Contribution of White Dwarfs to Cluster
                                                  Masses

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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A Gaia DR2 view of the open cluster population in the Milky Way

Astronomy and Astrophysics ◽

10.1051/0004-6361/201833476 ◽

2018 ◽

Vol 618 ◽

pp. A93 ◽

Cited By ~ 180

Author(s):

T. Cantat-Gaudin ◽

C. Jordi ◽

A. Vallenari ◽

A. Bragaglia ◽

L. Balaguer-Núñez ◽

...

Keyword(s):

Stellar Evolution ◽

Milky Way ◽

Galactic Plane ◽

Galactic Disk ◽

Open Cluster ◽

Open Clusters ◽

Number Of Clusters ◽

History Of ◽

Gaia Dr2

Context. Open clusters are convenient probes of the structure and history of the Galactic disk. They are also fundamental to stellar evolution studies. The second Gaia data release contains precise astrometry at the submilliarcsecond level and homogeneous photometry at the mmag level, that can be used to characterise a large number of clusters over the entire sky. Aims. In this study we aim to establish a list of members and derive mean parameters, in particular distances, for as many clusters as possible, making use of Gaia data alone. Methods. We compiled a list of thousands of known or putative clusters from the literature. We then applied an unsupervised membership assignment code, UPMASK, to the Gaia DR2 data contained within the fields of those clusters. Results. We obtained a list of members and cluster parameters for 1229 clusters. As expected, the youngest clusters are seen to be tightly distributed near the Galactic plane and to trace the spiral arms of the Milky Way, while older objects are more uniformly distributed, deviate further from the plane, and tend to be located at larger Galactocentric distances. Thanks to the quality of Gaia DR2 astrometry, the fully homogeneous parameters derived in this study are the most precise to date. Furthermore, we report on the serendipitous discovery of 60 new open clusters in the fields analysed during this study.

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Open cluster remnants in low-density Galactic fields

Proceedings of the International Astronomical Union ◽

10.1017/s1743921309991785 ◽

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.

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Dynamical Evolution of Rotating Globular Clusters

Symposium - International Astronomical Union ◽

10.1017/s0074180900001893 ◽

1996 ◽

Vol 174 ◽

pp. 375-376

Author(s):

P.-Y. Longaretti ◽

C. Lagoute

Keyword(s):

Angular Momentum ◽

Stellar Evolution ◽

Globular Cluster ◽

Globular Clusters ◽

Dynamical Evolution

We have computed simplified globular cluster evolutionary tracks which take into account the effects of internal relaxation, of the cluster rotation, of the galactic tidal field, and, in a cruder way, of stellar evolution and of gravitational shocking. The objectives are first to quantify the influence of rotation in the dynamical evolution of globular clusters; and second, to investigate the evolution of globular cluster angular momentum and flattening (Lagoute and Longaretti 1995a, Longaretti and Lagoute 1995b,c).

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The blue straggler population of the old open cluster Berkeley 17

Astronomy and Astrophysics ◽

10.1051/0004-6361/201834449 ◽

2019 ◽

Vol 624 ◽

pp. A26 ◽

Cited By ~ 4

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.

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An Example Demonstrating the Potential for Asteroseismology of DB White Dwarf Stars

International Astronomical Union Colloquium ◽

10.1017/s025292110011704x ◽

1993 ◽

Vol 139 ◽

pp. 116-116

Author(s):

P.A. Bradley ◽

M.A. Wood

Keyword(s):

Internal Structure ◽

Stellar Evolution ◽

White Dwarf ◽

White Dwarfs ◽

Galactic Disk ◽

Helium Surface ◽

Dwarf Stars ◽

University Of Texas ◽

White Dwarf Stars ◽

History Of

AbstractWe present the results of a parametric survey of evolutionary models of compositionally stratified white dwarfs with helium surface layers (DB white dwarfs). Because white dwarfs are the most common final end state of stellar evolution, determining their internal structure will offer us many clues about stellar evolution, the physics of matter under extreme conditions, plus the history of star formation and age of the local Galactic disk. As a first step towards determining the internal structure of DB white dwarf stars, we provide a comprehensive set of theoretical g-mode pulsation periods for comparison to observations.Because DB white dwarfs have a layered structure consisting of a helium layer overlying the carbon/oxygen core, some modes will have the same wavelength as the thickness of the helium layer, allowing a resonance to form. This resonance is called mode trapping (see Brassard et al. 1992 and references therein) and has directly observable consequences, because modes at or near the resonance have eigenfunctions and pulsation periods that are similar to each other. This results in much smaller period spacings between consecutive overtone modes of the same spherical harmonic index than the uniform period spacings seen between non-trapped modes. We demonstrate with an example how one can use the distribution of pulsation periods to determine the total stellar mass, the mass of the helium surface layer, and the extent of the helium/carbon and carbon/oxygen transition zones. With these tools, we have the prospect of being able to determine the structure of the observed DBV white dwarfs, once the requisite observations become available.We are grateful to C.J. Hansen, S.D. Kawaler, R.E. Nather, and D.E. Winget for their encouragement and many discussions. This research was supported by the National Science Foundation under grants 85-52457 and 90-14655 through the University of Texas and McDonald Observatory.

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Extended stellar systems in the solar neighborhood

Astronomy and Astrophysics ◽

10.1051/0004-6361/202037591 ◽

2020 ◽

Vol 639 ◽

pp. A64 ◽

Cited By ~ 1

Author(s):

Sebastian Ratzenböck ◽

Stefan Meingast ◽

João Alves ◽

Torsten Möller ◽

Immanuel Bomze

Keyword(s):

Support Vector Machines ◽

White Dwarfs ◽

Planet Formation ◽

Dynamical Evolution ◽

Solar Neighborhood ◽

Support Vector ◽

Stellar Systems ◽

High Fidelity ◽

Vector Machines ◽

Formation And Evolution

Context. Nearby stellar streams carry unique information on the dynamical evolution and disruption of stellar systems in the Galaxy, the mass distribution in the disk, and they provide unique targets for planet formation and evolution studies. Recently, Meingast 1, a 120° stellar stream with a length of at least 400 pc, was dicovered. Aims. We aim to revisit the Meingast 1 stream to search for new members within its currently known 400 pc extent, using Gaia DR2 data and an innovative machine learning approach. Methods. We used a bagging classifier of one-class support vector machines with Gaia DR2 data to perform a 5D search (positions and proper motions) for new stream members. The ensemble was created by randomly sampling 2.4 million hyper-parameter realizations admitting classifiers that fulfill a set of prior assumptions. We used the variable prediction frequency resulting from the multitude of classifiers to estimate a stream membership criterion, which we used to select high-fidelity sources. We used the HR diagram and the Cartesian velocity distribution as test and validation tools. Results. We find about 2000 stream members with high fidelity, or about an order of magnitude more than previously known, unveiling the stream’s population across the entire stellar mass spectrum, from B stars to M stars, including white dwarfs. We find that, apart from being slightly more metal poor, the HRD of the stream is indistinguishable from that of the Pleiades cluster. For the mass range at which we are mostly complete, ∼0.2 M⊙ < M < ∼4 M⊙, we find a normal IMF, allowing us to estimate the total mass of stream to be about 2000 M⊙, making this relatively young stream by far the most massive one known. In addition, we identify several white dwarfs as potential stream members. Conclusions. The nearby Meingast 1 stream, due to its richness, age, and distance, is a new fundamental laboratory for star and planet formation and evolution studies for the poorly studied and gravitationally unbound star formation mode. We also demonstrate that one-class support vector machines can be effectively used to unveil the full stellar populations of nearby stellar systems with Gaia data.

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Magellanic globulars as cosmological tools

Symposium - International Astronomical Union ◽

10.1017/s0074180900200260 ◽

1991 ◽

Vol 148 ◽

pp. 165-169

Author(s):

Alvio Renzini

Keyword(s):

Galaxy Formation ◽

Stellar Evolution ◽

Globular Clusters ◽

Star Clusters ◽

Dynamical Evolution ◽

Mass Range ◽

Magellanic Clouds ◽

Evolution Theory ◽

Mass Functions ◽

The Ideal

The globular clusters (GC) of the Magellanic Clouds play a very important role for many astrophysical and cosmological topics. For example, they represent the ideal testground for stellar evolution theory, they allow us to study the the early dynamical evolution of star clusters, to obtain accurate initial mass functions in a fairly extended mass range, to calibrate the Cepheid period-luminosity relation, and so on. In this brief paper I will touch upon two items which are of considerable cosmological interest, and about which Magellanic Cloud globulars provide unique information. These topics concern i) GC formation in galaxies, and ii) the epoch of galaxy formation.

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COMMISSION 37: STAR CLUSTERS AND ASSOCIATIONS

Proceedings of the International Astronomical Union ◽

10.1017/s1743921308025684 ◽

2008 ◽

Vol 4 (T27A) ◽

pp. 277-279

Author(s):

Despina Hatzidimitriou ◽

Charles J. Lada ◽

Ata Sarajedini ◽

Russell D. Cannon ◽

Kyle McC. Cudworth ◽

...

Keyword(s):

Chemical Evolution ◽

Globular Clusters ◽

Galactic Disk ◽

Star Clusters ◽

Open Clusters ◽

Stellar Rotation ◽

Star Clusters And Associations ◽

Stellar Spectroscopy ◽

Wide Range ◽

Massive Star Evolution

Star clusters are valuable tools for theoretical and observational astronomy across a wide range of disciplines from cosmology to stellar spectroscopy. For example, properties of globular clusters are used to constrain stellar evolutionary models, nucleosynthesis and chemical evolution, as well as the star formation and assembly histories of galaxies and the distribution of dark matter in present-day galaxies. Open clusters are widely used as stellar laboratories for the study of specific stellar phenomena (e.g., various emission-line stars, pulsating pre-MS stars, magnetic massive stars, binarity, stellar rotation, etc.). They also provide observational constraints on models of massive star evolution and of Galactic disk formation and chemical evolution.

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Gaia Data Release 2

Astronomy and Astrophysics ◽

10.1051/0004-6361/201832843 ◽

2018 ◽

Vol 616 ◽

pp. A10 ◽

Cited By ~ 289

Author(s):

◽

C. Babusiaux ◽

F. van Leeuwen ◽

M. A. Barstow ◽

C. Jordi ◽

...

Keyword(s):

Stellar Evolution ◽

White Dwarfs ◽

Stellar Population ◽

Open Clusters ◽

Data Release ◽

Low Mass ◽

Different Populations ◽

Fine Structures ◽

First Time ◽

Late Stages

Context. Gaia Data Release 2 provides high-precision astrometry and three-band photometry for about 1.3 billion sources over the full sky. The precision, accuracy, and homogeneity of both astrometry and photometry are unprecedented. Aims. We highlight the power of the Gaia DR2 in studying many fine structures of the Hertzsprung-Russell diagram (HRD). Gaia allows us to present many different HRDs, depending in particular on stellar population selections. We do not aim here for completeness in terms of types of stars or stellar evolutionary aspects. Instead, we have chosen several illustrative examples. Methods. We describe some of the selections that can be made in Gaia DR2 to highlight the main structures of the Gaia HRDs. We select both field and cluster (open and globular) stars, compare the observations with previous classifications and with stellar evolutionary tracks, and we present variations of the Gaia HRD with age, metallicity, and kinematics. Late stages of stellar evolution such as hot subdwarfs, post-AGB stars, planetary nebulae, and white dwarfs are also analysed, as well as low-mass brown dwarf objects. Results. The Gaia HRDs are unprecedented in both precision and coverage of the various Milky Way stellar populations and stellar evolutionary phases. Many fine structures of the HRDs are presented. The clear split of the white dwarf sequence into hydrogen and helium white dwarfs is presented for the first time in an HRD. The relation between kinematics and the HRD is nicely illustrated. Two different populations in a classical kinematic selection of the halo are unambiguously identified in the HRD. Membership and mean parameters for a selected list of open clusters are provided. They allow drawing very detailed cluster sequences, highlighting fine structures, and providing extremely precise empirical isochrones that will lead to more insight in stellar physics. Conclusions. Gaia DR2 demonstrates the potential of combining precise astrometry and photometry for large samples for studies in stellar evolution and stellar population and opens an entire new area for HRD-based studies.

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Open Clusters and Stellar Evolution

Symposium - International Astronomical Union ◽

10.1017/s0074180900091841 ◽

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.

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