Publications (36)10.61 Total impact
-
Article: The past and future evolution of a star like Betelgeuse
[show abstract] [hide abstract]
ABSTRACT: We discuss the physics and the evolution of a typical massive star passing through an evolutionary stage similar to that of Betelgeuse. After a brief introduction recalling various observed parameters of Betelgeuse, we discuss the Pre-Main-Sequence phase (PMS), the Main-Sequence (MS) phase, the physics governing the duration of the first crossing of the HR diagram, the red supergiant stage (RSG), the post-red supergiant phases and the final fate of solar metallicity stars with masses between 9 and 25 M$_\odot$. We examine the impact of different initial rotation and of various prescriptions for the mass loss rates during the red supergiant phase. We show that, whatever the initial rotation rate (chosen between 0 and 0.7$\times\upsilon_{\rm crit}$, $\upsilon_{\rm crit}$ being the surface equatorial velocity producing a centrifugal acceleration balancing exactly the gravity) and the mass loss rates during the RSG stage (varied between a standard value and 25 times that value), a 15 M$_\odot$ star always ends its lifetime as a RSG and explodes as a type II-P or II-L supernova.03/2013; -
Article: Rotating massive stars through the ages, with applications to WR stars, Pop III stars and Gamma Ray Bursts
[show abstract] [hide abstract]
ABSTRACT: This article first reviews the basic physics of rotating stars and their evolution. We examine in particular the changes of the mechanical and thermal equilibrium of rotating stars. An important (predicted and observed) effect is that rotating stars are hotter at the poles and cooler at the equator. We briefly discuss the mass loss by stellar winds, which are influenced by the anisotropic temperature distribution. These anisotropies in the interior are also driving circulation currents, which transports the chemical elements and the angular momentum in stars. Internal differential rotation, if present, creates instabilities and mixing, in particular the shear mixing, the horizontal turbulence and their interactions. A major check of the model predictions concerns the changes of the surface abundances, which are modified by mass loss in the very massive stars and by rotational mixing in O- and B-type stars. We show that the observations confirm the existence of rotational mixing, with much larger effects at lower metallicities. We discuss the predictions of stellar models concerning the evolution of the surface velocities, the evolutionary tracks in the HR diagram and lifetimes, the populations of blue, red supergiants and Wolf-Rayet stars, and the progenitors of type Ibc supernovae. We show, that in many aspects, rotating models provide a much better fit than non-rotating ones. Using the same physical ingredients as those which fit the best the observations of stars at near solar metallicities, we explore the consequences of rotating models for the status of Be stars, the progenitors of Gamma Ray Bursts, the evolution of Pop III stars and of very metal poor stars, the early chemical evolution of galaxies, the origin of the C-enhanced Metal Poor stars (CEMP) and of the chemical anomalies in globular clusters.09/2011; -
Article: Red Supergiants, Luminous Blue Variables and Wolf-Rayet stars: thesingle massive star perspective
[show abstract] [hide abstract]
ABSTRACT: We discuss, in the context of the single star scenario, the nature of the progenitors of Red Supergiants (RSG), of Luminous Blue Variables (LBV) and of Wolf-Rayet (WR) stars. These three different populations correspond to evolved phases of Main Sequence (MS) OB stars. Axial rotation and mass loss have a great influence on massive star evolution in general and more specifically on the durations of these different phases. Moderate rotation and mass loss, during the MS phase, favor the evolution towards the RSG stage. Fast rotation and strong mass loss during the MS phase, in contrast, prevent the star from becoming a RSG and allow the star to pass directly from the OB star phase into the WR phase. Mass loss during the RSG stage may make the star evolve back in the blue part of the HR diagram. We argue that such an evolution may be more common than presently accounted for in stellar models. This might be the reason for the lack of type IIP SNe with RSG progenitors having initial masses between 18 and 30 M$_\odot$. The LBVs do appear as a possible transition phase between O and WR stars or between WNL and WNE stars. Fast rotation and/or strong mass loss during the Main-Sequence phase prevent the formation of LBV stars. The mechanisms driving the very strong ejections shown by LBV stars are still unknown. (abridged)Bulletin de la Societe Royale des Sciences de Liege 01/2011; 80:266. -
Article: Massive star models with magnetic braking
[show abstract] [hide abstract]
ABSTRACT: Magnetic fields at the surface of a few early-type stars have been directly detected. These fields have magnitudes between a few hundred G up to a few kG. In one case, evidence of magnetic braking has been found. We investigate the effects of magnetic braking on the evolution of rotating ($\upsilon_{\rm ini}$=200 km s$^{-1}$) 10 M$_\odot$ stellar models at solar metallicity during the main-sequence (MS) phase. The magnetic braking process is included in our stellar models according to the formalism deduced from 2D MHD simulations of magnetic wind confinement by ud-Doula and co-workers. Various assumptions are made regarding both the magnitude of the magnetic field and of the efficiency of the angular momentum transport mechanisms in the stellar interior. When magnetic braking occurs in models with differential rotation, a strong and rapid mixing is obtained at the surface accompanied by a rapid decrease in the surface velocity. Such a process might account for some MS stars showing strong mixing and low surface velocities. When solid-body rotation is imposed in the interior, the star is slowed down so rapidly that surface enrichments are smaller than in similar models with no magnetic braking. In both kinds of models (differentially or uniformly rotating), magnetic braking due to a field of a few 100 G significantly reduces the angular momentum of the core during the MS phase. This reduction is much greater in solid-body rotating models. Comment: 4 pages, 4 figures, accepted for publication as a Letter in Astronomy and Astrophysics11/2010; -
Article: Origin of CEMP stars: What helium and lithium can tell us about CEMP stars?
[show abstract] [hide abstract]
ABSTRACT: We show that the peculiar surface abundance patterns of Carbon Enhanced Metal Poor (CEMP) stars has been inherited from material having been processed by H- and He-burning phases in a previous generation of stars (hereafter called the ``Source Stars''). In this previous generation, some mixing must have occurred between the He- and the H-burning regions in order to explain the high observed abundances of nitrogen. In addition, it is necessary to postulate that a very small fraction of the carbon-oxygen core has been expelled (either by winds or by the supernova explosion). Therefore only the most outer layers should have been released by the Source Stars. Some of the CEMP stars may be He-rich if the matter from the Source Star is not too much diluted with the InterStellar Medium (ISM). Those stars formed from nearly pure ejecta would also be Li-poor. Comment: 6 pages, 2 figures, contribution in Symposium UAI 268, Light elements in the Universe, C. Charbonnel, M. Tosi, F. Primas, C. Chiappini, eds01/2010; -
Article: Red Supergiants in the Andromeda Galaxy (M31)
[show abstract] [hide abstract]
ABSTRACT: Red supergiants are a short-lived stage in the evolution of moderately massive stars (10-25Mo), and as such their location in the H-R diagram provides an exacting test of stellar evolutionary models. Since massive star evolution is strongly affected by the amount of mass-loss a star suffers, and since the mass-loss rates depend upon metallicity, it is highly desirable to study the physical properties of these stars in galaxies of various metallicities. Here we identify a sample of red supergiants in M31 (the most metal-rich of the Local Group galaxies) and derive their physical properties by fitting MARCS atmosphere models to moderate resolution optical spectroscopy, and from V-K photometry. Comment: Accepted for publication in the Astrophysical Journal07/2009; -
Article: The Effective Temperature Scale of Galactic Red Supergiants: Cool, but Not as Cool as We Thought
[show abstract] [hide abstract]
ABSTRACT: We use moderate-resolution optical spectrophotometry and the new MARCS stellar atmosphere models to determine the effective temperatures of 74 Galactic red supergiants (RSGs). The stars are mostly members of OB associations or clusters with known distances, allowing a critical comparison with modern stellar evolutionary tracks. We find we can achieve excellent matches between the observations and the reddened model fluxes and molecular transitions, although the atomic lines Ca I λ4226 and Ca II H and K are found to be unrealistically strong in the models. Our new effective temperature scale is significantly warmer than those in the literature, with the differences amounting to 400 K for the latest type M supergiants (i.e., M5 I). We show that the newly derived temperatures and bolometric corrections give much better agreement with stellar evolutionary tracks. This agreement provides a completely independent verification of our new temperature scale. The combination of effective temperature and bolometric luminosities allows us to calculate stellar radii; the coolest and most luminous stars (KW Sgr, Case 75, KY Cyg, HD 206936=μ Cep) have radii of roughly 1500 R☉ (7 AU), in excellent accordance with the largest stellar radii predicted from current evolutionary theory, although smaller than that found by others for the binary VV Cep and for the peculiar star VY CMa. We find that similar results are obtained for the effective temperatures and bolometric luminosities using only the dereddened V - K colors, providing a powerful demonstration of the self-consistency of the MARCS models.The Astrophysical Journal 12/2008; 628(2):973. · 6.02 Impact Factor -
Article: Models for Pop I stars: implications for age determinations
[show abstract] [hide abstract]
ABSTRACT: Starting from a few topical astrophysical questions which require the knowledge of the age of Pop I stars, we discuss the needed precision on the age in order to make progresses in these areas of research. Then we review the effects of various inputs of the stellar models on the age determination and try to identify those affecting the most the lifetimes of stars.12/2008; -
Article: Massive star evolution: from the early to the present day Universe
[show abstract] [hide abstract]
ABSTRACT: Mass loss and axial rotation are playing key roles in shaping the evolution of massive stars. They affect the tracks in the HR diagram, the lifetimes, the surface abundances, the hardness of the radiation field, the chemical yields, the presupernova status, the nature of the remnant, the mechanical energy released in the interstellar medium, etc... In this paper, after recalling a few characteristics of mass loss and rotation, we review the effects of these two processes at different metallicities. Rotation probably has its most important effects at low metallicities, while mass loss and rotation deeply affect the evolution of massive stars at solar and higher than solar metallicities. Comment: 11 pages, 7 figures, IAU Symp. 252, L. CUP, Deng, K.L. Chan, C. Chiosi, edsProceedings of the International Astronomical Union 06/2008; 4:313. -
Article: Were the First Stars Fast Rotators?
[show abstract] [hide abstract]
ABSTRACT: Rapidly rotating massive stars are currently one of the most promising ways of explaining the high N∕O abundances measured in normal metal poor stars. Here we show the predicted impact of fast rotators on the 12C/13C ratio at very low metallicities. We show that upon the inclusion of fast rotating massive stars, low 12C/13C ratios are expected in extremely metal poor halo stars. Observations of 12C/13C ratios in metal poor dwarf and turnoff stars would offer a crucial test to the idea that fast rotating stars were a common phenomenona in the primordial Universe.AIP Conference Proceedings. 03/2008; 990(1):325-329. -
Article: Developments in physics of massive stars
[show abstract] [hide abstract]
ABSTRACT: New constraints on stellar models are provided by large surveys of massive stars, interferometric observations and asteroseismology. After a review of the main results so far obtained, we present new results from rotating models and discuss comparisons with observed features. We conclude that rotation is a key feature of massive star physics. Comment: 13 pages, 10 figures, IAU Symp. 250, Massive stars as Cosmic Engines, F. Bresolin, P.A. Crowther, J. Puls EdsProceedings of the International Astronomical Union 02/2008; 3:147. -
Article: Massive Stars as Cosmic Engines through the Ages
[show abstract] [hide abstract]
ABSTRACT: Some useful developments in the model physics are briefly presented, followed by model results on chemical enrichments and WR stars. We discuss the expected rotation velocities of WR stars. We emphasize that the (C+O)/He ratio is a better chemical indicator of evolution for WC stars than the C/He ratios. With or without rotation, at a given luminosity the (C+O)/He ratios should be higher in regions of lower metallicity Z. Also, for a given (C+O)/He ratio the WC stars in lower Z regions have higher luminosities. The WO stars, which are likely the progenitors of supernovae SNIc and of some GRBs, should preferentially be found in regions of low Z and be the descendants of very high initial masses. Finally, we emphasize the physical reasons why massive rotating low Z stars may also experience heavy mass loss Comment: 12 pages, 11 figures, to be published by CUP, F. Bresolin, P.A. Crowther, J. Puls EdsProceedings of the International Astronomical Union 01/2008; 3:3. -
Article: Mass loss and very low-metallicity stars
[show abstract] [hide abstract]
ABSTRACT: Mass loss plays a dominant role in the evolution of massive stars at solar metallicity. After discussing different mass loss mechanisms and their metallicity dependence, we present the possibility of strong mass loss at very low metallicity. Our models at Z=1e-8 show that stars more massive than about 60 solar masses may lose a significant fraction of their initial mass in the red supergiant phase. This mass loss is due to the surface enrichment in CNO elements via rotational and convective mixing. Our 85 solar mass model ends its life as a fast rotating WO type Wolf-Rayet star. Therefore the models predict the existence of type Ic SNe and long and soft GRBs at very low metallicities. Such strong mass loss in the red supergiant phase or the Omega-Gamma limit could prevent the most massive stars from ending as pair-creation supernovae. The very low metallicity models calculated are also very interesting from the nucleosynthesis point of view. Indeed, the wind of the massive star models can reproduce the CNO abundances of the most metal-poor carbon-rich star known to date, HE1327-2326. Finally, using chemical evolution models, we are able to reproduce the evolution of CNO elements as observed in the normal extremely metal poor stars. Comment: 8 pages, 3 figures, to appear in the proceedings of the conference on "Unsolved Problems in Stellar Physics", Cambridge, 2-6 July 200709/2007; -
Article: Populations of massive stars in galaxies, implications for the stellar evolution theory
[show abstract] [hide abstract]
ABSTRACT: After a brief review of the observational evidences indicating how the populations of Be stars, red/blue supergiants, Wolf-Rayet stars vary as a function of metallicity, we discuss the implications of these observed trend for our understanding of the massive star evolution. We show how the inclusion of the effects of rotation in stellar models improves significantly the correspondence between theory and observation. Comment: 8 pages, 10 figures, IAU Symposium 241, A. Vazdekis and R. Peletier eds., CUP02/2007; -
Article: Wind anisotropies and GRB progenitors
[show abstract] [hide abstract]
ABSTRACT: We study the effect of wind anisotropies on the stellar evolution leading to collapsars. Rotating models of a 60 M$_\odot$ star with $\Omega/\Omega_{\rm crit}=0.75$ on the ZAMS, accounting for shellular rotation and a magnetic field, with and without wind anisotropies, are computed at $Z$=0.002 until the end of the core He-burning phase. Only the models accounting for the effects of the wind anisotropies retain enough angular momentum in their core to produce a Gamma Ray Burst (GRB). The chemical composition is such that a type Ic supernova event occurs. Wind anisotropies appear to be a key physical ingredient in the scenario leading to long GRBs.02/2007; -
Article: Massive star evolution at high metallicity
[show abstract] [hide abstract]
ABSTRACT: After a review of the many effects of metallicity on the evolution of rotating and non-rotating stars, we discuss the consequences of a high metallicity on massive star populations and on stellar nucleosynthesis. The most striking effect of high metallicity is to enhance the amount of mass lost by stellar winds. Typically at a metallicity $Z=0.001$ only 9% of the total mass returned by non-rotating massive stars is ejected by winds (91% by supernovae explosion), while at solar metallicity this fraction may amount to more than 40%. High metallicity favors the formation of Wolf-Rayet stars and of type Ib supernovae. It however disfavors the occurrence of type Ic supernovae. We estimate empirical yields of carbon based on the observed population of WC stars in the solar neighborhood, and obtain that WC stars eject between 0.2 and 0.4% of the mass initially locked into stars under the form of new synthesized carbon. Models give values well in agreement with these empirical yields. Chemical evolution models indicate that such carbon yields may have important impacts on the abundance of carbon at high metallicity.12/2006; -
Article: Mass loss of rotating stars at very low metallicity
[show abstract] [hide abstract]
ABSTRACT: Some indirect observations, as the high fraction of Be stars at low metallicity, or the necessity for massive stars to be important sources of primary nitrogen, seem to indicate that very metal poor stars were fast rotators. As a consequence of this fast rotation, these stars, contrarily to current wisdom, might lose large amounts of mass during their lifetime. In this paper, we review various mechanisms triggered by rotation which may induce strong mass loss at very low metallicity. The most efficient process comes from surface enrichments in CNO elements which then drive mass loss by stellar winds. Due to this process, a fast rotating 60 M$_\odot$ with metallicities in the range of $Z=10^{-8}$ and $10^{-5}$, can lose between 30 and 55% of its initial mass. This rotationally wind ejected material participates to the chemical evolution of the interstellar medium, enriching it exclusively in H- and He-burning products. In particular, metal poor fast rotating stars may play a key role for explaining the origin of the peculiar abundance pattern observed at the surface of the extremely metal-poor C-rich stars, for explaining the chemical inhomogeneities observed in globular clusters, and the presence of stars in $\omega$ Cen with a very high helium content .10/2006; -
Article: The Effective Temperatures and Physical Properties of Magellanic Cloud Red Supergiants: The Effects of Metallicity
[show abstract] [hide abstract]
ABSTRACT: We use the MARCS stellar atmosphere to derive the physical properties of 36 red supergiants (RSGs) in the LMC, and 39 RSGs in the SMC using moderate-resolution optical spectrophotometry (4000-9000A) and broad-band colors (V-R, V-K). The results from the dereddened V-R colors are in good agreement with those derived from the spectrophotometry, but the dereddened V-K colors give temperatures that are 3-4% warmer for the SMC data, with the LMC and Milky Way showing a smaller but similar effect. We conclude that this discrepancy is due to the limitations of 1D models. Our newly derived effective temperatures and bolometric luminosities bring the Magellanic Cloud RSGs into good agreement with stellar evolutionary models that include the effects of rotation. A typical M2~I in the SMC is about 150 K cooler than its Galactic counterpart; one in the LMC is about 50 K cooler. This is in the sense expected due to the lower chemical abundances in the SMC and LMC, although it is not sufficient to explain the shift in average RSG spectral type seen between the SMC, LMC, and Milky Way. Instead, that is due primarily to the change in Hayashi limit with metallicity, as first proposed by Elias et al. (1985). Finally, our study confirms that many RSGs in the Magellanic Clouds are significantly more reddened than OB stars, consistent with our recent findings for Galactic stars that circumstellar dust may contribute several magnitudes of extra visual extinction. Comment: Accepted by the Astrophysical Journal03/2006; -
Article: Evolution of rotating stars at very low metallicity
[show abstract] [hide abstract]
ABSTRACT: At very low metallicity, the effects of differential rotation have a more important impact on the evolution of stars than at high metallicity. Rotational mixing leads to the production of great quantities of helium and of primary $^{14}$N by massive stars. Rotation induces important mass loss and allows stars to locally strongly enrich the interstellar medium in CNO elements. Stars formed from interstellar clouds enriched by the winds of fast rotating massive stars would present surface abundances similar to those of C-rich extremely metal-poor stars. C-rich stars can also be formed by mass accretion in a binary system where the primary would be a fast rotating intermediate mass star in the early-AGB phase. Fast rotation may also lead to the formation of collapsars even at very low metallicity and make the most massive stars avoid the pair instability.12/2005; -
Article: Single massive stars at the critical rotational velocity: possible links with Be and B[e] stars
[show abstract] [hide abstract]
ABSTRACT: Using single star models including the effects of shellular rotation with and without magnetic fields, we show that massive stars at solar metallicity with initial masses lower than about 20-25 M$_\odot$ and with an initial rotation above $\sim 350$ km s$^{-1}$ likely reach the critical velocity during their Main-Sequence phase. This results from the efficient outwards transport of angular momentum by the meridional circulation. This could be a scenario for explaining the Be stars. After the Main-Sequence phase, single star in this mass range can again reach the critical limit when they are on a blue loop after a red supergiant phase \citep{HL98}. This might be a scenario for the formation of B[e] stars, however as discussed by Langer & Heger (1998), this scenario would predict a short B[e] phase (only some 10$^4$ years) with correspondingly small amounts of mass lost. Comment: 11 pages, 13 figures, Stars with the B[e] phenomenon, M. Kraus and A. Miroshnichenko, ASP Conference Series, in press11/2005;
Top co-authors
Top Journals
Institutions
-
2000–2011
-
Université de Genève
- Observatory of Geneva
Carouge, GE, Switzerland
-
