scholarly journals The effect of rotation on RGB surface abundances

1997 ◽  
Vol 189 ◽  
pp. 349-354
Author(s):  
C. Charbonnel
Keyword(s):  
Stellar Evolution ◽  
Globular Cluster ◽  
Massive Stars ◽  
Observational Evidence ◽  
Evolution Theory ◽  
Mixing Processes ◽  
Giant Stars ◽  
The Subject ◽  
Abundance Anomalies ◽  
Chemical Anomalies

Pop II field and globular cluster giant stars (and, to a less extent, Pop I giants) exhibit chemical anomalies which are not predicted by standard stellar evolution theory. Two hypotheses have been proposed to explain these abundance variations, namely the primordial and the evolutionary explanations. A primordial origin for intracluster abundance anomalies (see e.g. Cottrel & Da Costa 1981) would be related to inhomogeneities in the cluster material due to pollution by a prior generation of massive stars. In the evolutionary hypothesis, abundance variations would be due to nuclear and mixing processes internal to the giant stars themselves. Many good reviews exist on the subject (see e.g. Briley et al. 1994a, Kraft 1994), in which observational evidence supporting both hypotheses are presented. In this conference, Da Costa recalls the most recent observational data, and some excellent poster contributions bring essential clues to the subject.

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.

scholarly journals Boron depletion in 9 to 15 M⊙ stars with rotation

2009 ◽  
Vol 5 (S268) ◽  
pp. 421-422
Author(s):  
U. Frischknecht ◽  
R. Hirschi ◽  
G. Meynet ◽  
S. Ekström ◽  
C. Georgy ◽  
...  
Keyword(s):  
Stellar Evolution ◽  
Main Sequence ◽  
Massive Stars ◽  
Nitrogen Enrichment ◽  
Rotating Stars ◽  
Mixing Processes ◽  
The Real ◽  
Real Effects ◽  
M Stars ◽  
Open Question

AbstractThe treatment of mixing is still one of the major uncertainties in stellar evolution models. One open question is how well the prescriptions for rotational mixing describe the real effects. We tested the mixing prescriptions included in the Geneva stellar evolution code (GENEC) by following the evolution of surface abundances of light isotopes in massive stars, such as boron and nitrogen. We followed 9, 12 and 15 M⊙ models with rotation from the zero age main sequence up to the end of He burning. The calculations show the expected behaviour with faster depletion of boron for faster rotating stars and more massive stars. The mixing at the surface is more efficient than predicted by prescriptions used in other codes and reproduces the majority of observations very well. However two observed stars with strong boron depletion but no nitrogen enrichment still can not be explained and let the question open whether additional mixing processes are acting in these massive stars.

scholarly journals Mass loss and evolution of massive stars

1981 ◽  
Vol 59 ◽  
pp. 229-253
Author(s):  
C. Chiosi
Keyword(s):  
Mass Loss ◽  
Stellar Wind ◽  
Evolutionary History ◽  
Massive Stars ◽  
Observational Evidence ◽  
Common Occurrence ◽  
Theoretical Understanding ◽  
The Past ◽  
History Of ◽  
The Subject

In the past few years both growing observational evidence and theoretical understanding have shown that mass loss by stellar wind is a common occurrence in the evolutionary history of many types of star. Recent reviews on the subject may be found in Conti (1978), Cassinelli (1979), Conti and Mc Cray (1980), Hutchings (1980a), de Loore (1979, 1980) and Sreenivasan (1979).Therefore, in this paper we will concentrate only on those observational and theoretical aspects of the problem that demand further investigation.

scholarly journals New prescriptions of turbulent transport from local numerical simulations

2014 ◽  
Vol 9 (S307) ◽  
pp. 70-75
Author(s):  
V. Prat ◽  
F. Lignières ◽  
G. Lesur
Keyword(s):  
Numerical Simulations ◽  
Stellar Evolution ◽  
Turbulent Mixing ◽  
Massive Stars ◽  
Turbulent Transport ◽  
Strong Impact ◽  
Evolution Theory ◽  
Transport Models ◽  
Chemical Stratification ◽  
The Impact

AbstractMassive stars often experience fast rotation, which is known to induce turbulent mixing with a strong impact on the evolution of these stars. Local direct numerical simulations of turbulent transport in stellar radiative zones are a promising way to constrain phenomenological transport models currently used in many stellar evolution codes. We present here the results of such simulations of stably-stratified sheared turbulence taking notably into account the effects of thermal diffusion and chemical stratification. We also discuss the impact of theses results on stellar evolution theory.

scholarly journals Wolf-Rayet stars as a diagnostic of internal mixing processes in massive mass losing stars

1988 ◽  
Vol 108 ◽  
pp. 90-91
Author(s):  
N. Langer
Keyword(s):  
Observational Data ◽  
Stellar Evolution ◽  
Chemical Structure ◽  
Large Scale ◽  
Massive Stars ◽  
The Other ◽  
Large Uncertainty ◽  
Mixing Processes ◽  
Internal Mixing ◽  
Convective Core

Massive stars (MZAMS ≳ 30 M⊙) develop during their observable hydrostatic evolutionary phases — i.e. central H- and He-burning — three different large scale convective zones, which are: 1) The H-burning convective core, 2) the intermediate convective shell (ICZ) above the hydrogen shell source, which forms at time of hydrogen exhaustion, and 3) the He-burning convective core. The spatial extent of these convective regions, wherein the chemical structure is rapidly homogenised, can be predicted from theory only with a large uncertainty. Different assumptions on the efficiency of these mixing processes in stellar evolution calculations lead to quite different evolutionary pictures for massive stars, especially regarding their Wolf-Rayet (WR) phases. On the other side, many observational data concerning WR stars became available in recent years. For this reason, we attempt to perform a comparison of theoretical evolutionary sequences with observed properties of WR stars in order to derive restrictions on the efficiency of the three mixing processes mentioned above.

scholarly journals Lithium in red giant stars: Constraining non-standard mixing with large surveys in the Gaia era

2020 ◽  
Vol 633 ◽  
pp. A34 ◽  
Author(s):  
C. Charbonnel ◽  
N. Lagarde ◽  
G. Jasniewicz ◽  
P. L. North ◽  
M. Shetrone ◽  
...  
Keyword(s):  
Stellar Evolution ◽  
Asymptotic Giant Branch ◽  
Mixing Processes ◽  
Giant Stars ◽  
Red Giant Stars ◽  
Red Giant ◽  
Good Tracer ◽  
The Impact ◽  
Maximum Likelihood Technique ◽  
Evolution Status

Context. Li is extensively known to be a good tracer of non-standard mixing processes occurring in stellar interiors. Aims. We present the results of a new large Li survey in red giant stars and combine it with surveys from the literature to probe the impact of rotation-induced mixing and thermohaline double-diffusive instability along stellar evolution. Methods. We determined the surface Li abundance for a sample of 829 giant stars with accurate Gaia parallaxes for a large sub-sample (810 stars) complemented with accurate HIPPARCOS parallaxes (19 stars). The spectra of our sample of northern and southern giant stars were obtained in three ground-based observatories (Observatoire de Haute-Provence, ESO-La Silla, and the Mc Donald Observatory). We determined the atmospheric parameters (Teff, log(g) and [Fe/H]), and the Li abundance. We used Gaia parallaxes and photometry to determine the luminosity of our objects and we estimated the mass and evolution status of each sample star with a maximum-likelihood technique using stellar evolution models computed with the STAREVOL code. We compared the observed Li behaviour with predictions from stellar models, including rotation and thermohaline mixing. The same approach was used for stars from selected Li surveys from the literature. Results. Rotation-induced mixing accounts nicely for the Li behaviour in stars warmer than about 4200 K, independently of the mass domain. For stars with masses lower than 2 M⊙ thermohaline mixing leads to further Li depletion below the Teff of the RGB bump (about 4000 K), and on the early asymptotic giant branch, as observed. Depending on the definition we adopt, we find between 0.8 and 2.2% of Li-rich giants in our new sample. Conclusions.Gaia puts a new spin on the understanding of mixing processes in stars, and our study confirms the importance of rotation-induced processes and of thermohaline mixing. However asteroseismology is required to definitively pinpoint the actual evolution status of Li-rich giants.

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 Massive binaries and the enrichment of the interstellar medium in globular clusters

2009 ◽  
Vol 5 (S266) ◽  
pp. 169-174
Author(s):  
S. E. de Mink ◽  
O. R. Pols ◽  
N. Langer ◽  
R. G. Izzard
Keyword(s):  
Globular Cluster ◽  
Globular Clusters ◽  
Massive Stars ◽  
Asymptotic Giant Branch ◽  
Low Velocity ◽  
Alternative Source ◽  
Hydrogen Burning ◽  
Processed Material ◽  
Abundance Anomalies ◽  
Interesting Alternative

AbstractAbundance anomalies observed in globular cluster stars indicate pollution with material processed by hydrogen burning. Two main sources have been suggested: asymptotic giant branch (AGB) stars and massive stars rotating near the break-up limit (spin stars). We discuss the idea that massive binaries may provide an interesting alternative source of processed material. We discuss observational evidence for mass shedding from interacting binaries. In contrast to the fast, radiatively driven winds of massive stars, this material is typically ejected with low velocity. We expect that it remains inside the potential well of a globular cluster and becomes available for the formation or pollution of a second generation of stars. We estimate that the amount of processed low-velocity material that can be ejected by massive binaries is larger than the contribution of the two previously suggested sources combined.

scholarly journals Globular cluster abundances: the imprint of first-generation massive stars

2009 ◽  
Vol 5 (S266) ◽  
pp. 131-142 ◽  
Author(s):  
Corinne Charbonnel
Keyword(s):  
Globular Cluster ◽  
First Generation ◽  
Massive Stars ◽  
Stellar Nucleosynthesis ◽  
Abundance Patterns ◽  
History Of ◽  
Pros And Cons ◽  
Abundance Anomalies ◽  
Intracluster Gas ◽  
Interesting Alternative

AbstractGalactic globular cluster (GC) stars exhibit abundance patterns that are not shared by their field counterparts, namely the well-documented O–Na, C–N and Mg–Al anticorrelations. Recent observations provide compelling evidence that these abundance anomalies were already present in the intracluster gas from which the presently observed stars formed. The current explanation is that the gas was polluted very early in the history of the GC by material processed through H burning at high temperatures and then lost by stars more massive than the long-lived stars we still observe today. However the ‘polluters’ have not yet been unambiguously identified. Most studies have focused on asymptotic giant brach stars, but rotating massive stars present an interesting alternative. Here, we critically analyse the pros and cons of both potential stellar polluters. We discuss the constraints that the observational data provide on stellar nucleosynthesis and hydrodynamics, as well as on the formation and early evolution of very massive star clusters.

Sign in / Sign up

Export Citation Format

Share Document