bluuebunny/crossref_metadata_2025_split huggingface dataset:
Hidden infrared star clusters in our Galaxy: follow-up observations
Authors: Borissova Jura , Kurtev Radostin , Hanson Margaret M. , Georgiev Leonid , Ivanov Valentin , Ortolani Sergio 
Published: January 2010

AbstractWe are reporting some recent results from our long-term program aimed at characterizing the obscured present-day star cluster population in the Galaxy. Our goal is to expand the current census of the Milky Way's inner stellar disk to guide models seeking to understand the structure and recent star-formation history of our Galaxy. The immediate goal is to derive accurate cluster physical parameters using precise infrared photometry and spectroscopy. So far, we observed approximately 60 star cluster candidates selected from different infrared catalogs. Their nature, reddening, distance, age and mass are analyzed. Two of them, Mercer 3 and Mercer 5, are new obscured Milky Way globular clusters. Among the newly identified open clusters, the objects [DBS2003] 179, Mercer 23, Mercer 30, Mercer 70, and [DBS2003] 106 are particularly interesting because they contain massive young OB and Wolf–Rayet stars with strong emission lines.
Building stable stellar systems with ρ as the only datum
Authors: Carpintero D. D. 
Published: January 2010

AbstractSchwarzschild's method to set up a model galaxy is most useful when the distribution in velocity space is unknown. Nevertheless, one has to know beforehand which kind of orbits are spawned by the potential of the model. Moreover, although the system thus generated is in equilibrium, it is not necessarily stable. Here, we present a new method that allows to build up a stable stellar system without any previous knowledge of its distribution in velocity space.
Membership probability via control-field colour–magnitude decontamination
Authors: Corradi Wagner J. B. , Maia Francisco F. S. , Santos João F. C. 
Published: January 2010

AbstractThe fundamental physical parameters of open clusters are important tools to understand the formation and evolution of the Galactic disk and to test star-formation and evolution models. However, only a small fraction of the known open clusters in the Milky Way have precise determinations of distance, reddening, age, metallicity, radial velocity and proper motion. One of the major problems in determining these parameters lies in the difficulty to separate cluster members from field stars and to assign membership. We propose a decontamination method by employing 2mass data in the regions around the clusters NGC 1981, NGC 2516, NGC 6494 and M11. We present decontaminated colour–magnitude diagrams of these objects showing the membership probabilities and structural parameters as derived from King-profile fitting.
Hierarchical stellar clusters in molecular clouds
Authors: Datta Srabani 
Published: January 2010

AbstractObservations show that massive stars always form in clusters or associations, and that the most massive stars form in the dense cores of large clusters. This suggests that accretion processes in cluster cores may be responsible for the formation of stars. In addition, young stellar clusters have been found to contain subclusters, so that star formation can be seen to be a hierarchical process that involves clustering on a range of scales. In this paper, we propose a fractal model of the parental molecular cloud, namely that of the Julia set given byf(z) =z2+c, wherezandcare complex numbers andc= −0.745430 + 0.113008i, to explain this phenomenon and the associated complex structures seen in star-forming regions.
No relation between the vertical velocity component and the absolute magnitude among globular clusters
Authors: De Souza–Rossetto E. A. , Rocha–Pinto H. J. 
Published: January 2010

AbstractThe globular cluster luminosity function distribution shows a peak at MV ≈ −7.5 mag. There are some indications that the kinematic parameters are correlated with luminosity. In particular, Alfaro et al. (2001) have studied the properties of the Galactic globular cluster system and they found a correlation between spatial-velocity component and globular cluster absolute magnitude. The authors assumed that the globular clusters can be separated into two groups. The first is composed of globular clusters with MV < −7.5 mag and moving preferentially towards the north Galactic pole, while the faintest globular clusters, composing the second group, move towards the Galactic disk. We have selected a sample of globular clusters using the same criteria as Alfaro et al. (2001) and have checked that this apparent relation indeed exists. Nevertheless, we decided to investigate whether it could be a fortuitous relation or an intrinsic property by checking its validity for eight different epochs at past and future times. The orbital parameters for the globular clusters at these eight epochs were found by orbital integration using a typical Galactic potential. We show that this relation between the vertical velocity component and the absolute magnitude among globular clusters is not coherent with time and the velocity distribution does not support the hypothesis of Alfaro et al. for the existence of two dynamical groups of globular clusters.
An unusual abundance of T Tauri stars? NIR study of the southern high-mass star-forming region RCW 34
Authors: de Villiers H. M. , Van der Walt D. J. 
Published: January 2010

AbstractRCW 34 is a special star-forming region with a few stars showing an infrared excess, but seems as if it has an uncommon abundance in T Tauri stars. This possibility was confirmed by (i) clustering of classical T Tauri (CTT) stars in the two-color diagram, (ii) clustering of pre-main-sequence stars in the color–magnitude diagram, as well as (iii) the significant clustering at dimensions larger than the image-frame size, indicated by the second ‘bump’ in the two-point correlation analysis. A possible explanation for the above features could be the existence of an underlying wide CTT cluster with a smaller cluster centered around the massive star. The Ks-band luminosity function (α = 0.31) of RCW 34 shows that it is indeed a region of low stellar masses with an age of about of 1 Myr. Spectroscopic confirmation of such an underlying T Tauri cluster is necessary before any definite conclusions can be reached.
A deep dive into NGC 604 with Gemini/NIRI imaging
Authors: Fariña Cecilia , Bosch Guillermo L. , Barbá Rodolfo R. 
Published: January 2010

AbstractThe giant Hii region NGC 604 constitutes a complex and rich population to study in detail many aspects of massive star formation, such as their environments and physical conditions, the evolutionary processes involved, the initial mass function for massive stars and star-formation rates, among many others. Here, we present our first results of a near-infrared study of NGC 604 performed with NIRI images obtained with Gemini North. Based on deep JHK photometry, 164 sources showing infrared excess were detected, pointing to the places where we should look for star-formation processes currently taking place. In addition, the color–color diagram reveals a great number of objects that could be giant/supergiant stars or unresolved, small, tight clusters. An extinction map obtained based on narrow-band images is also shown.
Gas trapping in extremely massive clusters in NGC 1365
Authors: Galliano Emmanuel , Alloin Danielle 
Published: January 2010

AbstractThree radio cm sources in the central star-forming kpc of the closeby barred Seyfert galaxy NGC 1365 are observed. The complete dataset includes VLT infrared J, K, L and N images and spectra. The main observed features include (i) a rising dust continuum towards the mid-infrared (MIR), (ii) bright H emission lines and PAH (polycyclic aromatic hydrocarbon) features, (iii) a bright MIR [Neii] line, and (iv) no detection of MIR [Siv] or [Ariii] lines. For a typical cluster star-formation history and initial mass function, the [Ariii]/[Neii] and [Siv]/[Neii] ratios exhibit an abrupt decrease of several orders of magnitude at an age of ~ 7 Myr. The nondetection of [Ariii] and [Siv] indicates that the clusters are of approximately this age.
Search for cluster candidates in the ukidss database
Authors: Gennaro Mario , Brandner Wolfgang , Henning Thomas , Stolte Andrea 
Published: January 2010

Abstractukidss gps is a deep and high-angular-resolution survey of the Galactic plane in the J, H, and K bands. Using this survey, we searched the inner region of the Galaxy (|l| < 10°) for young cluster candidates associated with molecular bubbles (MBs). The latter are observed in the mid-infrared survey glimpse ii. The underlying idea is that MBs may be blown out by powerful sources, such as young O and B stars; some of the MBs in the sample are indeed associated with Hii regions, a hint of the presence of young stars. One of the major observational problems in the Galactic plane is the high degree of interstellar absorption and its spatial variability. A significant effort is also devoted to quantifying this issue.
Distribution of very young stellar clusters in grand-design spirals
Authors: Grosbøl Preben , Dottori Horacio 
Published: January 2010

AbstractMany grand-design spiral galaxies display strings of knots along their arms on K-band images. Near-infrared (NIR) spectra and broad-band colours of such knots have identified them as very young, massive stellar complexes. The low absorption in the NIR makes it possible to derive complete statistics of such complexes and thereby estimate the associated star-formation rate. We have obtained deep NIR maps of eight grand-design spirals using VLT/HAWK-I and identified massive complexes with ages of < 10 Myr using NIR colour–colour diagrams. The youngest, most massive complexes are well-aligned and concentrated in the arm regions of the grand-design galaxies with strong spiral perturbations. Their absolute magnitudes have a bright tail reaching almost MK = −16 mag. Both the fraction of young to old sources and the ratio of diffuse to more compact objects suggest a dependence on the strength of the spiral pattern in the host galaxy.
High-velocity runaway stars from three-body encounters
Authors: Gvaramadze V. V. , Gualandris A. , Portegies Zwart S. 
Published: January 2010

AbstractWe performed numerical simulations of dynamical encounters between hard, massive binaries and a very massive star (VMS; formed through runaway mergers of ordinary stars in the dense core of a young massive star cluster) to explore the hypothesis that this dynamical process could be responsible for the origin of high-velocity (≥ 200 − 400 km s−1) early or late B-type stars. We estimated the typical velocities produced in encounters between very tight massive binaries and VMSs (of mass of ≥ 200 M⊙) and found that about 3 − 4% of all encounters produce velocities ≥ 400 km s−1, while in about 2% of encounters the escapers attain velocities exceeding the Milky Ways's escape velocity. We therefore argue that the origin of high-velocity (≥ 200 − 400 km s−1) runaway stars and at least some so-called hypervelocity stars could be associated with dynamical encounters between the tightest massive binaries and VMSs formed in the cores of star clusters. We also simulated dynamical encounters between tight massive binaries and single ordinary 50 − 100 M⊙ stars. We found that from 1 to ≃ 4% of these encounters can produce runaway stars with velocities of ≥ 300 − 400 km s−1 (typical of the bound population of high-velocity halo B-type stars) and occasionally (in less than 1% of encounters) produce hypervelocity (≥ 700 km s−1) late B-type escapers.
A high-spectral-resolution study of abundances and isotopic composition of BHB stars in NGC 6397 and NGC 6752
Authors: Hubrig S. , Castelli F. , De Silva G. , González J. F. , Momany Y. , Netopil M. , Moehler S. 
Published: January 2010

AbstractLarge abundance anomalies have previously been detected in horizontal-branch B-type stars. We present the first high-resolution study of isotopic anomalies and chemical abundances in six horizontal-branch B-type stars in the globular clusters NGC 6397 and NGC 6752, carried out with UVES on the VLT and compare them to those observed in chemically peculiar main-sequence stars.
First results of the Southern Open Cluster Study
Authors: Kinemuchi K. , Sarajedini A. , Geisler D. , Mauro F. , Carraro G. , Kafka S. , Jeffery E. 
Published: January 2010

AbstractGalactic open clusters are excellent laboratories to study stellar populations that are coeval and have a common chemical composition. These clusters allow for the investigation of stellar and chemical abundance evolution, binary star systems, mass and luminosity functions, Galactic metallicity gradient, and disk structure, among other things. The Southern Open Cluster Study (socs) is a database of a select set of 24 open clusters with a broad range of ages and metallicities. It is an extension of the northern WIYN Open Cluster Study (wocs). The main goal of both studies is to obtain comprehensive photometric, spectroscopic, and astrometric information of these key open clusters. Here, we provide an overview of the socs survey and present results of the wide-field photometry on two socs clusters, NGC 3532 and Tombaugh 2.
The origin of very wide binary systems
Authors: Kouwenhoven M. B. N. , Goodwin S. P. , Parker Richard J. , Davies M. B. , Malmberg D. , Kroupa P. 
Published: January 2010

AbstractThe majority of stars in the Galactic field and halo are part of binary or multiple systems. A significant fraction of these systems have orbital separations in excess of thousands of astronomical units, and systems wider than a parsec have been identified in the Galactic halo. These binary systems cannot have formed through the ‘normal’ star-formation process, nor by capture processes in the Galactic field. We propose that these wide systems were formed during the dissolution phase of young star clusters. We test this hypothesis using N-body simulations of evolving star clusters and find wide binary fractions of 1–30%, depending on initial conditions. Moreover, given that most stars form as part of a binary system, our theory predicts that a large fraction of the known wide ‘binaries’ are, in fact, multiple systems.
Kinematic parameters and membership lists of open clusters in the Bordeaux Carte du Ciel zone
Authors: Krone-Martins Alberto , Soubiran Caroline , Teixeira Ramachrisna , Ducourant Christine 
Published: January 2010

AbstractIn the study of open clusters, the distinction between cluster and field members and the assignment of membership probabilities for each individual star in the relevant region are central issues. Here, we present an analysis based on the use of a fully automated method that relies on a hybrid heuristics, based on genetic algorithms and hill-climbing optimisation, as well as different probability distribution functions for the observables. We analysed the use of some variations for the parameterisation of those distribution functions. Finally, a catalogue comprising kinematic parameters and associated membership probability lists for all the open clusters in the Bordeaux PM2000 region was derived.
Open cluster characterization via cross-correlation with a spectral library
Authors: Maia Francisco F. S. , Santos João F. C. , Corradi Wagner J. B. , Piatti Andrés E. 
Published: January 2010

AbstractWe present a characterization method based on spectral cross-correlation to obtain the physical parameters of the controversial stellar aggregate ESO442–SC04. The data used was obtained with GMOS at the Gemini South telescope, and includes spectra of 17 stars in the central region of the object and 6 standard stars. fxcor was used iteratively to obtain self-consistent radial velocities for the standard stars and average radial velocities for the science spectra. Spectral types, effective temperatures, surface gravities and metallicities were determined using fxcor to correlate cluster spectra with the ELODIE spectral library and select the best correlation matches using the Tonry & Davis ratio. Analysis of the results suggests that the stars in ESO442–SC04 are not bound and, therefore, they do not constitute a physical system.
Analysis of the B and Be-star populations of the double cluster h and χ Persei
Authors: Marsh Amber N. , McSwain M. Virginia , Currie Thayne 
Published: January 2010

AbstractWe present blue optical spectra of 92 members of h and χ Per obtained with the WIYN telescope at Kitt Peak National Observatory. From these spectra, several stellar parameters were measured for the B-type stars, including v sin i, Teff, log gpolar, M∗, and R∗. Strömgren photometry was used to measure Teff and log gpolar for the Be stars. We also analyze photometric data of cluster members and discuss the near- to mid-infrared excesses of Be stars.
Chemical abundances of the LMC cluster Hodge 11 and its surrounding field
Authors: Mateluna Renee , Geisler Douglas , Villanova Sandro 
Published: January 2010

AbstractWe have obtained high-resolution VLT/FLAMES spectra of a number of giants in the LMC cluster Hodge 11 and the surrounding field. We present results of a detailed model-atmosphere abundance analysis for a variety of elements, including Fe, Ca, Ti, Si, Sc, Ni and Cr.
Fundamental stellar properties from eclipsing binary analyses
Authors: Milone E. F. , Stagg R. , Guhathakurta P. , VandenBerg D. A. , Kallrath J. 
Published: January 2010

AbstractThe properties of the binary components of the eclipsing variables found in the 47 Tuc core region as part of a search for extrasolar planets have been re-examined following reanalysis of the image photometry and calibration. This is part of an ongoing study to find fundamental properties of stars of different metallicity in a variety of environments through eclipsing-binary analyses.
A global optimization technique for the fitting of color–magnitude diagrams
Authors: Monteiro Hektor , Dias Wilton S. , Caetano Thiago C. 
Published: January 2010

AbstractWe present a new technique to analyze color–magnitude diagrams, such as those of stellar clusters, based on the cross-entropy global-optimization procedure. The method uses theoretical isochrones available in the literature and minimizes an objective function that describes the quality of a fit to the color–color and color–magnitude diagrams. The objective function is based on the two-dimensional distances of the points in the color–magnitude and color–color diagrams to the theoretical curves and is modified by weights that take into account the stellar distance to the observed cluster center, observed magnitude uncertainties and the King profile of the cluster, among others. The parameters determined simultaneously are distance, reddening, age and metalicity. The method uses a Monte Carlo approach to obtain uncertainties on the determined parameters for the cluster. We present results for 10 well-studied open clusters and show that the results are consistent with previous studies.
Probing the structure of the Galactic disk through open clusters
Authors: Pang Xiaoying , Shu Chenggang 
Published: January 2010

AbstractThe WEBDA database of open clusters (hereafter OCs) in the Galaxy contains 970 OCs, of which 911 have age determinations, 920 have distance measurements, and 911 have color-excess data. Base on the statistical analysis of global properties of open clusters, we investigate disk properties such as the height above the Galactic plane. We find that old open clusters (age ≥ 1 Gyr) are preferentially located far from the Galactic plane with 〈|z|〉~394.5 pc. They lie in the outer part of the Galactic disk. The young open clusters are distributed in the Galactic plane almost symmetrically with respect to the Sun, with a scale height perpendicular to the Galactic plane of 50.5 pc. The age distribution of open clusters can be fit approximately with a two-component exponential decay function: one component has an age scale factor of 225.2 Myr, and the other consists of longer-lived clusters with an age scale of 1.8 Gyr, which are smaller than those derived by Janes & Phelps (1994) of 200 Myr and 4 Gyr for the young and old OCs, respectively. As a consequence of completeness effects, the observed radial distribution of OCs with respect to Galactocentric distance does not follow the expected exponential profile. Instead, it falls off both for regions external to the solar circle and more sharply towards the Galactic Center, which is probably due to giant molecular cloud disruption in the center. We simulate the effects of completeness, assuming that the observed distribution of the number of OCs with a given number of stars above the background is representative of the intrinsic distribution of OCs throughout the Galaxy. Two simulation models are considered, in which the intrinsic number of the observable stars are distributed (i) assuming the actual positions of the OCs in the sample, and (ii) random selection of OC positions. As a result, we derive completeness-corrected radial distributions which agree with an exponential disk throughout the observed Galactocentric distance in the range of 5–15 kpc, with scale lengths in the range of 1.6–2.8 kpc.
Intermediate-mass black holes in Galactic globular clusters
Authors: Pepe Carolina , Pellizza Leonardo J. 
Published: January 2010

AbstractOver the last few years, different observations have suggested the existence of intermediate-mass (~103 M⊙) black holes in the centers of globular clusters. However, the issue is still a matter of debate, as current observations have alternative explanations. We previously developed a hydrodynamical model for the interstellar medium in these systems to explain the luminosity of the central X-ray source found in NGC 6388, assuming a black hole accreting from the insterstellar medium. Here, we explore the predictions of our model regarding the flow of the interstellar matter in the inner cluster regions and find that the density and velocity profiles could help to determine the presence of a central black hole as well as its mass.
Washington photometry of five star clusters in the Large Magellanic Cloud
Authors: Piatti Andrés E. , Geisler Doug , Sarajedini Ata , Gallart Carme 
Published: January 2010

AbstractWe present CCD photometry in the Washington-system C and T1 passbands down to T1 ~ 22.5 mag in the fields of NGC 1697, SL 133, NGC 1997, SL 663, and OHSC 28, five mostly unstudied star clusters in the LMC. Cluster radii were estimated from star counts in appropriately sized boxes distributed throughout the entire observed fields. We perform a detailed analysis of field-star contamination and derive cluster colour–magnitude diagrams (CMDs). Based on the best fits of isochrones computed by the Padova group to the (C − T1, T1) CMDs, the δ(T1) index and the ‘standard giant-branch’ procedure, we derive metallicities and ages for the five clusters. With the exception of NGC 1697 (age = 0.7 Gyr, [Fe/H] = 0.0 dex), the remaining four clusters are of intermediate age (from 2.2 to 3.0 Gyr) and relatively metal poor ([Fe/H] = −0.7 dex). We combine our sample with clusters with ages and metallicities on a similar scale and examine relationships between position in the LMC, age and metallicity. We confirm previous results that clusters younger than ~ 1 Gyr were formed during an outside-in process; this occurred after a burst of cluster formation that took place mainly in the outer disk and peaked ~ 2 Gyr ago. Finally, the cluster and field age–metallicity relations (AMRs) show evidence for a metallicity offset but do overlap, particularly on the upper-envelope side of the cluster AMR.