scholarly journals Dynamical evolution of the Galactic disk

1985 ◽  
Vol 106 ◽  
pp. 481-490 ◽  
Author(s):  
Roland Wielen ◽  
Burkhard Fuchs
Keyword(s):  
Galactic Disk ◽  
Dynamical Evolution ◽  
Stellar Orbits ◽  
Stochastic Heating ◽  
Adiabatic Cooling ◽  
Theoretical Predictions

After some general remarks on the dynamical evolution of the galactic disk, we review mechanisms which may affect the velocities of disk stars: stochastic heating, deflections, adiabatic cooling or heating. We compare the observed velocities of nearby disk stars with theoretical predictions based on the diffusion of stellar orbits.

scholarly journals Contribution of White Dwarfs to Cluster Masses

1998 ◽  
Vol 11 (1) ◽  
pp. 430-432
Author(s):  
Ted Von Hippel
Keyword(s):  
Stellar Evolution ◽  
Mass Fraction ◽  
Globular Clusters ◽  
White Dwarfs ◽  
Literature Search ◽  
Galactic Disk ◽  
Dynamical Evolution ◽  
Open Clusters ◽  
Solar Neighborhood ◽  
Current Evidence

The study of cluster white dwarfs (WDs) has been invigorated recently bythe Hubble Space Telescope (HST). Recent WD studies have been motivated by the new and independent cluster distance (Renzini et al. 1996), age (von Hippel et al. 1995; Richer et al. 1997), and stellar evolution (Koester & Reimers 1996) information that cluster WDs can provide. An important byproduct of these studies has been an estimate of the WD mass contribution in open and globular clusters. The cluster WD mass fraction is of importance for understanding the dynamical state and history of star clusters. It also bears an important connection to the WD mass fractions of the Galactic disk and halo. Current evidence indicates that the open clusters (e.g. von Hippel et al. 1996; Reid this volume) have essentially the same luminosity function (LF) as the solar neighborhood population. The case for the halo is less clear, despite the number of very good globular cluster LFs down to nearly 0.1 solar masses (e.g. Cool et al. 1996; Piotto, this volume), as the field halo LF is poorly known. For most clusters dynamical evolution should cause evaporation of the lowest mass members, biasing clusters to have flatter present-day mass functions (PDMFs) than the disk and halo field populations. Dynamical evolution should also allow cluster WDs to escape, though not in the same numbers as the much lower mass main sequence stars. The detailed connection between cluster PDMFs and the field IMF awaits elucidation from observations and the new combined N-body and stellar evolution models (Tout, this volume). Nevertheless, the WD mass fraction of clusters already provides an estimate for the WD mass fraction of the disk and halo field populations. A literature search to collect cluster WDs and a simple interpretive model follow. This is a work in progress and the full details of the literature search and the model will be published elsewhere.

scholarly journals Open cluster remnants in low-density Galactic fields

2009 ◽  
Vol 5 (S266) ◽  
pp. 487-490
Author(s):  
D. B. Pavani ◽  
L. O. Kerber ◽  
E. Bica ◽  
W. J. Maciel
Keyword(s):  
Galactic Disk ◽  
Information Source ◽  
Open Cluster ◽  
Dynamical Evolution ◽  
Theoretical Models ◽  
Open Clusters ◽  
Low Density ◽  
Statistical Tool ◽  
General Picture ◽  
Disk Evolution

AbstractOpen cluster remnants (OCRs) are fundamental objects to investigate open cluster dissolution processes (e.g., Bica et al. 2001; Carraro 2002; Pavani et al. 2003; Carraro et al. 2007; Pavani & Bica 2007). They are defined as poorly populated concentrations of stars, with enough members to show evolutionary sequences in colour–magnitude diagrams (CMDs) as a result of the dynamical evolution of an initially more massive physical system. An OCR is intrinsically poorly populated, which makes its differentiation from field-star fluctuations difficult. Among the possible approaches to establish the nature of OCRs, we adopted CMD analysis combined with a robust statistical tool applied to 2mass data. In addition, photometry is the main information source available for possible OCRs (POCRs). We developed a statistical diagnostic tool to analyse the CMDs of POCRs and verify them as physical systems, explore membership probabilityies taking into account field contamination and derive age, distance and reddening values in a self-consistent way. We present the results of our analysis of 88 POCRs that are part of a larger sample that is widely distributed across the sky, with a significant density contrast of bright stars compared to the Galactic field. The 88 objects are projected onto low-density Galactic fields, at relatively high latitudes (|b| > 15°). Studies of larger POCR samples will provide a better understanding of OCR properties and constraints for theoretical models, including new insights into the evolution of open clusters and their dissolution rates. The results of this ongoing survey will provide a general picture of these fossil stellar systems and their connection to Galactic-disk evolution.

Dynamical Evolution of the Galactic Disk

The Galaxy ◽  
1987 ◽  
pp. 375-398 ◽  
Author(s):  
Burkhard Fuchs ◽  
Roland Wielen
Keyword(s):  
Galactic Disk ◽  
Dynamical Evolution

scholarly journals Mapping the Stellar Distribution in Globular Clusters: An Application to NGC 6809 = M55

1995 ◽  
Vol 164 ◽  
pp. 409-409
Author(s):  
S. R. Zaggia ◽  
G. Piotto ◽  
M. Capaccioli
Keyword(s):  
Globular Clusters ◽  
Galactic Center ◽  
Galactic Disk ◽  
Dynamical Evolution ◽  
Mass Function ◽  
Blue Stragglers ◽  
Set Constraints ◽  
Central Regions ◽  
Single Mass ◽  
The Rich

The principal aim of this work is to map the stellar distribution of a large sample of galactic globular clusters from the central regions to the outer envelope (beyond the tidal radius for an estimate of the foreground/background contamination) with a good statistical sampling of stars in the different branches of the color-magnitude diagram and with different masses. These new data will be used to investigate the dynamical evolution of stellar systems embedded in the gravitational field of our Galaxy, and, eventually, to set constraints on the mass distribution of the Milky Way. In this context, star counts have been carried out on V and I CCD frames of the rich, low concentration galactic globular cluster M55. The frames cover 35% of the cluster, from the center to 1.3 times the tidal radius (with total coverage inside 1rc). From V=14 (i.e. the horizontal branch level) to a limiting magnitude V=22 (MV = 7.9), a total of 36800 stars have been measured. A population of blue stragglers (BS) has been identified, but, at variance with other clusters of similar core concentration, the BS of M55 are only marginally more concentrated toward the center. No population gradient has been identified in M55. A luminosity function down to V = 21.3 has been obtained, after applying completeness and field star contamination correction to the star counts. The mass function is very flat (xglobal ≤ −0.5), as it was expected for this cluster located close to the galactic center and to the galactic disk. A single mass King model fitted to the radial star counts gives a core radius rc = 143″ and a tidal radius rt = 970″, ~ 10% greater than previously estimated.

scholarly journals Extended stellar systems in the solar neighborhood

2019 ◽  
Vol 621 ◽  
pp. L3 ◽  
Author(s):  
Stefan Meingast ◽  
João Alves
Keyword(s):  
Globular Clusters ◽  
Galactic Disk ◽  
Spatial Arrangement ◽  
Solar Neighborhood ◽  
Source Selection ◽  
The Galaxy ◽  
Theoretical Predictions ◽  
Direction Of Movement ◽  
Mass Segregation ◽  
Tidal Tails

We report the discovery of two well-defined tidal tails emerging from the Hyades star cluster. The tails were detected in Gaia DR2 data by selecting cluster members in the 3D galactocentric cylindrical velocity space. The robustness of our member selection is reinforced by the fact that the sources depict an almost noiseless, coeval stellar main sequence in the observational Hertzsprung-Russel diagram. The spatial arrangement of the selected members represents a highly flattened shape with respect to the direction of movement along the clusters’ orbit in the Galaxy. The size of the entire structure, within the limits of the observations, measures about 200 pc in its largest extent, while being only about 25 pc thick. This translates into an on-sky extent of well beyond 100 deg. Intriguingly, a top-down view on the spatial distribution reveals a distinct S-shape, reminiscent of tidal tails that have been observed for globular clusters and also of tails that were modeled for star clusters bound to the Galactic disk. Even more remarkable, the spatial arrangement as well as the velocity dispersion of our source selection is in excellent agreement with previously published theoretical predictions for the tidal tails of the Hyades. An investigation into observed signatures of equipartition of kinetic energy, that is, mass segregation, remains unsuccessful, most likely because of the sensitivity limit for radial velocity measurements with Gaia.

scholarly journals Properties of abundance gradient along the Galactic disk and the role of LAMOST

2013 ◽  
Vol 9 (S298) ◽  
pp. 304-309
Author(s):  
J.L. Hou ◽  
L. Chen ◽  
J.C. Yu ◽  
J. Sellwood ◽  
C. Pryor
Keyword(s):  
Radial Velocity ◽  
Main Sequence ◽  
Milky Way ◽  
Galactic Disk ◽  
Open Cluster ◽  
Dynamical Evolution ◽  
Open Clusters ◽  
Main Sequence Stars ◽  
Abundance Gradient

AbstractIn this paper, we present our recent work on the evolution of abundance gradients along the Milky Way disk based on the Geneva Copenhagen Survey (GCS) and Radial Velocity Experiment (RAVE) data. We will also discuss the role of the LAMOST Milky Way disk survey in clarifying the properties of metallicity breaks observed through open clusters and young tracers along the Milky Way disk. It is believed that the Galactic disk forms inside-out, in which the stellar population at increasing radii is younger and more metal poor. This picture is consistent with most Galactic Chemical Evolution (GCE) models which also predict a tight correlation between the metallicity and age of stars at a given radius. However, it is only a result of “steady state" and no dynamical evolution effects were taken into account. We have selected two stellar samples from GCS and RAVE, each sample contains about 10,000 local thin-disk, main-sequence stars. We use the guiding radius which is determined by the conservation of z-direction angular momentum, to eliminate the blurring effects. And also use the effective temperature of the main sequence stars as a proxy of stellar age. It is shown that the metallicity gradient flattens as the age increases. This is not consistent with our previous GCE prediction, but can be explained by radial mixing effects. In order to further demonstrate the abundance breaks observed in the Galactic disk we have proposed, and have been carrying out, an open cluster survey project based on LAMOST. We plan to observe at least 400 open clusters in the northern Galactic sky. From the observations, we will get uniform parameters for those clusters with radial velocity and metallicities. We anticipate that this uniform open cluster sample could clarify the observed abundance break around the Milky Way disk corotation radius and also give a more robust result concerning the evolution of the abundance gradient.

scholarly journals Dynamical evolution of star clusters in transient spiral arms

2012 ◽  
Vol 10 (H16) ◽  
pp. 359-359
Author(s):  
Michiko Fujii ◽  
Junichi Baba
Keyword(s):  
Galactic Disk ◽  
Star Clusters ◽  
Dynamical Evolution ◽  
Building Blocks ◽  
Stellar Disk ◽  
Galactic Rotation ◽  
Potential Well ◽  
Galactic Disks ◽  
Spiral Arms ◽  
Tidal Tails

AbstractStar clusters are one of fundamental building blocks of galactic disks. They form in a potential well of spiral arms and travel in the disk. We performed N-body simulation of star clusters in stellar disk with “live” spiral arms. In this simulation, both star clusters and stellar disks are modeled as N-body systems. We found that star clusters migrated in the galactic disk in a timescale of their galactic rotation. The tidal tails spread over a few kpc, but they might be detectable if we are able to measure their velocity.

scholarly journals Escapees from the bar resonances

2020 ◽  
Vol 638 ◽  
pp. A144 ◽  
Author(s):  
S. Khoperskov ◽  
P. Di Matteo ◽  
M. Haywood ◽  
A. Gómez ◽  
O. N. Snaith
Keyword(s):  
Milky Way ◽  
Galactic Disk ◽  
Age Distribution ◽  
Maximum Amplitude ◽  
Dynamical Evolution ◽  
Circular Orbits ◽  
Slowing Down ◽  
Eccentric Orbits ◽  
Outer Disk ◽  
Innermost Region

Understanding radial migration is a crucial point for building relevant chemical and dynamical evolution models of the Milky Way disk. In this paper we analyze a high-resolution N-body simulation of a Milky Way-type galaxy to study the role that the slowing down of a stellar bar has in generating migration from the inner to the outer disk. Stellar particles are trapped by the main resonances (corotation and outer Lindblad resonance, OLR) which then propagate outward across the disk due to the bar slowing down. Once the bar strength reaches its maximum amplitude, some of the stars delivered to the outer disk escape the resonances and some of them settle on nearly circular orbits. The number of escaped stars gradually increases, also due to the decrease in the bar strength when the boxy/peanut bulge forms. We show that this mechanism is not limited to stars on nearly circular orbits; stars initially on more eccentric orbits can also be transferred outward (out to the OLR location) and can end up on nearly circular orbits. Therefore, the propagation of the bar resonances outward can induce the circularization of the orbits of some of the migrating stars. The mechanism investigated in this paper can explain the presence of metal-rich stars at the solar vicinity and more generally in the outer Galactic disk. Our dynamical model predicts that up to 3% of stars between corotation and the OLR can be formed in the innermost region of the Milky Way. The epoch of the Milky Way bar formation can be potentially constrained by analyzing the age distribution of the most metal-rich stars at the solar vicinity.

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