scholarly journals Open Clusters and Stellar Evolution

1980 ◽  
Vol 85 ◽  
pp. 195-214
Author(s):  
Gretchen L.H. Harris
Keyword(s):  
Stellar Evolution ◽  
Initial Conditions ◽  
Dynamical Evolution ◽  
Open Clusters ◽  
Potential Importance ◽  
Helium Burning ◽  
The Core ◽  
Magnitude Diagram

Several topics relevant to the study of stellar evolution through open clusters are discussed. These include composite color-magnitude diagrams, the need for thorough studies of populous clusters, parameters affecting the core helium burning stage, and the potential importance of initial conditions and dynamical evolution on the cluster color-magnitude diagram.

scholarly journals The Clump Giants: A Spectroscopic Survey of G and K Giants in Open Clusters

1978 ◽  
Vol 80 ◽  
pp. 157-160
Author(s):  
Catherine A. Pilachowski ◽  
Walter K. Bonsack
Keyword(s):  
Stellar Evolution ◽  
Open Clusters ◽  
The Other ◽  
Similar Proportion ◽  
Helium Burning ◽  
The Core ◽  
Evolutionary State ◽  
Peculiar Stars ◽  
Absolute Magnitudes ◽  
Process Elements

The clump giants in old and middle-aged open clusters provide a sample of stars whose evolutionary state can be clearly identified as core helium burning (Cannon 1970). The evolutionary state of the Ba II stars, on the other hand, is at present undetermined. The enrichment of s-process elements in the atmospheres of these peculiar stars suggests that the stars have at least passed through double shell burning, where the heavy elements may be produced and mixed to the surface. The Ba II stars are, however, too faint to be associated with this phase of stellar evolution; the absolute magnitudes and temperatures are consistent with the core helium burning phase. The barium stars should then occur in the clumps of Population I clusters in similar proportion to their numbers among the field giants.

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 The blue straggler population of the old open cluster Berkeley 17

2019 ◽  
Vol 624 ◽  
pp. A26 ◽  
Author(s):  
Souradeep Bhattacharya ◽  
Kaushar Vaidya ◽  
W. P. Chen ◽  
Giacomo Beccari
Keyword(s):  
Radial Distribution ◽  
Globular Clusters ◽  
Minimum Spanning Tree ◽  
Open Cluster ◽  
Dynamical Evolution ◽  
Open Clusters ◽  
Blue Straggler ◽  
Magnitude Diagram ◽  
First Time ◽  
Giant Branch Stars

Context. Blue straggler stars (BSSs) are observed in Galactic globular clusters and old open clusters. The radial distribution of BSSs has been used to diagnose the dynamical evolution of globular clusters. For the first time, with a reliable sample of BSSs identified with Gaia DR2, we conduct such an analysis for an open cluster. Aims. We aim to identify members, including BSSs, of the oldest known Galactic open cluster Berkeley 17 with the Gaia DR2 proper motions and parallaxes. We study the radial distribution of the BSS population to understand the dynamical evolution of the cluster. Methods. We selected cluster members to populate the colour magnitude diagram in the Gaia filters. Cluster parameters are derived using the brightest members. The BSSs and giant branch stars are identified, and their radial distributions are compared. The segregation of BSSs is also evaluated with respect to the giant branch stars using the minimum spanning tree (MST) analysis. Results. We determine Berkeley 17 to be at 3138.6−352.9+285.5 pc. We find 23 BSS cluster members, only two of which were previously identified. We find a bimodal radial distribution of BSSs supported by findings from the MST method. Conclusions. The bimodal radial distribution of BSSs in Berkeley 17 indicates that they have just started to sink towards the cluster centre, placing Berkeley 17 with globular clusters of intermediate dynamical age. This is the first such determination for an open cluster.

scholarly journals Extended main sequence turnoffs in open clusters as seen by Gaia – II. The enigma of NGC 2509

2019 ◽  
Vol 491 (2) ◽  
pp. 2129-2136 ◽  
Author(s):  
M de Juan Ovelar ◽  
S Gossage ◽  
S Kamann ◽  
N Bastian ◽  
C Usher ◽  
...  
Keyword(s):  
Stellar Evolution ◽  
Main Sequence ◽  
Narrow Range ◽  
Open Cluster ◽  
Open Clusters ◽  
Stellar Rotation ◽  
Rotation Rates ◽  
Magnitude Diagram ◽  
Stellar Density

ABSTRACT We investigate the morphology of the colour–magnitude diagram (CMD) of the open cluster NGC 2509 in comparison with other Galactic open clusters of similar age using Gaia photometry. At ${\sim}900\,\rm {Myr}$ Galactic open clusters in our sample all show an extended main sequence turnoff (eMSTO) with the exception of NGC 2509, which presents an exceptionally narrow CMD. Our analysis of the Gaia data rules out differential extinction, stellar density, and binaries as a cause for the singular MSTO morphology in this cluster. We interpret this feature as a consequence of the stellar rotation distribution within the cluster and present the analysis with mesa Isochrones and Stellar Tracks (MIST) stellar evolution models that include the effect of stellar rotation on which we based our conclusion. In particular, these models point to an unusually narrow range of stellar rotation rates (Ω/Ωcrit, ZAMS = [0.4, 0.6]) within the cluster as the cause of this singular feature in the CMD of NGC 2509. Interestingly, models that do not include rotation are not as good at reproducing the morphology of the observed CMD in this cluster.

scholarly journals The Resolved Stellar Populations of Leo A & GR 8

1995 ◽  
Vol 164 ◽  
pp. 417-417
Author(s):  
Eline Tolstoy
Keyword(s):  
Numerical Simulation ◽  
Star Formation ◽  
Maximum Likelihood ◽  
Stellar Evolution ◽  
Dwarf Galaxies ◽  
Initial Conditions ◽  
Mass Function ◽  
Initial Mass Function ◽  
Magnitude Diagram ◽  
Maximum Likelihood Technique

The complex effects that determine the shape of an observed Colour Magnitude Diagram (CMD) are best disentangled through numerical simulation. We make synthetic CMDs by randomly extracting stars from theoretical stellar evolution tracks using a series of adopted initial conditions, including an Initial Mass Function. Utilizing reliable error estimates on our photometry provided by the program DoPHOT we apply a Maximum Likelihood technique to quantitatively determine which of the numerous different possible models is the most probable match to the data. From these comparisons we obtain a better understanding of how star formation proceeds in the relatively simple environments provided by Dwarf galaxies.

Fundamental parameters for 30 faint open clusters with Gaia EDR3 based on the more reliable members

2021 ◽  
Author(s):  
Xu Ding ◽  
Kai-Fan Ji ◽  
Xu-Zhi Li ◽  
Qi-Yuan Cheng ◽  
Jin-Liang Wang ◽  
...  
Keyword(s):  
Spatial Structure ◽  
Spatial Clustering ◽  
Open Cluster ◽  
Open Clusters ◽  
Monte Carlo Algorithm ◽  
Structure Parameters ◽  
Fundamental Parameters ◽  
The Core ◽  
Magnitude Diagram ◽  
Fitting Parameters

Abstract An open cluster is an ideal region to study the evolution of stars. In this work, we use Gaia Early Data Release 3 (Gaia EDR3) to derive the fundamental parameters of 30 faint open clusters listed in the catalogue given by Cantat-Gaudin et al. (2018, A&A, 618, A93), but the G magnitude of all of the member stars of that catalogue is brighter than ∼18 mag. This catalogue does not provide isochrone fitting parameters and spatial structure parameters. We acquired the member stars of 30 open clusters using the Density-Based Spatial Clustering of Applications with Noise algorithm in Gaia EDR3. The G magnitude of the member stars using our method can be found down to ∼21 mag. The G-band, GBP-band, and GRP-band data of the member stars construct a good color–magnitude diagram, which can further ensure the precision of isochrone fitting. We also calculated the spatial structure parameters, which are the core radius and the limiting radius, using Markov chain Monte Carlo algorithm.

Fractal statistics in young star clusters: structural parameters and dynamical evolution

2019 ◽  
Vol 490 (2) ◽  
pp. 2521-2541 ◽  
Author(s):  
Annibal Hetem ◽  
Jane Gregorio-Hetem
Keyword(s):  
Initial Conditions ◽  
Local Density ◽  
Structural Parameters ◽  
Cluster Structure ◽  
Dynamical Evolution ◽  
Young Star ◽  
Open Clusters ◽  
Statistical Parameters ◽  
Cluster Membership ◽  
Fractal Statistics

ABSTRACT We used fractal statistics to quantify the degree of observed substructures in a sample of 50 embedded clusters and more evolved open clusters (< 100 Myr) found in different galactic regions. The observed fractal parameters were compared with N-body simulations from the literature, which reproduce star-forming regions under different initial conditions and geometries that are related to the cluster's dynamical evolution. Parallax and proper motion from Gaia-DR2 were used to accurately determine cluster membership by using the Bayesian model and cross-entropy technique. The statistical parameters $\mathcal {Q}$, $\overline{m}$ and $\overline{s}$ were used to compare observed cluster structure with simulations. A low level of substructures ($\mathcal {Q} \lt $ 0.8) is found for most of the sample that coincides with simulations of regions showing fractal dimension D ∼ 2–3. Few clusters (<20 per cent) have uniform distribution with a radial density profile (α < 2). A comparison of $\mathcal {Q}$ with mass segregation (ΛMSR) and local density as a function of mass (ΣLDR) shows the clusters coinciding with models that adopt supervirial initial conditions. The age–crossing time plot indicates that our objects are dynamically young, similar to the unbound associations found in the Milky Way. We conclude that this sample may be expanding very slowly. The flat distribution in the $\mathcal {Q}$–age plot and the absence of trends in the distributions of ΛMSR and ΣLDR against age show that in the first 10 Myr the clusters did not change structurally and seem not to have expanded from a much denser region.

scholarly journals Abundances in Cool Evolved Stars

1988 ◽  
Vol 108 ◽  
pp. 17-30
Author(s):  
Catherine A. Pilachowski
Keyword(s):  
Stellar Evolution ◽  
Planetary Nebula ◽  
Asymptotic Giant Branch ◽  
Chemical Compositions ◽  
Helium Burning ◽  
The Core ◽  
Evolved Stars ◽  
Peculiar Stars

Nature has filled the upper right quadrant of the Hertzsprung-Russell diagram with more varieties of peculiar stars and odd chemical compositions than even our most speculative observers and theorists could dream up. To bring some structure to this vast subject I will categorize the phenomena we observe according to our model of stellar evolution, dividing the stars among the first ascent of the giant branch and the core-helium burning phase, the asymptotic giant branch (double shell-burning) phase, and the post-AGB and pre-planetary nebula stars. The types of stars found in these three groups are summarized below.

Core Helium Burning Evolution at 15 M⊙

1971 ◽  
Vol 2 (1) ◽  
pp. 23-24 ◽  
Author(s):  
J. W. Robertson
Keyword(s):  
Stellar Evolution ◽  
Main Sequence ◽  
Helium Burning ◽  
The Core ◽  
Red Supergiants

The existence of red supergiants such as those in the clusters h and χ Persei has puzzled stellar evolution theoreticians for some time. Suggested explanations for them have included stars in a stage of gravitational contraction to the main sequence, or between nuclear burnings, core helium burning stars, and stars burning carbon or oxygen in the core, but it is now generally accepted that most red supergiants are core helium burning stars.

scholarly journals The Dynamical Evolution of Young Open Clusters

1985 ◽  
Vol 113 ◽  
pp. 463-465
Author(s):  
Michael Margulis ◽  
Charles J. Lada ◽  
David Dearborn
Keyword(s):  
Potential Function ◽  
Molecular Clouds ◽  
Initial Conditions ◽  
Stellar System ◽  
Dynamical Evolution ◽  
Mass Function ◽  
Open Clusters ◽  
Stellar Systems ◽  
Spherically Symmetric ◽  
Star Forming

Using numerical N-body calculations we have simulated the dynamical evolution of young clusters as they emerge from molecular clouds. Starting with initially virialized systems of stars and gas we follow the evolution of these systems from the time immediately after the stars have formed in a cloud until a time long after all the residual star-forming gas has been dispersed. In the models stellar systems were composed of 50, and in some cases 100, stars and these stars were represented as point masses. The stellar mass function followed a power law with an index of −2.5 and ranged over two decades in mass (Scalo 1978). Gas in the models was represented as an extra term in the gravitational potential function governing stellar motions, and was set to follow a density distribution corresponding to a spherically symmetric Plummer potential function (Plummer 1911). Starting with these initial conditions, stellar motions were then integrated and evolution of each stellar system was followed as gas was dispersed from the vicinity of the stars as a function of time.

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