Chemical abundances of fast-rotating OB stars

AbstractFast rotation in massive stars is predicted to induce mixing in their interior, but a population of fast-rotating stars with normal nitrogen abundances at their surface has recently been revealed (Hunter et al.2009; Brott et al.2011, but see Maeder et al.2014). However, as the binary fraction of these stars is unknown, no definitive statements about the ability of single-star evolutionary models including rotation to reproduce these observations can be made. Our work combines for the first time a detailed surface abundance analysis with a radial-velocity monitoring for a sample of bright, fast-rotating Galactic OB stars to put strong constraints on stellar evolutionary and interior models.

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Non-standard s-process in massive rotating stars

Astronomy and Astrophysics ◽

10.1051/0004-6361/201833283 ◽

2018 ◽

Vol 618 ◽

pp. A133 ◽

Cited By ~ 17

Author(s):

Arthur Choplin ◽

Raphael Hirschi ◽

Georges Meynet ◽

Sylvia Ekström ◽

Cristina Chiappini ◽

...

Keyword(s):

Critical Velocity ◽

Rotation Rate ◽

Reaction Rate ◽

Massive Stars ◽

Strong Impact ◽

Light Elements ◽

Rotating Stars ◽

Stellar Models ◽

Fast Rotating

Context. Recent studies show that rotation significantly affects the s-process in massive stars. Aims. We provide tables of yields for non-rotating and rotating massive stars between 10 and 150 M⊙ at Z = 10−3 ([Fe/H] = −1.8). Tables for different mass cuts are provided. The complete s-process is followed during the whole evolution with a network of 737 isotopes, from hydrogen to polonium. Methods. A grid of stellar models with initial masses of 10, 15, 20, 25, 40, 60, 85, 120, and 150 M⊙ and with an initial rotation rate of both 0% or 40% of the critical velocity was computed. Three extra models were computed in order to investigate the effect of faster rotation (70% of the critical velocity) and of a lower 17O(α, γ) reaction rate. Results. At the considered metallicity, rotation has a strong impact on the production of s-elements for initial masses between 20 and 60 M⊙. In this range, the first s-process peak is boosted by 2−3 dex if rotation is included. Above 60 M⊙, s-element yields of rotating and non-rotating models are similar. Increasing the initial rotation from 40% to 70% of the critical velocity enhances the production of 40 ≲ Z ≲ 60 elements by ∼0.5−1 dex. Adopting a reasonably lower 17O(α, γ) rate in the fast-rotating model (70% of the critical velocity) boosts again the yields of s-elements with 55 ≲ Z ≲ 82 by about 1 dex. In particular, a modest amount of Pb is produced. Together with s-elements, some light elements (particularly fluorine) are strongly overproduced in rotating models.

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The Impact of Stellar Rotation on the Nitrogen Abundance Gradient from OB Stars in the Galactic Disk

Symposium - International Astronomical Union ◽

10.1017/s0074180900195610 ◽

2004 ◽

Vol 215 ◽

pp. 226-227

Author(s):

Simone Daflon ◽

Katia Cunha

Keyword(s):

Milky Way ◽

Galactic Disk ◽

Young Stars ◽

Evolutionary Models ◽

Rotating Stars ◽

Stellar Rotation ◽

Ob Stars ◽

Nitrogen Abundance ◽

N Enrichment ◽

The Impact

Massive young stars can be used to trace the current chemical composition of the Galactic disk and to define its metallicity gradient. However, evolutionary models of massive rotating stars predict changes of the surface abundances due to rotationally induced mixing. The abundance analysis of elements sensitive to mixing, such as CNO, can be used to test these rotating stellar models. In this study we identify those stars that show one particular signature of mixing, N-enrichment, in our sample of 70 OB stars for which we have conducted an abundance analysis. This sample is used to define radial metallicity gradients in the Milky Way and we investigate the variation of the calculated nitrogen gradient after the exclusion of these, probably mixing-induced, N-rich stars.

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The s -Process in Massive Stars at Low Metallicity: The Effect of Primary 14 N from Fast Rotating Stars

The Astrophysical Journal ◽

10.1086/593350 ◽

2008 ◽

Vol 687 (2) ◽

pp. L95-L98 ◽

Cited By ~ 107

Author(s):

M. Pignatari ◽

R. Gallino ◽

G. Meynet ◽

R. Hirschi ◽

F. Herwig ◽

...

Keyword(s):

Massive Stars ◽

Rotating Stars ◽

Low Metallicity ◽

Fast Rotating

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Asteroseismology of massive stars with the MOST satellite

Proceedings of the International Astronomical Union ◽

10.1017/s174392131000983x ◽

2009 ◽

Vol 5 (H15) ◽

pp. 366-366

Author(s):

Anthony F. J. Moffat ◽

Keyword(s):

Massive Stars ◽

Period Range ◽

Optical Photometry ◽

X Ray ◽

Ob Stars ◽

Stellar Oscillations ◽

Rotation Periods ◽

Minute Period ◽

Orbital Phase ◽

First Time

AbstractSince 2003 the MOST (Microvariability and Oscillations of STars) microsatellite has obtained typically a month of non-stop, minute-of-time resolution, high-precision, single-broadband optical photometry for each of a significant number of Galactic OB and WR stars. Numerous p- and g-modes were clearly detected in several OB stars, including discovery of g-modes for the first time in a blue supergiant (Saio et al. 2006). True rotation periods were found for some SPBe pulsators (Cameron et al. 2008). Many O stars are remarkably quiet. Five presumably single WR stars have been observed so far, each interesting in its own way. In particular, the cool WR stars WR123 (WN8) and WR103 (WC9d) both show mostly short-lived, multimode oscillations with most of the Fourier power occurring on a day or longer timescale (Moffat et al. 2008a). WR123 also revealed a fairly stable 10-hour periodicity (Lefèvre et al. 2005). All of these oscillations probably arise in the stellar cores. WR111 (WC5) shows no (coherent) oscillations above the detection limit of 0.05 mmag in the 10-minute period range predicted for strange-mode pulsations at a level of 2 mmag (Moffat et al. 2008b). WR110 (WN5-6 and a stronger-than-average X-ray source) and WR124 (WN8h, i.e. in contrast with the previously observed, hydrogen-free WR123 of otherwise similar subtype), both strongly variable with MOST, are currently being analyzed. The next target just observed (late-June to early Aug 2009) is the 30-day eclipsing binary CV Ser = WR113 (WC8d + O8-9IV). Besides stellar oscillations, we will also search for orbital-phase dependent, stochastic variability in CV Ser as wind clumps in the WR component's dense wind pass in front of the O-star.

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Modeling of the Wind/Disk Outflow from Be Stars

Universe ◽

10.3390/universe7100353 ◽

2021 ◽

Vol 7 (10) ◽

pp. 353

Author(s):

Sergey Bogovalov ◽

Maxim Petrov

Keyword(s):

Numerical Modeling ◽

Turbulent Viscosity ◽

Be Stars ◽

Rotating Stars ◽

Polar Wind ◽

Hydrodynamic Turbulence ◽

Plasma Ions ◽

High Level ◽

First Time ◽

Fast Rotating

The objective of this work is to reproduce the formation of the fast polar wind and viscous disk outflow from Be stars in a unified physical picture. Numerical modeling of the plasma outflow from fast rotating stars was performed taking into account the acceleration of the plasma due to scattering of the radiation of the star in lines of plasma ions and excitation of the hydrodynamic turbulence in the outflow. The fast polar wind naturally arises in this picture with an expected flow rate. For the first time, it is shown that a disk-like outflow with a relatively high level of turbulence is formed at the equator of fast rotating stars emitting radiation-driven wind. However, the level of turbulent viscosity is well below the level necessary for the formation of a Keplerian disk.

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Chemical abundances of fast-rotating massive stars

Astronomy and Astrophysics ◽

10.1051/0004-6361/201629841 ◽

2017 ◽

Vol 603 ◽

pp. A56 ◽

Cited By ~ 12

Author(s):

Constantin Cazorla ◽

Thierry Morel ◽

Yaël Nazé ◽

Gregor Rauw ◽

Thierry Semaan ◽

...

Keyword(s):

Massive Stars ◽

Chemical Abundances ◽

Fast Rotating

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Fast rotating stars resulting from binary evolution will often appear to be single

Proceedings of the International Astronomical Union ◽

10.1017/s174392131101132x ◽

2010 ◽

Vol 6 (S272) ◽

pp. 531-532 ◽

Cited By ~ 6

Author(s):

Selma E. de Mink ◽

Norbert Langer ◽

Robert G. Izzard

Keyword(s):

Binary System ◽

Binary Systems ◽

Large Fraction ◽

Supernova Explosion ◽

Binary Interaction ◽

Close Binaries ◽

Rotating Stars ◽

Single Star ◽

Rapidly Rotating Stars ◽

Fast Rotating

AbstractRapidly rotating stars are readily produced in binary systems. An accreting star in a binary system can be spun up by mass accretion and quickly approach the break-up limit. Mergers between two stars in a binary are expected to result in massive, fast rotating stars. These rapid rotators may appear as Be or Oe stars or at low metallicity they may be progenitors of long gamma-ray bursts.Given the high frequency of massive stars in close binaries it seems likely that a large fraction of rapidly rotating stars result from binary interaction. It is not straightforward to distinguish a a fast rotator that was born as a rapidly rotating single star from a fast rotator that resulted from some kind of binary interaction. Rapidly rotating stars resulting from binary interaction will often appear to be single because the companion tends to be a low mass, low luminosity star in a wide orbit. Alternatively, they became single stars after a merger or disruption of the binary system during the supernova explosion of the primary.The absence of evidence for a companion does not guarantee that the system did not experience binary interaction in the past. If binary interaction is one of the main causes of high stellar rotation rates, the binary fraction is expected to be smaller among fast rotators. How this prediction depend on uncertainties in the physics of the binary interactions requires further investigation.

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Equatorial mass loss from Be stars

Proceedings of the International Astronomical Union ◽

10.1017/s1743921311011756 ◽

2010 ◽

Vol 6 (S272) ◽

pp. 640-641

Author(s):

Cyril Georgy ◽

Sylvia Ekström ◽

Anahí Granada ◽

Georges Meynet

Keyword(s):

Mass Loss ◽

Be Stars ◽

Rotating Stars ◽

Single Star ◽

Star Models ◽

Total Mass Loss ◽

Rotation Phase ◽

Rotating Star ◽

Mechanical Mass ◽

Fast Rotating

AbstractBe stars are thought to be fast rotating stars surrounded by an equatorial disc. The formation, structure and evolution of the disc are still not well understood. In the frame of single star models, it is expected that the surface of an initially fast rotating star can reach its keplerian velocity (critical velocity). The Geneva stellar evolution code has been recently improved, in order to obtain some estimates of the total mass loss and of the mechanical mass loss rates in the equatorial disc during the whole critical rotation phase. We present here the first results of the computation of a grid of fast rotating B stars evolving towards the Be phase, and discuss the first estimates we obtained.

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NGC 3105: a young open cluster with low metallicity

Astronomy and Astrophysics ◽

10.1051/0004-6361/201833073 ◽

2018 ◽

Vol 616 ◽

pp. A124 ◽

Cited By ~ 5

Author(s):

J. Alonso-Santiago ◽

A. Marco ◽

I. Negueruela ◽

H. M. Tabernero ◽

N. Castro ◽

...

Keyword(s):

Open Cluster ◽

High Mass ◽

Complete Analysis ◽

Evolutionary Models ◽

Chemical Abundances ◽

Evolved Stars ◽

Young Open Cluster ◽

Red Supergiants ◽

Low Metallicity ◽

First Time

Context. NGC 3105 is a young open cluster hosting blue, yellow, and red supergiants. This rare combination makes it an excellent laboratory for constraining evolutionary models of high-mass stars. It has been poorly studied, and the fundamental parameters such as its age or distance are not well defined. Aims. We intend to characterise in an accurate way the cluster and its evolved stars, for which we derive for the first time atmospheric parameters and chemical abundances. Methods. We performed a complete analysis combining UBVR photometry with spectroscopy. We obtained spectra with classification purposes for 14 blue stars and high-resolution spectroscopy for an in-depth analysis of the six other evolved stars. Results. We identify 126 B-type likely members within a radius of 2.7 ± 0.6 arcmin, which implies an initial mass, Mcl ≈ 4100 M⊙. We find a distance of 7.2 ± 0.7 kpc for NGC 3105, placing it at RGC = 10.0 ± 1.2 kpc. Isochrone fitting supports an age of 28 ± 6 Ma, implying masses around 9.5 M⊙ for the supergiants. A high fraction of Be stars (≈25%) is found at the top of the main sequence down to spectral type b3. From the spectral analysis we estimate for the cluster an average νrad = +46.9 ± 0.9 km s−1 and a low metallicity, [Fe/H] = −0.29 ± 0.22. We also have determined, for the first time, chemical abundances for Li, O, Na, Mg, Si, Ca, Ti, Ni, Rb, Y, and Ba for the evolved stars. The chemical composition of the cluster is consistent with that of the Galactic thin disc. An overabundance of Ba is found, supporting the enhanced s-process. Conclusions. NGC 3105 has a low metallicity for its Galactocentric distance, comparable to typical LMC stars. It is a valuable spiral tracer in a very distant region of the Carina–Sagittarius spiral arm, a poorly known part of the Galaxy. As one of the few Galactic clusters containing blue, yellow, and red supergiants, it is massive enough to serve as a test bed for theoretical evolutionary models close to the boundary between intermediate- and high-mass stars.

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