Science.gov

Sample records for star cluster dissolution

  1. Simulating star clusters with the AMUSE software framework. I. Dependence of cluster lifetimes on model assumptions and cluster dissolution modes

    SciTech Connect

    Whitehead, Alfred J.; McMillan, Stephen L. W.; Vesperini, Enrico; Portegies Zwart, Simon

    2013-12-01

    We perform a series of simulations of evolving star clusters using the Astrophysical Multipurpose Software Environment (AMUSE), a new community-based multi-physics simulation package, and compare our results to existing work. These simulations model a star cluster beginning with a King model distribution and a selection of power-law initial mass functions and contain a tidal cutoff. They are evolved using collisional stellar dynamics and include mass loss due to stellar evolution. After studying and understanding that the differences between AMUSE results and results from previous studies are understood, we explored the variation in cluster lifetimes due to the random realization noise introduced by transforming a King model to specific initial conditions. This random realization noise can affect the lifetime of a simulated star cluster by up to 30%. Two modes of star cluster dissolution were identified: a mass evolution curve that contains a runaway cluster dissolution with a sudden loss of mass, and a dissolution mode that does not contain this feature. We refer to these dissolution modes as 'dynamical' and 'relaxation' dominated, respectively. For Salpeter-like initial mass functions, we determined the boundary between these two modes in terms of the dynamical and relaxation timescales.

  2. Star clusters

    NASA Astrophysics Data System (ADS)

    Labhardt, Lukas; Binggeli, Bruno

    Star clusters are at the heart of astronomy, being key objects for our understanding of stellar evolution and galactic structure. Observations with the Hubble Space Telescope and other modern equipment have revealed fascinating new facts about these galactic building blocks. This book provides two comprehensive and up-to-date, pedagogically designed reviews on star clusters by two well-known experts in the field. Bruce Carney presents our current knowledge of the relative and absolute ages of globular clusters and the chemical history of our Galaxy. Bill Harris addresses globular clusters in external galaxies and their use as tracers of galaxy formation and cosmic distance indicators. The book is written for graduate students as well as professionals in astronomy and astrophysics.

  3. Star Clusters within FIRE

    NASA Astrophysics Data System (ADS)

    Perez, Adrianna; Moreno, Jorge; Naiman, Jill; Ramirez-Ruiz, Enrico; Hopkins, Philip F.

    2017-01-01

    In this work, we analyze the environments surrounding star clusters of simulated merging galaxies. Our framework employs Feedback In Realistic Environments (FIRE) model (Hopkins et al., 2014). The FIRE project is a high resolution cosmological simulation that resolves star forming regions and incorporates stellar feedback in a physically realistic way. The project focuses on analyzing the properties of the star clusters formed in merging galaxies. The locations of these star clusters are identified with astrodendro.py, a publicly available dendrogram algorithm. Once star cluster properties are extracted, they will be used to create a sub-grid (smaller than the resolution scale of FIRE) of gas confinement in these clusters. Then, we can examine how the star clusters interact with these available gas reservoirs (either by accreting this mass or blowing it out via feedback), which will determine many properties of the cluster (star formation history, compact object accretion, etc). These simulations will further our understanding of star formation within stellar clusters during galaxy evolution. In the future, we aim to enhance sub-grid prescriptions for feedback specific to processes within star clusters; such as, interaction with stellar winds and gas accretion onto black holes and neutron stars.

  4. Nuclear Star Clusters

    NASA Astrophysics Data System (ADS)

    Neumayer, Nadine

    2017-03-01

    The centers of galaxies host two distinct, compact components: massive black holes and nuclear star clusters. Nuclear star clusters are the densest stellar systems in the universe, with masses of ~ 107M⊙ and sizes of ~ 5pc. They are almost ubiquitous at the centres of nearby galaxies with masses similar to, or lower than the Milky Way. Their occurrence both in spirals and dwarf elliptical galaxies appears to be a strong function of total galaxy light or mass. Nucleation fractions are up to 100% for total galaxy magnitudes of M B = -19mag or total galaxy luminosities of about L B = 1010 L ⊙ and falling nucleation fractions for both smaller and higher galaxy masses. Although nuclear star clusters are so common, their formation mechanisms are still under debate. The two main formation scenarios proposed are the infall and subsequent merging of star clusters and the in-situ formation of stars at the center of a galaxy. Here, I review the state-of-the-art of nuclear star cluster observations concerning their structure, stellar populations and kinematics. These observations are used to constrain the proposed formation scenarios for nuclear star clusters. Constraints from observations show, that likely both cluster infall and in-situ star formation are at work. The relative importance of these two mechanisms is still subject of investigation.

  5. Star cluster dynamics.

    PubMed

    Vesperini, Enrico

    2010-02-28

    Dynamical evolution plays a key role in shaping the current properties of star clusters and star cluster systems. A detailed understanding of the effects of evolutionary processes is essential to be able to disentangle the properties that result from dynamical evolution from those imprinted at the time of cluster formation. In this review, I focus my attention on globular clusters, and review the main physical ingredients driving their early and long-term evolution, describe the possible evolutionary routes and show how cluster structure and stellar content are affected by dynamical evolution.

  6. H-cluster stars

    NASA Astrophysics Data System (ADS)

    Lai, X. Y.; Gao, C. Y.; Xu, R. X.

    2013-06-01

    The study of dense matter at ultrahigh density has a very long history, which is meaningful for us to understand not only cosmic events in extreme circumstances but also fundamental laws of physics. It is well known that the state of cold matter at supranuclear density depends on the non-perturbative nature of quantum chromodynamics (QCD) and is essential for modelling pulsars. A so-called H-cluster matter is proposed in this paper as the nature of dense matter in reality. In compact stars at only a few nuclear densities but low temperature, quarks could be interacting strongly with each other there. That might render quarks grouped in clusters, although the hypothetical quark clusters in cold dense matter have not been confirmed due to the lack of both theoretical and experimental evidence. Motivated by recent lattice QCD simulations of the H-dibaryons (with structure uuddss), we therefore consider here a possible kind of quark clusters, H-clusters, that could emerge inside compact stars during their initial cooling as the dominant components inside (the degree of freedom could then be H-clusters there). Taking into account the in-medium stiffening effect, we find that at baryon densities of compact stars H-cluster matter could be more stable than nuclear matter. We also find that for the H-cluster matter with lattice structure, the equation of state could be so stiff that it would seem to be `superluminal' in the most dense region. However, the real sound speed for H-cluster matter is in fact difficult to calculate, so at this stage we do not put constraints on our model from the usual requirement of causality. We study the stars composed of H-clusters, i.e. H-cluster stars, and derive the dependence of their maximum mass on the in-medium stiffening effect, showing that the maximum mass could be well above 2 M⊙ as observed and that the resultant mass-radius relation fits the measurement of the rapid burster under reasonable parameters. Besides a general

  7. The Orion nebula star cluster

    NASA Technical Reports Server (NTRS)

    Panek, R. J.

    1982-01-01

    Photography through filters which suppress nebular light reveal a clustering of faint red stars centered on the Trapezium, this evidences a distinct cluster within the larger OB1 association. Stars within about 20 ft of trapezium comprise the Orion Nebula star cluster are considered. Topics discussed re: (1) extinction by dust grains; (2) photometric peculiarities; (3) spectroscopic peculiarities; (4) young variables; (5) the distribution and motion of gas within the cluster.

  8. Massive star clusters in galaxies.

    PubMed

    Harris, William E

    2010-02-28

    The ensemble of all star clusters in a galaxy constitutes its star cluster system. In this review, the focus of the discussion is on the ability of star clusters, particularly the systems of old massive globular clusters (GCs), to mark the early evolutionary history of galaxies. I review current themes and key findings in GC research, and highlight some of the outstanding questions that are emerging from recent work.

  9. Stellar populations in star clusters

    NASA Astrophysics Data System (ADS)

    Li, Cheng-Yuan; de Grijs, Richard; Deng, Li-Cai

    2016-12-01

    Stellar populations contain the most important information about star cluster formation and evolution. Until several decades ago, star clusters were believed to be ideal laboratories for studies of simple stellar populations (SSPs). However, discoveries of multiple stellar populations in Galactic globular clusters have expanded our view on stellar populations in star clusters. They have simultaneously generated a number of controversies, particularly as to whether young star clusters may have the same origin as old globular clusters. In addition, extensive studies have revealed that the SSP scenario does not seem to hold for some intermediate-age and young star clusters either, thus making the origin of multiple stellar populations in star clusters even more complicated. Stellar population anomalies in numerous star clusters are well-documented, implying that the notion of star clusters as true SSPs faces serious challenges. In this review, we focus on stellar populations in massive clusters with different ages. We present the history and progress of research in this active field, as well as some of the most recent improvements, including observational results and scenarios that have been proposed to explain the observations. Although our current ability to determine the origin of multiple stellar populations in star clusters is unsatisfactory, we propose a number of promising projects that may contribute to a significantly improved understanding of this subject.

  10. Sketching Star Clusters

    NASA Astrophysics Data System (ADS)

    Perez, Jeremy

    The next time you plan a quiet evening under a salted sky, with hopes of bathing your eyes in the ancient light of a majestic star cluster, be sure that your sketching kit comes with you! A casual glance at these celestial marvels will not give you a decent appreciation for an object whose history and character are as unique as the fingerprints you should be pressing into the side of your trusty pencil. I can think of no better way to connect with these stellar ballets, to understand their intricacies, and to recall your view later than to spend time sketching the soft glow or blazing pinpricks you see through the eyepiece.

  11. The star cluster formation history of the LMC

    NASA Astrophysics Data System (ADS)

    Baumgardt, H.; Parmentier, G.; Anders, P.; Grebel, E. K.

    2013-03-01

    The Large Magellanic Cloud (LMC) is one of the nearest galaxies to us and is one of only few galaxies where the star formation history can be determined from studying resolved stellar populations. We have compiled a new catalogue of ages, luminosities and masses of LMC star clusters and used it to determine the age distribution and dissolution rate of LMC star clusters. We find that the frequency of massive clusters with masses M > 5000 M⊙ is almost constant between 10 and 200 Myr, showing that the influence of residual gas expulsion is limited to the first 10 Myr of cluster evolution or clusters less massive than 5000 M⊙. Comparing the cluster frequency in that interval with the absolute star formation rate, we find that about 15 per cent of all stars in the LMC were formed in long-lived star clusters that survive for more than 10 Myr. We also find that the mass function of LMC clusters younger than 109 Gyr can be fitted by a power-law mass function N(m) ˜ m-α with slope α = 2.3, while older clusters follow a significantly shallower slope and interpret that this is a sign of either incompleteness or the ongoing dissolution of low-mass clusters. Our data show that for ages older than 200 Myr, about 90 per cent of all clusters are lost per dex of lifetime. The implied cluster dissolution rate is significantly faster than that based on analytic estimates and N-body simulations. Our cluster age data finally show evidence for a burst in cluster formation about 109 yr ago, but little evidence for bursts at other ages.

  12. DYNAMICS OF PLANETARY SYSTEMS IN STAR CLUSTERS

    SciTech Connect

    Spurzem, R.; Giersz, M.; Heggie, D. C.; Lin, D. N. C.

    2009-05-20

    At least 10%-15% of nearby Sunlike stars have known Jupiter-mass planets. In contrast, very few planets are found in mature open and globular clusters such as the Hyades and 47 Tuc. We explore here the possibility that this dichotomy is due to the postformation disruption of planetary systems associated with the stellar encounters in long-lived clusters. One supporting piece of evidence for this scenario is the discovery of freely floating low-mass objects in star forming regions. We use two independent numerical approaches, a hybrid Monte Carlo and a direct N-body method, to simulate the impact of the encounters. We show that the results of numerical simulations are in reasonable agreement with analytical determinations in the adiabatic and impulsive limits. They indicate that distant stellar encounters generally do not significantly modify the compact and nearly circular orbits. However, moderately close stellar encounters, which are likely to occur in dense clusters, can excite planets' orbital eccentricity and induce dynamical instability in systems that are closely packed with multiple planets. The disruption of planetary systems occurs primarily through occasional nearly parabolic, nonadiabatic encounters, though eccentricity of the planets evolves through repeated hyperbolic adiabatic encounters that accumulate small-amplitude changes. The detached planets are generally retained by the potential of their host clusters as free floaters in young stellar clusters such as {sigma} Orionis. We compute effective cross sections for the dissolution of planetary systems and show that, for all initial eccentricities, dissolution occurs on timescales that are longer than the dispersion of small stellar associations, but shorter than the age of typical open and globular clusters. Although it is much more difficult to disrupt short-period planets, close encounters can excite modest eccentricity among them, such that subsequent tidal dissipation leads to orbital decay

  13. Neutron star natal kicks and the long-term survival of star clusters

    NASA Astrophysics Data System (ADS)

    Contenta, Filippo; Varri, Anna Lisa; Heggie, Douglas C.

    2015-04-01

    We investigate the dynamical evolution of a star cluster in an external tidal field by using N-body simulations, with focus on the effects of the presence or absence of neutron star natal velocity kicks. We show that, even if neutron stars typically represent less than 2 per cent of the total bound mass of a star cluster, their primordial kinematic properties may affect the lifetime of the system by up to almost a factor of 4. We interpret this result in the light of two known modes of star cluster dissolution, dominated by either early stellar evolution mass-loss or two-body relaxation. The competition between these effects shapes the mass-loss profile of star clusters, which may either dissolve abruptly (`jumping'), in the pre-core-collapse phase, or gradually (`skiing'), after having reached core collapse.

  14. Hot stars in globular clusters.

    NASA Astrophysics Data System (ADS)

    Moehler, S.

    Globular clusters are ideal laboratories to study the evolution of low-mass stars. In this review, I shall concentrate on two types of hot stars observed in globular clusters: horizontal branch stars and UV bright stars. The third type, the white dwarfs, are covered by Bono in this volume. While the morphology of the horizontal branch correlates strongly with metallicity, it has been known for a long time that one parameter is not sufficient to describe the diversity of observed horizontal branch morphologies. A veritable zoo of candidates for this elusive ``2{nd} parameter'' has been suggested over the past decades, and the most prominent ones will be briefly discussed here. Adding to the complications, diffusion is active in the atmospheres of hot horizontal branch stars, which makes their analysis much more diffcult. The latest twist along the horizontal branch was added by the recent discovery of an extension to hotter temperatures and fainter magnitudes, the so-called ``blue hook''. The evolutionary origin of these stars is still under debate. I shall also give a brief overview of our current knowledge about hot UV bright stars and use them to illustrate the adverse effects of selection bias.

  15. Planetary systems in star clusters .

    NASA Astrophysics Data System (ADS)

    Kouwenhoven, M. B. N.; Shu, Qi; Cai, Maxwell Xu; Spurzem, Rainer

    Thousands of confirmed and candidate exoplanets have been identified in recent years. Consequently, theoretical research on the formation and dynamical evolution of planetary systems has seen a boost, and the processes of planet-planet scattering, secular evolution, and interaction between planets and gas/debris disks have been well-studied. Almost all of this work has focused on the formation and evolution of isolated planetary systems, and neglect the effect of external influences, such as the gravitational interaction with neighbouring stars. Most stars, however, form in clustered environments that either quickly disperse, or evolve into open clusters. Under these conditions, young planetary systems experience frequent close encounters with other stars, at least during the first 106-107 years, which affects planets orbiting at any period range, as well as their debris structures.

  16. The impact of galaxy geometry and mass evolution on the survival of star clusters

    SciTech Connect

    Madrid, Juan P.; Hurley, Jarrod R.; Martig, Marie

    2014-04-01

    Direct N-body simulations of globular clusters in a realistic Milky-Way-like potential are carried out using the code NBODY6 to determine the impact of the host galaxy disk mass and geometry on the survival of star clusters. A relation between disk mass and star-cluster dissolution timescale is derived. These N-body models show that doubling the mass of the disk from 5 × 10{sup 10} M {sub ☉} to 10 × 10{sup 10} M {sub ☉} halves the dissolution time of a satellite star cluster orbiting the host galaxy at 6 kpc from the galactic center. Different geometries in a disk of identical mass can determine either the survival or dissolution of a star cluster orbiting within the inner 6 kpc of the galactic center. Furthermore, disk geometry has measurable effects on the mass loss of star clusters up to 15 kpc from the galactic center. N-body simulations performed with a fine output time step show that at each disk crossing the outer layers of star clusters experiences an increase in velocity dispersion of ∼5% of the average velocity dispersion in the outer section of star clusters. This leads to an enhancement of mass loss—a clearly discernable effect of disk shocking. By running models with different inclinations, we determine that star clusters with an orbit that is perpendicular to the Galactic plane have larger mass loss rates than do clusters that evolve in the Galactic plane or in an inclined orbit.

  17. Star Cluster Buzzing With Pulsars

    NASA Astrophysics Data System (ADS)

    2005-01-01

    A dense globular star cluster near the center of our Milky Way Galaxy holds a buzzing beehive of rapidly-spinning millisecond pulsars, according to astronomers who discovered 21 new pulsars in the cluster using the National Science Foundation's 100-meter Robert C. Byrd Green Bank Telescope (GBT) in West Virginia. The cluster, called Terzan 5, now holds the record for pulsars, with 24, including three known before the GBT observations. Pulsar Diagram Pulsar Diagram: Click on image for more detail. "We hit the jackpot when we looked at this cluster," said Scott Ransom, an astronomer at the National Radio Astronomy Observatory in Charlottesville, VA. "Not only does this cluster have a lot of pulsars -- and we still expect to find more in it -- but the pulsars in it are very interesting. They include at least 13 in binary systems, two of which are eclipsing, and the four fastest-rotating pulsars known in any globular cluster, with the fastest two rotating nearly 600 times per second, roughly as fast as a household blender," Ransom added. Ransom and his colleagues reported their findings to the American Astronomical Society's meeting in San Diego, CA, and in the online journal Science Express. The star cluster's numerous pulsars are expected to yield a bonanza of new information about not only the pulsars themselves, but also about the dense stellar environment in which they reside and probably even about nuclear physics, according to the scientists. For example, preliminary measurements indicate that two of the pulsars are more massive than some theoretical models would allow. "All these exotic pulsars will keep us busy for years to come," said Jason Hessels, a Ph.D student at McGill University in Montreal. Globular clusters are dense agglomerations of up to millions of stars, all of which formed at about the same time. Pulsars are spinning, superdense neutron stars that whirl "lighthouse beams" of radio waves or light around as they spin. A neutron star is what is

  18. STAR cluster-finder ASIC

    SciTech Connect

    Botlo, M.; LeVine, M.J.; Scheetz, R.A.

    1997-12-31

    The STAR experiment reads out a TPC and an SVT (silicon vertex tracker), both of which require in-line pedestal subtraction, compression of ADC values from 10-bit to 8-bit, and location of time sequences representing responses to charged-particle tracks. The STAR cluster finder ASIC responds to all of these needs. Pedestal subtraction and compression are performed using lookup tables in attached RAM. We describe its design and implementation, as well as testing methodology and results of tests performed on foundry prototypes.

  19. Chemical evolution of star clusters.

    PubMed

    van Loon, Jacco Th

    2010-02-28

    I discuss the chemical evolution of star clusters, with emphasis on old Galactic globular clusters (GCs), in relation to their formation histories. GCs are clearly formed in a complex fashion, under markedly different conditions from any younger clusters presently known. Those special conditions must be linked to the early formation epoch of the Galaxy and must not have occurred since. While a link to the formation of GCs in dwarf galaxies has been suggested, present-day dwarf galaxies are not representative of the gravitational potential wells within which the GCs formed. Instead, a formation deep within the proto-Galaxy or within dark-matter mini-haloes might be favoured. Not all GCs may have formed and evolved similarly. In particular, we may need to distinguish Galactic Halo from Galactic Bulge clusters.

  20. Messier's nebulae and star clusters.

    NASA Astrophysics Data System (ADS)

    Jones, K. G.

    Charles Messier's Catalogue of nebulae and star clusters, published in 1784, marked the start of a new era of deep sky astronomy. Today, this tradition of observing galaxies and clusters is kept alive by serious amateur astronomers who study the objects of the deep sky. Nearly all the objects are visible in a small telescope. The author has revised his definitive version of Messier's Catalogue. His own observations and drawings, together with maps and diagrams, make this a valuable introduction to deep sky observing. Historical and astrophysical notes bring the science of these nebulae right up to date.

  1. Star Clusters in the Magellanic Clouds

    NASA Astrophysics Data System (ADS)

    Gallagher, J. S., III

    2014-09-01

    The Magellanic Clouds (MC) are prime locations for studies of star clusters covering a full range in age and mass. This contribution briefly reviews selected properties of Magellanic star clusters, by focusing first on young systems that show evidence for hierarchical star formation. The structures and chemical abundance patterns of older intermediate age star clusters in the Small Magellanic Cloud (SMC) are a second topic. These suggest a complex history has affected the chemical enrichment in the SMC and that low tidal stresses in the SMC foster star cluster survival.

  2. EXTENDED STAR FORMATION IN THE INTERMEDIATE-AGE LARGE MAGELLANIC CLOUD STAR CLUSTER NGC 2209

    SciTech Connect

    Keller, Stefan C.; Mackey, A. Dougal; Da Costa, Gary S.

    2012-12-10

    We present observations of the 1 Gyr old star cluster NGC 2209 in the Large Magellanic Cloud made with the GMOS imager on the Gemini South Telescope. These observations show that the cluster exhibits a main-sequence turnoff that spans a broader range in luminosity than can be explained by a single-aged stellar population. This places NGC 2209 amongst a growing list of intermediate-age (1-3 Gyr) clusters that show evidence for extended or multiple epochs of star formation of between 50 and 460 Myr in extent. The extended main-sequence turnoff observed in NGC 2209 is a confirmation of the prediction in Keller et al. made on the basis of the cluster's large core radius. We propose that secondary star formation is a defining feature of the evolution of massive star clusters. Dissolution of lower mass clusters through evaporation results in only clusters that have experienced secondary star formation surviving for a Hubble time, thus providing a natural connection between the extended main-sequence turnoff phenomenon and the ubiquitous light-element abundance ranges seen in the ancient Galactic globular clusters.

  3. Young and intermediate-age massive star clusters.

    PubMed

    Larsen, Søren S

    2010-02-28

    An overview of our current understanding of the formation and evolution of star clusters is given, with the main emphasis on high-mass clusters. Clusters form deeply embedded within dense clouds of molecular gas. Left-over gas is cleared within a few million years and, depending on the efficiency of star formation, the clusters may disperse almost immediately or remain gravitationally bound. Current evidence suggests that a small percentage of star formation occurs in clusters that remain bound, although it is not yet clear whether this fraction is truly universal. Internal two-body relaxation and external shocks will lead to further, gradual dissolution on time scales of up to a few hundred million years for low-mass open clusters in the Milky Way, while the most massive clusters (>10(5) M(o)) have lifetimes comparable to or exceeding the age of the Universe. The low-mass end of the initial cluster mass function is well approximated by a power-law distribution, dN/dM proportional to M(-2), but there is mounting evidence that quiescent spiral discs form relatively few clusters with masses M > 2 x 10(5) M(o). In starburst galaxies and old globular cluster systems, this limit appears to be higher, at least several x10(6) M(o). The difference is likely related to the higher gas densities and pressures in starburst galaxies, which allow denser, more massive giant molecular clouds to form. Low-mass clusters may thus trace star formation quite universally, while the more long-lived, massive clusters appear to form preferentially in the context of violent star formation.

  4. Stellar Dynamical Processes in Massive Star and Star Cluster Formation

    NASA Astrophysics Data System (ADS)

    Tan, Jonathan; Eyer, L.

    2009-01-01

    We study how high precision astrometric measurements by SIM and GAIA of stars involved in dynamical ejection events from star clusters can constrain theories of massive star and star cluster formation. We focus on the Orion Nebula Cluster (ONC). First, we investigate the scientific potential associated with an accurate measurement of the distance and proper motion of Theta 1 Ori C, which is the most massive star in the cluster and was recently involved (about 4000 years ago) in the ejection of a B star: the Becklin-Neugebauer (BN) star. The motion of the BN star has taken it close to a massive protostar, known as source I, where it appears to have influenced the accretion and outflow activity, most likely by a tidal interaction with the accretion disk. An accurate proper motion measurement of Theta 1 Ori C will constrain BN's initial motion, allowing us to search for deflections caused by the gravitational potential of the massive protostar. Second, we search the Hipparcos catalog for candidate runaway stars, i.e. that have been dynamically ejected from the cluster over the course of the last several Myr. SIM and GAIA observations of these stars will be needed to confirm their origin from the ONC. The results of this study will constrain the star cluster formation timescale and the statistics of the population of ejected stars. JCT acknowledges support from from NSF CAREER grant AST-0645412 and a grant from NASA for SIM Science Studies.

  5. The life and death of star clusters

    NASA Astrophysics Data System (ADS)

    Whitmore, B. C.

    It is generally believed that most stars are born in groups and clusters, rather than in the field. In recent years it has been demonstrated that merging galaxies produce large numbers of young massive star clusters, sometimes called super star clusters. Understanding what triggers the formation of these young massive clusters provides important information about the formation of stars in general. In recent years it has also become apparent that most clusters do not survive more than ~ 10 Myr (i.e., "infant mortality"). Hence, it is just as important to understand the disruption of star clusters as it is to to understand their formation if we want to understand the demographics of both star clusters and field stars. This talk will first discuss what triggers star cluster formation in merging galaxies (primarily in the Antennae galaxies) and will then outline a general framework designed to empirically fit observations of both star clusters and field stars in a wide variety of galaxies from mergers to quiescent spirals.

  6. THE SIZE SCALE OF STAR CLUSTERS

    SciTech Connect

    Madrid, Juan P.; Hurley, Jarrod R.; Sippel, Anna C.

    2012-09-10

    Direct N-body simulations of star clusters in a realistic Milky-Way-like potential are carried out using the code NBODY6. Based on these simulations, a new relationship between scale size and galactocentric distance is derived: the scale size of star clusters is proportional to the hyperbolic tangent of the galactocentric distance. The half-mass radius of star clusters increases systematically with galactocentric distance but levels off when star clusters orbit the galaxy beyond {approx}40 kpc. These simulations show that the half-mass radius of individual star clusters varies significantly as they evolve over a Hubble time, more so for clusters with shorter relaxation times, and remains constant through several relaxation times only in certain situations when expansion driven by the internal dynamics of the star cluster and the influence of the host galaxy tidal field balance each other. Indeed, the radius of a star cluster evolving within the inner 20 kpc of a realistic galactic gravitational potential is severely truncated by tidal interactions and does not remain constant over a Hubble time. Furthermore, the half-mass radius of star clusters measured with present-day observations bears no memory of the original cluster size. Stellar evolution and tidal stripping are the two competing physical mechanisms that determine the present-day size of globular clusters. These simulations also show that extended star clusters can form at large galactocentric distances while remaining fully bound to the host galaxy. There is thus no need to invoke accretion from an external galaxy to explain the presence of extended clusters at large galactocentric distances in a Milky-Way-type galaxy.

  7. Star clusters as simple stellar populations.

    PubMed

    Bruzual A, Gustavo

    2010-02-28

    In this paper, I review to what extent we can understand the photometric properties of star clusters, and of low-mass, unresolved galaxies, in terms of population-synthesis models designed to describe 'simple stellar populations' (SSPs), i.e. groups of stars born at the same time, in the same volume of space and from a gas cloud of homogeneous chemical composition. The photometric properties predicted by these models do not readily match the observations of most star clusters, unless we properly take into account the expected variation in the number of stars occupying sparsely populated evolutionary stages, owing to stochastic fluctuations in the stellar initial mass function. In this case, population-synthesis models reproduce remarkably well the full ranges of observed integrated colours and absolute magnitudes of star clusters of various ages and metallicities. The disagreement between the model predictions and observations of cluster colours and magnitudes may indicate problems with or deficiencies in the modelling, and does not necessarily tell us that star clusters do not behave like SSPs. Matching the photometric properties of star clusters using SSP models is a necessary (but not sufficient) condition for clusters to be considered SSPs. Composite models, characterized by complex star-formation histories, also match the observed cluster colours.

  8. Study of Stellar Clusters Containing Massive Stars

    NASA Astrophysics Data System (ADS)

    Costado, Teresa; Alfaro, E. J.; Delgado, A. J.; Djupvik, A. A.; Maíz Apellániz, J.

    2013-06-01

    Most stars form in clusters, but the percentage of stars born in dense stellar systems is currently matter of controversy and depends very much on the own definition of cluster. The cluster definition and hence the morphologies of individual clusters appear to vary significantly from region to region, as well as with age, which suggests that either, star formation in clusters is not universal and may depend on the local environment, or that all clusters form with the same morphology but early dynamical evolution quickly modifies the structure of the phase space distribution. In addition, young populated clusters containing massive stars are excellent labs for the study of the formation of the massive stellar component of the Galactic disk. Three main scenarios have been proposed for the formation of high-mass stars (M > 7-8 M_{⊙}): a) monolithic collapse of proto-stellar nuclei; b) competitive accretion inside the proto-cluster molecular cloud; and c) coalescence of proto-stellar nuclei and low-mass stars in very dense atmospheres. Both scientific questions: a) cluster formation and b) formation of high mass stars in clusters are intimately connected via the structural description of the phase space distribution of cluster stars and their Mass Function (MF). Models of static clusters with different initial spatial and kinematic distributions show how the spatial distribution dynamically evolves with time, allowing a characterization of their dynamical state from snapshots of their spatial distribution. Four are the main variables (and their distribution with mass and position) needed for a reliable characterization of the cluster dynamical state: a) Mass segregation parameter; b) Mapping of surface density for different ranges of masses; c) Q morphological parameter based on the minimum spanning tree graph and its variation with mass and cluster age, and d) MF of the cluster members. Two years ago, the Stellar System Group of IAA has begun an observational

  9. Probing Massive Star Cluster Formation with ALMA

    NASA Astrophysics Data System (ADS)

    Johnson, Kelsey

    2015-08-01

    Observationally constraining the physical conditions that give rise to massive star clusters has been a long-standing challenge. Now with the ALMA Observatory coming on-line, we can finally begin to probe the birth environments of massive clusters in a variety of galaxies with sufficient angular resolution. In this talk I will give an overview of ALMA observations of galaxies in which candidate proto-super star cluster molecular clouds have been identified. These new data probe the physical conditions that give rise to super star clusters, providing information on their densities, pressures, and temperatures. In particular, the observations indicate that these clouds may be subject to external pressures of P/k > 108 K cm-3, which is consistent with the prevalence of optically observed adolescent super star clusters in interacting galaxy systems and other high pressure environments. ALMA observations also enable an assessement of the molecular cloud chemical abundances in the regions surrounding super star clusters. Molecular clouds associated with existing super star clusters are strongly correlated with HCO+ emission, but appear to have relatively low ratio of CO/HCO+ emission compared to other clouds, indicating that the super star clusters are impacting the molecular abundances in their vicinity.

  10. Formation and Assembly of Massive Star Clusters

    NASA Astrophysics Data System (ADS)

    McMillan, Stephen

    The formation of stars and star clusters is a major unresolved problem in astrophysics. It is central to modeling stellar populations and understanding galaxy luminosity distributions in cosmological models. Young massive clusters are major components of starburst galaxies, while globular clusters are cornerstones of the cosmic distance scale and represent vital laboratories for studies of stellar dynamics and stellar evolution. Yet how these clusters form and how rapidly and efficiently they expel their natal gas remain unclear, as do the consequences of this gas expulsion for cluster structure and survival. Also unclear is how the properties of low-mass clusters, which form from small-scale instabilities in galactic disks and inform much of our understanding of cluster formation and star-formation efficiency, differ from those of more massive clusters, which probably formed in starburst events driven by fast accretion at high redshift, or colliding gas flows in merging galaxies. Modeling cluster formation requires simulating many simultaneous physical processes, placing stringent demands on both software and hardware. Simulations of galaxies evolving in cosmological contexts usually lack the numerical resolution to simulate star formation in detail. They do not include detailed treatments of important physical effects such as magnetic fields, radiation pressure, ionization, and supernova feedback. Simulations of smaller clusters include these effects, but fall far short of the mass of even single young globular clusters. With major advances in computing power and software, we can now directly address this problem. We propose to model the formation of massive star clusters by integrating the FLASH adaptive mesh refinement magnetohydrodynamics (MHD) code into the Astrophysical Multi-purpose Software Environment (AMUSE) framework, to work with existing stellar-dynamical and stellar evolution modules in AMUSE. All software will be freely distributed on-line, allowing

  11. INTERRUPTED STELLAR ENCOUNTERS IN STAR CLUSTERS

    SciTech Connect

    Geller, Aaron M.; Leigh, Nathan W. C. E-mail: nleigh@amnh.org

    2015-07-20

    Strong encounters between single stars and binaries play a pivotal role in the evolution of star clusters. Such encounters can also dramatically modify the orbital parameters of binaries, exchange partners in and out of binaries, and are a primary contributor to the rate of physical stellar collisions in star clusters. Often, these encounters are studied under the approximation that they happen quickly enough and within a small enough volume to be considered isolated from the rest of the cluster. In this paper, we study the validity of this assumption through the analysis of a large grid of single–binary and binary–binary scattering experiments. For each encounter we evaluate the encounter duration, and compare this with the expected time until another single or binary star will join the encounter. We find that for lower-mass clusters, similar to typical open clusters in our Galaxy, the percent of encounters that will be “interrupted” by an interloping star or binary may be 20%–40% (or higher) in the core, though for typical globular clusters we expect ≲1% of encounters to be interrupted. Thus, the assumption that strong encounters occur in relative isolation breaks down for certain clusters. Instead, many strong encounters develop into more complex “mini-clusters,” which must be accounted for in studying, for example, the internal dynamics of star clusters, and the physical stellar collision rate.

  12. Planet host stars in open clusters

    NASA Astrophysics Data System (ADS)

    Yang, XiaoLing; Chen, YuQin; Zhao, Gang

    2015-03-01

    We have compiled a list of all planet host star candidates reported in the literature, which are likely to be cluster members, and we checked their memberships by the spatial location, radial velocity, proper motion and photometric criteria. We found that only six stars, BD-13 2130, HD 28305, Kepler-66, Kepler-67, Pr0201 and Pr0211, are planet orbiting stars in open clusters to date. Two stars, HD 70573 and HD 89744, belong to moving groups and one star, TYC 8975-2606-1, may not be a planet host star, while three stars, HD 16175, HD 46375 and HD 108874 are not members of open clusters. We note that all these six planetary systems in the stellar cluster environment are younger than ˜1 Gyr, which might indicate that the planetary system in open cluster can not survive for a long time, and we speculate that close stellar encounters between member stars in open cluster can potentially destroy, or at least strongly affect, the presence of planetary systems.

  13. Effect of tidal fields on star clusters

    NASA Technical Reports Server (NTRS)

    Chernoff, David; Weinberg, Martin

    1991-01-01

    We follow the dynamical evolution of a star cluster in a galactic tidal field using a restricted N-body code. We find large asymmetric distortions in the outer profile of the cluster in the first 10 or so crossing times as material is lost. Prograde stars escape preferentially and establish a potentially observable retrograde rotation in the halo. We present the rate of particle loss and compare with the prescription proposed by Lee and Ostriker (1987).

  14. HUNTING FOR YOUNG DISPERSING STAR CLUSTERS IN IC 2574

    SciTech Connect

    Pellerin, Anne; Meyer, Martin M.; Calzetti, Daniella; Harris, Jason E-mail: martin.meyer@uwa.edu.au E-mail: jharris@30doradus.org

    2012-12-01

    Dissolving stellar groups are very difficult to detect using traditional surface photometry techniques. We have developed a method to find and characterize non-compact stellar systems in galaxies where the young stellar population can be spatially resolved. By carrying out photometry on individual stars, we are able to separate the luminous blue stellar population from the star field background. The locations of these stars are used to identify groups by applying the HOP algorithm, which are then characterized using color-magnitude and stellar density radial profiles to estimate age, size, density, and shape. We test the method on Hubble Space Telescope Advanced Camera for Surveys archival images of IC 2574 and find 75 dispersed stellar groups. Of these, 20 highly dispersed groups are good candidates for dissolving systems. We find few compact systems with evidence of dissolution, potentially indicating that star formation in this galaxy occurs mostly in unbound clusters or groups. These systems indicate that the dispersion rate of groups and clusters in IC 2574 is at most 0.45 pc Myr{sup -1}. The location of the groups found with HOP correlate well with H I contour map features. However, they do not coincide with H I holes, suggesting that those holes were not created by star-forming regions.

  15. Star formation and substructure in galaxy clusters

    SciTech Connect

    Cohen, Seth A.; Hickox, Ryan C.; Wegner, Gary A.; Einasto, Maret; Vennik, Jaan

    2014-03-10

    We investigate the relationship between star formation (SF) and substructure in a sample of 107 nearby galaxy clusters using data from the Sloan Digital Sky Survey. Several past studies of individual galaxy clusters have suggested that cluster mergers enhance cluster SF, while others find no such relationship. The SF fraction in multi-component clusters (0.228 ± 0.007) is higher than that in single-component clusters (0.175 ± 0.016) for galaxies with M{sub r}{sup 0.1}<−20.5. In both single- and multi-component clusters, the fraction of star-forming galaxies increases with clustercentric distance and decreases with local galaxy number density, and multi-component clusters show a higher SF fraction than single-component clusters at almost all clustercentric distances and local densities. Comparing the SF fraction in individual clusters to several statistical measures of substructure, we find weak, but in most cases significant at greater than 2σ, correlations between substructure and SF fraction. These results could indicate that cluster mergers may cause weak but significant SF enhancement in clusters, or unrelaxed clusters exhibit slightly stronger SF due to their less evolved states relative to relaxed clusters.

  16. Applying Machine Learning to Star Cluster Classification

    NASA Astrophysics Data System (ADS)

    Fedorenko, Kristina; Grasha, Kathryn; Calzetti, Daniela; Mahadevan, Sridhar

    2016-01-01

    Catalogs describing populations of star clusters are essential in investigating a range of important issues, from star formation to galaxy evolution. Star cluster catalogs are typically created in a two-step process: in the first step, a catalog of sources is automatically produced; in the second step, each of the extracted sources is visually inspected by 3-to-5 human classifiers and assigned a category. Classification by humans is labor-intensive and time consuming, thus it creates a bottleneck, and substantially slows down progress in star cluster research.We seek to automate the process of labeling star clusters (the second step) through applying supervised machine learning techniques. This will provide a fast, objective, and reproducible classification. Our data is HST (WFC3 and ACS) images of galaxies in the distance range of 3.5-12 Mpc, with a few thousand star clusters already classified by humans as a part of the LEGUS (Legacy ExtraGalactic UV Survey) project. The classification is based on 4 labels (Class 1 - symmetric, compact cluster; Class 2 - concentrated object with some degree of asymmetry; Class 3 - multiple peak system, diffuse; and Class 4 - spurious detection). We start by looking at basic machine learning methods such as decision trees. We then proceed to evaluate performance of more advanced techniques, focusing on convolutional neural networks and other Deep Learning methods. We analyze the results, and suggest several directions for further improvement.

  17. Probing the Birth of Super Star Clusters

    NASA Astrophysics Data System (ADS)

    Johnson, Kelsey

    2009-05-01

    Super star clusters are among the most extreme star formation environments known; they have incredible stellar densities, and each can harbor thousands of massive stars within radii of only a few parsecs. The most robust of these clusters may even be precursors to the ancient globular clusters ubiquitous around massive galaxies in the local universe today. Understanding the formation and feedback of super star clusters has the potential to provide us with insight into the evolution of starburst episodes throughout the universe. At present the relationship between the local physical conditions and the voracity of star formation is not well-constrained. Some progress has been made: over the last decade, a number of natal super star clusters have been discovered, providing us with a glimpse into their early evolution. However, the set of existing observations is anemic, and our current physical model for these natal clusters in simplistic. I will overview what we think we know about these objects based on existing observations and outline some of the most significant gaps in our current understanding.

  18. Towards Realistic Modeling of Massive Star Clusters

    NASA Astrophysics Data System (ADS)

    Gnedin, O.; Li, H.

    2016-06-01

    Cosmological simulations of galaxy formation are rapidly advancing towards smaller scales. Current models can now resolve giant molecular clouds in galaxies and predict basic properties of star clusters forming within them. I will describe new theoretical simulations of the formation of the Milky Way throughout cosmic time, with the adaptive mesh refinement code ART. However, many challenges - physical and numerical - still remain. I will discuss how observations of massive star clusters and star forming regions can help us overcome some of them. Video of the talk is available at https://goo.gl/ZoZOfX

  19. Ruprecht 3: An old star cluster remnant?

    NASA Astrophysics Data System (ADS)

    Pavani, D. B.; Bica, E.; Ahumada, A. V.; Clariá, J. J.

    2003-02-01

    2MASS J and H photometry and integrated spectroscopy are employed to study the nature of the poorly populated compact concentration of stars Ruprecht 3, which was previously catalogued as an open cluster. The integrated spectrum remarkably resembles that of a moderately metal-rich globular cluster. The distribution of the object stars in the colour-magnitude diagram is compatible with that of a 1.5 +/- 0.5 Gyr open cluster or older, depending on whether the bluer stars are interpreted as turnoff stars or blue stragglers, respectively. We derive for the object a distance from the Sun dsun = 0.72 +0.04-0.03 kpc and a colour excess E(B-V) = 0.04. Although a globular cluster remnant cannot be ruled out, the integrated spectrum resemblance to that of a globular cluster probably reflects a stochastic effect owing to the few brighter stars. The structural and photometric properties of Ruprecht 3 are compatible with what would be expected for an intermediate-age open cluster remnant. Based on observations made at Complejo Astronómico El Leoncito, which is operated under agreement between the Consejo Nacional de Investigaciones Científicas y Técnicas de la República Argentina and the National Universities of La Plata, Córdoba and San Juan, Argentina.

  20. Young star clusters in circumnuclear starburst rings

    NASA Astrophysics Data System (ADS)

    de Grijs, Richard; Ma, Chao; Jia, Siyao; Ho, Luis C.; Anders, Peter

    2017-03-01

    We analyse the cluster luminosity functions (CLFs) of the youngest star clusters in two galaxies exhibiting prominent circumnuclear starburst rings. We focus specifically on NGC 1512 and NGC 6951, for which we have access to Hα data that allow us to unambiguously identify the youngest sample clusters. To place our results on a firm statistical footing, we first explore in detail a number of important technical issues affecting the process from converting the observational data into the spectral energy distributions of the objects in our final catalogues. The CLFs of the young clusters in both galaxies exhibit approximate power-law behaviour down to the 90 per cent observational completeness limits, thus showing that star cluster formation in the violent environments of starburst rings appears to proceed similarly as that elsewhere in the local Universe. We discuss this result in the context of the density of the interstellar medium in our starburst-ring galaxies.

  1. SETI in star clusters: a theoretical approach

    NASA Astrophysics Data System (ADS)

    de La Fuente Marcos, R.; de La Fuente Marcos, C.

    2003-05-01

    For several decades, the search for extraterrestrial intelligence (SETI) has proceeded using advanced astronomical techniques. Different strategies have been proposed for target selection for targeted searches with goals of improving the chances of successful detection of signals from technological civilizations that may inhabit planets around solar-type stars, and to minimize the chances of missing signals from unexpected sites. In this paper we demonstrate that these goals are best achieved by observing star clusters. We show that standard open clusters are not appropriate for SETI scans because their disruption time scale is shorter than the characteristic time scale for the development of a protective atmospheric layer on a habitable planet. However, the old open clusters, those older than some Gy are optimal candidates for SETI surveys as their ages are older than the likely time for intelligent civilizations to emerge and the probability of catastrophic orbital modification as a result of close encounters with other cluster stars is, in general, rather negligible. The final performance of the proposed survey can be significantly increased by using initially a radio telescope beam larger than the cluster apparent size so that the entire cluster can be observed simultaneously. Globular clusters are also good candidates from the statistical point of view but only if hypothetical civilizations located in these clusters have been able to develop astronomical engineering technologies or have been involved in (rather speculative) cosmic colonization.

  2. STAR CLUSTERS IN PSEUDOBULGES OF SPIRAL GALAXIES

    SciTech Connect

    Di Nino, Daiana; Trenti, Michele; Stiavelli, Massimo; Carollo, C. Marcella; Scarlata, Claudia; Wyse, Rosemary F. G.

    2009-11-15

    We present a study of the properties of the star-cluster systems around pseudobulges of late-type spiral galaxies using a sample of 11 galaxies with distances from 17 Mpc to 37 Mpc. Star clusters are identified from multiband Hubble Space Telescope ACS and WFPC2 imaging data by combining detections in three bands (F435W and F814W with ACS and F606W with WFPC2). The photometric data are then compared to population synthesis models to infer the masses and ages of the star clusters. Photometric errors and completeness are estimated by means of artificial source Monte Carlo simulations. Dust extinction is estimated by considering F160W NICMOS observations of the central regions of the galaxies, augmenting our wavelength coverage. In all galaxies we identify star clusters with a wide range of ages, from young (age {approx}< 8 Myr) blue clusters, with typical mass of 10{sup 3} M {sub sun} to older (age >100-250 Myr), more massive, red clusters. Some of the latter might likely evolve into objects similar to the Milky Way's globular clusters. We compute the specific frequencies for the older clusters with respect to the galaxy and bulge luminosities. Specific frequencies relative to the galaxy light appear consistent with the globular cluster specific frequencies of early-type spirals. We compare the specific frequencies relative to the bulge light with the globular cluster specific frequencies of dwarf galaxies, which have a surface brightness profile that is similar to that of the pseudobulges in our sample. The specific frequencies we derive for our sample galaxies are higher than those of the dwarf galaxies, supporting an evolutionary scenario in which some of the dwarf galaxies might be the remnants of harassed late-type spiral galaxies that hosted a pseudobulge.

  3. Al-Sufi's Investigation of Stars, Star Clusters and Nebulae

    NASA Astrophysics Data System (ADS)

    Hafez, Ihsan; Stephenson, F. R.; Orchiston, W.

    2011-01-01

    The distinguished Arabic astronomer, Al-Sufi (AD 903-986) is justly famous for his Book of the Fixed Stars, an outstanding Medieval treatise on astronomy that was assembled in 964. Developed from Ptolemy's Algamest, but based upon al-Sufi's own stellar observations, the Book of the Fixed Stars has been copied down through the ages, and currently 35 copies are known to exist in various archival repositories around the world. Among other things, this major work contains 55 astronomical tables, plus star charts for 48 constellations. For the first time a long-overdue English translation of this important early work is in active preparation. In this paper we provide biographical material about Al-Sufi and the contents of his Book of the Fixed Stars, before examining his novel stellar magnitude system, and his listing of star clusters and nebulae (including the first-ever mention of the Great Nebula in Andromeda).

  4. The dearth of nuclear star clusters in bright galaxies

    NASA Astrophysics Data System (ADS)

    Arca-Sedda, M.; Capuzzo-Dolcetta, R.; Spera, M.

    2016-03-01

    We investigate the interaction of a massive globular cluster (GC) with a super massive black hole (SMBH), located at the centre of its host galaxy, by means of direct N-body simulations. The results show that tidal distortions induced by the stellar background and the SMBH act on a time shorter than that of dynamical friction decay for a 106 M⊙ GC whenever the SMBH mass exceeds ˜108 M⊙. This implies an almost complete dissolution of the infalling GC before it reaches the inner region (≲5 pc) of the parent galaxy. The generalization of this result to a larger sample of infalling GCs shows that such destructive process may prevent the formation and growth of a bright galactic nucleus. Another interesting, serendipitous, result we obtained is that the close interaction between the SMBH and the GC produces a `wave' of stars that escape from the cluster and, in a fraction, even from the whole galaxy.

  5. COCOA: Simulating Observations of Star Cluster Simulations

    NASA Astrophysics Data System (ADS)

    Askar, Abbas; Giersz, Mirek; Pych, Wojciech; Dalessandro, Emanuele

    2017-03-01

    COCOA (Cluster simulatiOn Comparison with ObservAtions) creates idealized mock photometric observations using results from numerical simulations of star cluster evolution. COCOA is able to present the output of realistic numerical simulations of star clusters carried out using Monte Carlo or N-body codes in a way that is useful for direct comparison with photometric observations. The code can simulate optical observations from simulation snapshots in which positions and magnitudes of objects are known. The parameters for simulating the observations can be adjusted to mimic telescopes of various sizes. COCOA also has a photometry pipeline that can use standalone versions of DAOPHOT (ascl:1104.011) and ALLSTAR to produce photometric catalogs for all observed stars.

  6. Gravothermal Star Clusters - Theory and Computer Modelling

    NASA Astrophysics Data System (ADS)

    Spurzem, Rainer

    2010-11-01

    In the George Darwin lecture, delivered to the British Royal Astronomical Society in 1960 by Viktor A. Ambartsumian he wrote on the evolution of stellar systems that it can be described by the "dynamic evolution of a gravitating gas" complemented by "a statistical description of the changes in the physical states of stars". This talk will show how this physical concept has inspired theoretical modeling of star clusters in the following decades up to the present day. The application of principles of thermodynamics shows, as Ambartsumian argued in his 1960 lecture, that there is no stable state of equilibrium of a gravitating star cluster. The trend to local thermodynamic equilibrium is always disturbed by escaping stars (Ambartsumian), as well as by gravothermal and gravogyro instabilities, as it was detected later. Here the state-of-the-art of modeling the evolution of dense stellar systems based on principles of thermodynamics and statistical mechanics (Fokker-Planck approximation) will be reviewed. Recent progress including rotation and internal correlations (primordial binaries) is presented. The models have also very successfully been used to study dense star clusters around massive black holes in galactic nuclei and even (in a few cases) relativistic supermassive dense objects in centres of galaxies (here again briefly touching one of the many research fields of V.A. Ambartsumian). For the modern present time of high-speed supercomputing, where we are tackling direct N-body simulations of star clusters, we will show that such direct modeling supports and proves the concept of the statistical models based on the Fokker-Planck theory, and that both theoretical concepts and direct computer simulations are necessary to support each other and make scientific progress in the study of star cluster evolution.

  7. UV-bright stars in globular clusters

    NASA Technical Reports Server (NTRS)

    Landsman, Wayne B.

    1994-01-01

    This paper highlights globular cluster studies with Ultraviolet Imaging Telescope (UIT) in three areas: the discrepancy between observed ultraviolet HB magnitudes and predictions of theoretical HB models; the discovery of two hot subdwarfs in NGC 1851, a globular not previously known to contain such stars; and spectroscopic follow up of newly identified UV-bright stars in M79 and w Cen. I also present results of a recent observation of NGC 6397 with the Voyager ultraviolet spectrometer.

  8. Phase Mixing of Popped Star Clusters

    NASA Astrophysics Data System (ADS)

    Candlish, G. N.; Smith, R.; Fellhauer, M.; Gibson, B. K.; Kroupa, P.; Assmann, P.

    2014-10-01

    As star clusters are expected to form with low star formation efficiencies, the gas in the cluster is expelled quickly and early in their development: the star cluster pops. This leads to an unbound stellar system. Previous N-body simulations have demonstrated the existence of a stepped number density distribution of cluster stars after popping, both in vertical position and vertical velocity, with a passing resemblance to a Christmas tree. Using numerical and analytical methods, we investigate the source of this structure, which arises due to the phase mixing of the out-of-equilibrium stellar system as it evolves in a background analytical potential. Considering only the vertical motions, we construct a theoretical model to describe the time evolution of the phase space distribution of stars in a Miyamoto-Nagai disk potential and a full Milky-Way type potential comprising bulge, halo and disk components, which is then compared with N- body simulations. Using our theoretical model, we investigate the possible observational signatures and the feasibility of detection.

  9. The STAR cluster-finder ASIC

    SciTech Connect

    Botlo, M.; LeVine, M.J.; Scheetz, R.A.; Schulz, M.W.; Short, P.; Woods, J.; Crosetto, D.

    1997-12-01

    STAR is a large TPC-based experiment at RHIC, the relativistic heavy ion collider at Brookhaven National Laboratory. The STAR experiment reads out a TPC and an SVT (silicon vertex tracker), both of which require in-line pedestal subtraction, compression of ADC values from 10-bit to 8-bit, and location of time sequences representing responses to charged-particle tracks. The STAR cluster finder ASIC responds to all of these needs. Pedestal subtraction and compression are performed using lookup tables in attached RAM. The authors describe its design and implementation, as well as testing methodology and results of tests performed on foundry prototypes.

  10. Blue straggler stars: lessons from open clusters.

    NASA Astrophysics Data System (ADS)

    Geller, Aaron M.

    Open clusters enable a deep dive into blue straggler characteristics. Recent work shows that the binary properties (frequency, orbital elements and companion masses and evolutionary states) of the blue stragglers are the most important diagnostic for determining their origins. To date the multi-epoch radial-velocity observations necessary for characterizing these blue straggler binaries have only been carried out in open clusters. In this paper, I highlight recent results in the open clusters NGC 188, NGC 2682 (M67) and NGC 6819. The characteristics of many of the blue stragglers in these open clusters point directly to origins through mass transfer from an evolved donor star. Additionally, a handful of blue stragglers show clear signatures of past dynamical encounters. These comprehensive, diverse and detailed observations also reveal important challenges for blue straggler formation models (and particularly the mass-transfer channel), which we must overcome to fully understand the origins of blue straggler stars and other mass-transfer products.

  11. Speckle Interferometry of Massive and Cluster Stars

    NASA Astrophysics Data System (ADS)

    Mason, Brian; Hartkopf, William I.; Gies, Douglas R.; Henry, Todd J.; Torres, Guillermo

    2005-08-01

    Conducted on NOAO 4-m telescopes in 1994, the first speckle survey of O stars (Mason et al. 1998) had success far in excess of our expectations. In addition to the frequently cited multiplicity analysis, many of the new systems which were first resolved in this paper are of significant astrophysical importance. To date, this paper has resulted in 86 citations in the refereed literature. Now, some ten years after the original survey, we propose to re-investigate all systems analyzed before (N=98) as well as make a first high-resolution inspection of the additional O stars (N=62) in the recent Galactic O Star Catalog of Maiz-Apellaniz & Walborn (2004). In addition, we propose to investigate several additional samples of interesting objects, including 10 accessible Galactic WR stars from the speckle survey of Hartkopf et al. (1999), 16 massive, hot stars with separations which would indicate their applicability for mass determinations (for fully detached O stars, we have only twelve mass determinations), 92 members of the Hyades and Pleiades clusters to complement RV studies of these clusters, and 197 Hyades & Pleiades stars, reobserved from the 1991 lists (Mason et al. 1993a,b).

  12. The luminosity of Population III star clusters

    NASA Astrophysics Data System (ADS)

    DeSouza, Alexander L.; Basu, Shantanu

    2015-06-01

    We analyse the time evolution of the luminosity of a cluster of Population III protostars formed in the early Universe. We argue from the Jeans criterion that primordial gas can collapse to form a cluster of first stars that evolve relatively independently of one another (i.e. with negligible gravitational interaction). We model the collapse of individual protostellar clumps using non-axisymmetric numerical hydrodynamics simulations. Each collapse produces a protostar surrounded by a massive disc (i.e. Mdisc /M* ≳ 0.1), whose evolution we follow for a further 30-40 kyr. Gravitational instabilities result in the fragmentation and the formation of gravitationally bound clumps within the disc. The accretion of these fragments by the host protostar produces accretion and luminosity bursts on the order of 106 L⊙. Within the cluster, we show that a simultaneity of such events across several protostellar cluster members can elevate the cluster luminosity to 5-10 times greater than expected, and that the cluster spends ˜15 per cent of its star-forming history at these levels. This enhanced luminosity effect is particularly enabled in clusters of modest size with ≃10-20 members. In one such instance, we identify a confluence of burst events that raise the luminosity to nearly 1000 times greater than the cluster mean luminosity, resulting in L > 108 L⊙. This phenomenon arises solely through the gravitational-instability-driven episodic fragmentation and accretion that characterizes this early stage of protostellar evolution.

  13. Tracking star formation in dwarf cluster galaxies

    NASA Astrophysics Data System (ADS)

    Rude, Cody Millard

    The evolution of galaxies in dense environments can be affected by close encounters with neighboring galaxies and interactions with the intracluster medium (ICM). Dwarf galaxies may be especially susceptible to these effects due to their low mass. The goal of my dissertation research is to look for signs of star formation in cluster dwarf galaxies by measuring and comparing the r- and u-band luminosity functions of 15 low redshift Abell galaxy clusters using archival data from the Canada-France-Hawaii Telescope (CFHT). Luminosity functions, dwarf-to-giant ratios, and blue fractions are measured in four cluster-centric annuli from stacked cluster data. To account for differences in cluster optical richness, each cluster is scaled according to r200, where r200 is the radius of a sphere, centered on the cluster, whose average density is 200 times the critical density of the universe. The outer region of the cluster sample shows an increase in the faint-end slope of the u-band luminosity function relative to the r-band, indicating star formation in dwarf galaxies. The blue fraction for dwarf galaxies steadily rises with increasing cluster-centric radii. The change in the blue fraction of giant galaxies also increases, but at a lower rate. Additionally, the inner regions of clusters ranging from 0.185 < z < 0.7 from the "Cluster Lensing and Supernova survey with Hubble (CLASH)" are used to generate blue- and red-band luminosity functions, dwarf-to-giant ratios, and blue fractions. Comparisons of the inner region of the CLASH and CFHT clusters show an increase in the blue fraction of dwarf galaxies with redshift that is not present in giant galaxies.

  14. A DYING STAR IN GLOBULAR CLUSTER

    NASA Technical Reports Server (NTRS)

    2002-01-01

    A DYING STAR IN GLOBULAR CLUSTER M15 The globular cluster Messier 15 is shown in this color image obtained with the NASA Hubble Space Telescope's Wide Field Planetary Camera 2 (WFPC2). Lying some 40,000 light-years from Earth in the direction of the constellation Pegasus, M15 is one of nearly 150 known globular clusters that form a vast halo surrounding our Milky Way galaxy. Each of these clusters is a spherical association of hundreds of thousands of ancient stars. The image, prepared by the Hubble Heritage team, attempts to show the stars in M15 in their true colors. The brightest cluster stars are red giants, with an orange color due to surface temperatures lower than our Sun's. Most of the fainter stars are hotter, giving them a bluish-white color. If we lived in the core of M15, our sky would blaze with tens of thousands of brilliant stars both day and night! Nestled among the myriads of stars visible in the Hubble image is an astronomical oddity. The pinkish object to the upper left of the cluster's core is a gas cloud surrounding a dying star. Known as Kuestner 648, this was the first planetary nebula to be identified in a globular cluster. In 1928, F. G. Pease, working at the 100-inch telescope of California's Mount Wilson Observatory, photographed the spectrum of K 648 and discovered the telltale bright emission of a nebular gas cloud rather than a normal star. In the ensuing 70 years, only three more planetary nebulae have been discovered in globular clusters. The stars in M15 and other globular clusters are estimated to be about 12 billion years old. They were among the first generations of stars to form in the Milky Way. Our Sun, by comparison, is a youthful 4.6 billion years old. As a star like the Sun ages, it exhausts the hydrogen that fuels its nuclear fusion, and increases in size to become a red giant. Then it ejects its outer layers into space, producing a planetary nebula. The remnant star at the center of the nebula gradually dies away as a

  15. A DYING STAR IN GLOBULAR CLUSTER

    NASA Technical Reports Server (NTRS)

    2002-01-01

    A DYING STAR IN GLOBULAR CLUSTER M15 The globular cluster Messier 15 is shown in this color image obtained with the NASA Hubble Space Telescope's Wide Field Planetary Camera 2 (WFPC2). Lying some 40,000 light-years from Earth in the direction of the constellation Pegasus, M15 is one of nearly 150 known globular clusters that form a vast halo surrounding our Milky Way galaxy. Each of these clusters is a spherical association of hundreds of thousands of ancient stars. The image, prepared by the Hubble Heritage team, attempts to show the stars in M15 in their true colors. The brightest cluster stars are red giants, with an orange color due to surface temperatures lower than our Sun's. Most of the fainter stars are hotter, giving them a bluish-white color. If we lived in the core of M15, our sky would blaze with tens of thousands of brilliant stars both day and night! Nestled among the myriads of stars visible in the Hubble image is an astronomical oddity. The pinkish object to the upper left of the cluster's core is a gas cloud surrounding a dying star. Known as Kuestner 648, this was the first planetary nebula to be identified in a globular cluster. In 1928, F. G. Pease, working at the 100-inch telescope of California's Mount Wilson Observatory, photographed the spectrum of K 648 and discovered the telltale bright emission of a nebular gas cloud rather than a normal star. In the ensuing 70 years, only three more planetary nebulae have been discovered in globular clusters. The stars in M15 and other globular clusters are estimated to be about 12 billion years old. They were among the first generations of stars to form in the Milky Way. Our Sun, by comparison, is a youthful 4.6 billion years old. As a star like the Sun ages, it exhausts the hydrogen that fuels its nuclear fusion, and increases in size to become a red giant. Then it ejects its outer layers into space, producing a planetary nebula. The remnant star at the center of the nebula gradually dies away as a

  16. Probing the faintest stars in a globular star cluster.

    PubMed

    Richer, Harvey B; Anderson, Jay; Brewer, James; Davis, Saul; Fahlman, Gregory G; Hansen, Brad M S; Hurley, Jarrod; Kalirai, Jasonjot S; King, Ivan R; Reitzel, David; Rich, R Michael; Shara, Michael M; Stetson, Peter B

    2006-08-18

    NGC 6397 is the second closest globular star cluster to the Sun. Using 5 days of time on the Hubble Space Telescope, we have constructed an ultradeep color-magnitude diagram for this cluster. We see a clear truncation in each of its two major stellar sequences. Faint red main-sequence stars run out well above our observational limit and near to the theoretical prediction for the lowest mass stars capable of stable hydrogen burning in their cores. We also see a truncation in the number counts of faint blue stars, namely white dwarfs. This reflects the limit to which the bulk of the white dwarfs can cool over the lifetime of the cluster. There is also a turn toward bluer colors in the least luminous of these objects. This was predicted for the very coolest white dwarfs with hydrogen-rich atmospheres as the formation of H(2) and the resultant collision-induced absorption cause their atmospheres to become largely opaque to infrared radiation.

  17. Hydrodynamic stellar interactions in dense star clusters

    NASA Technical Reports Server (NTRS)

    Rasio, Frederic A.

    1993-01-01

    Highly detailed HST observations of globular-cluster cores and galactic nuclei motivate new theoretical studies of the violent dynamical processes which govern the evolution of these very dense stellar systems. These processes include close stellar encounters and direct physical collisions between stars. Such hydrodynamic stellar interactions are thought to explain the large populations of blue stragglers, millisecond pulsars, X-ray binaries, and other peculiar sources observed in globular clusters. Three-dimensional hydrodynamics techniques now make it possible to perform realistic numerical simulations of these interactions. The results, when combined with those of N-body simulations of stellar dynamics, should provide for the first time a realistic description of dense star clusters. Here I review briefly current theoretical work on hydrodynamic stellar interactions, emphasizing its relevance to recent observations.

  18. STAR CLUSTERS, GALAXIES, AND THE FUNDAMENTAL MANIFOLD

    SciTech Connect

    Zaritsky, Dennis; Zabludoff, Ann I.; Gonzalez, Anthony H. E-mail: azabludoff@as.arizona.edu

    2011-02-01

    We explore whether global observed properties, specifically half-light radii, mean surface brightness, and integrated stellar kinematics, suffice to unambiguously differentiate galaxies from star clusters, which presumably formed differently and lack dark matter halos. We find that star clusters lie on the galaxy scaling relationship referred to as the fundamental manifold (FM), on the extension of a sequence of compact galaxies, and so conclude that there is no simple way to differentiate star clusters from ultracompact galaxies. By extending the validity of the FM over a larger range of parameter space and a wider set of objects, we demonstrate that the physics that constrains the resulting baryon and dark matter distributions in stellar systems is more general than previously appreciated. The generality of the FM implies (1) that the stellar spatial distribution and kinematics of one type of stellar system do not arise solely from a process particular to that set of systems, such as violent relaxation for elliptical galaxies, but are instead the result of an interplay of all processes responsible for the generic settling of baryons in gravitational potential wells, (2) that the physics of how baryons settle is independent of whether the system is embedded within a dark matter halo, and (3) that peculiar initial conditions at formation or stochastic events during evolution do not ultimately disturb the overall regularity of baryonic settling. We also utilize the relatively simple nature of star clusters to relate deviations from the FM to the age of the stellar population and find that stellar population models systematically and significantly overpredict the mass-to-light ratios of old, metal-rich clusters. We present an empirical calibration of stellar population mass-to-light ratios with age and color. Finally, we use the FM to estimate velocity dispersions for the low surface brightness, outer halo clusters that lack such measurements.

  19. Massive Star Clusters in Dwarf Galaxies

    NASA Astrophysics Data System (ADS)

    Larsen, Søren S.

    2017-03-01

    Dwarf galaxies can have very high globular cluster specific frequencies, and the GCs are in general significantly more metal-poor than the bulk of the field stars. In some dwarfs, such as Fornax, WLM, and IKN, the fraction of metal-poor stars that belong to GCs can be as high as 20%-25%, an order of magnitude higher than the 1%-2% typical of GCs in halos of larger galaxies. Given that chemical abundance anomalies appear to be present also in GCs in dwarf galaxies, this implies severe difficulties for self-enrichment scenarios that require GCs to have lost a large fraction of their initial masses. More generally, the number of metal-poor field stars in these galaxies is today less than what would originally have been present in the form of low-mass clusters if the initial cluster mass function was a power-law extending down to low masses. This may imply that the initial GC mass function in these dwarf galaxies was significantly more top-heavy than typically observed in present-day star forming environments.

  20. The Destructive Birth of Massive Stars and Massive Star Clusters

    NASA Astrophysics Data System (ADS)

    Rosen, Anna; Krumholz, Mark; McKee, Christopher F.; Klein, Richard I.; Ramirez-Ruiz, Enrico

    2017-01-01

    Massive stars play an essential role in the Universe. They are rare, yet the energy and momentum they inject into the interstellar medium with their intense radiation fields dwarfs the contribution by their vastly more numerous low-mass cousins. Previous theoretical and observational studies have concluded that the feedback associated with massive stars' radiation fields is the dominant mechanism regulating massive star and massive star cluster (MSC) formation. Therefore detailed simulation of the formation of massive stars and MSCs, which host hundreds to thousands of massive stars, requires an accurate treatment of radiation. For this purpose, we have developed a new, highly accurate hybrid radiation algorithm that properly treats the absorption of the direct radiation field from stars and the re-emission and processing by interstellar dust. We use our new tool to perform a suite of three-dimensional radiation-hydrodynamic simulations of the formation of massive stars and MSCs. For individual massive stellar systems, we simulate the collapse of massive pre-stellar cores with laminar and turbulent initial conditions and properly resolve regions where we expect instabilities to grow. We find that mass is channeled to the massive stellar system via gravitational and Rayleigh-Taylor (RT) instabilities. For laminar initial conditions, proper treatment of the direct radiation field produces later onset of RT instability, but does not suppress it entirely provided the edges of the radiation-dominated bubbles are adequately resolved. RT instabilities arise immediately for turbulent pre-stellar cores because the initial turbulence seeds the instabilities. To model MSC formation, we simulate the collapse of a dense, turbulent, magnetized Mcl = 106 M⊙ molecular cloud. We find that the influence of the magnetic pressure and radiative feedback slows down star formation. Furthermore, we find that star formation is suppressed along dense filaments where the magnetic field is

  1. Caloric curve of star clusters.

    PubMed

    Casetti, Lapo; Nardini, Cesare

    2012-06-01

    Self-gravitating systems, such as globular clusters or elliptical galaxies, are the prototypes of many-body systems with long-range interactions, and should be the natural arena in which to test theoretical predictions on the statistical behavior of long-range-interacting systems. Systems of classical self-gravitating particles can be studied with the standard tools of equilibrium statistical mechanics, provided the potential is regularized at small length scales and the system is confined in a box. The confinement condition looks rather unphysical in general, so that it is natural to ask whether what we learn with these studies is relevant to real self-gravitating systems. In order to provide an answer to this question, we consider a basic, simple, yet effective model of globular clusters: the King model. This model describes a self-consistently confined system, without the need of any external box, but the stationary state is a nonthermal one. In particular, we consider the King model with a short-distance cutoff on the interactions, and we discuss how such a cutoff affects the caloric curve, i.e., the relation between temperature and energy. We find that the cutoff stabilizes a low-energy phase, which is absent in the King model without cutoff; the caloric curve of the model with cutoff turns out to be very similar to that of previously studied confined and regularized models, but for the absence of a high-energy gaslike phase. We briefly discuss the possible phenomenological as well as theoretical implications of these results.

  2. Caloric curve of star clusters

    NASA Astrophysics Data System (ADS)

    Casetti, Lapo; Nardini, Cesare

    2012-06-01

    Self-gravitating systems, such as globular clusters or elliptical galaxies, are the prototypes of many-body systems with long-range interactions, and should be the natural arena in which to test theoretical predictions on the statistical behavior of long-range-interacting systems. Systems of classical self-gravitating particles can be studied with the standard tools of equilibrium statistical mechanics, provided the potential is regularized at small length scales and the system is confined in a box. The confinement condition looks rather unphysical in general, so that it is natural to ask whether what we learn with these studies is relevant to real self-gravitating systems. In order to provide an answer to this question, we consider a basic, simple, yet effective model of globular clusters: the King model. This model describes a self-consistently confined system, without the need of any external box, but the stationary state is a nonthermal one. In particular, we consider the King model with a short-distance cutoff on the interactions, and we discuss how such a cutoff affects the caloric curve, i.e., the relation between temperature and energy. We find that the cutoff stabilizes a low-energy phase, which is absent in the King model without cutoff; the caloric curve of the model with cutoff turns out to be very similar to that of previously studied confined and regularized models, but for the absence of a high-energy gaslike phase. We briefly discuss the possible phenomenological as well as theoretical implications of these results.

  3. Accelerating Star Formation in Clusters and Associations

    NASA Astrophysics Data System (ADS)

    Palla, Francesco; Stahler, Steven W.

    2000-09-01

    We use our own, recently developed pre-main-sequence evolutionary tracks to investigate the star formation histories of relatively nearby associations and clusters. We first employ published luminosities and effective temperatures to place the known members of each region in the H-R diagram. We then construct age histograms detailing that region's history. The groups studied include Taurus-Auriga, Lupus, Chamaeleon, ρ Ophiuchi, Upper Scorpius, IC 348, and NGC 2264. This study is the first to analyze a large number of star-forming regions with the same set of theoretical tracks. Our investigation corroborates and extends our previous results on the Orion Nebula Cluster. In all cases, we find that star formation began at a relatively low level some 107 yr in the past and has more recently undergone a steep acceleration. This acceleration, which lasts several million years, is usually continuing through the present epoch. The one clear exception is the OB association Upper Scorpius, where the formation rate climbed upward, peaked, and has now died off. Significantly, this is also the only region of our list that has been largely stripped of molecular gas. The acceleration represents a true physical phenomenon that cannot be explained away by incompleteness of the samples; nor is the pattern of stellar births significantly affected by observational errors or the presence of unresolved binaries. We speculate that increasing star formation activity arises from contraction of the parent cloud. Despite the short timescale for acceleration, the cloud is likely to evolve quasi-statically. Star formation itself appears to be a critical phenomenon, occurring only in locations exceeding some threshold density. The cloud's contraction must reverse itself, and the remnant gas dissipate, in less than 107 yr, even for aggregates containing no massive stars. In this case, molecular outflows from the stars themselves presumably accomplish the task, but the actual dispersal mechanism

  4. Panchromatic Hubble Andromeda Treasury. XVI. Star Cluster Formation Efficiency and the Clustered Fraction of Young Stars

    NASA Astrophysics Data System (ADS)

    Johnson, L. Clifton; Seth, Anil C.; Dalcanton, Julianne J.; Beerman, Lori C.; Fouesneau, Morgan; Lewis, Alexia R.; Weisz, Daniel R.; Williams, Benjamin F.; Bell, Eric F.; Dolphin, Andrew E.; Larsen, Søren S.; Sandstrom, Karin; Skillman, Evan D.

    2016-08-01

    We use the Panchromatic Hubble Andromeda Treasury survey data set to perform spatially resolved measurements of star cluster formation efficiency (Γ), the fraction of stellar mass formed in long-lived star clusters. We use robust star formation history and cluster parameter constraints, obtained through color-magnitude diagram analysis of resolved stellar populations, to study Andromeda’s cluster and field populations over the last ˜300 Myr. We measure Γ of 4%-8% for young, 10-100 Myr-old populations in M31. We find that cluster formation efficiency varies systematically across the M31 disk, consistent with variations in mid-plane pressure. These Γ measurements expand the range of well-studied galactic environments, providing precise constraints in an H i-dominated, low-intensity star formation environment. Spatially resolved results from M31 are broadly consistent with previous trends observed on galaxy-integrated scales, where Γ increases with increasing star formation rate surface density (ΣSFR). However, we can explain observed scatter in the relation and attain better agreement between observations and theoretical models if we account for environmental variations in gas depletion time (τ dep) when modeling Γ, accounting for the qualitative shift in star formation behavior when transitioning from a H2-dominated to a H i-dominated interstellar medium. We also demonstrate that Γ measurements in high ΣSFR starburst systems are well-explained by τ dep-dependent fiducial Γ models.

  5. N-body simulations of star clusters

    NASA Astrophysics Data System (ADS)

    Engle, Kimberly Anne

    1999-10-01

    We investigate the structure and evolution of underfilling (i.e. non-Roche-lobe-filling) King model globular star clusters using N-body simulations. We model clusters with various underfilling factors and mass distributions to determine their evolutionary tracks and lifetimes. These models include a self-consistent galactic tidal field, mass loss due to stellar evolution, ejection, and evaporation, and binary evolution. We find that a star cluster that initially does not fill its Roche lobe can live many times longer than one that does initially fill its Roche lobe. After a few relaxation times, the cluster expands to fill its Roche lobe. We also find that the choice of initial mass function significantly affects the lifetime of the cluster. These simulations were performed on the GRAPE-4 (GRAvity PipE) special-purpose hardware with the stellar dynamics package ``Starlab.'' The GRAPE-4 system is a massively-parallel computer designed to calculate the force (and its first time derivative) due to N particles. Starlab's integrator ``kira'' employs a 4th- order Hermite scheme with hierarchical (block) time steps to evolve the stellar system. We discuss, in some detail, the design of the GRAPE-4 system and the manner in which the Hermite integration scheme with block time steps is implemented in the hardware.

  6. ISM gas removal from starburst galaxies and the premature death of star clusters

    NASA Astrophysics Data System (ADS)

    Melioli, C.; de Gouveia dal Pino, E. M.

    2006-01-01

    Recent observational studies of the age distribution of star clusters in nearby merging galaxies and starburst (SB) galaxies indicate a premature death of the young clusters. The fate of an evolving star cluster crucially depends of its gas content. This behaves like a glue that helps to keep the star system gravitationally bound. In SB systems where the rate of supernovae (SNe) explosions is elevated one should expect an efficient heating of the gas and its complete removal which could then favor the rapid dissociation of the evolving star clusters. Based on a contemporaneous study of the dynamical evolution of the interstellar gas in SB environments (Melioli & de Gouveia Dal Pino 2004, A&A, 424, 817) where it has been considered also the presence of dense clouds that may inhibit the heating efficiency of the interstellar gas by the SNe, we have here computed the timescales for gas removal from young clusters embedded in these systems and found that they are consistent with the very short timescales for cluster dissolution which are inferred from the observational studies above. Our results indicate that typical SB proto-clusters should start to disperse after less than 5 Myr. For a given total gas mass content, this result is nearly insensitive to the initial star formation efficiency.

  7. Exploring the UV excess in star clusters of different mass

    NASA Astrophysics Data System (ADS)

    Hernández-Pérez, Fabiola; Bruzual, Gustavo; Gladis, Magris C.

    2017-03-01

    We compute the expected spectral energy distribution of stellar populations of mass characteristic of star clusters taking into account stochastic fluctuations in the number of stars populating the IMF, and the presence of interacting binary stars in the cluster population. We evaluate under what circumstances the UV excess phenomenon is expected to appear in star clusters of different mass, and which is its most likely source: the stochastic fluctuations, the result of binary interactions, or a mixture of both.

  8. How a Star Cluster Ruled Out MACHOs

    NASA Astrophysics Data System (ADS)

    Kohler, Susanna

    2016-08-01

    Are massive black holes hiding in the halos of galaxies, making up the majority of the universes mysterious dark matter? This possibility may have been ruled out by a star cluster in a small galaxy recently discovered orbiting the Milky Way.Dark Matter CandidatesThe relative amounts of the different constituents of the universe. Dark matter makes up ~27%. [ESA/Planck]Roughly 27% of the mass and energy in the observable universe is made up of dark matter matter invisible to us, which is neither accounted for by observable baryonic matter nor dark energy.What makes up this dark matter? Among the many proposed candidates, one of the least exotic is that of massive compact halo objects, or MACHOs. MACHOs are hypothesized to be black holes that formed in the early universe and now hide in galactic halos. We cant detect light from these objects but their mass adds to the gravitational pull of galaxies.So far, MACHOs prospects arent looking great. They have not been detected in gravitational lensing surveys, ruling out MACHOs between 10-7 and 30 solar masses as the dominant component of dark matter in our galaxy. MACHOs over 100 solar masses have also been ruled out, due to the existence of fragile wide halo binaries that would have been disrupted by the presence of such large black holes.But what about MACHOs between 30 and 100 solar masses? In a new study, Timothy Brandt (NASA Sagan Postdoctoral Fellow at the Institute for Advanced Study, in Princeton, NJ) uses a recently discovered faint galaxy, Eridanus II, to place constraints on MACHOs in this mass range.MACHO constraints from the survival of a star cluster in Eri II, assuming a cluster age of 3 Gyr (a lower bound; constraints increase when assuming an age of 12 Gyr). [Adapted from Brandt 2016]A Star Cluster in Eri IIEridanus II is an ultra-faint dwarf galaxy that lies roughly 1.2 million light-years away from us. This dim object is a satellite galaxy of the Milky Way, discovered as part of the Dark Energy Survey

  9. UVIS CTE Monitor: Star Clusters

    NASA Astrophysics Data System (ADS)

    Noeske, Kai

    2010-09-01

    *** NOTE 2: 2ND CHANGE MAR 26 2011: VISIT 13 HAD FAILED. APPROVED FOR REPETITION. ****** NEW VISIT 14 IS IDENTICAL TO FORMER VISIT 13, WITH EXCEPTIONS THAT SOME SUBEXPOSURES ARE REMOVED. ****** SEE OBSERVING DESCRIPTION FOR DETAILS. ****** NOTE: THIS IS A CHANGED PHASE II PROPOSAL AFTER VISITS 1,2,7 HAD BEEN EXECUTED ****** CHANGES BECAME NECESSARY AFTER ANALYSIS OF INCOMING CALIBRATION DATA FROM 12379 AND 12348 ****** THIS REVISED PHASE II {submission 14FEB2011} ADDS THE EVALUATION OF CHARGE INJECTION***The changes amount to:1} dropping the 3rd epoch {August 2011} of external CTE monitoring {3 orbits}2} simplifying the CTE monitor observations in the second epoch {March 2011}, freeing up 1 orbit3} using the freed up orbits from 1} and 2}, together with two additional external orbits that we were granted, to thoroughly assess the data quality of charge - injected data under realistic observing setups.These charge-injected observations will be obtained during the 2nd epoch of the CTE monitor program, in the March 2011 window.------ Original Text prior to 14 Feb 2011 below this line -----------This program extends the Cycle 17 external CTE calibration {CAL/WFC3 ID 11924} program for WFC3/UVIS over Cycle 18. Targets are {i} the sparse cluster NGC 6791 observed in Cycle 17, to continue a consistent set of observations that allows to isolate the time evolution of the CTE, and {ii} a denser field in 47 Tuc {NGC 104}. The latter will provide data to measure the dependence of the CTE on field crowding. It will also provide a consistent comparison between the CTE evolution of WFC3/UVIS and that of ACS/WFC at the same time into the flight {1 year}, because ACS/WFC CTE data were based on 47 Tuc observations. Additional observations of 47 Tuc in the CVZ will provide a wide range of background levels to measure the background dependence of the UVIS CTE.Goals are {i} the continued monitoring of the time evolution of the WFC3/UVIS CTE, {ii} establishing the detector X

  10. Spatial and kinematic segregation in star-cluster merger remnants

    NASA Astrophysics Data System (ADS)

    Cole, David R.; Debattista, Victor P.; Varri, Anna-Lisa; Adam, Markus; Seth, Anil C.

    2017-04-01

    Globular clusters that exhibit chemical and dynamical complexity have been suggested to be the stripped nuclei of dwarf galaxies(e.g. M54, ω Cen). We use N-body simulations of nuclear star clusters forming via the mergers of star clusters to explore the persistence of substructure in the phase space. We find that the observed level of differentiation is difficult to reconcile with the observed if nuclear clusters form wholly out of the mergers of star clusters. Only the star clusters that merged most recently retain sufficiently distinct density and kinematics to be distinguishable from the rest of the nuclear cluster. In situ star formation must therefore be included to explain the observed properties of nuclear star clusters, in good agreement with previous results.

  11. Interrupted Binary Mass Transfer in Star Clusters

    NASA Astrophysics Data System (ADS)

    Leigh, Nathan W. C.; Geller, Aaron M.; Toonen, Silvia

    2016-02-01

    Binary mass transfer (MT) is at the forefront of some of the most exciting puzzles of modern astrophysics, including SNe Ia, gamma-ray bursts, and the formation of most observed exotic stellar populations. Typically, the evolution is assumed to proceed in isolation, even in dense stellar environments such as star clusters. In this paper, we test the validity of this assumption via the analysis of a large grid of binary evolution models simulated with the SeBa code. For every binary, we calculate analytically the mean time until another single or binary star comes within the mean separation of the mass-transferring binary, and compare this timescale to the mean time for stable MT to occur. We then derive the probability for each respective binary to experience a direct dynamical interruption. The resulting probability distribution can be integrated to give an estimate for the fraction of binaries undergoing MT that are expected to be disrupted as a function of the host cluster properties. We find that for lower-mass clusters (≲ {10}4 {M}⊙ ), on the order of a few to a few tens of percent of binaries undergoing MT are expected to be interrupted by an interloping single, or more often binary, star, over the course of the cluster lifetime, whereas in more massive globular clusters we expect \\ll 1% to be interrupted. Furthermore, using numerical scattering experiments performed with the FEWBODY code, we show that the probability of interruption increases if perturbative fly-bys are considered as well, by a factor ˜2.

  12. Evolution of star clusters in a cosmological tidal field

    NASA Astrophysics Data System (ADS)

    Rieder, Steven; Ishiyama, Tomoaki; Langelaan, Paul; Makino, Junichiro; McMillan, Stephen L. W.; Portegies Zwart, Simon

    2013-12-01

    We present a method to couple N-body star cluster simulations to a cosmological tidal field, using AMUSE (Astrophysical Multipurpose Software Environment). We apply this method to star clusters embedded in the CosmoGrid dark matter only Lambda cold dark matter simulation. Our star clusters are born at z = 10 (corresponding to an age of the universe of about 500 Myr) by selecting a dark matter particle and initializing a star cluster with 32 000 stars on its location. We then follow the dynamical evolution of the star cluster within the cosmological environment. We compare the evolution of star clusters in two Milky Way size haloes with a different accretion history. The mass-loss of the star clusters is continuous irrespective of the tidal history of the host halo, but major merger events tend to increase the rate of mass-loss. From the selected two dark matter haloes, the halo that experienced the larger number of mergers tends to drive a smaller mass-loss rate from the embedded star clusters, even though the final masses of both haloes are similar. We identify two families of star clusters: native clusters, which become part of the main halo before its final major merger event, and the immigrant clusters, which are accreted upon or after this event; native clusters tend to evaporate more quickly than immigrant clusters. Accounting for the evolution of the dark matter halo causes immigrant star clusters to retain more mass than when the z = 0 tidal field is taken as a static potential. The reason for this is the weaker tidal field experienced by immigrant star clusters before merging with the larger dark matter halo.

  13. NanoClusters Surface Area Allows Nanoparticle Dissolution with Microparticle Properties

    PubMed Central

    Kuehl, Christopher; El-Gendy, Nashwa; Berkland, Cory

    2016-01-01

    Poorly water soluble drugs comprise the majority of new drug molecules. Nanoparticle agglomerates, called NanoClusters, can increase the dissolution rate of poorly soluble compounds by increasing particle surface area. Budesonide and danazol, two poorly soluble steroids, were studied as model compounds. NanoCluster suspensions were made using a Netzsch MiniCer media mill with samples collected between 5 and 15 hours and lyophilized. DSC and PXRD were used to evaluate the physicochemical properties of the powders and BET was used to determine surface area. SEM confirmed NanoClusters were between 1 and 5 μm. NanoCluster samples showed an increase in dissolution rate compared to the micronized stock and similar to a dried nanoparticle suspension. BET analysis determined an increase in surface area of 8 times for budesonide NanoClusters and 10 to 15 times for danazol NanoClusters compared to micronized stock. Melting temperatures decreased with increased mill time of NanoClusters by DSC. The increased surface area of NanoClusters provides a potential micron-sized alternative to nanoparticles to increase dissolution rate of poorly water soluble drugs. PMID:24788354

  14. Lithopanspermia in star-forming clusters.

    PubMed

    Adams, Fred C; Spergel, David N

    2005-08-01

    This paper considers the lithopanspermia hypothesis in star-forming groups and clusters, where the chances of biological material spreading from one solar system to another is greatly enhanced (relative to action in the field) because of the close proximity of the systems and lower relative velocities. These effects more than compensate for the reduced time spent in such crowded environments. This paper uses approximately 300,000 Monte Carlo scattering calculations to determine the cross sections for rocks to be captured by binaries and provides fitting formulae for other applications. We assess the odds of transfer as a function of the ejection speed v (eject) and number N(.) of members in the birth aggregate. The odds of any given ejected meteoroid being recaptured by another solar system are relatively low, about 1:10(3)-10(6) over the expected range of ejection speeds and cluster sizes. Because the number of ejected rocks (with mass m > 10 kg) per system can be large, N (R) approximately 10(16), virtually all solar systems are likely to share rocky ejecta with all of the other solar systems in their birth cluster. The number of ejected rocks that carry living microorganisms is much smaller and less certain, but we estimate that N (B) approximately 10(7) rocks can be ejected from a biologically active solar system. For typical birth environments, the capture of life-bearing rocks is expected to occur N (bio) asymptotically equal to 10-16,000 times (per cluster), depending on the ejection speeds. Only a small fraction (f (imp) approximately 10(4)) of the captured rocks impact the surfaces of terrestrial planets, so that N (lps) asymptotically equal to 10(3)-1.6 lithopanspermia events are expected per cluster (under favorable conditions). Finally, we discuss the question of internal versus external seeding of clusters and the possibility of Earth seeding young clusters over its biologically active lifetime.

  15. Spin alignment of stars in old open clusters

    NASA Astrophysics Data System (ADS)

    Corsaro, Enrico; Lee, Yueh-Ning; García, Rafael A.; Hennebelle, Patrick; Mathur, Savita; Beck, Paul G.; Mathis, Stephane; Stello, Dennis; Bouvier, Jérôme

    2017-03-01

    Stellar clusters form by gravitational collapse of turbulent molecular clouds, with up to several thousand stars per cluster1. They are thought to be the birthplace of most stars and therefore play an important role in our understanding of star formation, a fundamental problem in astrophysics2,3. The initial conditions of the molecular cloud establish its dynamical history until the stellar cluster is born. However, the evolution of the cloud's angular momentum during cluster formation is not well understood4. Current observations have suggested that turbulence scrambles the angular momentum of the cluster-forming cloud, preventing spin alignment among stars within a cluster5. Here we use asteroseismology6-8 to measure the inclination angles of spin axes in 48 stars from the two old open clusters NGC 6791 and NGC 6819. The stars within each cluster show strong alignment. Three-dimensional hydrodynamical simulations of proto-cluster formation show that at least 50% of the initial proto-cluster kinetic energy has to be rotational in order to obtain strong stellar-spin alignment within a cluster. Our result indicates that the global angular momentum of the cluster-forming clouds was efficiently transferred to each star and that its imprint has survived several gigayears since the clusters formed.

  16. The Assembly History of the Milky Way Nuclear Star Cluster

    NASA Astrophysics Data System (ADS)

    Feldmeier-Krause, A.; Neumayer, N.; Schödel, R.; Seth, A.; de Zeeuw, P. T.; Walcher, C. J.; Lützgendorf, N.; Kissler-Patig, M.; Hilker, M.; Kuntschner, H.

    2017-03-01

    Within the central 10 pc of our Galaxy lies a dense cluster of stars, the nuclear star cluster. This cluster forms a distinct component of our Galaxy. Nuclear star clusters are common objects and are detected in ~ 75% of nearby galaxies. It is, however, not fully understood how nuclear star clusters form. The Milky Way nuclear star cluster is the closest of its kind. At a distance of only 8 kpc we can spatially resolve its stellar populations and kinematics much better than in external galaxies. This makes the Milky Way nuclear star cluster the perfect local reference object for understanding the structure and assembly history of nuclear star clusters in general. There are of the order of 107 stars within the central 10 pc of the Galactic center. Most of these stars are several Gyr old late-type stars. However, there are also more than 100 hot early-type stars in the central parsec of the Milky Way, with ages of only a few Myr. Beyond a projected distance of 0.5 pc of the Galactic center, the density of young stars was largely unknown, since only very few spectroscopic observations existed so far. We covered the central >4 pc2 (0.75 sq.arcmin) of the Galactic center using the integral-field spectrograph KMOS (VLT). We extracted more than 1,000 spectra from individual stars and identified >20 new early-type stars based on their spectra. We studied the spatial distribution of the different populations and their kinematics to put constraints on the assembly history of the Milky Way nuclear star cluster.

  17. Stellar and Binary Evolution in Star Clusters

    NASA Technical Reports Server (NTRS)

    McMillan, Stephen L. W.

    2001-01-01

    This paper presents a final report on research activities covered on Stellar and Binary Evolution in Star Clusters. Substantial progress was made in the development and dissemination of the "Starlab" software environment. Significant improvements were made to "kira," an N-body simulation program tailored to the study of dense stellar systems such as star clusters and galactic nuclei. Key advances include (1) the inclusion of stellar and binary evolution in a self-consistent manner, (2) proper treatment of the anisotropic Galactic tidal field, (3) numerous technical enhancements in the treatment of binary dynamics and interactions, and (4) full support for the special-purpose GRAPE-4 hardware, boosting the program's performance by a factor of 10-100 over the accelerated version. The data-reduction and analysis tools in Starlab were also substantially expanded. A Starlab Web site (http://www.sns.ias.edu/-starlab) was created and developed. The site contains detailed information on the structure and function of the various tools that comprise the package, as well as download information, "how to" tips and examples of common operations, demonstration programs, animations, etc. All versions of the software are freely distributed to all interested users, along with detailed installation instructions.

  18. Absolute Spectrophotometry of 237 Open Cluster Stars

    NASA Astrophysics Data System (ADS)

    Clampitt, L.; Burstein, D.

    1994-12-01

    We present absolute spectrophotometry of 237 stars in 7 nearby open clusters: Hyades, Pleiades, Alpha Persei, Praesepe, Coma Berenices, IC 4665, and M 39. The observations were taken using the Wampler single-channel scanner (Wampler 1966) on the Crossley 0.9m telescope at Lick Observatory from July 1973 through December 1974. 21 bandpasses spanning the spectral range 3500 Angstroms to 7780 Angstroms were observed for each star, with bandwiths ranging from 32Angstroms to 64 Angstroms. Data are standardized to the Hayes--Latham (1975) system. Our measurements are compared to filter colors on the Johnson BV, Stromgren ubvy, and Geneva U V B_1 B_2 V_1 G systems, as well as to spectrophotometry of a few stars published by Gunn, Stryker & Tinsley and in the Spectrophotometric Standards Catalog (Adelman; as distributed by the NSSDC). Both internal and external comparisons to the filter systems indicate a formal statistical accuracy per bandpass of 0.01 to 0.02 mag, with apparent larger ( ~ 0.03 mag) differences in absolute calibration between this data set and existing spectrophotometry. These data will comprise part of the spectrophotometry that will be used to calibrate the Beijing-Arizona-Taipei-Connecticut Color Survey of the Sky (see separate paper by Burstein et al. at this meeting).

  19. HUBBLE SPIES HUGE CLUSTERS OF STARS FORMED

    NASA Technical Reports Server (NTRS)

    2002-01-01

    BY ANCIENT ENCOUNTER This stunningly beautiful image [right] taken with the NASA Hubble Space Telescope shows the heart of the prototypical starburst galaxy M82. The ongoing violent star formation due to an ancient encounter with its large galactic neighbor, M81, gives this galaxy its disturbed appearance. The smaller picture at upper left shows the entire galaxy. The image was taken in December 1994 by the Kitt Peak National Observatory's 0.9-meter telescope. Hubble's view is represented by the white outline in the center. In the Hubble image, taken by the Wide Field and Planetary Camera 2, the huge lanes of dust that crisscross M82's disk are another telltale sign of the flurry of star formation. Below the center and to the right, a strong galactic wind is spewing knotty filaments of hydrogen and nitrogen gas. More than 100 super star clusters -- very bright, compact groupings of about 100,000 stars -- are seen in this detailed Hubble picture as white dots sprinkled throughout M82's central region. The dark region just above the center of the picture is a huge dust cloud. A collaboration of European and American scientists used these clusters to date the ancient interaction between M82 and M81. About 600 million years ago, a region called 'M82 B' (the bright area just below and to the left of the central dust cloud) exploded with new stars. Scientists have discovered that this ancient starburst was triggered by the violent encounter with M81. M82 is a bright (eighth magnitude), nearby (12 million light-years from Earth) galaxy in the constellation Ursa Major (the Great Bear). The Hubble picture was taken Sept. 15, 1997. The natural-color composite was constructed from three Wide Field and Planetary Camera 2 exposures, which were combined in chromatic order: 4,250 seconds through a blue filter (428 nm); 2,800 seconds through a green filter (520 nm); and 2,200 seconds through a red (820 nm) filter. Credits for Hubble image: NASA, ESA, R. de Grijs (Institute of

  20. Hypervelocity stars from young stellar clusters in the Galactic Centre

    NASA Astrophysics Data System (ADS)

    Fragione, G.; Capuzzo-Dolcetta, R.; Kroupa, P.

    2017-01-01

    The enormous velocities of the so called hypervelocity stars (HVSs) derive, likely, from close interactions with massive black holes, binary stars encounters or supernova explosions. In this paper, we investigate the origin of hypervelocity stars as consequence of the close interaction between the Milky Way central massive black hole and a passing-by young stellar cluster. We found that both single and binary HVSs may be generated in a burst-like event, as the cluster passes near the orbital pericentre. High velocity stars will move close to the initial cluster orbital plane and in the direction of the cluster orbital motion at the pericentre. The binary fraction of these HVS jets depends on the primordial binary fraction in the young cluster. The level of initial mass segregation determines the value of the average mass of the ejected stars. Some binary stars will merge, continuing their travel across and out of the Galaxy as blue stragglers.

  1. Star clusters as laboratories for stellar and dynamical evolution.

    PubMed

    Kalirai, Jason S; Richer, Harvey B

    2010-02-28

    Open and globular star clusters have served as benchmarks for the study of stellar evolution owing to their supposed nature as simple stellar populations of the same age and metallicity. After a brief review of some of the pioneering work that established the importance of imaging stars in these systems, we focus on several recent studies that have challenged our fundamental picture of star clusters. These new studies indicate that star clusters can very well harbour multiple stellar populations, possibly formed through self-enrichment processes from the first-generation stars that evolved through post-main-sequence evolutionary phases. Correctly interpreting stellar evolution in such systems is tied to our understanding of both chemical-enrichment mechanisms, including stellar mass loss along the giant branches, and the dynamical state of the cluster. We illustrate recent imaging, spectroscopic and theoretical studies that have begun to shed new light on the evolutionary processes that occur within star clusters.

  2. The Prevalence and Impact of Wolf-Rayet Stars in Emerging Massive Star Clusters

    NASA Astrophysics Data System (ADS)

    Sokal, Kimberly R.; Johnson, Kelsey E.; Indebetouw, Rémy; Massey, Philip

    2016-08-01

    We investigate Wolf-Rayet (WR) stars as a source of feedback contributing to the removal of natal material in the early evolution of massive star clusters. Despite previous work suggesting that massive star clusters clear out their natal material before the massive stars evolve into the WR phase, WR stars have been detected in several emerging massive star clusters. These detections suggest that the timescale for clusters to emerge can be at least as long as the time required to produce WR stars (a few million years), and could also indicate that WR stars may be providing the tipping point in the combined feedback processes that drive a massive star cluster to emerge. We explore the potential overlap between the emerging phase and the WR phase with an observational survey to search for WR stars in emerging massive star clusters hosting WR stars. We select candidate emerging massive star clusters from known radio continuum sources with thermal emission and obtain optical spectra with the 4 m Mayall Telescope at Kitt Peak National Observatory and the 6.5 m MMT.4 We identify 21 sources with significantly detected WR signatures, which we term “emerging WR clusters.” WR features are detected in ˜50% of the radio-selected sample, and thus we find that WR stars are commonly present in currently emerging massive star clusters. The observed extinctions and ages suggest that clusters without WR detections remain embedded for longer periods of time, and may indicate that WR stars can aid, and therefore accelerate, the emergence process.

  3. The evolutionary tracks of young massive star clusters

    SciTech Connect

    Pfalzner, S.; Steinhausen, M.; Vincke, K.; Menten, K.; Parmentier, G.

    2014-10-20

    Stars mostly form in groups consisting of a few dozen to several ten thousand members. For 30 years, theoretical models have provided a basic concept of how such star clusters form and develop: they originate from the gas and dust of collapsing molecular clouds. The conversion from gas to stars being incomplete, the leftover gas is expelled, leading to cluster expansion and stars becoming unbound. Observationally, a direct confirmation of this process has proved elusive, which is attributed to the diversity of the properties of forming clusters. Here we take into account that the true cluster masses and sizes are masked, initially by the surface density of the background and later by the still present unbound stars. Based on the recent observational finding that in a given star-forming region the star formation efficiency depends on the local density of the gas, we use an analytical approach combined with N-body simulations to reveal evolutionary tracks for young massive clusters covering the first 10 Myr. Just like the Hertzsprung-Russell diagram is a measure for the evolution of stars, these tracks provide equivalent information for clusters. Like stars, massive clusters form and develop faster than their lower-mass counterparts, explaining why so few massive cluster progenitors are found.

  4. Spectral Types of Field and Cluster O-Type Stars

    NASA Astrophysics Data System (ADS)

    van den Bergh, Sidney

    2004-10-01

    The recent catalog of spectral types of Galactic O-type stars by Maíz-Apellániz et al. is used to study the differences between the frequencies of various subtypes of O-type stars in the field, in OB associations, and among runaway stars. At a high level of statistical significance, the data show that O stars in clusters and associations have earlier types (and, hence, presumably larger masses or younger ages) than those that are situated in the general field. Furthermore, it is found that the distribution of spectral subtypes among runaway O stars is indistinguishable from that among field stars and differs significantly from that of the O-type stars that are situated in clusters and associations. The difference is in the sense that runaway O stars, on average, have later subtypes than do those that are still located in clusters and associations.

  5. POTASSIUM IN GLOBULAR CLUSTER STARS: COMPARING NORMAL CLUSTERS TO THE PECULIAR CLUSTER NGC 2419

    SciTech Connect

    Carretta, E.; Bragaglia, A.; Sollima, A.; Gratton, R. G.; Lucatello, S.; D'Orazi, V.; Sneden, C. E-mail: angela.bragaglia@oabo.inaf.it E-mail: raffaele.gratton@oapd.inaf.it E-mail: valentina.dorazi@mq.edu.au

    2013-05-20

    Two independent studies recently uncovered two distinct populations among giants in the distant, massive globular cluster (GC) NGC 2419. One of these populations has normal magnesium (Mg) and potassium (K) abundances for halo stars: enhanced Mg and roughly solar K. The other population has extremely depleted Mg and very enhanced K. To better anchor the peculiar NGC 2419 chemical composition, we have investigated the behavior of K in a few red giant branch stars in NGC 6752, NGC 6121, NGC 1904, and {omega} Cen. To verify that the high K abundances are intrinsic and not due to some atmospheric features in giants, we also derived K abundances in less evolved turn-off and subgiant stars of clusters 47 Tuc, NGC 6752, NGC 6397, and NGC 7099. We normalized the K abundance as a function of the cluster metallicity using 21 field stars analyzed in a homogeneous manner. For all GCs of our sample, the stars lie in the K-Mg abundance plane on the same locus occupied by the Mg-normal population in NGC 2419 and by field stars. This holds for both giants and less-evolved stars. At present, NGC 2419 seems unique among GCs.

  6. Tracing galaxy evolution through resolved stellar populations and star clusters

    NASA Astrophysics Data System (ADS)

    Silva-Villa, E.

    2011-09-01

    Field stars and star clusters contain a big part of the galaxy’s history. To understand galaxy formation and evolution we need then to understand the parts of which galaxies are composed. It has commonly been assumed that most stars formed in clusters. However, the connection between these two systems is not clear, and the fraction of actual star formation happening in clusters is still uncertain. Through this thesis, we aim to use field stars and star clusters to attack different problems regarding galaxy formation and evolution, named: 1. the cluster formation efficiency and its (co-)relation with environment (i.e. the host galaxy), 2. the star formation rate in the arms and inter-arm regions of spiral galaxies, and 3. the indications of a possible interaction between two galaxies observed through their resolved stellar populations. We performed a systematic and homogeneous study over the galaxies NGC45, NGC1313, NGC4395, NGC5236 and NGC7793, where star clusters and field stars are analyze separately. For this aim, we used Hubble Space Telescope observations in the optical bands U, B, V and I, using the Advanced Camera for Surveys and the Wide Field Planetary Camera 2. Standard photometric procedures are use to study the properties of these two main parts of the galaxies. However, incompleteness constrains our results to ages younger than 100 Myr. Following the synthetic CMD method we recovered the star formation history for the last 100 Myr over the five galaxies. Comparing observed clusters properties with simple stellar population models, we estimate ages and masses of star clusters. We observe that the galaxies NGC5236 and NGC1313 show higher star and cluster formation rates, while NGC45, NGC4395 and NGC7793 show lower values. We found that the actual fraction of star formation happening in clusters presents low values (< 10%), contrary to common assumptions, however in agreement with studies in other galaxies. Observations of the surface star formation

  7. HUBBLE SPIES GIANT STAR CLUSTERS NEAR GALACTIC CENTER

    NASA Technical Reports Server (NTRS)

    2002-01-01

    Penetrating 25,000 light-years of obscuring dust and myriad stars, NASA's Hubble Space Telescope has provided the clearest view yet of a pair of the largest young clusters of stars inside our Milky Way galaxy, located less than 100 light-years from the very center of the Galaxy. Having the equivalent mass greater than 10,000 stars like our sun, the monster clusters are ten times larger than typical young star clusters scattered throughout our Milky Way. Both clusters are destined to be ripped apart in just a few million years by gravitational tidal forces in the Galaxy's core. But in the brief time they are around, they shine more brightly than any other star cluster in the Galaxy. Arches cluster (left): The more compact Arches cluster is so dense, over 100,000 of its stars would fill a spherical region in space whose radius is the distance between the Sun and its nearest neighbor, the star Alpha Centauri, 4.3 light-years away. At least 150 of its stars are among the brightest ever seen in the Galaxy. Quintuplet cluster (right): This 4-million-year-old cluster is more dispersed than the Arches cluster. It has stars on the verge of blowing up as supernovae. It is the home of the brightest star seen in the Galaxy, called the Pistol star. Both pictures were taken in infrared light by Hubble's NICMOS camera in September 1997. The false colors correspond to infrared wavelengths. The galactic center stars are white, the red stars are enshrouded in dust or behind dust, and the blue stars are foreground stars between us and the Milky Way's center. The clusters are hidden from direct view behind black dust clouds in the constellation Sagittarius. If the clusters could be seen from Earth they would appear to the naked eye as a pair of third magnitude 'stars,' 1/6th of a full moon's diameter apart. Credit: Don Figer (Space Telescope Science Institute) and NASA

  8. The High-mass Truncation of the Star Cluster Mass Function: Limits on Massive Cluster Formation

    NASA Astrophysics Data System (ADS)

    Johnson, L. C.; PHAT Team

    2017-01-01

    Long-lived star clusters serve as useful tracers of star formation, and massive clusters in particular are often associated with vigorous star formation activity. We examine how massive cluster formation varies as a function of star formation surface density (ΣSFR) by comparing cluster populations from galaxies that span a wide range of characteristic ΣSFR values. The Panchromatic Hubble Andromeda Treasury (PHAT) survey yielded an unparalleled census of young star clusters in M31 and allows us to examine massive cluster formation in a low intensity star formation environment. We measure the cluster mass function for a sample of 840 young star clusters with ages between 10-300 Myr. The data show clear evidence of a high-mass truncation: only 15 clusters more massive than 104 M⊙ are observed, compared to ~100 expected for a canonical M-2 power-law mass function with the same total number of clusters above the catalog completeness limit. Adopting a Schechter function parameterization, we fit a characteristic truncation mass (Mc) of 8.5×103 M⊙ — the lowest truncation mass ever reported. When combined with previous mass function results, we find that the cluster mass function truncation correlates strongly with the star formation rate surface density, where Mc ∝ ΣSFR1.3. We also find evidence that suggests the observed Mc-ΣSFR relation also holds for globular clusters, linking the two populations via a common formation pathway.

  9. Pulsar-irradiated stars in dense globular clusters

    NASA Technical Reports Server (NTRS)

    Tavani, Marco

    1992-01-01

    We discuss the properties of stars irradiated by millisecond pulsars in 'hard' binaries of dense globular clusters. Irradiation by a relativistic pulsar wind as in the case of the eclipsing millisecond pulsar PSR 1957+20 alter both the magnitude and color of the companion star. Some of the blue stragglers (BSs) recently discovered in dense globular clusters can be irradiated stars in binaries containing powerful millisecond pulsars. The discovery of pulsar-driven orbital modulations of BS brightness and color with periods of a few hours together with evidence for radio and/or gamma-ray emission from BS binaries would valuably contribute to the understanding of the evolution of collapsed stars in globular clusters. Pulsar-driven optical modulation of cluster stars might be the only observable effect of a new class of binary pulsars, i.e., hidden millisecond pulsars enshrouded in the evaporated material lifted off from the irradiated companion star.

  10. Clustered star formation and the origin of stellar masses.

    PubMed

    Pudritz, Ralph E

    2002-01-04

    Star clusters are ubiquitous in galaxies of all types and at all stages of their evolution. We also observe them to be forming in a wide variety of environments, ranging from nearby giant molecular clouds to the supergiant molecular clouds found in starburst and merging galaxies. The typical star in our galaxy and probably in others formed as a member of a star cluster, so star formation is an intrinsically clustered and not an isolated phenomenon. The greatest challenge regarding clustered star formation is to understand why stars have a mass spectrum that appears to be universal. This review examines the observations and models that have been proposed to explain these fundamental issues in stellar formation.

  11. UV spectroscopy of young star clusters

    NASA Astrophysics Data System (ADS)

    Maraston, Claudia

    We propose to take spectra of young star clusters (t < 1 Gyr) in the Magellanic Clouds. These data will serve to improve and extend the calibration of the UV spectral index system for stellar population models, which we have built with IUE spectra from the data bases of Fanelli et al. (1992) and Cassatella et al. (1987). We have developed evolutionary population synthesis models of the most relevant absorption features of stellar systems with ages in the range 1 Myr to 1 Gyr, covering the most important elements including C, Si, Fe and Mg (Nieves & Maraston 2004). The new data will allow the calibration of these spectral indices for different chemical abundances and ages. The calibrated stellar population models will provide an important tool to interpret spectra of high redshift galaxies

  12. The era of star formation in galaxy clusters

    SciTech Connect

    Brodwin, M.; Stanford, S. A.; Gonzalez, Anthony H.; Mancone, C. L.; Gettings, D. P.; Zeimann, G. R.; Snyder, G. F.; Ashby, M. L. N.; Pope, A.; Alberts, S.; Eisenhardt, P. R.; Stern, D.; Moustakas, L. A.; Brown, M. J. I.; Chary, R.-R.; Dey, Arjun; Galametz, A.; Jannuzi, B. T.; Miller, E. D.; Moustakas, J.

    2013-12-20

    We analyze the star formation properties of 16 infrared-selected, spectroscopically confirmed galaxy clusters at 1 < z < 1.5 from the Spitzer/IRAC Shallow Cluster Survey (ISCS). We present new spectroscopic confirmation for six of these high-redshift clusters, five of which are at z > 1.35. Using infrared luminosities measured with deep Spitzer/Multiband Imaging Photometer for Spitzer observations at 24 μm, along with robust optical + IRAC photometric redshifts and spectral-energy-distribution-fitted stellar masses, we present the dust-obscured star-forming fractions, star formation rates, and specific star formation rates in these clusters as functions of redshift and projected clustercentric radius. We find that z ∼ 1.4 represents a transition redshift for the ISCS sample, with clear evidence of an unquenched era of cluster star formation at earlier times. Beyond this redshift, the fraction of star-forming cluster members increases monotonically toward the cluster centers. Indeed, the specific star formation rate in the cores of these distant clusters is consistent with field values at similar redshifts, indicating that at z > 1.4 environment-dependent quenching had not yet been established in ISCS clusters. By combining these observations with complementary studies showing a rapid increase in the active galactic nucleus (AGN) fraction, a stochastic star formation history, and a major merging episode at the same epoch in this cluster sample, we suggest that the starburst activity is likely merger-driven and that the subsequent quenching is due to feedback from merger-fueled AGNs. The totality of the evidence suggests we are witnessing the final quenching period that brings an end to the era of star formation in galaxy clusters and initiates the era of passive evolution.

  13. Abundances in Globular Cluster Red Giant Stars

    NASA Astrophysics Data System (ADS)

    Cavallo, R. M.

    1997-12-01

    Observations of globular cluster red giant branch (RGB) stars have shown star-to-star variations in the abundances of C, N, O, Na, Mg, and Al, contrary to predictions of standard stellar evolutionary theory. I have modeled the variations in the abundance profiles around the hydrogen-burning shell (H shell) of metal-poor red giant stars by combining four RGB stellar evolutionary sequences of different metallicities with a detailed nuclear reaction network. This approach has significant advantages over previous research: (1) it allows for the variation in the temperature and density around the H shell; (2) it follows the effects of the changing H-shell structure as the sequence evolves; (3) it accounts for the effect of the metallicity on the abundance profiles; (4) it allows the reaction rates to be varied so that their uncertainties may be explored. The results are in good qualitative agreement with the observations. All the models show a region above the H shell in which first C, then O, is depleted in the CN and ON nuclear burning cycles. Within the C-depleted region, the (12) C/(13) C ratio is reduced to its equilibrium value. Just above the O-depleted region, Na is enhanced from proton captures on (22) Ne. In brighter models, Na becomes greatly enhanced within the O-depleted region as the NeNa cycle converts (20) Ne into (23) Na before attaining equilibrium inside the H shell. The more metal-poor models also show Al being increased around the H shell, first from (25,26) Mg, then from (24) Mg in the MgAl cycle. Despite the diminution (24) Mg suffers in synthesizing Al, the models show its abundance is increased due to the NeNa-cycle breakout reaction, (23) Na(p,γ)(24) Mg. This latter result is at odds with observations that show (24) Mg is depleted in a sample of M 13 and NGC 6752 giants (Shetrone 1996, 1997).

  14. Globular cluster formation with multiple stellar populations from hierarchical star cluster complexes

    NASA Astrophysics Data System (ADS)

    Bekki, Kenji

    2017-01-01

    Most old globular clusters (GCs) in the Galaxy are observed to have internal chemical abundance spreads in light elements. We discuss a new GC formation scenario based on hierarchical star formation within fractal molecular clouds. In the new scenario, a cluster of bound and unbound star clusters (`star cluster complex', SCC) that have a power-law cluster mass function with a slope (β) of 2 is first formed from a massive gas clump developed in a dwarf galaxy. Such cluster complexes and β = 2 are observed and expected from hierarchical star formation. The most massive star cluster (`main cluster'), which is the progenitor of a GC, can accrete gas ejected from asymptotic giant branch (AGB) stars initially in the cluster and other low-mass clusters before the clusters are tidally stripped or destroyed to become field stars in the dwarf. The SCC is initially embedded in a giant gas hole created by numerous supernovae of the SCC so that cold gas outside the hole can be accreted onto the main cluster later. New stars formed from the accreted gas have chemical abundances that are different from those of the original SCC. Using hydrodynamical simulations of GC formation based on this scenario, we show that the main cluster with the initial mass as large as [2 - 5] × 105M⊙ can accrete more than 105M⊙ gas from AGB stars of the SCC. We suggest that merging of hierarchical star cluster complexes can play key roles in stellar halo formation around GCs and self-enrichment processes in the early phase of GC formation.

  15. Stellar interactions in dense and sparse star clusters

    NASA Astrophysics Data System (ADS)

    Olczak, C.; Pfalzner, S.; Eckart, A.

    2010-01-01

    Context. Stellar encounters potentially affect the evolution of the protoplanetary discs in the Orion Nebula Cluster (ONC). However, the role of encounters in other cluster environments is less known. Aims: We investigate the effect of the encounter-induced disc-mass loss in different cluster environments. Methods: Starting from an ONC-like cluster we vary the cluster size and density to determine the correlation of the collision time scale and disc-mass loss. We use the nbody6++ code to model the dynamics of these clusters and analyse the disc-mass loss due to encounters. Results: We find that the encounter rate strongly depends on the cluster density but remains rather unaffected by the size of the stellar population. This dependency translates directly into the effect on the encounter-induced disc-mass loss. The essential outcome of the simulations are: i) even in clusters of four times lower density than the ONC, the effect of encounters is still apparent; ii) the density of the ONC itself marks a threshold: in less dense and less massive clusters it is the massive stars that dominate the encounter-induced disc-mass loss, whereas in denser and more massive clusters the low-mass stars play the major role for the disc-mass removal. Conclusions: It seems that in the central regions of young dense star clusters - the common sites of star formation - stellar encounters do affect the evolution of the protoplanetary discs. With higher cluster density low-mass stars become more heavily involved in this process. These results can also be applied to extreme stellar systems: in the case of the Arches cluster one would expect stellar encounters to destroy the discs of most of the low- and high-mass stars in several hundred thousand years, whereas intermediate mass stars are able to retain their discs to some extent even under these harsh environmental conditions.

  16. Variable stars in large Magellanic cloud globular clusters. III. Reticulum

    SciTech Connect

    Kuehn, Charles A.; Dame, Kyra; Smith, Horace A.; De Lee, Nathan E-mail: damekyra@msu.edu E-mail: nathan.delee@vanderbilt.edu; and others

    2013-06-01

    This is the third in a series of papers studying the variable stars in old globular clusters in the Large Magellanic Cloud. The primary goal of this series is to look at how the characteristics and behavior of RR Lyrae stars in Oosterhoff-intermediate systems compare to those of their counterparts in Oosterhoff-I/II systems. In this paper we present the results of our new time-series BVI photometric study of the globular cluster Reticulum. We found a total of 32 variables stars (22 RRab, 4 RRc, and 6 RRd stars) in our field of view. We present photometric parameters and light curves for these stars. We also present physical properties, derived from Fourier analysis of light curves, for some of the RR Lyrae stars. We discuss the Oosterhoff classification of Reticulum and use our results to re-derive the distance modulus and age of the cluster.

  17. SEARCH FOR RED DWARF STARS IN GLOBULAR CLUSTER NGC 6397

    NASA Technical Reports Server (NTRS)

    2002-01-01

    Left A NASA Hubble Space Telescope image of a small region (1.4 light-years across) in the globular star cluster NGC 6397. Simulated stars (diamonds) have been added to this view of the same region of the cluster to illustrate what astronomers would have expected to see if faint red dwarf stars were abundant in the Milky Way Galaxy. The field would then contain 500 stars, according to theoretical calculations. Right The unmodified HST image shows far fewer stars than would be expected, according to popular theories of star formation. HST resolves about 200 stars. The stellar density is so low that HST can literally see right through the cluster and resolve far more distant background galaxies. From this observation, scientists have identified the surprising cutoff point below which nature apparently doesn't make many stars smaller that 1/5 the mass of our Sun. These HST findings provide new insights into star formation in our Galaxy. Technical detail:The globular cluster NGC 6397, one of the nearest and densest agglomerations of stars, is located 7,200 light-years away in the southern constellation Ara. This visible-light picture was taken on March 3, 1994 with the Wide Field Planetary Camera 2, as part the HST parallel observing program. Credit: F. Paresce, ST ScI and ESA and NASA

  18. The INfrared Survey of Young Nebulous Clusters (IN-SYNC): Surveying the Dynamics and Star Formation Histories of Young Clusters with APOGEE

    NASA Astrophysics Data System (ADS)

    Covey, Kevin R.; Cottaar, Michiel; Foster, Jonathan B.; Da Rio, Nicola; Tan, Jonathan; Meyer, Michael; Nidever, David L.; Flaherty, Kevin M.; Arce, Hector G.; Rebull, Luisa M.; Chojnowski, S. Drew; Frinchaboy, Peter M.; Hearty, Fred R.; Majewski, Steven R.; Skrutskie, Michael F.; Stassun, Keivan; Wilson, John C.; Zasowski, Gail

    2015-01-01

    Young clusters are the most prolific sites of star formation in the Milky Way, but demographic studies indicate that relatively few of the Milky Way's stellar clusters persist as bound structures for 100 Myrs or longer. Uniform & precise measurements of the stellar populations and internal dynamics of these regions are difficult to obtain, however, particularly for extremely young clusters whose optical visibility is greatly hampered by their parental molecular cloud. The INfrared Survey of Young Nebulous Clusters (IN-SYNC), an SDSS-III ancillary science program, leverages the stability and multiplex capability of the APOGEE spectrograph to obtain high resolution spectra at near-infrared wavelengths, where photospheric emission is better able to penetrate the dusty shrouds that surround sites of active star formation. We summarize our recent measurements of the kinematics and stellar populations of IC 348 and NGC 1333, two young clusters in the Perseus Molecular Cloud, and of the members of the Orion Nebula Cluster (ONC) and L1641 filament in the Orion molecular complex. These measurements highlight the dynamically 'warm' environment within these young clusters, and suggest a range of stellar radii within these quasi-single-age populations. We close with a preview of plans for continuing this work as part of the APOGEE-2 science portfolio: self-consistent measurements of the kinematics and star formation histories for clusters spanning a range of initial conditions and ages will provide a opportunity to disentangle the mechanisms that drive the formation and dissolution of sites of active star formation.

  19. Simulating the Birth of Massive Star Clusters: Is Destruction Inevitable?

    NASA Astrophysics Data System (ADS)

    Rosen, Anna

    2013-10-01

    Very early in its operation, the Hubble Space Telescope {HST} opened an entirely new frontier: study of the demographics and properties of star clusters far beyond the Milky Way. However, interpretation of HST's observations has proven difficult, and has led to the development of two conflicting models. One view is that most massive star clusters are disrupted during their infancy by feedback from newly formed stars {i.e., "infant mortality"}, independent of cluster mass or environment. The other model is that most star clusters survive their infancy and are disrupted later by mass-dependent dynamical processes. Since observations at present have failed to discriminate between these views, we propose a theoretical investigation to provide new insight. We will perform radiation-hydrodynamic simulations of the formation of massive star clusters, including for the first time a realistic treatment of the most important stellar feedback processes. These simulations will elucidate the physics of stellar feedback, and allow us to determine whether cluster disruption is mass-dependent or -independent. We will also use our simulations to search for observational diagnostics that can distinguish bound from unbound clusters, and to predict how cluster disruption affects the cluster luminosity function in a variety of galactic environments.

  20. Star Clusters in Intermediate-Age Galaxy Merger Remnants

    NASA Astrophysics Data System (ADS)

    Miller, Bryan W.; Trancho, G.; Schweizer, F.

    2011-01-01

    Studies of globular cluster systems play a critical role in our understanding of galaxy formation. Star clusters are useful tracers of major star-formation events in galaxies since they are compact, relatively easy to detect, and have properties well described by simple-stellar-population models. Imaging with the Hubble Space Telescope has revealed that young compact star clusters are formed copiously during galaxy mergers, strengthening theories in which giant elliptical galaxies are formed through mergers of spirals. However, the formation and evolution of globular cluster systems is still not well understood. We should be able to observe how cluster systems evolve from the very young systems with power-law luminosity functions to old systems with log-normal luminosity functions like those observed in old elliptical galaxies. Finding intermediate-age cluster systems would constrain theories of cluster formation and destruction (evaporation, shocking, dynamical friction) as well as show the significance of merger events in the histories of galaxies. We present results of combining HST optical photometry with ground-based K-band photometry from NIRI and Flamingos-I on Gemini to study the star cluster systems of five intermediate-age merger remnants. The galaxies were chosen based on blue colors and fine structure such as shells and ripples that are indicative of past interactions. We find evidence for star clusters with ages consistent with the estimated merger ages. The properties of the star clusters systems and implications for galaxy and star cluster formation will be discussed. Based on observations obtained at the Gemini Observatory, which is operated by the Association of Universities for Research in Astronomy, Inc., under a cooperative agreement with the NSF on behalf of the Gemini partnership: the National Science Foundation (United States), the Particle Physics and Astronomy Research Council (United Kingdom), the National Research Council (Canada

  1. The efficiency of star formation in clustered and distributed regions

    NASA Astrophysics Data System (ADS)

    Bonnell, Ian A.; Smith, Rowan J.; Clark, Paul C.; Bate, Matthew R.

    2011-02-01

    We investigate the formation of both clustered and distributed populations of young stars in a single molecular cloud. We present a numerical simulation of a 104 M⊙ elongated, turbulent, molecular cloud and the formation of over 2500 stars. The stars form both in stellar clusters and in a distributed mode, which is determined by the local gravitational binding of the cloud. A density gradient along the major axis of the cloud produces bound regions that form stellar clusters and unbound regions that form a more distributed population. The initial mass function (IMF) also depends on the local gravitational binding of the cloud with bound regions forming full IMFs whereas in the unbound, distributed regions the stellar masses cluster around the local Jeans mass and lack both the high-mass and the low-mass stars. The overall efficiency of star formation is ≈ 15 per cent in the cloud when the calculation is terminated, but varies from less than 1 per cent in the regions of distributed star formation to ≈ 40 per cent in regions containing large stellar clusters. Considering that large-scale surveys are likely to catch clouds at all evolutionary stages, estimates of the (time-averaged) star formation efficiency (SFE) for the giant molecular cloud reported here is only ≈ 4 per cent. This would lead to the erroneous conclusion of slow star formation when in fact it is occurring on a dynamical time-scale.

  2. Hierarchical Star Formation in Turbulent Media: Evidence from Young Star Clusters

    NASA Astrophysics Data System (ADS)

    Grasha, Kathryn; Elmegreen, Bruce; Calzetti, Daniela

    2017-01-01

    We present an analysis of the positions and ages of star clusters in eight local galaxies and find a correlation between the age difference and separation of cluster pairs. We infer that cluster formation is correlated in time such that clusters that are close to each have similar ages. In addition, the age between cluster pairs increases with their separation to the 0.3 - 0.6 power, close to the expected slope of 0.5 that would arise in a turbulent-driven interstellar medium. This suggests that not only is star formation hierarchical both in space and in time, but that the duration of star formation depends on the region of interest: smaller regions will form stars over a shorter time frame whereas larger regions form stars over a longer time frame.

  3. Star Cluster Formation in Cosmological Simulations. I. Properties of Young Clusters

    NASA Astrophysics Data System (ADS)

    Li, Hui; Gnedin, Oleg Y.; Gnedin, Nickolay Y.; Meng, Xi; Semenov, Vadim A.; Kravtsov, Andrey V.

    2017-01-01

    We present a new implementation of star formation in cosmological simulations by considering star clusters as a unit of star formation. Cluster particles grow in mass over several million years at the rate determined by local gas properties, with high time resolution. The particle growth is terminated by its own energy and momentum feedback on the interstellar medium. We test this implementation for Milky Way-sized galaxies at high redshift by comparing the properties of model clusters with observations of young star clusters. We find that the cluster initial mass function is best described by a Schechter function rather than a single power law. In agreement with observations, at low masses the logarithmic slope is α ≈ 1.8{--}2, while the cutoff at high mass scales with the star formation rate (SFR). A related trend is a positive correlation between the surface density of the SFR and fraction of stars contained in massive clusters. Both trends indicate that the formation of massive star clusters is preferred during bursts of star formation. These bursts are often associated with major-merger events. We also find that the median timescale for cluster formation ranges from 0.5 to 4 Myr and decreases systematically with increasing star formation efficiency. Local variations in the gas density and cluster accretion rate naturally lead to the scatter of the overall formation efficiency by an order of magnitude, even when the instantaneous efficiency is kept constant. Comparison of the formation timescale with the observed age spread of young star clusters provides an additional important constraint on the modeling of star formation and feedback schemes.

  4. New Star Clusters Discovered in the GLIMPSE Survey

    NASA Astrophysics Data System (ADS)

    Mercer, E. P.; Clemens, D. P.; Meade, M. R.; Babler, B. L.; Indebetouw, R.; Whitney, B. A.; Watson, C.; Wolfire, M. G.; Wolff, M. J.; Bania, T. M.; Benjamin, R. A.; Cohen, M.; Dickey, J. M.; Jackson, J. M.; Kobulnicky, H. A.; Mathis, J. S.; Stauffer, J. R.; Stolovy, S. R.; Uzpen, B.; Churchwell, E. B.

    2005-12-01

    A systematic and automated search of the extensive GLIMPSE mid-infrared survey data of the inner Galaxy was carried out to uncover new star clusters. This search has yielded 59 new clusters. Using our automated search algorithm, these clusters were identified as significant localized overdensities in the GLIMPSE point-source catalog (GLMC) and archive (GLMA). Subsequent visual inspection of the GLIMPSE image mosaics confirmed the existence of these clusters plus an additional 33 heavily embedded clusters missed by our detection algorithm, for a total of 92 newly discovered clusters. These previously uncataloged clusters range in type from heavily embedded to fully exposed clusters. More than half of the clusters have memberships exceeding 35 stars, and nearly all the clusters have diameters of 3' or less. The Galactic latitude distribution of the clusters reveals that the majority are concentrated toward the Galactic midplane. There is an asymmetry in the number of clusters located above and below the midplane, with more clusters detected below the midplane. We also observe an asymmetry in the number of clusters detected in the northern and southern halves of the Galaxy, with more than twice as many clusters detected in the south.

  5. Blue straggler stars in Galactic open clusters and the effect of field star contamination

    NASA Astrophysics Data System (ADS)

    Carraro, G.; Vázquez, R. A.; Moitinho, A.

    2008-05-01

    Context: We investigate the distribution of blue straggler stars in the field of three open star clusters. Aims: The main purpose is to highlight the crucial role played by general Galactic disk fore-/back-ground field stars, which are often located in the same region of the color magnitude diagram as blue straggler stars. Methods: We analyze photometry taken from the literature of 3 open clusters of intermediate/old age rich in blue straggler stars, which are projected in the direction of the Perseus arm, and study their spatial distribution and the color magnitude diagram. Results: As expected, we find that a large portion of the blue straggler population in these clusters are simply young field stars belonging to the spiral arm. This result has important consequences on the theories of the formation and statistics of blue straggler stars in different population environments: open clusters, globular clusters, or dwarf galaxies. Conclusions: As previously emphasized by many authors, a detailed membership analysis is mandatory before comparing the blue straggler population in star clusters to theoretical models. Moreover, these sequences of young field stars (blue plumes) are potentially powerful tracers of Galactic structure and they require further consideration.

  6. Initial Dynamical Evolution of Star Clusters with Tidal Field

    NASA Astrophysics Data System (ADS)

    Park, So-Myoung; Goodwin, Simon P.; Kim, Sungsoo S.

    2017-03-01

    Observations have been suggested that star clusters could form from the rapid collapse and violent relaxation of substructured distributions. We investigate the collapse of fractal stellar distributions in no, weak, and very strong tidal fields. We find that the rapid collapse of substructure into spherical clusters happens quickly with no or a weak tidal field, but very strong tidal fields prevent a cluster forming. However, we also find that dense Plummer spheres are also rapidly destroyed in strong tidal fields. We suggest that this is why the low-mass star clusters cannot survive near the galactic centre which has strong tidal field.

  7. Super Star Clusters: the Engines of Galactic Outflows

    NASA Astrophysics Data System (ADS)

    Lockhart, Kelly; Lu, Jessica R.; Kewley, Lisa; Kudritzki, Rolf; Barnes, Joshua Edward

    2015-08-01

    Winds in starburst galaxies are ubiquitous; however, we still do not understand how winds from individual star clusters unite into a large-scale galactic outflow. Recent work suggests that radiation pressure from young (<7 Myr) massive super star clusters (SSCs) may be a necessary first step in launching global starburst winds. We have begun a program using integral field spectroscopy with Keck/OSIRIS to investigate the winds from these very young clusters, and how energy is transferred from the stellar population to the surrounding medium to launch galactic-scale outflows. We present preliminary work on a sample of young massive clusters from the Antennae.

  8. The relation between the most-massive star and its parental star cluster mass

    NASA Astrophysics Data System (ADS)

    Weidner, C.; Kroupa, P.; Bonnell, I. A. D.

    2010-01-01

    We present a thorough literature study of the most-massive star, mmax, in several young star clusters in order to assess whether or not star clusters are populated from the stellar initial mass function (IMF) by random sampling over the mass range 0.01 <= m <= 150Msolar without being constrained by the cluster mass, Mecl. The data reveal a partition of the sample into lowest mass objects (Mecl <= 102Msolar), moderate mass clusters (102Msolar < Mecl <= 103Msolar) and rich clusters above 103Msolar. Additionally, there is a plateau of a constant maximal star mass (mmax ~ 25Msolar) for clusters with masses between 103Msolar and 4 × 103Msolar. Statistical tests of this data set reveal that the hypothesis of random sampling from the IMF between 0.01 and 150Msolar is highly unlikely for star clusters more massive than 102Msolar with a probability of p ~ 2 × 10-7 for the objects with Mecl between 102 and 103Msolar and p ~ 3 × 10-9 for the more massive star clusters. Also, the spread of mmax values at a given Mecl is smaller than expected from random sampling. We suggest that the basic physical process able to explain this dependence of stellar inventory of a star cluster on its mass may be the interplay between stellar feedback and the binding energy of the cluster-forming molecular cloud core. Given these results, it would follow that an integrated galactic IMF (IGIMF) sampled from such clusters would automatically be steeper in comparison to the IMF within individual star clusters.

  9. star formation rates of z > 1 galaxy clusters in the IRAC shallow cluster survey

    SciTech Connect

    Zeimann, Gregory R.; Stanford, S. A.; Brodwin, Mark; Gonzalez, Anthony H.; Mancone, Conor; Snyder, Gregory F.; Stern, Daniel; Eisenhardt, Peter; Dey, Arjun; Moustakas, John

    2013-12-20

    We present Hubble Space Telescope near-IR spectroscopy for 18 galaxy clusters at 1.0 Cluster Survey. We use Wide Field Camera 3 grism data to spectroscopically identify Hα emitters in both the cores of galaxy clusters as well as in field galaxies. We find a large cluster-to-cluster scatter in the star formation rates within a projected radius of 500 kpc, and many of our clusters (∼60%) have significant levels of star formation within a projected radius of 200 kpc. A stacking analysis reveals that dust reddening in these star-forming galaxies is positively correlated with stellar mass and may be higher in the field than the cluster at a fixed stellar mass. This may indicate a lower amount of gas in star-forming cluster galaxies than in the field population. Also, Hα equivalent widths of star-forming galaxies in the cluster environment are still suppressed below the level of the field. This suppression is most significant for lower mass galaxies (log M {sub *} < 10.0 M {sub ☉}). We therefore conclude that environmental effects are still important at 1.0 star-forming galaxies in galaxy clusters with log M {sub *} ≲ 10.0 M {sub ☉}.

  10. A peculiar object in M 51: fuzzy star cluster or a background galaxy?

    NASA Astrophysics Data System (ADS)

    Scheepmaker, R. A.; Lamers, H. J. G. L. M.; Larsen, S. S.; Anders, P.

    2008-01-01

    Aims: We study a peculiar object with a projected position close to the nucleus of M 51. It is unusually large for a star cluster in M 51 and we therefore investigate the three most likely options to explain this object: (a) a background galaxy, (b) a cluster in the disk of M 51 and (c) a cluster in M 51, but in front of the disk. Methods: We use broad-band images of the Advanced Camera for Surveys and the Near Infrared Camera and Multi-Object Spectrometer, both on board the Hubble Space Telescope, to study the properties of this object. Assuming the object is a star cluster, we fit the metallicity, age, mass and extinction using simple stellar population models. Assuming the object is a background galaxy, we estimate the extinction from the colour of the background around the object. We study the structural parameters of the object by fitting the spatial profile with analytical models. Results: We find de-reddened colours of the object which are bluer than expected for a typical elliptical galaxy, and the central surface brightness is brighter than the typical surface brightness of a disc galaxy. It is therefore not likely that the object is a background galaxy. Assuming the object is a star cluster in the disc of M 51, we estimate an age and mass of 0.7+0.1-0.1 Gyr and 2.2+0.3-0.3× 105~M⊙, respectively (with the extinction fixed to E(B-V)= 0.2). Considering the large size of the object, we argue that in this scenario we observe the cluster just prior to final dissolution. If we fit for the extinction as a free parameter, a younger age is allowed and the object is not close to final dissolution. Alternatively, the object could be a star cluster in M 51, but in front of the disc, with an age of 1.4+0.5-0.2 Gyr, mass M = 1.7+0.8-0.3× 105~M⊙. Its effective radius is between ~12-25 pc. This makes the object a “fuzzy star cluster”, raising the issue of how an object of this age would end up outside the disc. Based on observations made with the NASA/ESA Hubble

  11. Young Star Cluster Aglow With Mysterious X-Ray Cloud

    NASA Technical Reports Server (NTRS)

    2002-01-01

    At a distance of 6,000 light years from Earth, the star cluster RCW 38 is a relatively close star-forming region. This area is about 5 light years across, and contains thousands of hot, very young stars formed less than a million years ago, 190 of which exposed x-rays to Chandra. Enveloping the star cluster, the diffused cloud of x-rays shows an excess of high energy x-rays, which indicates that the x-rays come from trillion-volt electrons moving in a magnetic field. Such particles are typically produced by exploding stars, or in the strong magnetic fields around neutron stars or black holes, none of which are evident in RCW 38. One possible origin for the particles, could be an undetected supernova that occurred in the cluster, possibly thousands of years ago, producing a shock wave that is interacting with the young stars. Regardless of the origin of these energetic electrons, their presence could change the chemistry of the disks that will eventually form planets around the stars in the cluster.

  12. Variable stars in the bulge globular cluster NGC 6401

    NASA Astrophysics Data System (ADS)

    Tsapras, Y.; Arellano Ferro, A.; Bramich, D. M.; Jaimes, R. Figuera; Kains, N.; Street, R.; Hundertmark, M.; Horne, K.; Dominik, M.; Snodgrass, C.

    2017-02-01

    We present a study of variable stars in globular cluster NGC 6401. The cluster is only 5.3° away from the Galactic Centre and suffers from strong differential reddening. The photometric precision afforded us by difference image analysis resulted in improved sensitivity to variability in formerly inaccessible interior regions of the cluster. We find 23 RRab and 11 RRc stars within one cluster radius (2.4 arcmin), for which we provide coordinates, finder-charts and time series photometry. Through Fourier decomposition of the RR Lyrae star light curves we derive a mean metallicity of [Fe/H]UVES = -1.13 ± 0.06 ([Fe/H]ZW = -1.25 ± 0.06), and a distance of d ≈ 6.35 ± 0.81 kpc. Using the RR Lyrae population, we also determine that NGC 6401 is an Oosterhoff type I cluster.

  13. Q+: characterizing the structure of young star clusters

    NASA Astrophysics Data System (ADS)

    Jaffa, S. E.; Whitworth, A. P.; Lomax, O.

    2017-04-01

    Many young star clusters appear to be fractal, i.e. they appear to be concentrated in a nested hierarchy of clusters within clusters. We present a new algorithm for statistically analysing the distribution of stars to quantify the level of substructure. We suggest that, even at the simplest level, the internal structure of a fractal cluster requires the specification of three parameters. (i) The 3D fractal dimension, D, measures the extent to which the clusters on one level of the nested hierarchy fill the volume of their parent cluster. (ii) The number of levels, L, reflects the finite ratio between the linear size of the large root-cluster at the top of the hierarchy, and the smallest leaf-clusters at the bottom of the hierarchy. (iii) The volume-density scaling exponent, C = -d ln [δ n]/d ln [L] measures the factor by which the excess density, δn, in a structure of scale L, exceeds that of the background formed by larger structures; it is similar, but not exactly equivalent, to the exponent in Larson's scaling relation between density and size for molecular clouds. We describe an algorithm that can be used to constrain the values of (D,L,C) and apply this method to artificial and observed clusters. We show that this algorithm is able to reliably describe the three-dimensional structure of an artificial star cluster from the two-dimensional projection, and quantify the varied structures observed in real and simulated clusters.

  14. NEW UBVRI PHOTOMETRY OF 234 M33 STAR CLUSTERS

    SciTech Connect

    Ma Jun

    2013-04-15

    This is the second paper of our series. In this paper, we present UBVRI photometry for 234 star clusters in the field of M33. For most of these star clusters, there is photometry in only two bands in previous studies. The photometry of these star clusters is performed using archival images from the Local Group Galaxies Survey, which covers 0.8 deg{sup 2} along the major axis of M33. Detailed comparisons show that, in general, our photometry is consistent with previous measurements, and in particular that our photometry is in good agreement with that of Zloczewski and Kaluzny. Combined with star cluster photometry in previous studies, we present some results: none of the M33 youngest clusters ({approx}10{sup 7} yr) have masses approaching 10{sup 5} M{sub Sun }, and comparisons with models of simple stellar populations suggest a large range of ages for M33 star clusters and some as old as the Galactic globular clusters.

  15. The Milky Way's nuclear star cluster and massive black hole

    NASA Astrophysics Data System (ADS)

    Schödel, Rainer

    2016-02-01

    Because of its nearness to Earth, the centre of the Milky Way is the only galaxy nucleus in which we can study the characteristics, distribution, kinematics, and dynamics of the stars on milli-parsec scales. We have accurate and precise measurements of the Galactic centre's central black hole, Sagittarius A*, and can study its interaction with the surrounding nuclear star cluster in detail. This contribution aims at providing a concise overview of our current knowledge about the Milky Way's central black hole and nuclear star cluster, at highlighting the observational challenges and limitations, and at discussing some of the current key areas of investigation.

  16. A revolution in star cluster research: setting the scene.

    PubMed

    de Grijs, Richard

    2010-02-28

    Star clusters and their stellar populations play a significant role in the context of galaxy evolution, across space (from local to high redshift) and time (from currently forming to fossil remnants). We are now within reach of answering a number of fundamental questions that will have a significant impact on our understanding of key open issues in contemporary astrophysics, ranging from the formation, assembly and evolution of galaxies to the details of the star-formation process. Our improved understanding of the physics driving star cluster formation and evolution has led to the emergence of crucial new open questions that will most probably be tackled in a systematic way in the next decade.

  17. Searching for Be stars in the open cluster NGC 663

    SciTech Connect

    Yu, P. C.; Lin, C. C.; Chen, W. P.; Lee, C. D.; Ip, W. H.; Ngeow, C. C.; Laher, Russ; Surace, Jason

    2015-02-01

    We present Be star candidates in the open cluster NGC 663, identified by Hα imaging photometry with the Palomar Transient Factory Survey, as a pilot program to investigate how the Be star phenomena, the emission spectra, extended circumstellar envelopes, and fast rotation, correlate with massive stellar evolution. Stellar membership of the candidates was verified by 2MASS magnitudes and colors and by proper motions (PMs). We discover four new Be stars and exclude one known Be star from being a member due to its inconsistent PMs. The fraction of Be stars to member stars [N(Be)/N(members)] in NGC 663 is 3.5%. The spectral type of the 34 Be stars in NGC 663 shows bimodal peaks at B0–B2 and B5–B7, which is consistent with the statistics in most star clusters. Additionally, we also discover 23 emission-line stars of different types, including non-member Be stars, dwarfs, and giants.

  18. STAR-TO-STAR IRON ABUNDANCE VARIATIONS IN RED GIANT BRANCH STARS IN THE GALACTIC GLOBULAR CLUSTER NGC 3201

    SciTech Connect

    Simmerer, Jennifer; Ivans, Inese I.; Filler, Dan; Francois, Patrick; Charbonnel, Corinne; Monier, Richard; James, Gaeel E-mail: iii@physics.utah.edu E-mail: patrick.francois@obspm.fr E-mail: richard.monier@unice.fr

    2013-02-10

    We present the metallicity as traced by the abundance of iron in the retrograde globular cluster NGC 3201, measured from high-resolution, high signal-to-noise spectra of 24 red giant branch stars. A spectroscopic analysis reveals a spread in [Fe/H] in the cluster stars at least as large as 0.4 dex. Star-to-star metallicity variations are supported both through photometry and through a detailed examination of spectra. We find no correlation between iron abundance and distance from the cluster core, as might be inferred from recent photometric studies. NGC 3201 is the lowest mass halo cluster to date to contain stars with significantly different [Fe/H] values.

  19. Dynamics of the coronas of open star clusters

    NASA Astrophysics Data System (ADS)

    Danilov, V. M.; Putkov, S. I.; Seleznev, A. F.

    2014-12-01

    A method for distinguishing coronas in models of open star clusters is proposed. The method uses trajectories of stars that do not leave the coronas over time intervals t comparable to the mean lifetime τ of the clusters. Corona models are constructed for six numerical cluster models, and the direction and character of the dynamical evolution of the coronas are determined. Retrograde stellar motions are dominant in the coronas. In spite of some signs of dynamical instability of the coronas (small densities compared to the critical density and accelerated expansion of the coronas), the formation of close-toequilibrium density and phase-density distributions at distances from one to three cluster tidal radii from the cluster center can be seen. Approximations are constructed for the corona and cluster phase density using distributions that depend on three parameters (the parameters of the stellar motion in the Lindblad rotating coordinate system). This temporary equilibrium of the corona is due to balance in the number of starsmoving from the central areas of the cluster to the corona, and from the corona to the corona periphery or beyond. Evidence that corona stars can be gravitationally bound at distances out to four tidal radii from the cluster center is found: the presence of nearly periodic retrograde mean motions of a large number of corona stars in the Galactic plane; 91-99% of corona stars satisfy the gravitational binding criterion of Ross, Mennim and Heggie over time intervals that are close to the mean cluster lifetime. The escape rate from the corona is estimated for t ≥ τ, and found to be from 0.03 to 0.23 of the number of corona stars per violent relaxation time.

  20. Star Cluster Mass Functions and Hierarchical Clustering: Learning from Koposov 1 and 2

    NASA Astrophysics Data System (ADS)

    Paust, Nathaniel; Wilson, Danielle; van Belle, Gerard

    2017-01-01

    We present photometry of two halo star clusters, Koposov 1 and 2. Found as over-densities in the Sloan Digital Sky Survey, these clusters were intially believed to be heavily stripped globular clusters, given the small number of stars per cluster. In this work, we have used isochrone fitting to determine the age, distance, and metallicity of the clusters. These results confirm tha tthe clusters are in the halo but also reveal surprisingly young ages and high metallicities. Investigation of the cluster mass functions reveals a steep negatively-sloped present day mass function in contrast to the flatish positively-sloped mass functions seen in heavily stripped Galactic globular clusters. The mass function slope, proximity to the Sagittarius stream, and common metallicity with M54, which is related to the Sagittarius dwarf, leads to a very interesting conclusion: Koposov 1 and 2 are open clusters removed from the Sagittarius dwarf through tidal stripping.

  1. The Role of Radiation Pressure in Assembling Super Star Clusters

    NASA Astrophysics Data System (ADS)

    Tsz-Ho Tsang, Benny; Milosavljevic, Milos

    2016-06-01

    Super star clusters are the most extreme star-forming regions of the Universe - they occupy the most massive end of the Kennicutt-Schmidt relation, forming stars at exceptionally high rates and gas surface densities. The radiation feedback from the dense population of massive stars is expected to play a dynamic role during the assembly of the clusters, and represents a potential mechanism for launching large-scale galactic outflows. Observationally, large distances and dust obscuration have been withholding clues about the early stages of massive cluster formation; theoretically, the lack of accurate and efficient radiation transfer schemes in multi-dimensional hydrodynamic simulations has been deterring our understanding of radiative feedback. By extending the adaptive mesh refinement code FLASH with a closure-free, Monte Carlo radiation transport scheme, we perform 3D radiation hydrodynamical simulations of super star cluster formation from the collapse of turbulent molecular clouds. Our simulations probe the star formation in densities typical for starbursts, with both non-ionizing UV and dust-reprocessed IR radiation treated self-consistently. We aim to determine the role of radiation pressure in regulating star formation, and its capacity in driving intense outflows.

  2. Rotation periods of open-cluster stars, 2

    NASA Technical Reports Server (NTRS)

    Prosser, Charles F.; Shetrone, Matthew D.; Marilli, Ettore; Catalano, Santo; Williams, Scott D.; Backman, Dana E.; Laaksonen, Bentley D.; Adige, Vikram; Marschall, Laurence A.; Stauffer, John R.

    1993-01-01

    We present the results from a photometric monitoring program of 21 stars observed during 1992 in the Pleiades and Alpha Persei open clusters. Period determinations for 16 stars are given, 13 of which are the first periods reported for these stars. Brightness variations for an additional five cluster stars are also given. One K dwarf member of the alpha Per cluster is observed to have a period of rotation of only 4.39 hr. perhaps the shortest period currently known among BY Draconis variables. The individual photometric measurements have been deposited with the NSSDC. Combining current X-ray flux determinations with known photometric periods, we illustrate the X-ray activity/rotation relation among Pleiades K dwarfs based on available data.

  3. VARIABLE STARS IN THE OPEN CLUSTER NGC 7142

    SciTech Connect

    Sandquist, Eric L.; Serio, Andrew W.; Shetrone, Matthew E-mail: aserio@gemini.edu

    2011-12-15

    We present new discoveries of variable stars near the turnoff of the old open cluster NGC 7142. Contrary to previous studies, we detect eight contact or near-contact eclipsing binaries (including three near the cluster turnoff), and most of these have good probability of being cluster members. We also identified one long-period variable that resides far to the red of the cluster giant branch, and four new detached eclipsing binaries. We have re-examined the question of distance and reddening for the cluster and find that the distance is larger and the reddening lower than in most previous studies. In turn this implies that NGC 7142 is probably slightly younger than M67, and is about 3 Gyr old. With an age of this size, NGC 7142 would be one of a small group of clusters with main-sequence turnoff stars at the transition between convective and radiative cores.

  4. Signatures of Star Cluster Formation by Cold Collapse

    NASA Astrophysics Data System (ADS)

    Kuznetsova, Aleksandra; Hartmann, Lee; Ballesteros-Paredes, Javier

    2015-12-01

    Subvirial gravitational collapse is one mechanism by which star clusters may form. Here we investigate whether this mechanism can be inferred from observations of young clusters. To address this question, we have computed smoothed particle hydrodynamics simulations of the initial formation and evolution of a dynamically young star cluster through cold (subvirial) collapse, starting with an ellipsoidal, turbulently seeded distribution of gas, and forming sink particles representing (proto)stars. While the initial density distributions of the clouds do not have large initial mass concentrations, gravitational focusing due to the global morphology leads to cluster formation. We use the resulting structures to extract observable morphological and kinematic signatures for the case of subvirial collapse. We find that the signatures of the initial conditions can be erased rapidly as the gas and stars collapse, suggesting that kinematic observations need to be made early in cluster formation and/or at larger scales, away from the growing cluster core. Our results emphasize that a dynamically young system is inherently evolving on short timescales, so that it can be highly misleading to use current-epoch conditions to study aspects such as star formation rates as a function of local density. Our simulations serve as a starting point for further studies of collapse including other factors such as magnetic fields and stellar feedback.

  5. SIGNATURES OF STAR CLUSTER FORMATION BY COLD COLLAPSE

    SciTech Connect

    Kuznetsova, Aleksandra; Hartmann, Lee; Ballesteros-Paredes, Javier

    2015-12-10

    Subvirial gravitational collapse is one mechanism by which star clusters may form. Here we investigate whether this mechanism can be inferred from observations of young clusters. To address this question, we have computed smoothed particle hydrodynamics simulations of the initial formation and evolution of a dynamically young star cluster through cold (subvirial) collapse, starting with an ellipsoidal, turbulently seeded distribution of gas, and forming sink particles representing (proto)stars. While the initial density distributions of the clouds do not have large initial mass concentrations, gravitational focusing due to the global morphology leads to cluster formation. We use the resulting structures to extract observable morphological and kinematic signatures for the case of subvirial collapse. We find that the signatures of the initial conditions can be erased rapidly as the gas and stars collapse, suggesting that kinematic observations need to be made early in cluster formation and/or at larger scales, away from the growing cluster core. Our results emphasize that a dynamically young system is inherently evolving on short timescales, so that it can be highly misleading to use current-epoch conditions to study aspects such as star formation rates as a function of local density. Our simulations serve as a starting point for further studies of collapse including other factors such as magnetic fields and stellar feedback.

  6. The SUNBIRD survey: characterizing the super star cluster populations of intensely star-forming galaxies

    NASA Astrophysics Data System (ADS)

    Randriamanakoto, Zara; Väisänen, Petri

    2017-03-01

    Super star clusters (SSCs) represent the youngest and most massive form of known gravitationally bound star clusters in the Universe. They are born abundantly in environments that trigger strong and violent star formation. We investigate the properties of these massive SSCs in a sample of 42 nearby starbursts and luminous infrared galaxies. The targets form the sample of the SUperNovae and starBursts in the InfraReD (SUNBIRD) survey that were imaged using near-infrared (NIR) K-band adaptive optics mounted on the Gemini/NIRI and the VLT/NaCo instruments. Results from i) the fitted power-laws to the SSC K-band luminosity functions, ii) the NIR brightest star cluster magnitude - star formation rate (SFR) relation and iii) the star cluster age and mass distributions have shown the importance of studying SSC host galaxies with high SFR levels to determine the role of the galactic environments in the star cluster formation, evolution and disruption mechanisms.

  7. STAR CLUSTERS IN A NUCLEAR STAR FORMING RING: THE DISAPPEARING STRING OF PEARLS

    SciTech Connect

    Väisänen, Petri; Barway, Sudhanshu; Randriamanakoto, Zara

    2014-12-20

    An analysis of the star cluster population in a low-luminosity early-type galaxy, NGC 2328, is presented. The clusters are found in a tight star forming nuclear spiral/ring pattern and we also identify a bar from structural two-dimensional decomposition. These massive clusters are forming very efficiently in the circumnuclear environment and they are young, possibly all less than 30 Myr of age. The clusters indicate an azimuthal age gradient, consistent with a ''pearls-on-a-string'' formation scenario, suggesting bar-driven gas inflow. The cluster mass function has a robust down turn at low masses at all age bins. Assuming clusters are born with a power-law distribution, this indicates extremely rapid disruption at timescales of just several million years. If found to be typical, it means that clusters born in dense circumnuclear rings do not survive to become old globular clusters in non-interacting systems.

  8. STAR FORMATION IN HIGH-REDSHIFT CLUSTER ELLIPTICALS

    SciTech Connect

    Wagner, Cory R.; Brodwin, Mark; Snyder, Gregory F.; Gonzalez, Anthony H.; Mancone, Conor L.; Stanford, S. A.; Alberts, Stacey; Pope, Alexandra; Stern, Daniel; Eisenhardt, Peter R. M.; Zeimann, Gregory R.; Chary, Ranga-Ram; Dey, Arjun; Moustakas, John

    2015-02-20

    We measure the star formation rates (SFRs) of massive (M {sub *} > 10{sup 10.1} M {sub ☉}) early-type galaxies (ETGs) in a sample of 11 high-redshift (1.0 < z < 1.5) galaxy clusters drawn from the IRAC Shallow Cluster Survey (ISCS). We identify ETGs visually from Hubble Space Telescope imaging and select likely cluster members as having either an appropriate spectroscopic redshift or red-sequence color. Mid-infrared SFRs are measured using Spitzer 24 μm data for isolated cluster galaxies for which contamination by neighbors, and active galactic nuclei, can be ruled out. Cluster ETGs show enhanced specific star formation rates (sSFRs) compared to cluster galaxies in the local universe, but have sSFRs more than four times lower than that of field ETGs at 1 < z < 1.5. Relative to the late-type cluster population, isolated ETGs show substantially quenched mean SFRs, yet still contribute 12% of the overall star formation activity measured in 1 < z < 1.5 clusters. We find that new ETGs are likely being formed in ISCS clusters; the fraction of cluster galaxies identified as ETGs increases from 34% to 56% from z ∼ 1.5 → 1.25. While the fraction of cluster ETGs that are highly star-forming (SFR ≥ 26 M {sub ☉} yr{sup –1}) drops from 27% to 10% over the same period, their sSFRs are roughly constant. All these factors taken together suggest that, particularly at z ≳ 1.25, the events that created these distant cluster ETGs—likely mergers, at least among the most massive—were both recent and gas-rich.

  9. Young star clusters in the circumnuclear region of NGC 2110

    SciTech Connect

    Durré, Mark; Mould, Jeremy

    2014-03-20

    High-resolution observations in the near infrared show star clusters around the active galactic nucleus (AGN) of the Seyfert 1 NGC 2110, along with a 90 × 35 pc bar of shocked gas material around its nucleus. These are seen for the first time in our imaging and gas kinematics of the central 100 pc with the Keck OSIRIS instrument with adaptive optics. Each of these clusters is two to three times brighter than the Arches cluster close to the center of the Milky Way. The core star formation rate is 0.3 M {sub ☉} yr{sup –1}. The photoionized gas (He I) dynamics imply an enclosed mass of 3-4 × 10{sup 8} M {sub ☉}. These observations demonstrate the physical linkage between AGN feedback, which triggers star formation in massive clusters, and the resulting stellar (and supernovae) winds, which cause the observed [Fe II] emission and feed the black hole.

  10. The physics and modes of star cluster formation: simulations.

    PubMed

    Clarke, Cathie

    2010-02-28

    We review progress in numerical simulations of star cluster formation. These simulations involve the bottom-up assembly of clusters through hierarchical mergers, which produces a fractal stellar distribution at young (approx. 0.5 Myr) ages. The resulting clusters are predicted to be mildly aspherical and highly mass-segregated, except in the immediate aftermath of mergers. The upper initial mass function within individual clusters is generally somewhat flatter than for the aggregate population. Recent work has begun to clarify the factors that control the mean stellar mass in a star-forming cloud and also the efficiency of star formation. The former is sensitive to the thermal properties of the gas while the latter depends both on the magnetic field and the initial degree of gravitational boundedness of the natal cloud. Unmagnetized clouds that are initially bound undergo rapid collapse, which is difficult to reverse by ionization feedback or stellar winds.

  11. STAR-FORMING GALAXY EVOLUTION IN NEARBY RICH CLUSTERS

    SciTech Connect

    Tyler, K. D.; Rieke, G. H.; Bai, L.

    2013-08-20

    Dense environments are known to quench star formation in galaxies, but it is still unknown what mechanism(s) are directly responsible. In this paper, we study the star formation of galaxies in A2029 and compare it to that of Coma, combining indicators at 24 {mu}m, H{alpha}, and UV down to rates of 0.03 M{sub Sun} yr{sup -1}. We show that A2029's star-forming galaxies follow the same mass-SFR relation as the field. The Coma cluster, on the other hand, has a population of galaxies with star formation rates (SFRs) significantly lower than the field mass-SFR relation, indicative of galaxies in the process of being quenched. Over half of these galaxies also host active galactic nuclei. Ram-pressure stripping and starvation/strangulation are the most likely mechanisms for suppressing the star formation in these galaxies, but we are unable to disentangle which is dominating. The differences we see between the two clusters' populations of star-forming galaxies may be related to their accretion histories, with A2029 having accreted its star-forming galaxies more recently than Coma. Additionally, many early-type galaxies in A2029 are detected at 24 {mu}m and/or in the far-UV, but this emission is not directly related to star formation. Similar galaxies have probably been classified as star forming in previous studies of dense clusters, possibly obscuring some of the effects of the cluster environment on true star-forming galaxies.

  12. Evolution of Star Clusters in Time-variable Tidal Fields

    NASA Astrophysics Data System (ADS)

    Mamikonyan, Ernest N.; McMillan, Stephen L. W.; Vesperini, Enrico; Mac Low, Mordecai-Mark

    2017-03-01

    Strong tidal forces can dominate star cluster evolution in merging galaxies, determining their mass-loss rates and lifetimes. In order to model this evolution, we have developed a second-order accurate numerical method for integrating a star cluster in an arbitrary time-variable tidal field. We extend the Kira N-body integrator to handle these external fields. We obtain realistic tidal histories from a galaxy merger simulation including sink particles, which we interpret as young star clusters. Coupling these tidal accelerations to N-body models of isolated clusters, we perform detailed dynamical studies. This generalizes the formalism previously used to explore the dynamical effects of the galactic tidal field on clusters in circular orbits. We find that, in contrast to previous studies that considered only stellar and dark matter dynamics, tidal interactions between clusters and dense gas in the galactic disk can significantly influence cluster mass loss and lifetimes. Using our models, we develop an effective semianalytic model that can be used for fast estimation of cluster mass loss in a galactic tidal field and to study the evolution of the globular cluster mass function in isolated and merging galaxies.

  13. Speckle Interferometry of Massive and Cluster Stars

    NASA Astrophysics Data System (ADS)

    Mason, Brian; Hartkopf, William I.; Gies, Douglas R.; Henry, Todd J.; Tokovinin, Andrei A.

    2006-02-01

    Conducted on NOAO 4-m telescopes in 1994, the first speckle survey of O stars (Mason et al. 1998) had success far in excess of our expectations. In addition to the frequently cited multiplicity analysis, many of the new systems which were first resolved in this paper are of significant astrophysical importance. Now, some ten years after the original survey, we propose to re-investigate all systems analyzed before (N=195). Improvements in detector technology will allow for the detection of companions missed before as well as systems which may have been closer than the resolution limit in 1994. We will also make a first high-resolution inspection of the additional O stars (N=108) in the recent Galactic O Star Catalog of Maiz- Apellaniz & Walborn (2004). Further, we propose to investigate several additional samples of interesting objects, including 15 accessible Galactic WR stars from the speckle survey of Hartkopf et al. (1999), 16 massive, hot stars with separations which would indicate their applicability for mass determinations (for fully detached O stars masses are presently known for only twelve pairs), and 56 multiple stars for a study of their co- planarity statistics.

  14. Variable stars in the globular cluster M 13

    NASA Astrophysics Data System (ADS)

    Kopacki, G.; Kołaczkowski, Z.; Pigulski, A.

    2003-02-01

    Results of a search for variable stars in the central region of the globular cluster M 13 are presented. Prior to this study, 36 variable and suspected variable stars were known in this cluster (Osborn \\cite{osborn00}; Clement et al. \\cite{clementetal01}). Of these stars, five were not observed by us. We find v3, v4, v10, v12, and v13 to be constant in light. Surprisingly, only two out of the ten variable star candidates of Kadla et al. (\\cite{kadlaetal80}) appear to be variable. Both are RRc variables. Additionally, three RR Lyrae stars and one SX Phoenicis variable are discovered. Three close frequencies are detected for an RRc star v36. It appears that this variable is another multi-periodic RR Lyrae star pulsating in non-radial modes. Light curves of the three known BL Herculis stars and all known RR Lyrae stars are presented. The total number of known RR Lyrae stars in M 13 is now nine. Only one is an RRab star. The mean period of RRc variables amounts to 0.36+/-0.05 d, suggesting that M 13 should be included in the group of Oosterhoff type II globular clusters. Mean V magnitudes and ranges of variation are derived for seven RR Lyrae and three BL Herculis variables. Almost all observed bright giants show some degree of variability. In particular, we confirm the variability of two red giants announced to be variable by Osborn (\\cite{osborn00}) and in addition find five new cases. The observations used in the paper are available in electronic form at the CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or via http://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/398/541

  15. PROGRESSIVE STAR FORMATION IN THE YOUNG GALACTIC SUPER STAR CLUSTER NGC 3603

    SciTech Connect

    Beccari, Giacomo; Spezzi, Loredana; De Marchi, Guido; Andersen, Morten; Paresce, Francesco; Young, Erick; Panagia, Nino; Bond, Howard; Balick, Bruce; Calzetti, Daniela; Carollo, C. Marcella; Disney, Michael J.; Dopita, Michael A.; Frogel, Jay A.; Hall, Donald N. B.; Holtzman, Jon A.; Kimble, Randy A.; McCarthy, Patrick J.; O'Connell, Robert W.; Saha, Abhijit

    2010-09-10

    Early Release Science observations of the cluster NGC 3603 with the WFC3 on the refurbished Hubble Space Telescope allow us to study its recent star formation history. Our analysis focuses on stars with H{alpha} excess emission, a robust indicator of their pre-main sequence (PMS) accreting status. The comparison with theoretical PMS isochrones shows that 2/3 of the objects with H{alpha} excess emission have ages from 1 to 10 Myr, with a median value of 3 Myr, while a surprising 1/3 of them are older than 10 Myr. The study of the spatial distribution of these PMS stars allows us to confirm their cluster membership and to statistically separate them from field stars. This result establishes unambiguously for the first time that star formation in and around the cluster has been ongoing for at least 10-20 Myr, at an apparently increasing rate.

  16. Population III star clusters in the reionized Universe

    NASA Astrophysics Data System (ADS)

    Johnson, Jarrett L.

    2010-05-01

    In reionized regions of the Universe, gas can only collapse to form stars in dark matter (DM) haloes which grow to be sufficiently massive. If star formation is prevented in the minihalo progenitors of such DM haloes at redshifts z >~ 20, then these haloes will not be self-enriched with metals and so may host Population (Pop) III star formation. We estimate an upper limit for the abundance of Pop III star clusters which thus form in the reionized Universe, as a function of redshift. Depending on the minimum DM halo mass for star formation, between of the order of 1 and of the order of 1000, Pop III star clusters per square degree may be observable at 2 <~ z <~ 7. Thus, there may be a sufficient number density of Pop III star clusters for detection in surveys such as the Deep-Wide Survey (DWS) to be conducted by the James Webb Space Telescope. We predict that Pop III clusters formed after reionization are most likely to be found at z >~ 3 and within ~40arcsec (~1Mpc comoving) of DM haloes with masses of ~1011Msolar, the descendants of the haloes at z ~ 20 which host the first galaxies that begin reionization. However, if star formation is inefficient in the haloes hosting Pop III clusters due to the photoionizing background radiation, these clusters may not be bright enough for detection by the Near-Infrared Camera which will conduct the DWS. None the less, if the stellar initial mass function (IMF) is top-heavy the clusters may have sufficiently high luminosities in both Lyα and HeII λ1640 to be detected and for constraints to be placed on the Pop III IMF. While a small fraction of DM haloes with masses as high as ~109Msolar at redshifts z <~ 4 are not enriched due to star formation in their progenitors, external metal enrichment due to galactic winds is likely to preclude Pop III star formation in a large fraction of otherwise unenriched haloes, perhaps even preventing star formation in pristine haloes altogether after reionization is complete at z ~ 6.

  17. Star formation in X-ray cluster cooling flows

    NASA Technical Reports Server (NTRS)

    White, Raymond E., III; Sarazin, Craig L.

    1987-01-01

    The basic equations for X-ray cluster cooling flows, including the effects of star formation, are derived. It is confirmed that cooling flows are thermally unstable, and it is found that the fastest-growing linear perturbations in the flow are radial, comoving, and isobaric. A local approximation for the star formation rate is developed which allows analytic solutions to be found for both isobaric and gravity-dominated cooling flows. These solutions are used to show how star formation reduces the gas density, thereby lowering the cooling rate, which raises the gas temperature relative to the non-star-forming case. The analytic solutions are also used to estimate the spatial distribution of newly formed stars. It is found that star formation must proceed at a nearly maximal rate if isothermal mass profiles are to result.

  18. Spontaneous magnetization of solid quark-cluster stars

    NASA Astrophysics Data System (ADS)

    Lai, Xiao-Yu; Xu, Ren-Xin

    2016-09-01

    Pulsar-like compact stars usually have strong magnetic fields, with strengths from ˜ 108 to ˜ 1012 G on the surface. How such strong magnetic fields can be generated and maintained is still an unsolved problem, which is, in principle, related to the interior structure of compact stars, i.e., the equation of state of cold matter at supra-nuclear density. In this paper we are trying to solve the problem in the regime of solid quark-cluster stars. Inside quark-cluster stars, the extremely low ratio of number density of electrons to that of baryons ne/nb and the screening effect from quark-clusters could reduce the long-range Coulomb interaction between electrons to short-range interaction. In this case, Stoner’s model could apply, and we find that the condition for ferromagnetism is consistent with that for the validity of Stoner’s model. Under the screened Coulomb repulsion, the electrons inside the stars could be spontaneously magnetized and become ferromagnetic, and hence would contribute non-zero net magnetic momentum to the whole star. We conclude that, for most cases in solid quark-cluster stars, the amount of net magnetic momentum, which is proportional to the amount of unbalanced spins ξ = (n+ - n-)/ne and depends on the number density of electrons ne = n+ + n-, could be significant with non-zero ξ. The net magnetic moments of electron system in solid quark-cluster stars could be large enough to induce the observed magnetic fields for pulsars with B ˜ 1011 to ˜ 1013 G. Supported by 973 Program (2012CB821801), West Light Foundation (XBBS-2014-23), National Natural Science Foundation of China (11203018, 11225314, 11365022), Science Project of Universities in Xinjiang (XJEDU2012S02) and Doctoral Science Foundation of Xinjiang University (BS120107)

  19. Search for OB stars running away from young star clusters. II. The NGC 6357 star-forming region

    NASA Astrophysics Data System (ADS)

    Gvaramadze, V. V.; Kniazev, A. Y.; Kroupa, P.; Oh, S.

    2011-11-01

    Dynamical few-body encounters in the dense cores of young massive star clusters are responsible for the loss of a significant fraction of their massive stellar content. Some of the escaping (runaway) stars move through the ambient medium supersonically and can be revealed via detection of their bow shocks (visible in the infrared, optical or radio). In this paper, which is the second of a series of papers devoted to the search for OB stars running away from young ( ≲ several Myr) Galactic clusters and OB associations, we present the results of the search for bow shocks around the star-forming region NGC 6357. Using the archival data of the Midcourse Space Experiment (MSX) satellite and the Spitzer Space Telescope, and the preliminary data release of the Wide-Field Infrared Survey Explorer (WISE), we discovered seven bow shocks, whose geometry is consistent with the possibility that they are generated by stars expelled from the young (~1-2 Myr) star clusters, Pismis 24 and AH03 J1725-34.4, associated with NGC 6357. Two of the seven bow shocks are driven by the already known OB stars, HD 319881 and [N78] 34. Follow-up spectroscopy of three other bow-shock-producing stars showed that they are massive (O-type) stars as well, while the 2MASS photometry of the remaining two stars suggests that they could be B0 V stars, provided that both are located at the same distance as NGC 6357. Detection of numerous massive stars ejected from the very young clusters is consistent with the theoretical expectation that star clusters can effectively lose massive stars at the very beginning of their dynamical evolution (long before the second mechanism for production of runaway stars, based on a supernova explosion in a massive tight binary system, begins to operate) and lends strong support to the idea that probably all field OB stars have been dynamically ejected from their birth clusters. A by-product of our search for bow shocks around NGC 6357 is the detection of three circular

  20. New cluster members and halo stars of the Galactic globular cluster NGC 1851

    NASA Astrophysics Data System (ADS)

    Navin, Colin A.; Martell, Sarah L.; Zucker, Daniel B.

    2015-10-01

    NGC 1851 is an intriguing Galactic globular cluster, with multiple stellar evolutionary sequences, light and heavy element abundance variations and indications of a surrounding stellar halo. We present the first results of a spectroscopic study of red giant stars within and outside of the tidal radius of this cluster. Our results identify nine probable new cluster members (inside the tidal radius) with heliocentric radial velocities consistent with that of NGC 1851. We also identify, based on their radial velocities, four probable extratidal cluster halo stars at distances up to ˜3.1 times the tidal radius, which are supportive of previous findings that NGC 1851 is surrounded by an extended stellar halo. Proper motions were available for 12 of these 13 stars and all are consistent with that of NGC 1851. Apart from the cluster members and cluster halo stars, our observed radial velocity distribution agrees with the expected distribution from a Besançon disc/N-body stellar halo Milky Way model generated by the GALAXIA code, suggesting that no other structures at different radial velocities are present in our field. The metallicities of these stars are estimated using equivalent width measurements of the near-infrared calcium triplet absorption lines and are found, within the limitations of this method, to be consistent with that of NGC 1851. In addition we recover 110 red giant cluster members from previous studies based on their radial velocities and identify three stars with unusually high radial velocities.

  1. Giant Star Clusters Near Galactic Core

    NASA Technical Reports Server (NTRS)

    2001-01-01

    A video sequence of still images goes deep into the Milky Way galaxy to the Arches Cluster. Hubble, penetrating through dust and clouds, peers into the core where two giant clusters shine more brightly than any other clusters in the galaxy. Footage shows the following still images: (1) wide view of Sagittarius constellation; (2) the Palomar Observatory's 2 micron all-sky survey; and (3) an image of the Arches Cluster taken with the Hubble Space Telescope NICMOS instrument. Dr. Don Figer of the Space Telescope Science Institute discusses the significance of the observations and relates his first reaction to the images.

  2. Ba STARS AND OTHER BINARIES IN FIRST AND SECOND GENERATION STARS IN GLOBULAR CLUSTERS

    SciTech Connect

    D'Orazi, Valentina; Gratton, Raffaele; Lucatello, Sara; Carretta, Eugenio; Bragaglia, Angela; Marino, Anna F.

    2010-08-20

    The determination of the Ba abundance in globular cluster (GC) stars is a very powerful test to address several issues in the framework of multiple population scenarios. We measured the Ba content for a sample of more than 1200 stars in 15 Galactic GCs, using high-resolution FLAMES/Giraffe spectra. We found no variation in [Ba/Fe] ratios for different stellar populations within each cluster; this means that low-mass asymptotic giant branch stars do not significantly contribute to the intracluster pollution. Very interestingly, we found that the fraction of Ba stars in first generation (FG) stars is close to the values derived for field stars ({approx}2%); on the other hand, second generation (SG) stars present a significantly lower fraction. An independent and successful test, based on radial velocity variations among giant stars in NGC 6121, confirms our finding: the binary fraction among FG stars is about {approx}12%, to be compared with {approx}1% of SG stars. This is an evidence that SG stars formed in a denser environment, where infant mortality of binary systems was particularly efficient.

  3. COMPACT STAR CLUSTERS IN THE M31 DISK

    SciTech Connect

    Vansevicius, V.; Narbutis, D.; Stonkute, R.; Bridzius, A.; Semionov, D.; Kodaira, K.; Deveikis, V.

    2009-10-01

    We have carried out a survey of compact star clusters (apparent size approx<3'') in the southwest part of the M31 galaxy, based on the high-resolution Suprime-Cam images (17.'5 x 28.'5), covering approx15% of the deprojected galaxy disk area. The UBVRI photometry of 285 cluster candidates (V approx< 20.5 mag) was performed using frames of the Local Group Galaxies Survey. The final sample, containing 238 high probability star cluster candidates (typical half-light radius r{sub h} approx 1.5 pc), was selected by specifying a lower limit of r{sub h} approx> 0.''15 (approx>0.6 pc). We derived cluster parameters based on the photometric data and multiband images by employing simple stellar population models. The clusters have a wide range of ages from approx5 Myr (young objects associated with 24 {mu}m and/or Halpha emission) to approx10 Gyr (globular cluster candidates), and possess mass in a range of 3.0 approx< log(m/m {sub sun}) approx< 4.3 peaking at m approx 4000 m {sub sun}. Typical age of these intermediate-mass clusters is in the range of 30 Myr approx< t approx< 3 Gyr, with a prominent peak at approx70 Myr. These findings suggest a rich intermediate-mass star cluster population in M31, which appears to be scarce in the Milky Way galaxy.

  4. Investigation of the open star cluster NGC 6800

    NASA Astrophysics Data System (ADS)

    Ananjevskaja, Yu. K.; Frolov, V. N.; Polyakov, E. V.

    2015-07-01

    The results of a comprehensive study of the Galactic open cluster NGC 6800 are presented. The positions of stars to a limiting magnitude B ≃ 16{./ m }5 in an 80' × 80' field centered at the cluster were measured on eight plates from the Pulkovo normal astrograph with a maximum epoch difference of 57 years. The measurements were performed with the Pulkovo "Fantasy" automated measuring system. The corresponding field from the 2MASS catalogue was used as an additional plate. As a result, the relative proper motions of stars were obtained with a root-mean-square error of 3.0 mas yr-1. A catalogue of BV and JHK magnitudes for objects in the investigated region was compiled from available published resources. The astrometric selection of cluster members was made by the maximum likelihood method. An individual cluster membership probability of a star P ≥ 60% served as the first selection criterion. The position of a star on the photometric color-magnitude ( V ~ B - V, J ~ J - K s ) diagrams was considered as the second selection criterion. On the basis of these criteria, it was established that 109 stars are members of NGC 6800, These data were used to refine the physical parameters of the cluster: the mean reddening E( B - V) = 0 m . 40, the true distance modulus ( V - M V )0 = 10{./ m }05, and the cluster age ~250 Myr. The luminosity and mass functions were constructed. The position of the center of the cluster NGC 6800 was improved: α = 19h27m11{./s}2 and δ = +25°07'24〃(2000). The catalogue of relative proper motions for stars in the field is available in electronic form only.

  5. Formation and evolution of star clusters in merging galaxies

    NASA Astrophysics Data System (ADS)

    Zhang, Qing

    2002-04-01

    Recent observations have revealed numerous young massive star clusters, often known as “young globular clusters”. Their formation and evolution are important astrophysical processes and may potentially have cosmological implications. In this work, we focus on the star clusters in the nearest ongoing merger NGC 4038/9 (the “Antennae”). With the Hubble Space Telescope, we identify clusters with all ages, most of which are younger than 20 Myr. Our goal is to study their formation mechanisms, and the relation with the interstellar medium environment, and their evolutionary connection with old globular clusters. We find that their luminosity function and mass function are best described as power laws with indices around -2. The masses of young star clusters cover the range 104 ≤ M ≤ 10 6 M⊙ . This result is distinctly different from that of old globular clusters that has a “preferred” scale at M ≈ 2 × 105 M⊙ . To understand the difference in MF between the young and old star clusters, we conduct a theoretical study on the effects of dynamical disruption of individual clusters on the mass function. We find that, for a wide variety of initial conditions, the mass function develops a characteristic scale, that is remarkably close to the observed one for globular clusters after 12 Gyr. In addition, we find that some radial anisotropy in the initial velocity distribution, especially when decreasing outward, is needed to account for the observed near-uniformity of the mass functions of globular clusters. This is consistent with the observed near-isotropy of the present velocity distributions because clusters on elongated orbits are preferentially destroyed. In order to understand the formation and feedback effects of young star clusters, we have also conducted a multi- wavelength study on the association between young star clusters and their interstellar environment in the Antennae galaxies. This is possible for the first time because various new

  6. Rotation periods of open-cluster stars, 3

    NASA Technical Reports Server (NTRS)

    Prosser, Charles F.; Shetrone, Matthew D.; Dasgupta, Amil; Backman, Dana E.; Laaksonen, Bentley D.; Baker, Shawn W.; Marschall, Laurence A.; Whitney, Barbara A.; Kuijken, Konrad; Stauffer, John R.

    1995-01-01

    We present the results from a photometric monitoring program of 15 open cluster stars and one weak-lined T Tauri star during late 1993/early 1994. Several show rotators which are members of the Alpha Persei, Pleiades, and Hyades open clusters have been monitored and period estimates derived. Using all available Pleiades stars with photometric periods together with current X-ray flux measurements, we illustrate the X-ray activity/rotation relation among Pleiades late-G/K dwarfs. The data show a clear break in the rotation-activity relation around P approximately 6-7 days -- in general accordance with previous results using more heterogeneous samples of G/K stars.

  7. Kinematics and Colors of Star Clusters in M101

    NASA Astrophysics Data System (ADS)

    Simanton, Lesley A.; Chandar, R.; Miller, B.

    2013-06-01

    Star formation is an ongoing process in the universe and one of the main drivers of change in galaxies. Most stars are born in clusters, and the properties of the cluster population of a galaxy can reveal information on the formation history of the galaxy itself. Here, we look at properties of the cluster population of the nearby, late-type spiral galaxy M101. We have identified a few thousand star clusters, including approximately 90 candidate ancient globular clusters (GCs), from multi-band Hubble Space Telescope images. We obtained follow-up low-resolution (R approximately 2000) optical spectroscopy from Gemini-GMOS for 43 total clusters, of which 18 are old GCs and 25 are young massive clusters (YMCs). Properties assessed include radial velocities (derived from spectra) and color distributions (derived from photometry). From the radial velocities, we find that GCs do not show evidence for rotation and have a much higher velocity dispersion than the YMCs, suggesting that the GCs are part of a stellar halo or thick disk in M101. We compare the color distributions to those in elliptical galaxies and other spirals such as our Milky Way.

  8. Variable Stars in Large Magellanic Cloud Globular Clusters. III. Reticulum

    NASA Astrophysics Data System (ADS)

    Kuehn, Charles A.; Dame, Kyra; Smith, Horace A.; Catelan, Márcio; Jeon, Young-Beom; Nemec, James M.; Walker, Alistair R.; Kunder, Andrea; Pritzl, Barton J.; De Lee, Nathan; Borissova, Jura

    2013-06-01

    This is the third in a series of papers studying the variable stars in old globular clusters in the Large Magellanic Cloud. The primary goal of this series is to look at how the characteristics and behavior of RR Lyrae stars in Oosterhoff-intermediate systems compare to those of their counterparts in Oosterhoff-I/II systems. In this paper we present the results of our new time-series BVI photometric study of the globular cluster Reticulum. We found a total of 32 variables stars (22 RRab, 4 RRc, and 6 RRd stars) in our field of view. We present photometric parameters and light curves for these stars. We also present physical properties, derived from Fourier analysis of light curves, for some of the RR Lyrae stars. We discuss the Oosterhoff classification of Reticulum and use our results to re-derive the distance modulus and age of the cluster. Based on observations taken with the SMARTS 1.3 m telescope operated by the SMARTS Consortium and observations taken at the Southern Astrophysical Research (SOAR) telescope, which is a joint project of the Ministério da Ciência, Tecnologia, e Inovação (MCTI) da República Federativa do Brasil, the U.S. National Optical Astronomy Observatory (NOAO), the University of North Carolina at Chapel Hill (UNC), and Michigan State University (MSU).

  9. VizieR Online Data Catalog: LAMOST DR2 star clusters candidate members (Zhang+, 2015)

    NASA Astrophysics Data System (ADS)

    Zhang, B.; Chen, X.-Y.; Liu, C.; Chen, L.; Deng, L.-C.; Hou, J.-L.; Shao, Z.-Y.; Yang, F.; Wu, Y.; Yang, M.; Zhang, Y.; Hou, Y.-H.; Wang, Y.-F.

    2015-11-01

    We adopt the Milky Way Star Cluster (MWSC) catalog (Kharchenko et al. 2012, Cat. J/A+A/543/A156; 2013, Cat. J/A+A/558/A53) as the list of target star clusters since it provides homogeneous parameters of Milky Way star clusters and is complete in the volume observed by LAMOST. Thus we use the MWSC radius parameters for star clusters, i.e., r0 in the MWSC is the angular radius of the core of the cluster, and r2 (hereafter rewritten as rc) stands for the angular radius of the cluster. A star cluster is covered by the LAMOST footprint if the number of stars located within 2rc of the cluster is larger than zero. In total, 457 star clusters, including open clusters, globular clusters, stellar associations and moving groups, are included in LAMOST DR2. (2 data files).

  10. STAR FORMATION AND RELAXATION IN 379 NEARBY GALAXY CLUSTERS

    SciTech Connect

    Cohen, Seth A.; Hickox, Ryan C.; Wegner, Gary A.

    2015-06-10

    We investigate the relationship between star formation (SF) and level of relaxation in a sample of 379 galaxy clusters at z < 0.2. We use data from the Sloan Digital Sky Survey to measure cluster membership and level of relaxation, and to select star-forming galaxies based on mid-infrared emission detected with the Wide-Field Infrared Survey Explorer. For galaxies with absolute magnitudes M{sub r} < −19.5, we find an inverse correlation between SF fraction and cluster relaxation: as a cluster becomes less relaxed, its SF fraction increases. Furthermore, in general, the subtracted SF fraction in all unrelaxed clusters (0.117 ± 0.003) is higher than that in all relaxed clusters (0.097 ± 0.005). We verify the validity of our SF calculation methods and membership criteria through analysis of previous work. Our results agree with previous findings that a weak correlation exists between cluster SF and dynamical state, possibly because unrelaxed clusters are less evolved relative to relaxed clusters.

  11. Star and cluster formation in NGC 1275

    NASA Technical Reports Server (NTRS)

    Richer, Harvey B.; Crabtree, Dennis R.; Fabian, A. C.; Lin, D. N. C.

    1993-01-01

    Luminous, blue, and unresolved objects have been found by imaging the nuclear region of the central galaxy in the Perseus Cluster, NGC 1275. Stellar formation in a cooling flow in which gas clouds confined by weak magnetic fields are allowed to remain at low densities is favored. Cloud-cloud collisions and coagulation in the high cloud density environment at the center of the galaxy then causes some clouds to become gravitationally unstable and to form globular clusters.

  12. New insights on the formation of nuclear star clusters

    NASA Astrophysics Data System (ADS)

    Guillard, Nicolas; Emsellem, Eric; Renaud, Florent

    2016-10-01

    Nuclear clusters (NCs) are common stellar systems in the centres of galaxies. Yet, the physical mechanisms involved in their formation are still debated. Using a parsec-resolution hydrodynamical simulation of a dwarf galaxy, we propose an updated formation scenario for NCs. In this `wet migration scenario', a massive star cluster forms in the gas-rich disc, keeping a gas reservoir, and growing further while it migrates to the centre via a combination of interactions with other substructures and dynamical friction. A wet merger with another dense cluster and its own gas reservoir can occur, although this is not a prerequisite for the actual formation of the NC. The merging process does significantly alter the properties of the NC (mass, morphology, star formation history), also quenching the ongoing local star formation activity, thus leading to interesting observational diagnostics for the physical origin of NCs. A population of lower mass clusters co-exist during the simulation, but these are either destroyed via tidal forces, or have high angular momentum preventing them to interact with the NC and contribute to its growth. The proposed updated scenario emphasizes the role of gas reservoirs associated with the densest star clusters formed in a gas-rich low-mass galaxy.

  13. Red giants in the vicinity of open clusters. Field stars

    NASA Astrophysics Data System (ADS)

    Pakhomov, Yu. V.; Antipova, L. I.; Boyarchuk, A. A.; Zhao, G.; Liang, Ya.

    2009-08-01

    We present a comparative analysis of the atmospheric abundances of red giants in the vicinity of open clusters. The atmospheric parameters, atmospheric abundances, masses, ages, Galactic velocities, and elements of the Galactic orbits are derived for all the studied stars. We have discovered high metal abundances (close to 0.3dex) for five stars, which we classify as super-metal-rich stars. Several stars have lower [Na/Fe] than normal red giants with similar atmospheric parameters. The kinematic characteristics of these stars are somewhat different from those for objects in the Galactic thin disk. We suggest that the observed effect can be explained by inhomogeneity of the chemical composition of gas-dust clouds, which could be due to different rates of SNe II supernovae in different regions of the Galaxy.

  14. Southern near-infrared photometric monitoring of Galactic young star clusters (NIP of Stars)

    NASA Astrophysics Data System (ADS)

    Barbá, R.; Morrell, N. I.; Gunthardt, G.; Torres Robledo, S.; Jaque, M.; Soto, M.; Ferrero, G.; Arias, J. I.; Roman-Lopes, A.; Gamen, R. C.; Astudillo Hormazabal, J.

    We have performed a near-infrared photometric monitoring of 39 galactic young star clusters and star-forming regions, known as NIP of Stars, be- tween the years 2009-2011, using the Swope telescope at Las Campanas Observatory (Chile) and the RetroCam camera. The primary objective of the campaign is to perform a census of photometric variability of such clus- ters and to discover massive eclipsing binary stars. In this work, we describe the general idea, the implementation of the survey, and the first preliminary results of some of the observed clusters. This monitoring program is com- plementary to the Vista Variables in the Vía Láctea (VVV), as the brightest sources observed in NIP of Stars are saturated in VVV.

  15. RR Lyrae stars in M31 globular clusters: B514

    NASA Astrophysics Data System (ADS)

    Contreras, R.; Federici, L.; Clementini, G.; Cacciari, C.; Merighi, R.; Kinemuchi, K.; Catelan, M.; Fusi Pecci, F.; Marconi, M.; Pritzl, B.; Smith, H.

    We present preliminary results of a variable star search in the metal-poor globular cluster B514 of the Andromeda galaxy (M31), based on Hubble Space Telescope Wide Field Planetary Camera 2 and Advanced Camera for Surveys observations. A large number of RR Lyrae stars have been identified for the first time in a globular cluster of M31. The average period of the RR Lyrae variables (< Pab > = 0.58 days and < Pc > = 0.35 days, for fundamental-mode and first-overtone pulsators, respectively) and the position in the period-amplitude diagram both suggest that B514 is likely an Oosterhoff I cluster, contrary to the general behaviour of the metal-poor globular clusters in the Milky Way, which show instead Oosterhoff type II pulsation properties.

  16. Are there two disk star cluster systems in the LMC?

    NASA Technical Reports Server (NTRS)

    Kontizas, Mary; Kontizas, Evangelos

    1991-01-01

    The surface distribution of star clusters in the LMC has revealed the existence of two elliptical systems superimposed. A small surface density outer ellipse outlining the large system and a higher density elliptical inner system. The major axis of the two subsystems form an angle of 60 deg. The central subsystem contains all youngest populous globular star clusters from both the stellar and dynamical point of view. The large outer system seems to contain all old globular clusters, showing a dumpy distribution and outlining two arms at the northeast and southwest. The small LMC clusters were found to have masses less than 1000 solar masses and are distributed all over the large elliptical system.

  17. THE STRUCTURE OF THE STAR-FORMING CLUSTER RCW 38

    SciTech Connect

    Winston, E.; Wolk, S. J.; Bourke, T. L.; Spitzbart, B.; Megeath, S. T.; Gutermuth, R.

    2011-12-20

    We present a study of the structure of the high-mass star-forming region RCW 38 and the spatial distribution of its young stellar population. Spitzer Infrared Array Camera (IRAC) photometry (3-8 {mu}m) is combined with Two Micron All Sky Survey near-IR data to identify young stellar objects (YSOs) by IR-excess emission from their circumstellar material. Chandra X-ray data are used to identify class III pre-main-sequence stars lacking circumstellar material. We identify 624 YSOs: 23 class 0/I and 90 flat spectrum protostars, 437 class II stars, and 74 class III stars. We also identify 29 (27 new) O star candidates over the IRAC field. Seventy-two stars exhibit IR-variability, including 7 class 0/I and 12 flat spectrum YSOs. A further 177 tentative candidates are identified by their location in the IRAC [3.6] versus [3.6]-[5.8] color-magnitude diagram. We find strong evidence of subclustering in the region. Three subclusters were identified surrounding the central cluster, with massive and variable stars in each subcluster. The central region shows evidence of distinct spatial distributions of the protostars and pre-main-sequence stars. A previously detected IR cluster, DB2001{sub O}bj36, has been established as a subcluster of RCW 38. This suggests that star formation in RCW 38 occurs over a more extended area than previously thought. The gas-to-dust ratio is examined using the X-ray derived hydrogen column density, N{sub H} and the K-band extinction, and found to be consistent with the diffuse interstellar medium, in contrast with Serpens and NGC 1333. We posit that the high photoionizing flux of massive stars in RCW 38 affects the agglomeration of the dust grains.

  18. STAR FORMATION IN THE BULLET CLUSTER. I. THE INFRARED LUMINOSITY FUNCTION AND STAR FORMATION RATE ,

    SciTech Connect

    Sun Mi Chung; Gonzalez, Anthony H.; Clowe, Douglas; Markevitch, Maxim; Zaritsky, Dennis

    2010-12-20

    The Bullet Cluster is a massive galaxy cluster at z = 0.297 undergoing a major supersonic (Mach 3) merger event. Using data from Spitzer MIPS and the Infrared Array Camera, optical imaging, and optical spectroscopy, we present the global star formation rate (SFR) of this unique cluster. Using a 90% spectroscopically complete sample of 37 star-forming MIPS confirmed cluster members out to R < 1.7 Mpc, and the Rieke et al. relation to convert from 24 {mu}m flux to SFR, we calculate an integrated obscured SFR of 267 M{sub sun} yr{sup -1} and a specific SFR of 28 M{sub sun} yr{sup -1} per 10{sup 14} M{sub sun}. The cluster mass normalized integrated SFR of the Bullet Cluster is among the highest in a sample of eight other clusters and cluster mergers from the literature. Five LIRGs and one ULIRG contribute 30% and 40% of the total SFR of the cluster, respectively. To investigate the origin of the elevated specific SFR, we compare the infrared luminosity function (IR LF) of the Bullet Cluster to those of Coma (evolved to z = 0.297) and CL1358+62. The Bullet Cluster IR LF exhibits an excess of sources compared to the IR LFs of the other massive clusters. A Schechter function fit of the Bullet Cluster IR LF yields L* = 44.68 {+-} 0.11 erg s{sup -1}, which is {approx}0.25 and 0.35 dex brighter than L* of evolved Coma and CL1358+62, respectively. The elevated IR LF of the Bullet Cluster relative to other clusters can be explained if we attribute the 'excess' star-forming IR galaxies to a population associated with the infalling group that has not yet been transformed into quiescent galaxies. In this case, the timescale required for quenching star formation in the cluster environment must be longer than the timescale since the group's accretion-a few hundred million years. We suggest that 'strangulation' is likely to be an important process in the evolution of star formation in clusters.

  19. Spectrophotometry of 237 Stars in 7 Open Clusters

    NASA Astrophysics Data System (ADS)

    Clampitt, Lori; Burstein, David

    1997-08-01

    Spectrophotometry is presented for 237 stars in 7 nearby open clusters: Hyades, Pleiades, Alpha Persei, Praesepe, Coma Berenices, IC 4665, and M39. The observations were taken by Lee McDonald and David Burstein using the Wampler single-channel scanner on the Crossley 0.9m telescope at Lick Observatory from July 1973 through December 1974. Sixteen bandpasses spanning the spectral range 3500 Angstroms to 7780 Angstroms were observed for each star, with bandwidths 32Angstroms, 48 Angstroms or 64 Angstroms. Data are standardized to the Hayes-Latham system to mutual accuracy of 0.016 mag per passband. The accuracy of the spectrophotometry is assessed in three ways on a star-by-star basis. First, comparisons are made with previously published spectrophotometry for 19 stars observed in common. Second, (B-V) colors and uvby colors are compared for 236 stars and 221 stars, respectively. Finally, comparsions are made for 200 main sequence stars to the spectral synthesis models of Kurucz, fixing log g = 4.0 and [Fe/H] = 0.0, and only varying effective temperature. The accuracy of tests using uvby colors and the Kurucz models are shown to track each other closely, yielding an accuracy estimate (1 sigma ) of 0.01 mag for the 13 colors formed from bandpasses longward of the Balmer jump, and 0.02 mag for the 3 colors formed from the three bandpasses below the Balmer jump. In contrast, larger scatter is found relative to the previously published spectrophotometry of Bohm-Vitense & Johnson (16 stars in common) and Gunn & Stryker (3 stars). We also show that the scatter in the fits of the spectrophotometric colors and the uvby filter colors is a reasonable way to identify the observations of which specific stars are accurate to 1 sigma , 2 sigma , .... As such, the residuals from both the filter color fits and the Kurucz model fits are tabulated for each star where it was possible to make a comparison, so users of these data can choose stars according to the accuracy of the data

  20. The Formation and Early Evolution of Embedded Massive Star Clusters

    NASA Astrophysics Data System (ADS)

    Barnes, Peter

    We propose to combine Spitzer, WISE, Herschel, and other archival spacecraft data with an existing ground- and space-based mm-wave to near-IR survey of molecular clouds over a large portion of the Milky Way, in order to systematically study the formation and early evolution of massive stars and star clusters, and provide new observational calibrations for a theoretical paradigm of this key astrophysical problem. Central Objectives: The Galactic Census of High- and Medium-mass Protostars (CHaMP) is a large, unbiased, uniform, and panchromatic survey of massive star and cluster formation and early evolution, covering 20°x6° of the Galactic Plane. Its uniqueness lies in the comprehensive molecular spectroscopy of 303 massive dense clumps, which have also been included in several archival spacecraft surveys. Our objective is a systematic demographic analysis of massive star and cluster formation, one which has not been possible without knowledge of our CHaMP cloud sample, including all clouds with embedded clusters as well as those that have not yet formed massive stars. For proto-clusters deeply embedded within dense molecular clouds, analysis of these space-based data will: 1. Yield a complete census of Young Stellar Objects in each cluster. 2. Allow systematic measurements of embedded cluster properties: spectral energy distributions, luminosity functions, protostellar and disk fractions, and how these vary with cluster mass, age, and density. Combined with other, similarly complete and unbiased infrared and mm data, CHaMP's goals include: 3. A detailed comparison of the embedded stellar populations with their natal dense gas to derive extinction maps, star formation efficiencies and feedback effects, and the kinematics, physics, and chemistry of the gas in and around the clusters. 4. Tying the demographics, age spreads, and timescales of the clusters, based on pre-Main Sequence evolution, to that of the dense gas clumps and Giant Molecular Clouds. 5. A

  1. HOT WHITE DWARF SHINES IN YOUNG STAR CLUSTER

    NASA Technical Reports Server (NTRS)

    2002-01-01

    A dazzling 'jewel-box' collection of over 20,000 stars can be seen in crystal clarity in this NASA Hubble Space Telescope image, taken with the Wide Field and Planetary Camera 2. The young (40 million year old) cluster, called NGC 1818, is 164,000 light-years away in the Large Magellanic Cloud (LMC), a satellite galaxy of our Milky Way. The LMC, a site of vigorous current star formation, is an ideal nearby laboratory for studying stellar evolution. In the cluster, astronomers have found a young white dwarf star, which has only very recently formed following the burnout of a red giant. Based on this observation astronomers conclude that the red giant progenitor star was 7.6 times the mass of our Sun. Previously, astronomers have estimated that stars anywhere from 6 to 10 solar masses would not just quietly fade away as white dwarfs but abruptly self-destruct in torrential explosions. Hubble can easily resolve the star in the crowded cluster, and detect its intense blue-white glow from a sizzling surface temperature of 50,000 degrees Fahrenheit. IMAGE DATA Date taken: December 1995 Wavelength: natural color reconstruction from three filters (I,B,U) Field of view: 100 light-years, 2.2 arc minutes TARGET DATA Name: NGC 1818 Distance: 164,000 light-years Constellation: Dorado Age: 40 million years Class: Rich star cluster Apparent magnitude: 9.7 Apparent diameter: 7 arc minutes Credit: Rebecca Elson and Richard Sword, Cambridge UK, and NASA (Original WFPC2 image courtesy J. Westphal, Caltech) Image files are available electronically via the World Wide Web at: http://oposite.stsci.edu/pubinfo/1998/16 and via links in http://oposite.stsci.edu/pubinfo/latest.html or http://oposite.stsci.edu/pubinfo/pictures.html. GIF and JPEG images are available via anonymous ftp to oposite.stsci.edu in /pubinfo/GIF/9816.GIF and /pubinfo/JPEG/9816.jpg.

  2. Formation and evolution of star clusters in interacting galaxies

    NASA Astrophysics Data System (ADS)

    Anders, P.

    2006-02-01

    My present PhD thesis "Formation and evolution of star clusters in interacting galaxies" and the associated work was performed in the Galaxy Evolution Group at the Institut für Astrophysik (Georg-August-Universität Göttingen, Germany) under supervision of apl. Prof. Dr. U. Fritze - v. Alvensleben. My co-supervisor - especially for the observational part of the thesis - was Dr. R. de Grijs (Department of Physics & Astronomy, University of Sheffield, UK). In the course of my PhD project I got involved in a number of projects, spanning a wide range of astrophysical topics. The results of these projects are reported in my PhD thesis: * evolutionary synthesis modeling: I played a leading role in the most recent updates of the GALEV code (originally built by U. Fritze - v. Alvensleben). I have implemented gaseous emission effects to the code (see Anders & Fritze - v. Alvensleben 2003). Only due to this update, models for younger ages than before became possible, allowing for more direct and detailed studies of star and star cluster formation processes. In addition, I have implemented a variety of new filter systems (models in a comprehensive set of regularly used filter sets, including all relevant filters on-board the HST, are now available) eliminating the need to transform between different filter systems and avoiding the associated uncertainties. * cluster parameter determination: I have developed and thoroughly tested the AnalySED tool (Anders et al. 2004b). This tool allows for statistically robust parameter determination from multi-wavelength broad-band observations of (initially) star clusters. The AnalySED tool has been successfully applied to a large number of star cluster systems (e.g. Anders et al. 2004a; de Grijs et al. (incl. Anders) 2003a,b,c, 2004; de Grijs & Anders 2006, MNRAS, in press) * uncertainties inherent to evolutionary synthesis modeling and parameter determination: I reported very detailed on a large number of tests on the accuracy of the

  3. STAR CLUSTER DISRUPTION IN THE STARBURST GALAXY MESSIER 82

    SciTech Connect

    Li, Shuo; Li, Chengyuan; De Grijs, Richard; Anders, Peter

    2015-01-01

    Using high-resolution, multiple-passband Hubble Space Telescope images spanning the entire optical/near-infrared wavelength range, we obtained a statistically complete U-band-selected sample of 846 extended star clusters across the disk of the nearby starburst galaxy M82. Based on a careful analysis of the clusters' spectral energy distributions, we determined their galaxy-wide age and mass distributions. The M82 clusters exhibit three clear peaks in their age distribution, thus defining relatively young, log (t yr{sup –1}) ≤ 7.5, intermediate-age, log (t yr{sup –1}) in [7.5, 8.5], and old samples, log (t yr{sup –1}) ≥ 8.5. Comparison of the completeness-corrected mass distributions offers a firm handle on the galaxy's star cluster disruption history. The most massive star clusters in the young and old samples are (almost) all concentrated in the most densely populated central region, while the intermediate-age sample's most massive clusters are more spatially dispersed, which may reflect the distribution of the highest-density gas throughout the galaxy's evolutionary history, combined with the solid-body nature of the galaxy's central region.

  4. Ages of intermediate-age Magellanic Cloud star clusters

    NASA Technical Reports Server (NTRS)

    Flower, P. J.

    1984-01-01

    Ages of intermediate-age Large Magellanic Cloud star clusters have been estimated without locating the faint, unevolved portion of cluster main sequences. Six clusters with established color-magnitude diagrams were selected for study: SL 868, NGC 1783, NGC 1868, NGC 2121, NGC 2209, and NGC 2231. Since red giant photometry is more accurate than the necessarily fainter main-sequence photometry, the distributions of red giants on the cluster color-magnitude diagrams were compared to a grid of 33 stellar evolutionary tracks, evolved from the main sequence through core-helium exhaustion, spanning the expected mass and metallicity range for Magellanic Cloud cluster red giants. The time-dependent behavior of the luminosity of the model red giants was used to estimate cluster ages from the observed cluster red giant luminosities. Except for the possibility of SL 868 being an old globular cluster, all clusters studied were found to have ages less than 10 to the 9th yr. It is concluded that there is currently no substantial evidence for a major cluster population of large, populous clusters greater than 10 to the 9th yr old in the Large Magellanic Cloud.

  5. Variable Stars In the Unusual, Metal-Rich Globular Cluster

    NASA Technical Reports Server (NTRS)

    Pritzl, Barton J.; Smith, Horace A.; Catelan, Marcio; Sweigart, Allen V.; Oegerle, William R. (Technical Monitor)

    2002-01-01

    We have undertaken a search for variable stars in the metal-rich globular cluster NGC 6388 using time-series BV photometry. Twenty-eight new variables were found in this survey, increasing the total number of variables found near NGC 6388 to approx. 57. A significant number of the variables are RR Lyrae (approx. 14), most of which are probable cluster members. The periods of the fundamental mode RR Lyrae are shown to be unusually long compared to metal-rich field stars. The existence of these long period RRab stars suggests that the horizontal branch of NGC 6388 is unusually bright. This implies that the metallicity-luminosity relationship for RR Lyrae stars is not universal if the RR Lyrae in NGC 6388 are indeed metal-rich. We consider the alternative possibility that the stars in NGC 6388 may span a range in [Fe/H]. Four candidate Population II Cepheids were also found. If they are members of the cluster, NGC 6388 would be the most metal-rich globular cluster to contain Population II Cepheids. The mean V magnitude of the RR Lyrae is found to be 16.85 +/- 0.05 resulting in a distance of 9.0 to 10.3 kpc, for a range of assumed values of (M(sub V)) for RR Lyrae. We determine the reddening of the cluster to be E(B - V) = 0.40 +/- 0.03 mag, with differential reddening across the face of the cluster. We discuss the difficulty in determining the Oosterhoff classification of NGC 6388 and NGC 6441 due to the unusual nature of their RR Lyrae, and address evolutionary constraints on a recent suggestion that they are of Oosterhoff type II.

  6. Clues on the Galactic evolution of sulphur from star clusters

    NASA Astrophysics Data System (ADS)

    Caffau, E.; Monaco, L.; Spite, M.; Bonifacio, P.; Carraro, G.; Ludwig, H.-G.; Villanova, S.; Beletsky, Y.; Sbordone, L.

    2014-08-01

    Context. The abundances of α-elements are a powerful diagnostic of the star formation history and chemical evolution of a galaxy. Sulphur, being moderately volatile, can be reliably measured in the interstellar medium (ISM) of damped Ly-α galaxies and extragalactic H ii regions. Measurements in stars of different metallicity in our Galaxy can then be readily compared to the abundances in external galaxies. Such a comparison is not possible for Si or Ca that suffer depletion onto dust in the ISM. Furthermore, studying sulphur is interesting because it probes nucleosynthetic conditions that are very different from those of O or Mg. In this context measurements in star clusters are a reliable tracers of the Galactic evolution of sulphur. Aims: The aim of this paper is to determine sulphur abundances in several Galactic clusters that span a metallicity range -1.5 < [Fe/H] < 0.0. Methods: We use a standard abundance analysis, based on 1D model atmospheres in local thermodynamical equilibrium (LTE) and literature corrections for non-LTE (NLTE), as well as 3D corrections based on hydrodynamical model atmospheres, to derive sulphur abundances in a sample of stars in the globular cluster M 4, and the open clusters Trumpler 5, NGC 2477, and NGC 5822. Results: We find ⟨ A(S) ⟩ NLTE = 6.11 ± 0.04 for M 4, ⟨ A(S) ⟩ NLTE = 7.17 ± 0.02 for NGC 2477, and ⟨ A(S) ⟩ NLTE = 7.13 ± 0.06 for NGC 5822. For the only star studied in Trumpler 5 we find A(S)NLTE = 6.43 ± 0.03 and A(S)LTE = 6.94 ± 0.05. Conclusions: Our measurements show that, by and large, the S abundances in Galactic clusters trace reliably those in field stars. The only possible exception is Trumpler 5, for which the NLTE sulphur abundance implies an [S/Fe] ratio lower by roughly 0.4 dex than observed in field stars of comparable metallicity, even though its LTE sulphur abundance is in line with abundances of field stars. Moreover the LTE sulphur abundance is consistent only with the abundance of another

  7. The Star Cluster Mass-Galactocentric Radius Relation: Implications for Cluster Formation

    NASA Astrophysics Data System (ADS)

    Sun, Weijia; de Grijs, Richard; Fan, Zhou; Cameron, Ewan

    2016-01-01

    Whether or not the initial star cluster mass function is established through a universal, galactocentric-distance-independent stochastic process, on the scales of individual galaxies, remains an unsolved problem. This debate has recently gained new impetus through the publication of a study that concluded that the maximum cluster mass in a given population is not solely determined by size-of-sample effects. Here, we revisit the evidence in favor and against stochastic cluster formation by examining the young (≲ a few × {10}8 year old) star cluster mass-galactocentric radius relation in M33, M51, M83, and the Large Magellanic Cloud. To eliminate size-of-sample effects, we first adopt radial bin sizes containing constant numbers of clusters, which we use to quantify the radial distribution of the first- to fifth-ranked most massive clusters using ordinary least-squares fitting. We supplement this analysis with an application of quantile regression, a binless approach to rank-based regression taking an absolute-value-distance penalty. Both methods yield, within the 1σ to 3σ uncertainties, near-zero slopes in the diagnostic plane, largely irrespective of the maximum age or minimum mass imposed on our sample selection, or of the radial bin size adopted. We conclude that, at least in our four well-studied sample galaxies, star cluster formation does not necessarily require an environment-dependent cluster formation scenario, which thus supports the notion of stochastic star cluster formation as the dominant star cluster-formation process within a given galaxy.

  8. Effects of intermediate mass black holes on nuclear star clusters

    SciTech Connect

    Mastrobuono-Battisti, Alessandra; Perets, Hagai B.; Loeb, Abraham

    2014-11-20

    Nuclear star clusters (NSCs) are dense stellar clusters observed in galactic nuclei, typically hosting a central massive black hole. Here we study the possible formation and evolution of NSCs through the inspiral of multiple star clusters hosting intermediate mass black holes (IMBHs). Using an N-body code, we examine the dynamics of the IMBHs and their effects on the NSC. We find that IMBHs inspiral to the core of the newly formed NSC and segregate there. Although the IMBHs scatter each other and the stars, none of them is ejected from the NSC. The IMBHs are excited to high eccentricities and their radial density profile develops a steep power-law cusp. The stars also develop a power-law cusp (instead of the central core that forms in their absence), but with a shallower slope. The relaxation rate of the NSC is accelerated due to the presence of IMBHs, which act as massive perturbers. This in turn fills the loss cone and boosts the tidal disruption rate of stars both by the MBH and the IMBHs to a value excluded by rate estimates based on current observations. Rate estimates of tidal disruptions can therefore provide a cumulative constraint on the existence of IMBHs in NSCs.

  9. The Lambda Orionis association. [star cluster anomalies

    NASA Technical Reports Server (NTRS)

    Murdin, P.; Penston, M. V.

    1977-01-01

    The Lambda Orionis association has the photometric properties of a typical young cluster with an age of about 4 million yr. Its distance is 400 + or - 40 pc. Attention is drawn to the lack of a dense molecular cloud and associated infrared sources in this young grouping

  10. The variable stars of the young LMC cluster NGC 2164

    NASA Technical Reports Server (NTRS)

    Welch, Douglas L.; Mateo, Mario; Olszewski, Edward W.; Fischer, Philippe; Takamiya, Marianne

    1993-01-01

    The present search of the LMC cluster NGC 2164 for variable stars has uncovered one new member classical Cepheid variable with 3.772-day period; attention is also given to photometry for a previously unknown field overtone Cepheid variable with 3.4626-day period, and the 10.6878-day period HV 12078, which may be a member of the young NGC 2156 cluster. The clear separation of fundamental and overtone pulsators in the period-luminosity-color relation of known LMC cluster Cepheids establishes that the NGC 2164 member is a true overtone.

  11. Drama of HII regions: Clustered and Triggered Star Formation

    NASA Astrophysics Data System (ADS)

    Li, Jinzeng; YUAN, Jinghua; LIU, Hongli; Wu, Yuefang; Huang, Yafang

    2015-08-01

    Intense ultraviolet radiation from young massive stars ionizes ambient material leading to the formation of HII regions which have keen impact upon the birth of new stars in the vicinities. The strong radiation may be responsible for the dispersal of molecular clouds to hinder star formation, while the expansion of HII regions would collect neutral material to form dense layers which may be gravitationally unstable to collapse to give birth to new stars.In order to understand the star formation process under the influence of HII regions, we have carried out extensive investigations to well selected star-forming regions which all have been profoundly affected by existing massive O type stars. On the basis of multi-wavelength data from mid-infrared to millimeter collected using Spitzer, Herschel, and ground based radio telescope, the physical status of interstellar medium and star formation in these regions have been revealed. Clustered and sequential star formation have been detected toward well known HII regions, such as IC1396 and Sh-155. In a relatively large infrared dust bubble, active star formation is undergoing and the shell is still expanding. Socked features and signs of triggered star formation have been tentatively detected in a relatively small bubble. The dense cores in the Rosette Molecular Complex detected at 1.1 mm using SMA have been speculated to have a likely triggered origin according to their spatial distribution. Although some observational results have been obtained, more efforts are necessary to reach trustworthy conclusions. And more regions will be extensively explored based on multi-wavelength observations, especially the data collected using the Herschel Space Observatory.

  12. Star Formation in Undergraduate ALFALFA Team Galaxy Groups and Clusters

    NASA Astrophysics Data System (ADS)

    Koopmann, Rebecca A.; Durbala, Adriana; Finn, Rose; Haynes, Martha P.; Coble, Kimberly A.; Craig, David W.; Hoffman, G. Lyle; Miller, Brendan P.; Crone-Odekon, Mary; O'Donoghue, Aileen A.; Troischt, Parker; Undergraduate ALFALFA Team; ALFALFA Team

    2017-01-01

    The Undergraduate ALFALFA Team (UAT) Groups project is a coordinated study of gas and star formation properties of galaxies in and around 36 nearby (z<0.03) groups and clusters of varied richness, morphological type mix, and X-ray luminosity. By studying a large range of environments and considering the spatial distributions of star formation, we probe mechanisms of gas depletion and morphological transformation. The project uses ALFALFA HI observations, optical observations, and digital databases like SDSS, and incorporates work undertaken by faculty and students at different institutions within the UAT. Here we present results from our wide area Hα and broadband R imaging project carried out with the WIYN 0.9m+MOSAIC/HDI at KPNO, including an analysis of radial star formation rates and extents of galaxies in the NGC 5846, Abell 779, NRGb331, and HCG 69 groups/clusters. This work has been supported by NSF grant AST-1211005 and AST-1637339.

  13. SUPERSONIC LINE BROADENING WITHIN YOUNG AND MASSIVE SUPER STAR CLUSTERS

    SciTech Connect

    Tenorio-Tagle, Guillermo; Silich, Sergiy; Wuensch, Richard; Munoz-Tunon, Casiana; Palous, Jan E-mail: richard@wunsch.c E-mail: cmt@ll.iac.e

    2010-01-10

    The origin of supersonic infrared and radio recombination nebular lines often detected in young and massive superstar clusters is discussed. We suggest that these arise from a collection of repressurizing shocks (RSs), acting effectively to re-establish pressure balance within the cluster volume and from the cluster wind which leads to an even broader although much weaker component. The supersonic lines here are shown to occur in clusters that undergo a bimodal hydrodynamic solution, that is within clusters that are above the threshold line in the mechanical luminosity or cluster mass versus the size of the cluster plane. A plethora of RSs is due to frequent and recurrent thermal instabilities that take place within the matter reinserted by stellar winds and supernovae. We show that the maximum speed of the RSs and of the cluster wind are both functions of the temperature reached at the stagnation radius. This temperature depends only on the cluster heating efficiency (eta). Based on our two-dimensional simulations we calculate the line profiles that result from several models and confirm our analytical predictions. From a comparison between the predicted and observed values of the half-width zero intensity of the two line components, we conclude that the thermalization efficiency in young super star clusters above the threshold line must be lower than 20%.

  14. OT2_baltieri_5: Star formation in proto-clusters

    NASA Astrophysics Data System (ADS)

    Altieri, B.

    2011-09-01

    Massive clusters of galaxies have been found to date from as early as 3-4 billion years after the Big Bang. Cosmological simulations using the current cold dark matter model predict that these systems should descend from 'proto-clusters' - early overdensities of massive galaxies that merge hierarchically to form a cluster. These protocluster regions themselves are built up hierarchically and so are expected to contain extremely massive galaxies, progenitors of the quiescent behemoths observed in cores of the present day massive galaxy clusters. Observational evidence for this picture, however, is sparse because high-redshift proto-clusters are rare and difficult to observe. Here we propose to probe with Herschel SPIRE the very beginning of the cluster and massive galaxies formation process by observing 5 proto-clusters at 3star formation at such high redshift, to compare the properties of the proto-cluster galaxies with those of field galaxies at similar redshift. Determining whether cluster galaxies differ from field galaxies when the proto-cluster was still forming, tells us whether any of the difference observed today is driven by nature as apposed to nurture.

  15. EVOLUTION OF SUPER STAR CLUSTER WINDS WITH STRONG COOLING

    SciTech Connect

    Wuensch, Richard; Palous, Jan; Silich, Sergiy; Tenorio-Tagle, Guillermo; Munoz-Tunon, Casiana

    2011-10-20

    We study the evolution of super star cluster winds driven by stellar winds and supernova explosions. Time-dependent rates at which mass and energy are deposited into the cluster volume, as well as the time-dependent chemical composition of the re-inserted gas, are obtained from the population synthesis code Starburst99. These results are used as input for a semi-analytic code which determines the hydrodynamic properties of the cluster wind as a function of cluster age. Two types of winds are detected in the calculations. For the quasi-adiabatic solution, all of the inserted gas leaves the cluster in the form of a stationary wind. For the bimodal solution, some of the inserted gas becomes thermally unstable and forms dense warm clumps which accumulate inside the cluster. We calculate the evolution of the wind velocity and energy flux and integrate the amount of accumulated mass for clusters of different mass, radius, and initial metallicity. We also consider conditions with low heating efficiency of the re-inserted gas or mass loading of the hot thermalized plasma with the gas left over from star formation. We find that the bimodal regime and the related mass accumulation occur if at least one of the two conditions above is fulfilled.

  16. Bright Young Star Clusters in NGC5253 with LEGUS

    NASA Astrophysics Data System (ADS)

    Calzetti, Daniela; Johnson, Kelsey E.; Adamo, Angela; Gallagher, John S.; Andrews, Jennifer E.; Smith, Linda J.; Clayton, Geoffrey C.; Lee, Janice C.; Sabbi, Elena; Ubeda, Leonardo; Kim, Hwihyun; Ryon, Jenna E.; Thilker, David A.; Bright, Stacey N.; Zackrisson, Erik; Kennicutt, Robert; de Mink, Selma E.; Whitmore, Bradley C.; Aloisi, Alessandra; Chandar, Rupali; Cignoni, Michele; Cook, David; Dale, Daniel A.; Elmegreen, Bruce; Elmegreen, Debra M.; Evans, Aaron S.; Fumagalli, Michele; Gouliermis, Dimitrios; Grasha, Kathryn; Grebel, Eva; Krumholz, Mark R.; Walterbos, Rene A. M.; Wofford, Aida; Brown, Thomas M.; Christian, Carol A.; Dobbs, Claire; Herrero-Davo`, Artemio; Kahre, Lauren; Messa, Matteo; Nair, Preethi; Nota, Antonella; Östlin, Göran; Pellerin, Anne; Sacchi, Elena; Schaerer, Daniel; Tosi, Monica

    2016-01-01

    Using UV-to-H broad and narrow-band HST imaging, we derive the ages and masses of the 11 brightest star clusters in the dwarf galaxy NGC5253. This galaxy, located at ~3 Mpc, hosts an intense starburst, which includes a centrally-concentrated dusty region with strong thermal radio emission (the `radio nebula'). The HST imaging includes data from the Cycle 21 Treasury Program LEGUS (Legacy ExtraGalactic UV Survey), in addition to narrow--band H-alpha (6563 A), P-beta (12820 A), and P-alpha (18756 A). The bright clusters have ages ~1-15 Myr and masses ~1E4 - 2.5E5 Msun. Two of the 11 star clusters are located within the radio nebula, and suffer from significant dust attenuation. Both are extremely young, with a best-fit age around 1 Myr, and masses ~7.5E4 and ~2.5E5 Msun, respectively. The most massive of the two `radio nebula' clusters is 2-4 times less massive than previously estimated and is embedded within a cloud of dust with A_V~50 mag. The two clusters account for about half of the ionizing photon rate in the radio nebula, and will eventually supply about 2/3 of the mechanical energy in present-day shocks. Additional sources are required to supply the remaining ionizing radiation, and may include very massive stars.

  17. THE STRUCTURAL EVOLUTION OF FORMING AND EARLY STAGE STAR CLUSTERS

    SciTech Connect

    Jaehnig, Karl O.; Da Rio, Nicola; Tan, Jonathan C. E-mail: ndario@ufl.edu

    2015-01-10

    We study the degree of angular substructure in the stellar position distribution of young members of Galactic star-forming regions, looking for correlations with distance from cluster center, surface number density of stars, and local dynamical age. To this end we adopt the catalog of members in 18 young (∼1-3 Myr) clusters from the Massive Young Star-Forming Complex Study in Infrared and X-ray Survey and the statistical analysis of the angular dispersion parameter, δ{sub ADP,} {sub N}. We find statistically significant correlation between δ{sub ADP,} {sub N} and physical projected distance from the center of the clusters, with the centers appearing smoother than the outskirts, consistent with more rapid dynamical processing on local dynamical, free-fall or orbital timescales. Similarly, smoother distributions are seen in regions of higher surface density, or older dynamical ages. These results indicate that dynamical processing that erases substructure is already well-advanced in young, sometimes still-forming, clusters. Such observations of the dissipation of substructure have the potential to constrain theoretical models of the dynamical evolution of young and forming clusters.

  18. Binary Black Holes from Dense Star Clusters

    NASA Astrophysics Data System (ADS)

    Rodriguez, Carl

    2017-01-01

    The recent detections of gravitational waves from merging binary black holes have the potential to revolutionize our understanding of compact object astrophysics. But to fully utilize this new window into the universe, we must compare these observations to detailed models of binary black hole formation throughout cosmic time. In this talk, I will review our current understanding of cluster dynamics, describing how binary black holes can be formed through gravitational interactions in dense stellar environments, such as globular clusters and galactic nuclei. I will review the properties and merger rates of binary black holes from the dynamical formation channel. Finally, I will describe how the spins of a binary black hole are determined by its formation history, and how we can use this to discriminate between dynamically-formed binaries and those formed from isolated evolution in galactic fields.

  19. THE BRIGHTEST YOUNG STAR CLUSTERS IN NGC 5253

    SciTech Connect

    Calzetti, D.; Johnson, K. E.; Adamo, A.; Gallagher III, J. S.; Ryon, J. E.; Andrews, J. E.; Smith, L. J.; Lee, J. C.; Sabbi, E.; Ubeda, L.; Bright, S. N.; Whitmore, B. C.; Aloisi, A.; Kim, H.; Thilker, D.; Zackrisson, E.; Kennicutt, R. C.; Mink, S. E. de; Chandar, R.; and others

    2015-10-01

    The nearby dwarf starburst galaxy NGC 5253 hosts a number of young, massive star clusters, the two youngest of which are centrally concentrated and surrounded by thermal radio emission (the “radio nebula”). To investigate the role of these clusters in the starburst energetics, we combine new and archival Hubble Space Telescope images of NGC 5253 with wavelength coverage from 1500 Å to 1.9 μm in 13 filters. These include Hα, Pβ, and Pα, and the imaging from the Hubble Treasury Program LEGUS (Legacy Extragalactic UV Survey). The extraordinarily well-sampled spectral energy distributions enable modeling with unprecedented accuracy the ages, masses, and extinctions of the nine optically brightest clusters (M{sub V} < −8.8) and the two young radio nebula clusters. The clusters have ages ∼1–15 Myr and masses ∼1 × 10{sup 4}–2.5 × 10{sup 5} M{sub ⊙}. The clusters’ spatial location and ages indicate that star formation has become more concentrated toward the radio nebula over the last ∼15 Myr. The most massive cluster is in the radio nebula; with a mass ∼2.5 × 10{sup 5} M{sub ⊙} and an age ∼1 Myr, it is 2–4 times less massive and younger than previously estimated. It is within a dust cloud with A{sub V} ∼ 50 mag, and shows a clear near-IR excess, likely from hot dust. The second radio nebula cluster is also ∼1 Myr old, confirming the extreme youth of the starburst region. These two clusters account for about half of the ionizing photon rate in the radio nebula, and will eventually supply about 2/3 of the mechanical energy in present-day shocks. Additional sources are required to supply the remaining ionizing radiation, and may include very massive stars.

  20. The SUNBIRD survey: characterizing the super star cluster populations of intensely star-forming galaxies

    NASA Astrophysics Data System (ADS)

    Randriamanakoto, Zara; Vaisanen, Petri; Escala, Andres

    2015-08-01

    This work investigates properties of young, massive and dense star clusters in a sample of 42 nearby starbursts and LIRGs with an average distance of 80 Mpc. The targets form the sample of the SUperNovae and starBursts in the InfraReD (SUNBIRD) survey that were imaged using near-infrared K-band adaptive optics mounted on the Gemini/NIRI and the VLT/NaCo instruments.We fitted power-laws to the SSC K-band luminosity functions and found index values ranging between 1.5 and 2.4 with a median value of α ˜ 1.86±0.24. This is shallower than the average of ≈ 2.4 associated with normal spiral galaxies indicating that SSCs hosted by star-forming galaxies are disrupted in a way depending on their mass or environment. Using simulations we found that blending effects are not significant for targets closer than ≈100Mpc. We also established the first ever near-infrared (NIR) brightest star cluster magnitude - star formation rate (SFR) relation. The correlation has a steeper slope compared to the one with optical data at lower SFRs which could indicate a simple statistical effect, though we argue that a physical truncation of the mass distribution at high masses would better explain the tight scatter of the observed relation.Finally, we combined new NIR imaging of seven LIRG targets with their optical HST archival data to derive the age, mass, and extinction distributions of optically-selected SSC candidates. Apart from having a high mass range of 10^4 - 10^8 M⊙, more than a quarter of the cluster population is younger than 30 Myr. We also derived the cluster initial mass functions and found that at least in one of the LIRGs, a mass-dependent disruption mechanism is responsible for the deficiency in low-mass star clusters. The cluster formation efficiencies Γ = 10 - 23 %, on the other hand, support the arguments that highly-pressurized environments favor SF in bound star clusters.This work has shown the importance of studying SSC host galaxies with high SFR levels to

  1. Star clusters in the Magellanic Clouds - I. Parametrization and classification of 1072 clusters in the LMC

    NASA Astrophysics Data System (ADS)

    Nayak, P. K.; Subramaniam, A.; Choudhury, S.; Indu, G.; Sagar, Ram

    2016-12-01

    We have introduced a semi-automated quantitative method to estimate the age and reddening of 1072 star clusters in the Large Magellanic Cloud (LMC) using the Optical Gravitational Lensing Experiment III survey data. This study brings out 308 newly parametrized clusters. In a first of its kind, the LMC clusters are classified into groups based on richness/mass as very poor, poor, moderate and rich clusters, similar to the classification scheme of open clusters in the Galaxy. A major cluster formation episode is found to happen at 125 ± 25 Myr in the inner LMC. The bar region of the LMC appears prominently in the age range 60-250 Myr and is found to have a relatively higher concentration of poor and moderate clusters. The eastern and the western ends of the bar are found to form clusters initially, which later propagates to the central part. We demonstrate that there is a significant difference in the distribution of clusters as a function of mass, using a movie based on the propagation (in space and time) of cluster formation in various groups. The importance of including the low-mass clusters in the cluster formation history is demonstrated. The catalogue with parameters, classification, and cleaned and isochrone fitted colour-magnitude diagrams of 1072 clusters, which are available as online material, can be further used to understand the hierarchical formation of clusters in selected regions of the LMC.

  2. Star formation in the massive cluster merger Abell 2744

    NASA Astrophysics Data System (ADS)

    Rawle, T. D.; Altieri, B.; Egami, E.; Pérez-González, P. G.; Richard, J.; Santos, J. S.; Valtchanov, I.; Walth, G.; Bouy, H.; Haines, C. P.; Okabe, N.

    2014-07-01

    We present a comprehensive study of star-forming (SF) galaxies in the Hubble Space Telescope (HST) Frontier Field recent cluster merger A2744 (z = 0.308). Wide-field, ultraviolet-infrared (UV-IR) imaging enables a direct constraint of the total star formation rate (SFR) for 53 cluster galaxies, with SFRUV+IR = 343 ± 10 M⊙ yr-1. Within the central 4 arcmin (1.1 Mpc) radius, the integrated SFR is complete, yielding a total SFRUV+IR = 201 ± 9 M⊙ yr-1. Focusing on obscured star formation, this core region exhibits a total SFRIR = 138 ± 8 M⊙ yr-1, a mass-normalized SFRIR of ΣSFR = 11.2 ± 0.7 M⊙ yr-1 per 1014 M⊙ and a fraction of IR-detected SF galaxies f_SF = 0.080^{+0.010}_{-0.037}. Overall, the cluster population at z ˜ 0.3 exhibits significant intrinsic scatter in IR properties (total SFRIR, Tdust distribution) apparently unrelated to the dynamical state: A2744 is noticeably different to the merging Bullet cluster, but similar to several relaxed clusters. However, in A2744 we identify a trail of SF sources including jellyfish galaxies with substantial unobscured SF due to extreme stripping (SFRUV/SFRIR up to 3.3). The orientation of the trail, and of material stripped from constituent galaxies, indicates that the passing shock front of the cluster merger was the trigger. Constraints on star formation from both IR and UV are crucial for understanding galaxy evolution within the densest environments.

  3. Quenching of the star formation activity in cluster galaxies

    NASA Astrophysics Data System (ADS)

    Boselli, A.; Roehlly, Y.; Fossati, M.; Buat, V.; Boissier, S.; Boquien, M.; Burgarella, D.; Ciesla, L.; Gavazzi, G.; Serra, P.

    2016-11-01

    We study the star formation quenching mechanism in cluster galaxies by fitting the spectral energy distribution (SED) of the Herschel Reference Survey, a complete volume-limited K-band-selected sample of nearby galaxies including objects in different density regions, from the core of the Virgo cluster to the general field. The SEDs of the target galaxies were fitted using the CIGALE SED modelling code. The truncated activity of cluster galaxies was parametrised using a specific star formation history with two free parameters, the quenching age QA and the quenching factor QF. These two parameters are crucial for the identification of the quenching mechanism, which acts on long timescales when starvation processes are at work, but is rapid and efficient when ram pressure occurs. To be sensitive to an abrupt and recent variation of the star formation activity, we combined twenty photometric bands in the UV to far-infrared in a new way with three age-sensitive Balmer line absorption indices extracted from available medium-resolution (R 1000) integrated spectroscopy and with Hα narrow-band imaging data. The use of a truncated star formation history significantly increases the quality of the fit in HI-deficient galaxies of the sample, that is to say, in those objects whose atomic gas content has been removed during the interaction with the hostile cluster environment. The typical quenching age of the perturbed late-type galaxies is QA ≲ 300 Myr whenever the activity of star formation is reduced by 50% < QF ≤ 80% and QA ≲ 500 Myr for QF > 80%, while that of the quiescent early-type objects is QA ≃ 1-3 Gyr. The fraction of late-type galaxies with a star formation activity reduced by QF > 80% and with an HI-deficiency parameter HI-def > 0.4 drops by a factor of 5 from the inner half virial radius of the Virgo cluster (R/Rvir < 0.5), where the hot diffuse X-ray emitting gas of the cluster is located, to the outer regions (R/Rvir > 4). The efficient quenching of the

  4. A star cluster at the edge of the Galaxy

    NASA Astrophysics Data System (ADS)

    Brand, J.; Wouterloot, J. G. A.

    2007-03-01

    Context: This paper is part of our ongoing study of star formation in the (far-) outer Galaxy. Aims: Our goal in this paper is to study stars and molecular gas in the direction of IRAS 06145+1455 (WB89-789). The kinematic distance of the associated molecular cloud is 11.9 kpc. With a galactocentric distance of ~ 20.2 kpc, this object is at the edge of the (molecular) disk of the Galaxy. Methods: We use near-IR (J, H, K), molecular line-, and dust continuum observations. Results: The near-IR data show the presence of an (embedded) cluster of about 60 stars, with a radius ˜ 1.3 pc and an average stellar surface density ~ 12 pc-2. We find at least 14 stars with NIR-excess, 3 of which are possibly Class I objects. The cluster is embedded in a ˜ 1000 M⊙ molecular/dust core, from which a molecular outflow originates. The temperature of most of the outflowing gas is ⪉ 40 K, and the total mass of the swept-up material is ⪉ 10 M⊙. Near the center of the flow, indications of much higher temperatures are found, probably due to shocks. A spectrum taken of one of the probable cluster members shows a tentative likeness to that of a K3 III-star (with an age of at least 20 Myr). If correct, this would confirm the kinematic distance. Conclusions: .This cluster is the furthest one from the Galactic center yet detected. The combination of old and recent activity implies that star formation has been going on for at least 20 Myr, which is difficult to understand considering the location of this object, where external triggers are either absent or weak, compared to the inner Galaxy. This suggests that once star formation is occurring, later generations of stars may form through the effect of the first generation of stars on the (remnants of) the original molecular cloud. Partly based on observations collected at the European Southern Observatory, Chile. Table 4 is only available in electronic form at http://www.aanda.org

  5. Variable Circumstellar Disks of Classical Be Stars in Clusters

    NASA Astrophysics Data System (ADS)

    Gerhartz, C.; Bjorkman, K. S.; Bjorkman, J. E.; Wisniewski, J. P.

    2016-11-01

    Circumstellar disks are common among many stars, at most spectral types, and at different stages of their lifetimes. Among the near-main-sequence classical Be stars, there is growing evidence that these disks form, dissipate, and reform on timescales that differ from star to star. Using data obtained with the Large Monolithic Imager (LMI) at the Lowell Observatory Discovery Channel Telescope (DCT), along with additional complementary data obtained at the University of Toledo Ritter Observatory (RO), we have begun a long-term monitoring project of a well-studied set of galactic star clusters that are known to contain Be stars. Our goal is to develop a statistically significant sample of variable circumstellar disk systems over multiple timescales. With a robust multi-epoch study we can determine the relative fraction of Be stars that exhibit disk-loss or disk-renewal phases, and investigate the range of timescales over which these events occur. A larger sample will improve our understanding of the prevalence and nature of the disk variability, and may provide insight about underlying physical mechanisms.

  6. The Investigation of Stars, Star Clusters and Nebulae in 'Abd al-Rahman-Sufi's Book of the Fixed Stars

    NASA Astrophysics Data System (ADS)

    Hafez, Ihsan; Stephenson, F. Richard; Orchiston, Wayne

    'Abd al-Rahān al-Sūfī (AD 903-986) is justly famous for his Book of the Fixed Stars. This is an outstanding Medieval treatise on astronomy that was written in AD 964. This work was developed from Ptolemy's Almagest, but was based upon al-Sūfī's own stellar observations. The Book of the Fixed Stars has been copied down through the ages, and currently 35 copies are known to exist in various archival repositories around the world. In this paper we begin with a brief introduction to the Book of the Fixed Stars and provide biographical material about al-Sūfī before reviewing his investigation of stars, star clusters, nebulae and galaxies in his book. We examine al-Sūfī's novel stellar magnitude system, his comments on star colours, and stars mentioned in his book but not in the Almagest. We conclude with a listing of star clusters, nebulae and galaxies, including the earliest-known mention of the Great Nebula in Andromeda.

  7. Star formation in shocked cluster spirals and their tails

    NASA Astrophysics Data System (ADS)

    Roediger, E.; Brüggen, M.; Owers, M. S.; Ebeling, H.; Sun, M.

    2014-09-01

    Recent observations of ram pressure stripped spiral galaxies in clusters revealed details of the stripping process, i.e. the truncation of all interstellar medium phases and of star formation (SF) in the disc, and multiphase star-forming tails. Some stripped galaxies, in particular in merging clusters, develop spectacular star-forming tails, giving them a jellyfish-like appearance. In merging clusters, merger shocks in the intracluster medium (ICM) are thought to have overrun these galaxies, enhancing the ambient ICM pressure and thus triggering SF, gas stripping, and tail formation. We present idealized hydrodynamical simulations of this scenario, including standard descriptions for SF and stellar feedback. To aid the interpretation of recent and upcoming observations, we focus on particular structures and dynamics in SF patterns in the remaining gas disc and in the near tails, which are easiest to observe. The observed jellyfish morphology is qualitatively reproduced for, both, face-on and edge-on stripping. In edge-on stripping, the interplay between the ICM wind and the disc rotation leads to asymmetries along the ICM wind direction and perpendicular to it. The apparent tail is still part of a highly deformed gaseous and young stellar disc. In both geometries, SF takes place in knots throughout the tail, such that the stars in the tails show no ordered age gradients. Significant SF enhancement in the disc occurs only at radii where the gas will be stripped in due course.

  8. Deriving physical parameters of M31 star clusters using the PHAT survey .

    NASA Astrophysics Data System (ADS)

    de Meulenaer, P.; Vansevičius, V.

    This work presents the derivation of the physical parameters of 1287 M31 star clusters using the catalog of the Panchromatic Hubble Andromeda Treasury survey. The star cluster parameters are derived using a large grid of star cluster models, generated with stochastically populated IMF, that are compared to the integrated broad-band WFC3+ACS photometry of the observed clusters. We derive the age, mass, and extinction of the sample of M31 star clusters with fixed solar metallicity. For clusters older than 1 Gyr, we also derive the metallicity. For globular clusters, we show that the metallicity derived is in good agreement with the metallicity previously derived using spectroscopy in literature.

  9. Chemical Compositions of Stars in Globular Cluster NGC 2419

    NASA Astrophysics Data System (ADS)

    Kadakia, Shimonee; Smecker-Hane, T.; Bosler, T.

    2007-05-01

    We determine the chemical abundances of 19 red giant branch stars in the Galactic globular cluster NGC 2419. Lying at a distance of 84.2 kpc and a galactocentric distance of 91.5 kpc, NGC 2419 is the fourth brightest globular cluster in the Milky Way with a total magnitude of M_V = -9.6 mag, which is significantly brighter than M_V = -7.5 mag, the typical peak of the globular cluster luminosity functions in external galaxies. Our results will give an insight of whether NGC 2419 is in fact a globular cluster or a core of a disrupted galaxy that merged with the Milky Way. We have used IRAF to reduce spectra we have taken with the DEIMOS spectrograph on the the Keck I 10-meter telescope. Using the strengths of the Ca II triplet absorption lines at approximately 8600 Angstrom, we will determine the chemical abundance of each star. If the chemical abundances differ by significantly more than the observational errors would predict then we can conclude the cluster is a remnant of the core of a galaxy that merged with the Milky Way and not a normal globular cluster, because most globular clusters formed quickly from a well mixed gas cloud, and thus their stars have nearly identical ages and chemical compositions. We gratefully acknowledge financial support from a UROP grant to SK and NSF grant AST-0307863 to TSH. These data were obtained at the Keck Observatory, operated by the California Inst. of Technology, Univ. of California and NASA and made possible by generous financial support from the W.M. Keck Foundation.

  10. Observational templates of star cluster disruption. The stellar group NGC 1901 in front of the Large Magellanic Cloud

    NASA Astrophysics Data System (ADS)

    Carraro, G.; de La Fuente Marcos, R.; Villanova, S.; Moni Bidin, C.; de La Fuente Marcos, C.; Baumgardt, H.; Solivella, G.

    2007-05-01

    Context: Observations indicate that present-day star formation in the Milky Way disk takes place in stellar ensembles or clusters rather than in isolation. Bound, long-lived stellar groups are known as open clusters. They gradually lose stars and are severely disrupted in their final evolutionary stages, leaving an open cluster remnant made up of a few stars. Aims: In this paper, we study in detail the stellar content and kinematics of the poorly populated star cluster NGC 1901. This object appears projected against the Large Magellanic Cloud. The aim of the present work is to derive the current evolutionary status, binary fraction, age, and mass of this stellar group. These are fundamental quantities to compare with those from N-body models in order to study the most general topic of star cluster evolution and dissolution. Methods: The analysis is performed using wide-field photometry in the UBVI pass-band, proper motions from the UCAC.2 catalog, and 3 epochs of high-resolution spectroscopy, as well as results from extensive N-body calculations. Results: The star group NGC 1901 is found to be an ensemble of solar metallicity stars, 400±100 Myr old, with a core radius of 0.23 pc, a tidal radius of 1.0 pc, and a location at 400±50 pc from the Sun. Out of 13 confirmed members, only 5 single stars have been found. Its estimated present-day binary fraction is at least 62%. The calculated heliocentric space motion of the cluster is not compatible with possible membership in the Hyades stream. Conclusions: Our results show that NGC 1901 is a clear prototype of an open cluster remnant characterized by a high value of the binary fraction and a significant depletion of low-mass stars. In light of numerical simulations, this is compatible with NGC 1901 being what remains of a larger system initially made of 500-750 stars. Data for Fig. 4 is only available in electronic form at the CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or via http

  11. TWO BARIUM STARS IN THE OPEN CLUSTER NGC 5822

    SciTech Connect

    Katime Santrich, O. J.; Pereira, C. B.; De Castro, D. B. E-mail: claudio@on.br

    2013-08-01

    Open clusters are very useful examples to explain the constraint of the nucleosynthesis process with the luminosities of stars because the distances of the clusters are better known than those of field stars. We carried out a detailed spectroscopic analysis to derive the chemical composition of two red giants in the young open cluster NGC 5822, NGC 5822-2, and NGC 5822-201. We obtained abundances of C, N, O, Na, Mg, Al, Ca, Si, Ti, Ni, Cr, Y, Zr, La, Ce, and Nd. The atmospheric parameters of the studied stars and their chemical abundances were determined using high-resolution optical spectroscopy. We employed the local thermodynamic equilibrium model atmospheres of Kurucz and the spectral analysis code MOOG. The abundances of the light elements were derived using the spectral synthesis technique. We found that NGC 5822-2 and -201 have, respectively, a mean overabundance of the elements created by the s-process, ''s'', with the notation [s/Fe] of 0.77 {+-} 0.12 and 0.83 {+-} 0.05. These values are higher than those for field giants of similar metallicity. We also found that NGC 5822-2 and -201 have, respectively, luminosities of 140 L{sub Sun} and 76 L{sub Sun }, which are much lower than the luminosity of an asymptotic giant branch star. We conclude that NGC 5822-2 and NGC 5822-201 are two new barium stars first identified in the open cluster NGC 5822. The mass transfer hypothesis is the best scenario to explain the observed overabundances.

  12. PHOTOMETRIC PROPERTIES OF THE M33 STAR CLUSTER SYSTEM

    SciTech Connect

    San Roman, Izaskun; Sarajedini, Ata; Aparicio, Antonio E-mail: ata@astro.ufl.ed

    2010-09-10

    We present a catalog of 2990 extended sources in a 1{sup 0} x 1{sup 0} area centered on M33 using the MegaCam camera on the 3.6 m Canada-France-Hawaii Telescope. The catalog includes 599 new candidate stellar clusters, 204 previously confirmed clusters, 1969 likely background galaxies, and 218 unknown extended objects. We present ugriz integrated magnitudes of the candidates and confirmed star clusters (SCs) as well as the full width at half maximum, ellipticity, and stellarity. Based on the properties of the confirmed SCs, we select a sub-sample of highly probable clusters composed of 246 objects. The integrated photometry of the complete cluster catalog reveals a wide range of colors of -0.4 < (g - r) < 1.5 and -1.0 < (r - i) < 1.0 with no obvious cluster subpopulations. Comparisons with models of simple stellar populations suggest a large range of ages some as old as {approx}10 Gyr. In addition, we find a sequence in the color-color diagrams that deviates from the expected direction of evolution. This feature could be associated with very young clusters (<10{sup 7} yr) possessing significant nebular emission. Analysis of the radial density distribution suggests that the cluster system of M33 has suffered from significant depletion possibly due to interactions with M31. We also detect a gap in the cluster distribution in the color-color diagram at (g - r) {approx_equal} 0.3 and (u - g) {approx_equal} 0.8. This gap could be interpreted as an evolutionary effect. This complete catalog provides promising targets for deep photometry and high-resolution spectroscopy to study the structure and star formation history of M33.

  13. Time-Series Monitoring of Open Star Clusters

    NASA Astrophysics Data System (ADS)

    Hojaev, A. S.; Semakov, D. G.

    2006-08-01

    Star clusters especially a compact ones (with diameter of few to ten arcmin) are suitable targets to search of light variability for orchestera of stars by means of ordinary Casegrain telescope plus CCD system. A special patroling with short time-fixed exposures and mmag accuracy could be used also to study of stellar oscillation for group of stars simultaneously. The last can be carried out both separately from one site and within international campaigns. Detection and study of optical variability of X-ray sources including X-ray binaries with compact objects might be as a result of a long-term monitoring of such clusters as well. We present the program of open star clusters monitoring with Zeiss 1 meter RCC telescope of Maidanak observatory has been recently automated. In combination with quite good seeing at this observatory (see, e.g., Sarazin, M. 1999, URL http://www.eso.org/gen-fac/pubs/astclim/) the automatic telescope equipped with large-format (2KX2K) CCD camera AP-10 available will allow to collect homogenious time-series for analysis. We already started this program in 2001 and had a set of patrol observations with Zeiss 0.6 meter telescope and AP-10 camera in 2003. 7 compact open clusters in the Milky Way (NGC 7801, King1, King 13, King18, King20, Berkeley 55, IC 4996) have been monitored for stellar variability and some results of photometry will be presented. A few interesting variables were discovered and dozens were suspected for variability to the moment in these clusters for the first time. We have made steps to join the Whole-Earth Telescope effort in its future campaigns.

  14. STAR FORMATION ACTIVITY IN CLASH BRIGHTEST CLUSTER GALAXIES

    SciTech Connect

    Fogarty, Kevin; Postman, Marc; Connor, Thomas; Donahue, Megan; Moustakas, John

    2015-11-10

    The CLASH X-ray selected sample of 20 galaxy clusters contains 10 brightest cluster galaxies (BCGs) that exhibit significant (>5σ) extinction-corrected star formation rates (SFRs). Star formation activity is inferred from photometric estimates of UV and Hα+[N ii] emission in knots and filaments detected in CLASH Hubble Space Telescope ACS and WFC3 observations. UV-derived SFRs in these BCGs span two orders of magnitude, including two with a SFR ≳ 100 M{sub ⊙} yr{sup −1}. These measurements are supplemented with [O ii], [O iii], and Hβ fluxes measured from spectra obtained with the SOAR telescope. We confirm that photoionization from ongoing star formation powers the line emission nebulae in these BCGs, although in many BCGs there is also evidence of a LINER-like contribution to the line emission. Coupling these data with Chandra X-ray measurements, we infer that the star formation occurs exclusively in low-entropy cluster cores and exhibits a correlation with gas properties related to cooling. We also perform an in-depth study of the starburst history of the BCG in the cluster RXJ1532.9+3021, and create 2D maps of stellar properties on scales down to ∼350 pc. These maps reveal evidence for an ongoing burst occurring in elongated filaments, generally on ∼0.5–1.0 Gyr timescales, although some filaments are consistent with much younger (≲100 Myr) burst timescales and may be correlated with recent activity from the active galactic nucleus. The relationship between BCG SFRs and the surrounding intracluster medium gas properties provide new support for the process of feedback-regulated cooling in galaxy clusters and is consistent with recent theoretical predictions.

  15. The First Three Catalogues of Southern Star Clusters and Nebulae

    NASA Astrophysics Data System (ADS)

    Cozens, Glen; Orchiston, W.; Walsh, A.

    2011-01-01

    Nicolas de la Caille, James Dunlop and John Herschel compiled the first three catalogues of southern star clusters and nebulae. Lacaille catalogued 42 objects from Cape Town, South Africa, in 1751 and 1752. Dunlop catalogued 629 objects from Parramatta, Australia, in 1826 and Herschel catalogued 1708 objects between 1834 and 1838 from Cape Town. Many of these objects had not been seen before; In this paper we discuss the new discoveries and the accuracy of the positions supplied by Lacaille, Dunlop and Herschel. Half of Dunlop's 629 objects turned out to be asterisms and faint double stars.

  16. Manganese Abundances in Globular Cluster and Halo Field Stars

    NASA Astrophysics Data System (ADS)

    Sobeck, J. S.; Simmerer, J. A.; Fulbright, J. P.; Sneden, C.; Kraft, R. P.; Ivans, I. I.

    2004-05-01

    We have derived Mn abundances for more than 100 stars in nine Galactic globular clusters: M3, M4, M5, M10, M13, M15, M71, Pal5 and NGC 7006. In addition, Mn abundance determinations have been made for a comparable number of halo field stars possessing an overlapping range of metallicities and stellar parameters. The spectra of the cluster giants were obtained as a part of the Lick-Texas investigations into globular cluster chemistry. The spectra of the field stars are a part of a large study by Simmerer et al. (2004, ApJ, submitted). Data were collected at the McDonald, Lick ,and Keck Observatories and were analyzed using the synthetic spectra of the 6000 Å Mn I triplet. Hyperfine structure parameters were included in the synthetic spectra computations. It is well known that metal-poor field stars possess [Mn/Fe] ratios approximately a factor of two lower than solar values (Wallerstein et al. 1963, Gratton et al.1989, McWilliam et al. 1997). Our analysis shows that for the metallicity range -0.5 > [Fe/H] > -2.8 field stars have a mean relative abundance of <[Mn/Fe]> = -0.28±0.01 (sigma = 0.08), a value esssentially identical to that of the nine globular clusters: <[Mn/Fe]> = -0.28±0.01 (sigma = 0.12). It is evident that [Mn/Fe] ratios of metal-poor stars do not depend upon their environment. Our Mn abundance results viewed in conjunction with the globular cluster Cu abundances of Simmerer et al. (2003) suggest the following possibilities: one, the production of these elements is extremely metallicity-dependent or two, these elements were manufactured in the Galactic halo prior to cluster formation. Ongoing support from NSF, currently through grants AST-0307495 to CS and AST-0098453 to RPK, is gratefully acknowledged. Research for III is currently supported by NASA through Hubble Fellowship grant HST-HF-01151.01-A from the Space Telescope Science Institute.

  17. Modeling jet and outflow feedback during star cluster formation

    SciTech Connect

    Federrath, Christoph; Schrön, Martin; Banerjee, Robi; Klessen, Ralf S.

    2014-08-01

    Powerful jets and outflows are launched from the protostellar disks around newborn stars. These outflows carry enough mass and momentum to transform the structure of their parent molecular cloud and to potentially control star formation itself. Despite their importance, we have not been able to fully quantify the impact of jets and outflows during the formation of a star cluster. The main problem lies in limited computing power. We would have to resolve the magnetic jet-launching mechanism close to the protostar and at the same time follow the evolution of a parsec-size cloud for a million years. Current computer power and codes fall orders of magnitude short of achieving this. In order to overcome this problem, we implement a subgrid-scale (SGS) model for launching jets and outflows, which demonstrably converges and reproduces the mass, linear and angular momentum transfer, and the speed of real jets, with ∼1000 times lower resolution than would be required without the SGS model. We apply the new SGS model to turbulent, magnetized star cluster formation and show that jets and outflows (1) eject about one-fourth of their parent molecular clump in high-speed jets, quickly reaching distances of more than a parsec, (2) reduce the star formation rate by about a factor of two, and (3) lead to the formation of ∼1.5 times as many stars compared to the no-outflow case. Most importantly, we find that jets and outflows reduce the average star mass by a factor of ∼ three and may thus be essential for understanding the characteristic mass of the stellar initial mass function.

  18. Analysis and Implementation of Graph Clustering for Digital News Using Star Clustering Algorithm

    NASA Astrophysics Data System (ADS)

    Ahdi, A. B.; SW, K. R.; Herdiani, A.

    2017-01-01

    Since Web 2.0 notion emerged and is used extensively by many services in the Internet, we see an unprecedented proliferation of digital news. Those digital news is very rich in term of content and link to other news/sources but lack of category information. This make the user could not easily identify or grouping all the news that they read into set of groups. Naturally, digital news are linked data because every digital new has relation/connection with other digital news/resources. The most appropriate model for linked data is graph model. Graph model is suitable for this purpose due its flexibility in describing relation and its easy-to-understand visualization. To handle the grouping issue, we use graph clustering approach. There are many graph clustering algorithm available, such as MST Clustering, Chameleon, Makarov Clustering and Star Clustering. From all of these options, we choose Star Clustering because this algorithm is more easy-to-understand, more accurate, efficient and guarantee the quality of clusters results. In this research, we investigate the accuracy of the cluster results by comparing it with expert judgement. We got quite high accuracy level, which is 80.98% and for the cluster quality, we got promising result which is 62.87%.

  19. Radial variation in the stellar mass functions of star clusters

    NASA Astrophysics Data System (ADS)

    Webb, Jeremy J.; Vesperini, Enrico

    2016-12-01

    A number of recent observational studies of Galactic globular clusters have measured the variation in the slope of a cluster's stellar mass function α with clustercentric distance r. In order to gather a deeper understanding of the information contained in such observations, we have explored the evolution of α(r) for star clusters with a variety of initial conditions using a large suite of N-body simulations. We have specifically studied how the time evolution of α(r) is affected by initial size, mass, binary fraction, primordial mass segregation, black hole retention, an external tidal field, and the initial mass function itself. Previous studies have shown that the evolution of αG is closely related to the amount of mass-loss suffered by a cluster. Hence, for each simulation, we have also followed the evolution of the slope of the cluster's global stellar mass function, αG, and have shown that clusters follow a well-defined track in the αG-dα(r)/d(ln(r/rm)) plane. The location of a cluster on the αG-dα(r)/d(ln(r/rm)) plane can therefore constrain its dynamical history and, in particular, constrain possible variations in the stellar initial mass function. The αG-dα(r)/d(ln(r/rm)) plane thus serves as a key tool for fully exploiting the information contained in wide-field studies of cluster stellar mass functions.

  20. The morphology of star clusters in the SMC

    SciTech Connect

    Kontizas, E.; Kontizas, M.; Sedmak, G.; Smareglia, R.; Dapergolas, A. Trieste Universita Osservatorio Astronomico, Trieste Athens National Observatory )

    1990-08-01

    The projected ellipticities of 34 populous SMC star clusters have been derived by means of PDS 1010A scans and a computer interactive method of reduction implemented on an Apollo 570 workstation. A pair of J and R plates taken with the 1.2 m UK Schmidt telescope in Australia were used. Radial ellipticity variations within individual globular clusters seem to be a common phenomenon for the SMC clusters, similar to that observed in the LMC clusters where the innerparts are more elliptical than the outer ones in 95 percent of the cases. The derived ellipticities which correspond to the innermost part of the cluster at radial distances near to half-mass radii have been found to be statistically more elliptical than those of the LMC, known to be more elliptical than those of the Galaxy. The dynamical masses of the clusters seem to correlate with ellipticities supporting the hypothesis that, either the gravitational field of the parent galaxy being a dominant factor affect slower the shape of the high mass clusters and/or the most massive clusters, being dynamically younger, retain their original shape. 30 refs.

  1. Gravitational Focusing and the Star Cluster Initial Mass Function

    NASA Astrophysics Data System (ADS)

    Kuznetsova, Aleksandra; Hartmann, Lee; Burkert, Andreas

    2017-02-01

    We discuss the possibility that gravitational focusing is responsible for the power-law mass function of star clusters N({log}M)\\propto {M}-1. This power law can be produced asymptotically when the mass accretion rate of an object depends upon the mass of the accreting body, as \\dot{M}\\propto {M}2. Although Bondi–Hoyle–Lyttleton accretion formally produces this dependence on mass in a uniform medium, realistic environments are much more complicated. However, numerical simulations in SPH that allow for sink formation yield such an asymptotic power-law mass function. We perform pure N-body simulations to isolate the effects of gravity from those of gas physics and to show that clusters naturally result with the power-law mass distribution. We also consider the physical conditions necessary to produce clusters on appropriate timescales. Our results help support the idea that gravitationally dominated accretion is the most likely mechanism for producing the cluster mass function.

  2. STAR CLUSTER POPULATIONS IN THE OUTER DISKS OF NEARBY GALAXIES

    SciTech Connect

    Herbert-Fort, Stephane; Zaritsky, Dennis; Di Paola, Andrea; Pogge, Richard W.; Ragazzoni, Roberto E-mail: dennis.zaritsky@gmail.com

    2012-08-01

    We present a Large Binocular Telescope imaging study that characterizes the star cluster component of nearby galaxy outer disks (beyond the optical radius R{sub 25}). Expanding on the pilot project of Herbert-Fort et al., we present deep ({approx}27.5 mag V-band point-source limiting magnitude) U- and V-band imaging of six galaxies: IC 4182, NGC 3351, NGC 4736, NGC 4826, NGC 5474, and NGC 6503. We find that the outer disk of each galaxy is populated with marginally resolved star clusters with masses {approx}10{sup 3} M{sub Sun} and ages up to {approx}1 Gyr (masses and ages are limited by the depth of our imaging and uncertainties are large given how photometry can be strongly affected by the presence or absence of a few stars in such low-mass systems), and that they are typically found out to at least 2 R{sub 25} but sometimes as far as 3-4 R{sub 25}-even beyond the apparent H I disk. The mean rate of cluster formation for 1 R{sub 25} {<=} R {<=} 1.5 R{sub 25} is at least one every {approx}2.5 Myr and the clusters are spatially correlated with the H I, most strongly with higher density gas near the periphery of the optical disk and with lower density neutral gas at the H I disk periphery. We hypothesize that the clusters near the edge of the optical disk are formed in the extension of spiral structure from the inner disk and are a fairly consistent phenomenon and that the clusters formed at the periphery of the H I disk are the result of accretion episodes.

  3. Synthetic clusters of massive stars to test stellar evolution models

    NASA Astrophysics Data System (ADS)

    Georgy, Cyril; Ekström, Sylvia; Granada, Anahi; Meynet, Georges; Bastian, Nate; Charbonnel, Corinne

    2015-08-01

    During the recent years, the Geneva stellar evolution group has published several sets of grids of stellar models, including the effect of rotation and with up to date input physics. These sets cover a wide range of initial masses, initial rotation rates and metallicities. In addition to these grids, we have also developed a toolbox (the SYCLIST code), allowing for the study of stellar populations as a function of time, and to build synthetic clusters of a given age.In this talk, I will present the SYCLIST code and the various effects that it is able to account for: initial distributions of rotation velocities, effect of the angle of view on the look of fast rotating stars (gravity darkening). I will show how the account for a rotation velocities distribution affects the HRD and CMD of clusters at different ages.Eventually, I will discuss how comparing our synthetic clusters with observed ones can help in understanding stellar physics. For example, I will show how the effects of rotation and of gravity darkening affects the region of the turn-off of young clusters. Rotation has also an impact on the look of the Hertzsprung gap of intermediate age clusters, by broadening the sequence of stars that lie in this region of the HRD.

  4. Nearby star cluster yields insights into early universe

    NASA Astrophysics Data System (ADS)

    1998-07-01

    The nebula offers a unique opportunity for a close-up glimpse of the "firestorm" accompanying the birth of extremely massive stars, each blazing with the brilliance of 300,000 of our suns. Such galactic fireworks were much more common billions of years ago in the early universe, when most star formation took place. "This is giving us new insights into the physical mechanisms governing star formation in far away galaxies that existed long ago," says Mohammad Heydari-Malayeri (Paris Observatory, France), who headed the international team of astronomers who made the discovery using Hubble's Wide Field and Planetary Camera 2. Because these stars are deficient in heavier elements, they also evolve much like the universe's earliest stars, which were made almost exclusively of the primordial elements hydrogen and helium that were created in the big bang. The Small Magellanic Cloud is a unique laboratory for studying star formation in the early universe since it is the closest and best seen galaxy containing so-called "metal-poor" first- and second -generation type stars. These observations show that massive stars may form in groups. "As a result, it is more likely some of these stars are members of double and multiple star systems," says Heydari-Malayeri. "The multiple systems will affect stellar evolution considerably by ejecting a great deal of matter into space." This furious rate of mass loss from these stars is evident in the Hubble picture, which reveals dramatic shapes sculpted in the nebula's wall of glowing gases by violent stellar winds and shock waves. "This implies a very turbulent environment typical of young star formation regions," Heydari-Malayeri adds. He believes one of the members of the cluster may be an extremely rare and short-lived class of super-hot star (50,000 degrees Kelvin) called a Wolf-Rayet. This star represents a violent, transitional phase in the final years of a massive star's existence - before it ultimately explodes as a supernova. "If

  5. Super Star Clusters in Luminous Infrared Galaxies: the SUNBIRD Survey

    NASA Astrophysics Data System (ADS)

    Väisänen, P.; Randriamanakoto, Z.; Escala, A.; Kankare, E.; Kniazev, A.; Kotilainen, J. K.; Mattila, S.; Ramphul, R.; Ryder, S.; Tekola, A.

    2014-09-01

    We summarize recent results from an Adaptive Optics (AO) imaging survey of 40 Luminous IR Galaxies (LIRGs). We have constructed the first statistically significant sample of Luminosity Functions (LFs) of Super Star Clusters (SSCs) in the near-IR, and find evidence that the LF slopes in LIRGs are shallower than in more quiescent spiral galaxies. Distance and blending effects were investigated in detail paving the way for SSC studies further out than done previously. We have also correlated the luminosities of the brightest clusters with the star formation rates of the hosts and find that the characteristics of the relation suggest an underlying physical driver rather than solely a size-of-sample effect. Finally we present early results of using SSC age and mass properties to trace the histories of the target LIRG systems.

  6. THE STAR FORMATION HISTORY OF THE MILKY WAY'S NUCLEAR STAR CLUSTER

    SciTech Connect

    Pfuhl, O.; Fritz, T. K.; Eisenhauer, F.; Genzel, R.; Gillessen, S.; Ott, T.; Dodds-Eden, K.; Zilka, M.; Sternberg, A.; Maness, H.

    2011-11-10

    We present spatially resolved imaging and integral field spectroscopy data for 450 cool giant stars within 1 pc from Sgr A*. We use the prominent CO bandheads to derive effective temperatures of individual giants. Additionally we present the deepest spectroscopic observation of the Galactic center (GC) so far, probing the number of B9/A0 main-sequence stars (2.2-2.8 M{sub sun}) in two deep fields. From spectrophotometry we construct a Hertzsprung-Russell diagram of the red giant population and fit the observed diagram with model populations to derive the star formation history of the nuclear cluster. We find (1) that the average nuclear star formation rate dropped from an initial maximum {approx}10 Gyr ago to a deep minimum 1-2 Gyr ago and increased again during the last few hundred Myrs, (2) that roughly 80% of the stellar mass formed more than 5 Gyr ago, and (3) that mass estimates within R {approx} 1 pc from Sgr A* favor a dominant star formation mode with a 'normal' Chabrier/Kroupa initial mass function for the majority of the past star formation in the GC. The bulk stellar mass seems to have formed under conditions significantly different from the young stellar disks, perhaps because at the time of the formation of the nuclear cluster the massive black hole and its sphere of influence were much smaller than today.

  7. Star formation in the starburst cluster in NGC 3603

    NASA Astrophysics Data System (ADS)

    Correnti, Matteo; Paresce, Francesco; Aversa, Rossella; Beccari, Giacomo; De Marchi, Guido; Di Criscienzo, Marcella; Pang, Xiaoying; Spezzi, Loredana; Valenti, Elena; Ventura, Paolo

    2012-08-01

    We have used new, deep, visible and near infrared observations of the compact starburst cluster in the giant HII region NGC 3603 and its surroundings with the WFC3 on HST and HAWK-I on the VLT to study in detail the physical properties of its intermediate mass (˜1-3 M⊙) stellar population. We show that after correction for differential extinction and actively accreting stars, and the study of field star contamination, strong evidence remains for a continuous spread in the ages of pre-main sequence stars in the range ˜2 to ˜30 Myr within the temporal resolution available. Existing differences among presently available theoretical models account for the largest possible variation in shape of the measured age histograms within these limits. We also find that this isochronal age spread in the near infrared and visible Colour-Magnitude Diagrams cannot be reproduced by any other presently known source of astrophysical or instrumental scatter that could mimic the luminosity spread seen in our observations except, possibly, episodic accretion. The measured age spread and the stellar spatial distribution in the cluster are consistent with the hypothesis that star formation started at least 20-30 Myrs ago progressing slowly but continuously up to at least a few million years ago. All the stars in the considered mass range are distributed in a flattened oblate spheroidal pattern with the major axis oriented in an approximate South-East-North-West direction, and with the length of the equatorial axis decreasing with increasing age. This asymmetry is most likely due to the fact that star formation occurred along a filament of gas and dust in the natal molecular cloud oriented locally in this direction.

  8. Determining the Locations of Brown Dwarfs in Young Star Clusters

    NASA Technical Reports Server (NTRS)

    Porter, Lauren A.

    2005-01-01

    Brown dwarfs are stellar objects with masses less than 0.08 times that of the Sun that are unable to sustain nuclear fusion. Because of the lack of fusion, they are relatively cold, allowing the formation of methane and water molecules in their atmospheres. Brown dwarfs can be detected by examining stars' absorption spectra in the near-infrared to see whether methane and water are present. The objective of this research is to determine the locations of brown dwarfs in Rho Ophiuchus, a star cluster that is only 1 million years old. The cluster was observed in four filters in the near-infrared range using the Wide-Field Infra-Red Camera (WIRC) on the 100" DuPont Telescope and Persson's Auxiliary Nasymith Infrared Camera (PANIC) on the 6.5-m Magellan Telescope. By comparing the magnitude of a star in each of the four filters, an absorption spectrum can be formed. This project uses standard astronomical techniques to reduce raw frames into final images and perform photometry on them to obtain publishable data. Once this is done, it will be possible to determine the locations and magnitudes of brown dwarfs within the cluster.

  9. DUST-OBSCURED STAR FORMATION IN INTERMEDIATE REDSHIFT GALAXY CLUSTERS

    SciTech Connect

    Finn, Rose A.; Desai, Vandana; Rudnick, Gregory; Poggianti, Bianca; Bell, Eric F.; Hinz, Joannah; Zaritsky, Dennis; Jablonka, Pascale; Milvang-Jensen, Bo; Moustakas, John; Rines, Kenneth E-mail: jmoustakas@ucsd.ed

    2010-09-01

    We present Spitzer MIPS 24 {mu}m observations of sixteen 0.4 < z < 0.8 galaxy clusters drawn from the ESO Distant Cluster Survey. This is the first large 24 {mu}m survey of clusters at intermediate redshift. The depth of our imaging corresponds to a total IR luminosity of 8 x 10{sup 10} L{sub sun}, just below the luminosity of luminous infrared galaxies (LIRGs), and 6{sup +1}{sub -1}% of M{sub V} < -19 cluster members show 24 {mu}m emission at or above this level. We compare with a large sample of coeval field galaxies and find that while the fraction of cluster LIRGs lies significantly below that of the field, the IR luminosities of the field and cluster galaxies are consistent. However, the stellar masses of the EDisCS LIRGs are systematically higher than those of the field LIRGs. A comparison with optical data reveals that {approx}80% of cluster LIRGs are blue and the remaining 20% lie on the red sequence. Of LIRGs with optical spectra, 88{sup +4} {sub -5}% show [O II] emission with EW([O II]) > 5 A, and {approx}75% exhibit optical signatures of dusty starbursts. On average, the fraction of cluster LIRGs increases with projected clustercentric radius but remains systematically lower than the field fraction over the area probed (<1.5x R {sub 200}). The amount of obscured star formation declines significantly over the 2.4 Gyr interval spanned by the EDisCS sample, and the rate of decline is the same for the cluster and field populations. Our results are consistent with an exponentially declining LIRG fraction, with the decline in the field delayed by {approx}1 Gyr relative to the clusters.

  10. Star Formation and Supercluster Environment of 107 nearby Galaxy Clusters

    NASA Astrophysics Data System (ADS)

    Cohen, Seth A.; Hickox, Ryan C.; Wegner, Gary A.; Einasto, Maret; Vennik, Jaan

    2017-01-01

    We analyze the relationship between star formation (SF), substructure, and supercluster environment in a sample of 107 nearby galaxy clusters using data from the Sloan Digital Sky Survey. Previous works have investigated the relationships between SF and cluster substructure, and cluster substructure and supercluster environment, but definitive conclusions relating all three of these variables has remained elusive. We find an inverse relationship between cluster SF fraction (fSF) and supercluster environment density, calculated using the Galaxy luminosity density field at a smoothing length of 8 h‑1 Mpc (D8). The slope of fSF versus D8 is ‑0.008 ± 0.002. The fSF of clusters located in low-density large-scale environments, 0.244 ± 0.011, is higher than for clusters located in high-density supercluster cores, 0.202 ± 0.014. We also divide superclusters, according to their morphology, into filament- and spider-type systems. The inverse relationship between cluster fSF and large-scale density is dominated by filament- rather than spider-type superclusters. In high-density cores of superclusters, we find a higher fSF in spider-type superclusters, 0.229 ± 0.016, than in filament-type superclusters, 0.166 ± 0.019. Using principal component analysis, we confirm these results and the direct correlation between cluster substructure and SF. These results indicate that cluster SF is affected by both the dynamical age of the cluster (younger systems exhibit higher amounts of SF); the large-scale density of the supercluster environment (high-density core regions exhibit lower amounts of SF); and supercluster morphology (spider-type superclusters exhibit higher amounts of SF at high densities).

  11. A Survey of Localized Star Clusters in NGC 1427A

    NASA Astrophysics Data System (ADS)

    Weaver, John R.; Gregg, Michael

    2016-01-01

    It is well established that galactic clusters provide dynamic environments in which to examine galaxy evolution. The starbursting dwarf irregular NGC 1427A presents an interesting case as it is being pulled into the nearby Fornax cluster at supersonic speeds, producing a visibly exceptional star formation rate and notably blue colors. It has been suggested that the highly deformed structure of NGC 1427A is due to ram pressure stripping as a result of interacting with a super-heated ICM provided by several nearby elliptical galaxies. The gas density profile of its leading edge is similar to a "bow-shock", containing several dozen super-star clusters (SSCs) and thousands of smaller star forming clusters. It is clearly evident that the properties of NGC 1427A change rapidly over relatively short distances. Using dithered HST/ACS images in Sloan equivalent g' r' i' z' and Hα filters, we present a morphological and photometric study of NGC 1427A using a novel approach in which stellar properties are measured from sources grouped within localized regions. Apertures are fitted for ~5000 sources at 4σ using a filter-combined master image. Four characteristic regions are chosen to study stellar properties, selected interactively through DS9. We then introduce COMET, a specially-designed source catalog handler for producing graphical figures of each region, cropping both spatially and photometrically. These are then batch-reviewed and analyzed using synthetic isochrones corresponding of each region. Hα bright sources are indicated to illustrate the significance of SSCs. Secondary analysis is carried out using smoothed color maps of source-subtracted diffuse light, yielding penetrative mapping of underlying stellar populations. We show for the first time how the dynamical stellar populations of NGC 1427A differ as a function of position across the surface of the galaxy, ultimately furthering our understanding of cluster interactions and the evolution of irregular galaxies

  12. UV-selected Young Massive Star Cluster Populations in Nearby Star-forming Galaxies

    NASA Astrophysics Data System (ADS)

    Smith, Linda J.

    2015-08-01

    The Legacy ExtraGalactic UV Survey (LEGUS) is an HST Treasury program aimed at the investigation of star-formation and its relationship to environment in nearby galaxies. The results of a UV-selected study of young massive star clusters in a sample of nearby galaxies (< 10 Mpc) using detections based on the WFC3/UVIS F275W filter will be presented. Previous studies have used V or I-band detections and tend to ignore clusters younger than 10 Myr old. This very young population, which represents the most recent cluster-forming event in the LEGUS galaxies will be discussed.This poster is presented on behalf of the LEGUS team (PI Daniela Calzetti).

  13. Embedded star clusters and the formation of the Oort Cloud

    NASA Astrophysics Data System (ADS)

    Brasser, R.; Duncan, M. J.; Levison, H. F.

    2006-09-01

    Observations suggest most stars originate in clusters embedded in giant molecular clouds [Lada, C.J., Lada, E.A., 2003. Annu. Rev. Astron. Astrophys. 41, 57-115]. Our Solar System likely spent 1-5 Myrs in such regions just after it formed. Thus the Oort Cloud (OC) possibly retains evidence of the Sun's early dynamical history and of the stellar and tidal influence of the cluster. Indeed, the newly found objects (90377) Sedna and 2000 CR 105 may have been put on their present orbits by such processes [Morbidelli, A., Levison, H.F., 2004. Astron. J. 128, 2564-2576]. Results are presented here of numerical simulations of the orbital evolution of comets subject to the influence of the Sun, Jupiter and Saturn (with their current masses on orbits appropriate to the period before the Late Heavy Bombardment (LHB) [Tsiganis, K., Gomes, R., Morbidelli, A., Levison, H.F., 2005. Nature 435, 459-461]), passing stars and tidal force associated with the gas and stars of an embedded star cluster. The cluster was taken to be a Plummer model with 200-400 stars, with a range of initial central densities. The Sun's orbit was integrated in the cluster potential together with Jupiter and Saturn and the test particles. Stellar encounters were incorporated by directly integrating the effects of stars passing within a sphere centred on the Sun of radius equal to the Plummer radius for low-density clusters and half a Plummer radius for high-density clusters. The gravitational influence of the gas was modeled using the tidal force of the cluster potential. For a given solar orbit, the mean density, <ρ>, was computed by orbit-averaging the density of material encountered. This parameter proved to be a good measure for predicting the properties of the OC. On average 2-18% of our initial sample of comets end up in the OC after 1-3 Myr. A comet is defined to be part of the OC if it is bound and has q>35 AU. Our models show that the median distance of an object in the OC scales approximately as

  14. A comprehensive set of simulations studying the influence of gas expulsion on star cluster evolution

    NASA Astrophysics Data System (ADS)

    Baumgardt, H.; Kroupa, P.

    2007-10-01

    We have carried out a large set of N-body simulations studying the effect of residual-gas expulsion on the survival rate, and final properties of star clusters. We have varied the star formation efficiency (SFE), gas expulsion time-scale and strength of the external tidal field, obtaining a three-dimensional grid of models which can be used to predict the evolution of individual star clusters or whole star cluster systems by interpolating between our runs. The complete data of these simulations are made available on the internet. Our simulations show that cluster sizes, bound mass fraction and velocity profile are strongly influenced by the details of the gas expulsion. Although star clusters can survive SFEs as low as 10 per cent if the tidal field is weak and the gas is removed only slowly, our simulations indicate that most star clusters are destroyed or suffer dramatic loss of stars during the gas removal phase. Surviving clusters have typically expanded by a factor of 3 or 4 due to gas removal, implying that star clusters formed more concentrated than as we see them today. Maximum expansion factors seen in our runs are around 10. If gas is removed on time-scales smaller than the initial crossing time, star clusters acquire strongly radially anisotropic velocity dispersions outside their half-mass radii. Observed velocity profiles of star clusters can therefore be used as a constraint on the physics of cluster formation.

  15. The Brightest Young Star Clusters in NGC 5253.

    NASA Astrophysics Data System (ADS)

    Calzetti, D.; Johnson, K. E.; Adamo, A.; Gallagher, J. S., III; Andrews, J. E.; Smith, L. J.; Clayton, G. C.; Lee, J. C.; Sabbi, E.; Ubeda, L.; Kim, H.; Ryon, J. E.; Thilker, D.; Bright, S. N.; Zackrisson, E.; Kennicutt, R. C.; de Mink, S. E.; Whitmore, B. C.; Aloisi, A.; Chandar, R.; Cignoni, M.; Cook, D.; Dale, D. A.; Elmegreen, B. G.; Elmegreen, D. M.; Evans, A. S.; Fumagalli, M.; Gouliermis, D. A.; Grasha, K.; Grebel, E. K.; Krumholz, M. R.; Walterbos, R.; Wofford, A.; Brown, T. M.; Christian, C.; Dobbs, C.; Herrero, A.; Kahre, L.; Messa, M.; Nair, P.; Nota, A.; Östlin, G.; Pellerin, A.; Sacchi, E.; Schaerer, D.; Tosi, M.

    2015-10-01

    The nearby dwarf starburst galaxy NGC 5253 hosts a number of young, massive star clusters, the two youngest of which are centrally concentrated and surrounded by thermal radio emission (the “radio nebula”). To investigate the role of these clusters in the starburst energetics, we combine new and archival Hubble Space Telescope images of NGC 5253 with wavelength coverage from 1500 Å to 1.9 μm in 13 filters. These include Hα, Pβ, and Pα, and the imaging from the Hubble Treasury Program LEGUS (Legacy Extragalactic UV Survey). The extraordinarily well-sampled spectral energy distributions enable modeling with unprecedented accuracy the ages, masses, and extinctions of the nine optically brightest clusters (MV < -8.8) and the two young radio nebula clusters. The clusters have ages ˜1-15 Myr and masses ˜1 × 104-2.5 × 105 M⊙. The clusters’ spatial location and ages indicate that star formation has become more concentrated toward the radio nebula over the last ˜15 Myr. The most massive cluster is in the radio nebula; with a mass ˜2.5 × 105 M⊙ and an age ˜1 Myr, it is 2-4 times less massive and younger than previously estimated. It is within a dust cloud with AV ˜ 50 mag, and shows a clear near-IR excess, likely from hot dust. The second radio nebula cluster is also ˜1 Myr old, confirming the extreme youth of the starburst region. These two clusters account for about half of the ionizing photon rate in the radio nebula, and will eventually supply about 2/3 of the mechanical energy in present-day shocks. Additional sources are required to supply the remaining ionizing radiation, and may include very massive stars. Based on observations obtained with the NASA/ESA Hubble Space Telescope, at the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS 5-26555.

  16. POST T-Tauri Stars in Galactic Clusters

    NASA Astrophysics Data System (ADS)

    Haro, G.

    1983-08-01

    spectral type and luminosity: the earlier the spectral type, the shorter the vanishing effect. Therefore, if we look for weakened T Tauri features in stellar aggregates of various ages from which the typical and extreme T Tauri stars have already disappeared, we find that the older the aggregate, the later the spectral type in which the last prominent features are detectable. Everything seems to suggest that it is within these possible evolved T Tauri objects that we can find the so-called post-T Tauri stars, and that a good number of flare stars detected in galactic clusters are among them. These clusters are: the Orion stellar aggregate, NOC 2264, the Pleiades, and possibly the flare stars in stellar aggregates of ages equal or superior to 108 years. As I have in the past, I would like to place special emphasis on the genetic relationship between certain flare stars and their T Tauri ancestors, based not only on the very rapid outbursts of the former but also, and primarily, on the fact that these flare stars show spectroscopic characteristics reminiscent of the T Tauri original stars. In other words, the simple fact that a star presents the "flare" phenomenon does not constitute necessary and sufficient proof that it should be regarded as an evolutionary product of a T Tauri star: in addition to the flare-up the spectral types of the investigated objects must present -during maximum and minimum light- clear and reminiscent spectroscopic evidences of the original T Tauri objects; that is, spectral types as late or later than G and some emission lines, at least in H and Call. There are some flare stars in Orion and NGC 2264 which, even during minimum light, can be classified spectroscopically as typical T Tauri stars. In the case of the Pleiades, where undoubtedly there are no T Tauri stars, many of the flare stars show spectral emission lines (H and Call) of great intensity during maximum and of detectable intensity in slit spectrograms of not high dispersion, during

  17. Generating a Magellanic star cluster catalog with ASteCA

    NASA Astrophysics Data System (ADS)

    Perren, G. I.; Piatti, A. E.; Vázquez, R. A.

    2016-08-01

    An increasing number of software tools have been employed in the recent years for the automated or semi-automated processing of astronomical data. The main advantages of using these tools over a standard by-eye analysis include: speed (particularly for large databases), homogeneity, reproducibility, and precision. At the same time, they enable a statistically correct study of the uncertainties associated with the analysis, in contrast with manually set errors, or the still widespread practice of simply not assigning errors. We present a catalog comprising 210 star clusters located in the Large and Small Magellanic Clouds, observed with Washington photometry. Their fundamental parameters were estimated through an homogeneous, automatized and completely unassisted process, via the Automated Stellar Cluster Analysis package ( ASteCA). Our results are compared with two types of studies on these clusters: one where the photometry is the same, and another where the photometric system is different than that employed by ASteCA.

  18. On the merger origin of nuclear star clusters

    NASA Astrophysics Data System (ADS)

    Tsatsi, Athanasia; Mastrobuono-Battisti, Alessandra

    2017-03-01

    Nuclear Star Clusters (NSCs) are commonly observed in the centers of most galaxies, including our Milky Way (MW). While their study can reveal important information about the innermost regions of galaxies, the physical processes regulating their formation are still poorly understood. We explore a possible merger origin of NSCs by studying direct N-body simulations of globular clusters (GCs) that are initially randomly distributed in the outskirts and consecutively infall to the center of a MW-like nuclear bulge. We find that the NSC that forms through this process shows a significant amount of rotation, and both morphological and kinematic properties are comparable with observations of the MW NSC. We show that no fine-tuning of the orientation of the infalling GCs is necessary to result in a rotating NSC. This study shows the plausibility of the cluster infall scenario and can help towards setting better constraints to the formation history of NSCs.

  19. On the rotation of nuclear star clusters formed by cluster inspirals

    NASA Astrophysics Data System (ADS)

    Tsatsi, Athanasia; Mastrobuono-Battisti, Alessandra; van de Ven, Glenn; Perets, Hagai B.; Bianchini, Paolo; Neumayer, Nadine

    2017-01-01

    Nuclear star clusters (NSCs) are commonly observed in the centres of most galactic nuclei, including our own Milky Way (MW). While their study can reveal important information about the build-up of the innermost regions of galaxies, the physical processes that regulate their formation are still poorly understood. NSCs might have been formed through gas infall and subsequent in situ star formation, and/or through the infall and merging of multiple star clusters into the centre of the galaxy. Here, we investigate the viability of the latter, by studying direct N-body simulations of inspiralling clusters to the centre of an MW-like nuclear bulge that hosts a massive black hole. We find that the NSC formed through this process can show both morphological and kinematical properties that make it comparable with observations of the MW NSC, including significant rotation - a fact that has so far been attributed mainly to gas infall. We explore its kinematic evolution to see if and how the merger history can imprint fossil records on its dynamical structure. Moreover, we study the effect of stellar foreground contamination in the line-of-sight kinematics of the NSC. Our study shows that no fine tuning of the orientation of the infalling globular clusters is necessary to result in a rotating NSC. We suggest that cluster inspiral is a viable mechanism for the formation of rotating NSCs.

  20. A NEW LOOK AT THE OLD STAR CLUSTER NGC 6791

    SciTech Connect

    Platais, I.; Cudworth, K. M.; Kozhurina-Platais, V.; McLaughlin, D. E.; Meibom, S.; Veillet, C.

    2011-05-20

    We present comprehensive cluster membership and g'r' photometry of the prototypical old, metal-rich Galactic star cluster NGC 6791. The proper-motion catalog contains 58,901 objects down to g'{approx} 24, limited to a circular area of radius 30'. The highest precision of the proper motions is 0.08 mas yr{sup -1}. Our proper motions confirm cluster membership of all main and also some rare constituents of NGC 6791. The total number of probable cluster members down to g' = 22 (M{sub V} {approx} +8) is {approx}4800, corresponding to M{sub tot} {approx} 5000 M{sub sun}. New findings include an extended horizontal branch in this cluster. The angular radius of NGC 6791 is at least 15' (the effective radius is R{sub h} {approx_equal} 4.'4 while the tidal radius is r{sub t} {approx_equal} 23'). The luminosity function of the cluster peaks at M{sub g}{sup '}{approx}+4.5 and then steadily declines toward fainter magnitudes. Our data provide evidence that differential reddening may not be ignored in NGC 6791.

  1. Stars and Star Clusters: A Look at Intermediate-Mass Star-Forming Regions

    NASA Astrophysics Data System (ADS)

    Lundquist, Michael J.; Kobulnicky, Henry A.; Lau, Ryan M.

    2017-01-01

    Star-forming regions hosting intermediate-mass stars straddle the boundary separating the the low- and high-mass regimes. These intermediate-mass star-forming regions can be used to probe this transition from low- to high-mass star formation. Our team has assembled an all-sky catalog of 616 candidate intermediate-mass star forming regions (IMSFRs) selected by IRAS colors and refined by visual inspection of WISE imagery. We present here two outer-Galaxy star-forming regions, IRAS22451+6154 and IRAS23448+6010, that despite having similar IRAS colors and mid-infrared morphologies, have vastly different stellar content. We combine Gemini and IRTF NIR spectroscopy with WIYN and SOFIA imaging for a thorough look at the stellar content of these two regions.

  2. Sequential clustering of star formations in IC 1396

    NASA Astrophysics Data System (ADS)

    Huang, Ya-Fang; Li, Jin-Zeng

    2013-05-01

    We present a comprehensive study of the H II region IC 1396 and its star forming activity, in which multi-wavelength data ranging from the optical to the near- and far-infrared were employed. The surface density distribution of all the 2MASS sources with a certain detection toward IC 1396 indicates the existence of a compact cluster spatially consistent with the position of the exciting source of the H II region, HD 206267. The spatial distribution of the sources with excessive infrared emission, selected based on archived 2MASS data, reveals the existence of four sub-clusters in this region. One is associated with the open cluster Trumpler 37. The other three are found to be spatially coincident with the bright rims of the H II region. All the sources with excessive emission in the near infrared are cross-identified with AKARI IRC data. An analysis of the spectral energy distributions (SEDs) of the resultant sample leads to the identification of eight CLASS I, 15 CLASS II and 15 CLASS III sources in IC 1396. Optical identification of the sample sources with R magnitudes brighter than 17 mag corroborates the results from the SED analysis. Based on the spatial distribution of the infrared young stellar objects at different evolutionary stages, the surrounding sub-clusters located in the bright rims are believed to be younger than the central one. This is consistent with a scenario of sequential star formation in this region. Imaging data of a dark patch in IC 1396 by Herschel SPIRE, on the other hand, indicate the presence of two far-infrared cores in LDN 1111, which are likely to be a new generation of protostellar objects in formation. So we infer that the star formation process in this H II region was not continuous but rather episodic.

  3. STELLAR COLLISIONS AND BLUE STRAGGLER STARS IN DENSE GLOBULAR CLUSTERS

    SciTech Connect

    Chatterjee, Sourav; Rasio, Frederic A.; Sills, Alison; Glebbeek, Evert

    2013-11-10

    Blue straggler stars (BSSs) are abundantly observed in all Galactic globular clusters (GGCs) where data exist. However, observations alone cannot reveal the relative importance of various formation channels or the typical formation times for this well-studied population of anomalous stars. Using a state-of-the-art Hénon-type Monte Carlo code that includes all relevant physical processes, we create 128 models with properties typical of the observed GGCs. These models include realistic numbers of single and binary stars, use observationally motivated initial conditions, and span large ranges in central density, concentration, binary fraction, and mass. Their properties can be directly compared with those of observed GGCs. We can easily identify the BSSs in our models and determine their formation channels and birth times. We find that for central densities above ∼10{sup 3} M{sub ☉} pc{sup –3}, the dominant formation channel is stellar collisions, while for lower density clusters, mass transfer in binaries provides a significant contribution (up to 60% in our models). The majority of these collisions are binary-mediated, occurring during three-body and four-body interactions. As a result, a strong correlation between the specific frequency of BSSs and the binary fraction in a cluster can be seen in our models. We find that the number of BSSs in the core shows only a weak correlation with the collision rate estimator Γ traditionally used by observers, in agreement with the latest Hubble Space Telescope Advanced Camera for Surveys data. Using an idealized 'full mixing' prescription for collision products, our models indicate that the BSSs observed today may have formed several Gyr ago. However, denser clusters tend to have younger (∼1 Gyr) BSSs.

  4. Stellar Collisions and Blue Straggler Stars in Dense Globular Clusters

    NASA Astrophysics Data System (ADS)

    Chatterjee, Sourav; Rasio, Frederic A.; Sills, Alison; Glebbeek, Evert

    2013-11-01

    Blue straggler stars (BSSs) are abundantly observed in all Galactic globular clusters (GGCs) where data exist. However, observations alone cannot reveal the relative importance of various formation channels or the typical formation times for this well-studied population of anomalous stars. Using a state-of-the-art Hénon-type Monte Carlo code that includes all relevant physical processes, we create 128 models with properties typical of the observed GGCs. These models include realistic numbers of single and binary stars, use observationally motivated initial conditions, and span large ranges in central density, concentration, binary fraction, and mass. Their properties can be directly compared with those of observed GGCs. We can easily identify the BSSs in our models and determine their formation channels and birth times. We find that for central densities above ~103 M ⊙ pc-3, the dominant formation channel is stellar collisions, while for lower density clusters, mass transfer in binaries provides a significant contribution (up to 60% in our models). The majority of these collisions are binary-mediated, occurring during three-body and four-body interactions. As a result, a strong correlation between the specific frequency of BSSs and the binary fraction in a cluster can be seen in our models. We find that the number of BSSs in the core shows only a weak correlation with the collision rate estimator Γ traditionally used by observers, in agreement with the latest Hubble Space Telescope Advanced Camera for Surveys data. Using an idealized "full mixing" prescription for collision products, our models indicate that the BSSs observed today may have formed several Gyr ago. However, denser clusters tend to have younger (~1 Gyr) BSSs.

  5. The Orion Nebula Cluster as a Paradigm of Star Formation

    NASA Astrophysics Data System (ADS)

    Robberto, Massimo

    2014-10-01

    We propose a 52-orbit Treasury Program to investigate two fundamental questions of star formation: a) the low-mass tail of the IMF, down to a few Jupiter masses; b) the dynamical evolution of clusters, as revealed by stellar proper motions. We target the Orion Nebula Cluster (ONC) using WFC3 and ACS in coordinated parallel mode to perform a synoptic survey in the 1.345micron H2O feature and Ic broad-band. Our main objectives are: 1) to discover and classify ~500 brown dwarfs and planetary-mass objects in the field, extending the IMF down to lowest masses formed by gravitational collapse. Using the latest generation of high contrast image processing we will also search for faint companions, reaching down to sub-arcsecond separations and 1E-4 flux ratios. 2) to derive high precision (~0.2km/s) relative proper motions of low-mass stars and substellar objects (about 1000 sources total), leveraging on first epoch data obtained by our previous HST Treasury Program about 10 years ago. These data will unveil the cluster dynamics: velocity dispersion vs. mass, substructures, and the fraction of escaping sources. Only HST can access the IR H2O absorption feature sensitive to the effective temperature of substellar objects, while providing the exceptionally stable PSF needed for the detection of faint companions, and the identical ACS platform for our second epoch proper-motion survey. This program will provide the definitive HST legacy dataset on the ONC. Our High-Level Science Products will be mined by the community, both statistically to constrain competing theories of star formation, and to study in depth the multitude of exotic sources harboured by the cluster.

  6. CALIBRATING STELLAR POPULATION MODELS WITH MAGELLANIC CLOUD STAR CLUSTERS

    SciTech Connect

    Noeel, N. E. D.; Carollo, C. M.; Greggio, L.; Renzini, A.; Maraston, C.

    2013-07-20

    Stellar population models are commonly calculated using star clusters as calibrators for those evolutionary stages that depend on free parameters. However, discrepancies exist among different models, even if similar sets of calibration clusters are used. With the aim of understanding these discrepancies, and of improving the calibration procedure, we consider a set of 43 Magellanic Cloud (MC) clusters, taking age and photometric information from the literature. We carefully assign ages to each cluster based on up-to-date determinations, ensuring that these are as homogeneous as possible. To cope with statistical fluctuations, we stack the clusters in five age bins, deriving for each of them integrated luminosities and colors. We find that clusters become abruptly red in optical and optical-infrared colors as they age from {approx}0.6 to {approx}1 Gyr, which we interpret as due to the development of a well-populated thermally pulsing asymptotic giant branch (TP-AGB). We argue that other studies missed this detection because of coarser age binnings. Maraston and Girardi et al. models predict the presence of a populated TP-AGB at {approx}0.6 Gyr, with a correspondingly very red integrated color, at variance with the data; Bruzual and Charlot and Conroy models run within the error bars at all ages. The discrepancy between the synthetic colors of Maraston models and the average colors of MC clusters results from the now obsolete age scale adopted. Finally, our finding that the TP-AGB phase appears to develop between {approx}0.6 and 1 Gyr is dependent on the adopted age scale for the clusters and may have important implications for stellar evolution.

  7. The swift UVOT stars survey. I. Methods and test clusters

    SciTech Connect

    Siegel, Michael H.; Porterfield, Blair L.; Linevsky, Jacquelyn S.; Bond, Howard E.; Hoversten, Erik A.; Berrier, Joshua L.; Gronwall, Caryl A.; Holland, Stephen T.; Breeveld, Alice A.; Brown, Peter J. E-mail: blp14@psu.edu E-mail: caryl@astro.psu.edu E-mail: aab@mssl.ucl.ac.uk

    2014-12-01

    We describe the motivations and background of a large survey of nearby stellar populations using the Ultraviolet Optical Telescope (UVOT) on board the Swift Gamma-Ray Burst Mission. UVOT, with its wide field, near-UV sensitivity, and 2.″3 spatial resolution, is uniquely suited to studying nearby stellar populations and providing insight into the near-UV properties of hot stars and the contribution of those stars to the integrated light of more distant stellar populations. We review the state of UV stellar photometry, outline the survey, and address problems specific to wide- and crowded-field UVOT photometry. We present color–magnitude diagrams of the nearby open clusters M67, NGC 188, and NGC 2539, and the globular cluster M79. We demonstrate that UVOT can easily discern the young- and intermediate-age main sequences, blue stragglers, and hot white dwarfs, producing results consistent with previous studies. We also find that it characterizes the blue horizontal branch of M79 and easily identifies a known post-asymptotic giant branch star.

  8. Star Formation Activity in CLASH Brightest Cluster Galaxies

    NASA Astrophysics Data System (ADS)

    Fogarty, Kevin; Postman, Marc; Connor, Thomas; Donahue, Megan; Moustakas, John

    2015-11-01

    The CLASH X-ray selected sample of 20 galaxy clusters contains 10 brightest cluster galaxies (BCGs) that exhibit significant (>5σ) extinction-corrected star formation rates (SFRs). Star formation activity is inferred from photometric estimates of UV and Hα+[N ii] emission in knots and filaments detected in CLASH Hubble Space Telescope ACS and WFC3 observations. UV-derived SFRs in these BCGs span two orders of magnitude, including two with a SFR ≳ 100 M⊙ yr-1. These measurements are supplemented with [O ii], [O iii], and Hβ fluxes measured from spectra obtained with the SOAR telescope. We confirm that photoionization from ongoing star formation powers the line emission nebulae in these BCGs, although in many BCGs there is also evidence of a LINER-like contribution to the line emission. Coupling these data with Chandra X-ray measurements, we infer that the star formation occurs exclusively in low-entropy cluster cores and exhibits a correlation with gas properties related to cooling. We also perform an in-depth study of the starburst history of the BCG in the cluster RXJ1532.9+3021, and create 2D maps of stellar properties on scales down to ˜350 pc. These maps reveal evidence for an ongoing burst occurring in elongated filaments, generally on ˜0.5-1.0 Gyr timescales, although some filaments are consistent with much younger (≲100 Myr) burst timescales and may be correlated with recent activity from the active galactic nucleus. The relationship between BCG SFRs and the surrounding intracluster medium gas properties provide new support for the process of feedback-regulated cooling in galaxy clusters and is consistent with recent theoretical predictions. Based on observations obtained at the Southern Astrophysical Research (SOAR) telescope, which is a joint project of the Ministério da Ciência, Tecnologia, e Inovação (MCTI) da República Federativa do Brasil, the U.S. National Optical Astronomy Observatory (NOAO), the University of North Carolina at Chapel

  9. Gravitational Landau damping for an isotropic cluster of stars

    NASA Technical Reports Server (NTRS)

    Habib, Salman; Kandrup, Henry E.; Yip, Ping F.

    1986-01-01

    The problem of ascertaining the dynamical stability and the existence of Landau damping in static, isotropic 'collisionless' star clusters is addressed. The second-order formalism of Kandrup and Sygnet (1985) is applied to a homogeneous and isotropic plasma, demonstrating formally that the unperturbed configuration will always be stable and that the modes must be purely oscillatory. The form of these modes is explicitly examined, culminating in an analytic expression for the time evolution of the density induced by an initial perturbation. It is shown how these considerations can be adapted trivially to localized, nonradial disturbances of a self-gravitating system of stars. The possible existence of gravitational Landau damping for more generic perturbations is discussed.

  10. Second neutron star in globular cluster M4 .

    NASA Astrophysics Data System (ADS)

    Różańska, A.; Kałużny, J.; Różyczka, M.; Krzemiński, W.; Thompson, I. B.

    We show that the optical counterpart of the brightest X-ray source C-X 1 in M4 is a ˜ 20th magnitude star, located in the color-magnitude diagram on (or very close to) the main sequence of the cluster, and exhibiting sinusoidal variations of the flux. We find the X-ray flux to be also periodically variable, with X-ray and optical minima coinciding. Stability of the optical light curve, lack of UV-excess, and unrealistic mean density resulting from period-density relation for semidetached systems speak against the original identification of CX 1 as a cataclysmic variable. We argue that the X-ray active component of this system is a neutron star, probably a millisecond pulsar.

  11. The DRAGON simulations: globular cluster evolution with a million stars

    NASA Astrophysics Data System (ADS)

    Wang, Long; Spurzem, Rainer; Aarseth, Sverre; Giersz, Mirek; Askar, Abbas; Berczik, Peter; Naab, Thorsten; Schadow, Riko; Kouwenhoven, M. B. N.

    2016-05-01

    Introducing the DRAGON simulation project, we present direct N-body simulations of four massive globular clusters (GCs) with 106 stars and 5 per cent primordial binaries at a high level of accuracy and realism. The GC evolution is computed with NBODY6++GPU and follows the dynamical and stellar evolution of individual stars and binaries, kicks of neutron stars and black holes (BHs), and the effect of a tidal field. We investigate the evolution of the luminous (stellar) and dark (faint stars and stellar remnants) GC components and create mock observations of the simulations (i.e. photometry, colour-magnitude diagrams, surface brightness and velocity dispersion profiles). By connecting internal processes to observable features, we highlight the formation of a long-lived `dark' nuclear subsystem made of BHs, which results in a two-component structure. The inner core is dominated by the BH subsystem and experiences a core-collapse phase within the first Gyr. It can be detected in the stellar (luminous) line-of-sight velocity dispersion profiles. The outer extended core - commonly observed in the (luminous) surface brightness profiles - shows no collapse features and is continuously expanding. We demonstrate how a King model fit to observed clusters might help identify the presence of post core-collapse BH subsystems. For global observables like core and half-mass radii, the direct simulations agree well with Monte Carlo models. Variations in the initial mass function can result in significantly different GC properties (e.g. density distributions) driven by varying amounts of early mass-loss and the number of forming BHs.

  12. Environmental effects on star formation in dwarf galaxies and star clusters

    NASA Astrophysics Data System (ADS)

    Pasetto, S.; Cropper, M.; Fujita, Y.; Chiosi, C.; Grebel, E. K.

    2015-01-01

    Context. The role of the environment in the formation of a stellar population is a difficult problem in astrophysics. The reason is that similar properties of a stellar population are found in star systems embedded in different environments or, vice versa, similar environments contain stellar systems with stellar populations having different properties. Aims: In this paper, we develop a simple analytical criterion to investigate the role of the environment on the onset of star formation. We will consider the main external agents that influence star formation (i.e. ram pressure, tidal interaction, Rayleigh-Taylor and Kelvin-Helmholtz instabilities) in a spherical galaxy moving through an external environment. The theoretical framework developed here has direct applications to the cases of dwarf galaxies in galaxy clusters and dwarf galaxies orbiting our Milky Way system, as well as any primordial gas-rich cluster of stars orbiting within its host galaxy. Methods: We develop an analytic formalism to solve the fluid dynamics equations in a non-inertial reference frame mapped with spherical coordinates. The two-fluids instability at the interface between a stellar system and its surrounding hotter and less dense environment is related to the star formation processes through a set of differential equations. The solution presented here is quite general, allowing us to investigate most kinds of orbits allowed in a gravitationally bound system of stars in interaction with a major massive companion. Results: We present an analytical criterion to elucidate the dependence of star formation in a spherical stellar system (as a dwarf galaxy or a globular cluster) on its surrounding environment useful in theoretical interpretations of numerical results as well as observational applications. We show how spherical coordinates naturally enlighten the interpretation of two-fluids instability in a geometry that directly applies to an astrophysical case. This criterion predicts the

  13. On the infant weight loss of low- to intermediate-mass star clusters

    NASA Astrophysics Data System (ADS)

    Weidner, C.; Kroupa, P.; Nürnberger, D. E. A.; Sterzik, M. F.

    2007-04-01

    Star clusters are born in a highly compact configuration, typically with radii of less than about 1 pc roughly independently of mass. Since the star formation efficiency is less than 50 per cent by observation and because the residual gas is removed from the embedded cluster, the cluster must expand. In the process of doing so it only retains a fraction fst of its stars. To date there are no observational constraints for fst, although N-body calculations by Kroupa, Aarseth & Hurley suggest it to be about 20-30 per cent for Orion-type clusters. Here we use the data compiled by Testi et al., Testi, Palla & Natta and Testi, Palla & Natta for clusters around young Ae/Be stars and by de Wit et al. and de Wit et al. around young O stars and the study of de Zeeuw et al. of OB associations and combine these measurements with the expected number of stars in clusters with primary Ae/Be and O stars, respectively, using the empirical correlation between maximal stellar mass and star cluster mass of Weidner & Kroupa. We find that fst < 50 per cent with a decrease to higher cluster masses/more massive primaries. The interpretation would be that cluster formation is very disruptive. It appears that clusters with a birth stellar mass in the range 10-103Msolar keep at most 50 per cent of their stars.

  14. Early turbulent mixing as the origin of chemical homogeneity in open star clusters.

    PubMed

    Feng, Yi; Krumholz, Mark R

    2014-09-25

    The abundances of elements in stars are critical clues to stars' origins. Observed star-to-star variations in logarithmic abundance within an open star cluster--a gravitationally bound ensemble of stars in the Galactic plane--are typically only about 0.01 to 0.05 over many elements, which is noticeably smaller than the variation of about 0.06 to 0.3 seen in the interstellar medium from which the stars form. It is unknown why star clusters are so homogenous, and whether homogeneity should also prevail in regions of lower star formation efficiency that do not produce bound clusters. Here we report simulations that trace the mixing of chemical elements as star-forming clouds assemble and collapse. We show that turbulent mixing during cloud assembly naturally produces a stellar abundance scatter at least five times smaller than that in the gas, which is sufficient to explain the observed chemical homogeneity of stars. Moreover, mixing occurs very early, so that regions with star formation efficiencies of about 10 per cent are nearly as well mixed as those with formation efficiencies of about 50 per cent. This implies that even regions that do not form bound clusters are likely to be well mixed, and improves the prospects of using 'chemical tagging' to reconstruct (via their unique chemical signatures, or tags) star clusters whose constituent stars have become unbound from one another and spread across the Galactic disk.

  15. Near-infrared studies of embedded star clusters

    NASA Astrophysics Data System (ADS)

    Park, Chan

    The Fan Mountain Near-Infrared Camera, FanCam, features an 8.7'x8.7' field of view on a 1024x1024 Teledyne Imaging Sensors HAWAII-1 detector array. The instrument mounts at the f/15.5 focus of the 31 inch telescope. Its seeing-limited optical design, optimized for the JHK atmospheric bands, includes a field stop at the telescope focus, a doublet collimator, two 8-position filterwheels straddling a Lyot stop, and a doublet reimager. The 0.51''pixel-1 plate scale leads to a slightly oversampled point spread function for the typical seeing of 1.5''. The entire optical train is encased in a cryogenic dewar cooled by a closed-loop cooling system. Chapter 2 describes the camera design and some early results of camera performance test. Long term near-infrared, J, H, and Ks, photometric monitoring of the embedded cluster NGC 1333 is presented in Chapter 3. We employ the Stetson variability index and reduced chi 2 to identify variable objects. Color-magnitude and color-color diagrams demonstrate that NGC 1333 is extremely young and highly extincted. Light curves in all three bands are well correlated. The spatial distribution of variable stars shows a strong correlation with the peak of the extinction map while non-variable stars are evenly spread over the whole field of view. Spitzer-2MASS-identified IR excess YSOs and Chandra X-ray sources were compared with our variable stars. A total of 25 previously-unknown member candidates are presented, with 15 objects in the mass range of brown dwarfs. The IMF and mass distribution of the cluster are presented. We discuss the implication of Ks vs. H--Ks color-magnitude diagram slope statistics in view of the evolutionary sequence of young star-forming embedded clusters. Another long term near-infrared, J, H, and Ks, photometric monitoring performed with FanCam for the embedded cluster NGC 7129 is presented in Chapter 4.

  16. Monitoring the dissolution process of metals in the gas phase: reactions of nanoscale Al and Ga metal atom clusters and their relationship to similar metalloid clusters.

    PubMed

    Burgert, Ralf; Schnöckel, Hansgeorg

    2008-05-14

    Formation and dissolution of metals are two of the oldest technical chemical processes. On the atomic scale, these processes are based on the formation and cleavage of metal-metal bonds. During the past 15 years we have studied intensively the intermediates during the formation process of metals, i.e. the formation of compounds containing many metal-metal bonds between naked metal atoms in the center and ligand-bearing metal atoms at the surface. We have called the clusters metalloid or, more generally, elementoid clusters. Via a retrosynthetic route, the many different Al and Ga metalloid clusters which have been structurally characterized allow us to understand also the dissolution process; i.e. the cleavage of metal-metal (M-M) bonds. However, this process can be detected much more directly by the reaction of single metal atom clusters in the gas phase under high vacuum conditions. A suitable tool to monitor the dissolution process of a metal cluster in the gas phase is FT-ICR (Fourier transform ion cyclotron resonance) mass spectrometry. Snapshots during these cleavage processes are possible because only every 1-10 s is there a contact between a cluster molecule and an oxidizing molecule (e.g. Cl2). This period is long, i.e. the formation of the primary product (a smaller metal atom cluster) is finished before the next collision happens. We have studied three different types of reaction:(1) Step-by-step fragmentation of a structurally known metalloid cluster allows us to understand the bonding principle of these clusters because in every step only the weakest bond is broken.(2) There are three oxidation reactions of an Al13(-) cluster molecule with Cl2, HCl and O2 central to this review. These three reactions represent three different reaction types, (a) an exothermic reaction (Cl2), (b) an endothermic reaction (HCl), and (c) a kinetically limited reaction based on spin conservation rules (O2).(3) Finally, we present the reaction of a metalloid cluster with Cl2

  17. Supernova enrichment of planetary systems in low-mass star clusters

    NASA Astrophysics Data System (ADS)

    Nicholson, Rhana B.; Parker, Richard J.

    2017-02-01

    The presence and abundance of short-lived radioisotopes 26Al and 60Fe in chondritic meteorites implies that the Sun formed in the vicinity of one or more massive stars that exploded as supernovae (SNe). Massive stars are more likely to form in massive star clusters (>1000 M⊙) than lower mass clusters. However, photoevaporation of protoplanetary discs from massive stars and dynamical interactions with passing stars can inhibit planet formation in clusters with radii of ˜1 pc. We investigate whether low-mass (50-200 M⊙) star clusters containing one or two massive stars are a more likely avenue for early Solar system enrichment as they are more dynamically quiescent. We analyse N-body simulations of the evolution of these low-mass clusters and find that a similar fraction of stars experience SN enrichment than in high-mass clusters, despite their lower densities. This is due to two-body relaxation, which causes a significant expansion before the first SN even in clusters with relatively low (100 stars pc-3) initial densities. However, because of the high number of low-mass clusters containing one or two massive stars, the absolute number of enriched stars is the same, if not higher than for more populous clusters. Our results show that direct enrichment of protoplanetary discs from SNe occurs as frequently in low-mass clusters containing one or two massive stars (>20 M⊙) as in more populous star clusters (1000 M⊙). This relaxes the constraints on the direct enrichment scenario and therefore the birth environment of the Solar system.

  18. The SMC star cluster Lindsay 1. First UI photometric study

    NASA Astrophysics Data System (ADS)

    Alcaino, G.; Alvarado, F.; Kurtev, R.

    2003-09-01

    We present new CCD photometry of the Small Magellanic Cloud star cluster Lindsay 1 in UBVI filters. It is the first photometry in U and I filters. We determine the reddening E(B-V)=0.014. Using a variety of metallicity indicators in the optical and the infrared regions we determine a cluster metallicity [Fe/H]_CG97=-1.05+/-0.14 and [M/H]=-0.83+/-0.14. We find that Lindsay 1 has an age of 9-10 Gyr. Tables 1 and 4 are only available at the CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or via http// cdsweb . u-strasbg . fr/cgi-bin/qcat?J /A+A/407/919

  19. Homogeneous photometry and star counts in the field of 9 Galactic star clusters

    NASA Astrophysics Data System (ADS)

    Seleznev, A. F.; Carraro, G.; Costa, E.; Loktin, A. V.

    2010-01-01

    We present homogeneous V, I CCD photometry of nine stellar fields in the two inner quadrants of the Galactic plane. The lines-of-view to most of these fields aim in the direction of the very inner Galaxy, where the Galactic field is very dense, and extinction is high and patchy. Our nine fields are, according to several catalogs, centred on Galactic star clusters, namely Trumpler 13, Trumpler 20, Lynga 4, Hogg 19, Lynga 12, Trumpler 25, Trumpler 26, Ruprecht 128, and Trumpler 34. Apart from their coordinates, and in some cases additional basic data (mainly from the 2MASS archive), their properties are poorly known. By means of star count techniques and field star decontaminated Color Magnitude diagrams, the nature and size of these visual over-densities has been established; and, when possible, new cluster fundamental parameters have been derived. To strengthen our findings, we complement our data-set with JHKs photometry from the 2MASS archive, that we analyze using a suitably defined Q-parameter. Most clusters are projected towards the Carina-Sagittarium spiral arm. Because of that, we detect in the Color Magnitude diagrams of most of the other fields several distinctive sequences produced by young population within the arm. All the clusters are of intermediate or old age. The most interesting cases detected by our study are, perhaps, that of Trumpler 20, which seems to be much older than previously believed, as indicated by its prominent - and double - red clump; and that of Hogg 19, a previously overlooked old open cluster, whose existence in such regions of the Milky Way is puzzling.

  20. The Herschel Virgo Cluster Survey. XVIII. Star-forming dwarf galaxies in a cluster environment

    NASA Astrophysics Data System (ADS)

    Grossi, M.; Hunt, L. K.; Madden, S. C.; Hughes, T. M.; Auld, R.; Baes, M.; Bendo, G. J.; Bianchi, S.; Bizzocchi, L.; Boquien, M.; Boselli, A.; Clemens, M.; Corbelli, E.; Cortese, L.; Davies, J.; De Looze, I.; di Serego Alighieri, S.; Fritz, J.; Pappalardo, C.; Pierini, D.; Rémy-Ruyer, A.; Smith, M. W. L.; Verstappen, J.; Viaene, S.; Vlahakis, C.

    2015-02-01

    To assess the effects of the cluster environment on the different components of the interstellar medium, we analyse the far-infrared (FIR) and submillimetre (submm) properties of a sample of star-forming dwarf galaxies detected by the Herschel Virgo Cluster Survey (HeViCS). We determine dust masses and dust temperatures by fitting a modified black body function to the spectral energy distributions (SEDs). Stellar and gas masses, star formation rates (SFRs), and metallicities are obtained from the analysis of a set of ancillary data. Dust is detected in 49 out of a total 140 optically identified dwarfs covered by the HeViCS field; considering only dwarfs brighter than mB = 18 mag, this gives a detection rate of 43%. After evaluating different emissivity indices, we find that the FIR-submm SEDs are best-fit by β = 1.5, with a median dust temperature Td = 22.4 K. Assuming β = 1.5, 67% of the 23 galaxies detected in all five Herschel bands show emission at 500 μm in excess of the modified black-body model. The fraction of galaxies with a submillimetre excess decreases for lower values of β, while a similarly high fraction (54%) is found if a β-free SED modelling is applied. The excess is inversely correlated with SFR and stellar masses. To study the variations in the global properties of our sample that come from environmental effects, we compare the Virgo dwarfs to other Herschel surveys,such as the Key Insights into Nearby Galaxies: Far-Infrared Survey with Herschel (KINGFISH), the Dwarf Galaxy Survey (DGS), and the HeViCS Bright Galaxy Catalogue (BGC). We explore the relations between stellar mass and Hi fraction, specific star formation rate, dust fraction, gas-to-dust ratio over a wide range of stellar masses (from 107 to 1011 M⊙) for both dwarfs and spirals. Highly Hi-deficient Virgo dwarf galaxies are mostly characterised by quenched star formation activity and lower dust fractions giving hints for dust stripping in cluster dwarfs. However, to explain the

  1. Radial velocities of stars in the globular cluster M4 and the cluster distance

    NASA Technical Reports Server (NTRS)

    Peterson, R. C.; Rees, Richard F.; Cudworth, Kyle M.

    1995-01-01

    The internal stellar velocity distribution of the globular cluster M4 is evaluated from nearly 200 new radial velocity measurements good to 1 km/s and a rederivation of existing proper motions. The mean radial velocity of the cluster is 70.9 +/- 0.6 km/s. The velocity dispersion is 3.5 +/- 0.3 km/s at the core, dropping marginally towards the outskirts. Such a low internal dispersion is somewhat at odds with the cluster's orbit, for which the perigalacticon is sufficiently close to the galactic center that the probability of cluster disruption is high; a tidal radius two-thirds the currently accepted value would eliminate the discrepancy. The cluster mass-to-light ratio is also small, M/L(sub V) = 1.0 +/- 0.4 in solar units. M4 thus joins M22 as a cluster of moderate and concentration with a mass-to-light ratio among the lowest known. The astrometric distance to the cluster is also smaller than expected, 1.72 +/- 0.14 kpc. This is only consistent with conventional estimates of the luminosity of horizontal branch stars provided an extinction law R = A(sub V)/E(B-V) approximately 4 is adopted, as has been suggested recently by several authors.

  2. Ionizing feedback from massive stars in massive clusters - II. Disruption of bound clusters by photoionization

    NASA Astrophysics Data System (ADS)

    Dale, J. E.; Ercolano, B.; Bonnell, I. A.

    2012-07-01

    We present a smoothed particle hydrodynamics parameter study of the dynamical effect of photoionization from O-type stars on star-forming clouds of a range of masses and sizes during the time window before supernovae explode. Our model clouds all have the same degree of turbulent support initially, the ratio of turbulent kinetic energy to gravitational potential energy being set to Ekin/|Epot|= 0.7. We allow the clouds to form stars and study the dynamical effects of the ionizing radiation from the massive stars or clusters born within them. We find that dense filamentary structures and accretion flows limit the quantities of gas that can be ionized, particularly in the higher density clusters. More importantly, the higher escape velocities in our more massive (106 M⊙) clouds prevent the H II regions from sweeping up and expelling significant quantities of gas, so that the most massive clouds are largely dynamically unaffected by ionizing feedback. However, feedback has a profound effect on the lower density 104 and 105 M⊙ clouds in our study, creating vast evacuated bubbles and expelling tens of per cent of the neutral gas in the 3-Myr time-scale before the first supernovae are expected to detonate, resulting in clouds highly porous to both photons and supernova ejecta.

  3. STAR CLUSTERS BORN IN THE WRECKAGE OF COSMIC COLLISIONS

    NASA Technical Reports Server (NTRS)

    2002-01-01

    This close-up view of Stephan's Quintet, a group of five galaxies, reveals a string of bright star clusters that sparkles like a diamond necklace. The clusters, each harboring up to millions of stars, were born from the violent interactions between some members of the group. The rude encounters also have distorted the galaxies' shapes, creating elongated spiral arms and long, gaseous streamers. The NASA Hubble Space Telescope photo showcases three regions of star birth: the long, sweeping tail and spiral arms of NGC 7319 [near center]; the gaseous debris of two galaxies, NGC 7318B and NGC 7318A [top right]; and the area north of those galaxies, dubbed the northern starburst region [top left]. The clusters' bluish color indicates that they're relatively young. Their ages span from about 2 million to more than 1 billion years old. The brilliant star clusters in NGC 7318B's spiral arm (about 30,000 light-years long) and the northern starburst region are between 2 million and more than 100 million years old. NGC 7318B instigated the starburst by barreling through the region. The bully galaxy is just below NGC 7318A at top right. Although NGC 7318B appears dangerously close to NGC 7318A, it's traveling too fast to merge with its close neighbor. The partial galaxy on the far right is NGC 7320, a foreground galaxy not physically bound to the other galaxies in the picture. About 20 to 50 of the clusters in the northern starburst region reside far from the coziness of galaxies. The clusters were born about 150,000 light-years from the nearest galaxy. A galaxy that is no longer part of the group triggered another collision that wreaked havoc. NGC 7320C [not in the photo] plowed through the quintet several hundred million years ago, pulling out the 100,000 light-year-long tail of gaseous debris from NGC 7319. The clusters in NGC 7319's streaming tail are 10 million to 500 million years old and may have formed at the time of the violent collision. The faint bluish object at

  4. THE CLUSTERED NATURE OF STAR FORMATION. PRE-MAIN-SEQUENCE CLUSTERS IN THE STAR-FORMING REGION NGC 602/N90 IN THE SMALL MAGELLANIC CLOUD

    SciTech Connect

    Gouliermis, Dimitrios A.; Gennaro, Mario; Schmeja, Stefan; Dolphin, Andrew E.; Tognelli, Emanuele; Prada Moroni, Pier Giorgio

    2012-03-20

    Located at the tip of the wing of the Small Magellanic Cloud (SMC), the star-forming region NGC 602/N90 is characterized by the H II nebular ring N90 and the young cluster of pre-main-sequence (PMS) and early-type main-sequence stars NGC 602, located in the central area of the ring. We present a thorough cluster analysis of the stellar sample identified with Hubble Space Telescope/Advanced Camera for Surveys in the region. We show that apart from the central cluster low-mass PMS stars are congregated in 13 additional small, compact sub-clusters at the periphery of NGC 602, identified in terms of their higher stellar density with respect to the average background density derived from star counts. We find that the spatial distribution of the PMS stars is bimodal, with an unusually large fraction ({approx}60%) of the total population being clustered, while the remaining is diffusely distributed in the intercluster area, covering the whole central part of the region. From the corresponding color-magnitude diagrams we disentangle an age difference of {approx}2.5 Myr between NGC 602 and the compact sub-clusters, which appear younger, on the basis of comparison of the brighter PMS stars with evolutionary models, which we accurately calculated for the metal abundance of the SMC. The diffuse PMS population appears to host stars as old as those in NGC 602. Almost all detected PMS sub-clusters appear to be centrally concentrated. When the complete PMS stellar sample, including both clustered and diffused stars, is considered in our cluster analysis, it appears as a single centrally concentrated stellar agglomeration, covering the whole central area of the region. Considering also the hot massive stars of the system, we find evidence that this agglomeration is hierarchically structured. Based on our findings, we propose a scenario according to which the region NGC 602/N90 experiences an active clustered star formation for the last {approx}5 Myr. The central cluster NGC 602 was

  5. SeaStar: Subsea cluster manifold system design and installation

    SciTech Connect

    Mason, P.G.T.; Upchurch, J.L.

    1996-12-31

    The SeaStar Cluster Manifold system was engineered as a low cost alternative to larger and more expensive completion template designs. Utilizing field-proven equipment and installation techniques, it was the first of its kind to be installed in the Gulf of Mexico. The Cluster Manifold system allows the connection of flowlines from adjacent satellite wells and numerous infield flowlines consisting of export, service, and methanol lines. With new technological advances, and a variety of flowline connection systems on the market today, deep water completions are being used with increasing frequency. Subsea operations are becoming more routine and installation times are being reduced. The SeaStar system was successfully installed in Garden Banks Block 70/71 in the Gulf of Mexico during the first quarter of 1995. Currently two 4 x 2-in. 10,000 psi lay-away trees are installed and connected to the manifold. Production is being processed at a Marathon platform in Vermilion Block 386B approximately 13.5 miles away from the subsea installation.

  6. Search for Carbon-Rich Asymptotic Giant Branch Stars in Milky Way Globular Clusters

    NASA Astrophysics Data System (ADS)

    Indahl, Briana; Pessev, P.

    2014-01-01

    From our current understanding of stellar evolution, it would not be expected to find carbon rich asymptotic giant branch (AGB) stars in Milky Way globular clusters. Due to the low metallicity of the population II stars making up the globular clusters and their age, stars large enough to fuse carbon should have already evolved off of the asymptotic giant branch. Recently, however, there have been serendipitous discoveries of these types of stars. Matsunaga et al. (2006) discovered a Mira variable in the globular cluster Lynga 7. It was later confirmed by Feast et al. (2012) that the star is a member of the cluster and must be a product of a stellar merger. In the same year, Sharina et al. (2012) discovered a carbon star in the low metallicity globular cluster NGC6426 and reports it to be a CH star. Five more of these types of stars have been made as serendipitous discoveries and have been reported by Harding (1962), Dickens (1972), Cote et al. (1997), and Van Loon (2007). The abundance of these types of carbon stars in Milky Way globular clusters has been unknown because the discovery of these types of objects has only ever been a serendipitous discovery. These stars could have been easily overlooked in the past as they are outside the typical parameter space of galactic globular clusters. Also advances in near-infrared instruments and observing techniques have made it possible to detect the fainter carbon stars in binary systems. Having an understanding of the abundances of carbon stars in galactic globular clusters will aid in the modeling of globular cluster and galaxy formation leading to a better understanding of these processes. To get an understanding of the abundances of these stars we conducted the first comprehensive search for AGB carbon stars into all Milky Way globular clusters listed in the Harris Catalog (expect for Pyxis). I have found 128 carbon star candidates using methods of comparing color magnitude diagrams of the clusters with the carbon

  7. NGC 346: Looking in the Cradle of a Massive Star Cluster

    NASA Astrophysics Data System (ADS)

    Gouliermis, Dimitrios A.; Hony, Sacha

    2017-03-01

    How does a star cluster of more than few 10,000 solar masses form? We present the case of the cluster NGC 346 in the Small Magellanic Cloud, still embedded in its natal star-forming region N66, and we propose a scenario for its formation, based on observations of the rich stellar populations in the region. Young massive clusters host a high fraction of early-type stars, indicating an extremely high star formation efficiency. The Milky Way galaxy hosts several young massive clusters that fill the gap between young low-mass open clusters and old massive globular clusters. Only a handful, though, are young enough to study their formation. Moreover, the investigation of their gaseous natal environments suffers from contamination by the Galactic disk. Young massive clusters are very abundant in distant starburst and interacting galaxies, but the distance of their hosting galaxies do not also allow a detailed analysis of their formation. The Magellanic Clouds, on the other hand, host young massive clusters in a wide range of ages with the youngest being still embedded in their giant HII regions. Hubble Space Telescope imaging of such star-forming complexes provide a stellar sampling with a high dynamic range in stellar masses, allowing the detailed study of star formation at scales typical for molecular clouds. Our cluster analysis on the distribution of newly-born stars in N66 shows that star formation in the region proceeds in a clumpy hierarchical fashion, leading to the formation of both a dominant young massive cluster, hosting about half of the observed pre-main-sequence population, and a self-similar dispersed distribution of the remaining stars. We investigate the correlation between stellar surface density (and star formation rate derived from star-counts) and molecular gas surface density (derived from dust column density) in order to unravel the physical conditions that gave birth to NGC 346. A power law fit to the data yields a steep correlation between these

  8. The ACS Fornax Cluster Survey. XII. Diffuse Star Clusters in Early-type Galaxies

    NASA Astrophysics Data System (ADS)

    Liu, Yiqing; Peng, Eric W.; Lim, Sungsoon; Jordán, Andrés; Blakeslee, John; Côté, Patrick; Ferrarese, Laura; Pattarakijwanich, Petchara

    2016-10-01

    Diffuse star clusters (DSCs) are old and dynamically hot stellar systems that have lower surface brightness and more extended morphology than globular clusters (GCs). Using the images from Hubble Space Telescope (HST)/ACS Fornax Cluster Survey, we find that 12 out of 43 early-type galaxies (ETGs) in the Fornax Cluster host significant numbers of DSCs. Together with literature data from the HST/ACS Virgo Cluster Survey, where 18 out of 100 ETGs were found to host DSCs, we systematically study the relationship of DSCs with GCs and their host galaxy environment. Two DSC hosts are post-merger galaxies, with most of the other hosts either having low mass or showing clear disk components. We find that while the number ratio of DSCs to GCs is nearly constant in massive galaxies, the DSC-to-GC ratio becomes systematically higher in lower-mass hosts. This suggests that DSCs may be more efficient at forming (or surviving) in low-density environments. DSC hosts are not special either in their position in the cluster or in the galactic color-magnitude diagram. Why some disk and low-mass galaxies host DSCs while others do not is still a puzzle, however. The mean ages of DSC hosts and nonhosts are similar at similar masses, implying that formation efficiency rather than survival is the reason behind different DSC number fractions in ETGs.

  9. Exploring Sources of Gravitational Waves From Star Cluster Dynamics

    NASA Astrophysics Data System (ADS)

    Fuhrman, Joshua; Geller, Aaron M.; Rodriguez, Carl L.; Rasio, Frederic A.

    2017-01-01

    The recent detection of ripples in space-time by the Laser Interferometer Gravitational-wave Observatory (LIGO) has ushered in the age of gravitational wave astronomy. Binary black hole systems formed in the center of modest star clusters offer a possible gravitational wave source detectable by the LIGO or Laser Interferometer Space Antennae (LISA) collaborations. We simulate clusters containing 1-40K objects using direct integration from a customized version of NBODY6++GPU. We identify Binary Black Hole (BBH) objects of interest by an inspiral time sufficiently less than the age of the universe such that their coalescence might be detectable. Such objects are tracked through time within our N-body simulations to characterize the role of dynamics in the evolution of the BBH system using member exchanges and large orbital eccentricity changes as indicators of dynamic’s influence. We produce 41 BBH system candidates for detection by LIGO, all of which are dynamically formed. We observe several trends in the production of these potential BBH LIGO sources: a low-N cutoff in initial cluster size between 1-5K objects, high eccentricity oscillations, and the frequent formation of stable triple systems with the BBH as the inner binary.

  10. ALE OF TWO CLUSTERS YIELDS SECRETS OF STAR BIRTH IN THE EARLY UNIVERSE

    NASA Technical Reports Server (NTRS)

    2002-01-01

    This NASA Hubble Space Telescope (HST) image shows rich detail, previously only seen in neighboring star birth regions, in a pair of star clusters 166,000 light-years away in the Large Magellanic Cloud (LMC), in the southern constellation Doradus. The field of view is 130 light-years across and was taken with the Wide Field Planetary Camera 2. HST's unique capabilities -- ultraviolet sensitivity, ability to see faint stars, and high resolution -- have been utilized fully to identify three separate populations in this concentration of nearly 10,000 stars down to the 25th magnitude (more that twice as many as can be seen over the entire sky with the naked eye on a clear night on Earth). The field of view is only 130 light-years across. Previous observations with ground-based telescopes resolve less than 1,000 stars in the same region. About 60 percent of the stars belong to the dominant yellow cluster called NGC 1850, which is estimated to be 50 million years old. A scattering of white stars in the image are massive stars that are only about 4 million years old and represent about 20 percent of the stars in the image. (The remainder are field stars in the LMC.) Besides being much younger, the white stars are much more loosely distributed than the yellow cluster. The significant difference between the two cluster ages suggests these are two separate star groups that lie along the same line of sight. The younger, more open cluster probably lies 200 light-years beyond the older cluster. If it were in the foreground, then dust contained in the white cluster would obscure stars in the older yellow cluster. To observe two well-defined star populations separated by such a small gap of space is unusual. This juxtaposition suggests that supernova explosions in the older cluster might have triggered the birth of the younger cluster. This color composite image is assembled from exposures taken in ultraviolet, visible, and near-infrared light. Yellow stars correspond to Main

  11. OGLE Collection of Star Clusters. New Objects in the Outskirts of the Large Magellanic Cloud

    NASA Astrophysics Data System (ADS)

    Sitek, M.; Szymański, M. K.; Skowron, D. M.; Udalski, A.; Kostrzewa-Rutkowska, Z.; Skowron, J.; Karczmarek, P.; Cieślar, M.; Wyrzykowski, Ł.; Kozłowski, S.; Pietrukowicz, P.; Soszyński, I.; Mróz, P.; Pawlak, M.; Poleski, R.; Ulaczyk, K.

    2016-09-01

    The Magellanic System (MS), consisting of the Large Magellanic Cloud (LMC), the Small Magellanic Cloud (SMC) and the Magellanic Bridge (MBR), contains diverse sample of star clusters. Their spatial distribution, ages and chemical abundances may provide important information about the history of formation of the whole System. We use deep photometric maps derived from the images collected during the fourth phase of the Optical Gravitational Lensing Experiment (OGLE-IV) to construct the most complete catalog of star clusters in the Large Magellanic Cloud using the homogeneous photometric data. In this paper we present the collection of star clusters found in the area of about 225 square degrees in the outer regions of the LMC. Our sample contains 679 visually identified star cluster candidates, 226 of which were not listed in any of the previously published catalogs. The new clusters are mainly young small open clusters or clusters similar to associations.

  12. Cannibal Stars Cause Giant Explosions in Fornax Cluster Galaxy

    NASA Astrophysics Data System (ADS)

    2000-07-01

    . After reaching maximum light within some days or weeks, it begins to fade as the hydrogen supply is exhausted and blown into space. The processed material is ejected at high speeds, up to ~1000 km/sec, and may later be visible as an expanding shell of emitting gas. Altogether, the tremendous flash of light involves the release of about 10 45 ergs in a few weeks, or about as much energy as our Sun produces in 10,000 years. Supernovae explosions that completely destroy heavier stars at the end of their lives are even more powerful. However, in contrast to supernovae and despite the colossal energy production, the progenitor of a nova is not destroyed during the explosion. Some time after an outburst, transfer of hydrogen from the companion star begins anew, and the process repeats itself with explosions taking place about once every 100,000 years. The nova star will finally die of "old age" when the cool companion has been completely cannibalized. Novae as Distance Indicators Due to their exceptional luminosity, novae can be used as powerful beacons that allow relative distances to different types of galaxies to be measured. The measurement is based on the assumption that novae of the same type are intrinsically equally bright, together with the physical law that states that an object's observed brightness decreases with the square of the distance to the observer. Thus, if we observe that a nova in a certain galaxy is one million times fainter than a nearby one, we know that it must be one thousand times more distant. In addition, observations of novae in other galaxies shed light on the history of formation of their stars. Despite their scientific importance, surveys of novae in distant, rich clusters of galaxies have not been very popular among astronomers. Major reasons are probably the inherent observational difficulties and the comparatively low rates of discovery. In the past, with 4-m class telescopes, tens of hours of monitoring of several galaxies have indeed

  13. A Stacked Search for Intermediate-mass Black Holes in 337 Extragalactic Star Clusters

    NASA Astrophysics Data System (ADS)

    Wrobel, J. M.; Nyland, K. E.; Miller-Jones, J. C. A.

    2015-10-01

    Forbes et al. recently used the Hubble Space Telescope to localize hundreds of candidate star clusters in NGC 1023, an early-type galaxy at a distance of 11.1 Mpc. Old stars dominate the light of 92% of the clusters and intermediate-age stars dominate the light of the remaining 8%. Theory predicts that clusters with such ages can host intermediate-mass black holes (IMBHs) with masses To investigate this prediction, we used 264 s of 5.5 GHz data from the Karl G. Jansky Very Large Array to search for the radiative signatures of IMBH accretion from 337 candidate clusters in an image spanning 492″ (26 kpc) with a resolution of 0.″40 (22 pc). None of the individual clusters are detected, nor are weighted-mean image stacks of the 311 old clusters, the 26 intermediate-age clusters, and the 20 clusters with stellar masses The clusters thus lack radio analogs of HLX-1, a strong IMBH candidate in a cluster in the early-type galaxy ESO 243-49. This suggests that HLX-1 is accreting gas related to its cluster's light-dominating young stars. Alternatively, the HLX-1 phenomenon could be so rare that no radio analog is expected in NGC 1023. Also, using a formalism heretofore applied to star clusters in the Milky Way, the radio-luminosity upper limit for the massive-cluster stack corresponds to a 3σ IMBH mass of suggesting black hole mass fractions of

  14. A STACKED SEARCH FOR INTERMEDIATE-MASS BLACK HOLES IN 337 EXTRAGALACTIC STAR CLUSTERS

    SciTech Connect

    Wrobel, J. M.; Nyland, K. E.; Miller-Jones, J. C. A. E-mail: nyland@astron.nl

    2015-10-15

    Forbes et al. recently used the Hubble Space Telescope to localize hundreds of candidate star clusters in NGC 1023, an early-type galaxy at a distance of 11.1 Mpc. Old stars dominate the light of 92% of the clusters and intermediate-age stars dominate the light of the remaining 8%. Theory predicts that clusters with such ages can host intermediate-mass black holes (IMBHs) with masses To investigate this prediction, we used 264 s of 5.5 GHz data from the Karl G. Jansky Very Large Array to search for the radiative signatures of IMBH accretion from 337 candidate clusters in an image spanning 492″ (26 kpc) with a resolution of 0.″40 (22 pc). None of the individual clusters are detected, nor are weighted-mean image stacks of the 311 old clusters, the 26 intermediate-age clusters, and the 20 clusters with stellar masses The clusters thus lack radio analogs of HLX-1, a strong IMBH candidate in a cluster in the early-type galaxy ESO 243-49. This suggests that HLX-1 is accreting gas related to its cluster's light-dominating young stars. Alternatively, the HLX-1 phenomenon could be so rare that no radio analog is expected in NGC 1023. Also, using a formalism heretofore applied to star clusters in the Milky Way, the radio-luminosity upper limit for the massive-cluster stack corresponds to a 3σ IMBH mass of suggesting black hole mass fractions of.

  15. CHEMICAL ABUNDANCE ANTICORRELATIONS IN GLOBULAR CLUSTER STARS: THE EFFECT ON CLUSTER INTEGRATED SPECTRA

    SciTech Connect

    Coelho, P.; Percival, S. M.; Salaris, M. E-mail: smp@astro.livjm.ac.uk

    2011-06-10

    It is widely accepted that individual Galactic globular clusters harbor two coeval generations of stars, the first one born with the 'standard' {alpha}-enhanced metal mixture observed in field halo objects and the second one characterized by an anticorrelated CNONa abundance pattern overimposed on the first generation, {alpha}-enhanced metal mixture. We have investigated with appropriate stellar population synthesis models how this second generation of stars affects the integrated spectrum of a typical metal-rich Galactic globular cluster, like 47 Tuc, focusing our analysis on the widely used Lick-type indices. We find that the only indices appreciably affected by the abundance anticorrelations are Ca4227, G4300, CN{sub 1}, CN{sub 2}, and NaD. The age-sensitive Balmer line, Fe line, and the [MgFe] indices widely used to determine age, Fe, and total metallicity of extragalactic systems are largely insensitive to the second generation population. Enhanced He in second generation stars affects also the Balmer line indices of the integrated spectra, through the change of the turnoff temperature and-with the assumption that the mass-loss history of both stellar generations is the same-the horizontal branch morphology of the underlying isochrones.

  16. The Evolutionary Status of Be Stars: Results from a Photometric Study of Southern Open Clusters

    NASA Astrophysics Data System (ADS)

    McSwain, M. Virginia; Gies, Douglas R.

    2005-11-01

    Be stars are a class of rapidly rotating B stars with circumstellar disks that cause Balmer and other line emission. There are three possible reasons for the rapid rotation of Be stars: they may have been born as rapid rotators, spun up by binary mass transfer, or spun up during the main-sequence (MS) evolution of B stars. To test the various formation scenarios, we have conducted a photometric survey of 55 open clusters in the southern sky. Of these, five clusters are probably not physically associated groups and our results for two other clusters are not reliable, but we identify 52 definite Be stars and an additional 129 Be candidates in the remaining clusters. We use our results to examine the age and evolutionary dependence of the Be phenomenon. We find an overall increase in the fraction of Be stars with age until 100 Myr, and Be stars are most common among the brightest, most massive B-type stars above the zero-age main sequence (ZAMS). We show that a spin-up phase at the terminal-age main sequence (TAMS) cannot produce the observed distribution of Be stars, but up to 73% of the Be stars detected may have been spun-up by binary mass transfer. Most of the remaining Be stars were likely rapid rotators at birth. Previous studies have suggested that low metallicity and high cluster density may also favor Be star formation. Our results indicate a possible increase in the fraction of Be stars with increasing cluster distance from the Galactic center (in environments of decreasing metallicity). However, the trend is not significant and could be ruled out due to the intrinsic scatter in our data. We also find no relationship between the fraction of Be stars and cluster density.

  17. WFPC2 Observations of Star Clusters in the Magellanic Clouds. Report 2; The Oldest Star Clusters in the Small Magellanic Cloud

    NASA Technical Reports Server (NTRS)

    Mighell, Kenneth J.; Sarajedini, Ata; French, Rica S.

    1998-01-01

    We present our analysis of archival Hubble Space Telescope Wide Field Planetary Camera 2 (WFPC2) observations in F45OW ( approximately B) and F555W (approximately V) of the intermediate-age populous star clusters NGC 121, NGC 339, NGC 361, NGC 416, and Kron 3 in the Small Magellanic Cloud. We use published photometry of two other SMC populous star clusters, Lindsay 1 and Lindsay 113, to investigate the age sequence of these seven populous star clusters in order to improve our understanding of the formation chronology of the SMC. We analyzed the V vs B-V and M(sub V) vs (B-V)(sub 0) color-magnitude diagrams of these populous Small Magellanic Cloud star clusters using a variety of techniques and determined their ages, metallicities, and reddenings. These new data enable us to improve the age-metallicity relation of star clusters in the Small Magellanic Cloud. In particular, we find that a closed-box continuous star-formation model does not reproduce the age-metallicity relation adequately. However, a theoretical model punctuated by bursts of star formation is in better agreement with the observational data presented herein.

  18. New constraints on the star formation history of the star cluster NGC 1856

    NASA Astrophysics Data System (ADS)

    Correnti, Matteo; Goudfrooij, Paul; Puzia, Thomas H.; de Mink, Selma E.

    2015-07-01

    We use the Wide Field Camera 3 onboard the Hubble Space Telescope to obtain deep, high-resolution photometry of the young (age ˜ 300 Myr) star cluster NGC 1856 in the Large Magellanic Cloud. We compare the observed colour-magnitude diagram (CMD), after having applied a correction for differential reddening, with Monte Carlo simulations of simple stellar populations (SSPs) of various ages. We find that the main-sequence turn-off (MSTO) region is wider than that derived from the simulation of a single SSP. Using constraints based on the distribution of stars in the MSTO region and the Red Clump, we find that the CMD is best reproduced using a combination of two different SSPs with ages separated by 80 Myr (0.30 and 0.38 Gyr, respectively). However, we cannot formally exclude that the width of the MSTO could be due to a range of stellar rotation velocities if the efficiency of rotational mixing is higher than typically assumed. Using a King-model fit to the surface number density profile in conjunction with dynamical evolution models, we determine the evolution of cluster mass and escape velocity from an age of 10 Myr to the present age, taking into account the possible effects of primordial mass segregation. We find that the cluster has an escape velocity Vesc ≃ 17 km s-1 at an age of 10 Myr, and it remains high enough during a period of ≃100 Myr to retain material ejected by slow winds of first-generation stars. Our results are consistent with the presence of an age spread in NGC 1856, in contradiction to the results of Bastian & Silva-Villa.

  19. Are there any first-generation stars in globular clusters today?

    NASA Astrophysics Data System (ADS)

    Charbonnel, Corinne; Chantereau, William; Krause, Martin; Primas, Francesca; Wang, Yue

    2014-09-01

    Context. Several models compete to explain the abundance properties of stellar populations in globular clusters. One of the main constraints is the present-day ratio of first- and second-generation stars that are currently identified based on their sodium content. Aims: We propose an alternative interpretation of the observed sodium distribution, and suggest that stars with low sodium abundance that are counted as members of the first stellar generation could actually be second-generation stars. Methods: We compute the number ratio of second-generation stars along the Na distribution following the fast rotating massive star model using the same constraints from the well-documented case of NGC 6752 as in our previous developments. Results: We reproduce the typical percentage of low-sodium stars usually classified as first-generation stars by invoking only secondary star formation from material ejected by massive stars and mixed with original globular cluster material in proportions that account for the Li-Na anti-correlation in this cluster. Conclusions: Globular clusters could be totally devoid of first-generation low-mass stars today. This can be tested with the determination of the carbon isotopic ratio and nitrogen abundance in turn-off globular cluster stars. Consequences and related issues are briefly discussed.

  20. VizieR Online Data Catalog: SMC BV photometry of 9 star cluster fields (Dias+, 2016)

    NASA Astrophysics Data System (ADS)

    Dias, B.; Kerber, L.; Barbuy, B.; Bica, E.; Ortolani, S.

    2016-05-01

    Photometric magnitudes from SOAR Optical Imager for individual stars in nine stellar clusters in the Small Magellanic Cloud are presented. The following clusters are presented: Bruck2, Bruck4, Bruck6, HW5, HW6, Kron8, Kron11, Lindsay14, and NGC152. For each star equatorial coordinates and B, V (Bessel) magnitudes with their errors are given. (10 data files).

  1. The same frequency of planets inside and outside open clusters of stars.

    PubMed

    Meibom, Søren; Torres, Guillermo; Fressin, Francois; Latham, David W; Rowe, Jason F; Ciardi, David R; Bryson, Steven T; Rogers, Leslie A; Henze, Christopher E; Janes, Kenneth; Barnes, Sydney A; Marcy, Geoffrey W; Isaacson, Howard; Fischer, Debra A; Howell, Steve B; Horch, Elliott P; Jenkins, Jon M; Schuler, Simon C; Crepp, Justin

    2013-07-04

    Most stars and their planets form in open clusters. Over 95 per cent of such clusters have stellar densities too low (less than a hundred stars per cubic parsec) to withstand internal and external dynamical stresses and fall apart within a few hundred million years. Older open clusters have survived by virtue of being richer and denser in stars (1,000 to 10,000 per cubic parsec) when they formed. Such clusters represent a stellar environment very different from the birthplace of the Sun and other planet-hosting field stars. So far more than 800 planets have been found around Sun-like stars in the field. The field planets are usually the size of Neptune or smaller. In contrast, only four planets have been found orbiting stars in open clusters, all with masses similar to or greater than that of Jupiter. Here we report observations of the transits of two Sun-like stars by planets smaller than Neptune in the billion-year-old open cluster NGC6811. This demonstrates that small planets can form and survive in a dense cluster environment, and implies that the frequency and properties of planets in open clusters are consistent with those of planets around field stars in the Galaxy.

  2. PROTOSTARS AND STARS IN THE CORONET CLUSTER: AGE, EVOLUTION, AND CLUSTER STRUCTURE

    SciTech Connect

    Sicilia-Aguilar, Aurora; Henning, Thomas; Kainulainen, Jouni; Roccatagliata, Veronica

    2011-08-01

    We present new optical spectroscopy with the FLAMES spectrograph at the Very Large Telescope (VLT), near-IR imaging with VLT/HAWK-I, and 870 {mu}m mapping with APEX/LABOCA of the Coronet cluster. The optical data allow us to estimate spectral types, extinction, and the presence of accretion in 6 more M-type members, in addition to the 12 that we had previously studied. The submillimeter maps and near-IR data reveal the presence of nebular structures and high extinction regions, which are in some cases associated to known IR, optical, and X-ray sources. Most star formation is associated to two elongated structures crossing in the central part of the cluster. Placing all the 18 objects with known spectral types and extinction in an H-R diagram suggests that the cluster is younger than previously thought (<2 Myr, and probably {approx}0.5-1 Myr). The new age estimate is in agreement with the evolutionary status of the various protostars in the region and with its compactness (<1.3 pc across), but results in a conflict with the low disk and accretion fraction (only 50%-65% of low-mass stars appear to have protoplanetary disks, and most transitional and homologously depleted disks are consistent with no accretion) and with the evolutionary features observed in the mid-IR spectra and spectral energy distributions of the disks.

  3. A KINEMATIC AND PHOTOMETRIC STUDY OF THE GALACTIC YOUNG STAR CLUSTER NGC 7380

    SciTech Connect

    Chen, W. P.; Chen, C. W.; Pandey, A. K.; Sharma, Saurabh; Chen Li; Sperauskas, J.; Ogura, K.; Chuang, R. J.; Boyle, R. P.

    2011-09-15

    We present proper motions, radial velocities, and a photometric study of the Galactic open cluster NGC 7380, which is associated with prominent emission nebulosity and dark molecular clouds. On the basis of the sample of highly probable member stars, the star cluster is found to be at a distance of 2.6 {+-} 0.4 kpc, has an age of around 4 Myr, and a physical size of {approx}6 pc across with a tidal structure. The binary O-type star DH Cep is a member of the cluster in its late stage of clearing the surrounding material, and may have triggered the ongoing star formation in neighboring molecular clouds which harbor young stars that are coeval and comoving with, but not gravitationally bound by, the star cluster.

  4. Photometry and spectroscopy of stars in the region of a highly reddened cluster in ARA

    NASA Astrophysics Data System (ADS)

    Westerlund, B. E.

    1987-09-01

    VRI photographic photometry is presented for 258 stars in the region of the cluster Wd1 in Ara together with near-infrared spectrophotometry of the brightest stars. The brightest member stars of the cluster are shown to be of spectral types B2 Ia to M2 Ia, forming a well defined sequence of supergiants with the maximum visual luminosity being reached in classes A2 and G0. One of the stars is of type Be with an extremely extended shell. Weak hydrogen emission can be traced in the spectra of a number of the stars as well as in between the stars. The interstellar absorption is very heavy, reaching A(V) = 10 mag; the surrounding field has an average absorption of about 3 mag. A redetermination of the distance of the cluster leads to a value of about 5 kpc as most likely. The age of the cluster is estimated to about seven million years.

  5. The dynamical importance of binary systems in young massive star clusters

    NASA Astrophysics Data System (ADS)

    de Grijs, Richard; Li, Chengyuan; Geller, Aaron M.

    2017-03-01

    Characterization of the binary fractions in star clusters is of fundamental importance for many fields in astrophysics. Observations indicate that the majority of stars are found in binary systems, while most stars with masses greater than 0.5M ⊙ are formed in star clusters. In addition, since binaries are on average more massive than single stars, in resolved star clusters these systems are thought to be good tracers of (dynamical) mass segregation. Over time, dynamical evolution through two-body relaxation will cause the most massive objects to migrate to the cluster center, while the relatively lower-mass objects remain in or migrate to orbits at greater radii. This process will globally dominate a cluster's stellar distribution. However, close encounters involving binary systems may disrupt `soft' binaries. This process will occur more frequently in a cluster's central, dense region than in its periphery, which may mask the effects of mass segregation. Using high resolution Hubble Space Telescope observations, combined with sophisticated N-body simulations, we investigate the radial distributions of the main-sequence binary fractions in massive young Large Magellanic Cloud star clusters. We show that binary disruption may play an important role on very short timescales, depending on the environmental conditions in the cluster cores. This may lead to radial binary fractions that initially decline in the cluster centers, which is contrary to the effects expected from dynamical mass segregation.

  6. A highly efficient measure of mass segregation in star clusters

    NASA Astrophysics Data System (ADS)

    Olczak, C.; Spurzem, R.; Henning, Th.

    2011-08-01

    Context. Investigations of mass segregation are of vital interest for the understanding of the formation and dynamical evolution of stellar systems on a wide range of spatial scales. A consistent analysis requires a robust measure among different objects and well-defined comparison with theoretical expectations. Various methods have been used for this purpose but usually with limited significance, quantifiability, and application to both simulations and observations. Aims: We aim at developing a measure of mass segregation with as few parameters as possible, robustness against peculiar configurations, independence of mass determination, simple implementation, stable algorithm, and that is equally well adoptable for data from either simulations or observations. Methods: Our method is based on the minimum spanning tree (MST) that serves as a geometry-independent measure of concentration. Compared to previous such approaches we obtain a significant refinement by using the geometrical mean as an intermediate-pass. Results: The geometrical mean boosts the sensitivity compared to previous applications of the MST. It thus allows the detection of mass segregation with much higher confidence and for much lower degrees of mass segregation than other approaches. The method shows in particular very clear signatures even when applied to small subsets of the entire population. We confirm with high significance strong mass segregation of the five most massive stars in the Orion nebula cluster (ONC). Conclusions: Our method is the most sensitive general measure of mass segregation so far and provides robust results for both data from simulations and observations. As such it is ideally suited for tracking mass segregation in young star clusters and to investigate the long standing paradigm of primordial mass segregation by comparison of simulations and observations.

  7. Photometrically-derived properties of massive-star clusters obtained with different massive-star evolution tracks and deterministic models

    NASA Astrophysics Data System (ADS)

    Wofford, Aida; Charlot, Stéphane; Eldridge, John

    2015-08-01

    We compute libraries of stellar + nebular spectra of populations of coeval stars with ages of <100 Myr and metallicities of Z=0.001 to 0.040, using different sets of massive-star evolution tracks, i.e., new Padova tracks for single non-rotating stars, the Geneva tracks for single non-rotating and rotating stars, and the Auckland tracks for single non-rotating and binary stars. For the stellar component, we use population synthesis codes galaxev, starburst99, and BPASS, depending on the set of tracks. For the nebular component we use photoionization code cloudy. From these spectra, we obtain magnitudes in filters F275W, F336W, F438W, F547M, F555W, F657N, and F814W of the Hubble Space Telescope (HST) Wide Field Camera Three. We use i) our computed magnitudes, ii) new multi-band photometry of massive-star clusters in nearby (<11 Mpc) galaxies spanning the metallicity range 12+log(O/H)=7.2-9.2, observed as part of HST programs 13364 (PI Calzetti) and 13773 (PI Chandar), and iii) Bayesian inference to a) establish how well the different models are able to constrain the metallicities, extinctions, ages, and masses of the star clusters, b) quantify differences in the cluster properties obtained with the different models, and c) assess how properties of lower-mass clusters are affected by the stochastic sampling of the IMF. In our models, the stellar evolution tracks, stellar atmospheres, and nebulae have similar chemical compositions. Different metallicities are available with different sets of tracks and we compare results from models of similar metallicities. Our results have implications for studies of the formation and evolution of star clusters, the cluster age and mass functions, and the star formation histories of galaxies.

  8. Do open star clusters evolve towards energy equipartition?

    NASA Astrophysics Data System (ADS)

    Spera, Mario; Mapelli, Michela; Jeffries, Robin D.

    2016-07-01

    We investigate whether open clusters (OCs) tend to energy equipartition, by means of direct N-body simulations with a broken power-law mass function. We find that the simulated OCs become strongly mass segregated, but the local velocity dispersion does not depend on the stellar mass for most of the mass range: the curve of the velocity dispersion as a function of mass is nearly flat even after several half-mass relaxation times, regardless of the adopted stellar evolution recipes and Galactic tidal field model. This result holds both if we start from virialized King models and if we use clumpy sub-virial initial conditions. The velocity dispersion of the most massive stars and stellar remnants tends to be higher than the velocity dispersion of the lighter stars. This trend is particularly evident in simulations without stellar evolution. We interpret this result as a consequence of the strong mass segregation, which leads to Spitzer's instability. Stellar winds delay the onset of the instability. Our simulations strongly support the result that OCs do not attain equipartition, for a wide range of initial conditions.

  9. Star Formation in Galaxy Clusters Over the Past 10 Billion Years

    NASA Astrophysics Data System (ADS)

    Tran, Kim-Vy

    2012-01-01

    Galaxy clusters are the largest gravitationally bound systems in the universe and include the most massive galaxies in the universe; this makes galaxy clusters ideal laboratories for disentangling the nature versus nurture aspect of how galaxies evolve. Understanding how galaxies form and evolve in clusters continues to be a fundamental question in astronomy. The ages and assembly histories of galaxies in rich clusters test both stellar population models and hierarchical formation scenarios. Is star formation in cluster galaxies simply accelerated relative to their counterparts in the lower density field, or do cluster galaxies assemble their stars in a fundamentally different manner? To answer this question, I review multi-wavelength results on star formation in galaxy clusters from Coma to the most distant clusters yet discovered at look-back times of 10 billion years (z 2).

  10. Observational Investigations on Contact Binaries in Multiple-star Systems and Star Clusters

    NASA Astrophysics Data System (ADS)

    Liu, L.

    2013-01-01

    The W UMa-type contact binaries are strongly interacting systems whose components both fill their critical Roche lobes and share a convective common envelope. The models of contact binaries are bottlenecked due to too many uncertain parameters. In the 1960s and 1970s, the common convective envelope model was accepted after several fierce controversies. And then, the thermal relaxation oscillation (TRO) model, the discontinuity model, and the angular momentum loss (AML) model appeared. However, in the past forty years, there lacked remarkable advance. The coexistence of many unknown parameters blocks the theoretical development of contact binaries. A study on the contact binaries in multiple star systems and star clusters, which could provide lots of information for their formation and evolution, may be a potential growing point for understanding these objects. More and more evidence shows that many of contact binaries are located in multiple star systems and star clusters. In this thesis, we observed and analyzed contact binaries in the forementioned systems. The observational and theoretical studies for contact binary are also summarized briefly. The results obtained are as follows: (1) Three contact binaries V1128 Tau, GZ And, VW Boo which possess visual companions show periodic oscillations. The period ranges from 16.7 years to 46.5 years. These oscillations probably come from the orbital movement of a close third body. (2) Four contact binaries GSC 02393-00680, V396 Mon, FU Dra, SS Ari which do not have visual companions also present periodic oscillations. Whether they are real members of multiple star systems needs further investigations. These oscillations probably result from the orbital movement of a close M-type companion. (3) The periods of three contact binaries EQ Cep, ER Cep and V371 Cep in the old open cluster NGC 188 show a long-term increase. There is a cyclic period oscillation in ER Cep, with a period of 5.4 years. We find that the total mass of

  11. Discovery of two low-luminosity star clusters in the Milky Way halo

    NASA Astrophysics Data System (ADS)

    Kim, Dongwon

    2015-08-01

    Star clusters in the halo of the Milky Way (MW) hold important clues to the formation and structure of their host galaxy. In the talk, I present the discovery of two new low-luminosity star clusters in the inner and outer halo of the Milky Way. These two star clusters, named as Kim 1 and Kim 2, were first detected in the Sloan Digital Sky Survey and our independent 500 sqr degree survey using the Dark Energy Survey camera (DECam) at the 4m Blanco telescope at CTIO repectively. Their true identies were confirmed by deep follow-up imaging using DECam and Gemini-South 8-m telescope. Kim 1 and Kim 2 both exhibit unsual physical properties compared to other classically known star clusters. Kim 1, located at a heliocentric distance of 17 kpc, features extremely low luminosity (Mv~0.3 mag) and low star concentration. Together with the high ellipticity (e ~ 0.4) and irregular isophotes, these properties suggest that we are seeing an intermediate mass star cluster being stripped by the Galactic tidal field. In the case of Kim 2, ~ 104 kpc away from the sun, is the faintest globular cluster ever found in the outer halo of the Milky Way. The globular cluster exhibits evidence of significant mass loss such as extra-tidal stars and mass-segregation. The observed properties of the new star cluster also raise the question about how such a low luminosity star cluster could have survived until today. One possible scenario is that Kim 2 is a star cluster originally located in a satellite dwarf galaxy and was accreted into the Milky Way's halo.

  12. The Structure of the Nearest Nuclear Star Clusters

    NASA Astrophysics Data System (ADS)

    DiLullo, Christopher

    2015-01-01

    The occupation fraction of massive black holes in low-mass galaxies is a poorly constrained quantity. Understanding the rate at which tidal disruption events occur is critical to constraining the occupation fraction of black holes. It is known that most, if not all, galaxies with sub-Milky Way mass have a nuclear star cluster present. We have proposed to survey an extensive archive of HST observations of 80 galactic nuclei within 10 Mpc from Earth. At these distances, HST supplies us with adequate spatial resolution to create accurate surface brightness profiles that can then be used to create models of the nuclei's mass distribution and morphology. Our collaborators will use these data to generate models, based on black hole mass and cluster mass distribution, that predict occurrence rates of tidal disruption events. These models will then be compared to observations of tidal disruption events.We have begun the survey by generating models of the surface brightness profiles for two galaxies in our selection: M51 and NGC 404. I will discuss how these models were generated and what challenges were faced throughout the process. Finally, I present these models along with color maps and radial residual plots of each galaxy.

  13. Characterization of the Praesepe Star Cluster by Photometry and Proper Motions With 2MASS, PPMXL, and Pan-STARRS

    DTIC Science & Technology

    2014-03-20

    distinct from that of the field stars , so contamination is minimized when identifying member stars . Third, in contrast to a star cluster at birth , for...reserved. Printed in the U.S.A. CHARACTERIZATION OF THE PRAESEPE STAR CLUSTER BY PHOTOMETRY AND PROPER MOTIONS WITH 2MASS, PPMXL, AND Pan-STARRS P. F. Wang1...properties of a star cluster. Low-mass members in particular could be used to trace the dynamical history, such as mass segregation, stellar evaporation, or

  14. The influence of feedback from massive stars on the formation and emergence of massive clusters

    NASA Astrophysics Data System (ADS)

    Dale, James E.

    2017-03-01

    Massive star clusters are of fundamental importance both observationally, since they are visible at such great distances, and theoretically, because of their influence on the large-scale ISM. Understanding stellar feedback is a prerequisite for making sense of their formation and early evolution, since feedback influences cluster structure, star formation efficiency, and sets the timescales on which clusters emerge from their parent clouds to become optically visible. I review the progress made in understanding these issues from a numerical perspective.

  15. MOCCA-SURVEY Database I: Is NGC 6535 a dark star cluster harbouring an IMBH?

    NASA Astrophysics Data System (ADS)

    Askar, Abbas; Bianchini, Paolo; de Vita, Ruggero; Giersz, Mirek; Hypki, Arkadiusz; Kamann, Sebastian

    2017-01-01

    We describe the dynamical evolution of a unique type of dark star cluster model in which the majority of the cluster mass at Hubble time is dominated by an intermediate-mass black hole (IMBH). We analysed results from about 2000 star cluster models (Survey Database I) simulated using the Monte Carlo code MOnte Carlo Cluster simulAtor and identified these dark star cluster models. Taking one of these models, we apply the method of simulating realistic `mock observations' by utilizing the Cluster simulatiOn Comparison with ObservAtions (COCOA) and Simulating Stellar Cluster Observation (SISCO) codes to obtain the photometric and kinematic observational properties of the dark star cluster model at 12 Gyr. We find that the perplexing Galactic globular cluster NGC 6535 closely matches the observational photometric and kinematic properties of the dark star cluster model presented in this paper. Based on our analysis and currently observed properties of NGC 6535, we suggest that this globular cluster could potentially harbour an IMBH. If it exists, the presence of this IMBH can be detected robustly with proposed kinematic observations of NGC 6535.

  16. CHEMICAL ABUNDANCES OF MEMBER STARS IN THE OPEN CLUSTER NGC 2632 (PRAESEPE)

    SciTech Connect

    Yang, X. L.; Chen, Y. Q.; Zhao, G.

    2015-11-15

    Based on high-resolution, high signal-to-noise ratio spectra, we present abundances of 17 elements (Fe, O, Na, Mg, Al, Si, Ca, Sc, Ti, V, Cr, Co, Ni, Y, Zr, Ba, La) for six stars (one Am star, one F dwarf star, and four GK giant stars) and radial velocities for 18 proper-motion selected member stars in the open cluster NGC 2632. In the Am star, s-process elements Y and Ba are clearly overabundant, which may be considered as an indicator of a peculiar Am star. The average [Fe/H] is 0.16 ± 0.06 from four GK giant member stars, which is similar to that of solar-type stars in the literature. As compared with dwarf stars, significant overabundances are found for Na, Mg, and Ba elements in our giant stars, which can be explained by the evolutionary effect. We also detect a star-to-star scatter of [Na/Fe] ratios among four giants which locate approximately at the same position in the CMD. Finally, we perform an analysis on the possible connection between the abundance and spatial structure of NGC 2632, but we find no inhomogeneous abundance among different clumps of stars in this cluster based on our limited sample.

  17. Chemical Abundances of Member Stars in the Open Cluster NGC 2632 (Praesepe)

    NASA Astrophysics Data System (ADS)

    Yang, X. L.; Chen, Y. Q.; Zhao, G.

    2015-11-01

    Based on high-resolution, high signal-to-noise ratio spectra, we present abundances of 17 elements (Fe, O, Na, Mg, Al, Si, Ca, Sc, Ti, V, Cr, Co, Ni, Y, Zr, Ba, La) for six stars (one Am star, one F dwarf star, and four GK giant stars) and radial velocities for 18 proper-motion selected member stars in the open cluster NGC 2632. In the Am star, s-process elements Y and Ba are clearly overabundant, which may be considered as an indicator of a peculiar Am star. The average [Fe/H] is 0.16 ± 0.06 from four GK giant member stars, which is similar to that of solar-type stars in the literature. As compared with dwarf stars, significant overabundances are found for Na, Mg, and Ba elements in our giant stars, which can be explained by the evolutionary effect. We also detect a star-to-star scatter of [Na/Fe] ratios among four giants which locate approximately at the same position in the CMD. Finally, we perform an analysis on the possible connection between the abundance and spatial structure of NGC 2632, but we find no inhomogeneous abundance among different clumps of stars in this cluster based on our limited sample.

  18. Hubble Space Telescope imaging of super-star clusters in NGC 1569 and NGC 1705

    NASA Technical Reports Server (NTRS)

    O'Connell, Robert W.; Gallagher, John S., III; Hunter, Deidre A.

    1994-01-01

    We examine the structural properties of three super-star clusters in the nearby, H I-rich galaxies NGC 1569 and NGC 1705. The clusters, which have total absolute V magnitudes between -13.3 and -14.1, appear to be point sources on ground-based images but are partially resolved in new images obtained with the Hubble Space Telescope (HST) Planetary Camera. From deconvolved V- and I-band images we find that the three clusters have very compact cores with extended halos that are partially resolved into individual stars. Using new distances to the galaxies derived from color-magnitude diagrams for field stars, we find that the half-light radii are 2.2-3.4 pc. The cluster in NGC 1705 is barely resolved in the HST images. The clusters in NGC 1569, on the other hand, show significant substructure in their cores and ellipticities that are comparable to the flattenings seen in young clusters in the Large Magellanic Cloud (LMC). The clusters show internal (V-I) color gradients. The properties of these clusters are similar to R136, the core of the luminous star-forming complex 30 Doradus in the LMC, except that R136 has a lower luminosity and central surface brightness. The half-light surface brightness of the brightest cluster (NGC 1569 A) is 1.3 x 10(exp 6) L(sub v) solar/ sq cm, which is over 65 times higher than R136 and 1200 times higher than the mean rich LMC star cluster other than R136 after allowing for aging effects. The next brightest clusters in each of these galaxies are greater than or = 2 mag fainter. Thus, the super-star clusters represent an extreme but uncommon mode of star formation. In terms of luminosity and size, they appear to be good analogs of young globular clusters.

  19. Constraining the Star Forming History in Monoceros: A Study of Embedded Cluster Ages and Spatial Structure

    NASA Astrophysics Data System (ADS)

    Marinas, Naibi; Lada, Elizabeth; Ybarra, Jason; Fleming, Scott

    2010-08-01

    We propose to use FLAMINGOS multi-object spectrometer on the KPNO 4 meter telescope to complete a spectroscopic survey of 5 clusters in the Monoceros GMC. The data will be combined with existing FLAMINGOS photometry to determine the ages and masses of the stars in the clusters using the HR Diagram and PMS evolutionary models. This information, combined with the spatial distribution of clusters in the cloud, determined from previous observations, will allow us to investigate the ages and age spreads of the embedded clusters and the star forming histories of the clusters and the molecular cloud.

  20. Constraining the Star Forming History in Monoceros: A Study of Embedded Cluster Ages and Spatial Structure

    NASA Astrophysics Data System (ADS)

    Lada, Elizabeth A.; Marinas, Naibi; Levine, Joanna L.; Ferreira, Bruno

    2009-08-01

    We propose to use FLAMINGOS multi-object spectrometer on the KPNO 4 meter telescope to complete a spectroscopic survey of 7 clusters in the Monoceros GMC. The data will be combined with existing FLAMINGOS photometry to determine the ages and masses of the stars in the clusters using the HR Diagram and PMS evolutionary models. This information, combined with the spatial distribution of clusters in the cloud, determined from previous observations, will allow us to investigate the ages and age spreads of the embedded clusters and the star forming histories of the clusters and the molecular cloud.

  1. MOCCA code for star cluster simulations - V. Initial globular cluster conditions influence on blue stragglers

    NASA Astrophysics Data System (ADS)

    Hypki, Arkadiusz; Giersz, Mirek

    2017-04-01

    In this paper, we present an analysis of the properties of blue straggler (BS) populations based on MOCCA simulations covering a range of initial globular cluster conditions. We broadly separate the BSs created in our simulations into two distinct types corresponding to their formation mechanism, namely evolutionary BSs formed from binary evolution and dynamical BSs formed from collisions or mergers induced by direct dynamical interactions between stars and binaries. We find that the dominant type of BS strongly depends on the initial semi-major axis distribution. With mostly compact binaries, the number of evolutionary BSs dominates. Conversely, with mostly wide binaries, dynamical BSs dominate. Higher cluster concentrations increase the contribution from dynamical BSs without affecting the numbers of evolutionary BSs, which are thus mostly descended from primordial binaries. We further consider the ratio between the number of BSs in binaries and as single stars (RB/S). Models that prefer compact and wide binaries begin with, respectively, high and low values of the ratio RB/S before converging to a nearly universal value ∼ 0.4. Finally, the initial eccentricity distribution has little to no influence on BS formation.

  2. Abundance anomalies in hot horizontal-branch stars of the globular cluster NGC 6752

    SciTech Connect

    Glaspey, J.W.; Michaud, G.; Moffat, A.F.J.; Demers, S.

    1989-04-01

    High-resolution spectra of two blue stars on the horizontal branch of the metal-poor globular cluster NGC 6752 have been obtained with an echelle spectrograph and a CCD detector on the CTIO 4 m telescope. A helium underabundance is confirmed in the blue star CL 1083 (Teff = 16,000 K). An overabundance of iron by a factor of 50 compared to the cluster metallicity is also obtained. No abundance anomaly is measured in the cooler star CL 1007 (Teff = 10,000 K). Presumably all stars of this cluster had the same original abundances; hence, the anomalies must be explained by the different properties of individual stars. These results are discussed in the context of the diffusion model originally developed to explain the He underabundance in horizontal-branch stars. 47 refs.

  3. Formation of new stellar populations from gas accreted by massive young star clusters.

    PubMed

    Li, Chengyuan; de Grijs, Richard; Deng, Licai; Geller, Aaron M; Xin, Yu; Hu, Yi; Faucher-Giguère, Claude-André

    2016-01-28

    Stars in clusters are thought to form in a single burst from a common progenitor cloud of molecular gas. However, massive, old 'globular' clusters--those with ages greater than ten billion years and masses several hundred thousand times that of the Sun--often harbour multiple stellar populations, indicating that more than one star-forming event occurred during their lifetimes. Colliding stellar winds from late-stage, asymptotic-giant-branch stars are often suggested to be triggers of second-generation star formation. For this to occur, the initial cluster masses need to be greater than a few million solar masses. Here we report observations of three massive relatively young star clusters (1-2 billion years old) in the Magellanic Clouds that show clear evidence of burst-like star formation that occurred a few hundred million years after their initial formation era. We show that such clusters could have accreted sufficient gas to form new stars if they had orbited in their host galaxies' gaseous disks throughout the period between their initial formation and the more recent bursts of star formation. This process may eventually give rise to the ubiquitous multiple stellar populations in globular clusters.

  4. Sodium content as a predictor of the advanced evolution of globular cluster stars.

    PubMed

    Campbell, Simon W; D'Orazi, Valentina; Yong, David; Constantino, Thomas N; Lattanzio, John C; Stancliffe, Richard J; Angelou, George C; Wylie-de Boer, Elizabeth C; Grundahl, Frank

    2013-06-13

    The asymptotic giant branch (AGB) phase is the final stage of nuclear burning for low-mass stars. Although Milky Way globular clusters are now known to harbour (at least) two generations of stars, they still provide relatively homogeneous samples of stars that are used to constrain stellar evolution theory. It is predicted by stellar models that the majority of cluster stars with masses around the current turn-off mass (that is, the mass of the stars that are currently leaving the main sequence phase) will evolve through the AGB phase. Here we report that all of the second-generation stars in the globular cluster NGC 6752--70 per cent of the cluster population--fail to reach the AGB phase. Through spectroscopic abundance measurements, we found that every AGB star in our sample has a low sodium abundance, indicating that they are exclusively first-generation stars. This implies that many clusters cannot reliably be used for star counts to test stellar evolution timescales if the AGB population is included. We have no clear explanation for this observation.

  5. Sodium content as a predictor of the advanced evolution of globular cluster stars

    NASA Astrophysics Data System (ADS)

    Campbell, Simon W.; D'Orazi, Valentina; Yong, David; Constantino, Thomas N.; Lattanzio, John C.; Stancliffe, Richard J.; Angelou, George C.; Wylie-de Boer, Elizabeth C.; Grundahl, Frank

    2013-06-01

    The asymptotic giant branch (AGB) phase is the final stage of nuclear burning for low-mass stars. Although Milky Way globular clusters are now known to harbour (at least) two generations of stars, they still provide relatively homogeneous samples of stars that are used to constrain stellar evolution theory. It is predicted by stellar models that the majority of cluster stars with masses around the current turn-off mass (that is, the mass of the stars that are currently leaving the main sequence phase) will evolve through the AGB phase. Here we report that all of the second-generation stars in the globular cluster NGC 6752--70 per cent of the cluster population--fail to reach the AGB phase. Through spectroscopic abundance measurements, we found that every AGB star in our sample has a low sodium abundance, indicating that they are exclusively first-generation stars. This implies that many clusters cannot reliably be used for star counts to test stellar evolution timescales if the AGB population is included. We have no clear explanation for this observation.

  6. The Clusters AgeS Experiment (CASE). Variable stars in the field of the globular cluster NGC 362

    NASA Astrophysics Data System (ADS)

    Rozyczka, M.; Thompson, I. B.; Narloch, W.; Pych, W.; Schwarzenberg-Czerny, A.

    2016-09-01

    The field of the globular cluster NGC 362 was monitored between 1997 and 2015 in a search for variable stars. BV light curves were obtained for 151 periodic or likely periodic variable stars, over a hundred of which are new detections. Twelve newly detected variable stars are proper-motion members of the cluster: two SX Phe and two RR Lyr pulsators, one contact binary, three detached or semi-detached eclipsing binaries, and four spotted variable stars. The most interesting objects among these are the binary blue straggler V20 with an asymmetric light curve, and the 8.1 d semidetached binary V24 located on the red giant branch of NGC 362, which is a Chandra X-ray source. We also provide substantial new data for 24 previously known variable stars.

  7. High Mass X-ray Binaries and Star Clusters in Starburst Galaxies

    NASA Astrophysics Data System (ADS)

    Prestwich, Andrea H.; Chandar, R.; Rangelov, B.; Jackson, F.

    2011-09-01

    High Mass X-ray Binaries (HMXB) are formed in copious numbers in starburst galaxies. Is there any relationship between HMXBs and young star clusters? Do HMXBs form preferentially in star clusters? What can star clusters tell us about nearby HMXBs, even if they are not directly related? We have studied a variety of nearby starburst galaxies -- including the Antennae, NGC 4449 (a star-bursting dwarf) and NGC 922 (a collisional ring galaxy). In all these systems, we find evidence that a large fraction of (but not all) HMXBs are spatially coincident with (or very close to) a star cluster. Approximately 50 percent of the clusters hosting bright HMXBs are extremely young -- less than 6 Myr. Stellar evolutionary models predict that all stars with initial masses higher than ≈ 30 M⊙ will have completed their main-sequence lifetime after 6 Myr. While still somewhat uncertain, models predict that stars this massive will end their lives as black holes. We therefore conclude that HMXBs coincident with these very young clusters are most likely black hole binaries. We also find evidence for a population of young (30-50 Myr) and intermediate age X-ray sources (100-300 Myr) that are associated with older clusters. The implications of these results for models of HMXB formation and evolution will be briefly discussed.

  8. Observational constraints on star cluster formation theory. I. The mass-radius relation

    NASA Astrophysics Data System (ADS)

    Pfalzner, S.; Kirk, H.; Sills, A.; Urquhart, J. S.; Kauffmann, J.; Kuhn, M. A.; Bhandare, A.; Menten, K. M.

    2016-02-01

    Context. Stars form predominantly in groups usually denoted as clusters or associations. The observed stellar groups display a broad spectrum of masses, sizes, and other properties, so it is often assumed that there is no underlying structure in this diversity. Aims: Here we show that the assumption of an unstructured multitude of cluster or association types might be misleading. Current data compilations of clusters in the solar neighbourhood show correlations among cluster mass, size, age, maximum stellar mass, etc. In this first paper we take a closer look at the correlation of cluster mass and radius. Methods: We use literature data to explore relations in cluster and molecular core properties in the solar neighbourhood. Results: We show that for embedded clusters in the solar neighbourhood a clear correlation exists between cluster mass and half-mass radius of the form Mc = CRcγ with γ = 1.7 ± 0.2. This correlation holds for infrared K-band data, as well as for X-ray sources and clusters containing a hundred stars up to those consisting of a few tens of thousands of stars. The correlation is difficult to verify for clusters containing fewer than 30 stars owing to low-number statistics. Dense clumps of gas are the progenitors of the embedded clusters. We find almost the same slope for the mass-size relation of dense, massive clumps as for the embedded star clusters. This might point to a direct translation from gas to stellar mass: however, it is difficult to relate size measurements for clusters (stars) to those for gas profiles. Taking multiple paths for clump mass into cluster mass into account, we obtain an average star-formation efficiency of 18%+9.3-5.7 for the embedded clusters in the solar neighbourhood. Conclusions: The derived mass-radius relation gives constraints for the theory of clustered star formation. Analytical models and simulations of clustered star formation have to reproduce this relation in order to be realistic.

  9. Open Clusters as Laboratories: The Angular Momentum Evolution of Young Stars

    NASA Technical Reports Server (NTRS)

    Stauffer, John R.

    1998-01-01

    The core group concentrated on three primary research topics: (1) ROSAT observation of the coronal activity of low mass stars in young open clusters; (2) the determination of stellar ages and the determination of the timescale for dissipation of circumstellar disks around young stars; and (3) the determination of rotation velocities of low mass stars in young open cluster and the inferred angular momentum evolution of low mass stars. With accurate ages for the clusters, we can then derive an independent estimate of the timescale for debris disks to dissipate. As the second half of that project, we are using the Caltech/UC/NASA Keck telescopes to obtain spectra of brown dwarf candidates in a number of nearby, young open clusters, from which we can determine new and accurate cluster ages. The final primary program that we have addressed was the determination of rotational velocities for low mass stars in our target open clusters. Our group has obtained rotational velocities for a large number of stars in several open clusters during this LTSA program, and we have published the results in several papers. One particularly time-consuming aspect of our program was the development of a database of the photometry and rotational velocities for nearby open clusters, which we have made available to the community.

  10. Protostars and Stars in the Coronet Cluster: Age, Evolution, and Cluster Structure

    NASA Astrophysics Data System (ADS)

    Sicilia-Aguilar, Aurora; Henning, Thomas; Kainulainen, Jouni; Roccatagliata, Veronica

    2011-08-01

    We present new optical spectroscopy with the FLAMES spectrograph at the Very Large Telescope (VLT), near-IR imaging with VLT/HAWK-I, and 870 μm mapping with APEX/LABOCA of the Coronet cluster. The optical data allow us to estimate spectral types, extinction, and the presence of accretion in 6 more M-type members, in addition to the 12 that we had previously studied. The submillimeter maps and near-IR data reveal the presence of nebular structures and high extinction regions, which are in some cases associated to known IR, optical, and X-ray sources. Most star formation is associated to two elongated structures crossing in the central part of the cluster. Placing all the 18 objects with known spectral types and extinction in an H-R diagram suggests that the cluster is younger than previously thought (<2 Myr, and probably ~0.5-1 Myr). The new age estimate is in agreement with the evolutionary status of the various protostars in the region and with its compactness (<1.3 pc across), but results in a conflict with the low disk and accretion fraction (only 50%-65% of low-mass stars appear to have protoplanetary disks, and most transitional and homologously depleted disks are consistent with no accretion) and with the evolutionary features observed in the mid-IR spectra and spectral energy distributions of the disks. Based on observations collected at the European Southern Observatory, Paranal, Chile (Proposal IDs: 081.C-0204(A), 083.C-0079(A), and 083.C-0079(B)).

  11. Size Distribution of Star Clusters and Stellar Groups in IC2574

    NASA Astrophysics Data System (ADS)

    Pellerin, Anne; Meyer, Martin J.; Calzetti, Daniela

    2017-01-01

    We present an HST/ACS archival study of compact and dispersed star clusters and stellar groups found in the nearby galaxy IC 2574. In this work, we identified and characterized the properties of clusters with spatially unresolved stars. We combined these properties with those found in a companion work on the dispersed stellar groups in IC 2574 with spatially resolved stars. We find that the size distribution of all young stellar groups, sparse and compact together, is consistent with the hierarchical model of star formation.

  12. The internal velocity dispersions of three young star clusters in the Large Magellanic Cloud

    NASA Technical Reports Server (NTRS)

    Lupton, Robert H.; Fall, S. Michael; Freeman, Kenneth C.; Elson, Rebecca A. W.

    1989-01-01

    The radial velocities of 11 to 37 stars have been measured in each of three rich young star clusters in the LMC: NGC 1866, NGC 2164, and NGC 2214. A thorough analysis of the observational errors and contamination by field stars is presented along with a new method to assign confidence limits to the velocity dispersions. Limits are set to the central densities, total masses, and mass-to-light ratios of the clusters, and the question of whether they have unbound halos is addressed. From the small velocity dispersion and large radial extent of NGC 1866, it is inferred that the cluster is not yet tidally limited by the LMC.

  13. Weakly damped modes in star clusters and galaxies

    NASA Technical Reports Server (NTRS)

    Weinberg, Martin D.

    1994-01-01

    A perturber may excite a coherent mode in a star cluster or galaxy. If the stellar system is stable, it is commonly assumed that such a mode will be strongly damped and therefore of little practical consequence other than redistributing momentum and energy deposited by the perturber. This paper demonstrates that this assumption is false; weakly damped modes exist and may persist long enough to have observable consequences. To do this, a method for investigating the dispersion relation for spherical stellar systems and for locating weakly damped modes in particular is developed and applied to King models of varying concentration. This leads to a following remarkable result: King models exhibit very weakly damped m = 1 modes over a wide range of concentration (0.67 less than or equal to c less than or equal to 1.5 have been examined). The predicted damping time is tens of hundreds of crossing times. This mode causes the peak density to shift from and slowly revolve about the initial center. The existence of the mode is supported by n-body simulation. Higher order modes and possible astronomical consequences are discussed. Weakly damped modes, for example, may provide a neutral explanation for observed discrepancies between density and kinematic centers in galaxies, off-center nuclei, the location of velocity cusps due to massive black holes, and both m = 1 and barlike disturbances of disks enbedded in massive halos or spheroids. Gravitational shocking may excite the m = 1 mode in globular clusters, which could modify their subsequent evolution and displace the positions of exotic remnants.

  14. First detections of FS Canis Majoris stars in clusters. Evolutionary state as constrained by coeval massive stars

    NASA Astrophysics Data System (ADS)

    de la Fuente, D.; Najarro, F.; Trombley, C.; Davies, B.; Figer, D. F.

    2015-03-01

    Context. FS CMa stars are low-luminosity objects showing the B[e] phenomenon whose evolutionary state remains a puzzle. These stars are surrounded by compact disks of warm dust of unknown origin. Hitherto, membership of FS CMa stars to coeval populations has never been confirmed. Aims: The discovery of low-luminosity line emitters in the young massive clusters Mercer 20 and Mercer 70 prompts us to investigate the nature of such objects. We intend to confirm membership to coeval populations in order to characterize these emission-line stars through the cluster properties. Methods: Based on ISAAC/VLT medium-resolution spectroscopy and NICMOS/HST photometry of massive cluster members, new characterizations of Mercer 20 and Mercer 70 are performed. Coevality of each cluster and membership of the newly-discovered B[e] objects are investigated using our observations as well as literature data of the surroundings. Infrared excess and narrow-band photometric properties of the B[e] stars are also studied. Results: We confirm and classify 22 new cluster members, including Wolf-Rayet stars and blue hypergiants. Spectral types (O9-B1.5 V) and radial velocities of B[e] objects are compatible with the remaining cluster members, while emission features of Mg ii, Fe ii], and [Fe ii] are identified in their spectra. The ages of these stars are 4.5 and 6 Myr, and they show mild infrared excesses. Conclusions: We confirm the presence of FS CMa stars in the coeval populations of Mercer 20 and Mercer 70. We discuss the nature and evolutionary state of FS CMa stars, discarding a post-AGB nature and introducing a new hypothesis about mergers. A new search method for FS CMa candidates in young massive clusters based on narrow-band Paschen-α photometry is proposed and tested in photometric data of other clusters, yielding three new candidates. Based on observations collected at the European Organisation for Astronomical Research in the Southern Hemisphere, Chile, under program IDs 083.D

  15. PULSATING B-TYPE STARS IN THE OPEN CLUSTER NGC 884: FREQUENCIES, MODE IDENTIFICATION, AND ASTEROSEISMOLOGY

    SciTech Connect

    Saesen, S.; Briquet, M.; Aerts, C.; Carrier, F.; Miglio, A.

    2013-10-01

    Recent progress in the seismic interpretation of field β Cep stars has resulted in improvements of the physical description in the stellar structure and evolution model computations of massive stars. Further asteroseismic constraints can be obtained from studying ensembles of stars in a young open cluster, which all have similar age, distance, and chemical composition. We present an observational asteroseismology study based on the discovery of numerous multi-periodic and mono-periodic B stars in the open cluster NGC 884. We describe a thorough investigation of the pulsational properties of all B-type stars in the cluster. Overall, our detailed frequency analysis resulted in 115 detected frequencies in 65 stars. We found 36 mono-periodic, 16 bi-periodic, 10 tri-periodic, and 2 quadru-periodic stars and one star with nine independent frequencies. We also derived the amplitudes and phases of all detected frequencies in the U, B, V, and I filter, if available. We achieved unambiguous identifications of the mode degree for 12 of the detected frequencies in nine of the pulsators. Imposing the identified degrees and measured frequencies of the radial, dipole, and quadrupole modes of five pulsators led to a seismic cluster age estimate of log (age/yr) = 7.12-7.28 from a comparison with stellar models. Our study is a proof-of-concept for and illustrates the current status of ensemble asteroseismology of a young open cluster.

  16. Be Stars and Physical Properties of the Young Open Cluster NGC 6834

    NASA Astrophysics Data System (ADS)

    Miller, G. J.; Grebel, E. K.; Yoss, K. M.

    1996-12-01

    We present initial results for the young open cluster NGC 6834 obtained with the 1-m telescope at Mount Laguna Observatory. We observed this cluster as part of a CCD-photometric survey for Be stars using B,V filters and two narrow-band interference filters at Hα and Hα continuum. Through a census of Be stars in clusters, where stars are coeval, equidistant, have the same metallicities, and share a common origin, we hope to gain a better understanding of the properties and origins of the still enigmatic Be phenomenon. Our B,V color-magnitude diagram of NGC 6834 shows an extended blue main sequence widened at fainter magnitudes by field star contamination. Fitting Geneva isochrones with solar metallicity to the cluster population, we find an age of ~ 50 Myr, a mean reddening of E(B-V)~ 0.7 mag, and a distance modulus of 12.2 mag (i.e. a distance of ~ 2750 pc). Our data reach roughly 4 magnitudes fainter in V than previous photographic or photoelectric studies. For the detection of Be stars, we use a two-color diagram. The most prominent feature distinguishing Be stars from B stars is their Balmer emission. The (Hα \\ continuum - Hα ) index allows us to find stars bright in Hα . The (B-V) color index serves to distinguish blue stars from red giants and red supergiants, which also may exhibit Hα emission. We find six Be star candidates in NGC 6834, that stand out clearly through their enhanced Balmer emission. Only one was known previously in this cluster. The brightness in Hα is well-correlated with reddened (B-V) colors. The relatively small number of Be stars in NGC 6834 is consistent with the young age of the cluster and the spectral type (B5) at the main-sequence turnoff.

  17. The jet feedback mechanism (JFM) in stars, galaxies and clusters

    NASA Astrophysics Data System (ADS)

    Soker, Noam

    2016-12-01

    I review the influence jets and the bubbles they inflate might have on their ambient gas as they operate through a negative jet feedback mechanism (JFM). I discuss astrophysical systems where jets are observed to influence the ambient gas, in many cases by inflating large, hot, and low-density bubbles, and systems where the operation of the JFM is still a theoretical suggestion. The first group includes cooling flows in galaxies and clusters of galaxies, star-forming galaxies, young stellar objects, and bipolar planetary nebulae. The second group includes core collapse supernovae, the common envelope evolution, the grazing envelope evolution, and intermediate luminosity optical transients. The suggestion that the JFM operates in these four types of systems is based on the assumption that jets are much more common than what is inferred from objects where they are directly observed. Common to all eight types of systems reviewed here is the presence of a compact object inside an extended ambient gas. The ambient gas serves as a potential reservoir of mass to be accreted on to the compact object. If the compact object launches jets as it accretes mass, the jets might reduce the accretion rate as they deposit energy to the ambient gas, or even remove the entire ambient gas, hence closing a negative feedback cycle.

  18. Clustering-based Feature Learning on Variable Stars

    NASA Astrophysics Data System (ADS)

    Mackenzie, Cristóbal; Pichara, Karim; Protopapas, Pavlos

    2016-04-01

    The success of automatic classification of variable stars depends strongly on the lightcurve representation. Usually, lightcurves are represented as a vector of many descriptors designed by astronomers called features. These descriptors are expensive in terms of computing, require substantial research effort to develop, and do not guarantee a good classification. Today, lightcurve representation is not entirely automatic; algorithms must be designed and manually tuned up for every survey. The amounts of data that will be generated in the future mean astronomers must develop scalable and automated analysis pipelines. In this work we present a feature learning algorithm designed for variable objects. Our method works by extracting a large number of lightcurve subsequences from a given set, which are then clustered to find common local patterns in the time series. Representatives of these common patterns are then used to transform lightcurves of a labeled set into a new representation that can be used to train a classifier. The proposed algorithm learns the features from both labeled and unlabeled lightcurves, overcoming the bias using only labeled data. We test our method on data sets from the Massive Compact Halo Object survey and the Optical Gravitational Lensing Experiment; the results show that our classification performance is as good as and in some cases better than the performance achieved using traditional statistical features, while the computational cost is significantly lower. With these promising results, we believe that our method constitutes a significant step toward the automation of the lightcurve classification pipeline.

  19. CLUSTERING-BASED FEATURE LEARNING ON VARIABLE STARS

    SciTech Connect

    Mackenzie, Cristóbal; Pichara, Karim; Protopapas, Pavlos

    2016-04-01

    The success of automatic classification of variable stars depends strongly on the lightcurve representation. Usually, lightcurves are represented as a vector of many descriptors designed by astronomers called features. These descriptors are expensive in terms of computing, require substantial research effort to develop, and do not guarantee a good classification. Today, lightcurve representation is not entirely automatic; algorithms must be designed and manually tuned up for every survey. The amounts of data that will be generated in the future mean astronomers must develop scalable and automated analysis pipelines. In this work we present a feature learning algorithm designed for variable objects. Our method works by extracting a large number of lightcurve subsequences from a given set, which are then clustered to find common local patterns in the time series. Representatives of these common patterns are then used to transform lightcurves of a labeled set into a new representation that can be used to train a classifier. The proposed algorithm learns the features from both labeled and unlabeled lightcurves, overcoming the bias using only labeled data. We test our method on data sets from the Massive Compact Halo Object survey and the Optical Gravitational Lensing Experiment; the results show that our classification performance is as good as and in some cases better than the performance achieved using traditional statistical features, while the computational cost is significantly lower. With these promising results, we believe that our method constitutes a significant step toward the automation of the lightcurve classification pipeline.

  20. A study of variable stars in the open cluster NGC 1582 and its surrounding field

    NASA Astrophysics Data System (ADS)

    Song, Fang-Fang; Esamdin, Ali; Ma, Lu; Liu, Jin-Zhong; Zhang, Yu; Niu, Hu-Biao; Yang, Tao-Zhi

    2016-10-01

    This paper presents Charge-Coupled Device time-series photometric observations of the open cluster NGC 1582 and its surrounding field with Johnson B, V and R filters by using the Nanshan 1 m telescope administered by Xinjiang Astronomical Observatory. 19 variable stars and three variable candidates were detected in a 45‧ × 48.75‧ field around the cluster. 12 of the variable stars are newly-discovered variable objects. The physical properties, classifications and memberships of these 22 objects are studied through their light curves, their positions on the color-magnitude diagram and with archival data from the Naval Observatory Merged Astrometric Dataset. Among these objects, five are eclipsing binary systems, six are pulsating variable stars including one known δ Scuti star and one newly-discovered RR Lyrae star. The distance to the RR Lyrae star is estimated to be 7.9 ± 0.3 kpc, indicating that the star is located far behind the cluster. Four variable stars are probable members of the cluster, and 13 of the 22 objects are confirmed to be field stars.

  1. DISCOVERY OF 14 NEW SLOWLY PULSATING B STARS IN THE OPEN CLUSTER NGC 7654

    SciTech Connect

    Luo, Y. P.; Han, Z. W.

    2012-02-10

    We carried out time-series BV CCD photometric observations of the open cluster NGC 7654 (Messier 52) to search for variable stars. Eighteen slowly pulsating B (SPB) stars have been detected, among which 14 candidates are newly discovered, three known ones are confirmed, and a previously found {delta} Scuti star is also identified as an SPB candidate. Twelve SPBs are probable cluster members based on membership analysis. This makes NGC 7654 the richest galactic open cluster in terms of SPB star content. It is also a new discovery that NGC 7654 hosts three {gamma} Dor star candidates. We found that all these stars (18 SPB and 3 {gamma} Dor stars) have periods longer than their corresponding fundamental radial mode. With such a big sample of g-mode pulsators in a single cluster, it is clear that multi-mode pulsation is more common in the upper part of the main sequence than in the lower part. All the stars span a narrow strip on the period-luminosity plane, which also includes the {gamma} Dor stars at the low-luminosity extension. This result implies that there may be a single period-luminosity relation applicable to all g-mode main-sequence pulsators. As a by-product, three EA-type eclipsing binaries and an EW-type eclipsing binary are also discovered.

  2. Exploring the origin of magnetic fields in massive stars. II. New magnetic field measurements in cluster and field stars

    NASA Astrophysics Data System (ADS)

    Hubrig, S.; Schöller, M.; Ilyin, I.; Kharchenko, N. V.; Oskinova, L. M.; Langer, N.; González, J. F.; Kholtygin, A. F.; Briquet, M.; Magori Collaboration

    2013-03-01

    Context. Theories on the origin of magnetic fields in massive stars remain poorly developed, because the properties of their magnetic field as function of stellar parameters could not yet be investigated. Additional observations are of utmost importance to constrain the conditions that are conducive to magnetic fields and to determine first trends about their occurrence rate and field strength distribution. Aims: To investigate whether magnetic fields in massive stars are ubiquitous or appear only in stars with a specific spectral classification, certain ages, or in a special environment, we acquired 67 new spectropolarimetric observations for 30 massive stars. Among the observed sample, roughly one third of the stars are probable members of clusters at different ages, whereas the remaining stars are field stars not known to belong to any cluster or association. Methods: Spectropolarimetric observations were obtained during four different nights using the low-resolution spectropolarimetric mode of FOcal Reducer low dispersion Spectrograph (FORS 2) mounted on the 8-m Antu telescope of the VLT. Furthermore, we present a number of follow-up observations carried out with the high-resolution spectropolarimeters SOFIN mounted at the Nordic Optical Telescope (NOT) and HARPS mounted at the ESO 3.6 m between 2008 and 2011. To assess the membership in open clusters and associations, we used astrometric catalogues with the highest quality kinematic and photometric data currently available. Results: The presence of a magnetic field is confirmed in nine stars previously observed with FORS 1/2: HD 36879, HD 47839, CPD-28 2561, CPD-47 2963, HD 93843, HD 148937, HD 149757, HD 328856, and HD 164794. New magnetic field detections at a significance level of at least 3σ were achieved in five stars: HD 92206c, HD 93521, HD 93632, CPD-46 8221, and HD 157857. Among the stars with a detected magnetic field, five stars belong to open clusters with high membership probability. According to

  3. Constraints on the low-mass IMF in young super-star clusters in starburst galaxies

    NASA Astrophysics Data System (ADS)

    Greissl, Julia Jennifer

    2010-12-01

    As evidence for variations in the initial mass function (IMF) in nearby star forming regions remains elusive we are forced to expand our search to more extreme regions of star formation. Starburst galaxies, which contain massive young clusters have in the past been reported to have IMFs different than that characterizing the field star IMF. In this thesis we use high signal-to-noise near-infrared spectra to place constraints on the shape of the IMF in extreme regions of extragalactic star formation and also try to understand the star formation history in these regions. Through high signal-to-noise near-infrared spectra it is possible to directly detect low-mass PMS stars in unresolved young super-star clusters, using absorption features that trace cool stars. Combining Starburst99 and available PMS tracks it is then possible to constrain the IMF in young super-star clusters using a combination of absorption lines each tracing different ranges of stellar masses and comparing observed spectra to models. Our technique can provide a direct test of the universality of the IMF compared to the Milky Way. We have obtained high signal-to-noise H- and K-band spectra of two young super-star clusters in the starburst galaxies NGC 4039/39 and NGC 253 in order to constrain the low-mass IMF and star formation history in the clusters. The cluster in NGC 4038/39 shows signs of youth such as thermal radio emission and strong hydrogen emission lines as well as late-type absorption lines indicative of cool stars. The strength and ratio of these absorption lines cannot be reproduced through either late-type pre-main sequence stars or red supergiants alone. We interpret the spectrum as a superposition of two star clusters of different ages over the physical region of 90 pc our spectrum represents. One cluster is young (≤ 3 Myr) and is responsible for part of the late-type absorption features, which are due to PMS stars in the cluster, and the hydrogen emission lines. The second

  4. STAR CLUSTER FORMATION WITH STELLAR FEEDBACK AND LARGE-SCALE INFLOW

    SciTech Connect

    Matzner, Christopher D.; Jumper, Peter H.

    2015-12-10

    During star cluster formation, ongoing mass accretion is resisted by stellar feedback in the form of protostellar outflows from the low-mass stars and photo-ionization and radiation pressure feedback from the massive stars. We model the evolution of cluster-forming regions during a phase in which both accretion and feedback are present and use these models to investigate how star cluster formation might terminate. Protostellar outflows are the strongest form of feedback in low-mass regions, but these cannot stop cluster formation if matter continues to flow in. In more massive clusters, radiation pressure and photo-ionization rapidly clear the cluster-forming gas when its column density is too small. We assess the rates of dynamical mass ejection and of evaporation, while accounting for the important effect of dust opacity on photo-ionization. Our models are consistent with the census of protostellar outflows in NGC 1333 and Serpens South and with the dust temperatures observed in regions of massive star formation. Comparing observations of massive cluster-forming regions against our model parameter space, and against our expectations for accretion-driven evolution, we infer that massive-star feedback is a likely cause of gas disruption in regions with velocity dispersions less than a few kilometers per second, but that more massive and more turbulent regions are too strongly bound for stellar feedback to be disruptive.

  5. Chemical Abundances of Two Stars in the Large Magellanic Cloud Globular Cluster NGC 1718

    NASA Astrophysics Data System (ADS)

    Sakari, Charli M.; McWilliam, Andrew; Wallerstein, George

    2017-01-01

    Detailed chemical abundances of two stars in the intermediate-age Large Magellanic Cloud (LMC) globular cluster NGC 1718 are presented, based on high resolution spectroscopic observations with the MIKE spectrograph. The detailed abundances confirm NGC 1718 to be a fairly metal-rich cluster, with an average [{Fe/H}] ˜ -0.55± 0.01. The two red giants appear to have primordial O, Na, Mg, and Al abundances, with no convincing signs of a composition difference between the two stars-hence, based on these two stars, NGC 1718 shows no evidence for hosting multiple populations. The Mg abundance is lower than Milky Way field stars, but is similar to LMC field stars at the same metallicity. The previous claims of very low [Mg/Fe] in NGC 1718 are therefore not supported in this study. Other abundances (Si, Ca, Ti, V, Mn, Ni, Cu, Rb, Y, Zr, La, and Eu) all follow the LMC field star trend, demonstrating yet again that (for most elements) globular clusters trace the abundances of their host galaxy's field stars. Similar to the field stars, NGC 1718 is found to be mildly deficient in explosive α-elements, but moderately to strongly deficient in O, Na, Mg, Al, and Cu, elements which form during hydrostatic burning in massive stars. NGC 1718 is also enhanced in La, suggesting that it was enriched in ejecta from metal-poor AGB stars.

  6. Environmental effects on stellar populations of star clusters and dwarf galaxies

    NASA Astrophysics Data System (ADS)

    Pasetto, Stefano; Cropper, Mark; Fujita, Yutaka; Chiosi, Cesare; Grebel, Eva K.

    2017-03-01

    We investigate the competitive role of the different dissipative phenomena acting on the onset of star formation of gravitationally bound systems in an external environment. Ram pressure, Kelvin-Helmholtz and Rayleigh-Taylor instabilities, and tidal forces are accounted for separately in an analytical framework and compared in their role in influencing the star forming regions. We present an analytical criterion to elucidate the dependence of star formation in a spherical stellar system on its surrounding environment. We consider the different signatures of these phenomena in synthetically realized colour-magnitude diagrams (CMDs) of the orbiting system thus investigating the detectability limits of these different effects for future observational projects and their relevance. The developed theoretical framework has direct applications to the cases of massive star clusters, dwarf galaxies in galaxy clusters and dwarf galaxies orbiting our Milky Way system, as well as any primordial gas-rich cluster of stars orbiting within its host galaxy.

  7. The super star cluster driven feedback in ESO338-IG04 and Haro 11

    NASA Astrophysics Data System (ADS)

    Bik, A.; Östlin, G.; Menacho, V.; Adamo, A.; Hayes, M.; Melinder, J.; Amram, P.

    2017-03-01

    The stellar content of young massive star clusters emit large amounts of Lyman continuum photons and inject momentum into the inter stellar medium (ISM) by the strong stellar winds of the most massive stars in the cluster. When the most massive stars explode as supernovae, large amounts of mechanical energy are injected in the ISM. A detailed study of the ISM around these massive cluster provides insights on the effect of cluster feedback. We present high quality integral field spectroscopy taken with VLT/MUSE of two starburst galaxies: ESO 338-IG04 and Haro 11. Both galaxies contain a significant number of super star clusters. The MUSE data provide us with an unprecedented view of the state and kinematics of the ionized gas in the galaxy allowing us to study the effect of stellar feedback on small and large spatial scales. We present our recent results on studying the ISM state of these two galaxies. The data of both galaxies show that the mechanical and ionization feedback of the super star clusters in the galaxy modify the state and kinematics of the ISM substancially by creating highly ionized bubbles around the cluster, making the central part of the galaxy highly ionized. This shows that the HII regions around the individual clusters are density bounded, allowing the ionizing photons to escape and ionize the ISM further out.

  8. Evolution of star cluster systems in isolated galaxies: first results from direct N-body simulations

    NASA Astrophysics Data System (ADS)

    Rossi, L. J.; Bekki, K.; Hurley, J. R.

    2016-11-01

    The evolution of star clusters is largely affected by the tidal field generated by the host galaxy. It is thus in principle expected that under the assumption of a `universal' initial cluster mass function the properties of the evolved present-day mass function of star cluster systems should show a dependence on the properties of the galactic environment in which they evolve. To explore this expectation, a sophisticated model of the tidal field is required in order to study the evolution of star cluster systems in realistic galaxies. Along these lines, in this work we first describe a method developed for coupling N-body simulations of galaxies and star clusters. We then generate a data base of galaxy models along the Hubble sequence and calibrate evolutionary equations to the results of direct N-body simulations of star clusters in order to predict the clusters' mass evolution as function of the galactic environment. We finally apply our methods to explore the properties of evolved `universal' initial cluster mass functions and any dependence on the host galaxy morphology and mass distribution. The preliminary results show that an initial power-law distribution of the masses `universally' evolves into a lognormal distribution, with the properties correlated with the stellar mass and stellar mass density of the host galaxy.

  9. Probing the link between dynamics and stellar evolution: Blue Straggler Stars in Globular clusters

    NASA Astrophysics Data System (ADS)

    Ferraro, F. R.; Lanzoni, B.

    2009-11-01

    In this contribution we review the main observational properties of Blue Straggler Stars (BSS) in Galactic Globular Clusters. A flower of results on the BSS frequency, radial distribution, and chemical composition are presented and discussed.

  10. Two New Ultra-Faint Star Clusters in the Milky Way Halo

    NASA Astrophysics Data System (ADS)

    Kim, Dongwon

    2016-08-01

    Kim 1 & 2 are two new star clusters discovered in the Stromlo Missing Satellite Survey. Kim 1, located at a heliocentric distance of 19.8 +/- 0.9 kpc, features an extremely low total luminosity (M V = 0.3 +/- 0.5 mag) and low star concentration. Together with the large ellipticity (ɛ = 0.42 +/- 0.10) and irregular isophotes, these properties suggest that Kim 1 is an intermediate mass star cluster being stripped by the Galactic tidal field. Kim 2 is a rare ultra-faint outer halo globular cluster located at a heliocentric distance of 104.7 +/- 4.1 kpc. The cluster exhibits evidence of significant mass loss such as extra-tidal stars and mass-segregation. Kim 2 is likely to follow an orbit confined to the peripheral region of the Galactic halo, and/or to have formed in a dwarf galaxy that was later accreted into the Galactic halo.

  11. Star formation trends in the unrelaxed, post-merger cluster A2255

    SciTech Connect

    Tyler, K. D.; Rieke, G. H.; Bai, L.

    2014-10-10

    The effects of dense environments on normal field galaxies are still up for debate despite much study since Abell published his catalog of nearby clusters in 1958. There are changes in color, morphology, and star formation properties when galaxies fall into groups and clusters, but the specifics of how and where these modifications occur are not fully understood. To look for answers, we focused on star-forming galaxies in A2255, an unrelaxed cluster thought to have recently experienced a merger with another cluster or large group. We used Hα, MIPS 24 μm, and WISE 22 μm to estimate total star formation rates (SFRs) and Sloan Digital Sky Survey photometry to find stellar masses (M {sub *}) for galaxies out to ∼5 r {sub 200}. We compared the star-forming cluster galaxies with the field SFR-mass distribution and found no enhancement or suppression of star formation in currently star-forming galaxies of high mass (log (M {sub *}/M {sub ☉}) ≳ 10). This conclusion holds out to very large distances from the cluster center. However, the core (r {sub proj} < 3 Mpc) has a much lower fraction of star-forming galaxies than anywhere else in the cluster. These results indicate that for the mass range studied here, the majority of the star formation suppression occurs in the core on relatively short timescales, without any enhancement prior to entering the central region. If any significant enhancement or quenching of star formation occurs, it will be in galaxies of lower mass (log (M {sub *}/M {sub ☉}) < 10).

  12. Massive Star Clusters and the high-mass population in the Galactic center

    NASA Astrophysics Data System (ADS)

    Stolte, A.

    2013-06-01

    With a star formation rate of 10% of the SFR in the Milky Way disc, the Galactic center is the most active star-forming environment in the Milky Way today. The small volume of the central molecular zone (CMZ), spanning a diameter of merely 400 pc, appears to foster especially the formation of high-mass stars. The CMZ is host to three of the most massive, young star clusters and a quarter of the known Wolf-Rayet population in the Galaxy. In this review, I will present the census of high-mass star formation that emerged from the recent Galactic center surveys, and will summarise the properties of the starburst clusters as the most productive sites of high-mass star formation.

  13. Binaries in star clusters and the origin of the field stellar population.

    PubMed

    Goodwin, Simon P

    2010-02-28

    Many, possibly most, stars form in binary and higher order multiple systems. Therefore, the properties and frequency of binary systems provide strong clues to the star-formation process, and constraints on star-formation models. However, the majority of stars also form in star clusters in which the birth binary properties and frequency can be altered rapidly by dynamical processing. Thus, we almost never see the birth population, which makes it very difficult to know whether star formation (as traced by binaries, at least) is universal or whether it depends on the environment. In addition, the field population consists of a mixture of systems from different clusters that have all been processed in different ways.

  14. The emergence of super-canonical stars in R136-type starburst clusters

    NASA Astrophysics Data System (ADS)

    Banerjee, Sambaran; Kroupa, Pavel; Oh, Seungkyung

    2012-10-01

    Among the most remarkable features of the stellar population of R136, the central, young, massive star cluster in the 30 Doradus complex of the Large Magellanic Cloud, are the single stars whose masses substantially exceed the canonical stellar upper mass limit of 150 M⊙. A recent study by Banerjee, Kroupa & Oh (hereafter Paper I), indicates that such 'super-canonical' (SC) stars can be formed out of a dense stellar population with a canonical initial mass function (IMF) through dynamically induced mergers of the most massive binaries. The above study consists of realistic N-body computations of fully mass-segregated star clusters mimicking R136 in which all the massive stars are in primordial binaries. In the present work, we study the formation of SC stars in the computed R136 models of Paper I in detail. Taking into consideration that extraneous SC stars form in the computed models of Paper I due to the primordial binaries' initial eccentricities, we compute additional models where all primordial binaries are initially circular. We also take into account the evolution of the mass of the SC stars and the resulting lifetime in their SC phase using detailed stellar evolutionary models over the SC mass range that incorporate updated treatments of the stellar winds. In all these computations, we find that SC stars begin to form via dynamical mergers of massive binaries from ≈1 Myr cluster age. We obtain SC stars with initial masses up to ≈250 M⊙ from these computations. Multiple SC stars are found to remain bound to the cluster simultaneously within an SC lifetime. However, we also note that SC stars can be formed at runaway velocities which escape the cluster at birth. These properties of the dynamically formed SC stars, as obtained from our computations, are consistent with the observed SC stellar population in R136. In fact, the evolutionary models of SC stars imply that had they formed primordially along with the rest of the R136 cluster, i.e. violating

  15. The Spatial Distribution of the Young Stellar Clusters in the Star-forming Galaxy NGC 628

    NASA Astrophysics Data System (ADS)

    Grasha, K.; Calzetti, D.; Adamo, A.; Kim, H.; Elmegreen, B. G.; Gouliermis, D. A.; Aloisi, A.; Bright, S. N.; Christian, C.; Cignoni, M.; Dale, D. A.; Dobbs, C.; Elmegreen, D. M.; Fumagalli, M.; Gallagher, J. S., III; Grebel, E. K.; Johnson, K. E.; Lee, J. C.; Messa, M.; Smith, L. J.; Ryon, J. E.; Thilker, D.; Ubeda, L.; Wofford, A.

    2015-12-01

    We present a study of the spatial distribution of the stellar cluster populations in the star-forming galaxy NGC 628. Using Hubble Space Telescope broadband WFC3/UVIS UV and optical images from the Treasury Program LEGUS (Legacy ExtraGalactic UV Survey), we have identified 1392 potential young (≲ 100 Myr) stellar clusters within the galaxy using a combination of visual inspection and automatic selection. We investigate the clustering of these young stellar clusters and quantify the strength and change of clustering strength with scale using the two-point correlation function. We also investigate how image boundary conditions and dust lanes affect the observed clustering. The distribution of the clusters is well fit by a broken power law with negative exponent α. We recover a weighted mean index of α ∼ -0.8 for all spatial scales below the break at 3.″3 (158 pc at a distance of 9.9 Mpc) and an index of α ∼ -0.18 above 158 pc for the accumulation of all cluster types. The strength of the clustering increases with decreasing age and clusters older than 40 Myr lose their clustered structure very rapidly and tend to be randomly distributed in this galaxy, whereas the mass of the star cluster has little effect on the clustering strength. This is consistent with results from other studies that the morphological hierarchy in stellar clustering resembles the same hierarchy as the turbulent interstellar medium.

  16. MOCCA code for star cluster simulation: comparison with optical observations using COCOA

    NASA Astrophysics Data System (ADS)

    Askar, Abbas; Giersz, Mirek; Pych, Wojciech; Olech, Arkadiusz; Hypki, Arkadiusz

    2016-02-01

    We introduce and present preliminary results from COCOA (Cluster simulatiOn Comparison with ObservAtions) code for a star cluster after 12 Gyr of evolution simulated using the MOCCA code. The COCOA code is being developed to quickly compare results of numerical simulations of star clusters with observational data. We use COCOA to obtain parameters of the projected cluster model. For comparison, a FITS file of the projected cluster was provided to observers so that they could use their observational methods and techniques to obtain cluster parameters. The results show that the similarity of cluster parameters obtained through numerical simulations and observations depends significantly on the quality of observational data and photometric accuracy.

  17. A prescription and fast code for the long-term evolution of star clusters - III. Unequal masses and stellar evolution

    NASA Astrophysics Data System (ADS)

    Alexander, Poul E. R.; Gieles, Mark; Lamers, Henny J. G. L. M.; Baumgardt, Holger

    2014-08-01

    We present a new version of the fast star cluster evolution code EVOLVE ME A CLUSTER OF STARS (EMACSS). While previous versions of EMACSS reproduced clusters of single-mass stars, this version models clusters with an evolving stellar content. Stellar evolution dominates early evolution, and leads to: (1) reduction of the mean mass of stars due to the mass loss of high-mass stars; (2) expansion of the half-mass radius; (3) for (nearly) Roche Volume filling clusters, the induced escape of stars. Once sufficient relaxation has occurred (≃10 relaxation times-scales), clusters reach a second, `balanced' state whereby the core releases energy as required by the cluster as a whole. In this state: (1) stars escape due to tidal effects faster than before balanced evolution; (2) the half-mass radius expands or contracts depending on the Roche volume filling factor; and (3) the mean mass of stars increases due to the preferential ejection of low-mass stars. We compare the EMACSS results of several cluster properties against N-body simulations of clusters spanning a range of initial number of stars, mass, half-mass radius, and tidal environments, and show that our prescription accurately predicts cluster evolution for this data base. Finally, we consider applications for EMACSS, such as studies of galactic globular cluster populations in cosmological simulations.

  18. Structural Parameters of Seven Small Magellanic Cloud Intermediate-Age and Old Star Clusters

    NASA Astrophysics Data System (ADS)

    Glatt, Katharina; Grebel, Eva K.; Gallagher, John S., III; Nota, Antonella; Sabbi, Elena; Sirianni, Marco; Clementini, Gisella; Da Costa, Gary; Tosi, Monica; Harbeck, Daniel; Koch, Andreas; Kayser, Andrea

    2009-11-01

    We present structural parameters for the seven intermediate-age and old star clusters NGC 121, Lindsay 1, Kron 3, NGC 339, NGC 416, Lindsay 38, and NGC 419 in the Small Magellanic Cloud (SMC). We fit King profiles and Elson, Fall, and Freeman profiles to both surface-brightness and star-count data taken with the Advanced Camera for Surveys aboard the Hubble Space Telescope. Clusters older than ~1 Gyr show a spread in cluster core radii that increases with age, while the youngest clusters have relatively compact cores. No evidence for post-core-collapse clusters was found. We find no correlation between core radius and distance from the SMC center, although consistent with other studies of dwarf galaxies, some relatively old and massive clusters have low densities. The oldest SMC star cluster, the only globular NGC121, is the most elliptical object of the studied clusters. No correlation is seen between ellipticity and distance from the SMC center. The structures of these massive intermediate-age (1-8 Gyr) SMC star clusters thus appear to primarily result from internal evolutionary processes. Based on observations made with the NASA/ESA Hubble Space Telescope, obtained at the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS 5-26555. These observations are associated with program GO-10396.

  19. Signatures of multiple stellar populations in unresolved extragalactic globular/young massive star clusters

    SciTech Connect

    Peacock, Mark B.; Zepf, Stephen E.; Finzell, Thomas

    2013-06-01

    We present an investigation of potential signatures of the formation of multiple stellar populations in recently formed extragalactic star clusters. All of the Galactic globular clusters for which good samples of individual stellar abundances are available show evidence for multiple populations. This appears to require that multiple episodes of star formation and light element enrichment are the norm in the history of a globular cluster. We show that there are detectable observational signatures of multiple formation events in the unresolved spectra of massive, young extragalactic star clusters. We present the results of a pilot program to search for one of the cleanest signatures that we identify—the combined presence of emission lines from a very recently formed population and absorption lines from a somewhat older population. A possible example of such a system is identified in the Antennae galaxies. This source's spectrum shows evidence of two stellar populations with ages of 8 Myr and 80 Myr. Further investigation shows that these populations are in fact physically separated, but only by a projected distance of 59 pc. We show that the clusters are consistent with being bound and discuss the possibility that their coalescence could result in a single globular cluster hosting multiple stellar populations. While not the prototypical system proposed by most theories of the formation of multiple populations in clusters, the detection of this system in a small sample is both encouraging and interesting. Our investigation suggests that expanded surveys of massive young star clusters should detect more clusters with such signatures.

  20. Physical properties of star clusters in the outer LMC as observed by the DES

    NASA Astrophysics Data System (ADS)

    Pieres, A.; Santiago, B.; Balbinot, E.; Luque, E.; Queiroz, A.; da Costa, L. N.; Maia, M. A. G.; Drlica-Wagner, A.; Roodman, A.; Abbott, T. M. C.; Allam, S.; Benoit-Lévy, A.; Bertin, E.; Brooks, D.; Buckley-Geer, E.; Burke, D. L.; Rosell, A. Carnero; Kind, M. Carrasco; Carretero, J.; Cunha, C. E.; Desai, S.; Diehl, H. T.; Eifler, T. F.; Finley, D. A.; Flaugher, B.; Fosalba, P.; Frieman, J.; Gerdes, D. W.; Gruen, D.; Gruendl, R. A.; Gutierrez, G.; Honscheid, K.; James, D. J.; Kuehn, K.; Kuropatkin, N.; Lahav, O.; Li, T. S.; Marshall, J. L.; Martini, P.; Miller, C. J.; Miquel, R.; Nichol, R. C.; Nord, B.; Ogando, R.; Plazas, A. A.; Romer, A. K.; Sanchez, E.; Scarpine, V.; Schubnell, M.; Sevilla-Noarbe, I.; Smith, R. C.; Soares-Santos, M.; Sobreira, F.; Suchyta, E.; Swanson, M. E. C.; Tarle, G.; Thaler, J.; Thomas, D.; Tucker, D. L.; Walker, A. R.

    2016-09-01

    The Large Magellanic Cloud (LMC) harbours a rich and diverse system of star clusters, whose ages, chemical abundances and positions provide information about the LMC history of star formation. We use Science Verification imaging data from the Dark Energy Survey (DES) to increase the census of known star clusters in the outer LMC and to derive physical parameters for a large sample of such objects using a spatially and photometrically homogeneous data set. Our sample contains 255 visually identified cluster candidates, of which 109 were not listed in any previous catalogue. We quantify the crowding effect for the stellar sample produced by the DES Data Management pipeline and conclude that the stellar completeness is <10 per cent inside typical LMC cluster cores. We therefore reanalysed the DES co-add images around each candidate cluster and remeasured positions and magnitudes for their stars. We also implement a maximum-likelihood method to fit individual density profiles and colour-magnitude diagrams. For 117 (from a total of 255) of the cluster candidates (28 uncatalogued clusters), we obtain reliable ages, metallicities, distance moduli and structural parameters, confirming their nature as physical systems. The distribution of cluster metallicities shows a radial dependence, with no clusters more metal rich than [Fe/H] ≃ -0.7 beyond 8 kpc from the LMC centre. The age distribution has two peaks at ≃1.2 and ≃2.7 Gyr.

  1. HUBBLE SPIES HUGE CLUSTERS OF STARS FORMED BY ANCIENT ENCOUNTER

    NASA Technical Reports Server (NTRS)

    2002-01-01

    NASA's Hubble Space Telescope snapped these two views of the heart of the galaxy M82. The image at left was taken in visible light; the picture at right, in infrared light. In the infrared view, the telescope's Near Infrared Camera and Multi-Object Spectrometer peered through thick dust lanes to find some of the galaxy's more than 100 super star clusters. The clusters are the larger pink and yellow dots scattered throughout the picture. They were formed during a violent collision with the galaxy M81 about 600 million years ago. The galaxy is 12 million light-years from Earth in the constellation Ursa Major. The pictures were taken Sept. 15, 1997. Credits: NASA, ESA, R. de Grijs (Institute of Astronomy, Cambridge, UK) NOTE TO EDITORS: For additional information, please contact Richard de Grijs, Institute of Astronomy, Cambridge University, Madingley Road, Cambridge CB3 0HA, UK, +44(0)1223-337528 (phone), +44(0)1223-337523 (fax), grijs@ast.cam.ac.uk (e-mail). The Space Telescope Science Institute (STScI) is operated by the Association of Universities for Research in Astronomy, Inc. (AURA), for NASA, under contract with the Goddard Space Flight Center, Greenbelt, MD. The Hubble Space Telescope is a project of international cooperation between NASA and the European Space Agency (ESA). This image is issued jointly by NASA and ESA. Electronic images, animation and additional information are available at: http://oposite.stsci.edu/pubinfo/pr/2001/08 and via links in http://oposite.stsci.edu/pubinfo/latest.html http://oposite.stsci.edu/pubinfo/pictures.html http://hubble.stsci.edu/go/news http://hubble.esa.int To receive STScI press releases electronically, send an Internet electronic mail message to public-request@stsci.edu. Leave the subject line blank, and type the word subscribe in the body of the message. The system will respond with a confirmation of the subscription, and you will receive new press releases as they are issued. Please subscribe using the email account

  2. Star-to-Star Abundance Variations among Bright Giants in the Mildly Metal-poor Globular Cluster M4

    NASA Astrophysics Data System (ADS)

    Ivans, Inese I.; Sneden, Christopher; Kraft, Robert P.; Suntzeff, Nicholas B.; Smith, Verne V.; Langer, G. Edward; Fulbright, Jon P.

    1999-09-01

    We present a chemical composition analysis of 36 giants in the nearby mildly metal-poor (<[Fe/H]>=-1.18) ``CN-bimodal'' globular cluster M4. The stars were observed at the Lick and McDonald Observatories using high-resolution échelle spectrographs and at the Cerro Tololo Inter-American Observatory using the multiobject spectrometer. Confronted with a cluster having interstellar extinction that is large and variable across the cluster face, we combined traditional spectroscopic abundance methods with modifications to the line depth ratio technique pioneered by Gray to determine the atmospheric parameters of our stars. We derive a total-to-selective extinction ratio of 3.4+/-0.4 and an average reddening of 0.33+/-0.01, which is significantly lower than that estimated by using the dust maps made by Schlegel and coworkers. We determine abundance ratios typical of halo field and cluster stars for scandium, titanium, vanadium, nickel, and europium with star-to-star variations in these elements of less than +/-0.1. Silicon, aluminum, barium, and lanthanum are overabundant with respect to what is seen in other globular clusters of similar metallicity. These overabundances confirm the results of an earlier study by Brown & Wallerstein based on a much smaller sample of M4 giants. Superposed on the primordial abundance distribution is evidence for the existence of proton capture synthesis of carbon, oxygen, neon, and magnesium. We recover some of the C, N, O, Na, Mg, and Al abundance swings and correlations found in other more metal-poor globular clusters, but the range of variation is muted. In the case of Mg and Al, this is compatible with the idea that the Al enhancements are derived from the destruction of ^25,26Mg, not ^24Mg. We determine that the C+N+O abundance sum is constant to within the observational errors and agrees with the C+N+O total that might be expected for M4 stars at birth. The asymptotic giant branch (AGB) stars in M4 have C, N, and O

  3. New variable stars in open clusters. I. Methods and results for 20 open clusters

    NASA Astrophysics Data System (ADS)

    Paunzen, E.; Zwintz, K.; Maitzen, H. M.; Pintado, O. I.; Rode-Paunzen, M.

    2004-04-01

    We present high precision CCD photometry of 1791 objects in 20 open clusters with an age of 10 Myr to 1 Gyr. These observations were performed within the Δ a photometric system which is primarily used to detect chemically peculiar stars of the upper main sequence. Time bases range from 30 min up to 60 days with data from several nights. We describe the time series analysis reaching a detection limit of down to 0.006 mag for apparent variability. In total, we have detected 35 variable objects of which four are not members of their corresponding clusters. The variables cover the entire Hertzsprung-Russell diagram, hence they are interesting targets for follow-up observations. Based on observations obtained at Complejo Astronómico el Leoncito (CASLEO), operated under the agreement between the Consejo Nacional de Investigaciones Científicas y Técnicas de la República Argentina and the National Universities of La Plata, Córdoba y San Juan; ESO-La Silla and UTSO-Las Campanas.

  4. ON THE MODULATION OF RR LYRAE STARS IN THE GLOBULAR CLUSTER M3

    SciTech Connect

    Jurcsik, J.; Smitola, P.; Nuspl, J.; Hajdu, G.

    2014-12-10

    New, extended time-series photometry of M3 RR Lyrae stars has revealed that 4 of the 10 double-mode stars show large-amplitude Blazhko modulation of both radial modes. The first, detailed analysis of the peculiar behavior of the unique, Blazhko RRd stars is given. While the P1/P0 period ratio is normal, and the overtone mode is dominant in the other RRd stars of the cluster, the period ratio is anomalous and the fundamental mode has a larger (or similar) mean amplitude than the overtone has in Blazhko RRd stars. The modulations of the fundamental and overtone modes are synchronized only in one of the Blazhko RRd stars. No evidence of any connection between the modulations of the modes in the other three stars is found. The Blazhko modulation accounts, at least partly, for the previously reported amplitude and period changes of these stars. Contrary to the ∼50% Blazhko statistics of RRab and RRd stars, Blazhko modulation occurs only in 10% of the overtone variables in M3. Four of the five Blazhko RRc stars are bright, evolved objects, and one has a period and brightness similar to those of Blazhko RRd stars. The regions of the instability strip with high and low occurrence rates of the Blazhko modulation overlap with the regions populated by first- and second-generation stars according to theoretical and observational studies, raising up the possibility that the Blazhko modulation occurs preferentially in first-generation RR Lyrae stars.

  5. The dynamical fate of binary star clusters in the Galactic tidal field

    NASA Astrophysics Data System (ADS)

    Priyatikanto, R.; Kouwenhoven, M. B. N.; Arifyanto, M. I.; Wulandari, H. R. T.; Siregar, S.

    2016-04-01

    Fragmentation and fission of giant molecular clouds occasionally results in a pair of gravitationally bound star clusters that orbit their mutual centre of mass for some time, under the influence of internal and external perturbations. We investigate the evolution of binary star clusters with different orbital configurations, with a particular focus on the Galactic tidal field. We carry out N-body simulations of evolving binary star clusters and compare our results with estimates from our semi-analytic model. The latter accounts for mass-loss due to stellar evolution and two-body relaxation, and for evolution due to external tides. Using the semi-analytic model, we predict the long-term evolution for a wide range of initial conditions. It accurately describes the global evolution of such systems, until the moment when a cluster merger is imminent. N-body simulations are used to test our semi-analytic model and also to study additional features of evolving binary clusters, such as the kinematics of stars, global cluster rotation, evaporation rates, and the cluster merger process. We find that the initial orientation of a binary star cluster with respect to the Galactic field, and also the initial orbital phase, is crucial for its fate. Depending on these properties, the binaries may experience orbital reversal, spiral-in, or vertical oscillation about the Galactic plane before they actually merge at t ≈ 100 Myr, and produce rotating star clusters with slightly higher evaporation rates. The merger process of a binary cluster induces an outburst that ejects ˜10 per cent of the stellar members into the Galactic field.

  6. Formation of massive black holes through runaway collisions in dense young star clusters.

    PubMed

    Zwart, Simon F Portegies; Baumgardt, Holger; Hut, Piet; Makino, Junichiro; McMillan, Stephen L W

    2004-04-15

    A luminous X-ray source is associated with MGG 11--a cluster of young stars approximately 200 pc from the centre of the starburst galaxy M 82 (refs 1, 2). The properties of this source are best explained by invoking a black hole with a mass of at least 350 solar masses (350 M(o)), which is intermediate between stellar-mass and supermassive black holes. A nearby but somewhat more massive cluster (MGG 9) shows no evidence of such an intermediate-mass black hole, raising the issue of just what physical characteristics of the clusters can account for this difference. Here we report numerical simulations of the evolution and motion of stars within the clusters, where stars are allowed to merge with each other. We find that for MGG 11 dynamical friction leads to the massive stars sinking rapidly to the centre of the cluster, where they participate in a runaway collision. This produces a star of 800-3,000 M(o) which ultimately collapses to a black hole of intermediate mass. No such runaway occurs in the cluster MGG 9, because the larger cluster radius leads to a mass segregation timescale a factor of five longer than for MGG 11.

  7. The regulation of star formation in cool-core clusters: imprints on the stellar populations of brightest cluster galaxies

    NASA Astrophysics Data System (ADS)

    Loubser, S. I.; Babul, A.; Hoekstra, H.; Mahdavi, A.; Donahue, M.; Bildfell, C.; Voit, G. M.

    2016-02-01

    A fraction of brightest cluster galaxies (BCGs) show bright emission in the ultraviolet and the blue part of the optical spectrum, which has been interpreted as evidence of recent star formation. Most of these results are based on the analysis of broad-band photometric data. Here, we study the optical spectra of a sample of 19 BCGs hosted by X-ray luminous galaxy clusters at 0.15 Cluster Comparison Project sample. We identify plausible star formation histories of the galaxies by fitting simple stellar populations as well as composite populations, consisting of a young stellar component superimposed on an intermediate/old stellar component, to accurately constrain their star formation histories. We detect prominent young (˜200 Myr) stellar populations in four of the 19 galaxies. Of the four, the BCG in Abell 1835 shows remarkable A-type stellar features indicating a relatively large population of young stars, which is extremely unusual even amongst star-forming BCGs. We constrain the mass contribution of these young components to the total stellar mass to be typically between 1 and 3 per cent, but rising to 7 per cent in Abell 1835. We find that the four of the BCGs with strong evidence for recent star formation (and only these four galaxies) are found within a projected distance of 5 kpc of their host cluster's X-ray peak, and the diffuse, X-ray gas surrounding the BCGs exhibits a ratio of the radiative cooling-to-free-fall time (tc/tff) of ≤10. These are also some of the clusters with the lowest central entropy. Our results are consistent with the predictions of the precipitation-driven star formation and active galactic nucleus feedback model, in which the radiatively cooling diffuse gas is subject to local thermal instabilities once the instability parameter tc/tff falls below ˜10, leading to the condensation and precipitation of cold gas. The number of galaxies in our sample where the host cluster satisfies all the

  8. Local Group and Star Cluster Dynamics from HSTPROMO: The Hubble Space Telescope Proper Motion Collaboration

    NASA Astrophysics Data System (ADS)

    van der Marel, R. P.; Anderson, J.; Bellini, A.; Besla, G.; Bianchini, P.; Boylan-Kolchin, M.; Chaname, J.; Deason, A.; Do, T.; Guhathakurta, P.; Kallivayalil, N.; Lennon, D.; Massari, D.; Meyer, E.; Platais, I.; Sabbi, E.; Sohn, S. T.; Soto, M.; Trenti, M.; Watkins, L.

    2014-03-01

    The Hubble Space Telescope (HST) has proven to be uniquely suited for the measurement of proper motions (PMs) of stars and galaxies in the nearby Universe. Here we summarize the main results and ongoing studies of the HSTPROMO collaboration, which over the past decade has executed some two dozen observational and theoretical HST projects on this topic. This is continuing to revolutionize our dynamical understanding of many objects, including: globular clusters; young star clusters; stars and stellar streams in the Milky Way halo; Local Group galaxies, including dwarf satellite galaxies, the Magellanic Clouds, and the Andromeda galaxy; and AGN black hole Jets.

  9. The physics and modes of star cluster formation: observations.

    PubMed

    Lada, Charles J

    2010-02-28

    Stellar clusters are born in cold and dusty molecular clouds and the youngest clusters are embedded to various degrees in a dusty dark molecular material. Such embedded clusters can be considered protocluster systems. The most deeply buried examples are so heavily obscured by dust that they are only visible at infrared wavelengths. These embedded protoclusters constitute the nearest laboratories for a direct astronomical investigation of the physical processes of cluster formation and early evolution. I review the present state of empirical knowledge concerning embedded-cluster systems and discuss the implications for understanding their formation and subsequent evolution to produce bound stellar clusters.

  10. ASSESSMENT OF STELLAR STRATIFICATION IN THREE YOUNG STAR CLUSTERS IN THE LARGE MAGELLANIC CLOUD

    SciTech Connect

    Gouliermis, Dimitrios A.; Rochau, Boyke; Mackey, Dougal; Xin Yu E-mail: rochau@mpia-hd.mpg.d E-mail: yxin@astro.uni-bonn.d

    2010-01-20

    We present a comprehensive study of stellar stratification in young star clusters in the Large Magellanic Cloud (LMC). We apply our recently developed effective radius method for the assessment of stellar stratification on imaging data obtained with the Advanced Camera for Surveys of three young LMC clusters to characterize the phenomenon and develop a comparative scheme for its assessment in such clusters. The clusters of our sample, NGC 1983, NGC 2002, and NGC 2010, are selected on the basis of their youthfulness, and their variety in appearance, structure, stellar content, and surrounding stellar ambient. Our photometry is complete for magnitudes down to m{sub 814} approx = 23 mag, allowing the calculation of the structural parameters of the clusters, the estimation of their ages, and the determination of their stellar content. Our study shows that each cluster in our sample demonstrates stellar stratification in a quite different manner and at different degree from the others. Specifically, NGC 1983 shows partial segregation, with the effective radius increasing with fainter magnitudes only for the faintest stars of the cluster. Our method on NGC 2002 provides evidence of strong stellar stratification for both bright and faint stars; the cluster demonstrates the phenomenon with the highest degree in the sample. Finally, NGC 2010 is not segregated, as its bright stellar content is not centrally concentrated, the relation of effective radius to magnitude for stars of intermediate brightness is rather flat, and we find no evidence of stratification for its faintest stars. For the parameterization of the phenomenon of stellar stratification and its quantitative comparison among these clusters, we propose the slope derived from the change in the effective radius over the corresponding magnitude range as indicative parameter of the degree of stratification in the clusters. A positive value of this slope indicates mass segregation in the cluster, while a negative or

  11. X-ray Emission from the Star Clusters Near the Galactic Center

    NASA Astrophysics Data System (ADS)

    Yusef-Zadeh, F.; Law, C.; Fruscione, A.

    2001-09-01

    The detection of two thermal X-ray sources from an extraordinarily compact massive star cluster, the Arches cluster (G0.12-0.02), is reported. This cluster is embedded within a bath of diffuse X-ray emission extending beyond the edge of the cluster to at least 90''×60'' (3.6 pc × 2.4 pc). The diffuse emission beyond the boundary of the cluster is discussed in the context of combined shocked stellar winds escaping from the cluster. The presence of such a high velocity wind flow has implications for other dense systems of mass-losing hot stars such as the IRS 16 at the Galactic center. IRS 16 consists of a number of hot mass-losing stars which could produce an X-ray emitting high cluster wind flow with a velocity of ≈1000 km s-1 as predicted by Canto et al. and detected in the Arches cluster. The interaction of such a hot cluster wind flow with Sgr A* may affect the mass accretion rate. We also present the distribution of the 6.4 keV emission from the Arches cluster as well as discuss the relationship between the X-ray filaments at the edge of the nonthermal radio filaments of the Arc.

  12. The luminosity function of star clusters in 20 star-forming galaxies based on Hubble legacy archive photometry

    SciTech Connect

    Whitmore, Bradley C.; Bowers, Ariel S.; Lindsay, Kevin; Ansari, Asna; Evans, Jessica; Chandar, Rupali; Larsen, Soeren

    2014-04-01

    Luminosity functions (LFs) have been determined for star cluster populations in 20 nearby (4-30 Mpc), star-forming galaxies based on Advanced Camera for Surveys source lists generated by the Hubble Legacy Archive (HLA). These cluster catalogs provide one of the largest sets of uniform, automatically generated cluster candidates available in the literature at present. Comparisons are made with other recently generated cluster catalogs demonstrating that the HLA-generated catalogs are of similar quality, but in general do not go as deep. A typical cluster LF can be approximated by a power law, dN/dL∝L {sup α}, with an average value for α of –2.37 and rms scatter = 0.18 when using the F814W ('I') band. A comparison of fitting results based on methods that use binned and unbinned data shows good agreement, although there may be a systematic tendency for the unbinned (maximum likelihood) method to give slightly more negative values of α for galaxies with steeper LFs. We find that galaxies with high rates of star formation (or equivalently, with the brightest or largest numbers of clusters) have a slight tendency to have shallower values of α. In particular, the Antennae galaxy (NGC 4038/39), a merging system with a relatively high star formation rate (SFR), has the second flattest LF in the sample. A tentative correlation may also be present between Hubble type and values of α, in the sense that later type galaxies (i.e., Sd and Sm) appear to have flatter LFs. Hence, while there do appear to be some weak correlations, the relative similarity in the values of α for a large number of star-forming galaxies suggests that, to first order, the LFs are fairly universal. We examine the bright end of the LFs and find evidence for a downturn, although it only pertains to about 1% of the clusters. Our uniform database results in a small scatter (≈0.4 to 0.5 mag) in the correlation between the magnitude of the brightest cluster (M {sub brightest}) and log of the number

  13. Triaxial orbit-based modelling of the Milky Way Nuclear Star Cluster

    NASA Astrophysics Data System (ADS)

    Feldmeier-Krause, A.; Zhu, L.; Neumayer, N.; van de Ven, G.; de Zeeuw, P. T.; Schödel, R.

    2016-12-01

    We construct triaxial dynamical models for the Milky Way nuclear star cluster using Schwarzschild's orbit superposition technique. We fit the stellar kinematic maps presented in Feldmeier et al. (2014). The models are used to constrain the supermassive black hole mass M•, dynamical mass-to-light ratio Υ, and the intrinsic shape of the cluster. Our best-fitting model has M• = (3.0^{+1.1}_{-1.3}) × 106 M⊙, Υ = (0.90^{+0.76}_{-0.08}) M⊙/L⊙, 4.5μm, and a compression of the cluster along the line-of-sight. Our results are in agreement with the direct measurement of the supermassive black hole mass using the motion of stars on Keplerian orbits. The mass-to-light ratio is consistent with stellar population studies of other galaxies in the mid-infrared. It is possible that we underestimate M• and overestimate the cluster's triaxiality due to observational effects. The spatially semi-resolved kinematic data and extinction within the nuclear star cluster bias the observations to the near side of the cluster, and may appear as a compression of the nuclear star cluster along the line-of-sight. We derive a total dynamical mass for the Milky Way nuclear star cluster of MMWNSC = (2.1±0.7) × 107 M⊙ within a sphere with radius r = 2 × reff = 8.4 pc. The best-fitting model is tangentially anisotropic in the central r = 0.5-2 pc of the nuclear star cluster, but close to isotropic at larger radii. Our triaxial models are able to recover complex kinematic substructures in the velocity map.

  14. Reassessing the formation of the inner Oort cloud in an embedded star cluster

    NASA Astrophysics Data System (ADS)

    Brasser, R.; Duncan, M. J.; Levison, H. F.; Schwamb, M. E.; Brown, M. E.

    2012-01-01

    We re-examine the formation of the inner Oort comet cloud while the Sun was in its birth cluster with the aid of numerical simulations. This work is a continuation of an earlier study (Brasser, R., Duncan, M.J., Levison, H.F. [2006]. Icarus 184, 59-82) with several substantial modifications. First, the system consisting of stars, planets and comets is treated self-consistently in our N-body simulations, rather than approximating the stellar encounters with the outer Solar System as hyperbolic fly-bys. Second, we have included the expulsion of the cluster gas, a feature that was absent previously. Third, we have used several models for the initial conditions and density profile of the cluster - either a Hernquist or Plummer potential - and chose other parameters based on the latest observations of embedded clusters from the literature. These other parameters result in the stars being on radial orbits and the cluster collapses. Similar to previous studies, in our simulations the inner Oort cloud is formed from comets being scattered by Jupiter and Saturn and having their pericentres decoupled from the planets by perturbations from the cluster gas and other stars. We find that all inner Oort clouds formed in these clusters have an inner edge ranging from 100 AU to a few hundred AU, and an outer edge at over 100,000 AU, with little variation in these values for all clusters. All inner Oort clouds formed are consistent with the existence of (90377) Sedna, an inner Oort cloud dwarf planetoid, at the inner edge of the cloud: Sedna tends to be at the innermost 2% for Plummer models, while it is 5% for Hernquist models. We emphasise that the existence of Sedna is a generic outcome. We define a 'concentration radius' for the inner Oort cloud and find that its value increases with increasing number of stars in the cluster, ranging from 600 AU to 1500 AU for Hernquist clusters and from 1500 AU to 4000 AU for Plummer clusters. The increasing trend implies that small star

  15. The star-forming history of the young cluster NGC 2264

    NASA Technical Reports Server (NTRS)

    Adams, M. T.; Strom, K. M.; Strom, S. E.

    1983-01-01

    UBVRI H-alpha photographic photometry was obtained for a sample of low-mass stars in the young open cluster NGC 2264 in order to investigate the star-forming history of this region. A theoretical H-R diagram was constructed for the sample of probable cluster members. Isochrones and evolutionary tracks were adopted from Cohen and Kuhi (1979). Evidence for a significant age spread in the cluster was found amounting to over ten million yr. In addition, the derived star formation rate as a function of stellar mass suggests that the principal star-forming mass range in NGC 2264 has proceeded sequentially in time from the lowest to the highest masses. The low-mass cluster stars were the first cluster members to form in significant numbers, although their present birth rate is much lower now than it was about ten million yr ago. The star-formation rate has risen to a peak at successively higher masses and then declined.

  16. Accretion-driven star formation in central dominant galaxies in X-ray clusters

    NASA Astrophysics Data System (ADS)

    Sarazin, C. L.; Oconnell, R. W.

    1983-05-01

    Analytical and observational evidence for the formation of low-mass stars in the gas accreting in the central dominant galaxies in clusters is presented. Observations of the (U-V) and (K-V) color gradients in accreting galaxies are suggested to reveal colors altered by the appearance of young stars, e.g., the excess blue and the A star spectrum detected in NGC 1275. Low-temperature X ray line emissions from accreting galaxies have been partially surveyed with the result that 10 pct of the brightest cluster galaxies in a magnitude-limited sample show evidence of significant accretion. Photometric data from the quasar 3C 48, located in a galaxy with a very blue population, also suggests low-mass star formation, especially when compared to measurements of NGC 1275, which has the highest accretion rate among observed central dominant cluster galaxies. The quasar, however, would not be accreting interstellar gas.

  17. RR Lyrae stars and color-magnitude diagram of the globular cluster NGC 6388

    NASA Technical Reports Server (NTRS)

    Silbermann, N. A.; Smith, Horace A.; Bolte, Michael; Hazen, Martha L.

    1994-01-01

    We present new V, B-V, and V, V-R color-magnitude diagrams for the bulge globular cluster NGC 6388. These diagrams indicate that NGC 6388 is a metal-rich globular cluster with color-magnitude morphology similar to that of 47 Tucanae. We have conducted a search for new variable stars close to NGC 6388, finding three new RR Lyrae stars. The membership of these and previously discovered RR Lyrae stars near NGC 6388 is discussed. There is reason for believing that some of these variables are nonmembers. Others, however, may belong to the cluster and may be similar to the RR Lyrae star V9 in 47 Tuc.

  18. The location, clustering, and propagation of massive star formation in giant molecular clouds

    NASA Astrophysics Data System (ADS)

    Ochsendorf, Bram; Meixner, Margaret; Chastenet, Jeremy; Tielens, A. G. G. M.; Roman-Duval, Julia

    2017-01-01

    Massive stars are key players in the evolution of galaxies, yet their formation pathway remains unclear. In this talk, I will highlight results from a project utilizing data from several galaxy-wide surveys to build an unbiased dataset of ~700 massive young stellar objects (MYSOs), ~200 giant molecular clouds (GMCs), and ~100 young (< 10 Myr) optical stellar clusters (SCs) in the Large Magellanic Cloud. We have employed this data to quantitatively study the location and clustering of massive star formation and its relation to the internal structure of GMCs. The main results are as follows: (1) Massive stars do not typically form at the highest column densities nor centers of their parent GMCs. (2) Massive star formation clusters over multiple generations and on size scales much smaller than the size of the parent GMC. (3) The rate of massive star formation is significantly boosted in clouds near SCs. Yet, comparison of molecular clouds associated with SCs with those that are not reveals no significant difference in their global properties. These results reveal a connection between different generations of massive stars on timescales up to 10 Myr. I will compare our findings with Galactic studies and discuss this in terms of GMC collapse, triggered star formation, and a potential dichotomy between low- and high-mass star formation.

  19. The Location, Clustering, and Propagation of Massive Star Formation in Giant Molecular Clouds

    NASA Astrophysics Data System (ADS)

    Ochsendorf, Bram B.; Meixner, Margaret; Chastenet, Jérémy; Tielens, Alexander G. G. M.; Roman-Duval, Julia

    2016-11-01

    Massive stars are key players in the evolution of galaxies, yet their formation pathway remains unclear. In this work, we use data from several galaxy-wide surveys to build an unbiased data set of ∼600 massive young stellar objects, ∼200 giant molecular clouds (GMCs), and ∼100 young (<10 Myr) optical stellar clusters (SCs) in the Large Magellanic Cloud. We employ this data to quantitatively study the location and clustering of massive star formation and its relation to the internal structure of GMCs. We reveal that massive stars do not typically form at the highest column densities nor centers of their parent GMCs at the ∼6 pc resolution of our observations. Massive star formation clusters over multiple generations and on size scales much smaller than the size of the parent GMC. We find that massive star formation is significantly boosted in clouds near SCs. However, whether a cloud is associated with an SC does not depend on either the cloud’s mass or global surface density. These results reveal a connection between different generations of massive stars on timescales up to 10 Myr. We compare our work with Galactic studies and discuss our findings in terms of GMC collapse, triggered star formation, and a potential dichotomy between low- and high-mass star formation.

  20. INTERMEDIATE-AGE CLUSTERS IN A FIELD CONTAINING M31 AND M32 STARS

    SciTech Connect

    Rudenko, Pavlo; Worthey, Guy; Mateo, Mario E-mail: gworthey@wsu.edu

    2009-12-15

    Hubble Space Telescope/Advanced Camera for Surveys fields toward M31 and M32 were examined for the presence of possible star clusters. On the basis of stellar photometry, two intermediate-age clusters were found in the field that contains both M31 and M32 stars. One is approximately 200 Myr of age with a mass {approx}400 M {sub sun}, and the other is 1 Gyr old with mass {approx}8 x 10{sup 4} M {sub sun}. Several other cluster candidates are identified, but their stellar populations are more similar to the field: old and slightly metal-poor.

  1. FORMATION AND EVOLUTION OF NUCLEAR STAR CLUSTERS WITH IN SITU STAR FORMATION: NUCLEAR CORES AND AGE SEGREGATION

    SciTech Connect

    Aharon, Danor; Perets, Hagai B.

    2015-02-01

    Nuclear stellar cluster (NSCs) are known to exist around massive black holes (MBHs) in galactic nuclei. Two formation scenarios were suggested for their origin: (1) buildup of NSCs from consecutive infall of stellar clusters and (2) continuous in situ star formation. Though the cluster infall scenario has been extensively studied, the in situ formation scenario has been hardly explored. Here we use Fokker-Planck (FP) calculations to study the effects of star formation on the buildup of NSCs and its implications for their long-term evolution and their resulting structure. We use the FP equation to describe the evolution of stellar populations and add appropriate source terms to account for the effects of newly formed stars. We show that continuous star formation even 1-2 pc away from the MBH can lead to the buildup of an NSC with properties similar to those of the Milky Way NSC. We find that the structure of the old stellar population in the NSC with in situ star formation could be very similar to the steady-state Bahcall-Wolf cuspy structure. However, its younger populations do not yet achieve a steady state. In particular, formed/evolved NSCs with in situ star formation contain differential age-segregated stellar populations that are not yet fully mixed. Younger stellar populations formed in the outer regions of the NSC have a cuspy structure toward the NSC outskirts, while showing a core-like distribution inward, with younger populations having larger core sizes. In principal, such a structure can give rise to an apparent core-like radial distribution of younger stars, as observed in the Galactic center.

  2. A runaway collision in a young star cluster as the origin of the brightest supernova.

    PubMed

    Portegies Zwart, Simon F; van den Heuvel, Edward P J

    2007-11-15

    Supernova SN 2006gy in the galaxy NGC 1260 is the most luminous recorded. Its progenitor might have been a very massive (>100 Mo, where is the mass of the Sun) star, but that interpretation is incompatible with hydrogen in the spectrum of the supernova; stars >40 Moare believed to have shed their hydrogen envelopes several hundred thousand years before the explosion. Alternatively, the progenitor might have arisen from the merger of two massive stars. Here we show that the collision frequency of massive stars in a dense and young cluster (of the kind to be expected near the centre of a galaxy) is sufficient to provide a reasonable chance that SN 2006gy resulted from such a bombardment. If this is the correct explanation, then we predict that when the supernova fades (in a year or so) a dense cluster of massive stars will become visible at the site of the explosion.

  3. The rarity of star formation in brightest cluster galaxies as measured by WISE

    NASA Astrophysics Data System (ADS)

    Fraser-McKelvie, Amelia; Brown, Michael J. I.; Pimbblet, Kevin A.

    2014-10-01

    We present the mid-infrared star formation rates of 245 X-ray selected, nearby (z < 0.1) brightest cluster galaxies (BCGs). A homogeneous and volume limited sample of BCGs was created by X-ray selecting clusters with Lx > 1 × 1044 erg s- 1. The Wide-Field Infrared Survey Explorer (WISE) All WISE Data Release provides the first measurement of the 12 μm star formation indicator for all BCGs in the nearby Universe. Perseus A and Cygnus A are the only galaxies in our sample to have star formation rates of > 40 M⊙ yr- 1, indicating that these two galaxies are highly unusual at current times. Stellar populations of 99 ± 0.6 per cent of local BCGs are (approximately) passively evolving, with star formation rates of < 10 M⊙ yr- 1. We find that in general, star formation produces only modest BCG growth at the current epoch.

  4. INTER- AND INTRA-CLUSTER AGE GRADIENTS IN MASSIVE STAR FORMING REGIONS AND INDIVIDUAL NEARBY STELLAR CLUSTERS REVEALED BY MYStIX

    NASA Astrophysics Data System (ADS)

    Getman, Konstantin V.; Feigelson, Eric; Kuhn, Michael A.; Broos, Patrick S; Townsley, Leisa K.; Naylor, Tim; Povich, Matthew S.; Luhman, Kevin; Garmire, Gordon

    2014-08-01

    The MYStIX (Massive Young Star-Forming Complex Study in Infrared and X-ray) project seeks to characterize 20 OB-dominated young star forming regions (SFRs) at distances <4 kpc using photometric catalogs from the Chandra X-ray Observatory, Spitzer Space Telescope, UKIRT and 2MASS surveys. As part of the MYStIX project, we developed a new stellar chronometer that employs near-infrared and X-ray photometry data, AgeJX. Computing AgeJX averaged over MYStIX (sub)clusters reveals previously unknown age gradients across most of the MYStIX regions as well as within some individual rich clusters. Within the SFRs, the inferred AgeJX ages are youngest in obscured locations in molecular clouds, intermediate in revealed stellar clusters, and oldest in distributed stellar populations. Noticeable intra-cluster gradients are seen in the NGC 2024 (Flame Nebula) star cluster and the Orion Nebula Cluster (ONC): stars in cluster cores appear younger and thus were formed later than stars in cluster halos. The latter result has two important implications for the formation of young stellar clusters. Clusters likely form slowly: they do not arise from a single nearly-instantaneous burst of star formation. The simple models where clusters form inside-out are likely incorrect, and more complex models are needed. We provide several star formation scenarios that alone or in combination may lead to the observed core-halo age gradients.

  5. A Multi-Wavelength View of the Environments of Extreme Clustered Star Formation

    NASA Astrophysics Data System (ADS)

    De Buizer, James M.

    2017-01-01

    It is believed that the vast majority of, if not all, stars form within OB clusters. Most theories of star formation assume a star forms in isolation and ignore the fact that the cluster environment and, especially, the presence of extremely energetic and high mass young stellar objects nearby, may have a profound impact on the formation process of a typical cluster member. Giant HII (GHII) regions are Galactic analogs to starburst regions seen in external galaxies, hosting the most active areas of clustered star formation. As such, GHII regions represent a population of objects that can reveal a wealth of information on the environment of the earliest stages of clustered star formation and how it is affected by feedback from the most massive cluster members. This study employs new mid-infrared imaging data obtained from the airborne observatory, SOFIA, as well as archival imaging data from the near-infrared to cm radio wavelengths to create a rich multi-wavelength dataset of a dozen galactic GHII regions. These data allow quantification of the detailed physical conditions within GHII regions individually and as a population on both global and small scales.

  6. Global survey of star clusters in the Milky Way. IV. 63 new open clusters detected by proper motions

    NASA Astrophysics Data System (ADS)

    Scholz, R.-D.; Kharchenko, N. V.; Piskunov, A. E.; Röser, S.; Schilbach, E.

    2015-09-01

    Context. The global Milky Way Star Clusters (MWSC) survey provided new cluster membership lists and mean cluster parameters for nearly 80% of all previously known Galactic clusters. The MWSC data reduction pipeline involved the catalogue of positions and proper motions (PPMXL) on the International Celestial Reference System (ICRS) and near-infrared photometry from the Two Micron All Sky Survey (2MASS). Aims: In the first extension to the MWSC, photometric filters were applied to the 2MASS catalogue to find new cluster candidates that were subsequently confirmed or rejected by the MWSC pipeline. To further extend the MWSC census, particularly of nearby clusters, we aimed at discovering new clusters by conducting an almost global search in proper motion catalogues as a starting point. Methods: We first selected high-quality samples from the PPMXL and the Fourth US Naval Observatory CCD Astrograph Catalog (UCAC4) for comparison and verification of the proper motions. For 441 circular proper motion bins (radius 15 mas/yr) within ±50 mas/yr, the sky outside a thin Galactic plane zone (| b | < 5°) was binned in small areas ("sky pixels") of 0.25 × 0.25 deg2. Sky pixels with enhanced numbers of stars with a certain common proper motion in both catalogues were considered as cluster candidates. After visual inspection of the sky images, we built an automated procedure that combined these representations of the sky for neighbouring proper motion subsamples after a background correction. The 692 compact cluster candidates detected above a threshold that was equivalent to a minimum of 12 to 130 cluster stars in dependence on the Galactic latitude were then cross-checked with known star clusters and clusters of galaxies. New candidates served as input for the MWSC pipeline. Results: About half of our candidates overlapped with known clusters (46 globular and 68 open clusters in the Galaxy, about 150 known clusters of galaxies) or the Magellanic Clouds. About 10% of our

  7. A Complete Sample of Hot Post-AGB Stars in Globular Clusters

    NASA Technical Reports Server (NTRS)

    Landsman, W.; Moehler, S.; Napiwotzki, R.; Heber, U.; Sweigart, A.; Catelan, M.; Stecher, T.

    1999-01-01

    Ultraviolet images of globular clusters are often dominated by one or two "UV-bright" stars. The most luminous of these are believed to be post-AGB stars, which go through a luminous UV-bright phase as they leave the AGB and move rapidly across the HR diagram toward their final white dwarf state. During the two flights of the ASTRO observatory in 1990 and 1995, the Ultraviolet Imaging Telescope (UIT, Stecher 1997, PASP, 109, 584) was used to obtained ultraviolet (1600 A) images of 14 globular clusters. These images provide a complete census of hot (> 8000 K) post-AGB stars in the observed globular clusters, because the 40' field of view of UIT is large enough to image the entire population of most Galactic globulars, and because the dominant cool star population is suppressed in ultraviolet images, allowing UV-bright stars to be detected into the cluster core. We have begun a program of optical and STIS ultraviolet spectroscopy to determine the fundamental stellar parameters (\\log L, T_eff, \\log g) of all the hot post-AGB candidates discovered on the UIT images. Among the goals of our program are to test theoretical post-AGB lifetimes across the HR diagram, and to estimate the mass of the currently forming white dwarfs in globular clusters. Two trends are already apparent in our survey. First, the UV-selected sample has removed a bias against the detection of the hottest post-AGB stars, and resulted in the discovery of five cluster post-AGB stars with Teff > 50,000 K. Second, most of the new discoveries have been lower luminosity (2.5 $<$\\log L $<$ 3.0) than expected for stars which leave the AGB during the thermally pulsating phase.

  8. Star Formation in the Cluster Merger DLSCL J0916.2+2953

    NASA Astrophysics Data System (ADS)

    Mansheim, A. S.; Lemaux, B. C.; Dawson, W. A.; Lubin, L. M.; Wittman, D.; Schmidt, S.

    2017-01-01

    We investigate star formation in DLSCL J0916.2+2953, a dissociative merger of two clusters at z = 0.53 that has progressed {1.1}-0.4+1.3 Gyr since the first pass-through. We attempt to reveal the effects a collision may have had on the evolution of the cluster galaxies by tracing their star formation history. We probe current and recent activity to identify a possible star formation event at the time of the merger, using EW({{H}}δ ), EW([{{O}} {{II}}]), and {D}n(4000) measured from the composite spectra of 64 cluster and 153 coeval field galaxies. We supplement Keck DEep Imaging Multi-Object Spectrograph spectra with DLS and Hubble Space Telescope imaging, to determine the color, stellar mass, and morphology of each galaxy. We also conduct a comprehensive study of the populations in this complex structure. Spectral results indicate the average cluster and cluster red sequence galaxies experienced no enhanced star formation relative to the surrounding field during the merger, ruling out a predominantly merger-quenched population. We find that the average blue galaxy in the North cluster is currently active, and that the South cluster is currently post-starburst, having undergone a recent star formation event. Although the North activity could be latent or long-term merger effects, a young blue stellar population and irregular geometry suggest the cluster was still forming prior the collision. Even though the South activity coincides with the time of the merger, the blue early-type population could be a result of secular cluster processes. The evidence suggests that the dearth or surfeit of activity is indiscernible from normal cluster galaxy evolution.

  9. Photometric binary stars in Praesepe and the search for globular cluster binaries

    NASA Technical Reports Server (NTRS)

    Bolte, Michael

    1991-01-01

    A radial velocity study of the stars which are located on a second sequence above the single-star zero-age main sequence at a given color in the color-magnitude diagram of the open cluster Praesepe, (NGC 2632) shows that 10, and possibly 11, of 17 are binary systems. Of the binary systems, five have full amplitudes for their velocity variations that are greater than 50 km/s. To the extent that they can be applied to globular clusters, these results suggests that (1) observations of 'second-sequence' stars in globular clusters would be an efficient way of finding main-sequence binary systems in globulars, and (2) current instrumentation on large telescopes is sufficient for establishing unambiguously the existence of main-sequence binary systems in nearby globular clusters.

  10. HUBBLE UNCOVERS MYSTERY OBJECTS IN THE DENSE CORE OF A NEARBY STAR CLUSTER

    NASA Technical Reports Server (NTRS)

    2002-01-01

    Piercing the heart of a glittering swarm of stars, NASA's sharp-eyed Hubble Space Telescope unveils the central region of the globular cluster M22, a 12- to 14-billion-year-old grouping of stars in the constellation Sagittarius. The telescope's view of the cluster's core measures 3.3 light-years across. The stars near the cluster's core are 100,000 times more numerous than those in the Sun's neighborhood. Buried in the glow of starlight are about six 'mystery objects,' which astronomers estimate are no larger than one quarter the mass of the giant planet Jupiter, the solar system's heftiest planet. The mystery objects are too far and dim for Hubble to see directly. Instead, the orbiting observatory detected these unseen celestial bodies by looking for their gravitational effects on the light from far distant stars. In this case, the stars are far beyond the cluster in the galactic bulge, about 30,000 light-years from Earth at the center of the Milky Way Galaxy. M22 is 8,500 light-years away. The invisible objects betrayed their presence by bending the starlight gravitationally and amplifying it, a phenomenon known as microlensing. From February 22 to June 15, 1999, Hubble's Wide Field and Planetary Camera 2 looked through this central region and monitored 83,000 stars. During that time the orbiting observatory recorded six unexpectedly brief microlensing events. In each case a background star jumped in brightness for less than 20 hours before dropping back to normal. These transitory spikes in brightness mean that the object passing in front of the star must have been much smaller than a normal star. Hubble also detected one clear microlensing event. In that observation a star appeared about 10 times brighter over an 18-day span before returning to normal. Astronomers traced the leap in brightness to a dwarf star in the cluster floating in front of the background star. The inset photo shows the entire globular cluster of about 10 million stars. M22 is about 60

  11. THE INFLUENCE OF ORBITAL ECCENTRICITY ON TIDAL RADII OF STAR CLUSTERS

    SciTech Connect

    Webb, Jeremy J.; Harris, William E.; Sills, Alison; Hurley, Jarrod R.

    2013-02-20

    We have performed N-body simulations of star clusters orbiting in a spherically symmetric smooth galactic potential. The model clusters cover a range of initial half-mass radii and orbital eccentricities in order to test the historical assumption that the tidal radius of a cluster is imposed at perigalacticon. The traditional assumption for globular clusters is that since the internal relaxation time is larger than its orbital period, the cluster is tidally stripped at perigalacticon. Instead, our simulations show that a cluster with an eccentric orbit does not need to fully relax in order to expand. After a perigalactic pass, a cluster recaptures previously unbound stars, and the tidal shock at perigalacticon has the effect of energizing inner region stars to larger orbits. Therefore, instead of the limiting radius being imposed at perigalacticon, it more nearly traces the instantaneous tidal radius of the cluster at any point in the orbit. We present a numerical correction factor to theoretical tidal radii calculated at perigalacticon which takes into consideration both the orbital eccentricity and current orbital phase of the cluster.

  12. Physical properties of star clusters in the outer LMC as observed by the DES

    DOE PAGES

    Pieres, A.; Santiago, B.; Balbinot, E.; ...

    2016-05-26

    The Large Magellanic Cloud (LMC) harbors a rich and diverse system of star clusters, whose ages, chemical abundances, and positions provide information about the LMC history of star formation. We use Science Verification imaging data from the Dark Energy Survey to increase the census of known star clusters in the outer LMC and to derive physical parameters for a large sample of such objects using a spatially and photometrically homogeneous data set. Our sample contains 255 visually identified cluster candidates, of which 109 were not listed in any previous catalog. We quantify the crowding effect for the stellar sample producedmore » by the DES Data Management pipeline and conclude that the stellar completeness is < 10% inside typical LMC cluster cores. We therefore develop a pipeline to sample and measure stellar magnitudes and positions around the cluster candidates using DAOPHOT. We also implement a maximum-likelihood method to fit individual density profiles and colour-magnitude diagrams. For 117 (from a total of 255) of the cluster candidates (28 uncatalogued clusters), we obtain reliable ages, metallicities, distance moduli and structural parameters, confirming their nature as physical systems. The distribution of cluster metallicities shows a radial dependence, with no clusters more metal-rich than [Fe/H] ~ -0.7 beyond 8 kpc from the LMC center. Furthermore, the age distribution has two peaks at ≃ 1.2 Gyr and ≃ 2.7 Gyr.« less

  13. Physical properties of star clusters in the outer LMC as observed by the DES

    SciTech Connect

    Pieres, A.; Santiago, B.; Balbinot, E.; Luque, E.; Queiroz, A.; da Costa, L. N.; Maia, M. A. G.; Drlica-Wagner, A.; Roodman, A.; Abbott, T. M. C.; Allam, S.; Benoit-Lévy, A.; Bertin, E.; Brooks, D.; Buckley-Geer, E.; Burke, D. L.; Rosell, A. Carnero; Kind, M. Carrasco; Carretero, J.; Cunha, C. E.; Desai, S.; Diehl, H. T.; Eifler, T. F.; Finley, D. A.; Flaugher, B.; Fosalba, P.; Frieman, J.; Gerdes, D. W.; Gruen, D.; Gruendl, R. A.; Gutierrez, G.; Honscheid, K.; James, D. J.; Kuehn, K.; Kuropatkin, N.; Lahav, O.; Li, T. S.; Marshall, J. L.; Martini, P.; Miller, C. J.; Miquel, R.; Nichol, R. C.; Nord, B.; Ogando, R.; Plazas, A. A.; Romer, A. K.; Sanchez, E.; Scarpine, V.; Schubnell, M.; Sevilla-Noarbe, I.; Smith, R. C.; Soares-Santos, M.; Sobreira, F.; Suchyta, E.; Swanson, M. E. C.; Tarle, G.; Thaler, J.; Thomas, D.; Tucker, D. L.; Walker, A. R.

    2016-05-26

    The Large Magellanic Cloud (LMC) harbors a rich and diverse system of star clusters, whose ages, chemical abundances, and positions provide information about the LMC history of star formation. We use Science Verification imaging data from the Dark Energy Survey to increase the census of known star clusters in the outer LMC and to derive physical parameters for a large sample of such objects using a spatially and photometrically homogeneous data set. Our sample contains 255 visually identified cluster candidates, of which 109 were not listed in any previous catalog. We quantify the crowding effect for the stellar sample produced by the DES Data Management pipeline and conclude that the stellar completeness is < 10% inside typical LMC cluster cores. We therefore develop a pipeline to sample and measure stellar magnitudes and positions around the cluster candidates using DAOPHOT. We also implement a maximum-likelihood method to fit individual density profiles and colour-magnitude diagrams. For 117 (from a total of 255) of the cluster candidates (28 uncatalogued clusters), we obtain reliable ages, metallicities, distance moduli and structural parameters, confirming their nature as physical systems. The distribution of cluster metallicities shows a radial dependence, with no clusters more metal-rich than [Fe/H] ~ -0.7 beyond 8 kpc from the LMC center. Furthermore, the age distribution has two peaks at ≃ 1.2 Gyr and ≃ 2.7 Gyr.

  14. HST Snapshot Study of Variable Stars in Globular Clusters: Inner Region of NGC 6441

    NASA Technical Reports Server (NTRS)

    Pritzl, Barton J.; Smith, Horace A.; Stetson, Peter B.; Catelan, Marcio; Sweigart, Allen V.; Layden, Andrew C.; Rich, R. Michael

    2003-01-01

    We present the results of a Hubble Space Telescope snapshot program to survey the inner region of the metal-rich globular cluster NGC 6441 for its variable stars. A total of 57 variable stars was found including 38 RR Lyrae stars, 6 Population II Cepheids, and 12 long period variables. Twenty-four of the RR Lyrae stars and all of the Population II Cepheids were previously undiscovered in ground-based surveys. Of the RR Lyrae stars observed in h s survey, 26 are pulsating in the fundamental mode with a mean period of 0.753 d and 12 are first-overtone mode pulsators with a mean period of 0.365 d. These values match up very well with those found in ground-based surveys. Combining all the available data for NGC 6441, we find mean periods of 0.759 d and 0.375 d for the RRab and RRc stars, respectively. We also find that the RR Lyrae in this survey are located in the same regions of a period-amplitude diagram as those found in ground-based surveys. The overall ratio of RRc to total RR Lyrae is 0.33. Although NGC 6441 is a metal-rich globular cluster and would, on that ground, be expected either to have few RR Lyrae stars, or to be an Oosterhoff type I system, its RR Lyrae more closely resemble those in Oosterhoff type II globular clusters. However, even compared to typical Oosterhoff type II systems, the mean period of its RRab stars is unusually long. We also derived I-band period-luminosity relations for the RR Lyrae stars. Of the six Population II Cepheids, five are of W Virginis type and one is a BL Herculis variable star. This makes NGC 6441, along with NGC 6388, the most metal-rich globular cluster known to contain these types of variable stars. Another variable, V118, may also be a Population II Cepheid given its long period and its separation in magnitude from the RR Lyrae stars. We examine the period-luminosity relation for these Population II Cepheids and compare it to those in other globular clusters and in the Large Magellanic Cloud. We argue that there does

  15. Clustering of Pre-Main-Sequence Stars in the Orion, Ophiuchus, Chamaeleon, Vela, and Lupus Star-forming Regions

    NASA Astrophysics Data System (ADS)

    Nakajima, Yasushi; Tachihara, Kengo; Hanawa, Tomoyuki; Nakano, Makoto

    1998-04-01

    We study clustering of pre-main-sequence stars in the Orion, Ophiuchus, Chamaeleon, Vela, and Lupus star-forming regions. We calculate the average surface density of companions, Σ(θ), as a function of angular distance, θ, from each star. We employ the method developed by Larson in a 1995 study for the calculation. In most of the regions studied, the function can be fitted by two power laws (Σ ~ θγ) with a break as found by Larson for the Taurus star-forming region. The power index, γ, is smaller at small separations than at large separations. The power index at large separations shows significant variation from region to region (-0.8 < γ < -0.1), while the power index at small separations does not (γ ~ -2). The power index at large separations relates to the distribution of the nearest-neighbor distance. When the latter can be fitted by the Poisson distribution, the power index is close to 0. When the latter is broader than the Poisson distribution, the power index is negatively large. This correlation can be interpreted as the result of the variation in the surface density within the region. At large separations, the power-law fit may indicate star formation history in the region and not the spatial structure like the self-similar hierarchical, or fractal, one. Because of the velocity dispersion, stars move from their birthplaces, and the surface density of coeval stars decreases with their age. When a star-forming region contains several groups of stars with different ages, a power law may fit the average surface density of companions for it. The break of the power law is located around 0.01-0.1 pc. There is a clear correlation between the break position and the mean nearest-neighbor distance. The break position may reflect dispersal of newly formed stars.

  16. Clustered star formation as a natural explanation for the Halpha cut-off in disk galaxies.

    PubMed

    Pflamm-Altenburg, Jan; Kroupa, Pavel

    2008-10-02

    The rate of star formation in a galaxy is often determined by the observation of emission in the Halpha line, which is related to the presence of short-lived massive stars. Disk galaxies show a strong cut-off in Halpha radiation at a certain galactocentric distance, which has led to the conclusion that star formation is suppressed in the outer regions of disk galaxies. This is seemingly in contradiction to recent observations in the ultraviolet which imply that disk galaxies have star formation beyond the Halpha cut-off, and that the star-formation-rate surface density is linearly related to the underlying gas surface density, which is a shallower relationship than that derived from Halpha luminosities. In a galaxy-wide formulation, the clustered nature of star formation has recently led to the insight that the total galactic Halpha luminosity is nonlinearly related to the galaxy-wide star formation rate. Here we show that a local formulation of the concept of clustered star formation naturally leads to a steeper radial decrease in the Halpha surface luminosity than in the star-formation-rate surface density, in quantitative agreement with the observations, and that the observed Halpha cut-off arises naturally.

  17. NEARBY MASSIVE STAR CLUSTER YIELDS INSIGHTS INTO EARLY UNIVERSE

    NASA Technical Reports Server (NTRS)

    2002-01-01

    A NASA Hubble Space Telescope 'family portrait' of young, ultra-bright stars nested in their embryonic cloud of glowing gases. The celestial maternity ward, called N81, is located 200,000 light-years away in the Small Magellanic Cloud (SMC), a small irregular satellite galaxy of our Milky Way. Hubble's exquisite resolution allows astronomers to pinpoint 50 separate stars tightly packed in the nebula's core within a 10 light-year diameter - slightly more than twice the distance between earth and the nearest star to our sun. The closest pair of stars is only 1/3 of a light-year apart (0.3 arcseconds in the sky). This furious rate of mass loss from these super-hot stars is evident in the Hubble picture that reveals dramatic shapes sculpted in the nebula's wall of glowing gases by violent stellar winds and shock waves. A pair of bright stars in the center of the nebula is pouring out most of the ultraviolet radiation to make the nebula glow. Just above them, a small dark knot is all that's left of the cold cloud of molecular hydrogen and dust the stars were born from. Dark absorption lanes of residual dust trisect the nebula. The nebula offers a unique opportunity for a close-up glimpse at the 'firestorm' accompanying the birth of extremely massive stars, each blazing with the brilliance of 300,000 of our suns. Such galactic fireworks were much more common billions of years ago in the early universe, when most star formation took place. The 'natural-color' view was assembled from separate images taken with the Wide Field and Planetary Camera 2, in ultraviolet light and two narrow emission lines of ionized Hydrogen (H-alpha, H-beta). The picture was taken on September 4, 1997. Credit: Mohammad Heydari-Malayeri (Paris Observatory, France), NASA/ESA

  18. An IUE survey of the Hyades star cluster

    NASA Technical Reports Server (NTRS)

    Zolcinski, M. C.; Kay, L.; Antiochos, S.; Stern, R.; Walker, A. B. C.

    1982-01-01

    To date 11 of the brightest X-Ray stars (F-K dwarfs) in the Hyades have been observed with the IUE satellite with the short wavelength spectrograph. The IUE results and the X-Ray observations from the Hyades survey with the Einstein Observatory were combined. The differential emission measure function was estimated for each of the 7 stars which showed evidence of emission lines. Constraints on stellar atmospheric parameters (chromospheric pressure, coronal temperature and filling factor were derived. The implications of these results in the context of loop models for the corona and transition region (TR) of these stars are discussed.

  19. Herbig Ae/Be Candidate Stars in the Innermost Galactic Disk: Quartet Cluster

    NASA Astrophysics Data System (ADS)

    Yasui, Chikako; Kobayashi, Naoto; Hamano, Satoshi; Kondo, Sohei; Izumi, Natsuko; Saito, Masao; Tokunaga, Alan T.

    2016-02-01

    In order to investigate the Galactic-scale environmental effects on the evolution of protoplanetary disks, we explored the near-infrared (NIR) disk fraction of the Quartet cluster, which is a young cluster in the innermost Galactic disk at the Galactocentric radius {R}g˜ 4 {{kpc}}. Because this cluster has a typical cluster mass of ˜103 {M}⊙ as opposed to very massive clusters, which have been observed in previous studies (>104 {M}⊙ ), we can avoid intra-cluster effects such as strong UV field from OB stars. Although the age of the Quartet is previously estimated to be 3-8 Myr old, we find that it is most likely ˜3-4.5 Myr old. In moderately deep JHK images from the United Kingdom Infrared Telescope Infrared Deep Sky Survey, we found eight HAeBe candidates in the cluster, and performed K-band medium-resolution (R\\equiv {{Δ }}λ /λ ˜ 800) spectroscopy for three of them with the Subaru 8.2 m telescope. These are found to have both Brγ absorption lines as well as CO bandhead emission, suggesting that they are HAeBe stars with protoplanetary disks. We estimated the intermediate-mass disk fraction (IMDF) to be ˜25% for the cluster, suggesting slightly higher IMDF compared to those for young clusters in the solar neighborhood with similar cluster age, although such a conclusion should await future spectroscopic study of all candidates of cluster members.

  20. STAR CLUSTERS IN M33: UPDATED UBVRI PHOTOMETRY, AGES, METALLICITIES, AND MASSES

    SciTech Connect

    Fan, Zhou; De Grijs, Richard E-mail: grijs@pku.edu.cn

    2014-04-01

    The photometric characterization of M33 star clusters is far from complete. In this paper, we present homogeneous UBVRI photometry of 708 star clusters and cluster candidates in M33 based on archival images from the Local Group Galaxies Survey, which covers 0.8 deg{sup 2} along the galaxy's major axis. Our photometry includes 387, 563, 616, 580, and 478 objects in the UBVRI bands, respectively, of which 276, 405, 430, 457, and 363 do not have previously published UBVRI photometry. Our photometry is consistent with previous measurements (where available) in all filters. We adopted Sloan Digital Sky Survey ugriz photometry for complementary purposes, as well as Two Micron All Sky Survey near-infrared JHK photometry where available. We fitted the spectral-energy distributions of 671 star clusters and candidates to derive their ages, metallicities, and masses based on the updated PARSEC simple stellar populations synthesis models. The results of our χ{sup 2} minimization routines show that only 205 of the 671 clusters (31%) are older than 2 Gyr, which represents a much smaller fraction of the cluster population than that in M31 (56%), suggesting that M33 is dominated by young star clusters (<1 Gyr). We investigate the mass distributions of the star clusters—both open and globular clusters—in M33, M31, the Milky Way, and the Large Magellanic Cloud. Their mean values are log (M {sub cl}/M {sub ☉}) = 4.25, 5.43, 2.72, and 4.18, respectively. The fraction of open to globular clusters is highest in the Milky Way and lowest in M31. Our comparisons of the cluster ages, masses, and metallicities show that our results are basically in agreement with previous studies (where objects in common are available); differences can be traced back to differences in the models adopted, the fitting methods used, and stochastic sampling effects.

  1. NGC346: Looking in the Cradle of a Massive Star Cluster

    NASA Astrophysics Data System (ADS)

    Gouliermis, Dimitrios; Hony, Sacha; Dib, Sami; Galliano, Frederic; Cormier, Diane; Ralf, Klessen

    2015-08-01

    How a star cluster of more than few 10,000 solar masses forms? We present the case of the cluster NGC 346 in the Small Magellanic Cloud, still embedded in its natal star-forming region N66, and we propose a scenario for its formation, based on the rich resolved stellar populations found in the region. Young massive clusters (YMCs) host a significant amount of early-type stars, indicating an extremely high star formation efficiency. The Milky Way galaxy hosts several YMCs that fill the gap between young low-mass open clusters and old massive globular clusters. Only a handful, though, is relatively close to their formation, and the investigation of their gaseous natal environments suffers from contamination by the Galactic disk. YMCs are very abundant in distant starburst and interacting galaxies, but the distance of their hosting galaxies do not also allow a detailed analysis of their formation. The Magellanic Clouds, on the other hand, host YMCs in a wide range of ages with the youngest being still embedded in their giant HII regions. Hubble Space Telescope (HST) imaging of such star-forming complexes provide a complete stellar sampling with a high dynamic range in stellar masses, allowing the detailed study of star formation at scales typical for molecular clouds. The distribution of newly-born stars in N66 shows that star formation in the region proceeds in a clumpy hierarchical fashion, leading to the formation of both a dominant YMC, hosting about half of the observed pre--main-sequence (PMS) stars, and a self-similar dispersed distribution of the remaining PMS population. We investigate the correlation between stellar surface density (and star formation rate derived from star-counts) and molecular gas surface density (derived from dust column density) in an attempt to disentangle the physical conditions that gave birth to NGC 346. We discuss our findings in terms of stellar clustering, its relation to the turbulent interstellar medium, and the observed

  2. The Evolution of Star Formation Activity in Cluster Galaxies Over 0.15 < z < 1.5

    NASA Astrophysics Data System (ADS)

    Wagner, Cory R.

    In this thesis, we explore 7.5 billion years of evolution in cluster galaxy star formation activity using a sample of 11 high-redshift (1 < z < 1.5) clusters from the IRAC Shallow Cluster Survey, and 25 low-redshift (0.15 < z < 1) clusters from The Cluster Lensing And Supernova survey with Hubble. We compare cluster galaxy star formation to that of the field over 0.15 < z < 1.5 using 8000 galaxies from the UltraVISTA survey. Mid-infrared star formation rates are measured using Spitzer 24 mum data for isolated high-redshift galaxies. We calculate rest-frame ultraviolet star formation rates for low-redshift cluster members using Hubble Space Telescope observations. Using publically available mid-infrared and ultraviolet data for our field sample, we empirically derive scaling relations to adjust low-redshift cluster galaxy ultraviolet star formation rates to mid-infrared levels. We classify cluster galaxy morphology by visual inspection, and use quantitatively measured morphologies for field galaxies. Cluster late-type galaxies at z > 1 show enhanced star formation activity relative to the field, and account for nearly 90% of the overall star formation activity in high-redshift clusters. While high-redshift early-type galaxies are substantially quenched relative to cluster late-types, they still contribute 13% of the total cluster star formation activity. With early-type fractions increasing from 34 to 56% from z 1.5 → 1.16, we find that new cluster early-type galaxies are likely being formed around z 1.4. The fraction of early-type galaxies that are star-forming drops from 29 to 11% over this period, yet their specific star formation rates are roughly constant. These factors suggest that the events that created these new galaxies, possibly mergers, were both recent and gas-rich. With typical coverages of 50% of z < 1 cluster virial radii, we can only probe the cores of low-redshift clusters. We find that in this regime, the star formation activity of cluster

  3. Chemically peculiar A/F stars in open clusters of the Milky Way

    NASA Astrophysics Data System (ADS)

    Gebran, M.; Monier, R.

    2010-12-01

    Abundance anomalies have been determined at the surface of many field and open cluster A and F dwarfs. These abundance anomalies are most likely caused by microscopic diffusion at work within the stable envelopes of A stars. However diffusion can be counteracted by several other mixing processes such as convection, rotational mixing and mass loss. We present a short review of the surface abundance patterns of A/F stars in the Pleiades (100 Myr), Coma Berenices (450 Myr) and Hyades (650 Myr) open clusters. Real star-to-star variations of the abundances were found for several chemical elements in the A dwarfs in these clusters. The derived abundances are then compared to evolutionary models from the Montreal group. These comparisons strongly suggest the occurence of hydrodynamical processes at play within the radiative zones of these stars and hindering the effects of microscopic diffusion (mixing processes/mass loss). In the frame of Gaia mission, simulations are presented that predict the number of A stars and open clusters that Gaia will observe in the Galaxy.

  4. Updated census of RR Lyrae stars in the globular cluster ω Centauri (NGC 5139)

    NASA Astrophysics Data System (ADS)

    Navarrete, C.; Contreras Ramos, R.; Catelan, M.; Clement, C. M.; Gran, F.; Alonso-García, J.; Angeloni, R.; Hempel, M.; Dékány, I.; Minniti, D.

    2015-05-01

    Aims: ω Centauri (NGC 5139) contains many variable stars of different types and, in particular, more than one hundred RR Lyrae stars. This enabled gathering a homogeneous sample (in terms of instrument, image quality, and time coverage) of high-quality near-infrared (NIR) RR Lyrae light curves by performing an extensive time-series campaign aimed at this object. We have conducted a variability survey of ω Cen in the NIR, using ESO's 4.1 m Visible and Infrared Survey Telescope for Astronomy (VISTA). This is the first paper of a series describing our results. Methods: ω Cen was observed using VIRCAM mounted on VISTA. A total of 42 epochs in J and 100 epochs in KS were obtained, distributed over a total timespan of 352 days. Point-spread function photometry was performed using DAOPHOT in the inner and DoPhot in the outer regions of the cluster. Periods of the known variable stars were improved when necessary using an ANOVA analysis. Results: We collected an unprecedented homogeneous and complete NIR catalog of RR Lyrae stars in the field of ω Cen, allowing us to study for the first time all the RR Lyrae stars associated with the cluster, except for four stars that are located far away from the cluster center. We derived membership status, subclassifications between RRab and RRc subtypes, periods, amplitudes, and mean magnitudes for all the stars in our sample. Additionally, four new RR Lyrae stars were discovered, two of which are very likely cluster members. We also discuss here the distribution of ω Cen stars in the Bailey (period-amplitude) diagram. We provide reference lines in this plane for both Oosterhoff Type I (OoI) and Oosterhoff Type II (OoII) components in J and KS. Conclusions: We clarify the status of many (candidate) RR Lyrae stars that have been reported as unclear in previous studies. This includes stars with anomalous positions in the color-magnitude diagram, uncertain periods or/and variability types, and possible field interlopers. We conclude

  5. On Iron Enrichment, Star Formation, and Type Ia Supernovae in Galaxy Clusters

    NASA Technical Reports Server (NTRS)

    Loewenstein, Michael

    2006-01-01

    The nature of star formation and Type Ia supernovae (SNIa) in galaxies in the field and in rich galaxy clusters are contrasted by juxtaposing the buildup of heavy metals in the universe inferred from observed star formation and supernovae rate histories with data on the evolution of Fe abundances in the intracluster medium (ICM). Models for the chemical evolution of Fe in these environments are constructed, subject to observational constraints, for this purpose. While models with a mean delay for SNIa of 3 Gyr and standard initial mass function (IMF) are fully consistent with observations in the field, cluster Fe enrichment immediately tracked a rapid, top-heavy phase of star formation - although transport of Fe into the ICM may have been more prolonged and star formation likely continued beyond redshift 1. The means of this prompt enrichment consisted of SNII yielding greater than or equal to 0.1 solar mass per explosion (if the SNIa rate normalization is scaled down from its value in the field according to the relative number of candidate progenitor stars in the 3 - 8 solar mass range) and/or SNIa with short delay times originating during the rapid star formation epoch. Star formation is greater than 3 times more efficient in rich clusters than in the field, mitigating the overcooling problem in numerical cluster simulations. Both the fraction of baryons cycled through stars, and the fraction of the total present-day stellar mass in the form of stellar remnants, are substantially greater in clusters than in the field.

  6. Proper motions and CCD photometry of stars in the region of the open cluster NGC 6866

    NASA Astrophysics Data System (ADS)

    Frolov, V. N.; Ananjevskaja, Yu. K.; Gorshanov, D. L.; Polyakov, E. V.

    2010-05-01

    We present the results of our comprehensive study of the Galactic open star cluster NGC 6866. The positions of stars in the investigated region have been obtained with the “Fantasy” automatic measuring machine from 10 plates of the normal astrograph at the Pulkovo Astronomical Observatory. The size of the investigated field is 40' × 40', the limiting magnitude is B ˜ 16{·/ m }6, and the maximum epoch difference is 79 yr. For 1202 field stars, we have determined the relative proper motions with an rms error of 2.5 mas yr-1. Out of them, 423 stars may be considered cluster members with a probability P > 70% according to the astrometric criterion. Photometric diagrams have been used as an additional criterion. We have performed two-color BV CCD photometry of stars with the Pulkovo ZA-320M mirror astrograph. The U magnitudes from the literature have also been used to construct the two-color diagrams. A total of 267 stars have turned out to be members of NGC 6866 according to the two criteria. We present refined physical parameters of the cluster and its age estimate (5.6 × 108 yr). The cluster membership of red and blue giants, variable, double, and multiple stars is considered. We have found an almost complete coincidence of the positions of one of the stars in the region (a cluster nonmember) and a soft X-ray source in the ROSAT catalog. The “Fantasy” automatic measuring machine is described in the Appendix.

  7. Submillimeter View of Gas and Dust in the Forming Super Star Cluster in NGC 5253

    NASA Astrophysics Data System (ADS)

    Turner, Jean L.

    2015-08-01

    Measuring the molecular gas content of young super star clusters is necessary to assess the efficiency of the birth process. Submillimeter arrays allow the detection of individual giant molecular clouds (GMCs) in young massive clusters in nearby galaxies to constrain star formation efficiency and feedback. We have detected CO(3-2) and dust emission toward the super star cluster and supernebula in NGC 5253 with the Submillimeter Array. The GMC associated with the supernebula, “Cloud D”, is warm (T>200K), dense (log n~4.3) and optically thin in CO(3-2). We cannot get a mass from CO. Instead we estimate the molecular gas mass by subtracting the stellar mass from the gravitational mass of Cloud D; we find a star formation efficiency of over 60%. This cloud is extremely dusty; the gas-to-dust ratio is 50, half to one-third of the Galactic value and a tenth of the ~500-700 value scaled from the metallicity of NGC 5253. We propose that the dust mass is enhanced by mass loss from Wolf-Rayet stars within the cluster, which is consistent with STARBURST99 modeling of the cluster yields. Finally, the CO linewidth is sigma~9 km/s, not much broader than predicted for quiescent Galactic GMCs from the size-linewidth relation. There is little evidence for the effects of the roughly 7000 O stars embedded within Cloud D. We seem to be catching this cluster at a special time, at an age of 3.5 to 4 Myr, before its first supernova but after mass loss has begun from the O stars.

  8. Variable Stars in the 50BiN Open Cluster Survey. I. NGC 2301

    NASA Astrophysics Data System (ADS)

    Wang, Kun; Deng, Licai; Zhang, Xiaobin; Xin, Yu; Yan, Zhengzhou; Tian, Jianfeng; Luo, Yangping; Luo, Changqing; Zhang, Chunguang; Peng, Yingjiang; Pan, Yang; Sun, Jinjiang; Luo, Zhiquan

    2015-11-01

    The current work is the first contribution from the 50 cm Binocular Network, whose primary goal is to systematically detect and characterize variable stars in Galactic open clusters. In this paper, we report the results of a search for variables in the open cluster NGC 2301. Eighteen variable stars including 12 new objects were detected in a 20‧ × 20‧ field around the cluster. The physical properties, classifications, and memberships are discussed using the behaviors of the light curves, the positions on the color-magnitude diagram, and the archival proper-motion data. Among the 12 new objects, 5 are low-amplitude δ Scuti stars, 4 of which are probable members of the cluster. One of them is discovered to be a δ Scuti star in an eclipsing binary system. One γ Doradus candidate is identified as a cluster member, but is apparently located very close to the blue edge of the γ Doradus instability strip and therefore can be used to pin down the blue edge of the instability strip. The remaining five new variables are classified as an EW-type eclipsing binary with an orbital period of 0.5785 days and four unknown type variable stars. In addition, revised basic data for the six known variables are given according to our observations.

  9. Spectroscopic and photometric characteristics of stars in the field of the cluster vdB 130

    NASA Astrophysics Data System (ADS)

    Tatarnikova, A. A.; Tatarnikov, A. M.; Sitnik, T. G.; Egorov, O. V.

    2016-12-01

    The observational data for 24 stars toward the young cluster vdB 130 are analyzed. The spectroscopic and photometric BV RIJHK observations have been carried out with the following telescopes: 6-m at the Special Astrophysical Observatory of the Russian Academy of Sciences, 60-cm at the Southern Station of the Moscow State University, and 2.5-m at the Caucasus Observatory of the Sternberg Astronomical Institute of theMoscow State University. Nine stars previously selected as cluster members have been found to belong to different subtypes of type B. A minimum color excess toward the cluster, E( B - V) = 0.9 mag, has been revealed for the vdB 130 stars lying outside the molecular cloud. Maximum color excesses, E( B - V) = 1.3-1.4 mag, have been found in the spectra of cluster stars 1r and 5r observed in dust blobs. Inside the cluster R v is shown to differ from the standard one. The overwhelming majority of the remaining investigated stars belong to late types and have minor color excesses (≤0.3) typical of close distances.

  10. Simulating radiative feedback and star cluster formation in GMCs - I. Dependence on gravitational boundedness

    NASA Astrophysics Data System (ADS)

    Howard, Corey S.; Pudritz, Ralph E.; Harris, William E.

    2016-09-01

    Radiative feedback is an important consequence of cluster formation in giant molecular clouds (GMCs) in which newly formed clusters heat and ionize their surrounding gas. The process of cluster formation, and the role of radiative feedback, has not been fully explored in different GMC environments. We present a suite of simulations which explore how the initial gravitational boundedness, and radiative feedback, affect cluster formation. We model the early evolution (<5 Myr) of turbulent, 106 M⊙ clouds with virial parameters ranging from 0.5 to 5. To model cluster formation, we use cluster sink particles, coupled to a raytracing scheme, and a custom subgrid model which populates a cluster via sampling an initial mass function (IMF) with an efficiency of 20 per cent per free-fall time. We find that radiative feedback only decreases the cluster particle formation efficiency by a few per cent. The initial virial parameter plays a much stronger role in limiting cluster formation, with a spread of cluster formation efficiencies of 37-71 per cent for the most unbound to the most bound model. The total number of clusters increases while the maximum mass cluster decreases with an increasing initial virial parameter, resulting in steeper mass distributions. The star formation rates in our cluster particles are initially consistent with observations but rise to higher values at late times. This suggests that radiative feedback alone is not responsible for dispersing a GMC over the first 5 Myr of cluster formation.

  11. Deep Washington photometry of inconspicuous star cluster candidates in the Large Magellanic Cloud

    SciTech Connect

    Choudhury, Samyaday; Subramaniam, Annapurni; Piatti, Andrés E.

    2015-02-01

    We present deep Washington photometry of 45 poorly populated star cluster candidates in the Large Magellanic Cloud (LMC). We have performed a systematic study to estimate the parameters of the cluster candidates by matching theoretical isochrones to the cleaned and dereddened cluster color–magnitude diagrams. We were able to estimate the basic parameters for 33 clusters, out of which 23 are identified as single clusters and 10 are found to be members of double clusters. The other 12 cluster candidates have been classified as possible clusters/asterisms. About 50% of the true clusters are in the 100–300 Myr age range, whereas some are older or younger. We have discussed the distribution of age, location, and reddening with respect to field, as well as the size of true clusters. The sizes and masses of the studied sample are found to be similar to that of open clusters in the Milky Way. Our study adds to the lower end of cluster mass distribution in the LMC, suggesting that the LMC, apart from hosting rich clusters, also has formed small, less massive open clusters in the 100–300 Myr age range.

  12. Multiband Fourier Analysis and Interstellar Reddening of Variable Stars in the Globular Cluster NGC 6584

    NASA Astrophysics Data System (ADS)

    Villiger, Nathan J.; Weinschenk, Sedrick; Hettinger, Paul T.; Murphy, Brian W.

    2017-01-01

    Globular clusters are excellent objects to study to help us understand the ways in which stars evolve. Key to this understanding are RR Lyrae variable stars. This research focused on the RR Lyrae stars in the globular cluster NGC 6584 to gain a better knowledge of post main sequence stellar evolution, horizontal branch morphology, and interstellar reddening to cluster variables. Using the 0.6 m SARA telescope at CTIO, we obtained nearly 1000 images in B, V, and I bands from July 2014 through July 2015. In addition to our prior work in V-band, this research adds B and I bands. By using difference image analysis, we found 77 variable stars in our 13’ x 13’ field of view. These consisted of 66 RR Lyrae stars, 7 long period variables, and 4 eclipsing binaries. The RR Lyrae stars were divided into 50 RR0 type stars, of which 14 exhibit the Blazhko effect, and 16 RR1 type stars. We found an average period for the RR0 variables of 0.56465 days and 0.30610 for the RR1 variables. By applying Fourier decomposition and examining the light curves in B, V, and I bands for each RR Lyrae variable, we were able to determine an average [Fe/H]JKZW of -1.619 ± 0.090, an average E(B-V) of 0.100 ± 0.032, and a distance to the cluster of 13527 ± 939 pc. This is the first detailed study to use RR Lyrae variable stars to estimate these parameters and the results are consistent with those obtained by other methods.

  13. Extragalactic Ultracompact HII Regions: Probing the Birth Environments of Super Star Clusters

    NASA Astrophysics Data System (ADS)

    Johnson, K. E.

    2004-12-01

    In recent years, a number of extragalactic massive star clusters that are still deeply embedded in their birth material have been discovered. These objects represent the youngest stage of massive star cluster evolution yet observed, and the most massive and dense of these may be proto globular clusters. Their properties appear to be similar to those of ultracompact HII regions in the Galaxy, but scaled up in total mass and luminosity. In many cases, these clusters are only visible at mid-IR to radio wavelengths, and they have typically been detected as ``inverted'' spectrum radio sources. However, the set of existing observations is anemic, and our current physical model for these natal clusters in simplistic. This article will overview what we think we know about these objects based on existing observations and outline some of the most significant gaps in our current understanding.

  14. Age and metallicity of star clusters in the Small Magellanic Cloud from integrated spectroscopy

    NASA Astrophysics Data System (ADS)

    Dias, B.; Coelho, P.; Barbuy, B.; Kerber, L.; Idiart, T.

    2010-09-01

    Context. Analysis of ages and metallicities of star clusters in the Magellanic Clouds provide information for studies on the chemical evolution of the Clouds and other dwarf irregular galaxies. Aims: The aim is to derive ages and metallicities from integrated spectra of 14 star clusters in the Small Magellanic Cloud, including a few intermediate/old age star clusters. Methods: Making use of a full-spectrum fitting technique, we compared the integrated spectra of the sample clusters to three different sets of single stellar population models, using two fitting codes available in the literature. Results: We derive the ages and metallicities of 9 intermediate/old age clusters, some of them previously unstudied, and 5 young clusters. Conclusions: We point out the interest of the newly identified as intermediate/old age clusters HW1, NGC 152, Lindsay 3, Lindsay 11, and Lindsay 113. We also confirm the old ages of NGC 361, NGC 419, Kron 3, and of the very well-known oldest SMC cluster, NGC 121. Appendix A is only available in electronic form at http://www.aanda.org

  15. Big Fish in Small Ponds: Massive Stars in the Low-mass Clusters of M83

    NASA Astrophysics Data System (ADS)

    Andrews, J. E.; Calzetti, D.; Chandar, R.; Elmegreen, B. G.; Kennicutt, R. C.; Kim, Hwihyun; Krumholz, Mark R.; Lee, J. C.; McElwee, Sean; O'Connell, R. W.; Whitmore, B.

    2014-09-01

    We have used multi-wavelength Hubble Space Telescope WFC3 data of the starbursting spiral galaxy M83 in order to measure variations in the upper end of the stellar initial mass function (uIMF) using the production rate of ionizing photons in unresolved clusters with ages <= 8 Myr. As in earlier papers on M51 and NGC 4214, the uIMF in M83 is consistent with a universal IMF, and stochastic sampling of the stellar populations in the lap103 M ⊙ clusters are responsible for any deviations in this universality. The ensemble cluster population, as well as individual clusters, also imply that the most massive star in a cluster does not depend on the cluster mass. In fact, we have found that these small clusters seem to have an over-abundance of ionizing photons when compared to an expected universal or truncated IMF. This also suggests that the presence of massive stars in these clusters does not affect the star formation in a destructive way.

  16. Big Fish in Small Ponds: massive stars in the low-mass clusters of M83

    SciTech Connect

    Andrews, J. E.; Calzetti, D.; McElwee, Sean; Chandar, R.; Elmegreen, B. G.; Kennicutt, R. C.; Kim, Hwihyun; Krumholz, Mark R.; Lee, J. C.; Whitmore, B.; O'Connell, R. W. E-mail: callzetti@astro.umass.edu

    2014-09-20

    We have used multi-wavelength Hubble Space Telescope WFC3 data of the starbursting spiral galaxy M83 in order to measure variations in the upper end of the stellar initial mass function (uIMF) using the production rate of ionizing photons in unresolved clusters with ages ≤ 8 Myr. As in earlier papers on M51 and NGC 4214, the uIMF in M83 is consistent with a universal IMF, and stochastic sampling of the stellar populations in the ∼<10{sup 3} M {sub ☉} clusters are responsible for any deviations in this universality. The ensemble cluster population, as well as individual clusters, also imply that the most massive star in a cluster does not depend on the cluster mass. In fact, we have found that these small clusters seem to have an over-abundance of ionizing photons when compared to an expected universal or truncated IMF. This also suggests that the presence of massive stars in these clusters does not affect the star formation in a destructive way.

  17. THE STAR CLUSTER POPULATION OF THE COLLISIONAL RING GALAXY NGC 922

    SciTech Connect

    Pellerin, Anne; Meurer, Gerhardt R.; Bekki, Kenji; Elmegreen, Debra M.; Wong, O. Ivy; Knezek, Patricia M. E-mail: Gerhardt.Meurer@icrar.org E-mail: elmegreen@vassar.edu E-mail: knezek@noao.edu

    2010-04-15

    We present a detailed study of the star cluster population detected in the galaxy NGC 922, one of the closest collisional ring galaxies known to date, using Hubble Space Telescope/Wide Field Planetary Camera 2 UBVI photometry, population synthesis models, and N-body/smoothed particle hydrodynamics simulations. We find that 69% of the clusters are younger than 7 Myr, and that most of them are located in the ring or along the bar, consistent with the strong H{alpha} emission. The cluster luminosity function slope of 2.1-2.3 for NGC 922 is in agreement with those of young clusters in nearby galaxies. Models of the cluster age distribution match the observations best when cluster disruption is considered. We also find clusters with ages (>50 Myr) and masses (>10{sup 5} M {sub sun}) that are excellent progenitors for faint fuzzy clusters. The images also show a tidal plume pointing toward the companion. Its stellar age from our analysis is consistent with pre-existing stars that were stripped off during the passage of the companion. Finally, a comparison of the star-forming complexes observed in NGC 922 with those of a distant ring galaxy from the GOODS field indicates very similar masses and sizes, suggesting similar origins.

  18. The Star Cluster Population of the Collisional Ring Galaxy NGC 922

    NASA Astrophysics Data System (ADS)

    Pellerin, Anne; Meurer, Gerhardt R.; Bekki, Kenji; Elmegreen, Debra M.; Wong, O. Ivy; Knezek, Patricia M.

    2010-04-01

    We present a detailed study of the star cluster population detected in the galaxy NGC 922, one of the closest collisional ring galaxies known to date, using Hubble Space Telescope/Wide Field Planetary Camera 2 UBVI photometry, population synthesis models, and N-body/smoothed particle hydrodynamics simulations. We find that 69% of the clusters are younger than 7 Myr, and that most of them are located in the ring or along the bar, consistent with the strong Hα emission. The cluster luminosity function slope of 2.1-2.3 for NGC 922 is in agreement with those of young clusters in nearby galaxies. Models of the cluster age distribution match the observations best when cluster disruption is considered. We also find clusters with ages (>50 Myr) and masses (>105 M sun) that are excellent progenitors for faint fuzzy clusters. The images also show a tidal plume pointing toward the companion. Its stellar age from our analysis is consistent with pre-existing stars that were stripped off during the passage of the companion. Finally, a comparison of the star-forming complexes observed in NGC 922 with those of a distant ring galaxy from the GOODS field indicates very similar masses and sizes, suggesting similar origins.

  19. Near-infrared spectroscopy of candidate red supergiant stars in clusters

    NASA Astrophysics Data System (ADS)

    Messineo, Maria; Zhu, Qingfeng; Ivanov, Valentin D.; Figer, Donald F.; Davies, Ben; Menten, Karl M.; Kudritzki, Rolf P.; Chen, C.-H. Rosie

    2014-11-01

    Context. Clear identifications of Galactic young stellar clusters farther than a few kpc from the Sun are rare, despite the large number of candidate clusters. Aims: We aim to improve the selection of candidate clusters rich in massive stars with a multiwavelength analysis of photometric Galactic data that range from optical to mid-infrared wavelengths. Methods: We present a photometric and spectroscopic analysis of five candidate stellar clusters, which were selected as overdensities with bright stars (Ks< 7 mag) in GLIMPSE and 2MASS images. Results: A total of 48 infrared spectra were obtained. The combination of photometry and spectroscopy yielded six new red supergiant stars with masses from 10 M⊙ to 15 M⊙. Two red supergiants are located at Galactic coordinates (l,b) = (16.°7, -0.°63) and at a distance of about ~3.9 kpc; four other red supergiants are members of a cluster at Galactic coordinates (l,b) = (49.°3, + 0.°72) and at a distance of ~7.0 kpc. Conclusions: Spectroscopic analysis of the brightest stars of detected overdensities and studies of interstellar extinction along their line of sights are fundamental to distinguish regions of low extinction from actual stellar clusters. The census of young star clusters containing red supergiants is incomplete; in the existing all-sky near-infrared surveys, they can be identified as overdensities of bright stars with infrared color-magnitude diagrams characterized by gaps. Based on observations collected at the European Southern Observatory (ESO Programme 60.A-9700(E), and 089.D-0876), and on observations collected at the UKIRT telescope (programme ID H243NS).MM is currently employed by the MPIfR. Part of this work was performed at RIT (2009), at ESA (2010), and at the MPIfR.Tables 3, 4, and 6 are available in electronic form at http://www.aanda.org

  20. THE FRACTION OF GLOBULAR CLUSTER SECOND-GENERATION STARS IN THE GALACTIC HALO

    SciTech Connect

    Vesperini, Enrico; McMillan, Stephen L. W.; D'Antona, Francesca; D'Ercole, Annibale

    2010-08-01

    Many observational studies have revealed the presence of multiple stellar generations in Galactic globular clusters. These studies suggest that second-generation stars make up a significant fraction of the current mass of globular clusters, with the second-generation mass fraction ranging from {approx}50% to 80% in individual clusters. In this Letter, we carry out hydrodynamical simulations to explore the dependence of the mass of second-generation stars on the initial mass and structural parameters and stellar initial mass function (IMF) of the parent cluster. We then use the results of these simulations to estimate the fraction f{sub SG,H} of the mass of the Galactic stellar halo composed of second-generation stars that originated in globular clusters. We study the dependence of f{sub SG,H} on the parameters of the IMF of the Galactic globular cluster system. For a broad range of initial conditions, we find that the fraction of mass of the Galactic stellar halo in second-generation stars is always small, f{sub SG,H} < 4%-6% for a Kroupa-1993 IMF and f{sub SG,H} < 7%-9% for a Kroupa-2001 IMF.

  1. Effects of Stellar-Mass Black Holes on Massive Star Cluster Evolution

    NASA Astrophysics Data System (ADS)

    Chatterjee, Sourav; Morscher, Meagan; Rodriguez, Carl L.; Pattabiraman, Bharat; Rasio, Frederic A.

    2017-03-01

    Recent observations have revealed the existence of stellar mass black hole (BH) candidates in some globular clusters (GC) in the Milky Way and in other galaxies. Given that the detection of BHs is challenging, these detections likely indicate the existence of large populations of BHs in these clusters. This is in direct contrast to the past understanding that at most a handful of BHs may remain in old GCs due to quick mass segregation and rapid mutual dynamical ejection. Modern realistic star-by-star numerical simulations suggest that the retention fraction of BHs is typically much higher than what was previously thought. The BH dynamics near the cluster center leads to dynamical formation of new binaries and dynamical ejections, and acts as a persistent and significant energy source for these clusters. We have started exploring effects of BHs on the global evolution and survival of star clusters. We find that the evolution as well as survival of massive star clusters can critically depend on the details of the initial assumptions related to BH formation physics, such as natal kick distribution, and the initial stellar mass function (IMF). In this article we will present our latest results.

  2. UPDATED MASS SCALING RELATIONS FOR NUCLEAR STAR CLUSTERS AND A COMPARISON TO SUPERMASSIVE BLACK HOLES

    SciTech Connect

    Scott, Nicholas; Graham, Alister W.

    2013-02-15

    We investigate whether or not nuclear star clusters and supermassive black holes (SMBHs) follow a common set of mass scaling relations with their host galaxy's properties, and hence can be considered to form a single class of central massive object (CMO). We have compiled a large sample of galaxies with measured nuclear star cluster masses and host galaxy properties from the literature and fit log-linear scaling relations. We find that nuclear star cluster mass, M {sub NC}, correlates most tightly with the host galaxy's velocity dispersion: log M {sub NC} = (2.11 {+-} 0.31)log ({sigma}/54) + (6.63 {+-} 0.09), but has a slope dramatically shallower than the relation defined by SMBHs. We find that the nuclear star cluster mass relations involving host galaxy (and spheroid) luminosity and stellar and dynamical mass, intercept with but are in general shallower than the corresponding black hole scaling relations. In particular, M {sub NC}{proportional_to}M {sup 0.55{+-}0.15} {sub Gal,dyn}; the nuclear cluster mass is not a constant fraction of its host galaxy or spheroid mass. We conclude that nuclear stellar clusters and SMBHs do not form a single family of CMOs.

  3. ON THE HEATING EFFICIENCY DERIVED FROM OBSERVATIONS OF YOUNG SUPER STAR CLUSTERS IN M82

    SciTech Connect

    Silich, Sergiy; Tenorio-Tagle, Guillermo; Torres-Campos, Ana; Munoz-Tunon, Casiana; Monreal-Ibero, Ana; Melo, Veronica E-mail: cmt@ll.iac.es

    2009-08-01

    Here, we discuss the mechanical feedback that massive stellar clusters provide to the interstellar medium of their host galaxy. We apply an analytic theory developed in a previous study for M82-A1 to a sample of 10 clusters located in the central zone of the starburst galaxy M82, all surrounded by compact and dense H II regions. We claim that the only way that such H II regions can survive around the selected clusters, is if they are embedded into a high-pressure ISM and if the majority of their mechanical energy is lost within the star cluster volume via strong radiative cooling. The latter implies that these clusters have a low heating efficiency, {eta}, and evolve in the bimodal hydrodynamic regime. In this regime, the shock-heated plasma in the central zones of a cluster becomes thermally unstable, loses its pressure and is accumulated there, whereas the matter injected by supernovae and stellar winds outside this volume forms a high-velocity outflow-the star cluster wind. We calculated the heating efficiency for each of the selected clusters and found that in all cases it does not exceed 10%. Such low heating efficiency values imply a low mechanical energy output and the impact that the selected clusters provide to the ISM of M82 is thus much smaller than what one would expect using stellar cluster synthetic models.

  4. Mining the UKIDSS Galactic Plane Survey: star formation and embedded clusters

    NASA Astrophysics Data System (ADS)

    Solin, O.; Ukkonen, E.; Haikala, L.

    2012-06-01

    Context. Data mining techniques must be developed and applied to analyse the large public data bases containing hundreds to thousands of millions entries. Aims: We develop methods for locating previously unknown stellar clusters from the UKIDSS Galactic Plane Survey (GPS) catalogue data. Methods: The cluster candidates are computationally searched from pre-filtered catalogue data using a method that fits a mixture model of Gaussian densities and background noise using the expectation maximization algorithm. The catalogue data contains a significant number of false sources clustered around bright stars. A large fraction of these artefacts were automatically filtered out before or during the cluster search. The UKIDSS data reduction pipeline tends to classify marginally resolved stellar pairs and objects seen against variable surface brightness as extended objects (or "galaxies" in the archive parlance). 10% or 66 × 106 of the sources in the UKIDSS GPS catalogue brighter than 17m in the K band are classified as "galaxies". Young embedded clusters create variable NIR surface brightness because the gas/dust clouds in which they were formed scatters the light from the cluster members. Such clusters appear therefore as clusters of "galaxies" in the catalogue and can be found using only a subset of the catalogue data. The detected "galaxy clusters" were finally screened visually to eliminate the remaining false detections due to data artefacts. Besides the embedded clusters the search also located locations of non clustered embedded star formation. Results: The search covered an area of 1302 deg2 and 137 previously unknown cluster candidates and 30 previously unknown sites of star formation were found. Appendices A-C are available in electronic form at http://www.anda.org

  5. How do Super Star Clusters Form?: The Anomalous Luminosity Function of Natal Clusters in Henize 2-10

    NASA Astrophysics Data System (ADS)

    Biswas, I.; Johnson, K. E.

    2005-12-01

    Super Star Clusters (SSCs) are the most extreme star forming environments in the local universe. Results from optical observations have suggested that SSCs are simply the statistical tail of a power law luminosity (mass) distribution of index ˜ -2. However, optical luminosity functions are complicated by evolution effects and extinction. Free of these constraints, centimeter wave radio observations pin down the cluster luminosity function to the first few Myrs when natal SSCs are still embedded in ultradense H II regions. We investigate the earliest stages of SSCs in the starburst galaxy Henize 2-10 using high resolution Very Large Array observations at 5, 8.3, 15, and 23 GHz. We use the Pie Town link at lower frequencies to obtain relatively well matched beams to obtain a linear resolution of ˜ 10 pc. Such a high resolution should allow us to detect natal clusters with masses ˜ 104 M⊙ as 10σ detections. The 23 GHz flux (high frequency emission is dominated by optically thin, thermal emission) indicates that all of the detected SSCs in Henize 2-10 have a mass greater than ˜ 105 M⊙. We rule out the possibility of the clusters being self gravitating from the H92α line width of ˜ 200 km s-1. The absence of the formation of lower mass clusters is inconsistent with a power law luminosity function, which we verify with a KS test. Thus, the luminosity function of natal clusters, which we dub the Initial Cluster Luminosity Function (ICLF), suggests that SSCs require a special mode of star formation. We plan follow-up radio observations to investigate the behavior of the ICLF in a variety of starburst and merger environments.

  6. Do All Stars Form in Clusters?: Masses and Ages of Young Supergiants in Andromeda

    NASA Astrophysics Data System (ADS)

    Choudhury, Zareen; Debs, C.; Kirby, E. N.; Guhathakurta, P.

    2013-01-01

    Currently it is not understood whether seemingly isolated stars formed in situ or were ejected from star clusters as runaway stars. Previous studies determined the origins of isolated stars by measuring their velocities, but past research was limited to OB stars in the Milky Way and Magellanic Clouds due to the difficulty of computing velocities of distant objects. This study proposed an innovative velocity test to statistically determine whether six seemingly isolated BA-type supergiants in Andromeda are runaways. We calculated the minimum relative transverse velocity needed for each supergiant to travel to its current location from the nearest open cluster. By comparing the minimum velocity with Andromeda’s known velocity dispersion, a statistical measure of the stars’ actual velocities, we determined whether the star had the necessary velocity to be a runaway. Minimum velocity was computed from the age of the star, which was calculated from its effective temperature and surface gravity. To compute effective temperature and surface gravity, we applied three new techniques based on Balmer absorption features. The results suggest that all six supergiants had the necessary velocities to be runaways. Although the proposed velocity test is a statistical assessment, it offers a valuable new tool for future investigation of isolated stars beyond the Milky Way and its satellites. This research was supported by the Science Internship Program (SIP) at UCSC, the National Science Foundation, NASA, and Palomar Observatory.

  7. Time-Series Photometry of Variable Stars in the Globular Cluster NGC 288

    NASA Astrophysics Data System (ADS)

    Lee, Dong-Joo; Koo, Jae-Rim; Hong, Kyeongsoo; Kim, Seung-Lee; Lee, Jae Woo; Lee, Chung-Uk; Jeon, Young-Beom; Kim, Yun-Hak; Lim, Beomdu; Ryu, Yoon-Hyun; Cha, Sang-Mok; Lee, Yongseok; Kim, Dong-Jin; Park, Byeong-Gon; Kim, Chun-Hwey

    2016-12-01

    We present the results of BV time-series photometry of the globular cluster NGC 288. Observations were carried out to search for variable stars using the Korea Microlensing Telescope Network (KMTNet) 1.6-m telescopes and a 4k pre-science CCD camera during a test observation from August to December, 2014. We found a new SX Phe star and confirmed twelve previously known variable stars in NGC 288. For the semi-regular variable star V1, we newly determined a period of 37.3 days from light curves spanning 137 days. The light-curve solution of the eclipsing binary V10 indicates that the system is probably a detached system. The pulsation properties of nine SX Phe stars were examined by applying multiple frequency analysis to their light curves. We derived a new Period-Luminosity (P-L) relation, < M_{V} rangle = -2.476(±0.300) log P - 0.354(±0.385), from six SX Phe stars showing the fundamental mode. Additionally, the period ratios of three SX Phe stars that probably have a double-radial mode were investigated; P_{FO}/P_{F} = 0.779 for V5, P_{TO}/P_{FO} = 0.685 for V9, P_{SO}/P_{FO} = 0.811 for V11. This paper is the first contribution in a series assessing the detections and properties of variable stars in six southern globular clusters with the KMTNet system.

  8. Star Cluster Formation from Turbulent Clumps. I. The Fast Formation Limit

    NASA Astrophysics Data System (ADS)

    Farias, Juan P.; Tan, Jonathan C.; Chatterjee, Sourav

    2017-04-01

    We investigate the formation and early evolution of star clusters, assuming that they form from a turbulent starless clump of a given mass bounded inside a parent self-gravitating molecular cloud characterized by a particular mass surface density. As a first step, we assume instantaneous star cluster formation and gas expulsion. We draw our initial conditions from observed properties of starless clumps. We follow the early evolution of the clusters up to 20 Myr, investigating the effects of different star formation efficiencies, primordial binary fractions and eccentricities, and primordial mass segregation levels. We investigate clumps with initial masses of {M}{cl}=3000 {M}ȯ embedded in ambient cloud environments with mass surface densities {{{Σ }}}{cloud}=0.1 and 1 {{g}} {{cm}}-2. We show that these models of fast star cluster formation result, in the fiducial case, in clusters that expand rapidly, even considering only the bound members. Clusters formed from higher {{{Σ }}}{cloud} environments tend to expand more quickly and thus are soon larger than clusters born from lower {{{Σ }}}{cloud} conditions. To form a young cluster of a given age, stellar mass, and mass surface density, these models need to assume a parent molecular clump that is many times denser, which is unrealistic compared to observed systems. We also show that, in these models, the initial binary properties are only slightly modified by interactions, meaning that the binary properties, e.g., at 20 Myr, are very similar to those at birth. With this study, we set up the foundation for future work, where we will investigate more realistic models of star formation compared to this instantaneous, baseline case.

  9. DISCOVERY OF A POSSIBLY SINGLE BLUE SUPERGIANT STAR IN THE INTRA-CLUSTER REGION OF VIRGO CLUSTER OF GALAXIES

    SciTech Connect

    Ohyama, Youichi; Hota, Ananda

    2013-04-20

    IC 3418 is a dwarf irregular galaxy falling into the Virgo cluster, and a 17 kpc long trail is seen behind the galaxy, which is considered to have formed due to ram pressure stripping. The trail contains compact knots and diffuse blobs of ultraviolet and blue optical emission and, thus, it is a clear site of recent star formation but in an unusual environment, surrounded by a million degree intra-cluster medium. We report on our optical spectroscopy of a compact source in the trail, SDSS J122952.66+112227.8, and show that the optical spectrum is dominated by emission from a massive blue supergiant star. If confirmed, our report would mark the farthest star with spectroscopic observation. We interpret that a massive O-type star formed in situ in the trail has evolved recently out of the main sequence into this blue supergiant phase, and now lacks any detectable spectral sign of its associated H II region. We argue that turbulence within the ram pressure striped gaseous trail may play a dominant role for the star formation within such trails.

  10. INFRARED OBSERVATIONAL MANIFESTATIONS OF YOUNG DUSTY SUPER STAR CLUSTERS

    SciTech Connect

    Martínez-González, Sergio; Tenorio-Tagle, Guillermo; Silich, Sergiy

    2016-01-01

    The growing evidence pointing at core-collapse supernovae as large dust producers makes young massive stellar clusters ideal laboratories to study the evolution of dust immersed in a hot plasma. Here we address the stochastic injection of dust by supernovae, and follow its evolution due to thermal sputtering within the hot and dense plasma generated by young stellar clusters. Under these considerations, dust grains are heated by means of random collisions with gas particles which result in the appearance of  infrared spectral signatures. We present time-dependent infrared spectral energy distributions that are to be expected from young stellar clusters. Our results are based on hydrodynamic calculations that account for the stochastic injection of dust by supernovae. These also consider gas and dust radiative cooling, stochastic dust temperature fluctuations, the exit of dust grains out of the cluster volume due to the cluster wind, and a time-dependent grain size distribution.

  11. Outflow Feedback Regulated Massive Star Formation in Parsec-Scale Cluster Forming Clumps

    SciTech Connect

    Wang, Peng; Li, Zhi-Yun; Abel, Tom; Nakamura, Fumitaka; /Niigata U.

    2010-02-15

    We investigate massive star formation in turbulent, magnetized, parsec-scale clumps of molecular clouds including protostellar outflow feedback using three dimensional numerical simulations of effective resolution 2048{sup 3}. The calculations are carried out using a block structured adaptive mesh refinement code that solves the ideal MHD equations including self-gravity and implements accreting sink particles. We find that, in the absence of regulation by magnetic fields and outflow feedback, massive stars form readily in a turbulent, moderately condensed clump of {approx} 1,600 M{sub {circle_dot}} (containing {approx} 10{sup 2} initial Jeans masses), along with a cluster of hundreds of lower mass stars. The massive stars are fed at high rates by (1) transient dense filaments produced by large-scale turbulent compression at early times, and (2) by the clump-wide global collapse resulting from turbulence decay at late times. In both cases, the bulk of the massive star's mass is supplied from outside a 0.1 pc-sized 'core' that surrounds the star. In our simulation, the massive star is clump-fed rather than core-fed. The need for large-scale feeding makes the massive star formation prone to regulation by outflow feedback, which directly opposes the feeding processes. The outflows reduce the mass accretion rates onto the massive stars by breaking up the dense filaments that feed the massive star formation at early times, and by collectively slowing down the global collapse that fuel the massive star formation at late times. The latter is aided by a moderate magnetic field of strength in the observed range (corresponding to a dimensionless clump mass-to-flux ratio {lambda} {approx} a few); the field allows the outflow momenta to be deposited more efficiently inside the clump. We conclude that the massive star formation in our simulated turbulent, magnetized, parsec-scale clump is outflow-regulated and clump-fed (ORCF for short). An important implication is that the

  12. Stellar encounters involving neutron stars in globular cluster cores

    NASA Technical Reports Server (NTRS)

    Davies, M. B.; Benz, W.; Hills, J. G.

    1992-01-01

    Encounters between a 1.4 solar mass neutron star and a 0.8 solar mass red giant (RG) and between a 1.4 solar mass neutron star (NS) and an 0.8 solar mass main-sequence (MS) star have been successfully simulated. In the case of encounters involving an RG, bound systems are produced when the separation at periastron passage R(MIN) is less than about 2.5 R(RG). At least 70 percent of these bound systems are composed of the RG core and NS forming a binary engulfed in a common envelope of what remains of the former RG envelope. Once the envelope is ejected, a tight white dwarf-NS binary remains. For MS stars, encounters with NSs will produce bound systems when R(MIN) is less than about 3.5 R(MS). Some 50 percent of these systems will be single objects with the NS engulfed in a thick disk of gas almost as massive as the original MS star. The ultimate fate of such systems is unclear.

  13. Massive open star clusters using the VVV survey. IV. WR 62-2, a new very massive star in the core of the VVV CL041 cluster

    NASA Astrophysics Data System (ADS)

    Chené, A.-N.; Ramírez Alegría, S.; Borissova, J.; O'Leary, E.; Martins, F.; Hervé, A.; Kuhn, M.; Kurtev, R.; Consuelo Amigo Fuentes, P.; Bonatto, C.; Minniti, D.

    2015-12-01

    Context. The ESO Public Survey VISTA Variables in the Vía Láctea (VVV) provides deep multi-epoch infrared observations for an unprecedented 562 sq. deg of the Galactic bulge and adjacent regions of the disk. Nearly 150 new open clusters and cluster candidates have been discovered in this survey. Aims: We present the fourth article in a series of papers focussed on young and massive clusters discovered in the VVV survey. This article is dedicated to the cluster VVV CL041, which contains a new very massive star candidate, WR 62-2. Methods: Following the methodology presented in the first paper of the series, wide-field, deep JHKs VVV observations, combined with new infrared spectroscopy, are employed to constrain fundamental parameters (distance, reddening, mass, age) of VVV CL041. Results: We confirm that the cluster VVV CL041 is a young (less than 4 Myr) and massive (3 ± 2 × 103 M⊙) cluster, and not a simple asterism. It is located at a distance of 4.2 ± 0.9 kpc, and its reddening is AV = 8.0 ± 0.2 mag, which is slightly lower than the average for the young clusters towards the centre of the Galaxy. Spectral analysis shows that the most luminous star of the cluster, of the WN8h spectral type, is a candidate to have an initial mass larger than 100 M⊙. Based on observations taken within the ESO VISTA Public Survey VVV, Programme ID 179.B-2002, and on observations with VLT/ISAAC at ESO (programme 087.D.0341A) and Flamingos-2 at Gemini (programme GS-2014A-Q-72).The photometric catalogue is only available at the CDS via anonymous ftp to http://cdsarc.u-strasbg.fr (ftp://130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/584/A31

  14. On star formation in stellar systems. I - Photoionization effects in protoglobular clusters

    NASA Technical Reports Server (NTRS)

    Tenorio-Tagle, G.; Bodenheimer, P.; Lin, D. N. C.; Noriega-Crespo, A.

    1986-01-01

    The progressive ionization and subsequent dynamical evolution of nonhomogeneously distributed low-metal-abundance diffuse gas after star formation in globular clusters are investigated analytically, taking the gravitational acceleration due to the stars into account. The basic equations are derived; the underlying assumptions, input parameters, and solution methods are explained; and numerical results for three standard cases (ionization during star formation, ionization during expansion, and evolution resulting in a stable H II region at its equilibrium Stromgren radius) are presented in graphs and characterized in detail. The time scale of residual-gas loss in typical clusters is found to be about the same as the lifetime of a massive star on the main sequence.

  15. Probing the super star cluster environment of NGC 1569 using FISICA

    NASA Astrophysics Data System (ADS)

    Clark, D. M.; Eikenberry, S. S.; Raines, S. N.; Gruel, N.; Elston, R.; Guzman, R.; Boreman, G.; Glenn, P. E.

    2013-01-01

    We present near-IR JH spectra of the central regions of the dwarf starburst galaxy NGC 1569 using the Florida Image Slicer for Infrared Cosmology and Astrophysics (FISICA). The dust-penetrating properties and available spectral features of the near-IR, combined with the integral field unit (IFU) capability to take spectra of a field, make FISICA an ideal tool for this work. We use the prominent [He i] (1.083 μm) and Paβ (1.282 μm) lines to probe the dense star-forming regions as well as characterize the general star-forming environment around the super star clusters (SSCs) in NGC 1569. We find [He i] coincident with CO clouds to the north and west of the SSCs, which provides the first, conclusive evidence for embedded star clusters here.

  16. Young and old massive star clusters: Theoretical challenges for the next decade

    NASA Astrophysics Data System (ADS)

    Charbonnel, Corinne

    2015-08-01

    Breakthrough results of high resolution observations both with HST and from the ground have revolutionized our view and our understanding of massive star clusters, young and old, in the Galaxy, in the Local Group, as well as in merging and interacting galaxies. This drastic paradigm shift has revealed the complexity of these systems and has raised a number of fundamental questions on the physical processes that drive the formation and evolution of massive star clusters in different environments, on the star cluster initial mass function, and on the contribution of these objects to the general galactic field stellar population. In this talk we review some of the main theoretical challenges that have to be faced in the field at the very same moment when we enter a golden age for observations and numerical multi-dimensional simulations.

  17. A Luminous Yellow Post-AGB Star in the Galactic Globular Cluster M79

    NASA Astrophysics Data System (ADS)

    Bond, Howard E.; Ciardullo, Robin; Siegel, Michael H.

    2016-02-01

    We report the discovery of a luminous F-type post-asymptotic-giant-branch (PAGB) star in the Galactic globular cluster (GC) M79 (NGC 1904). At visual apparent and absolute magnitudes of V=12.20 and {M}V=-3.46, this “yellow” PAGB star is by a small margin the visually brightest star known in any GC. It was identified using CCD observations in the uBVI photometric system, which is optimized to detect stars with large Balmer discontinuities, indicative of very low surface gravities. Follow-up observations with the SMARTS 1.3 and 1.5 m telescopes show that the star is not variable in light or radial velocity, and that its velocity is consistent with cluster membership. Near- and mid-infrared observations with 2MASS and WISE show no evidence for circumstellar dust. We argue that a sharp upper limit to the luminosity function exists for yellow PAGB stars in old populations, making them excellent candidates for Population II standard candles, which are four magnitudes brighter than RR Lyrae variables. Their luminosities are consistent with the stars being in a PAGB evolutionary phase, with core masses of ˜ 0.53 {M}⊙ . We also detected four very hot stars lying above the horizontal branch (“AGB-manqué” stars); along with the PAGB star, they are the brightest objects in M79 in the near-ultraviolet. In the Appendix, we give periods and light curves for five variables in M79: three RR Lyrae stars, a Type II Cepheid, and a semiregular variable. Based in part on observations with the 1.3 and 1.5 m telescopes operated by the SMARTS Consortium at Cerro Tololo Interamerican Observatory.

  18. Are superluminous supernovae and long GRBs the products of dynamical processes in young dense star clusters?

    SciTech Connect

    Van den Heuvel, E. P. J.; Portegies Zwart, S. F.

    2013-12-20

    Superluminous supernovae (SLSNe) occur almost exclusively in small galaxies (Small/Large Magellanic Cloud (SMC/LMC)-like or smaller), and the few SLSNe observed in larger star-forming galaxies always occur close to the nuclei of their hosts. Another type of peculiar and highly energetic supernovae are the broad-line Type Ic SNe (SN Ic-BL) that are associated with long-duration gamma-ray bursts (LGRBs). Also these have a strong preference for occurring in small (SMC/LMC-like or smaller) star-forming galaxies, and in these galaxies LGRBs always occur in the brightest spots. Studies of nearby star-forming galaxies that are similar to the hosts of LGRBs show that these brightest spots are giant H II regions produced by massive dense young star clusters with many hundreds of O- and Wolf-Rayet-type stars. Such dense young clusters are also found in abundance within a few hundred parsecs from the nucleus of larger galaxies like our own. We argue that the SLSNe and the SNe Ic-BL/LGRBs are exclusive products of two types of dynamical interactions in dense young star clusters. In our model the high angular momentum of the collapsing stellar cores required for the engines of an SN Ic-BL results from the post-main-sequence mergers of dynamically produced cluster binaries with almost equal-mass components. The merger produces a critically rotating single helium star with sufficient angular momentum to produce an LGRB; the observed 'metal aversion' of LGRBs is a natural consequence of the model. We argue that, on the other hand, SLSNe could be the products of runaway multiple collisions in dense clusters, and we present (and quantize) plausible scenarios of how the different types of SLSNe can be produced.

  19. The exclusion of a significant range of ages in a massive star cluster.

    PubMed

    Li, Chengyuan; de Grijs, Richard; Deng, Licai

    2014-12-18

    Stars spend most of their lifetimes on the main sequence in the Hertzsprung-Russell diagram. The extended main-sequence turn-off regions--containing stars leaving the main sequence after having spent all of the hydrogen in their cores--found in massive (more than a few tens of thousands of solar masses), intermediate-age (about one to three billion years old) star clusters are usually interpreted as evidence of internal age spreads of more than 300 million years, although young clusters are thought to quickly lose any remaining star-forming fuel following a period of rapid gas expulsion on timescales of order 10(7) years. Here we report, on the basis of a combination of high-resolution imaging observations and theoretical modelling, that the stars beyond the main sequence in the two-billion-year-old cluster NGC 1651, characterized by a mass of about 1.7 × 10(5) solar masses, can be explained only by a single-age stellar population, even though the cluster has a clearly extended main-sequence turn-off region. The most plausible explanation for the existence of such extended regions invokes a population of rapidly rotating stars, although the secondary effects of the prolonged stellar lifetimes associated with such a stellar population mixture are as yet poorly understood. From preliminary analysis of previously obtained data, we find that similar morphologies are apparent in the Hertzsprung-Russell diagrams of at least five additional intermediate-age star clusters, suggesting that an extended main-sequence turn-off region does not necessarily imply the presence of a significant internal age dispersion.

  20. Variable Stars in the Unusual, Metal-Rich Globular Cluster NGC-6441

    NASA Technical Reports Server (NTRS)

    Pritzl, Barton J.; Smith, Horace A.; Catelan, Marcio; Sweigart, Allen V.; Fisher, Richard R. (Technical Monitor)

    2001-01-01

    We have undertaken a search for variable stars in the metal-rich globular cluster NGC 6441 using time-series BV photometry. The total number of variables found near NGC 6441 has been increased to approx. 104, with 48 new variables being found in this survey. A significant number of the variables are RR Lyrae stars (approx. 46), most of which are probable cluster members. As was noted by Layden et al. (1999), the periods of the fundamental mode RR Lyrae are unusually long compared to field stars of similar metallicity. The existence of these long period RRab stars is consistent with Sweigart & Catelan's (1998) prediction that the horizontal branch of NGC 6441 is unusually bright. This result implies that the metallicity-luminosity relationship for RR Lyrae stars is not universal. We discuss the difficulty in determining the Oosterhoff classification of NGC 6441 due to the unusual nature of its RR Lyrae. A number of ab-type RR Lyrae are found to be both brighter and redder than the other probable RRab found along the horizontal branch, which may be a result of blending with stars of redder color. A smaller than usual gap is found between the shortest period fundamental mode and the longest period first-overtone mode RR Lyrae. We determine the reddening of the cluster to be E(B - V) = 0.51 +/- 0.02 mag, with substantial differential reddening across the face of the cluster. The mean V magnitude of the RR Lyrae is found to be 17.51 +/- 0.02 resulting in a distance of 10.4 to 11.9 kpc, for a range of assumed values of < M(sub V)> for RR Lyrae stars. The possibility that stars in NGC 6441 may span a range in [Fe/H] is also discussed.

  1. Extinction in the Star Cluster SAI 113 and Galactic Structure in Carina

    NASA Astrophysics Data System (ADS)

    Carraro, Giovanni; Turner, David G.; Majaess, Daniel J.; Baume, Gustavo L.; Gamen, Roberto; Molina Lera, José A.

    2017-04-01

    Photometric CCD UB VI C photometry obtained for 4860 stars surrounding the embedded southern cluster SAI 113 (Skiff 8) is used to examine the reddening in the field and derive the distance to the cluster and nearby van Genderen 1. Spectroscopic color excesses for bright cluster stars, photometric reddenings for A3 dwarfs, and dereddening of cluster stars imply that the reddening and extinction laws match results derived for other young clusters in Carina: {E}U-B/{E}B-V≃ 0.64 and {R}V≃ 4. SAI 113 displays features that may be linked to a history of dynamical interactions among member stars: possible circumstellar reddening and rapid rotation of late B-type members, ringlike features in star density, and a compact core, with most stars distributed randomly across the field. The group van Genderen 1 resembles a stellar asterism, with potential members distributed randomly across the field. Distances of 3.90 ± 0.19 kpc and 2.49 ± 0.09 kpc are derived for SAI 113 and van Genderen 1, respectively, with variable reddenings {E}B-V ranging from 0.84 to 1.29 and 0.23 to 1.28. The SRC variables CK Car and EV Car may be outlying members of van Genderen 1, thereby of use for calibrating the period–luminosity relation for pulsating M supergiants. More importantly, the anomalous reddening and extinction evident in Carina and nearby regions of the Galactic plane in the fourth quadrant impact the mapping of spiral structure from young open clusters. The distribution of spiral arms in the fourth quadrant may be significantly different from how it is often portrayed.

  2. AGES OF STAR CLUSTERS IN THE TIDAL TAILS OF MERGING GALAXIES

    SciTech Connect

    Mulia, A. J.; Chandar, R.; Whitmore, B. C.

    2015-06-01

    We study the stellar content in the tidal tails of three nearby merging galaxies, NGC 520, NGC 2623, and NGC 3256, using BVI imaging taken with the Advanced Camera for Surveys on board the Hubble Space Telescope. The tidal tails in all three systems contain compact and fairly massive young star clusters, embedded in a sea of diffuse, unresolved stellar light. We compare the measured colors and luminosities with predictions from population synthesis models to estimate cluster ages and find that clusters began forming in tidal tails during or shortly after the formation of the tails themselves. We find a lack of very young clusters (≤10 Myr old), implying that eventually star formation shuts off in the tails as the gas is used up or dispersed. There are a few clusters in each tail with estimated ages that are older than the modeled tails themselves, suggesting that these may have been stripped out from the original galaxy disks. The luminosity function of the tail clusters can be described by a single power-law, dN/dL ∝ L{sup α}, with −2.6 < α < −2.0. We find a stellar age gradient across some of the tidal tails, which we interpret as a superposition of (1) newly formed stars and clusters along the dense center of the tail and (2) a sea of broadly distributed, older stellar material ejected from the progenitor galaxies.

  3. Panchromatic observations of dwarf starburst galaxies: Infant super star clusters and a low-luminosity AGN

    NASA Astrophysics Data System (ADS)

    Reines, Amy Ellen

    2011-01-01

    Globular star clusters and supermassive black holes are fundamental components of today's massive galaxies, with origins dating back to the very early universe. Both globular clusters and the seeds of supermassive black holes are believed to have formed in the progenitors of modern massive galaxies, although the details are poorly understood. Direct observations of these low-mass, distant, and hence faint systems are unobtainable with current capabilities. However, gas-rich dwarf starburst galaxies in the local universe, analogous in many ways to protogalaxies at high-redshift, can provide critical insight into the early stages of galaxy evolution including the formation of globular clusters and massive black holes. This thesis presents a panchromatic study of nearby dwarf starburst galaxies harboring nascent globular clusters still embedded in their birth material. Infant clusters are identified via their production of thermal radio emission at centimeter wavelengths, which comes from dense gas ionized by young massive stars. By combining radio observations with complementary data at ultraviolet, optical and infrared wavelengths, we obtain a comprehensive view of massive clusters emerging from their gaseous and dusty birth cocoons. This thesis also presents the first example of a nearby dwarf starburst galaxy hosting an actively accreting massive central black hole. The black hole in this dwarf galaxy is unusual in that it is not associated with a bulge, a nuclear star cluster, or any other well-defined nucleus, likely reflecting an early phase of black hole and galaxy evolution that has not been previously observed.

  4. The rise and fall of star formation in z ˜ 0.2 merging galaxy clusters

    NASA Astrophysics Data System (ADS)

    Stroe, Andra; Sobral, David; Dawson, William; Jee, M. James; Hoekstra, Henk; Wittman, David; van Weeren, Reinout J.; Brüggen, Marcus; Röttgering, Huub J. A.

    2015-06-01

    CIZA J2242.8+5301 (`Sausage') and 1RXS J0603.3+4213 (`Toothbrush') are two low-redshift (z ˜ 0.2), massive (˜2 × 1015 M⊙), post-core passage merging clusters, which host-shock waves traced by diffuse radio emission. To study their star formation properties, we uniformly survey the `Sausage' and `Toothbrush' clusters in broad- and narrow-band filters and select a sample of 201 and 463 line emitters, down to a rest-frame equivalent width (13 Å). We robustly separate between Hα and higher redshift emitters using a combination of optical multiband (B, g, V, r, i, z) and spectroscopic data. We build Hα luminosity functions for the entire cluster region, near the shock fronts, and away from the shock fronts and find striking differences between the two clusters. In the dynamically younger, 1 Gyr old `Sausage' cluster we find numerous (59) Hα emitters above a star formation rate (SFR) of 0.17 M⊙ yr-1 surprisingly located in close proximity to the shock fronts, embedded in very hot intracluster medium plasma. The SFR density for the cluster population is at least at the level of typical galaxies at z ˜ 2. Down to the same SFR, the possibly dynamically more evolved `Toothbrush' cluster has only nine Hα galaxies. The cluster Hα galaxies fall on the SFR-stellar mass relation z ˜ 0.2 for the field. However, the `Sausage' cluster has an Hα emitter density >20 times that of blank fields. If the shock passes through gas-rich cluster galaxies, the compressed gas could collapse into dense clouds and excite star formation for a few 100 Myr. This process ultimately leads to a rapid consumption of the molecular gas, accelerating the transformation of gas-rich field spirals into cluster S0s or ellipticals.

  5. An H-alpha survey of cluster spirals - Comparison of star formation in clusters and the field

    NASA Technical Reports Server (NTRS)

    Moss, C.; Whittle, M.

    1993-01-01

    In an objective prism survey of eight nearby Abell clusters, we have detected H-alpha emission from 77 out of a total of 201 CGCG spiral galaxies. We find that detection of H alpha emission is approximately independent of galaxy absolute magnitude, distance to the cluster center, and the presence of a bar. However, tidally distorted spirals are much more likely to be detected than undistorted spirals. Furthermore, there is a strong tendency for tidally distorted spirals to have compact nuclear emission rather than more extended disk-wide emission. When compared to field spirals, we find that late-type (Sc and Sc-Irr) cluster spirals have less H alpha emission, while early-type (Sa and Sab) cluster spirals can have significantly enhanced emission. The enhanced emission is most likely to be due to tidally induced star formation from galaxy-galaxy interactions.

  6. ACS imaging of star clusters in M 51. I. Identification and radius distribution

    NASA Astrophysics Data System (ADS)

    Scheepmaker, R. A.; Haas, M. R.; Gieles, M.; Bastian, N.; Larsen, S. S.; Lamers, H. J. G. L. M.

    2007-07-01

    Context: Size measurements of young star clusters are valuable tools to put constraints on the formation and early dynamical evolution of star clusters. Aims: We use HST/ACS observations of the spiral galaxy M 51 in F435W, F555W and F814W to select a large sample of star clusters with accurate effective radius measurements in an area covering the complete disc of M 51. We present the dataset and study the radius distribution and relations between radius, colour, arm/interarm region, galactocentric distance, mass and age. Methods: We select a sample of 7698 (F435W), 6846 (F555W) and 5024 (F814W) slightly resolved clusters and derive their effective radii (R_eff) by fitting the spatial profiles with analytical models convolved with the point spread function. The radii of 1284 clusters are studied in detail. Results: We find cluster radii between 0.5 and ~10 pc, and one exceptionally large cluster candidate with R_eff = 21.6 pc. The median R_eff is 2.1 pc. We find 70 clusters in our sample which have colours consistent with being old GC candidates and we find 6 new “faint fuzzy” clusters in, or projected onto, the disc of M 51. The radius distribution can not be fitted with a power law similar to the one for star-forming clouds. We find an increase in R_eff with colour as well as a higher fraction of clusters with B-V ⪆ 0.05 in the interarm regions. We find a correlation between R_eff and galactocentric distance (RG) of the form R_eff∝ RG0.12±0.02, which is considerably weaker than the observed correlation for old Milky Way GCs. We find weak relations between cluster luminosity and radius: R_eff∝ L0.15±0.02 for the interarm regions and R_eff∝ L-0.11±0.01 for the spiral arm regions, but we do not observe a correlation between cluster mass and radius. Conclusions: The observed radius distribution indicates that shortly after the formation of the clusters from a fractal gas, the radii of the clusters have changed in a non-uniform way. We find tentative

  7. STAR CLUSTERS AS TRACERS OF INTERACTIONS IN STEPHAN'S QUINTET (HICKSON COMPACT GROUP 92)

    SciTech Connect

    Fedotov, K.; Gallagher, S. C.; Konstantopoulos, I. S.; Charlton, J. C.; Chandar, R.; Bastian, N.; Whitmore, B.; Trancho, G.

    2011-08-15

    Stephan's Quintet (SQ; also known as Hickson Compact Group 92) is a compact group of galaxies that exhibits numerous signs of interactions between its members. Using high-resolution (0.''04 per pixel) images of SQ in B{sub 438}, V{sub 606}, and I{sub 814} bands from the Early Release Science project obtained with the Wide Field Camera 3 on the Hubble Space Telescope, we identify 496 star cluster candidates (SCCs), located throughout the galaxies themselves as well as in intergalactic regions. Our photometry goes {approx}2 mag deeper and covers an additional three regions, the Old Tail, NGC 7317, and the southern debris region (SDR), compared to previous work. Through comparison of the B{sub 438} - V{sub 606} and V{sub 606} - I{sub 814} colors of the SCCs with simple stellar population synthesis models, we are able to constrain cluster ages. In particular, the most massive galaxy of SQ, NGC 7319, exhibits continuous star formation throughout its history, although at a lower rate over the past few tens of Myr. NGC 7318 A/B and the northern star burst region both show ongoing active star formation; there are a number of star clusters that are younger than 10 Myr. NGC 7318 A/B also features a peculiar gap in the color distribution of the star clusters that can be used to date the onset of the recent burst. The majority of the SCCs detected in the Young Tail were formed 150-200 Myr ago, whereas the tight distribution of star cluster colors in the Old Tail allows us to constrain its age of formation to {approx}400 Myr ago. The star clusters in the SDR are seemingly divided into two groups with ages of 50 and {approx}500 Myr, and virtually all of the SCCs detected in NGC 7317 are over 2 Gyr old. Based on these ages, we estimate time intervals for the interactions between SQ members that triggered the massive star cluster formation.

  8. Discovery of 27 New Variable Stars in the Globular Cluster NGC 6584

    NASA Astrophysics Data System (ADS)

    Toddy, Joseph; Johnson, E. W.; Darragh, A. N.; Murphy, B. W.

    2012-01-01

    Using the Southeastern Association for Research in Astronomy 0.6 meter telescope located at Cerro Tololo, we searched for variable stars in the globular cluster NGC 6584. We obtained images for 10 nights between 28 May and 6 July of 2011. After processing the images, we used the image subtraction technique developed by Alard (2000) to search for the variable stars. We detected a total of 69 variable stars in our 10x10 arc-minute field, including 42 previously known variables cataloged by Millis & Liller (1980) and 27 hereto undetected variables. In total, we classified 44 as type RRab, with a mean period of 0.56776 days, 16 as type RRc with a mean period of 0.30886 days, 6 eclipsing binaries, and 3 long period (P > 2 days) variable stars. Many of the RR Lyrae stars exhibited the Blazhko Effect. Furthermore, the RR Lyrae stars exhibit a period/amplitude relationship consistent with NGC 6584 being an Oosterhoff Type I cluster. Here we present refined periods, complete multi-color light curves, and classifications for each of the 69 variables, as well Oosterhoff and color-magnitude diagrams for the cluster. This project was funded in part by the National Science Foundation Research Experiences for Undergraduates (REU) program through grant NSF AST-1004 872 and by a grant from the Butler Institute for Research and Scholarship.

  9. Age and metallicity of star clusters in the Small Magellanic Cloud from integrated spectroscopy

    NASA Astrophysics Data System (ADS)

    Dias, Bruno; Coelho, Paula; Kerber, Leandro; Barbuy, Beatriz; Idiart, Thais

    2010-04-01

    Analysis of integrated spectra of star clusters in the Magellanic Clouds can bring important information for studies on the chemical evolution of the Clouds. The aim of the present work is to derive ages and metallicities from integrated spectra of 15 star clusters in the Small Magellanic Cloud (SMC), some of them not studied so far. Making use of a full spectrum fitting technique, we compared the integrated spectra of the sample clusters to three different sets of single stellar population models available in the literature. We derived ages and metallicities for the sample clusters employing the codes STARLIGHT and ULySS. Out of the 15 clusters in our sample, 9 are old/intermediate age clusters and 6 are young clusters. We point out the results for the newly identified as old/intermediate age clusters HW1, NGC 152, Lindsay 3 and 11. We also confirm old ages for NGC 361, NGC 419 and Kron 3, and the oldest well-known SMC cluster NGC 121.

  10. Atmospheric parameters and metallicities for 2191 stars in the globular cluster M4

    SciTech Connect

    Malavolta, Luca; Piotto, Giampaolo; Nascimbeni, Valerio; Sneden, Christopher; Milone, Antonino P.; Bedin, Luigi R. E-mail: giampaolo.piotto@unipd.it E-mail: luigi.bedin@oapd.inaf.it E-mail: milone@mso.anu.edu.au

    2014-02-01

    We report new metallicities for stars of Galactic globular cluster M4 using the largest number of stars ever observed at high spectral resolution in any cluster. We analyzed 7250 spectra for 2771 cluster stars gathered with the Very Large Telescope (VLT) FLAMES+GIRAFFE spectrograph at VLT. These medium-resolution spectra cover a small wavelength range, and often have very low signal-to-noise ratios. We approached this data set by reconsidering the whole method of abundance analysis of large stellar samples from beginning to end. We developed a new algorithm that automatically determines the atmospheric parameters of a star. Nearly all of the data preparation steps for spectroscopic analyses are processed on the syntheses, not the observed spectra. For 322 red giant branch (RGB) stars with V ≤ 14.7, we obtain a nearly constant metallicity, ([Fe/H]) = –1.07 (σ = 0.02). No difference in the metallicity at the level of 0.01 dex is observed between the two RGB sequences identified by Monelli et al. For 1869 subgiant and main-sequence stars with V > 14.7, we obtain ([Fe/H]) = –1.16 (σ = 0.09) after fixing the microturbulent velocity. These values are consistent with previous studies that have performed detailed analyses of brighter RGB stars at higher spectroscopic resolution and wavelength coverage. It is not clear if the small mean metallicity difference between brighter and fainter M4 members is real or is the result of the low signal-to-noise characteristics of the fainter stars. The strength of our approach is shown by recovering a metallicity close to a single value for more than 2000 stars, using a data set that is non-optimal for atmospheric analyses. This technique is particularly suitable for noisy data taken in difficult observing conditions.

  11. Atmospheric Parameters and Metallicities for 2191 Stars in the Globular Cluster M4

    NASA Astrophysics Data System (ADS)

    Malavolta, Luca; Sneden, Christopher; Piotto, Giampaolo; Milone, Antonino P.; Bedin, Luigi R.; Nascimbeni, Valerio

    2014-02-01

    We report new metallicities for stars of Galactic globular cluster M4 using the largest number of stars ever observed at high spectral resolution in any cluster. We analyzed 7250 spectra for 2771 cluster stars gathered with the Very Large Telescope (VLT) FLAMES+GIRAFFE spectrograph at VLT. These medium-resolution spectra cover a small wavelength range, and often have very low signal-to-noise ratios. We approached this data set by reconsidering the whole method of abundance analysis of large stellar samples from beginning to end. We developed a new algorithm that automatically determines the atmospheric parameters of a star. Nearly all of the data preparation steps for spectroscopic analyses are processed on the syntheses, not the observed spectra. For 322 red giant branch (RGB) stars with V <= 14.7, we obtain a nearly constant metallicity, lang[Fe/H]rang = -1.07 (σ = 0.02). No difference in the metallicity at the level of 0.01 dex is observed between the two RGB sequences identified by Monelli et al. For 1869 subgiant and main-sequence stars with V > 14.7, we obtain lang[Fe/H]rang = -1.16 (σ = 0.09) after fixing the microturbulent velocity. These values are consistent with previous studies that have performed detailed analyses of brighter RGB stars at higher spectroscopic resolution and wavelength coverage. It is not clear if the small mean metallicity difference between brighter and fainter M4 members is real or is the result of the low signal-to-noise characteristics of the fainter stars. The strength of our approach is shown by recovering a metallicity close to a single value for more than 2000 stars, using a data set that is non-optimal for atmospheric analyses. This technique is particularly suitable for noisy data taken in difficult observing conditions.

  12. Ultraviolet properties of individual hot stars in globular cluster cores. 1: NGC 1904 (M 79)

    NASA Technical Reports Server (NTRS)

    Altner, Bruce; Matilsky, Terry A.

    1992-01-01

    As part of an observing program using the International Ultraviolet Explorer (IUE) satellite to investigate the ultraviolet properties of stars found within the cores of galactic globular clusters with blue horizontal branches (HBs), we obtained three spectra of the cluster NGC 1904 (M 79). All three were long integration-time, short-wavelength (SWP) spectra obtained at the so called 'center of light' and all three showed evidence of sources within the IUE large aperture (21.4 in. by 10 in.). In this paper we shall describe the analysis of these spectra and present evidence that the UV sources represent individual hot stars in the post-HB stage of evolution.

  13. Isochrone Fittings for the Open Star Clusters NGC 3680 and Melotte 66

    NASA Astrophysics Data System (ADS)

    Guillemaud, Nikolas; Frinchaboy, P. M.; Thompson, B. A.

    2013-01-01

    I will be displaying the results from isochrone fittings on two open star clusters. The stellar evolution models used to generate the isochrones are from Dartmouth (Dotter et al. 2007) and Padova (Mango et al. 2008). Both of the models were applied to two star clusters: NGC 3680 and Melotte 66. The analysis is performed by utilizing infrared observations from the CPAPIR instrument; which is operated in conjunction with CTIO’s 1.5m telescope. This research was made possible by the NSF’s REU grant; award number 0851558.

  14. VizieR Online Data Catalog: CCD UBVRI photometry of 7 open star clusters (Sagar+, 2001)

    NASA Astrophysics Data System (ADS)

    Sagar, R.; Munari, U.; de Boer, K. S.

    2002-01-01

    We derive cluster parameters and mass functions from new UBVRI CCD photometric observations of ~3500 stars reaching down to V~20mag for the distant southern open star clusters NGC 3105, NGC 3603, Melotte 105, Hogg 15, NGC 4815, Pismis 20 and NGC 6253. For NGC 3105 and Hogg 15, CCD data are presented for the first time. The observations were carried out in 1992 between February 28 and March 8, June 5 and 9, and July 9 and 12 in the Cousins U, B, V, R and I photometric bands using CCD detector at the 1.0-m Elizabeth Telescope at the South African Astronomical Observatory (SAAO), Sutherland. (8 data files).

  15. The complex star cluster system of NGC 1316 (Fornax A)

    NASA Astrophysics Data System (ADS)

    Sesto, Leandro A.; Faifer, Favio R.; Forte, Juan C.

    2016-10-01

    This paper presents Gemini-gri' high-quality photometry for cluster candidates in the field of NGC 1316 (Fornax A) as part of a study that also includes GMOS spectroscopy. A preliminary discussion of the photometric data indicates the presence of four stellar cluster populations with distinctive features in terms of age, chemical abundance and spatial distribution. Two of them seem to be the usually old (metal poor and metal rich) populations typically found in elliptical galaxies. In turn, an intermediate-age (5 Gyr) globular cluster population is the dominant component of the sample (as reported by previous papers). We also find a younger cluster population with a tentative age of ≈ 1 Gyr.

  16. Early nucleosynthesis and chemical abundances of stars in globular clusters.

    NASA Astrophysics Data System (ADS)

    Gratton, R. G.

    This cycle of lectures presents a self consistent sketch of current understanding about chemcial composition of globular clusters and its aftermaths. The first two lectures give basic about nucleosynthesis, chemical models, and abundance determinations. Main results for globular clusters are presented in the next two lectures. In the final lecture the author reviews various indices used to derive abundances from photometry and low dispersion spectroscopy.

  17. STAR FORMATION AND UV COLORS OF THE BRIGHTEST CLUSTER GALAXIES IN THE REPRESENTATIVE XMM-NEWTON CLUSTER STRUCTURE SURVEY

    SciTech Connect

    Donahue, Megan; Bruch, Seth; Wang, Emily; Voit, G. Mark; Hicks, Amalia K.; Haarsma, Deborah B.; Croston, Judith H.; Pratt, Gabriel W.; O'Connell, Robert W.

    2010-06-01

    We present UV broadband photometry and optical emission-line measurements for a sample of 32 brightest cluster galaxies (BCGs) in clusters of the Representative XMM-Newton Cluster Structure Survey (REXCESS) with z = 0.06-0.18. The REXCESS clusters, chosen to study scaling relations in clusters of galaxies, have X-ray measurements of high quality. The trends of star formation and BCG colors with BCG and host properties can be investigated with this sample. The UV photometry comes from the XMM-Newton Optical Monitor, supplemented by existing archival Galaxy Evolution Explorer photometry. We detected H{alpha} and forbidden line emission in seven (22%) of these BCGs, in optical spectra obtained using the Southern Astrophysical Research Goodman spectrograph. All of these emission-line BCGs occupy clusters classified as cool cores (CCs) based on the central cooling time in the cluster core, for an emission-line incidence rate of 70% for BCGs in REXCESS CC clusters. Significant correlations between the H{alpha} equivalent widths, excess UV production in the BCG, and the presence of dense, X-ray bright intracluster gas with a short cooling time are seen, including the fact that all of the H{alpha} emitters inhabit systems with short central cooling times and high central intracluster medium densities. Estimates of the star formation rates based on H{alpha} and UV excesses are consistent with each other in these seven systems, ranging from 0.1to8 solar masses per year. The incidence of emission-line BCGs in the REXCESS sample is intermediate, somewhat lower than in other X-ray-selected samples ({approx}35%), and somewhat higher than but statistically consistent with optically selected, slightly lower redshift BCG samples ({approx}10%-15%). The UV-optical colors (UVW1 - R {approx}4.7 {+-} 0.3) of REXCESS BCGs without strong optical emission lines are consistent with those predicted from templates and observations of ellipticals dominated by old stellar populations. We see no

  18. Photometric variability of Sun-like stars in the old open cluster M67

    NASA Astrophysics Data System (ADS)

    Tobin, Ryan Wesley

    Few physical processes can affect the earth's climate on a global scale. The variability of the Sun is one such process. The Sun is known to vary by about 0.1% due to Sunspots and other surface activity. We do not yet know whether the Sun's variability is normal. Using the well-known properties of the old open cluster M67, we look for variations in Sun-like stars. In this thesis, we present the results of observation, calibration, correction and analysis of stars in M67. We focus on Sun-like stars and binary systems. We also determine the limits of observation using a small research-grade telescope. We find several known variable stars with comparable amplitudes of variability. Our precision is as high as 10 millimagnitudes, ranging 10-20 for Sun-like stars. Variability is detected as low as 20 millimagnitudes in amplitude. Our current precision, however, fails to detect solar-like variations.

  19. Evidence for temporal evolution in the M33 disc as traced by its star clusters

    NASA Astrophysics Data System (ADS)

    Beasley, Michael A.; San Roman, Izaskun; Gallart, Carme; Sarajedini, Ata; Aparicio, Antonio

    2015-08-01

    We present precision radial velocities and stellar population parameters for 77 star clusters in the Local Group galaxy M33. Our Gran Telescopio de Canarias and William Herschel Telescope observations sample both young, massive clusters and known/candidate globular clusters (GCs), spanning ages ˜106-1010 yr, and metallicities, [M/H] ˜ -1.7 to solar. The cluster system exhibits an age-metallicity relation; the youngest clusters are the most metal rich. When compared to H I data, clusters with [M/H] ˜ -1.0 and younger than ˜4 Gyr are clearly identified as a disc population. The clusters show evidence for strong time evolution in the disc radial metallicity gradient (d[M/H]dt/dR = 0.03 dex kpc-1 Gyr-1). The oldest clusters have stronger, more negative gradients than the youngest clusters in M33. The clusters also show a clear age-velocity dispersion relation. The line-of-sight velocity dispersions of the clusters increases with age similar to Milky Way open clusters and stars. The general shape of the relation is reproduced by disc heating simulations, and the similarity between the relations in M33 and the Milky Way suggests that heating by substructure and cooling of the interstellar medium both play a role in shaping this relation. We identify 12 `classical' GCs, six of which are newly identified GC candidates. The GCs are more metal rich than Milky Way halo clusters, and show weak rotation. The inner (R < 4.5 kpc) GCs exhibit a steep radial metallicity gradient (d[M/H]/dR = -0.29 ± 0.11 dex kpc-1) and an exponential-like surface density profile. We argue that these inner GCs are thick disc rather than halo objects.

  20. ON THE DISRUPTION OF STAR CLUSTERS IN A HIERARCHICAL INTERSTELLAR MEDIUM

    SciTech Connect

    Elmegreen, Bruce G.; Hunter, Deidre A. E-mail: dah@lowell.ed

    2010-03-20

    The distribution of the number of clusters as a function of mass M and age T suggests that clusters get eroded or dispersed in a regular way over time, such that the cluster number decreases inversely as an approximate power law with T within each fixed interval of M. This power law is inconsistent with standard dispersal mechanisms such as cluster evaporation and cloud collisions. In the conventional interpretation, it requires the unlikely situation where diverse mechanisms stitch together over time in a way that is independent of environment or M. Here, we consider another model in which the large-scale distribution of gas in each star-forming region plays an important role. We note that star clusters form with positional and temporal correlations in giant cloud complexes, and suggest that these complexes dominate the tidal force and collisional influence on a cluster during its first several hundred million years. Because the cloud complex density decreases regularly with position from the cluster birth site, the harassment and collision rates between the cluster and the cloud pieces decrease regularly with age as the cluster drifts. This decrease is typically a power law of the form required to explain the mass-age distribution. We reproduce this distribution for a variety of cases, including rapid disruption, slow erosion, combinations of these two, cluster-cloud collisions, cluster disruption by hierarchical disassembly, and partial cluster disruption. We also consider apparent cluster mass loss by fading below the surface brightness limit of a survey. In all cases, the observed log M-log T diagram can be reproduced under reasonable assumptions.

  1. The colour-magnitude relation of globular clusters in Centaurus and Hydra. Constraints on star cluster self-enrichment with a link to massive Milky Way globular clusters

    NASA Astrophysics Data System (ADS)

    Fensch, J.; Mieske, S.; Müller-Seidlitz, J.; Hilker, M.

    2014-07-01

    Aims: We investigate the colour-magnitude relation of metal-poor globular clusters, the so-called blue tilt, in the Hydra and Centaurus galaxy clusters and constrain the primordial conditions for star cluster self-enrichment. Methods: We analyse U,I photometry for about 2500 globular clusters in the central regions of Hydra and Centaurus, based on VLT/FORS1 data. We measure the relation between mean colour and luminosity for the blue and red subpopulation of the globular cluster samples. We convert these relations into mass-metallicity space and compare the obtained GC mass-metallicity relation with predictions from the star cluster self-enrichment model by Bailin & Harris (2009, ApJ, 695, 1082). For this we include effects of dynamical and stellar evolution and a physically well motivated primordial mass-radius scaling. Results: We obtain a mass-metallicity scaling of Z ∝ M0.27 ± 0.05 for Centaurus GCs and Z ∝ M0.40 ± 0.06 for Hydra GCs, consistent with the range of observed relations in other environments. We find that the GC mass-metallicity relation already sets in at present-day masses of a few and is well established in the luminosity range of massive MW clusters like ω Centauri. The inclusion of a primordial mass-radius scaling of star clusters significantly improves the fit of the self-enrichment model to the data. The self-enrichment model accurately reproduces the observed relations for average primordial half-light radii rh ~ 1-1.5 pc, star formation efficiencies f⋆ ~ 0.3-0.4, and pre-enrichment levels of [Fe/H] - 1.7 dex. The slightly steeper blue tilt for Hydra can be explained either by a ~30% smaller average rh at fixed f⋆ ~ 0.3, or analogously by a ~20% smaller f⋆ at fixed rh ~ 1.5 pc. Within the self-enrichment scenario, the observed blue tilt implies a correlation between GC mass and width of the stellar metallicity distribution. We find that this implied correlation matches the trend of width with GC mass measured in Galactic GCs

  2. Bar star clusters in the LMC - Formation history from UBV integrated photometry

    NASA Astrophysics Data System (ADS)

    Bica, E.; Claria, J. J.; Dottori, H.

    1992-06-01

    The sample of star clusters in the LMC Bar region with integrated UBV photometry was enlarged by approximately a factor four, totaling 129 objects. The (B-V) histogram gap between blue and red clusters disappears with this deeper sample. Age groups in terms of equivalent SWB types were derived and their spatial distribution studied. Clusters younger than t about 200 Myr are not homogeneously distributed through the bar. In particular a strong star forming event at t about 100 Myr was detected in the eastern part of the Bar, consisting of a compact grouping of seven coeval clusters around NGC 2058 and NGC 2065. Also, 11 close pairs and two trios are analyzed, and the colors indicate that only four pairs are clearly not coeval.

  3. VizieR Online Data Catalog: Milky Way global survey of star clusters. V. (Kharchenko+, 2016)

    NASA Astrophysics Data System (ADS)

    Kharchenko, N. V.; Piskunov, A. E.; Schilbach, E.; Roeser, S.; Scholz, R.-D.

    2015-11-01

    The catalogue presents integrated parameters in near-infrared (JHKs) passbands for 3208 Galactic star clusters. The integrated magnitudes are based on the most probable cluster members selected from the high-precision, homogeneous all-sky catalogue 2MAst that is constructed on the basis of catalogues PPMXL (Roeser et al., 2010, Cat. I/317) and 2MASS (Cutri et al., 2003, Cat. II/246). The integrated magnitudes are computed by adding the individual luminosities of the most secure cluster members. In order to put the computed magnitudes into a uniform and unbiased system they were corrected for the effect of unseen stars in the 2MAst. The clusters in the catalogue are sorted according to their numbers in the MWSC. (1 data file).

  4. The Mass Function of Young Star Clusters in the "Antennae" Galaxies.

    PubMed

    Zhang; Fall

    1999-12-20

    We determine the mass function of young star clusters in the merging galaxies known as the "Antennae" (NGC 4038/9) from deep images taken with the Wide Field Planetary Camera 2 on the refurbished Hubble Space Telescope. This is accomplished by means of reddening-free parameters and a comparison with stellar population synthesis tracks to estimate the intrinsic luminosity and age, and hence the mass, of each cluster. We find that the mass function of the young star clusters (with ages less, similar160 Myr) is well represented by a power law of the form psi&parl0;M&parr0;~M-2 over the range 104 less, similarM less, similar106 M middle dot in circle. This result may have important implications for our understanding of the origin of globular clusters during the early phases of galactic evolution.

  5. Social Stars: Modeling the Interactive Lives of Stars in Dense Clusters

    NASA Astrophysics Data System (ADS)

    MacLeod, Morgan

    2017-01-01

    This talk discusses computational modeling of phases of dramatic interaction that intersperse stellar lifetimes. In galactic centers stars trace dangerously wandering orbits dictated by the combined gravitational force of a central, supermassive black hole and all of the surrounding stars. During this talk, I will describe how stellar dynamics intertwines with stellar evolution and hydrodynamics to determine the properties of interactions between stars and black holes in galactic centers. These interactions can partially or completely disrupt stars through tidal forces, and they can fuel accretion-driven flares of the black hole. Disruptions of stars across the evolutionary spectrum give rise to transients with different characteristic timescales, luminosities, and wavelengths. I will focus on how the properties of these transients can reveal the demographics of black holes and the stellar populations that surround them.

  6. VARIABLE STARS IN LARGE MAGELLANIC CLOUD GLOBULAR CLUSTERS. I. NGC 1466

    SciTech Connect

    Kuehn, Charles A.; Smith, Horace A.; De Lee, Nathan; Catelan, Marcio; Pritzl, Barton J.; Borissova, Jura E-mail: smith@pa.msu.edu E-mail: mcatelan@astro.puc.cl E-mail: jura.borissova@uv.cl

    2011-10-15

    This is the first in a series of papers studying the variable stars in Large Magellanic Cloud globular clusters. The primary goal of this series is to better understand how the RR Lyrae stars in Oosterhoff-intermediate systems compare to those in Oosterhoff I/II systems. In this paper, we present the results of our new time-series BV photometric study of NGC 1466. A total of 62 variables were identified in the cluster, of which 16 are new discoveries. The variables include 30 RRab stars, 11 RRc stars, 8 RRd stars, 1 candidate RR Lyrae, 2 long-period variables, 1 potential anomalous Cepheid, and 9 variables of undetermined classification. We present photometric parameters for these variables. For the RR Lyrae stars physical properties derived from Fourier analysis of their light curves are presented. The RR Lyrae stars were used to determine a reddening-corrected distance modulus of (m - M){sub 0} = 18.43 {+-} 0.15. We discuss several different indicators of Oosterhoff type and find NGC 1466 to be an Oosterhoff-intermediate object.

  7. Star formation activity of intermediate redshift cluster galaxies out to the infall regions

    NASA Astrophysics Data System (ADS)

    Gerken, B.; Ziegler, B.; Balogh, M.; Gilbank, D.; Fritz, A.; Jäger, K.

    2004-07-01

    We present a spectroscopic analysis of two galaxy clusters at z≈0.2, out to ˜4 Mpc. The two clusters VMF73 and VMF74 as identified by \\citet{VMFJQH98} were observed with multiple object spectroscopy using MOSCA at the Calar Alto 3.5 m telescope. Both clusters lie in the ROSAT Position Sensitive Proportional Counter field R285 and were selected from the X-ray Dark Cluster Survey \\citep{GBCZ04} that provides optical V- and I-band data. VMF73 and VMF74 are located at respective redshifts of z=0.25 and z=0.18 with velocity dispersions of 671 km s-1 and 442 km s-1, respectively. Both cluster velocity dispersions are consistent with Gaussians. The spectroscopic observations reach out to ˜2.5 virial radii. Line strength measurements of the emission lines Hα and [O II]λ3727 are used to assess the star formation activity of cluster galaxies which show radial and density dependences. The mean and median of both line strength distributions as well as the fraction of star forming galaxies increase with increasing clustercentric distance and decreasing local galaxy density. Except for two galaxies with strong Hα and [O II] emission, all of the cluster galaxies are normal star forming or passive galaxies. Our results are consistent with other studies that show the truncation in star formation occurs far from the cluster centre. Table A.1 is only available in electronic from at http//www.edpsciences.org

  8. VizieR Online Data Catalog: Updated catalog of variable stars in globular clusters (Clement+ 2017)

    NASA Astrophysics Data System (ADS)

    Clement, C. M.

    2017-02-01

    This Catalogue is an update to Helen Sawyer Hogg's Third Catalogue on Variable Stars in Globular Clusters (1973, David Dunlap Observatory Publications, Volume 3, Number 6: 1973PDDO....3....6S; see Cat V/97; see also Clement+, 2001AJ....122.2587C). This catalogue is based on the individual cluster files downloaded on http://www.astro.utoronto.ca/~cclement/cat/listngc.html on the 01-Feb-2017. (7 data files).

  9. INFRARED AND ULTRAVIOLET STAR FORMATION IN BRIGHTEST CLUSTER GALAXIES IN THE ACCEPT SAMPLE

    SciTech Connect

    Hoffer, Aaron S.; Donahue, Megan; Hicks, Amalia; Barthelemy, R. S. E-mail: donahue@pa.msu.edu E-mail: ramon.s.barthelemy@wmich.edu

    2012-03-01

    We present infrared (IR) and ultraviolet (UV) photometry for a sample of brightest cluster galaxies (BCGs). The BCGs are from a heterogeneous but uniformly characterized sample, the Archive of Chandra Cluster Entropy Profile Tables (ACCEPT), of X-ray galaxy clusters from the Chandra X-ray telescope archive with published gas temperature, density, and entropy profiles. We use archival Galaxy Evolution Explorer (GALEX), Spitzer Space Telescope, and Two Micron All Sky Survey (2MASS) observations to assemble spectral energy distributions (SEDs) and colors for BCGs. We find that while the SEDs of some BCGs follow the expectation of red, dust-free old stellar populations, many exhibit signatures of recent star formation in the form of excess UV or mid-IR emission, or both. We establish a mean near-UV (NUV) to 2MASS K color of 6.59 {+-} 0.34 for quiescent BCGs. We use this mean color to quantify the UV excess associated with star formation in the active BCGs. We use both fits to a template of an evolved stellar population and library of starburst models and mid-IR star formation relations to estimate the obscured star formation rates (SFRs). We show that many of the BCGs in X-ray clusters with low central gas entropy exhibit enhanced UV (38%) and mid-IR emission (43%) from 8 to 160 {mu}m, above that expected from an old stellar population. These excesses are consistent with ongoing star formation activity in the BCG, star formation that appears to be enabled by the presence of high-density, X-ray-emitting intergalactic gas in the core of the cluster of galaxies. This hot, X-ray-emitting gas may provide the enhanced ambient pressure and some of the fuel to trigger star formation. This result is consistent with previous works that showed that BCGs in clusters with low central gas entropies host H{alpha} emission-line nebulae and radio sources, while clusters with high central gas entropy exhibit none of these features. GALEX UV and Spitzer mid-IR measurements combined

  10. Reconstructing merger timelines using star cluster age distributions: the case of MCG+08-11-002

    NASA Astrophysics Data System (ADS)

    Davies, Rebecca L.; Medling, Anne M.; U, Vivian; Max, Claire E.; Sanders, David; Kewley, Lisa J.

    2016-05-01

    We present near-infrared imaging and integral field spectroscopy of the centre of the dusty luminous infrared galaxy merger MCG+08-11-002, taken using the Near InfraRed Camera 2 (NIRC2) and the OH-Suppressing InfraRed Imaging Spectrograph (OSIRIS) on Keck II. We achieve a spatial resolution of ˜25 pc in the K band, allowing us to resolve 41 star clusters in the NIRC2 images. We calculate the ages of 22/25 star clusters within the OSIRIS field using the equivalent widths of the CO 2.3 μm absorption feature and the Br γ nebular emission line. The star cluster age distribution has a clear peak at ages ≲ 20 Myr, indicative of current starburst activity associated with the final coalescence of the progenitor galaxies. There is a possible second peak at ˜65 Myr which may be a product of the previous close passage of the galaxy nuclei. We fit single and double starburst models to the star cluster age distribution and use Monte Carlo sampling combined with two-sided Kolmogorov-Smirnov tests to calculate the probability that the observed data are drawn from each of the best-fitting distributions. There is a >90 per cent chance that the data are drawn from either a single or double starburst star formation history, but stochastic sampling prevents us from distinguishing between the two scenarios. Our analysis of MCG+08-11-002 indicates that star cluster age distributions provide valuable insights into the timelines of galaxy interactions and may therefore play an important role in the future development of precise merger stage classification systems.

  11. Surface photometry of brightest cluster galaxies and intracluster stars in ΛCDM

    NASA Astrophysics Data System (ADS)

    Cooper, A. P.; Gao, L.; Guo, Q.; Frenk, C. S.; Jenkins, A.; Springel, V.; White, S. D. M.

    2015-08-01

    We simulate the phase-space distribution of stellar mass in nine massive Λ cold dark matter galaxy clusters by applying the semi-analytic particle tagging method of Cooper et al. to the Phoenix suite of high-resolution N-body simulations (M200 ≈ 7.5-33 × 1014 M⊙). The resulting surface brightness (SB) profiles of brightest cluster galaxies (BCGs) match well to observations. On average, stars formed in galaxies accreted by the BCG account for ≳90 per cent of its total mass (the remainder is formed in situ). In circular BCG-centred apertures, the superposition of multiple debris clouds (each ≳10 per cent of the total BCG mass) from different progenitors can result in an extensive outer diffuse component, qualitatively similar to a `cD envelope'. These clouds typically originate from tidal stripping at z ≲ 1 and comprise both streams and the extended envelopes of other massive galaxies in the cluster. Stars at very low SB contribute a significant fraction of the total cluster stellar mass budget: in the central 1 Mpc2 of a z ˜ 0.15 cluster imaged at SDSS-like resolution, our fiducial model predicts 80-95 per cent of stellar mass below a SB of μV ˜ 26.5 mag arcsec-2 is associated with accreted stars in the envelope of the BCG. The ratio of BCG stellar mass (including this diffuse component) to total cluster stellar mass is ˜30 per cent.

  12. Spectral energy distributions and masses of 304 M31 old star clusters

    SciTech Connect

    Ma, Jun; Wang, Song; Wu, Zhenyu; Zhang, Tianmeng; Zou, Hu; Nie, Jun dan; Zhou, Zhiming; Zhou, Xu; Wu, Jianghua; Du, Cuihua; Yuan, Qirong

    2015-02-01

    This paper presents CCD multicolor photometry for 304 old star clusters in the nearby spiral galaxy M31, from which the photometry of 55 star clusters is first obtained. The observations were carried out as a part of the Beijing–Arizona–Taiwan–Connecticut Multicolor Sky Survey from 1995 February to 2008 March, using 15 intermediate-band