Dependency of Dynamical Ejections of O Stars on the Masses of Very Young Star Clusters

Oh, Seungkyung; Kroupa, Pavel; Pflamm-Altenburg, Jan

doi:10.1088/0004-637x/805/2/92

Cited by 106 publications

(162 citation statements)

References 101 publications

(197 reference statements)

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“…Note that some of our models have a high initial binary fraction. Such an assumption is justified by the fact that both theory and observations suggest that the angular momentum of a collapsing cloud core may be distributed more efficiently into two stars (Goodwin & Kroupa 2005;Leigh et al 2015;Oh et al 2015) rather than into a single star or a higher order multipole system. Initially masssegregated clusters are generated with the method developed in Baumgardt, De Marchi & Kroupa (2008).…”

Section: Methodsmentioning

confidence: 99%

Hypervelocity stars from young stellar clusters in the Galactic Centre

Fragione

Capuzzo-Dolcetta

Kroupa

2017

Mon. Not. R. Astron. Soc.

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The enormous velocities of the so called hypervelocity stars (HVSs) derive, likely, from close interactions with massive black holes, binary stars encounters or supernova explosions. In this paper, we investigate the origin of hypervelocity stars as consequence of the close interaction between the Milky Way central massive black hole and a passing-by young stellar cluster. We found that both single and binary HVSs may be generated in a burst-like event, as the cluster passes near the orbital pericentre. High velocity stars will move close to the initial cluster orbital plane and in the direction of the cluster orbital motion at the pericentre. The binary fraction of these HVS jets depends on the primordial binary fraction in the young cluster. The level of initial mass segregation determines the value of the average mass of the ejected stars. Some binary stars will merge, continuing their travel across and out of the Galaxy as blue stragglers.

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Section: Methodsmentioning

confidence: 99%

Hypervelocity stars from young stellar clusters in the Galactic Centre

Fragione

Capuzzo-Dolcetta

Kroupa

2017

Mon. Not. R. Astron. Soc.

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“…Hoogerwerf et al (2001) discuss the two preferred formation channels of runaway OB stars. First, gravitational interactions between massive stars in dense open clusters can lead to dynamical ejections of a small fraction of OB stars (Poveda et al 1967;Oh et al 2015). Second, OB companions in massive binaries receive large recoil kicks when the primaries explode as supernovae (Blaauw 1961).…”

Section: Binary-star Evolutionmentioning

confidence: 99%

Mind Your Ps and Qs: The Interrelation between Period (P) and Mass-ratio (Q) Distributions of Binary Stars

Moe

Stefano

2017

ApJS

1,060

1,200

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We compile observations of early-type binaries identified via spectroscopy, eclipses, long-baseline interferometry, adaptive optics, common proper motion, etc. Each observational technique is sensitive to companions across a narrow parameter space of orbital periods P and mass ratios q=M comp /M 1 . After combining the samples from the various surveys and correcting for their respective selection effects, we find that the properties of companions to O-type and B-type main-sequence (MS) stars differ among three regimes. First, at short orbital periods P20days (separations a0.4 au), the binaries have small eccentricities e0.4, favor modest mass ratios á ñ » q 0.5, and exhibit a small excess of twins q>0.95. Second, the companion frequency peaks at intermediate periods log P (days)≈3.5 (a ≈ 10 au), where the binaries have mass ratios weighted toward small values q≈0.2-0.3 and follow a Maxwellian "thermal" eccentricity distribution. Finally, companions with long orbital periods log P (days)≈5.5-7.5 (a ≈ 200-5000 au) are outer tertiary components in hierarchical triples and have a mass ratio distribution across q≈0.1-1.0 that is nearly consistent with random pairings drawn from the initial mass function. We discuss these companion distributions and properties in the context of binary-star formation and evolution. We also reanalyze the binary statistics of solar-type MS primaries, taking into account that 30% ±10% of single-lined spectroscopic binaries likely contain white dwarf companions instead of low-mass stellar secondaries. The mean frequency of stellar companions with q>0.1 and log P (days)<8.0 per primary increases from 0.50±0.04 for solar-type MS primaries to 2.1±0.3 for O-type MS primaries. We fit joint probability density functions ¹ ( ) ( ) ( ) ( ) ( ) f M q P e f M f q f P f e , , , 1 1 to the corrected distributions, which can be incorporated into binary population synthesis studies.

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“…It is, however, expected that many clusters would have re-virialized by the time of observation (Baumgardt & Kroupa 2007;Gieles et al 2010;Portegies Zwart et al 2010). An interpretation in terms of a large contribution from binaries to the velocity dispersion (compare, e.g., Leigh et al 2015;Oh et al 2015) seems more probable Rochau et al 2010;Cottaar et al 2012;Clarkson et al 2012;Hénault-Brunet et al 2012;Cottaar & Hénault-Brunet 2014). Therefore, it is also difficult to constrain gas expulsion in this way.…”

Section: Constraints On Gas Expulsionmentioning

confidence: 99%

Gas expulsion in massive star clusters?

Krause

Charbonnel

Bastian

et al. 2016

A&A

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Context. Gas expulsion is a central concept in some of the models for multiple populations and the light-element anti-correlations in globular clusters. If the star formation efficiency was around 30 per cent and the gas expulsion happened on the crossing timescale, this process could preferentially expel stars born with the chemical composition of the proto-cluster gas, while stars with special composition born in the centre would remain bound. Recently, a sample of extragalactic, gas-free, young massive clusters has been identified that has the potential to test the conditions for gas expulsion. Aims. We investigate the conditions required for residual gas expulsion on the crossing timescale. We consider a standard initial mass function and different models for the energy production in the cluster: metallicity-dependent stellar winds, radiation, supernovae and more energetic events, such as hypernovae, which are related to gamma ray bursts. The latter may be more energetic than supernovae by up to two orders of magnitude. Methods. We computed a large number of thin-shell models for the gas dynamics, and calculated whether the Rayleigh-Taylor instability is able to disrupt the shell before it reaches the escape speed. Results. We show that the success of gas expulsion depends on the compactness index of a star cluster C 5 ≡ (M * /10 5 M )/(r h /pc), with initial stellar mass M * and half-mass radius r h . For given C 5 , a certain critical, local star formation efficiency is required to remove the rest of the gas. Common stellar feedback processes may not lead to gas expulsion with significant loss of stars above C 5 ≈ 1. Considering pulsar winds and hypernovae, the limit increases to C 5 ≈ 30. If successful, gas expulsion generally takes place on the crossing timescale. Some observed young massive clusters have 1 < C 5 < 10 and are gas-free at ≈10 Myr. This suggests that gas expulsion does not affect their stellar mass significantly, unless powerful pulsar winds and hypernovae are common in such objects. By comparison to observations, we show that C 5 is a better predictor for the expression of multiple populations than stellar mass. The best separation between star clusters with and without multiple populations is achieved by a stellar winds-based gas expulsion model, where gas expulsion would occur exclusively in star clusters without multiple populations. Single and multiple population clusters also have little overlap in metallicity and age. Conclusions. Globular clusters should initially have C 5 100, if the gas expulsion paradigm was correct. Early gas expulsion, which is suggested by the young massive cluster observations, hence would require special circumstances, and is excluded for several objects. Most likely, the stellar masses did not change significantly at the removal of the primordial gas. Instead, the predictive power of the C 5 index for the expression of multiple populations is consistent with the idea that gas expulsion may prevent the expression of multiple populations. On this bas...

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Dependency of Dynamical Ejections of O Stars on the Masses of Very Young Star Clusters

Cited by 106 publications

References 101 publications

Hypervelocity stars from young stellar clusters in the Galactic Centre

Hypervelocity stars from young stellar clusters in the Galactic Centre

Mind Your Ps and Qs: The Interrelation between Period (P) and Mass-ratio (Q) Distributions of Binary Stars

Gas expulsion in massive star clusters?

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