Populations of rotating stars

Georgy, Cyril; Ekstr, S.; Granada, A.; Meynet, Georges; Mowlavï, N.; Eggenberger, P.; Maeder, A.

doi:10.1051/0004-6361/201220558

Cited by 268 publications

(418 citation statements)

References 29 publications

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“…On the other hand, younger clusters such as NGC 1850 and NGC 1856, offer an excellent chance to obtain rotational velocities for large samples of stars along the MSTO due to their increased brightness at this age. Another crucial test of the rotational scenario will be to measure chemical abundances of stars across the MSTO, which are expected to be affected by rotational mixing, especially [N/H] (e.g., Georgy et al 2013). …”

Section: Discussionmentioning

confidence: 99%

“…While initial works cast doubt on this mechanism (Girardi et al 2011), stellar models that include rotation have been developed in recent years (e.g., Ekström et al 2012, Georgy et al 2013) which can be directly compared against observations. Such comparisons have been done for intermediate age clusters (Brandt & Huang 2015a,b) and it seems that for realistic rotational distributions (like those observed in open clusters -Huang et al 2010) extended MSTOs are expected to be a common feature.…”

Section: Introductionmentioning

confidence: 99%

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A young cluster with an extended main-sequence turnoff: confirmation of a prediction of the stellar rotation scenario

Bastian

Niederhofer

Kozhurina-Platais

et al. 2016

Monthly Notices of the Royal Astronomical Society: Letters

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We present Hubble Space Telescope photometry of NGC 1850, a ∼ 100 Myr, ∼ 10 5 M ⊙ cluster in the Large Magellanic Cloud. The colour magnitude diagram clearly shows the presence of an extended main sequence turnoff (eMSTO). The use of non-rotating stellar isochrones leads to an age spread of ∼ 40 Myr. This is in good agreement with the age range expected when the effects of rotation in MSTO stars are wrongly interpreted in terms of age spread. We also do not find evidence for multiple, isolated episodes of star-formation bursts within the cluster, in contradiction to scenarios that invoke actual age spreads to explain the eMSTO phenomenon. NGC 1850 therefore continues the trend of eMSTO clusters where the inferred age spread is proportional to the age of the cluster. While our results confirm a key prediction of the scenario where stellar rotation causes the eMSTO feature, direct measurements of the rotational rate of MSTO stars is required to definitively confirm or refute whether stellar rotation is the origin of the eMSTO phenomenon or if it is due to an as yet undiscovered effect.

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Section: Discussionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

A young cluster with an extended main-sequence turnoff: confirmation of a prediction of the stellar rotation scenario

Bastian

Niederhofer

Kozhurina-Platais

et al. 2016

Monthly Notices of the Royal Astronomical Society: Letters

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“…Scrutiny of 15-M models from Georgy et al (2013b) suggests that surface enrichment of CNO-cycle products can be increased significantly (by up to a factor of 3 compared to normally rotating stars) through adopting initial rotation rates close to the break-up velocity. It is therefore tempting to speculate that the nitrogen abundances of ON stars can be attributed to the enhanced efficiency of rotational mixing in extremely fastrotating stars.…”

Section: Rotation and The On Phenomenonmentioning

confidence: 99%

Surface abundances of ON stars

Martins

Simón‐Díaz

Palacios

et al. 2015

A&A

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Context. Massive stars burn hydrogen through the CNO cycle during most of their evolution. When mixing is efficient or when mass transfer in binary systems occurs, chemically processed material is observed at the surface of O and B stars. Aims. ON stars show stronger lines of nitrogen than morphologically normal counterparts. Whether this corresponds to the presence of material processed through the CNO cycle is not known. Our goal is to answer this question. Methods. We performed a spectroscopic analysis of a sample of ON stars with atmosphere models. We determined the fundamental parameters as well as the He, C, N, and O surface abundances. We also measured the projected rotational velocities. We compared the properties of the ON stars to those of normal O stars. Results. We show that ON stars are usually rich in helium. Their CNO surface abundances are fully consistent with predictions of nucleosynthesis. ON stars are more chemically evolved and rotate − on average − faster than normal O stars. Evolutionary models including rotation cannot account for the extreme enrichment observed among ON main sequence stars. Some ON stars are members of binary systems, but others are single stars as indicated by stable radial velocities. Mass transfer is therefore not a simple explanation for the observed chemical properties. Conclusions. We conclude that ON stars show extreme chemical enrichment at their surface, consistent with nucleosynthesis through the CNO cycle. Its origin is not clear at present.

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“…In Sect. 3 we present our new models of rapidly rotating stars from the ZAMS with a large angular momentum content, we describe their main characteristics, and show how they compare with the grids presented by Georgy et al (2013). We conclude in Sect.…”

Section: Introductionmentioning

confidence: 90%

“…We refer to Ekström et al (2008Ekström et al ( , 2012 and Georgy et al (2013Georgy et al ( , 2011 for extensive explanations and details of the physical processes and assumptions made in our calculations. We plan to use our rotating grids to produce synthetic populations of stars and study their evolution in time, fully accounting for mass, rotation and metallicity distributions, with our new population synthesis code (Georgy et al 2014).…”

Section: Introductionmentioning

confidence: 99%

Evolution of single B-type stars with a large angular momentum content

Granada

Haemmerlé

2014

A&A

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Context. The Geneva Stellar Evolution Group has recently presented an extended database of rotating stellar models at three different metallicities for nine different initial rotation parameters and ten different masses corresponding to spectral types from early-F to late-O. With these grids we have contributed to the understanding of the evolution of single rotating stars, and we intend to use them to produce synthetic stellar populations that fully account for the effects of stellar rotation. However, up to now we still lacked stellar evolutionary tracks that rotate close to the critical limit during the whole main-sequence (MS) phase. This occurs because the flat internal profile of rotation imposed at the zero-age main sequence (ZAMS) is modified by the action of meridional currents immediately after the ZAMS, causing the surface rotational velocity to decrease abruptly until it reaches a quasi-stationary state. Aims. We compute stellar models with non-solid rotation at the ZAMS, which allows us to obtain stellar evolutionary tracks with a larger content of angular momentum that rotate close to the breakup limit throughout the whole MS. Methods. We produced stellar models by removing the assumption that stars rotate as solid bodies at the ZAMS. We obtained the stellar structure at the ZAMS with a differentially rotating profile for three different metallicities by performing pre-MS calculations and by proposing ad hoc initial rotational profiles. We then computed the MS evolution and later phases of stellar evolution of these models, which attain rotational equatorial velocities close to the critical limit throughout their whole MS phase.Results. Stellar models with solid rotation at the ZAMS adequately represent the overall characteristics and evolution of differentially rotating models of identical angular momentum content, but with a lower initial surface rotational velocity rate, at Z = 0.014, Z = 0.006, and Z = 0.002. For models with solid rotation at the ZAMS we therefore recommend to use as the initial rotational rate the values derived once the quasi-stationary state is reached, that is, after the abrupt decrease in surface velocity. By producing stellar structures at the ZAMS with differentially rotating profiles and larger angular momentum content than in our previous works, we obtain models that rotate close to the critical limit throughout the whole MS. These models have a longer MS lifetime and a higher surface chemical enrichment already at the end of the MS, particularly at Z = 0.002. Interestingly, the initial equatorial rotational velocities are virtually metallicity independent for all stellar models we computed in the B-type star range with the same mass and angular momentum content at the ZAMS. If, as some observational evidence indicates, B-type stars at Z = 0.002 rotate with a higher equatorial velocity at the ZAMS than stars with Z = 0.014, our finding would indicate that the angular momentum content of B-type stars in the SMC is higher than their Galactic counterparts.

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Populations of rotating stars

Cited by 268 publications

References 29 publications

A young cluster with an extended main-sequence turnoff: confirmation of a prediction of the stellar rotation scenario

A young cluster with an extended main-sequence turnoff: confirmation of a prediction of the stellar rotation scenario

Surface abundances of ON stars

Evolution of single B-type stars with a large angular momentum content

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