Cluster-assisted Accretion for Massive Stars

Pfalzner, Susanne

doi:10.1086/510290

Cited by 8 publications

(14 citation statements)

References 25 publications

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“…A typical example of such an environment is the Orion nebula cluster (ONC). In an earlier paper (Pfalzner 2006), we demonstrated that encounters cause a 3−5% specific angular momentum loss in the ONC, rising to 10−15% in the dense inner Trapezium region. Since specific angular momentum loss is a prerequisite for accretion, we suggested that in the final star formation stages an additional growth mechanism for massive stars exist (cluster-assisted accretion) as massive stars lose their Article published by EDP Sciences specific angular momentum to a higher degree than low-mass stars.…”

Section: Introductionmentioning

confidence: 70%

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Accretion bursts in young stars driven by the cluster environment

Pfalzner¹,

Tackenberg²,

Steinhausen³

2008

A&A

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Context. The standard picture of accretion is a steady flow of matter from the disc onto the young star -a concept that assumes the star-disc system is completely isolated. However, in a dense cluster environment star-disc systems do interact gravitationally. Aims. The aim here is to estimate the encounter-induced accretion rate in an ONC-like environment. Methods. By combining simulations of the cluster dynamics with simulations of the effect of encounters on star-disc systems, we determine the likelihood and degree of encounter-triggered accretion processes. Results. We show that accretion bursts triggered by encounters of star-disc systems are common in young dense clusters like the ONC, leading in the outburst phase to typical accretion rates of 10 −7 −10 −4 M /yr. Up to a third of the stars presently in the Trapezium region have accreted at least 1% of their disc mass via this mechanism in the past 1 Myr. Accretion of over 6−7% of the disc material can occur in a single encounter. Despite losing their discs quickly, the total percentage of disc matter accreted per star is greatest for the massive stars. Conclusions. Supplementing the steady accretion flow are episodic periods of high accretion in dense cluster environments. Because of their high accretion rate, these processes should be observable even now in some of the low-mass stars in the ONC.

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Section: Introductionmentioning

confidence: 70%

“…We have combined simulations of the cluster dynamics performed with the Nbody6++ code (Spurzem 1999) with tree code simulations, to study the effect of encounters on star-disc systems as described in Pfalzner (2006). Here we determine the likelihood and degree of the encounter-triggered accretion processes.…”

Section: Methodsmentioning

confidence: 99%

Accretion bursts in young stars driven by the cluster environment

Pfalzner¹,

Tackenberg²,

Steinhausen³

2008

A&A

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“…This approach is justified by the interplay of three effects: (i) A disc-mass loss of this order lowers the density in the disc significantly, in particular in the outer parts; the disc size decreases. (ii) The accompanying angular momentum loss enhances accretion of the extant material onto the star (Pfalzner 2006). This leads temporarily to an increase of the infrared excess but soon fades after a short intense accretion phase (Pfalzner 2008, subm.…”

Section: Numerical Simulationsmentioning

confidence: 99%

Encounters in the ONC – observing imprints of star-disc interactions

Olczak¹,

Pfalzner²,

Eckart

2008

A&A

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Context. The external destruction of protoplanetary discs in a clustered environment acts mainly due to two mechanisms: gravitational drag by stellar encounters and evaporation by strong stellar winds and radiation. It is a fundamental question whether either of these mechanisms is important for the stellar evolution and planet formation process in young star clusters. Aims. We focus on the effect of stellar encounters in young dense clusters and investigate whether there are any observables that could trace this mechanism and its impact on disc evolution. If encounters play a role in disc destruction, one would expect that stars devoid of disc material would show unexpectedly high velocities as an outcome of close interactions. We want to quantify this effect by numerical simulations and compare it to observations. Methods. As a model cluster we chose the Orion Nebula Cluster (ONC). We reanalyzed observational data of the ONC to find encounter signatures in the velocity distribution and a possible correlation with signatures of circumstellar discs. We use the nbody6++ code to model the dynamics of an ONC-like cluster and analyze the velocity distribution and the disc-mass loss due to encounters. Results. We found from the observational data that 8 to 18 stars leave the ONC with velocities several times the velocity dispersion. The majority of these high-velocity stars are young low-mass stars (t 10 5 yr, m ≈ 0.2-0.3 M ), among them several lacking infrared excess emission. Interestingly, the high-velocity stars are found only in two separate regions of the ONC -i) close to the cluster centre and ii) in the outer cluster region. Our simulations give an explanation for the location of the high-velocity stars and provide evidence for a strong correlation between location and disc destruction. Conclusions. The high-velocity stars can be explained as the outcome of close three-body encounters; the partial lack of disc signatures is attributed to gravitational interaction. The spatial distribution of the high-velocity stars reflects the initial structure and dynamics of the ONC. Our approach can be generalized to study the evolution of other young dense star clusters, like the Arches cluster, back in time.

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“…Lada & Lada 2003;Porras et al 2003;Evans et al 2009). The accretion discs of these stars are thus exposed to environmental effects that could affect their evolution (Richling & Yorke 1998;Hollenbach et al 2000;Scally & Clarke 2001;Adams et al 2004;Olczak et al 2006;Pfalzner 2006;Pfalzner et al 2006;Pfalzner & Olczak 2007;Clarke 2007;Olczak et al 2010). As these discs are the prerequisites for the formation of planetary systems this process might be influenced by the olczak@ari.uni-heidelberg.de 1 Max-Planck-Institut für Astronomie (MPIA), Königstuhl 17, 69117 Heidelberg, Germany 2 National Astronomical Observatories of China, Chinese Academy of Sciences (NAOC/CAS), 20A Datun Lu, Chaoyang District, Beijing 100012, China 3 The Kavli Institute for Astronomy and Astrophysics at Peking University (KIAA), Yi He Yuan Lu 5, Hai Dian Qu, Beijing 100871, China cluster environment.…”

Section: Introductionmentioning

confidence: 99%

The Evolution of Protoplanetary Disks in the Arches Cluster

Olczak

Kaczmarek

Harfst

et al. 2012

ApJ

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Most stars form in a cluster environment. These stars are initially surrounded by discs from which potentially planetary systems form. Of all cluster environments starburst clusters are probably the most hostile for planetary systems in our Galaxy. The intense stellar radiation and extreme density favour rapid destruction of circumstellar discs via photoevaporation and stellar encounters. Evolving a virialized model of the Arches cluster in the Galactic tidal field we investigate the effect of stellar encounters on circumstellar discs in a prototypical starburst cluster. Despite its proximity to the deep gravitational potential of the Galactic centre only a moderate fraction of members escapes to form an extended pair of tidal tails. Our simulations show that encounters destroy one third of the circumstellar discs in the cluster core within the first 2.5 Myr of evolution, preferentially affecting the least and most massive stars. A small fraction of these events causes rapid ejection and the formation of a weaker second pair of tidal tails that is overpopulated by disc-poor stars. Two predictions arise from our study: (i) If not destroyed by photoevaporation protoplanetary discs of massive late B-and early O-type stars represent the most likely hosts of planet formation in starburst clusters. (ii) Multiepoch Kand L-band photometry of the Arches cluster would provide the kinematically selected membership sample required to detect the additional pair of disc-poor tidal tails.

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Cluster-assisted Accretion for Massive Stars

Cited by 8 publications

References 25 publications

Accretion bursts in young stars driven by the cluster environment

Accretion bursts in young stars driven by the cluster environment

Encounters in the ONC – observing imprints of star-disc interactions

The Evolution of Protoplanetary Disks in the Arches Cluster

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