Massive star formation by accretion

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

doi:10.1051/0004-6361/201630149

Cited by 20 publications

(25 citation statements)

References 68 publications

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“…It strongly impacts the nature of the ionizing flux released in the cavity that is normal to the disc plane (see also discussion Section 5). The proper timescale of this phenomenon is difficult to predict without self-consistent stellar evolution calculations, which time-dependently account for the physics of accretion, such as the GENEC (Haemmerlé 2014;Haemmerlé et al 2016Haemmerlé et al , 2017 or the STELLAR (Yorke & Kruegel 1977;Hosokawa & Omukai 2009;Hosokawa et al 2010) codes. Only then the structure and upper layer thermodynamics of the MYSOs can be calculated.…”

Section: Bursts Propertiesmentioning

confidence: 99%

Parameter study for the burst mode of accretion in massive star formation

Meyer

Vorobyov

Elbakyan

et al. 2020

Monthly Notices of the Royal Astronomical Society

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It is now a widely held view that, in their formation and early evolution, stars build up mass in bursts. The burst mode of star formation scenario proposes that the stars grow in mass via episodic accretion of fragments migrating from their gravitationally-unstable circumstellar discs and it naturally explains the existence of observed pre-main-sequence bursts from high-mass protostars. We present a parameter study of hydrodynamical models of massive young stellar objects (MYSOs) that explores the initial masses of the collapsing clouds (Mc = 60–$200\, \rm M_{\odot }$) and ratio of rotational-to-gravitational energies (β = 0.005 − −0.33). An increase in Mc and/or β produces protostellar accretion discs that are more prone to develop gravitational instability and to experience bursts. We find that all MYSOs have bursts even if their pre-stellar core is such that β ≤ 0.01. Within our assumptions, the lack of stable discs is therefore a major difference between low- and high-mass star formation mechanisms. All our disc masses and disk-to-star mass ratios Md/M⋆ > 1 scale as a power-law with the stellar mass. Our results confirm that massive protostars accrete about 40-60% of their mass in the burst mode. The distribution of time periods between two consecutive bursts is bimodal: there is a short duration ($\sim 1-10~\rm yr$) peak corresponding to the short, faintest bursts and a long-duration peak (at $\sim 10^{3}-10^{4} \rm yr$) corresponding to the long, FU-Orionis-type bursts appearing in later disc evolution, i.e., around $30\, \rm kyr$ after disc formation. We discuss this bimodality in the context of the structure of massive protostellar jets as potential signatures of accretion burst history.

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Section: Bursts Propertiesmentioning

confidence: 99%

Parameter study for the burst mode of accretion in massive star formation

Meyer

Vorobyov

Elbakyan

et al. 2020

Monthly Notices of the Royal Astronomical Society

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“…More massive objects might form at higher rates during the main accretion phase, before the rate declines. Many reasons might explain the decrease in the accretion rate as a function of the mass of the accretor, such as the effect of the rising UV feedback (Peters et al 2010c) as the stellar surface heats up, the increase of radiation pressure (Kuiper et al 2010b), or the angular momentum barrier (Haemmerlé et al 2017).…”

Section: Constraints On Accretion History From Observationsmentioning

confidence: 99%

The IACOB project. VI. On the elusive detection of massive O-type stars close to the ZAMS

Holgado,

Simón-Díaz,

Haemmerlé

et al. 2020

Preprint

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Context. The apparent lack of massive O-type stars near the zero-age main sequence, or ZAMS (at ages < 2 Myr), is a topic that has been widely discussed in the past 40 years. Different explanations for the elusive detection of these young massive stars have been proposed from the observational and theoretical side, but no firm conclusions have been reached yet. Aims. We reassess this empirical result here, benefiting from the high-quality spectroscopic observations of (more than 400) Galactic O-type stars gathered by the IACOB and OWN surveys. Methods. We used effective temperatures and surface gravities resulting from a homogeneous semi-automatized iacob-gbat/fastwind spectroscopic analysis to locate our sample of stars in the Kiel and spectroscopic Hertzsprung-Russell (sHR) diagrams. We evaluated the completeness of our magnitude-limited sample of stars as well as potential observational biases affecting the compiled sample using information from the Galactic O star catalog (GOSC). We discuss limitations and possible systematics of our analysis method, and compare our results with other recent studies using smaller samples of Galactic O-type stars. We mainly base our discussion on the distribution of stars in the sHR diagram in order to avoid the use of still uncertain distances to most of the stars in our sample. However, we also performed a more detailed study of the young cluster Trumpler-14 as an illustrative example of how Gaia cluster distances can help to construct the associated classical HR diagram. Results. We find that the apparent lack of massive O-type stars near the ZAMS with initial evolutionary masses in the range between ≈30 and 70 M still persist even when spectroscopic results from a large non-biased sample of stars are used. We do not find any correlation between the dearth of stars close to the ZAMS and obvious observational biases, limitations of our analysis method, and/or the use of one example spectroscopic HR diagram instead of the classical HR diagram. Finally, by investigating the effect of the efficiency of mass accretion during the formation process of massive stars, we conclude that an adjustment of the mass accretion rate towards lower values than canonically assumed might reconcile the hotter boundary of the empirical distribution of optically detected O-type stars in the spectroscopic HR diagram and the theoretical birthline for stars with masses above ≈30 M . Last, we also discuss how the presence of a small sample of O2-O3.5 stars found much closer to the ZAMS than the main distribution of Galactic O-type star might be explained in the context of this scenario when the effect of nonstandard star evolution (e.g. binary interaction, mergers, and/or homogeneous evolution) is taken into account.

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“…A general description of the code with rotation, without accretion, can be found in Eggenberger et al (2008). The treatment of accretion is detailed in Haemmerlé et al (2016Haemmerlé et al ( , 2017a. …”

Section: Stellar Evolution Codementioning

confidence: 99%

“…The critical velocity v crit,1 , which corresponds to the Keplerian velocity at the stellar surface, is the maximum rotational velocity a star can reach in hydrostatic equilibrium. For massive Population I (Pop I) stars, the critical limit constrains the accreted angular momentum to be less than 1/3 of the Keplerian angular momentum (Haemmerlé et al 2017a). If it exceeds this value, internal angular momentum redistribution by convection leads the stellar surface to rotate above the critical limit.…”

Section: Introductionmentioning

confidence: 99%

On the Rotation of Supermassive Stars

Haemmerlé

Woods

Klessen

et al. 2018

ApJL

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Supermassive stars born from pristine gas in atomically-cooled haloes are thought to be the progenitors of supermassive black holes at high redshifts. However, the way they accrete their mass is still an unsolved problem. In particular, for accretion to proceed, a large amount of angular momentum has to be extracted from the collapsing gas. Here, we investigate the constraints stellar evolution imposes on this angular momentum problem. We present an evolution model of a supermassive Population III star including simultaneously accretion and rotation. We find that, for supermassive stars to form by accretion, the accreted angular momentum has to be about 1% of the Keplerian angular momentum. This tight constraint comes from the ΩΓ-limit, at which the combination of radiation pressure and centrifugal force cancels gravity. It implies that supermassive stars are slow rotators, with a surface velocity less than 10 -20% of their first critical velocity, at which the centrifugal force alone cancels gravity. At such low velocities, the deformation of the star due to rotation is negligible.

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Massive star formation by accretion

Cited by 20 publications

References 68 publications

Parameter study for the burst mode of accretion in massive star formation

Parameter study for the burst mode of accretion in massive star formation

The IACOB project. VI. On the elusive detection of massive O-type stars close to the ZAMS

On the Rotation of Supermassive Stars

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