Star formation with disc accretion and rotation

Haemmerlé, L.; Eggenberger, P.; Meynet, Georges; Maeder, A.; Charbonnel, C.

doi:10.1051/0004-6361/201321359

Cited by 25 publications

(45 citation statements)

References 30 publications

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“…In Sect. 2 we describe the assumptions made by Haemmerlé et al (2013) to obtain the internal rotation profile at the ZAMS, and describe the results obtained by these authors, which are relevant to the present work. Because we present here models with different metallicities, we also show that the results obtained for Z = 0.014 are valid for lower metallicities as well.…”

Section: Introductionmentioning

confidence: 93%

“…In the following subsection, we extend the work by Haemmerlé et al (2013) to lower metallicities by studying the impact of different initial rotation profiles on the evolution of a 9 M at Z = 0.002.…”

Section: Relevance Of the Internal Rotational Profilementioning

confidence: 99%

“…of a star at the ZAMS for its subsequent evolution Haemmerlé et al (2013) showed that stars that form through different pre-MS accretion prescriptions, but have the same content of total angular momentum at the ZAMS, follow the same subsequent evolution in terms of evolutionary tracks, surface velocities, and abundances, independently of their formation history. These authors computed pre-MS tracks for stars between 2 and 22 M at solar metallicity, using the Geneva stellar evolution code (Eggenberger et al 2008;Ekström et al 2012), including shellular rotation, and following different scenarios, with accretion or at constant mass.…”

Section: Relevance Of the Internal Rotational Profilementioning

confidence: 99%

“…Similar values were obtained for constant mass. Then, Haemmerlé et al (2013) were able to compare the MS evolution of stars with this rotation profile on the ZAMS, with the MS evolution of stars rotating as a solid body on the ZAMS. The authors obtained that after a re-adjustment phase that lasts for ∼15% of the total MS time, models with the same mass and angular momentum content with different internal rotation profiles at the ZAMS converge to the same internal rotation profile.…”

Section: Relevance Of the Internal Rotational Profilementioning

confidence: 99%

“…The recent work by Haemmerlé et al (2013), who computed models of pre-MS stellar evolution, can help us solve this problem. On the one hand, it allows us to study the validity of the assumption of solid-body rotation at the ZAMS, that is, to understand how stars with the same mass, metallicity and angular momentum content but different internal rotation profile at the ZAMS evolve.…”

Section: Introductionmentioning

confidence: 99%

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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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Section: Introductionmentioning

confidence: 93%

Section: Relevance Of the Internal Rotational Profilementioning

confidence: 99%

Section: Relevance Of the Internal Rotational Profilementioning

confidence: 99%

Section: Relevance Of the Internal Rotational Profilementioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

See 3 more Smart Citations

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

Granada

Haemmerlé

2014

A&A

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Grids of stellar models with rotation

Georgy

Ekström

Eggenberger

et al. 2013

A&A

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355

414

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Aims. We study the impact of a subsolar metallicity on various properties of non-rotating and rotating stars, such as surface velocities and abundances, lifetimes, evolutionary tracks, and evolutionary scenarios. Methods. We provide a grid of single star models covering a mass range of 0.8 to 120 M with an initial metallicity Z = 0.002 with and without rotation. We discuss the impact of a change in the metallicity by comparing the current tracks with models computed with exactly the same physical ingredients but with a metallicity Z = 0.014 (solar). Results. We show that the width of the main-sequence (MS) band in the upper part of the Hertzsprung-Russell diagram (HRD), for luminosity above log (L/L ) > 5.5, is very sensitive to rotational mixing. Strong mixing significantly reduces the MS width. Here for the first time over the whole mass range, we confirm that surface enrichments are stronger at low metallicity provided that comparisons are made for equivalent initial mass, rotation, and evolutionary stage. We show that the enhancement factor due to a lowering of the metallicity (all other factors kept constant) increases when the initial mass decreases. Present models predict an upper luminosity for the red supergiants (RSG) of log (L/L ) around 5.5 at Z = 0.002 in agreement with the observed upper limit of RSG in the Small Magellanic Cloud. We show that models using shear diffusion coefficient, which is calibrated to reproduce the surface enrichments observed for MS B-type stars at Z = 0.014, can also reproduce the stronger enrichments observed at low metallicity. In the framework of the present models, we discuss the factors governing the timescale of the first crossing of the Hertzsprung gap after the MS phase. We show that any process favouring a deep localisation of the H-burning shell (steep gradient at the border of the H-burning convective core, low CNO content), and/or the low opacity of the H-rich envelope favour a blue position in the HRD for the whole, or at least a significant fraction, of the core He-burning phase.

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Massive star formation by accretion

Haemmerlé

Eggenberger

Meynet

et al. 2015

A&A

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Context. Massive stars likely form by accretion and the evolutionary track of an accreting forming star corresponds to what is called the birthline in the Hertzsprung-Russell (HR) diagram. The shape of this birthline is quite sensitive to the evolution of the entropy in the accreting star. Aims. We first study the reasons why some birthlines published in past years present different behaviours for a given accretion rate. We then revisit the question of the accretion rate, which allows us to understand the distribution of the observed pre-main-sequence (pre-MS) stars in the HR diagram. Finally, we identify the conditions needed to obtain a large inflation of the star along its pre-MS evolution that may push the birthline towards the Hayashi line in the upper part of the HR diagram. Methods. We present new pre-MS models including accretion at various rates and for different initial structures of the accreting core. We compare them with previously published equivalent models. From the observed upper envelope of pre-MS stars in the HR diagram, we deduce the accretion law that best matches the accretion history of most of the intermediate-mass stars. Results. In the numerical computation of the time derivative of the entropy, some treatment leads to an artificial loss of entropy and thus reduces the inflation that the accreting star undergoes along the birthline. In the case of cold disc accretion, the existence of a significant swelling during the accretion phase, which leads to radii > ∼ 100 R and brings the star back to the red part of the HR diagram, depends sensitively on the initial conditions. For an accretion rate of 10 −3 M yr −1 , only models starting from a core with a significant radiative region evolve back to the red part of the HR diagram. We also obtain that, in order to reproduce the observed upper envelope of pre-MS stars in the HR diagram with an accretion law deduced from the observed mass outflows in ultra-compact HII regions, the fraction of the mass that is accreted onto the star should represent a decreasing fraction of the mass outflows when the mass of the accreting object increases. In other words, the accretion efficiency (mass effectively accreted onto the star with respect to the total in falling matter) decreases when the mass of the star increases.

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Star formation with disc accretion and rotation

Cited by 25 publications

References 30 publications

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

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

Grids of stellar models with rotation

Massive star formation by accretion

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