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Mass segregation
About: Mass segregation is a research topic. Over the lifetime, 1024 publications have been published within this topic receiving 57729 citations.
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TL;DR: In this article, a boundary value for the density of a star forming clump of given mass, such that, stellar clusters born in clumps which have densities higher than this, could emerge bound after gas loss, and a critical mass such that subcondensations with larger masses than this could suffer significant segregation within the clump.
Abstract: Two puzzles associated with open clusters have attracted a lot of attention -- their formation, with densities and velocity dispersions that are not too different from those of the star forming regions in the Galaxy, given that the observed Star Formation Efficiencies (SFE) are low and, the mass segregation observed / inferred in some of them, at ages significantly less than the dynamical relaxation times in them. Gas dynamical friction has been considered before as a mechanism for contracting embedded stellar clusters, by dissipating their energy. This would locally raise the SFE which might then allow bound clusters to form. Noticing that dynamical friction is inherently capable of producing mass segregation, since here, the dissipation rate is proportional to the mass of the body experiencing the force, we explore further, some of the details and implications of such a scenario, vis-a-vis observations. Making analytical approximations, we obtain a boundary value for the density of a star forming clump of given mass, such that, stellar clusters born in clumps which have densities higher than this, could emerge bound after gas loss, and for a clump of given mass and density, we find a critical mass such that, subcondensations with larger masses than this could suffer significant segregation within the clump.
5 citations
TL;DR: In this article, the authors carried out UBVRcIc photometric study of three poorly studied young open clusters IC 1442, King 21, and Trumpler 7 (Tr 7), and obtained 263, 244, and 128 member stars using Gaia DR2 proper motions and parallaxes.
Abstract: We carried out UBVRcIc photometric study of three poorly studied young open clusters IC 1442, King 21, and Trumpler 7 (Tr 7). We obtained 263, 244, and 128 member stars using Gaia DR2 proper motions and parallaxes in IC 1442, King 21, and Tr 7, respectively. The reddening, E(B-V), was derived to be 0.54+/-0.04, 0.76+/-0.06, and 0.38+/-0.04 mag for these clusters. The comparison of observed colour-magnitude diagrams (CMDs) with solar metallicity isochrones yields log(Age) = 7.40+/-0.30, 7.70+/-0.20, and 7.85+/-0.25 yr and corresponding distances 2847+/-238, 2622+/-156, and 1561+/-74 pc for IC 1442, King 21, and Tr 7, respectively. The estimated mass function (MF) slopes are found to be -1.94+/-0.18, -1.54+/-0.32, and -2.31+/-0.29 for IC 1442, King 21, and Tr 7, respectively. The study of MF slopes determined separately in the inner and the outer regions of these clusters gives a steeper slope in outer region which suggests spatial variation in slope and mass segregation in the clusters. We found evidence of mass segregation after dynamical study in these clusters. The obtained relaxation time is 74, 26, and 34 Myr for the clusters IC 1442, King 21, and Tr 7, respectively. The mass segregation in IC 1442 may be caused by early dynamical relaxation. The estimated relaxation time is well below to the ages of King 21 and Tr 7 which indicates that these clusters are dynamically relaxed.
5 citations
TL;DR: In this article, the authors explore the evolution of rotating multi-mass star clusters during the violent relaxation phase, in the presence of a weak external tidal field, and show that massive stars tend to rotate more rapidly than low-mass stars around the axis of cluster rotation.
Abstract: We present the results of a study aimed at exploring, by means of N-body simulations, the evolution of rotating multi-mass star clusters during the violent relaxation phase, in the presence of a weak external tidal field. We study the implications of the initial rotation and the presence of a mass spectrum for the violent relaxation dynamics and the final properties of the equilibria emerging at the end of this stage. Our simulations show a clear manifestation of the evolution towards spatial mass segregation and evolution towards energy equipartition during and at the end of the violent relaxation phase. We study the final rotational kinematics and show that massive stars tend to rotate more rapidly than low-mass stars around the axis of cluster rotation. Our analysis also reveals that during the violent relaxation phase, massive stars tend to preferentially segregate into orbits with angular momentum aligned with the cluster's angular momentum, an effect previously found in the context of the long-term evolution of star clusters driven by two-body relaxation.
5 citations
TL;DR: In this article, the authors obtained a good fit to the measured main sequence mass function (MF) of a large sample of Galactic clusters (young and old) with a tapered Salpeter power law distribution function with an exponential truncation.
Abstract: We show that one can obtain a good fit to the measured main sequence mass function (MF) of a large sample of Galactic clusters (young and old) with a tapered Salpeter power law distribution function with an exponential truncation. The average value of the power law index is very close to Salpeter (~2.3), whereas the characteristic mass is in the range 0.1 - 0.5 Msolar and does not seem to vary in a systematic way with the present cluster parameters such as metal abundance and central concentration. However, a remarkable correlation with age is seen, in that the peak mass of young clusters increases with it. This trend does not extend to globular clusters, whose peak mass is firmly at ~0.35 Msolar. This correlation is due to the onset of mass segregation following early dynamical interactions in the loose cluster cores. Differences between globular and younger clusters may depend on the initial environment of star formation, which in turn affects their total mass.
5 citations
TL;DR: In this paper, the authors investigated the role of a primordial binary population in the loss of primordial mass segregation of young star clusters, and found that the initially completely mass segregated clusters, even with binaries, are more compatible with the present-day ONC than the non-segregated ones.
Abstract: Observations of young star-forming regions suggest that star clusters are born completely mass segregated. These initial conditions are, however, gradually lost as the star cluster evolves dynamically. For star clusters with single stars only and a canonical initial mass function, it has been suggested that traces of these initial conditions vanish at a time $\tau_\mathrm{v}$ between 3 and $3.5\,t_\mathrm{rh}$ (initial half-mass relaxation times). Since a significant fraction of stars are observed in binary systems and it is widely accepted that most stars are born in binary systems, we aim to investigate what role a primordial binary population (even up to $100\,\%$ binaries) plays in the loss of primordial mass segregation of young star clusters. We used numerical $N$-body models similar in size to the Orion Nebula Cluster (ONC) -- a representative of young open clusters -- integrated over several relaxation times to draw conclusions on the evolution of its mass segregation. We also compared our models to the observed ONC. We found that $\tau_\mathrm{v}$ depends on the binary star fraction and the distribution of initial binary parameters that include a semi-major axis, eccentricity, and mass ratio. For instance, in the models with $50\,\%$ binaries, we find $\tau_\mathrm{v} = (2.7 \pm 0.8)\,t_\mathrm{rh}$, while for $100\,\%$ binary fraction, we find a lower value $\tau_\mathrm{v} = (2.1 \pm 0.6)\,t_\mathrm{rh}$. We also conclude that the initially completely mass segregated clusters, even with binaries, are more compatible with the present-day ONC than the non-segregated ones.
4 citations