bluuebunny/crossref_metadata_2025_split huggingface dataset:
An overview of the rotational behavior of metal-poor stars
Authors: Cortés C. , Silva J. R. P. , Recio–Blanco A. , Catelan M. , Do Nascimento J. D. , De Medeiros J. R. 
Published: January 2010

AbstractWe describe the behavior of the rotational velocity in metal-poor stars ([Fe/H] ~ −0.5 dex) at different evolutionary stages, based on v sin i values from the literature. Our sample is composed of stars in the field and in some Galactic globular clusters, including stars on the main sequence (MS), red-giant branch (RGB), and horizontal branch (HB). The metal-poor stars are mainly slow rotators, and their v sin i distribution along the Hertzsprung–Russell diagram is quite homogeneous. Nevertheless, a few moderate to high values of v sin i are found for stars located on the MS and the HB. We show that the overall distribution of v sin i values is basically independent of metallicity for the stars in our sample. In particular, the fast-rotating MS stars in our sample exhibit similar rotation rates as their metal-rich counterparts, suggesting that some may actually be fairly young, in spite of their low metallicity, or else that at least some would be better classified as blue straggler stars. We do not find significant evidence of evolution in v sin i values as a function of position on the RGB. In particular, we do not confirm previous suggestions that stars close to the RGB tip rotate faster than their less-evolved counterparts. While the presence of fast rotators among moderately cool blue-HB stars has been suggested as due to angular-momentum transport from a stellar core that has retained significant angular momentum during its prior evolution, we find that any such transport mechanisms must likely operate very fast as the star arrives on the zero-age HB (ZAHB), since we do not find a link between evolution off the ZAHB and v sin i values.
Clusters of PMS stars in the Magellanic Clouds: the case of LH95
Authors: Da Rio Nicola 
Published: January 2010

AbstractWe present a study of the pre-main-sequence (PMS) population in the stellar association LH95 in the LMC, based on the deepest HST/ACS photometry ever taken in a region of the Magellanic Clouds. This association hosts ~ 2500 PMS stars, distributed in three main subclusters. We isolate this population by subtracting the LMC field, study the reddening distribution which peaks at AV ~ 0.5 mag, and assign masses, down to 0.2 M⊙, to each member using a newly derived conversion of evolutionary models for the LMC metallicity and the ACS photometric system. We derive the first IMF in the subsolar regime ever measured outside our Galaxy, complete down to 0.4 M⊙. It presents a flattening at 1 M⊙, changing its slope from x = 2.05 for intermediate-mass stars to x = 1.05 in the subsolar regime. Correcting for unresolved binarity, it is compatible with the Galactic IMF. We do not find evidence of spatial variations of the IMF in the region. We study the ages of the PMS members using maximum-likelihood methods based on the location of the stars in the color–magnitude diagram with respect to 2D isochrones obtained by applying intrinsic and observational biases (differential extinction, variability, confusion, unresolved binarity) to modeled simple stellar populations. We find a most likely global age of ~ 10 Myr, and demonstrate that neglecting the aforementioned biases leads to an underestimation of the cluster age of up to 50%. We find that the observed luminosity spread is more than twice larger than can be explained by such biases, confirming that the star formation in LH95 lasted a few Myr.
Open clusters: a program to analyse the color–magnitude diagram with the help of stellar kinematic data
Authors: Dias Wilton S. , Caetano Thiago Costa 
Published: January 2010

AbstractWe constructed a program that allows one to use simultaneously and interactively photometric and astrometric stellar data (proper motion) to analyse color–color and color–magnitude diagrams. With this program, we are able to determine, based on photometric membership, the distance and age as well as the mean proper motion and radial velocity of several open clusters which had very uncertain parameters in previous analyses.
The dynamics of an extremely young cluster probed for the first time
Authors: Ducourant Christine , Bontemps Sylvain , Despois Didier , André Philippe , Teixeira Ramachrisna , Moraux Estelle , Bouvier Jerome , Krone–Martins Alberto , Sinachopoulos Dimitris 
Published: January 2010

AbstractWe present a proper-motion program that we have developed at ESO to measure, for the first time, proper motions of members of the nearby (125 pc), very young (4 × 105 yr) infrared ρ Ophiuchi cluster. Repeated imaging over an extended period will allow us to measure the global proper motion of the cluster and its velocity dispersion and will provide access to the ~ 1 km s−1 velocities for objects as faint as K = 15.7 mag. Access to the velocity field of such an extremely young cluster is of crucial importance to investigate the origin and early evolution of open cluster systems.
The globular cluster M 69: color–magnitude diagram and variable stars
Authors: Escobar M. E. , Catelan M. , Zoccali M. , Smith H. A. , Pritzl B. J. , Layden A. , Gregorsok J. , Welch D. L. , Webb T. 
Published: January 2010

AbstractWe present BV photometry and the results of a search for stellar variability in the Galactic globular cluster M 69. The resulting color–magnitude diagram shows significant contamination by field stars. In our variability search we found 62 variable stars, 54 of which were new discoveries.
Determination of kinematic distances of pre-main-sequence stars in star-forming regions
Authors: Galli Phillip A. B. , Teixeira Ramachrisna , Ducourant Christine , Bertout Claude 
Published: January 2010

AbstractMany studies of star-forming regions have been carried out since the discovery of compact Hii regions in the late 1960s. The kinematic properties of young stars in the nearest regions with ongoing and recent star formation provide essential tests of their formation mechanisms. The detection of coeval moving groups allows determination of individual distances through the convergent-point method. As a result, the main physical properties of these stars and their early evolutionary stages can be determined if we know how distant they are.
Nuclear clusters in dwarf irregular galaxies and their connection to massive galactic clusters
Authors: Georgiev Iskren Y. , Hilker Michael , Puzia Thomas H. , Goudfrooij Paul , Baumgardt Holger 
Published: January 2010

AbstractWe compare nuclear globular clusters (nGCs) in dwarf galaxies and Galactic GCs with extended (hot) horizontal branches (EHB–GCs) to test the suggested external origin of the latter and the conditions under which GC self-enrichment can operate. We show that the present-day escape velocity (vesc) of stellar ejecta to reach the cluster tidal radius compares with those of EHB–GCs. For EHB–GCs, we find a correlation between the present-day vesc and their metallicity as well as (V − I) colour. The similar vesc and (V − I) distribution of nGCs and EHB–GCs implies that nGCs could also have complex stellar populations. The vesc–[Fe/H] relation could reflect the known relation of increasing stellar-wind velocity with metallicity, which in turn explains why more metal-poor clusters typically show more peculiarities in their stellar population than more metal-rich clusters of the same mass.
Star clusters: age, metallicity and extinction from integrated spectra
Authors: González Delgado Rosa M. , Cid Fernandes Roberto 
Published: January 2010

AbstractIntegrated optical spectra of star clusters in the Magellanic Clouds and a few Galactic globular clusters are fitted using high-resolution spectral models for single stellar populations. The goal is to estimate the age, metallicity and extinction of the clusters, and evaluate the degeneracies among these parameters. Several sets of evolutionary models that were computed with recent high-spectral-resolution stellar libraries (MILES, GRANADA, STELIB), are used as inputs to the starlight code to perform the fits. The comparison of the results derived from this method and previous estimates available in the literature allow us to evaluate the pros and cons of each set of models to determine star cluster properties. In addition, we quantify the uncertainties associated with the age, metallicity and extinction determinations resulting from variance in the ingredients for the analysis.
Lithium abundances of main-sequence and subgiant stars in the globular cluster NGC 6397
Authors: González Hernández J. I. , Bonifacio P. , Caffau E. , Steffen M. , Ludwig H.-G. , Behara N. , Sbordone L. , Cayrel R. , Zaggia S. 
Published: January 2010

AbstractWe present FLAMES/GIRAFFE spectroscopy obtained with the Very Large Telescope (VLT). Using these observations, we have been able (for the first time) to observe the Lii doublet in the main-sequence (MS) stars of a globular cluster. We also observed Li in a sample of subgiant (SG) stars of the same B − V colour. Our final sample is composed of 84 SG and 79 MS stars. In spite of the fact that SG and MS stars span the same temperature range, we find that the equivalent widths of the Lii doublet in SG stars are systematically greater than in MS stars, suggesting a higher Li content among SG stars. This is confirmed by our quantitative analysis, which makes use of both 1D and 3D model atmospheres. We find that SG stars show, on average, a higher Li abundance, by 0.1 dex, than MS stars. We also detect a positive slope of Li abundance with effective temperature: the higher the temperature the higher the Li abundance, both for SG and MS stars, although the slope is slightly steeper for MS stars. These results provide unambiguous evidence that the Li abundance changes with evolutionary state. The physical mechanisms that contribute to this are not yet clear, since none of the proposed models seem to describe accurately the observations. Whether such a mechanism can explain the cosmological lithium problem is still an open question.
Looking for building blocks of the Galactic halo: variable stars in the Fornax, Bootes I, Canes Venatici II dwarfs and in NGC 2419
Authors: Greco Claudia , Clementini Gisella , Held E. V. , Poretti E. , Catelan M. , Federici L. , Maio M. , Gullieuszik M. , Ripepi V. , Dall'Ora M. , Di Fabrizio L. , Kinemuchi K. , Di Crescienzo M. , Marconi M. , Musella I. , Pritzl B. , Rest A. , De Lee N. , Smith H. 
Published: January 2010

AbstractΛ cold-dark-matter hierarchical models of galaxy formation suggest that the halo of the Milky Way (MW) has been assembled, at least in part, through accretion of protogalactic fragments partially resembling the present-day dwarf spheroidal (dSph) satellites of the MW. Investigation of the stellar populations of the MW's globular clusters (GCs) and dSph companions can thus provide excellent tests to infer the dominant Galaxy-formation scenario, whether merger/accretion or cloud collapse. Pulsating variable stars offer a very powerful tool in this context, since variables of different types allow tracing the different stellar generations in a galaxy and to reconstruct the galaxy's star-formation history and assembly back to the first epochs of galaxy formation. In particular, the RR Lyrae stars, belonging to the old population (t > 10 Gyr), witnessed the epoch of halo formation, and thus hold a crucial role to identify the MW satellites that may have contributed to build up the Galactic halo. In the MW, most GCs with an RR Lyrae population sharply divide into two distinct groups (Oosterhoff types I and II) based on the mean periods and relative proportion of fundamental-mode (RRab) and first-overtone (RRc) RR Lyrae stars. On the other hand, the Galactic-halo field RR Lyrae stars show a dominance of Oosterhoff I properties. Here, we investigate the Oosterhoff properties of a number of different stellar systems, starting from relatively undisturbed dwarf galaxies (the Fornax dSph and its globular clusters), through distorted and tidally disrupting ones (the Bootes and Canes Venatici II dSphs), to possible final relics of the disruption process (the Galactic globular cluster NGC 2419). We are addressing the crucial question of whether the RR Lyrae pulsation properties in these systems conform to the Oosterhoff dichotomy characterizing the MW variables. If they do not, the Galaxy's halo cannot have been assembled by dSph-like protogalactic fragments resembling the present-day dSph companions of the MW. We have reduced and combined long time series from different telescopes, both ground- and space-based. Variable stars have been detected with image-subtraction techniques using the package isis2.1. Periods, amplitudes and Oosterhoff type for all variable stars, as well as color–magnitude diagrams of the stellar populations are discussed for each stellar cluster analyzed.
Galactic consequences of clustered star formation
Authors: Haas M. R. , Anders P. 
Published: January 2010

AbstractIf all stars form in clusters and both stars and clusters follow a power-law distribution which favours the creation of low-mass objects, the numerous low-mass clusters will be deficient in high-mass stars. Therefore, the stellar mass function integrated over the entire galaxy (the integrated galactic initial mass function; IGIMF) will be steeper at the high-mass end than the underlying stellar IMF. We show how the steepness of the IGIMF depends on the sampling method and on the assumptions made regarding the star cluster mass function. We also investigate the O-star content, integrated photometry and chemical enrichment of galaxies that result from several IGIMFs compared to more standard IMFs.
Proper-motion measurements in the Quintuplet cluster
Authors: Hußmann Benjamin , Stolte Andrea , Brandner Wolfgang 
Published: January 2010

AbstractThe three young, massive star clusters found in the Galactic Centre region (Young Nuclear Cluster, the Arches and Quintuplet clusters) are among the six most massive star clusters in our Galaxy, with masses similar to low-mass, extragalactic starburst clusters. The conditions for star formation in this region are extreme and likely comparable to those found in the Hii regions in starburst galaxies and tidal-interaction zones of mergers. As the inner Galactic star clusters can be resolved, they can serve as templates for extragalactic starburst clusters. With knowledge of the spectral types, masses and ages of the individual stars, their stellar population can be studied in detail, allowing derivation of their present-day mass function (PDMF). The Quintuplet cluster, with an age of about 4 Myr, is the most extended of the three clusters and also displays a lower spatial density. To determine its mass function correctly, the distinction between cluster and field stars is therefore of particular importance. We present the first determination of a proper-motion-membership sample for the Quintuplet cluster. By comparing two high-precision astrometric VLT/NACO data sets with a time baseline of 5 years, the displacement of the Quintuplet cluster relative to the field population was measured and a selection of the proper-motion cluster members could be established, from which the PDMF can be derived.
Tracing star cluster formation in the interacting galaxy M51
Authors: Hwang Narae , Lee Myung Gyoon 
Published: January 2010

AbstractWe present a study of star clusters in the interacting galaxy M51 using a star cluster catalog that includes about 3600 star clusters with mF555W < 23 mag, compiled by Hwang & Lee (2008). Combined with mF336W-band imaging data taken with the Hubble Space Telescope (HST)'s WFPC2 camera, we have derived the ages and masses of star clusters in M51 using theoretical population synthesis models. The cluster age distribution displays multiple peaks that correspond to the epochs of dynamical encounters predicted by theoretical model studies and the cluster-formation rate appears to increase around the same epochs.
The field of Lacerta OB1
Authors: Kaltcheva Nadia T. 
Published: January 2010

AbstractWe present a new analysis of the Galactic structure in the field of Lacerta. The investigation uses precise uvbyβ photometry and the recalculated Hipparcos parallaxes to provide an improved homogeneous distance scale to the main stellar groups in the field. The OB association Lac OB1 (Lac OB1b) is reliably identified as a very compact young group at an average distance of 520 ± 80 pc. The characteristics of the older Lac OB1a group and the open cluster NGC 7243 are extensively studied based on photometric diagrams and the inferred distances. A good agreement between the photometry-derived distances and the recalculated Hipparcos parallaxes is found for the Lac OB1 group, but in general discrepancies still exist for this particular field.
Super star clusters in Hii galaxies
Authors: Lagos Patricio , Telles Eduardo , Carrasco E. R. 
Published: January 2010

AbstractWe summarize our results based on observations with the NIRI camera on the Gemini North telescope of three Hii galaxies (Mrk 36, UM 408 and UM 461), obtained to identify and determine the ages and masses of the elementary components (the star cluster population) of the starburst regions in compact Hii galaxies. Our preliminary results indicate that the masses of the stellar clusters in these galaxies range from ~104 to ~106 M⊙, with associated ages of a few Myr. The most massive star clusters fall in the so-called super star cluster category. The identification of these clusters suggests that the formation and evolution of massive star clusters is the dominant mode of star formation in these galaxies. Their spatial distribution and ages seem to indicate that star formation is simultaneous over these timescales in some of our objects. We also review our recent description of the spatial distribution of physical conditions in the Hii galaxy UM 408 using the GMOS integral-field unit on Gemini South. The spatial distribution of the oxygen abundance does not show any significant variation or gradient across the galaxy on scales of hundreds of parsecs, within our observational uncertainties, confirming that this compact Hii galaxy, like other previously studied dwarf irregular galaxies, is chemically homogeneous.
W UMa-type systems in globular clusters
Authors: Li Lifang , Zhang Fenghui , Han Zhanwen 
Published: January 2010

AbstractW UMa systems can be found everywhere in the Galaxy. They can be used as a distance tracer. Therefore, W UMa systems are very important to investigate the structure of the Galaxy. The distance to W UMa systems in globular clusters (GCs) is determined using a period–color–luminosity relation. It is found that the mean distance (ra) of W UMa systems is consistent with their host cluster distances (rGC) deduced from their intrinsic distance moduli if rGC ≤ 10 kpc. There is a significant difference between ra and rGC for rGC ≥ 10 kpc. We discuss the reasons causing this deviation.
Star clusters in the starburst galaxy M82
Authors: Lim Sungsoon , Hwang Narae , Lee Myung Gyoon 
Published: January 2010

AbstractWe present a study of star clusters in the starburst galaxy M82 using the BVI mosaic images taken with the Hubble Space Telescope's Advanced Camera for Surveys. We have selected about 850 clusters with V < 23 mag based on their morphological information. The brightest cluster is as bright as V ~ 16.5 mag (MV ~ −11.2 mag) and most clusters are fainter than V = 18 mag (MV = −9.7 mag). The V-band luminosity function is represented by a power law with a slope α ~ −2.0 in the range of −9.5 < MV < −7 mag. The star clusters in M82 are mainly distributed in the galaxy's disk. However, about a dozen clusters are found far from the disk and are considered to belong to the halo of M82. The color–magnitude diagrams of star clusters show that most star clusters are highly reddened. We have derived the age of the star clusters using a spectral-energy-distribution fitting method with Bruzual & Charlot simple stellar population models. We discuss the age distribution as well as the photometric properties of the star clusters in regard to the formation history of the M82 cluster population.
Young open clusters in the Milky Way and Small Magellanic Cloud
Authors: Martayan C. 
Published: January 2010

AbstractNGC 6611, Trumpler 14, Trumpler 15, Trumpler 16, and Collinder 232 are very young open clusters located in star-formation regions in the Eagle Nebula and Carina in the Milky Way, and NGC 346 in the Small Magellanic Cloud. With different instrumentation and techniques, it has been possible to detect and classify new Herbig Ae/Be and classical Be stars and to provide new tests/comparisons of the Be stars' appearance models. Special (He-strong) stars in these star-formation regions are also discussed.
Metallicity analysis of an SMC cluster sample using Caii-triplet spectroscopy
Authors: Parisi M. C. , Grocholski A. , Geisler D. , Sarajedini A. , Clariá J. J. 
Published: January 2010

AbstractThe metallicities of 15 Small Magellanic Cloud (SMC) clusters are determined from the Calcium ii-triplet lines in spectra obtained using the FORS2 multi-object spectrograph on the VLT (Paranal, Chile). The metallicity distribution, metallicity gradient and age–metallicity relationship in the SMC are determined and analyzed using new and literature data for these and other, previously studied SMC objects. Only the main results regarding these topics are presented and discussed.
Open cluster remnants in low-density Galactic fields
Authors: Pavani D. B. , Kerber L. O. , Bica E. , Maciel W. J. 
Published: January 2010

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.