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 Production of Helium by Stellar Evolution

1971 ◽  
Vol 2 ◽  
pp. 296-300
Author(s):  
R. Kippenhahn
Keyword(s):  
Stellar Evolution ◽  
Mass Fraction ◽  
Review Paper ◽  
Recent Model ◽  
Solar Mass ◽  
Helium Burning ◽  
Model Calculations ◽  
Helium Content ◽  
The Galaxy

In order to maintain the luminosity of the Galaxy ⅓ of a solar mass of hydrogen has to be transformed into helium every year. This rate of production is too small by a factor 10 or 20 in order to give a helium content of Y = 0.3-04. within the age of the galaxy if the mass fraction Y of helium was zero at the beginning. The situation is even worse if the destruction of helium by helium burning is taken into account. In his review paper Tayler (1967) came already to this conclusion. I shall discuss the problem here using more recent model calculations, but we shall come up with the same result.

scholarly journals Grids of stellar models with rotation

2019 ◽  
Vol 627 ◽  
pp. A24 ◽  
Author(s):  
J. H. Groh ◽  
S. Ekström ◽  
C. Georgy ◽  
G. Meynet ◽  
A. Choplin ◽  
...  
Keyword(s):  
Stellar Evolution ◽  
Massive Stars ◽  
Stellar Winds ◽  
Pulsation Period ◽  
Instability Strip ◽  
Helium Burning ◽  
Red Supergiants ◽  
Low Metallicity ◽  
Effects Of Rotation ◽  
The Impact

The effects of rotation on stellar evolution are particularly important at low metallicity, when mass loss by stellar winds diminishes and the surface enrichment due to rotational mixing becomes relatively more pronounced than at high metallicities. Here we investigate the impact of rotation and metallicity on stellar evolution. Using similar physics as in our previous large grids of models at Z = 0.002 and Z = 0.014, we compute stellar evolution models with the Geneva code for rotating and nonrotating stars with initial masses (Mini) between 1.7 and 120 M⊙ and Z = 0.0004 (1/35 solar). This is comparable to the metallicities of the most metal poor galaxies observed so far, such as I Zw 18. Concerning massive stars, both rotating and nonrotating models spend most of their core-helium burning phase with an effective temperature higher than 8000 K. Stars become red supergiants only at the end of their lifetimes, and few red supergiants are expected. Our models predict very few to no classical Wolf–Rayet stars as a results of weak stellar winds at low metallicity. The most massive stars end their lifetimes as luminous blue supergiants or luminous blue variables, a feature that is not predicted by models with higher initial metallicities. Interestingly, due to the behavior of the intermediate convective zone, the mass domain of stars producing pair-instability supernovae is smaller at Z = 0.0004 than at Z = 0.002. We find that during the main sequence (MS) phase, the ratio between nitrogen and carbon abundances (N/C) remains unchanged for nonrotating models. However, N/C increases by factors of 10–20 in rotating models at the end of the MS. Cepheids coming from stars with Mini >  4 − 6 M⊙ are beyond the core helium burning phase and spend little time in the instability strip. Since they would evolve towards cooler effective temperatures, these Cepheids should show an increase of the pulsation period as a function of age.

scholarly journals Common envelope evolution of massive stars

2018 ◽  
Vol 14 (S346) ◽  
pp. 449-454 ◽  
Author(s):  
Paul M. Ricker ◽  
Frank X. Timmes ◽  
Ronald E. Taam ◽  
Ronald F. Webbink
Keyword(s):  
Black Hole ◽  
Stellar Evolution ◽  
Massive Stars ◽  
Evolution Theory ◽  
Helium Burning ◽  
Massive Black Hole ◽  
Common Envelope ◽  
Binary Black Hole ◽  
Low Metallicity ◽  
The Common

AbstractThe discovery via gravitational waves of binary black hole systems with total masses greater than 60Mʘ has raised interesting questions for stellar evolution theory. Among the most promising formation channels for these systems is one involving a common envelope binary containing a low metallicity, core helium burning star with mass ⁓30 – 40Mʘ and a black hole with mass ⁓30 – 40Mʘ. For this channel to be viable, the common envelope binary must eject more than half the giant star’s mass and reduce its orbital separation by as much as a factor of 80. We discuss issues faced in numerically simulating the common envelope evolution of such systems and present a 3D AMR simulation of the dynamical inspiral of a low-metallicity red supergiant with a massive black hole companion.

scholarly journals New insight on the far-UV SED and He ii emission from low metallicity galaxies

2019 ◽  
Vol 15 (S352) ◽  
pp. 79-83
Author(s):  
Daniel Schaerer ◽  
Yuri Izotov ◽  
Tassos Fragos
Keyword(s):  
Stellar Evolution ◽  
Massive Stars ◽  
Population Synthesis ◽  
Physical Processes ◽  
X Ray ◽  
Large Samples ◽  
Distant Galaxies ◽  
Multi Wavelength ◽  
Low Metallicity ◽  
X Ray Binaries

AbstractUnderstanding the ionizing spectrum of low-metallicity galaxies is of great importance for modeling and interpreting emission line observations of early/distant galaxies.Although a wide suite of stellar evolution, atmosphere, population synthesis, and photoionization models, taking many physical processes into account now exist, all models face a common problem: the inability to explain the presence of nebular Heii emission, which is observed in many low metallicity galaxies, both in UV and optical spectra. Several possible explanations have been proposed in the literature, including Wolf-Rayet (WR) stars, binaries, very massive stars, X-ray sources, or shocks. However, none has so far been able to explain the major observations.We briefly discuss the He ii problem, available empirical data, and observed trends combining X-ray, optical and other studies. We present a simple and consistent physical model showing that X-ray binaries could explain the long-standing nebular Heii problem. Our model, described in Schaerer et al. (2019), successfully explains the observed trends and strength of nebular He ii emission in large samples of low metallicity galaxies and in individual galaxies, which have been studied in detail and with multi-wavelength observations. Our results have in particular important implications for the interpretation of galaxy spectra in the early Universe, which will be obtained with upcoming and future facilities.

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 A hot and fast ultra-stripped supernova that likely formed a compact neutron star binary

Science ◽  
2018 ◽  
Vol 362 (6411) ◽  
pp. 201-206 ◽  
Author(s):  
K. De ◽  
M. M. Kasliwal ◽  
E. O. Ofek ◽  
T. J. Moriya ◽  
J. Burke ◽  
...  
Keyword(s):  
Neutron Star ◽  
Kinetic Energy ◽  
Light Curve ◽  
Stellar Evolution ◽  
Binary Systems ◽  
Massive Stars ◽  
Compact Binary ◽  
Compact Binary Systems ◽  
Supernova Explosions ◽  
Star Binary

Compact neutron star binary systems are produced from binary massive stars through stellar evolution involving up to two supernova explosions. The final stages in the formation of these systems have not been directly observed. We report the discovery of iPTF 14gqr (SN 2014ft), a type Ic supernova with a fast-evolving light curve indicating an extremely low ejecta mass (≈0.2 solar masses) and low kinetic energy (≈2 × 1050ergs). Early photometry and spectroscopy reveal evidence of shock cooling of an extended helium-rich envelope, likely ejected in an intense pre-explosion mass-loss episode of the progenitor. Taken together, we interpret iPTF 14gqr as evidence for ultra-stripped supernovae that form neutron stars in compact binary systems.

scholarly journals Bimodal regime in young massive clusters leading to subsequent stellar generations

2015 ◽  
Vol 12 (S316) ◽  
pp. 294-301
Author(s):  
Richard Wünsch ◽  
Jan Palouš ◽  
Guillermo Tenorio-Tagle ◽  
Casiana Muñoz-Tuñón ◽  
Soňa Ehlerová
Keyword(s):  
Stellar Evolution ◽  
Column Density ◽  
First Generation ◽  
Massive Stars ◽  
Ionising Radiation ◽  
Cluster Center ◽  
Stellar Winds ◽  
Hot Gas ◽  
Massive Clusters ◽  
By Products

AbstractMassive stars in young massive clusters insert tremendous amounts of mass and energy into their surroundings in the form of stellar winds and supernova ejecta. Mutual shock-shock collisions lead to formation of hot gas, filling the volume of the cluster. The pressure of this gas then drives a powerful cluster wind. However, it has been shown that if the cluster is massive and dense enough, it can evolve in the so–called bimodal regime, in which the hot gas inside the cluster becomes thermally unstable and forms dense clumps which are trapped inside the cluster by its gravity. We will review works on the bimodal regime and discuss the implications for the formation of subsequent stellar generations. The mass accumulates inside the cluster and as soon as a high enough column density is reached, the interior of the clumps becomes self-shielded against the ionising radiation of stars and the clumps collapse and form new stars. The second stellar generation will be enriched by products of stellar evolution from the first generation, and will be concentrated near the cluster center.

scholarly journals Massive stars in their death throes

2008 ◽  
Vol 366 (1884) ◽  
pp. 4441-4452 ◽  
Author(s):  
John J Eldridge
Keyword(s):  
Stellar Evolution ◽  
Massive Stars ◽  
Evolution Theory ◽  
Luminous Blue Variables ◽  
Show Evidence ◽  
Red Supergiants ◽  
Working Backwards

The study of the stars that explode as supernovae used to be a forensic study, working backwards from the remnants of the star. This changed in 1987 when the first progenitor star was identified in pre-explosion images. Currently, there are eight detected progenitors with another 21 non-detections, for which only a limit on the pre-explosion luminosity can be placed. This new avenue of supernova research has led to many interesting conclusions, most importantly that the progenitors of the most common supernovae, type IIP, are red supergiants, as theory has long predicted. However, no progenitors have been detected thus far for the hydrogen-free type Ib/c supernovae, which, given the expected progenitors, is an unlikely result. Also, observations have begun to show evidence that luminous blue variables, which are among the most massive stars, may directly explode as supernovae. These results contradict the current stellar evolution theory. This suggests that we may need to update our understanding.

Sign in / Sign up

Export Citation Format

Share Document