these are thought to have produced pair creation supernovae (PCSNe) at the end of their life. However, the chemical signature of PCSNe is not observed in extremely metal poor stars (e.g. Umeda and Nomoto 2002) and it raises the following questions: Were stars born less (or more massive) than the mass range expected to lead to the PCSNe? Or was mass loss too strong during the evolution of these stars and prevented them from retaining enough mass to produce PCSNe? The discovery of very massive stars (VMS, M > 100 M⊙) in the Milky Way and LMC (Crowther et al. 2010) shows that VMS can form and exist. The observations of PCSN candidates (2006gy & 2007bi) also seems to indicate that such SNe may occur. Mass loss plays a crucial role in the life of VMS since the star will only die as a PCSN if the star retains a high mass throughout its life. In this paper, we shall describe the dependence of VMS evolution on metallicity and present stellar evolution models at various metallicities, including the effects of mass loss and rotation. Based on our models, we will give our predictions concerning the fate of these VMS, either a PCSN or SNIc (possibly GRBs in some cases) as a function of metallicity.

scholarly journals Pre-Supernova Evolution of Rotating Massive Stars

2005 ◽  
Vol 192 ◽  
pp. 209-213
Author(s):  
Raphael Hirschi ◽  
Georges Meynet ◽  
André Maeder ◽  
Stéphane Goriely
Keyword(s):  
Mass Loss ◽  
Stellar Evolution ◽  
Crucial Role ◽  
Massive Stars ◽  
Total Metal ◽  
Solar Metallicity ◽  
Advanced Stages ◽  
Rotating Star ◽  
Fast Rotating

SummaryThe Geneva evolutionary code has been modified to study the advanced stages (Ne, O, Si burnings) of rotating massive stars. Here we present the results of four 20 M⊙ stars at solar metallicity with initial rotational velocities, vini, of 0, 100, 200 and 300 km/s in order to show the crucial role of rotation in stellar evolution. As already known, rotation increases mass loss and core masses [4]. A fast rotating 20 M⊙ star has the same central evolution as a non-rotating 26 M⊙. Rotation also increases strongly net total metal yields. Furthermore, rotation changes the SN type so that more SNIb are predicted (see [5] and [6]). Finally, SN1987A-like supernovae progenitor colors can be explained in a single rotating star scenario.

Non-Radial Oscillations of Massive Stars

1967 ◽  
Vol 1 (1) ◽  
pp. 16-17
Author(s):  
R. Van Der Borght
Keyword(s):  
Molecular Weight ◽  
Differential Equations ◽  
Numerical Integration ◽  
Massive Stars ◽  
Mass Range ◽  
Review Article ◽  
Basic System ◽  
System Of Differential Equations ◽  
Uniform Composition

The basic system of differential equations governing the non-radial adiabatic oscillations of stars are given in the review article by P. Ledoux and Th. Walraven. The numerical integration of these equations has been undertaken by P. Smeyers and by R. Van der Borght and Wan Fook Sun, in the latter case for stars of uniform composition in the mass range.where μ is the molecular weight of the stellar material. These integrations were based on models derived by R. Van der Borght.

scholarly journals The fates of massive stars: exploring uncertainties in stellar evolution with metisse

2020 ◽  
Vol 497 (4) ◽  
pp. 4549-4564
Author(s):  
Poojan Agrawal ◽  
Jarrod Hurley ◽  
Simon Stevenson ◽  
Dorottya Szécsi ◽  
Chris Flynn
Keyword(s):  
Stellar Evolution ◽  
Main Sequence ◽  
Massive Stars ◽  
Mass Range ◽  
Radial Expansion ◽  
Single Star ◽  
New Approach ◽  
Star Evolution ◽  
Order Of Magnitude ◽  
The Impact

ABSTRACT In the era of advanced electromagnetic and gravitational wave detectors, it has become increasingly important to effectively combine and study the impact of stellar evolution on binaries and dynamical systems of stars. Systematic studies dedicated to exploring uncertain parameters in stellar evolution are required to account for the recent observations of the stellar populations. We present a new approach to the commonly used single-star evolution (sse) fitting formulae, one that is more adaptable: method of interpolation for single star evolution (metisse). It makes use of interpolation between sets of pre-computed stellar tracks to approximate evolution parameters for a population of stars. We have used metisse with detailed stellar tracks computed by the modules for experiments in stellar astrophysics (mesa), the bonn evolutionary code (bec), and the Cambridge stars code. metisse better reproduces stellar tracks computed using the stars code compared to sse, and is on average three times faster. Using stellar tracks computed with mesa and bec, we apply metisse to explore the differences in the remnant masses, the maximum radial expansion, and the main-sequence lifetime of massive stars. We find that different physical ingredients used in the evolution of stars, such as the treatment of radiation-dominated envelopes, can impact their evolutionary outcome. For stars in the mass range 9–100 M⊙, the predictions of remnant masses can vary by up to 20 M⊙, while the maximum radial expansion achieved by a star can differ by an order of magnitude between different stellar models.

scholarly journals Is GW190521 the merger of black holes from the first stellar generations?

2020 ◽  
Author(s):  
Eoin J Farrell ◽  
Jose H Groh ◽  
Raphael Hirschi ◽  
Laura Murphy ◽  
Etienne Kaiser ◽  
...  
Keyword(s):  
Black Holes ◽  
Mass Loss ◽  
Stellar Evolution ◽  
Massive Stars ◽  
Compact Star ◽  
Binary Interaction ◽  
Core Mass ◽  
Convective Mixing ◽  
Low Metallicity ◽  
Instability Regime

Abstract GW190521 challenges our understanding of the late-stage evolution of massive stars and the effects of the pair-instability in particular. We discuss the possibility that stars at low or zero metallicity could retain most of their hydrogen envelope until the pre-supernova stage, avoid the pulsational pair-instability regime and produce a black hole with a mass in the mass gap by fallback. We present a series of new stellar evolution models at zero and low metallicity computed with the Geneva and MESA stellar evolution codes and compare to existing grids of models. Models with a metallicity in the range 0 – 0.0004 have three properties which favour higher BH masses. These are (i) lower mass-loss rates during the post-MS phase, (ii) a more compact star disfavouring binary interaction and (iii) possible H-He shell interactions which lower the CO core mass. We conclude that it is possible that GW190521 may be the merger of black holes produced directly by massive stars from the first stellar generations. Our models indicate BH masses up to 70-75 M⊙. Uncertainties related to convective mixing, mass loss, H-He shell interactions and pair-instability pulsations may increase this limit to ∼85M⊙.

scholarly journals On the possibility of partial matter mixing in rotating massive stars

2003 ◽  
Vol 212 ◽  
pp. 427-428
Author(s):  
Eugenij I. Staritsin
Keyword(s):  
Molecular Weight ◽  
Massive Stars ◽  
Principal Role ◽  
Inhibiting Effect ◽  
Horizontal Diffusion ◽  
Convective Core ◽  
Rotating Star ◽  
Mean Molecular Weight

The principal role of strong horizontal diffusion in overcoming the inhibiting effect of mean molecular weight gradient and in producing partial matter mixing between convective core and radiative envelope of a rotating star, is shown.

scholarly journals Fitting formulae for evolution tracks of massive stars under extreme metal-poor environments for population synthesis calculations and star cluster simulations

2020 ◽  
Vol 495 (4) ◽  
pp. 4170-4191 ◽  
Author(s):  
Ataru Tanikawa ◽  
Takashi Yoshida ◽  
Tomoya Kinugawa ◽  
Koh Takahashi ◽  
Hideyuki Umeda
Keyword(s):  
Stellar Evolution ◽  
Massive Stars ◽  
Star Cluster ◽  
Population Synthesis ◽  
Solar Mass ◽  
Helium Burning ◽  
Binary Black Holes ◽  
Extreme Metal ◽  
Hertzsprung Gap ◽  
Good Agreement

ABSTRACT We have devised fitting formulae for evolution tracks of massive stars with 8 ≲ M/M⊙ ≲ 160 under extreme metal-poor (EMP) environments for log (Z/Z⊙) = −2, −4, −5, −6, and −8, where M⊙ and Z⊙ are the solar mass and metallicity, respectively. Our fitting formulae are based on reference stellar models which we have newly obtained by simulating the time evolutions of EMP stars. Our fitting formulae take into account stars ending with blue supergiant (BSG) stars, and stars skipping Hertzsprung gap phases and blue loops, which are characteristics of massive EMP stars. In our fitting formulae, stars may remain BSG stars when they finish their core Helium burning phases. Our fitting formulae are in good agreement with our stellar evolution models. We can use these fitting formulae on the sse, bse, nbody4, and nbody6 codes, which are widely used for population synthesis calculations and star cluster simulations. These fitting formulae should be useful to make theoretical templates of binary black holes formed under EMP environments.

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.

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