bluuebunny/crossref_metadata_2025_split huggingface dataset:
Embedded and open star clusters: basic questions
Authors: Zinnecker Hans 
Published: January 2010

AbstractThis paper provides an introduction to IAU Symposium 266 on star clusters as basic building blocks in space and time. We define clusters as bound systems and discriminate them from general stellar clusterings or groups and unbound associations. We give a few examples of young, embedded, compact clusters which may evolve into looser, open clusters after dynamical relaxation due to mass loss and secular relaxation processes. We ask how and where star clusters form (in normal and interacting galaxies) and provide statistics of open clusters in terms of cluster masses and ages in the solar neighborhood (where observational data are most complete). Finally, we list a number of basic questions for current and future star cluster research and discuss the prospects for cluster studies with the next generation infrared and submillimeter telescopes (Herschel; JWST, E–ELT; ALMA, NOEMA).
The VLT–FLAMES Tarantula Survey
Authors: Evans C. J. , Bastian N. , Beletsky Y. , Brott I. , Cantiello M. , Clark J. S. , Crowther P. A. , de Koter A. , de Mink S. E. , Dufton P. L. , Dunstall P. , Gieles M. , Gräfener G. , Hénault-Brunet V. , Herrero A. , Howarth I. D. , Langer N. , Lennon D. J. , Apellániz J. Maíz , Markova N. , Najarro F. , Puls J. , Sana H. , Simón-Díaz S. , Smartt S. J. , Stroud V. E. , Taylor W. D. , Trundle C. , van Loon J. Th. , Vink J. S. , Walborn N. R. 
Published: January 2010

AbstractThe Tarantula Survey is an ambitious ESO Large Programme that has obtained multi-epoch spectroscopy of over 1000 massive stars in the 30 Doradus region in the Large Magellanic Cloud. Here, we introduce the scientific motivations of the survey and give an overview of the observational sample. Ultimately, quantitative analysis of every star, paying particular attention to the effects of rotational mixing and binarity, will be used to address fundamental questions in both stellar and cluster evolution.
Stellar feedback and triggered star formation
Authors: Palouš Jan , Wünsch Richard , Dale James E. , Sidorin Vojtěch , Whitworth Anthony 
Published: January 2010

AbstractYoung, massive stars influence their ambient medium through winds and radiation. The outcome of this feedback depends on the number of massive stars in a star cluster and on the density of the ambient medium. This contribution is based on a comparison of observations to the results of numerical simulations. We discuss the gravitational fragmentation of feedback-driven shells expanding from young stellar clusters. The thin-shell approximation is compared to 3D hydrodynamical simulations with smoothed-particle hydrodynamics and adaptive-mesh refinement codes. We explore the influence of external pressure and propose a thick-shell dispersion relation, where the pressure of the external medium is included. The mass spectrum of the shell fragments is constructed and we speculate about the origin of the deficit of low-mass objects.
Nuclear star clusters
Authors: Böker Torsten 
Published: January 2010

AbstractThe centers of most galaxies in the local Universe are occupied by compact, barely resolved sources. Based on their structural properties, position in the Fundamental Plane, and integrated spectra, these sources clearly have a stellar origin. They are therefore called ‘nuclear star clusters’ (NCs) or ‘stellar nuclei’. NCs are found in galaxies of all Hubble types, suggesting that their formation is intricately linked to galaxy evolution. Here, I review some recent studies of NCs, describe ideas for their formation and subsequent growth, and touch on their possible evolutionary connection with both supermassive black holes and globular clusters.
Star cluster disruption
Authors: Gieles Mark 
Published: January 2010

AbstractStar clusters are often used as tracers of major star-formation events in external galaxies as they can be studied out to much greater distances than individual stars. It is vital to understand their evolution if they are used to derive, for example, the star-formation history of their host galaxy. More specifically, we want to know how cluster lifetimes depend on their environment and on structural properties such as mass and radius. This review presents a theoretical overview of the early evolution of star clusters and the consequent long-term survival chances. It is suggested that clusters forming with initial densities of ≳104 M⊙ pc−3 survive the gas expulsion, or ‘infant mortality,’ phase. At ~10Myr, they are bound and have densities of ~103±1 M⊙ pc−3. After this time, they are stable against expansion through stellar evolution, encounters with giant molecular clouds and will most likely survive for another Hubble time if they are located in a moderate tidal field. Clusters with lower initial densities (≲100 M⊙ pc−3) will disperse into the field within a few 10s of Myrs. Some discussion is given on how extragalactic star cluster populations, and especially their age distributions, can be used to gain insight into disruption.
The distance and space distribution of bulge globular clusters
Authors: Ortolani Sergio , Barbuy Beatriz , Bica Eduardo 
Published: January 2010

AbstractWe present the distribution of Galactic bulge globular clusters and a method based on simultaneous detection of field and cluster horizontal branches to derive the cluster distances. This method has the advantage of being independent of both reddening and the reddening law, RV = AV/E(B−V). The vast majority of clusters projected in the direction of the Galactic bulge are located on the near side of the Galactic Center. Deviations from the reddening law do not seem to be responsible for this peculiarity. We need to introduce a peculiar, steep dependence of the absolute horizontal-branch magnitude with metallicity in the metal-rich regime if we want to reproduce a symmetrical distribution. Instead, if the observed distribution is correct, we expect a rather large number of bulge globular clusters are still to be discovered.
The range of validity of cluster masses and ages derived from broad-band photometry
Authors: Apellániz J. Maíz 
Published: January 2010

AbstractI analyze the stochastic effects introduced by sampling the stellar initial mass function (SIMF) in the derivation of the individual masses and the cluster mass function (CMF) from broad-band visible/near-infrared unresolved photometry. The classical method of using unweighted U BV photometry to simultaneously establish ages and extinctions of stellar clusters is found to be unreliable for clusters older than ≈30 Myr, even for relatively large cluster masses. On the other hand, augmenting the filter set to include longer-wavelength filters and using weights for each filter increases the range of masses and ages that can be measured accurately with unresolved photometry. Nevertheless, a relatively large range of masses and ages is found to be dominated by SIMF sampling effects that render the observed masses useless, even when using U BV RI JHK photometry.
Globular cluster abundances: the imprint of first-generation massive stars
Authors: Charbonnel Corinne 
Published: January 2010

AbstractGalactic globular cluster (GC) stars exhibit abundance patterns that are not shared by their field counterparts, namely the well-documented O–Na, C–N and Mg–Al anticorrelations. Recent observations provide compelling evidence that these abundance anomalies were already present in the intracluster gas from which the presently observed stars formed. The current explanation is that the gas was polluted very early in the history of the GC by material processed through H burning at high temperatures and then lost by stars more massive than the long-lived stars we still observe today. However the ‘polluters’ have not yet been unambiguously identified. Most studies have focused on asymptotic giant brach stars, but rotating massive stars present an interesting alternative. Here, we critically analyse the pros and cons of both potential stellar polluters. We discuss the constraints that the observational data provide on stellar nucleosynthesis and hydrodynamics, as well as on the formation and early evolution of very massive star clusters.
Globular cluster abundances and what they can tell us about galaxy formation
Authors: Cohen Judith G. 
Published: January 2010

AbstractWe review the properties of globular clusters (GCs) which make them useful for studying the Galactic halo, Galactic chemical evolution and the early stages of the formation of the Milky Way. We review the evidence that GCs have a chemical inventory similar to those of halo field stars. We discuss the abundance ratios for dSph galaxies and show that it is possible to have formed at least part of the Galactic-halo field stellar population by dissolving GCs and/or accreting dSph galaxies, but only if this occurred at an early stage in the formation of the Galaxy. We review the constraints on halo-formation timescales deduced from the low magnesium isotopic ratios in metal-poor halo field dwarfs, which indicate that asymptotic giant-branch (AGB) stars did not have time to contribute significantly, while M71 contains two populations, one without and also one with a substantial AGB contribution. We review the limited evidence for GCs with a second population showing additional contributions from Type II supernovae, currently confined to ω Cen, M54 and M22, all of which may have been the nuclei or central regions of accreted galaxies. We check our own data for additional similar GCs and find preliminary indications that NGC 2419, a massive GC far in the outer Galactic halo, may also belong to this group.
Massive binaries and the enrichment of the interstellar medium in globular clusters
Authors: de Mink S. E. , Pols O. R. , Langer N. , Izzard R. G. 
Published: January 2010

AbstractAbundance anomalies observed in globular cluster stars indicate pollution with material processed by hydrogen burning. Two main sources have been suggested: asymptotic giant branch (AGB) stars and massive stars rotating near the break-up limit (spin stars). We discuss the idea that massive binaries may provide an interesting alternative source of processed material. We discuss observational evidence for mass shedding from interacting binaries. In contrast to the fast, radiatively driven winds of massive stars, this material is typically ejected with low velocity. We expect that it remains inside the potential well of a globular cluster and becomes available for the formation or pollution of a second generation of stars. We estimate that the amount of processed low-velocity material that can be ejected by massive binaries is larger than the contribution of the two previously suggested sources combined.
Insights into star cluster formation from λ ≳ 1μm
Authors: Indebetouw Rémy , Chen Rosie , Brogan Crystal , Whitney Barbara , Robitaille Thomas , Looney Leslie 
Published: January 2010

AbstractWe would like to know how molecular clouds turn into stellar clusters, and with what efficiency massive stars form in those clusters, since massive stars are the main agents responsible for evolution of the interstellar medium of galaxies, and their subsequent star-formation history. The imprint of ‘precluster’ molecular cloud conditions can be observed, but only in the least evolved, most embedded clusters, necessarily at wavelengths that can penetrate more than 10 visual magnitudes of extinction. Mid-infrared photometric imaging, most recently and extensively from Spitzer, can be used to select young stellar objects in clustered star-formation environments in our Galaxy and nearby galaxies. Relatively sophisticated methods have been developed, but the fundamental principle remains the selection of sources that have excess infrared emission from circumstellar dust. By fitting radiative-transfer models to a source's spectral-energy distribution between ~1 and ~100μm, we constrain the circumstellar dust distribution and evolutionary state. We can explore many things with this protostellar distribution in mass/luminosity and time/evolutionary state. For example we do not see strong evidence for primordial mass segregation in initial studies. We find evidence of primordial hierarchical substructure, greater clustering at the youngest stages, and even imprints of the pre-stellar Jeans scale. We see correlation of the youngest sources with dense molecular clumps and constrain the timescales for chemical processing and dispersal of those clumps. We have only begun to mine the wealth of existing Spitzer, emerging Herschel and soon ALMA data.
HST's hunt for intermediate-mass black holes in star clusters
Authors: Chanamé Julio , Bruursema Justice , Chandar Rupali , Anderson Jay , van der Marel Roeland , Ford Holland 
Published: January 2010

AbstractEstablishing or ruling out, either through solid mass measurements or upper limits, the presence of intermediate-mass black holes (IMBHs; with masses of 102 − 105 M⊙) at the centers of star clusters would profoundly impact our understanding of problems ranging from the formation and long-term dynamical evolution of stellar systems, to the nature of the seeds and the growth mechanisms of supermassive black holes. While there are sound theoretical arguments both for and against their presence in today's clusters, observational studies have so far not yielded truly conclusive IMBH detections nor upper limits. We argue that the most promising approach to solving this issue is provided by the combination of measurements of the proper motions of stars at the centers of Galactic globular clusters and dynamical models able to take full advantage of this type of data set. We present a program based on HST observations and recently developed tools for dynamical analysis designed to do just that.
The progeny of stellar dynamics and stellar evolution within an N-body model of NGC 188
Authors: Geller Aaron M. , Hurley Jarrod R. , Mathieu Robert D. 
Published: January 2010

AbstractWe present a direct N-body simulation modeling the evolution of the old (7 Gyr) open cluster NGC 188. This is the first N-body open cluster simulation whose initial binary population is directly defined by observations of a specific open cluster: M35 (150 Myr). We compare the simulated color–magnitude diagram at 7 Gyr to that of NGC 188, and discuss the blue stragglers produced in the simulation. We compare the solar-type main-sequence binary period and eccentricity distributions of the simulation to detailed observations of similar binaries in NGC 188. These results demonstrate the importance of detailed observations in guiding N-body open cluster simulations. Finally, we discuss the implications of a few discrepancies between the NGC 188 model and observations and suggest a few methods for bringing N-body open cluster simulations into better agreement with observations.
Globular clusters as laboratories for stellar evolution
Authors: Catelan Márcio , Valcarce Aldo A. R. , Sweigart Allen V. 
Published: January 2010

AbstractGlobular clusters have long been considered the closest approximation to a physicist's laboratory in astrophysics, and as such a near-ideal laboratory for (low-mass) stellar evolution. However, recent observations have cast a shadow on this long-standing paradigm, suggesting the presence of multiple populations with widely different abundance patterns, and—crucially– with widely different helium abundances as well. In this review we discuss which features of the Hertzsprung–Russel diagram may be used as helium-abundance indicators, and present an overview of available constraints on the helium abundance in globular clusters.
Star clusters with dual red clumps
Authors: Girardi Léo , Rubele Stefano , Kerber Leandro 
Published: January 2010

AbstractA few star clusters in the Magellanic Clouds exhibit composite structures in the red-clump region of their colour–magnitude diagrams. The most striking case is NGC 419 in the Small Magellanic Cloud (SMC), where the red clump is composed of a main blob as well as a distinct secondary feature. This structure is demonstrated to be real and corresponds to the simultaneous presence of stars which passed through electron degeneracy after central-hydrogen exhaustion and those that did not. This rare occurrence in a single cluster allows us to set stringent constraints on its age and on the efficiency of convective-core overshooting during main-sequence evolution. We present a more detailed analysis of NGC 419, together with a first look at other populous Large Magellanic Cloud clusters which are apparently in the same phase: NGC 1751, NGC 1783, NGC 1806, NGC 1846, NGC 1852 and NGC 1917. We also compare these Magellanic Cloud cases with their Galactic counterparts, NGC 752 and NGC 7789. We emphasise the extraordinary potential of these clusters as absolute calibration marks on the age scale of stellar populations.
Primordial binary evolution and blue stragglers
Authors: Chen Xuefei , Han Zhanwen 
Published: January 2010

AbstractBlue stragglers have been found in all populations. They are important in both stellar evolution and stellar population synthesis. Much evidence shows that blue stragglers are relevant to primordial binaries. Here, we summarize the links between binary evolution and blue stragglers, describe the characteristics of blue stragglers originating from different binary evolutionary channels and show their consequences for binary population synthesis, such as for the integrated spectral-energy distribution, the colour–magnitude diagram, their specific frequency, and their influence on colours, etc.
Measuring the GC luminosity function up to z ~ 0.2
Authors: Alamo-Martínez K. A. , González-Lópezlira R. A. , Blakeslee J. 
Published: January 2010

AbstractGlobular clusters (GCs) are stellar systems (~106 M⊙) with very regular symmetry, single age, and single metallicity. Spectroscopic studies have revealed very old ages, suggesting that GCs were formed in the earliest stages of galaxy formation and assembly. The aim of this work is to find out how far we can measure the GC luminosity function, specific frequency, and radial distribution, applying the surface-brightness-fluctuations (SBF) technique to deep ACS images. To this end, we apply the effects caused by higher redshift to HST/ACS images (in two optical bands, F606W and F814W) of M87, an elliptical galaxy with a very well-studied GC system. The effects involved are: (i) evolution, (ii) inverse k correction, (iii) binning of the image to smaller angular size, (iv) cosmological dimming of surface brightness, and (v) noise addition to account for different exposure times. After processing the images we detect the brightest GCs through direct photometry (e.g., with SExtractor), whereas the unresolved clusters are measured through SBFs. The above treatment is repeated for z=0.05, 0.1, 0.14, and 0.18, and the results are compared to the measurements at z=0 to estimate biases and incompleteness.
Determination of astrophysical parameters of open clusters using classical and semi-automated isochrone-fitting methods
Authors: Alves Virginia Mello , Bica Eduardo , Pavani Daniela Borges 
Published: January 2010

AbstractWhen we use optical isochrone-fitting solutions from the literature to 2mass CMDs, they are often not the best solutions in the infrared domain. We analysed 10 open clusters with 2mass, nine of them previously studied with optical photometry (NGC 1245, NGC 1342, NGC 1502, NGC 2104, NGC 2204, NGC 2243, NGC 2281, NGC 6709 and NGC 744) and one using integrated spectroscopy (BH 132). The study involved the classical (by eye) and a semi-automated method of isochrone fitting. We used the solutions of the first method as input for the second, looking for refined solutions. The semi-automated method uses a synthetic color–magnitude diagram (CMD), based on different Padova isochrones, to compare with the observed CMDs by means of likelihood statistics. The derived astrophysical parameters are age, distance and reddening values. The present results show better fits than those implied by the optical values. We also show that the semi-automated method decreases the parameter uncertainties.
Multicolor CCD photometry of the open cluster NGC 752
Authors: Bartašiūtė Stanislava , Janusz Robert , Boyle Richard P. , Philip A. G. Davis , Deveikis Viktoras 
Published: January 2010

AbstractWe obtained CCD observations of the open cluster NGC 752 with the 1.8m Vatican Advanced Technology Telescope (Mt. Graham, Arizona) with a 4K CCD camera and eight intermediate-band filters of the Stromvil (Strömgren + Vilnius) system. Four 12′ × 12′ fields were observed, covering the central part of the cluster. The good-quality multicolor data made it possible to obtain precise estimates of distance moduli, metallicity and foreground reddening for individual stars down to the limiting magnitude, V = 17.5, enabling photometric identification of faint cluster members. The new observations provide an extension of the lower main sequence to three magnitudes beyond the previous (photographic) limit. A relatively small number of photometric members identified at fainter magnitudes seems to be indicative of actual dissolution of the cluster from the low-mass end.
Limits on the dark matter content of globular clusters
Authors: Baumgardt H. , Côté P. , Hilker M. , Rejkuba M. , Mieske S. , Djorgovski S. G. , Stetson P. 
Published: January 2010

AbstractWe have measured the velocity dispersion of the Galactic globular cluster NGC 2419 to determine if a substantial amount of dark matter is present in this cluster. NGC 2419 is one of the best globular clusters to look for dark matter due to its large mass, long relaxation time and large Galactocentric distance, which makes tidal stripping of dark matter unlikely. Our results can be summarized as follows. (i) We found a global velocity dispersion of 4.14 ± 0.48 km s−1, which leads to a total cluster mass of (9.02 ± 2.22) × 105 M⊙ and implies a global mass-to-light ratio of 2.05 ± 0.50 M⊙/L⊙. (ii) Our derived mass-to-light ratio is completely consistent with the mass-to-light ratio of a standard stellar population at the metallicity and age of NGC 2419. In addition, the mass-to-light ratio of NGC 2419 does not increase towards the outer cluster parts. (iii) We can therefore rule out the presence of a dark-matter halo with a central density greater than about 0.02 M⊙ pc−3. Similar limits are found for other halo globular clusters, like Pal 14. These observations therefore indicate that NGC 2419 and other halo globular clusters did not form at the centers of dark-matter halos similar to those surrounding dwarf galaxies. Instead, an origin driven by gas-dynamical processes during mergers between galaxies or proto-galactic fragments seems to be the more likely explanation for the formation of even the lowest-metallicity globular clusters.
Lithium survey in evolved stars observed in the sacy project
Authors: Martins B. L. Canto , Vieira S. , Torres C. A. O. , Quast G. R. , da Silva L. , de La Reza R. , de Melo C. H. F. , de Medeiros J. R. 
Published: January 2010

AbstractThe primary goal of the sacy project (Search for Associations Containing Young Stars) was to identify possible associations of stars younger than the Pleiades association among optical counterparts of ROSAT X-ray-bright sources. The study of the chemical abundance in stars located in regions of stellar formation is extremely important to understand stellar nucleo-synthesis, the physical mechanisms controlling mixing in stellar interiors, and chemical enrichment in the Galaxy. The present work highights the first results of a chemical-abundance study of evolved stars identified in the sacy survey. For this, we performed a detailed spectroscopic analysis for the determination of atmospheric parameters and Li abundance for a sample of giant and subgiant stars. The observations were carried out with high resolution using the FEROS (R = 48 000) échelle spectrograph. We measured the stellar parameters (Teff, log g, vmic, [Fe/H]) from LTE analysis in the complete range of 420-1100 nm. Li abundance was derived from the region around the lithium line at 6707.78 Å for the entire sample of stars.