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Post Info TOPIC: Stellar clusters
Blobrana


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RE: Stellar clusters
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Most stars are born in clusters, some leave "home"

New modelling studies from Carnegie's Alan Boss demonstrate that most of the stars we see were formed when unstable clusters of newly formed protostars broke up. These protostars are born out of rotating clouds of dust and gas, which act as nurseries for star formation. Rare clusters of multiple protostars remain stable and mature into multi-star systems. The unstable ones will eject stars until they achieve stability and end up as single or binary stars. The work is published in The Astrophysical Journal.
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Blobrana


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Title: Age Dating Stellar Populations in the Near Infrared: An absolute age indicator from the presence/absence of red supergiants
Authors: J. Zachary Gazak, N. Bastian, R. P. Kudritzki, A. Adamo, B. Davies, B. Plez, M. A. Urbaneja

The determination of age is a critical component in the study of a population of stellar clusters. In this letter we present a new absolute age indicator for young massive star clusters based on J-H colour. This novel method identifies clusters as older or younger than 5.7 ± 0.8 Myr based on the appearance of the first population of red supergiant stars. We test the technique on the stellar cluster population of the nearby spiral galaxy, M83, finding good agreement with the theoretical predictions. The localisation of this technique to the near-IR promises that it may be used well into the future with space-- and ground--based missions optimised for near-IR observations.

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Blobrana


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Posts: 131433
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Cool Stars in Hot Places
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Title: Cool Stars in Hot Places
Authors: S. T. Megeath (University of Toledo), E. Gaidos (University of Hawaii), J. J. Hester (Arizona State University), F. C. Adams (University of Michigan), J. Bally (University of Colorado), J.-E. Lee (University of California Los Angeles), S. Wolk (Harvard-Smithsonian Centre for Astrophysics)

During the last three decades, evidence has mounted that star and planet formation is not an isolated process, but is influenced by current and previous generations of stars. Although cool stars form in a range of environments, from isolated globules to rich embedded clusters, the influences of other stars on cool star and planet formation may be most significant in embedded clusters, where hundreds to thousands of cool stars form in close proximity to OB stars. At the cool stars 14 meeting, a splinter session was convened to discuss the role of environment in the formation of cool stars and planetary systems; with an emphasis on the ''hot'' environment found in rich clusters. We review here the basic results, ideas and questions presented at the session. We have organised this contribution into five basic questions: what is the typical environment of cool star formation, what role do hot star play in cool star formation, what role does environment play in planet formation, what is the role of hot star winds and supernovae, and what was the formation environment of the Sun? The intention is to review progress made in addressing each question, and to underscore areas of agreement and contention.

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Blobrana


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Posts: 131433
Date:
Stellar clusters
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Title: The effect of spiral arm passages on the evolution of stellar clusters
Authors: M. Gieles (1,2,3), E. Athanassoula (2), S.F. Portegies Zwart (3) ((1) Utrecht, (2) Marseille, (3) Amsterdam)

We study the effect of spiral arm passages on the evolution of star clusters on planar and circular orbits around the centres of galaxies. Individual passages with different relative velocity (V_drift) and arm width are studied using N-body simulations. When the ratio of the time it takes the cluster to cross the density wave to the crossing time of stars in the cluster is much smaller than one, the energy gain of stars can be predicted accurately in the impulsive approximation. When this ratio is much larger than one, the cluster is heated adiabatically and the net effect of heating is largely damped. For a given duration of the perturbation, this ratio is smaller for stars in the outer parts of the cluster compared to stars in the inner part. The cluster energy gain due to perturbations of various duration as obtained from our N-body simulations is in good agreement with theoretical predictions taking into account the effect of adiabatic damping. Perturbations by the broad stellar component of the spiral arms on a cluster are in the adiabatic regime and, therefore, hardly contribute to the energy gain and mass loss of the cluster. We consider the effect of crossings through the high density shocked gas in the spiral arms, which result in a more impulsive compression of the cluster. The time scale of disruption is shortest at ~0.8-0.9 R_CR since there V_drift is low. This location can be applicable to the solar neighbourhood. In addition, the four-armed spiral pattern of the Milky Way makes spiral arms contribute more to the disruption of clusters than in a similar but two-armed galaxy. Still, the disruption time due to spiral arm perturbations there is about an order of magnitude higher than what is observed for the solar neighbourhood.

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