Mass segregation

About: Mass segregation is a research topic. Over the lifetime, 1024 publications have been published within this topic receiving 57729 citations.

On the survivability of planets in young massive clusters

Abstract: As of March 2019, there is only one exoplanet among nearly 4000 confirmed exoplanets detected in dense GCs. Young massive Star clusters (YMCs) are widely considered as the progenitor of globular clusters (GCs). Motivated by the lack of planet detections in GCs, we use direct $N$-body simulations to study the survivability of planets in young massive clusters, and thereby constrain the probability that GCs inherit planets from YMCs. We conclude that most wide-orbit planets ($a\geq 20$~au), should they form in a YMC similar to Westerlund-1, will be ejected on a timescale of 10 Myr. Consequently, a majority of surviving exoplanets will have semi-major axes smaller than 20 au. Ignoring planet-planet scattering and tidal damping, the survival probability as a function of initial semi-major axis in au can be described as $f_{\rm surv}(a_0)=-0.33\log_{10}(a_0)+1$. About $28.8\%$ of free-floating planets (FFPs) have sufficient speeds to escape from the host YMC at a crossing timescale upon their ejection. The other FFPs will remain bound to the cluster potential, but the subsequent mass segregation process could cause their delayed ejection from the host cluster during its course to evolve into a GC. As such, we expect that GCs are rich in short-period terrestrial planets, but are deprived of FFPs due to dynamical instability and Jovian planets due to the planet-metallicity correlation.

Young cluster Berkeley 59 : Properties, evolution and star formation

Abstract: Berkeley 59 is a nearby ($\sim$1 kpc) young cluster associated with the Sh2-171 H{\sc ii} region. We present deep optical observations of the central $\sim$2.5$\times$2.5 pc$^2$ area of the cluster, obtained with the 3.58-m Telescopio Nazionale Galileo. The $V$/($V$-$I$) color-magnitude diagram manifests a clear pre-main-sequence (PMS) population down to $\sim$ 0.2 M$_\odot$. Using the near-infrared and optical colors of the low-mass PMS members we derive a global extinction of A$_V$= 4 mag and a mean age of $\sim$ 1.8 Myr, respectively, for the cluster. We constructed the initial mass function and found that its global slopes in the mass ranges of 0.2 - 28 M$_\odot$ and 0.2 - 1.5 M$_\odot$ are -1.33 and -1.23, respectively, in good agreement with the Salpeter value in the solar neighborhood. We looked for the radial variation of the mass function and found that the slope is flatter in the inner region than in the outer region, indicating mass segregation. The dynamical status of the cluster suggests that the mass segregation is likely primordial. The age distribution of the PMS sources reveals that the younger sources appear to concentrate close to the inner region compared to the outer region of the cluster, a phenomenon possibly linked to the time evolution of star-forming clouds is discussed. Within the observed area, we derive a total mass of $\sim$ 10$^3$ M$_\odot$ for the cluster. Comparing the properties of Berkeley 59 with other young clusters, we suggest it resembles more to the Trapezium cluster.

A close look at the heart of RCW 108

Abstract: Context. The IRAS 16362-4845 star-forming site in the RCW 108 complex contains an embedded compact cluster that includes some massive O-type stars. Star formation in the complex, and in particular in IRAS 16362-4845, has been proposed to be externally triggered by the action of NGC 6193. Aims. We present a photometric study of the IRAS 16362-4845 cluster sensitive enough to probe the massive brown dwarf regime. In particular, we try to verify an apparent scarcity of solar-type and low-mass stars reported in a previous paper (Comeron et al. 2005, A&A, 433, 955). Methods. Using NACO at the VLT we have carried out adaptive optics-assisted imaging in the JHKSLbands, as well as through narrow-band filters centered on the Brγ and the H2 S (1) v = 1 → 0 lines. We estimate individual line-of-sight extinctions and, for stars detected in the three JHKS filters, we estimate the contribution to the KS flux caused by light reprocessed in the circumstellar environment. We also resolve close binary and multiple systems. We use the K luminosity function as a diagnostic tool for the char- acteristics of the underlying mass function. Results. IRAS 16362-4845 does contain young low-mass stars. Nevertheless, they are far less than those expected from the extrapo- lation of the bright end of the K luminosity function towards fainter magnitudes. We estimate a total stellar mass of 370 M� . Nearly all the cluster members display Lexcesses, whereas KS excesses are in general either absent or moderate ( 9, likely to be a Class I source. Conclusions. The fact that solar-type and low-mass stars are present in numbers much smaller than those expected from the number of more massive members hints at an initial mass function deficient in low mass stars as compared to that of other young clusters such as the Trapezium. The origin of this difference is unclear, and we speculate that it might be due to external triggering having started star formation in the cluster, perhaps producing a top-heavy initial mass function. We also note that there are no detectable systematic differences between the spatial distributions of bright and faint cluster members. Such absence of mass segregation in the spatial distribution of stars may also support external triggering having played an important role in the history of the RCW 108 region.

Evolution of mass segregation in open clusters: some observational evidences ?

Abstract: On the basis of the best available member list and duplicity information, we have studied the radial structure of Praesepe and of the very young open cluster NGC 6231. We have found mass segregation among the cluster members and between binaries and single stars, which is explained by the greater average mass of the multiple systems. However, the de- gree of mass segregation for stars between 1.5 and 2.3 M is less pronounced in Praesepe than in the Pleiades. Furthermore, mass segregation is already present in the very young open clus- ter NGC 6231 although this cluster is likely still not dynamically relaxed. We discuss the implications of these results and pro- pose a qualitative scenario for the evolution of mass segregation in open clusters. In Praesepe the mass function of single stars and primaries appears to be significantly different, like in the Pleiades. We observe an absence of ellipticity of the outer part of Praesepe. radial structure of the Pleiades, using the detailed knowledge of the membership based on proper motions, radial velocities and photometry (Raboud & Mermilliod 1998, referred to as RM98), confirms the presence of an extended corona around the cluster core and the existence of a clear mass segregation among cluster members found by van Leeuwen (1983). It also shows that the corona boundary is elliptical and that the mass function for the binary and single stars are different. Additional open clusters are known to present mass segregation: the Hyades (Perryman et al. 1997), M11, M35 and M67 (Mathieu 1983, 1984). Results are similar: the most massive and the multiple stars are always concentrated and the mass segregation is less important among the low mass stars ( M< 1 - 1.5 M) in these clusters.

Kinematics and binaries in young stellar aggregates. II. NGC 6913 ≡ M 29

Abstract: Between 1996 and 2003 we obtained 226 high resolution spectra of 16 stars in the field of the young open cluster NGC 6913, to constrain its main properties and study its internal kinematics. Twelve of the program stars turned out to be members, one of them probably unbound. Nine are binaries (one eclipsing and another double lined) and for seven of them the observations allowed us to derive the orbital elements. All but two of the nine discovered binaries are cluster members. In spite of the young age (a few Myr), the cluster already shows signs that could be interpreted as evidence of dynamical relaxation and mass segregation. However, they may be also the result of an unconventional formation scenario. The dynamical (virial) mass as estimated from the radial velocity dispersion is larger than the cluster luminous mass, which may be explained by a combination of the optically thick interstellar cloud that occults part of the cluster, the unbound state or undetected very wide binary orbit of some of the members that inflate the velocity dispersion and a high inclination for the axis of possible cluster angular momentum. All the discovered binaries are hard enough to survive average close encounters within the cluster and do not yet show signs of relaxation of the orbital elements to values typical of field binaries.