Stellar mergers as the origin of the blue main-sequence band in young star clusters

Wang, Chen; Langer, N.; Schootemeijer, A.; Milone, A. P.; Hastings, Ben; Xu, Xiao-Tian; Bodensteiner, J.; Sana, H.; Castro, N.; Lennon, D. J.; Marchant, Pablo; Koter, A. de; Mink, S. E. de

doi:10.1038/s41550-021-01597-5

Cited by 44 publications

(37 citation statements)

References 79 publications

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“…All of this simulated behavior should be considered with caution, since it relies on some physics that are not fully constrained. There are still different criteria when considering the amount of mass and angular momentum that is lost in collisions and mass transfer events (Wang et al 2022), as well as in the generation of a magnetic field and its braking properties in mergers events (Schneider et al 2019).…”

Section: Exploring the Effect Of Binary Interactionsmentioning

confidence: 99%

The IACOB project

Holgado

Herrero

Barbá

2022

A&A

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Context. Stellar rotation is of key importance in the formation process, the evolution, and the final fate of massive stars. Aims. We perform a reassessment of the empirical rotational properties of Galactic massive O-type stars using the results from a detailed analysis of ground-based multi-epoch optical spectra obtained in the framework of the IACOB & OWN surveys. Methods. Using high-quality optical spectroscopy, we established the velocity distribution for a sample of 285 apparently single and single-line spectroscopic binary (SB1) Galactic O-type stars. We also made use of the rest of the parameters from the quantitative spectroscopic analysis presented in prior IACOB papers (mainly T eff , log g, and multiplicity) to study the v sin i behavior and evolution from the comparison of subsamples in different regions of the spectroscopic Hertzsprung-Rusell diagram (sHRD). Our results are compared to the main predictions -regarding current and initial rotational velocities -of two sets of well-established evolutionary models for single stars, as well as from population synthesis simulations of massive stars that include binary interaction. Results. We reassess the known bimodal nature of the v sin i distribution, and find a non-negligible difference between the v sin i distribution of single and SB1 stars. We provide empirical evidence supporting the proposed scenario that the tail of fast rotators is mainly produced by binary interactions. Stars with extreme rotation (>300 km s −1 ) appear as single stars that are located in the lower zone of the sHRD. We notice little rotational braking during the main sequence, a braking effect independent of mass (and wind strength). The rotation rates of the youngest observed stars lean to an empirical initial velocity distribution with 20% of critical velocity. Lastly, a limit in v sin i detection below 40-50 km s −1 seems to persist, especially in the upper part of the sHRD, possibly associated with the effect of microturbulence in the measurement methodology used.

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Section: Exploring the Effect Of Binary Interactionsmentioning

confidence: 99%

The IACOB project

Holgado

Herrero

Barbá

2022

A&A

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“…Wang et al [274] proposed that blue MS stars are slow rotators formed from stellar mergers. In their scenario, stars gain mass through two channels: by disk accretion, which leads red MS stars to rapid rotation, or by binary merger, leading to the slow rotating blue MS stars.…”

Section: The Origin Of Emstos and Split Mssmentioning

confidence: 99%

Multiple Populations in Star Clusters

Milone

Marino

2022

Universe

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We review the multiple population (MP) phenomenon of globular clusters (GCs): i.e., the evidence that GCs typically host groups of stars with different elemental abundances and/or distinct sequences in photometric diagrams. Most Galactic and extragalactic clusters exhibit internal variations of He, C, N, O, Na, and Al. They host two distinct stellar populations: the first population of stars, which resemble field stars with similar metallicities, and one or more second stellar populations that show the signature of high-temperature H-burning. In addition, a sub-sample of clusters hosts stellar populations with different heavy-element abundances. The MP origin remains one of the most puzzling, open issues of stellar astrophysics. We summarize the scenarios for the MP formation and depict the modern picture of GCs and their stellar populations along with the main evolutionary phases. We show that the MP behavior dramatically changes from one cluster to another and investigate their complexity to define common properties. We investigate relations with the host galaxy, the parameters of the host clusters (e.g., GC’s mass, age, orbit), and stellar mass. We summarize results on spatial distribution and internal kinematics of MPs. Finally, we review the relation between MPs and the so-called second-parameter problem of the horizontal-branch morphology of GCs and summarize the main findings on the extended main sequence phenomenon in young clusters.

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“…The basis of our analysis is a large grid of detailed binary evolution models with the Small Magellanic Cloud (SMC) metallicity calculated by Wang et al (2022), using MESA version 8845 (Paxton et al 2011(Paxton et al , 2013(Paxton et al , 2015. Their initial zero age main sequence (ZAMS) equatorial velocity is set to 0.55 times the critical velocity, corresponding to the high velocity peak of the bimodal distribution of Dufton et al (2013).…”

Section: Methodsmentioning

confidence: 99%

The spins of stripped B stars support magnetic internal angular momentum transport

Schürmann

Langer

et al. 2022

A&A

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In order to predict the spins of stellar remnants we need to understand the evolution of the internal rotation of stars, and to identify at which stage the rotation of the contracting cores of evolved stars decouples from their expanding envelopes. The donor stars of mass transferring binaries lose almost their entire envelope and may thus offer a direct view on their core rotation. After the mass transfer event they contract and fade rapidly, although they are well observable when caught in the short-lived B-star phase. The B-type primary of the galactic binary system LB-1, which was originally suggested to contain a massive black hole, is nicely explained as a stripped star accompanied by a fainter Be star. The narrow absorption lines in the primary's spectrum signify extremely slow rotation, atypical of B-type main-sequence stars. Here we investigate the evolution of mass donors in generic grids of detailed binary evolution models, where both stars include differential rotation, internal angular momentum transport, and spin-orbit coupling. Whereas the mass gainers are typically spun-up during the mass transfer, we find that the spins of the stripped donor models depend sensitively on the employed mechanism for internal angular momentum transport. Purely hydrodynamic transport cannot explain the observed slow rotation, while models including magnetic angular momentum transport are able to reproduce the observed rotation of LB-1 and similar stars, independent of the initial rotation rate. In such models the spin of the white dwarfs that emerge at the end of the evolution is independent of the mass stripping. We find evidence that the mass transfer in LB-1 was moderately non-conservative.

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Stellar mergers as the origin of the blue main-sequence band in young star clusters

Cited by 44 publications

References 79 publications

The IACOB project

The IACOB project

Multiple Populations in Star Clusters

The spins of stripped B stars support magnetic internal angular momentum transport

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