scholarly journals Radial velocities with CORAVEL: results on stellar variability and duplicity

1986 ◽  
Vol 118 ◽  
pp. 385-400
Author(s):  
G. Burki ◽  
M. Mayor
Keyword(s):  
Dynamical Evolution ◽  
Distribution Functions ◽  
Open Clusters ◽  
Formation Mechanisms ◽  
Radial Velocity Curve ◽  
Stellar Radius ◽  
Orbital Parameters ◽  
Pulsating Stars ◽  
Rr Lyrae ◽  
The Galaxy

The complete radial velocity curve has been determined with CORAVEL for many pulsating stars of various classes: cepheid stars in the Galaxy and in the Magellanic Clouds, RR Lyrae, δ Scuti and SX Phoenicis stars. These measurements allow the determination of the radius variation and of the surface acceleration of these stars. In addition, the mean stellar radius of many of these stars has been determined by applying the Baade-Wesselink method.Systematic surveys of definite groups of binary or multiple stars are in progress with CORAVEL in order to determine the distribution functions of the orbital parameters. The eccentricity distributions for the binaries in the open clusters Pleiades, Praesepe, Coma Ber and Hyades are presented and their dependence on the physical processes (star formation mechanisms, mass exchange, tidal circularization, dynamical evolution) is briefly discussed.

scholarly journals Observational Aspects of RR Lyrae Variables in Globular Clusters

1973 ◽  
Vol 21 ◽  
pp. 51-67 ◽  
Author(s):  
L. Rosino
Keyword(s):  
Globular Clusters ◽  
Absolute Magnitude ◽  
Good Test ◽  
Rr Lyrae Stars ◽  
Pulsating Stars ◽  
Rr Lyrae ◽  
Powerful Means ◽  
The Galaxy ◽  
Points Of View ◽  
Lyrae Stars

RR Lyrae variables play a prominent role in many of the problems of globular clusters, and from several points of view. In the first place they can be considered as pretty good indicators of population and distance; although they do not form a completely homogeneous set of stars, the knowledge of their mean absolute magnitude gives a powerful means of establishing distances within and outside the Galaxy, and hence of determining the form and size of the Galaxy itself. Moreover, the number of RR Lyrae stars in clusters, the relative frequency of RRc and RRab, types, the length of the transition periods, the array of colors, when correctly interpreted, give important information on the degree of evolution, age and chemical composition of the clusters. Placed as they are in a peculiar region of the H — R diagram of Population II, the RR Lyr variables can be used as a good test of the theories of advanced evolution or the models of pulsating stars.

scholarly journals Orbit circularization time in binary stellar systems

1984 ◽  
Vol 105 ◽  
pp. 411-414 ◽  
Author(s):  
M. Mayor ◽  
J.-C. Mermilliod
Keyword(s):  
Time Scale ◽  
Dynamical Evolution ◽  
Open Clusters ◽  
Spectroscopic Binaries ◽  
Stellar Systems ◽  
Orbital Parameters ◽  
Short Period ◽  
Red Giant

We have analyzed the orbital parameters of 33 red dwarf and 17 red giant spectroscopic binaries belonging to open clusters to deduce the time-scale for orbital circularization. The dynamical evolution of BD +23°635, a short period binary member of the Hyades, should result in the formation either of a cataclysmic binary or a WUMa system.

scholarly journals The LMC Globular Cluster Hodge 11 (=SL 868)

1984 ◽  
Vol 108 ◽  
pp. 43-44
Author(s):  
L. L. Stryker ◽  
J. M. Nemec ◽  
J. E. Hesser ◽  
R.D. McClure
Keyword(s):  
Globular Clusters ◽  
Main Sequence ◽  
Star Cluster ◽  
Open Clusters ◽  
Rr Lyrae Stars ◽  
Rr Lyrae ◽  
Magnitude Diagram ◽  
The Galaxy ◽  
Lyrae Stars ◽  
Termination Point

The age of the star cluster H11 has been controversial for a number of years. The color-magnitude diagram (CMD) of Walker (1979) to V=21.5 was interpreted as an “…evolved main-sequence, whose termination point corresponds to an age of about 0.6 Gyr, but with a giant branch which is displaced blueward by about Δ (B-V)o=0.4 from the positions of the giant branches of open clusters of similar age in our Galaxy.” On the other hand, the integrated colors are similar to those of metal-poor globular clusters in the Galaxy (Freeman and Gascoigne 1977, and references therein), and “…incompatible with an age of say 0.3 Gyr.” Searle, Wilkinson and Bagnuolo (1980) classify it as Group VII, the oldest group. The system has no RR Lyrae stars (Graham and Nemec 1984).

scholarly journals The initial luminosity and mass functions of Galactic open clusters

2008 ◽  
Vol 4 (S254) ◽  
pp. 221-226
Author(s):  
Hans Zinnecker ◽  
Anatoly E. Piskunov ◽  
Nina V. Kharchenko ◽  
Siegfried Röser ◽  
Elena Schilbach ◽  
...  
Keyword(s):  
Dynamical Evolution ◽  
Distribution Functions ◽  
Open Clusters ◽  
Solar Neighborhood ◽  
High Mass ◽  
Cluster Mass ◽  
Initial Cluster ◽  
High Infant Mortality ◽  
The Difference ◽  
Mass Functions

AbstractWe have derived a complete magnitude-limited sample of 440 Galactic open clusters in the solar neighborhood, with integrated V-magnitude brighter than 8 mag. This sample can be used to infer the present-day luminosity and mass functions of open clusters up to a given age; it can even be used to construct the initial mass and luminosity function (IMF, ILF) of clusters (defined as visible clusters with age 4 – 8 Myr). The high-mass end of the cluster IMF is a power-law with a slope of −2 or slightly shallower (−1.7) while the luminous cluster ILF has a power-slope of −1, in agreement with what is found for extragalactic clusters. Both distribution functions show a turnover, starting at 300 M⊙ and integrated magnitude −3 mag, respectively. The overall birthrate of clusters is 0.4 clusters per kpc2 and per Myr. The average present-day cluster mass is 700 M⊙, while the average initial cluster mass is 4500 M⊙. The difference of these two average masses indicates the high infant mortality and/or weight loss of Galactic open clusters (due to dynamical evolution).

scholarly journals Globular clusters in the inner Galaxy classified from dynamical orbital criteria

2019 ◽  
Author(s):  
Angeles Pérez-Villegas ◽  
Beatriz Barbuy ◽  
Leandro Kerber ◽  
Sergio Ortolani ◽  
Stefano O Souza ◽  
...  
Keyword(s):  
Globular Clusters ◽  
Clustering Algorithm ◽  
Galactic Center ◽  
Dynamical Evolution ◽  
Thick Disk ◽  
Orbital Parameters ◽  
Rr Lyrae ◽  
Bar Formation ◽  
Disk Component ◽  
Gaia Dr2

Abstract Globular clusters (GCs) are the most ancient stellar systems in the Milky Way. Therefore, they play a key role in the understanding of the early chemical and dynamical evolution of our Galaxy. Around 40% of them are placed within ∼4 kpc from the Galactic center. In that region, all Galactic components overlap, making their disentanglement a challenging task. With Gaia DR2, we have accurate absolute proper motions for the entire sample of known GCs that have been associated with the bulge/bar region. Combining them with distances, from RR Lyrae when available, as well as radial velocities from spectroscopy, we can perform an orbital analysis of the sample, employing a steady Galactic potential with a bar. We applied a clustering algorithm to the orbital parameters apogalactic distance and the maximum vertical excursion from the plane, in order to identify the clusters that have high probability to belong to the bulge/bar, thick disk, inner halo, or outer halo component. We found that $\sim 30\%$ of the clusters classified as bulge GCs based on their location are just passing by the inner Galaxy, they appear to belong to the inner halo or thick disk component, instead. Most of GCs that are confirmed to be bulge GCs are not following the bar structure and are older than the epoch of the bar formation.

scholarly journals Photometry of early type stars in open clusters (NGC 1444, NGC 1662, NGC 2129, NGC 2169 and NGC 7209)

1994 ◽  
Vol 162 ◽  
pp. 303-304
Author(s):  
J. H. Peña ◽  
R. Peniche
Keyword(s):  
Open Clusters ◽  
Early Type ◽  
Number Of Clusters ◽  
Pulsating Stars ◽  
Blue Stragglers ◽  
Chemical Enrichment ◽  
Short Period ◽  
The Galaxy ◽  
Early Type Stars ◽  
Delta Scuti

This is part of a series which has the purpose of examining the nature of the stars belonging to open clusters. The aim of this series is, among others things, to study short period pulsating stars, mainly of the Delta Scuti type, by first establishing the membership of each star to the cluster, to determine the abundance of the Be and Ap phenomena and blue stragglers in open clusters for clusters of different ages and metalicities and, eventually, to study the chemical enrichment of the galaxy when age, dynamics and metalicity are known for a fair number of clusters.

scholarly journals Planetary Systems in Star Clusters: the dynamical evolution and survival

2018 ◽  
Vol 14 (S345) ◽  
pp. 293-294 ◽  
Author(s):  
F. Flammini Dotti ◽  
Maxwell Xu Cai ◽  
Rainer Spurzem ◽  
M.B.N. Kouwenhoven
Keyword(s):  
Globular Clusters ◽  
Large Fraction ◽  
Planetary Systems ◽  
Dynamical Evolution ◽  
Star Cluster ◽  
Open Clusters ◽  
Star Forming ◽  
Star Forming Regions ◽  
The Galaxy ◽  
Exoplanet Systems

AbstractMost stars form in crowded stellar environments. Such star forming regions typically dissolve within ten million years, while others remain bound as stellar groupings for hundreds of millions to billions of years, and then become the open clusters or globular clusters that are present in our Milky Way galaxy today. A large fraction of stars in the Galaxy hosts planetary companions. To understand the origin and dynamical evolution of such exoplanet systems, it is necessary to carefully study the effect of their environments. Here, we combine theoretical estimates with state-of-the-art numerical simulations of evolving planetary systems similar to our own solar system in different star cluster environments. We combine the planetary system evolution code, and the star cluster evolution code, integrated in the multi-physics environment. With our study we can constrain the effect of external perturbations of different environments on the planets and debris structures of a wide variety of planetary systems, which may play a key role for the habitability of exoplanets in the Universe.

Galactic orbits of stars

1966 ◽  
Vol 25 ◽  
pp. 93-97
Author(s):  
Richard Woolley
Keyword(s):  
Globular Cluster ◽  
Potential Field ◽  
High Velocity ◽  
Velocity Vector ◽  
Variable Stars ◽  
The Sun ◽  
Proper Motions ◽  
Rr Lyrae ◽  
The Galaxy

It is now possible to determine proper motions of high-velocity objects in such a way as to obtain with some accuracy the velocity vector relevant to the Sun. If a potential field of the Galaxy is assumed, one can compute an actual orbit. A determination of the velocity of the globular clusterωCentauri has recently been completed at Greenwich, and it is found that the orbit is strongly retrograde in the Galaxy. Similar calculations may be made, though with less certainty, in the case of RR Lyrae variable stars.

scholarly journals Are we observing an NSC in course of formation in the NGC 4654 galaxy?

2021 ◽  
Vol 503 (1) ◽  
pp. 594-602
Author(s):  
R Schiavi ◽  
R Capuzzo-Dolcetta ◽  
I Y Georgiev ◽  
M Arca-Sedda ◽  
A Mastrobuono-Battisti
Keyword(s):  
Central Zone ◽  
Effective Radius ◽  
Host Galaxy ◽  
Galactic Centre ◽  
Future Evolution ◽  
Orbital Parameters ◽  
Relative Orbit ◽  
The Future ◽  
The Galaxy ◽  
Massive Clusters

ABSTRACT We use direct N-body simulations to explore some possible scenarios for the future evolution of two massive clusters observed towards the centre of NGC 4654, a spiral galaxy with mass similar to that of the Milky Way. Using archival HST data, we obtain the photometric masses of the two clusters, M = 3 × 105 M⊙ and M = 1.7 × 106 M⊙, their half-light radii, Reff ∼ 4 pc and Reff ∼ 6 pc, and their projected distances from the photometric centre of the galaxy (both <22 pc). The knowledge of the structure and separation of these two clusters (∼24 pc) provides a unique view for studying the dynamics of a galactic central zone hosting massive clusters. Varying some of the unknown cluster orbital parameters, we carry out several N-body simulations showing that the future evolution of these clusters will inevitably result in their merger. We find that, mainly depending on the shape of their relative orbit, they will merge into the galactic centre in less than 82 Myr. In addition to the tidal interaction, a proper consideration of the dynamical friction braking would shorten the merging times up to few Myr. We also investigate the possibility to form a massive nuclear star cluster (NSC) in the centre of the galaxy by this process. Our analysis suggests that for low-eccentricity orbits, and relatively long merger times, the final merged cluster is spherical in shape, with an effective radius of few parsecs and a mass within the effective radius of the order of $10^5\, \mathrm{M_{\odot }}$. Because the central density of such a cluster is higher than that of the host galaxy, it is likely that this merger remnant could be the likely embryo of a future NSC.

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.

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