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Sample records for globular clusters induced

  1. Binaries in globular clusters

    NASA Technical Reports Server (NTRS)

    Hut, Piet; Mcmillan, Steve; Goodman, Jeremy; Mateo, Mario; Phinney, E. S.; Pryor, Carlton; Richer, Harvey B.; Verbunt, Frank; Weinberg, Martin

    1992-01-01

    Recent observations have shown that globular clusters contain a substantial number of binaries most of which are believed to be primordial. We discuss different successful optical search techniques, based on radial-velocity variables, photometric variables, and the positions of stars in the color-magnitude diagram. In addition, we review searches in other wavelengths, which have turned up low-mass X-ray binaries and more recently a variety of radio pulsars. On the theoretical side, we give an overview of the different physical mechanisms through which individual binaries evolve. We discuss the various simulation techniques which recently have been employed to study the effects of a primordial binary population, and the fascinating interplay between stellar evolution and stellar dynamics which drives globular-cluster evolution.

  2. Globular clusters with Gaia

    NASA Astrophysics Data System (ADS)

    Pancino, E.; Bellazzini, M.; Giuffrida, G.; Marinoni, S.

    2017-01-01

    The treatment of crowded fields in Gaia data will only be a reality in a few years from now. In particular, for globular clusters, only the end-of-mission data (public in 2022-2023) will have the necessary full crowding treatment and will reach sufficient quality for the faintest stars. As a consequence, the work on the deblending and decontamination pipelines is still ongoing. We describe the present status of the pipelines for different Gaia instruments, and we model the end-of-mission crowding errors on the basis of available information. We then apply the nominal post-launch Gaia performances, appropriately worsened by the estimated crowding errors, to a set of 18 simulated globular clusters with different concentration, distance, and field contamination. We conclude that there will be 103-104 stars with astrometric performances virtually untouched by crowding (contaminated by <1 mmag) in the majoritiy of clusters. The most limiting factor will be field crowding, not cluster crowding: the most contaminated clusters will only contain 10-100 clean stars. We also conclude that: (i) the systemic proper motions and parallaxes will be determined to 1% or better up to ≃15 kpc, and the nearby clusters will have radial velocities to a few km s-1 ; (ii) internal kinematics will be of unprecendented quality, cluster masses will be determined to ≃10% up to 15 kpc and beyond, and it will be possible to identify differences of a few km s-1 or less in the kinematics (if any) of cluster sub-populations up to 10 kpc and beyond; (iii) the brightest stars (V≃17 mag) will have space-quality, wide-field photometry (mmag errors), and all Gaia photometry will have 1-3% errors on the absolute photometric calibration.

  3. Globular clusters with Gaia

    NASA Astrophysics Data System (ADS)

    Pancino, E.; Bellazzini, M.; Giuffrida, G.; Marinoni, S.

    2017-05-01

    The treatment of crowded fields in Gaia data will only be a reality in a few years from now. In particular, for globular clusters, only the end-of-mission data (public in 2022-2023) will have the necessary full crowding treatment and will reach sufficient quality for the faintest stars. As a consequence, the work on the deblending and decontamination pipelines is still ongoing. We describe the present status of the pipelines for different Gaia instruments, and we model the end-of-mission crowding errors on the basis of available information. We then apply the nominal post-launch Gaia performances, appropriately worsened by the estimated crowding errors, to a set of 18 simulated globular clusters with different concentration, distance and field contamination. We conclude that there will be 103-104 stars with astrometric performances virtually untouched by crowding (contaminated by <1 mmag) in the majority of clusters. The most limiting factor will be field crowding, not cluster crowding: the most contaminated clusters will only contain 10-100 clean stars. We also conclude that (i) the systemic proper motions and parallaxes will be determined to 1 per cent or better up to ≃15 kpc, and the nearby clusters will have radial velocities to a few km s-1; (ii) internal kinematics will be of unprecedented quality, cluster masses will be determined to ≃10 per cent up to 15 kpc and beyond, and it will be possible to identify differences of a few km s-1 or less in the kinematics (if any) of cluster sub-populations up to 10 kpc and beyond; (iii) the brightest stars (V ≃ 17 mag) will have space-quality, wide-field photometry (mmag errors), and all Gaia photometry will have 1-3 per cent errors on the absolute photometric calibration.

  4. The youngest globular clusters

    NASA Astrophysics Data System (ADS)

    Beck, Sara

    2015-11-01

    It is likely that all stars are born in clusters, but most clusters are not bound and disperse. None of the many protoclusters in our Galaxy are likely to develop into long-lived bound clusters. The super star clusters (SSCs) seen in starburst galaxies are more massive and compact and have better chances of survival. The birth and early development of SSCs takes place deep in molecular clouds, and during this crucial stage the embedded clusters are invisible to optical or UV observations but are studied via the radio-infrared supernebulae (RISN) they excite. We review observations of embedded clusters and identify RISN within 10 Mpc whose exciting clusters have ≈ 106 M⊙ or more in volumes of a few pc3 and which are likely to not only survive as bound clusters, but to evolve into objects as massive and compact as Galactic globulars. These clusters are distinguished by very high star formation efficiency η, at least a factor of 10 higher than the few percent seen in the Galaxy, probably due to the violent disturbances their host galaxies have undergone. We review recent observations of the kinematics of the ionized gas in RISN showing outflows through low-density channels in the ambient molecular cloud; this may protect the cloud from feedback by the embedded H II region.

  5. Neutron stars and millisecond pulsars from accretion-induced collapse in globular clusters

    NASA Technical Reports Server (NTRS)

    Bailyn, Charles D.; Grindlay, Jonathan E.

    1990-01-01

    This paper examines the limits on the number of millisecond pulsars which could be formed in globular clusters by the generally accepted scenario (in which a neutron star is created by the supernova of an initially massive star and subsequently captures a companion to form a low-mass X-ray binary which eventually becomes a millisecond pulsar). It is found that, while the number of observed low-mass X-ray binaries can be adequately explained in this way, the reasonable assumption that the pulsar luminosity function in clusters extends below the current observational limits down to the luminosity of the faintest millisecond pulsars in the field suggests a cluster population of millisecond pulsars which is substantially larger than the standard model can produce. Alleviating this problem by postulating much shorter lifetimes for the X-ray binaries requires massive star populations sufficiently large that the mass loss resulting from their evolution would be likely to unbind the cluster. It is argued that neutron star formation in globular clusters by accretion-induced collapse of white dwarfs may resolve the discrepancy in birthrates.

  6. Dynamical evolution of globular clusters: Recent developments

    NASA Astrophysics Data System (ADS)

    Merafina, Marco

    We analyze structural parameters of the globular clusters belonging to the Milky Way system which were listed in the latest edition of the Harris Catalogue. We search for observational evidences of the effect of tidal forces induced by the Galaxy on the dynamical and thermodynamical evolution of a globular cluster. The behavior for the W0 distribution exhibited by the globular cluster population seems to be in contrast with theoretical results in literature about gravothermal instability, and suggest a new limit value smaller than the previous one.

  7. Relativistic Binaries in Globular Clusters.

    PubMed

    Benacquista, Matthew J; Downing, Jonathan M B

    2013-01-01

    Galactic globular clusters are old, dense star systems typically containing 10(4)-10(6) stars. As an old population of stars, globular clusters contain many collapsed and degenerate objects. As a dense population of stars, globular clusters are the scene of many interesting close dynamical interactions between stars. These dynamical interactions can alter the evolution of individual stars and can produce tight binary systems containing one or two compact objects. In this review, we discuss theoretical models of globular cluster evolution and binary evolution, techniques for simulating this evolution that leads to relativistic binaries, and current and possible future observational evidence for this population. Our discussion of globular cluster evolution will focus on the processes that boost the production of tight binary systems and the subsequent interaction of these binaries that can alter the properties of both bodies and can lead to exotic objects. Direct N-body integrations and Fokker-Planck simulations of the evolution of globular clusters that incorporate tidal interactions and lead to predictions of relativistic binary populations are also discussed. We discuss the current observational evidence for cataclysmic variables, millisecond pulsars, and low-mass X-ray binaries as well as possible future detection of relativistic binaries with gravitational radiation.

  8. SIZES OF GALACTIC GLOBULAR CLUSTERS

    SciTech Connect

    Van den Bergh, Sidney

    2012-02-20

    A study is made of deviations from the mean power-law relationship between the Galactocentric distances and the half-light radii of Galactic globular clusters. Surprisingly, deviations from the mean R{sub h} versus R{sub gc} relationship do not appear to correlate with cluster luminosity, cluster metallicity, or horizontal-branch morphology. Differences in orbit shape are found to contribute to the scatter in the R{sub h} versus R{sub gc} relationship of Galactic globular clusters.

  9. Secondary Globular Cluster populations

    NASA Astrophysics Data System (ADS)

    Fritze-v. Alvensleben, U.

    2004-02-01

    This study is motivated by two facts: 1. The formation of populous star cluster systems is widely observed to accompany violent star formation episodes in gas-rich galaxies as e.g. those triggered by strong interactions or merging. 2. The Globular Cluster (GC) systems of most but not all early-type galaxies show bimodal optical color distributions with fairly universal blue peaks and somewhat variable red peak colors, yet their Luminosity Functions (LFs) look like simple Gaussians with apparently universal turn-over magnitudes that are used for distance measurements and the determination of Ho. Based on a new set of evolutionary synthesis models for Simple (= single burst) Stellar Populations (SSPs) of various metallicities using the latest Padova isochrones I study the color and luminosity evolution of GC populations over the wavelength range from U through K, providing an extensive grid of models for comparison with observations. I assume the intrinsic widths of the color distributions and LFs to be constant in time at the values observed today for the Milky Way or M 31 halo GC populations. Taking the color distributions and LFs of the Milky Way or M 31 halo GC population as a reference for old metal-poor GC populations in general, I study for which combinations of age and metallicity a secondary GC population formed in some violent star formation event in the history of its parent galaxy may or may not be detected in the observed GC color distributions. I also investigate the effect of these secondary GCs on the LFs of the total GC system. Significant differences are found among the diagnostic efficiencies in various wavelength regions. In particular, we predict the NIR to be able to reveal the presence of GC subpopulations with different age - metallicity combinations that may perfectly hide within one inconspicuous optical color peak. If the entire manifold of possible age - metallicity combinations is admitted for a secondary GC population, we find several

  10. Globular cluster systems in spiral galaxies

    NASA Astrophysics Data System (ADS)

    Nantais, Julie Beth

    We have performed a comprehensive spectroscopic and photometric analysis of the M81 globular cluster system, using Hubble Space Telescope (HST) Advanced Camera for Surveys (ACS) imaging in the B, V, and I bands and 74 globular cluster spectra from Hectospec at the MMT. We have also performed a small spectroscopic study of the NGC 300 globular cluster system using the Boller & Chivens (B&C) Spectrograph on the Baade Telescope in Chile. We confirm 9 probable globular clusters in NGC 300 and 3 possible clusters with very low radial velocities. For our full NGC 300 cluster sample, plus one cluster from the literature, we find a mean [Fe/H] = --0.94 +/- 0.15; without the 3 "possible" clusters we find a mean [Fe/H] = --0.98 +/- 0.12. We identify over 200 globular cluster candidates in HST I-band imaging, and spectroscopically confirm 62 new globular clusters in M81. The M81 globular cluster system shows marginal evidence for a bimodal metallicity distribution. The mean metallicity of 107 confirmed M81 globular clusters is [Fe/H] = 1.06 +/- 0.07. The M81 globular cluster system shows significant rotation, at 108 +/- 22 km s-1. There is evidence for a metallicity gradient among the metal-poor clusters. We perform HST ACS BV I photometry and radial profile fitting on 85 spectroscopically confirmed globular clusters, 136 "good" globular cluster candidates, and 198 other star cluster candidates. The globular cluster luminosity function peaks at V0 ˜20.26. The properties of the M81 globular cluster system are very similar to those of the Milky Way and M31, suggesting a similar origin for all three galaxies. Our understanding of the origins of spiral galaxy globular cluster systems would be vastly improved by comprehensive studies of low-mass and late-type spiral galaxies, including HST I-band imaging to identify globular cluster candidates for spectroscopic confirmation.

  11. Gravitational interactions between globular and open clusters: an introduction

    NASA Astrophysics Data System (ADS)

    de la Fuente Marcos, R.; de la Fuente Marcos, C.; Reilly, D.

    2014-01-01

    Historically, it has been assumed that globular and open clusters never interact. However, recent evidence suggests that: globular clusters passing through the disk may be able to perturb giant molecular clouds (GMCs) triggering formation of open clusters and some old open clusters may be linked to accreted globulars. Here, we further explore the existence of possible dynamical connections between globular and open clusters, and realize that the most obvious link must be in the form of gravitational interactions. If open clusters are born out of GMCs, they have to move in similar orbits. If we accept that globulars can interact with GMCs, triggering star formation, it follows that globular and open clusters must also interact. Consistently, theoretical arguments as well as observational evidence, show that globular and open clusters certainly are interacting populations and their interactions are far more common than usually thought, especially for objects part of the bulge/disk. Monte Carlo calculations confirm that conclusion. Globular clusters seem capable of not only inducing formation of open clusters but, more often, their demise. Relatively frequent high speed cluster encounters or cluster harassment may also cause, on the long-term, slow erosion and tidal truncation on the globulars involved. The disputed object FSR 1767 (2MASS-GC04) may be, statistically speaking, the best example of an ongoing interaction.

  12. Featured Image: Globular Cluster Orbits

    NASA Astrophysics Data System (ADS)

    Kohler, Susanna

    2017-04-01

    This figure (click for the full view) shows the meridional galactic orbits of 12 globular clusters that orbit the Milky Way. The recent release of stellar parallax data from Gaia allowed a team of scientists at Dartmouth College to improve measurements of a number of galactic globular clusters very old clusters of stars that can either orbit within the galactic disk and bulge or more distantly in the galactic halo. In a recent publication led by Erin OMalley, the team presents their findings and combines their new measurements for the clusters with proper motions from past studies to calculate the orbits that these globulars take. These calculations show us whether the clusters reside in the galactic disk and bulge (as only NGC 104 does in the sample shown here, since its orbit is confined to 8 kpc radially and 4 kpc vertically of the galactic center), or if they are halo clusters. To learn more about the authors work, you can check out the paper below!CitationErin M. OMalley et al 2017 ApJ 838 162. doi:10.3847/1538-4357/aa6574

  13. The galactic globular cluster system

    NASA Technical Reports Server (NTRS)

    Djorgovski, S.; Meylan, G.

    1994-01-01

    We explore correlations between various properties of Galactic globular clusters, using a database on 143 objects. Our goal is identify correlations and trends which can be used to test and constrain theoretical models of cluster formation and evolution. We use a set of 13 cluster parameters, 9 of which are independently measured. Several arguments suggest that the number of clusters still missing in the obscured regions of the Galaxy is of the order of 10, and thus the selection effects are probably not severe for our sample. Known clusters follow a power-law density distribution with a slope approximately -3.5 to -4, and an apparent core with a core radius approximately 1 kpc. Clusters show a large dynamical range in many of their properties, more so for the core parameters (which are presumably more affected by dynamical evolution) than for the half-light parameters. There are no good correlations with luminosity, although more luminous clusters tend to be more concentrated. When data are binned in luminosity, several trends emerge: more luminous clusters tend to have smaller and denser cores. We interpret this as a differential survival effect, with more massive clusters surviving longer and reaching more evolved dynamical states. Cluster core parameters and concentrations also correlate with the position in the Galaxy, with clusters closer to the Galactic center or plane being more concentrated and having smaller and denser cores. These trends are more pronounced for the fainter (less massive) clusters. This is in agreement with a picture where tidal shocks form disk or bulge passages accelerate dynamical evolution of clusters. Cluster metallicities do not correlate with any other parameter, including luminosity and velocity dispersion; the only detectable trend is with the position in the Galaxy, probably reflecting Zinn's disk-halo dichotomy. This suggests that globular clusters were not self-enriched systems. Velocity dispersions show excellent correlations

  14. Globular Clusters for Faint Galaxies

    NASA Astrophysics Data System (ADS)

    Kohler, Susanna

    2017-07-01

    The origin of ultra-diffuse galaxies (UDGs) has posed a long-standing mystery for astronomers. New observations of several of these faint giants with the Hubble Space Telescope are now lending support to one theory.Faint-Galaxy MysteryHubble images of Dragonfly 44 (top) and DFX1 (bottom). The right panels show the data with greater contrast and extended objects masked. [van Dokkum et al. 2017]UDGs large, extremely faint spheroidal objects were first discovered in the Virgo galaxy cluster roughly three decades ago. Modern telescope capabilities have resulted in many more discoveries of similar faint galaxies in recent years, suggesting that they are a much more common phenomenon than we originally thought.Despite the many observations, UDGs still pose a number of unanswered questions. Chief among them: what are UDGs? Why are these objects the size of normal galaxies, yet so dim? There are two primary models that explain UDGs:UDGs were originally small galaxies, hence their low luminosity. Tidal interactions then puffed them up to the large size we observe today.UDGs are effectively failed galaxies. They formed the same way as normal galaxies of their large size, but something truncated their star formation early, preventing them from gaining the brightness that we would expect for galaxies of their size.Now a team of scientists led by Pieter van Dokkum (Yale University) has made some intriguing observations with Hubble that lend weight to one of these models.Globulars observed in 16 Coma-cluster UDGs by Hubble. The top right panel shows the galaxy identifications. The top left panel shows the derived number of globular clusters in each galaxy. [van Dokkum et al. 2017]Globulars GaloreVan Dokkum and collaborators imaged two UDGs with Hubble: Dragonfly 44 and DFX1, both located in the Coma galaxy cluster. These faint galaxies are both smooth and elongated, with no obvious irregular features, spiral arms, star-forming regions, or other indications of tidal interactions

  15. Formation of globular clusters induced by external ultraviolet radiation - II. Three-dimensional radiation hydrodynamics simulations

    NASA Astrophysics Data System (ADS)

    Abe, Makito; Umemura, Masayuki; Hasegawa, Kenji

    2016-12-01

    We explore the possibility of the formation of globular clusters (GCs) under ultraviolet (UV) background radiation. One-dimensional spherical symmetric radiation hydrodynamics (RHD) simulations by Hasegawa et al. have demonstrated that the collapse of low-mass (106-7 M⊙) gas clouds exposed to intense UV radiation can lead to the formation of compact star clusters like GCs if gas clouds contract with supersonic infall velocities. However, three-dimensional effects, such as the anisotropy of background radiation and the inhomogeneity in gas clouds, have not been studied so far. In this paper, we perform three-dimensional RHD simulations in a semicosmological context, and reconsider the formation of compact star clusters in strong UV radiation fields. As a result, we find that although anisotropic radiation fields bring an elongated shadow of neutral gas, almost spherical compact star clusters can be procreated from a `supersonic infall' cloud, since photodissociating radiation suppresses the formation of hydrogen molecules in the shadowed regions and the regions are compressed by UV heated ambient gas. The properties of resultant star clusters match those of GCs. On the other hand, in weak UV radiation fields, dark-matter-dominated star clusters with low stellar density form due to the self-shielding effect as well as the positive feedback by ionizing photons. Thus, we conclude that the `supersonic infall' under a strong UV background is a potential mechanism to form GCs.

  16. Mass Segregation in Globular Clusters

    NASA Astrophysics Data System (ADS)

    Fregeau, J. M.; Joshi, K. J.; Portegies Zwart, S. F.; Rasio, F. A.

    2002-05-01

    We present the results of a new study of mass segregation in two-component star clusters, based on a large number of numerical N-body simulations using our recently developed dynamical Monte Carlo code. Specifically, we follow the dynamical evolution of clusters containing stars with individual masses m1 as well as a tracer population of objects with individual masses m2. We consider both light tracers (μ≡m2/m1<1) and heavy tracers (μ>1) and a variety of King model initial conditions. In all of our simulations we use a realistically large number of stars for globular clusters, N=105, but we ignore the effects of binaries and stellar evolution. For heavy tracers, which could represent stellar remnants such as neutron stars or black holes in a globular cluster, we characterize in a variety of ways the tendency for these objects to concentrate in or near the cluster core. In agreement with simple theoretical arguments, we find that the characteristic time for this mass segregation process varies as 1/μ. For models with very light tracers (μ<~10-2), which could represent free-floating planets or brown dwarfs, we find the expected depletion of light objects in the cluster core but also sometimes a significant enhancement in the halo. That is, for some initial conditions, the number density of light objects in the cluster halo increases over time, in spite of the higher overall evaporation rate of lighter objects through the tidal boundary. Using these results along with a simplified initial mass function, we estimate the optical depth to gravitational microlensing by planetary mass objects or brown dwarfs in typical globular clusters. For some initial conditions, the optical depth in the halo owing to very low mass objects could be much greater than that of luminous stars. If we apply our results to M22, using the recent null detection of Sahu, Anderson, & King, we find an upper limit of ~25% at the 63% confidence level for the current mass fraction of M22 in the

  17. 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.

  18. Stellar astrophysics: The mystery of globular clusters

    NASA Astrophysics Data System (ADS)

    Nota, Antonella; Charbonnel, Corinne

    2016-01-01

    The discovery of multiple stellar populations -- formed at different times -- in several young star clusters adds to the debate on the nature and origin of such populations in globular clusters from the early Universe. See Letter p.502

  19. Where Are the Universe's Globular Clusters?

    NASA Astrophysics Data System (ADS)

    Kohler, Susanna

    2016-04-01

    Observations of globular clusters gravitationally-bound, spherical clusters of stars that orbit galaxies as satellites are critical to studies of galactic and stellar evolution. What type of galaxies host the largest total number of globular clusters in todays universe? A recent study answers this question.Total number of globular clusters vs. host galaxy luminosity for a catalog of ~400 galaxies of all types. [Harris 2016]Globular FavoritismGlobular clusters can be found in the halos of all galaxies above a critical brightness of about 107 solar luminosities (in practice, all but the smallest of dwarfs). The number of globulars a galaxy hosts is related to its luminosity: the Milky Way is host to ~150 globulars, the slightly brighterAndromeda galaxy may have several hundred globulars, and the extremelybright giant elliptical galaxy M87 likely has over ten thousand.But the number of galaxies is not evenly distributed in luminosity; tiny dwarf galaxies are extremely numerous in the universe, whereas giant ellipticals are far less common. So are most of the universes globulars found around dwarfs, simply because there are more dwarfs to host them? Or are the majority ofglobular clusters orbiting large galaxies? A scientist at McMaster University in Canada, William Harris, has done some calculations to find the answer.Finding the PeakHarris combines two components in his estimates:The Schechter function, a function that describes the relative number of galaxies per unit luminosity. This function drops off near a characteristic luminosity roughly that of our galaxy.Empirical data from ~400 galaxies that describe the average number of globulars per galaxy as a function of galaxy luminosity.Relative number of globular clusters in all galaxies at a given luminosity, for metal-poor globulars only (blue), metal-rich globulars only (red), and all globulars (black). The curves peak around the Schechter characteristic luminosity, and metal-poor globulars outnumber metal

  20. Contribution of globular clusters to halos

    NASA Astrophysics Data System (ADS)

    Bragaglia, Angela

    2017-03-01

    The contribution of massive star clusters to their hosting halo dramatically depends on their formation mechanism and their early evolution. Massive globular clusters in the Milky Way (and in other galaxies) have been shown to display peculiar chemical patterns (light-elements correlations and anti-correlations) indicative of a complex star formation, confirmed by photometric evidence (spread or split sequences). I use these chemical signatures to try to understand what is the fraction of halo stars originally born in globular clusters.

  1. Hot Subdwarfs in Globular Clusters

    NASA Astrophysics Data System (ADS)

    Moehler, S.; Heber, U.; Saffer, R.; Thejll, P.

    1995-12-01

    We will present data on sdB stars in the globular clusters M 15, M 22, and NGC 6752. While NGC 6752 has been known to harbour sdBs for quite some time already (Heber et al., 1986), it has also been the only globular cluster known to do so. Only recently, sdB candidates in M 15 (Durrell & Harris, 1993) and in M 22 (Thejll, priv. comm) have been discovered. An analysis of one of the sdBs in M 15 was presented recently (Moehler, in press), while the data on the ones in M 22 will be shown at this meeting for the first time. The physical parameters of these stars (teff and log g ) are derived from optical and IUE spectrophotometric data, intermediate resolution spectroscopy and Stromgren photometry. Knowing the distances of the clusters we can also determine masses. We want to compare the physical parameters of these stars for the different clusters to see what their evolutionary status is and how (or whether at all) it is affected by metallicity. We will also compare our findings to sdB stars found in the field of the Milky Way. In addition we want to see whether the problems encountered with the analyses of blue HB stars (Moehler et al., 1995) apply also to the sdB stars. These analyses showed the BHB stars to have significantly lower surface gravities and masses than predicted by theory. It turned out that this effect did not extend to the sdBs in NGC 6752 studied by Heber et al. (1986) which however constituted a sample too small to draw any meaningful conclusions. Durrell P.R., Harris W.E., 1993, AJ{105}{1420} Heber U., Kudritzki R.P., Caloi V., Castellani V., Danziger J., Gilmozzi R., 1986, \\aua{162}{171--179} Moehler S., Heber U., de Boer K.S., 1995, \\aua{294}{65} Moehler S., 1995, to appear in The Formation of the Galactic Halo - Inside and Out}, Proceedings of the meeting at Tucson, Oct. 9-11, 1995, ASP Conf. Ser.

  2. Modeling Black Holes in Globular Clusters

    NASA Astrophysics Data System (ADS)

    Ivanova, Natalia

    2013-04-01

    I will review the current theoretical understanding of what is the population of black holes in globular clusters, as well as challenges in their modeling. Black hole binaries are the tip of the iceberg, and our best link to observations. In a dense stellar environment, such binaries are formed via dynamical encounters. The analyses show that the formation path of black hole X-ray binaries is very different from the well-known formation channels for neutron star X-ray binaries, like binary exchanges and physical collisions. This formation path is composed of several distinct formation stages, where the most crucial one is triple-induced mass transfer.

  3. Gamma-ray Emission from Globular Clusters

    NASA Astrophysics Data System (ADS)

    Tam, Pak-Hin T.; Hui, Chung Y.; Kong, Albert K. H.

    2016-03-01

    Over the last few years, the data obtained using the Large Area Telescope (LAT) aboard the Fermi Gamma-ray Space Telescope has provided new insights on high-energy processes in globular clusters, particularly those involving compact objects such as MilliSecond Pulsars (MSPs). Gamma-ray emission in the 100 MeV to 10 GeV range has been detected from more than a dozen globular clusters in our galaxy, including 47 Tucanae and Terzan 5. Based on a sample of known gammaray globular clusters, the empirical relations between gamma-ray luminosity and properties of globular clusters such as their stellar encounter rate, metallicity, and possible optical and infrared photon energy densities, have been derived. The measured gamma-ray spectra are generally described by a power law with a cut-off at a few gigaelectronvolts. Together with the detection of pulsed γ-rays from two MSPs in two different globular clusters, such spectral signature lends support to the hypothesis that γ-rays from globular clusters represent collective curvature emission from magnetospheres of MSPs in the clusters. Alternative models, involving Inverse-Compton (IC) emission of relativistic electrons that are accelerated close to MSPs or pulsar wind nebula shocks, have also been suggested. Observations at >100 GeV by using Fermi/LAT and atmospheric Cherenkov telescopes such as H.E.S.S.-II, MAGIC-II, VERITAS, and CTA will help to settle some questions unanswered by current data.

  4. Globular Cluster Contributions to the Galactic Halo

    NASA Astrophysics Data System (ADS)

    Martell, Sarah; Grebel, Eva; Lai, David

    2010-08-01

    The goal of this project is to confirm chemically that globular clusters are the source of as much as half the population of the Galactic halo. Using moderate-resolution spectroscopy from the SEGUE survey, we have identified a previously unknown population of halo field giants with distinctly strong CN features. CN variations are typically only observed in globular clusters, so these stars are interpreted as immigrants to the halo that originally formed in globular clusters. In one night of Keck/HIRES time, we will obtain high-quality, high- resolution spectra for five such stars, and determine abundances of O, Na, Mg, Al, alpha, iron-peak and neutron-capture elements. With this information we can state clearly whether these unusual CN-strong halo stars carry the full abundance pattern seen in CN-strong globular cluster stars, with depleted C, O, and Mg and enhanced N, Na, and Al. This type of coarse ``chemical tagging'' will allow a clearer division of the Galactic halo into contributions from globular clusters and from dwarf galaxies, and will place constraints on theoretical models of globular cluster formation and evolution.

  5. Stellar black holes in globular clusters

    NASA Technical Reports Server (NTRS)

    Kulkarni, S. R.; Hut, Piet; Mcmillan, Steve

    1993-01-01

    The recent discovery of large populations of millisec pulsars associated with neutron stars in globular clusters indicates that several hundred stellar black holes of about 10 solar masses each can form within a typical cluster. While, in clusters of high central density, the rapid dynamical evolution of the black-hole population leads to an ejection of nearly all holes on a short timescale, systems of intermediate density may involve a normal star's capture by one of the surviving holes to form a low-mass X-ray binary. One or more such binaries may be found in the globular clusters surrounding our galaxy.

  6. Stellar black holes in globular clusters

    NASA Technical Reports Server (NTRS)

    Kulkarni, S. R.; Hut, Piet; Mcmillan, Steve

    1993-01-01

    The recent discovery of large populations of millisec pulsars associated with neutron stars in globular clusters indicates that several hundred stellar black holes of about 10 solar masses each can form within a typical cluster. While, in clusters of high central density, the rapid dynamical evolution of the black-hole population leads to an ejection of nearly all holes on a short timescale, systems of intermediate density may involve a normal star's capture by one of the surviving holes to form a low-mass X-ray binary. One or more such binaries may be found in the globular clusters surrounding our galaxy.

  7. Globular cluster X-ray sources

    NASA Astrophysics Data System (ADS)

    Pooley, D.

    We know from observations that globular clusters are very efficient catalysts in forming unusual binary systems, such as low-mass X-ray binaries (LMXBs), cataclysmic variables (CVs), and millisecond pulsars (MSPs), with formation rates per unit mass exceeding those in the Galactic disk by orders of magnitude. The high stellar densities in globular clusters trigger various dynamical interactions: exchange encounters, direct collisions, destruction of binaries, and tidal capture. This binary population is, in turn, critical to the stabilization of globular clusters against gravitational collapse; the long-term stability of a cluster is thought to depend on tapping into the gravitational binding energy of such close binaries. I will present an overview of the current state of globular cluster X-ray observations, as well as our work on deep Chandra observations of M4, where we reach some of the lowest X-ray luminosities in any globular cluster (comparable to the deep observations of 47 Tuc and NGC 6397). One of M4 X-ray sources previously classified as a white dwarf binary is likely a neutron star binary, and another X-ray source is a sub-subgiant, the nature of which is still unclear. skip=3pt

  8. 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.

  9. Millisecond radio pulsars in globular clusters

    NASA Astrophysics Data System (ADS)

    Verbunt, Frank; Lewin, Walter H. G.; van Paradijs, Jan

    1989-04-01

    It is shown that the number of millisecond radio pulsars, in globular clusters, should be larger than 100, applying the standard scenario that all the pulsars descend from low-mass X-ray binaries. Moreover, most of the pulsars are located in a small number of clusters. The prediction that Teran 5 and Liller 1 contain at least about a dozen millisecond radio pulsars each is made. The observations of millisecond radio pulsars in globular clusters to date, in particular the discovery of two millisecond radio pulsars in 47 Tuc, are in agreement with the standard scenario, in which the neutron star is spun up during the mass transfer phase.

  10. Millisecond radio pulsars in globular clusters

    NASA Astrophysics Data System (ADS)

    Verbunt, Frank; Lewin, Walter H. G.; van Paradijs, Jan

    1989-11-01

    It is shown that the number of millisecond radio pulsars, in globular clusters, should be larger than 100, applying the standard scenario that all the pulsars descend from low-mass X-ray binaries. Moreover, most of the pulsars are located in a small number of clusters. The prediction that Teran 5 and Liller 1 contain at least about a dozen millisecond radio pulsars each is made. The observations of millisecond radio pulsars in globular clusters to date, in particular the discovery of two millisecond radio pulsars in 47 Tuc, are in agreement with the standard scenario, in which the neutron star is spun up during the mass transfer phase.

  11. Millisecond radio pulsars in globular clusters

    NASA Technical Reports Server (NTRS)

    Verbunt, Frank; Lewin, Walter H. G.; Vanparadijs, Jan

    1989-01-01

    It is shown that the number of millisecond radio pulsars, in globular clusters, should be larger than 100, applying the standard scenario that all the pulsars descend from low-mass X-ray binaries. Moreover, most of the pulsars are located in a small number of clusters. The prediction that Teran 5 and Liller 1 contain at least about a dozen millisecond radio pulsars each is made. The observations of millisecond radio pulsars in globular clusters to date, in particular the discovery of two millisecond radio pulsars in 47 Tuc, are in agreement with the standard scenario, in which the neutron star is spun up during the mass transfer phase.

  12. Large scale structure of the globular cluster population in Coma

    NASA Astrophysics Data System (ADS)

    Gagliano, Alexander T.; O'Neill, Conor; Madrid, Juan P.

    2016-01-01

    A search for globular cluster candidates in the Coma Cluster was carried out using Hubble Space Telescope data taken with the Advanced Camera for Surveys. We combine different observing programs including the Coma Treasury Survey in order to obtain the large scale distribution of globular clusters in Coma. Globular cluster candidates were selected through careful morphological inspection and a detailed analysis of their magnitude and colors in the two available wavebands, F475W (Sloan g) and F814W (I). Color Magnitude Diagrams, radial density plots and density maps were then created to characterize the globular cluster population in Coma. Preliminary results show the structure of the intergalactic globular cluster system throughout Coma, among the largest globular clusters catalogues to date. The spatial distribution of globular clusters shows clear overdensities, or bridges, between Coma galaxies. It also becomes evident that galaxies of similar luminosity have vastly different numbers of associated globular clusters.

  13. Variable stars in the VVV globular clusters

    NASA Astrophysics Data System (ADS)

    Alonso-García, Javier; Catelan, Márcio; Ramos, Rodrigo Contreras; Dékány, István; Minniti, Dante

    2017-09-01

    The VVV survey observed some of the most crowded and most obscured regions in the inner MilkyWay during the last years. A significant sample of the less known globular clusters in our galaxy lie there. Combining the high-resolution, wide-field, nearinfrared capabilities of the survey camera, the use of 5 different filters, and multi-epoch observations, we are able to overcome many of the previous challenges that prevented a proper study of these objects. Particularly, the identification of the RR Lyrae stars in these globular clusters is proving to be a fundamental tool to establish accurately their distances and reddenings, and to infer information about the Oosterhoff dichotomy that Galactic globular clusters seem to follow.

  14. Globular Cluster Messier 2 in Aquarius

    NASA Technical Reports Server (NTRS)

    2003-01-01

    This image of the Globular cluster Messier 2 (M2) was taken by Galaxy Evolution Explorer on August 20, 2003. This image is a small section of a single All Sky Imaging Survey exposure of only 129 seconds in the constellation Aquarius. This picture is a combination of Galaxy Evolution Explorer images taken with the far ultraviolet (colored blue) and near ultraviolet detectors (colored red). Globular clusters are gravitationally bound systems of hundreds of thousands of stars that orbit in the halos of galaxies. The globular clusters in out Milky Way galaxy contain some of the oldest stars known. M2 lies 33,000 light years from our Sun with stars distributed in a spherical system with a radius of approximately 100 light years.

  15. Globular Cluster Messier 2 in Aquarius

    NASA Image and Video Library

    2003-12-11

    This image of the Globular cluster Messier 2 (M2) was taken by Galaxy Evolution Explorer on August 20, 2003. This image is a small section of a single All Sky Imaging Survey exposure of only 129 seconds in the constellation Aquarius. This picture is a combination of Galaxy Evolution Explorer images taken with the far ultraviolet (colored blue) and near ultraviolet detectors (colored red). Globular clusters are gravitationally bound systems of hundreds of thousands of stars that orbit in the halos of galaxies. The globular clusters in out Milky Way galaxy contain some of the oldest stars known. M2 lies 33,000 light years from our Sun with stars distributed in a spherical system with a radius of approximately 100 light years. http://photojournal.jpl.nasa.gov/catalog/PIA04926

  16. Pixel lensing observations towards globular clusters

    NASA Astrophysics Data System (ADS)

    Cardone, V. F.; Cantiello, M.

    2003-07-01

    It has been suggested that a monitoring program employing the pixel lensing method to search for microlensing events towards galactic globular clusters may increase the statistics and discriminate among different halo models. Stimulated by this proposal, we evaluate an upper limit to the pixel lensing event rate for such a survey. Four different dark halo models have been considered changing both the flattening and the slope of the mass density profile. The lens mass function has been modelled as a homogenous power - law for mu in (mul, muu) and both the mass limits and the slope of the mass function have been varied to investigate their effect on the rate. The target globular clusters have been selected in order to minimize the disk contribution to the event rate. We find that a pixel lensing survey towards globular clusters is unable to discriminate among different halo models since the number of detectable events is too small to allow any reliable statistical analysis.

  17. The self-enrichment of globular clusters

    SciTech Connect

    Morgan, S.; Lake, G.

    1989-04-01

    It is shown that protoglobular clusters of primordial gas can confine the supernovae needed to enrich themselves. The required protocluster cloud masses and structural parameters are the same as those currently observed for the clusters. Two causal scenarios for star formation are examined to calculate the initial enrichment of primordial clouds. In the 'Christmas tree' scheme, the maximum final (Fe/H) is about 0.1. Since the time scale for formation and evolution of massive stars at the center of a cluster is nearly an order of magnitude less than the collapse time of the cluster, every globular cluster may have to survive a supernova detonation. If this is the case, the minimum mass of a globular cluster is about 10 to the 4.6th solar mass. 24 refs.

  18. Chemical Abundances of Giants in Globular Clusters

    NASA Astrophysics Data System (ADS)

    Gratton, Raffaele G.; Bragaglia, Angela; Carretta, Eugenio; D'Orazi, Valentina; Lucatello, Sara

    A large fraction of stars form in clusters. According to a widespread paradigma, stellar clusters are prototypes of single stellar populations. According to this concept, they formed on a very short time scale, and all their stars share the same chemical composition. Recently it has been understood that massive stellar clusters (the globular clusters) rather host various stellar populations, characterized by different chemical composition: these stellar populations have also slightly different ages, stars of the second generations being formed from the ejecta of part of those of an earlier one. Furthermore, it is becoming clear that the efficiency of the process is quite low: many more stars formed within this process than currently present in the clusters. This implies that a significant, perhaps even dominant fraction of the ancient population of galaxies formed within the episodes that lead to formation the globular clusters.

  19. The self-enrichment of globular clusters

    NASA Astrophysics Data System (ADS)

    Morgan, Siobahn; Lake, George

    1989-04-01

    It is shown that protoglobular clusters of primordial gas can confine the supernovae needed to enrich themselves. The required protocluster cloud masses and structural parameters are the same as those currently observed for the clusters. Two causal scenarios for star formation are examined to calculate the initial enrichment of primordial clouds. In the 'Christmas tree' scheme, the maximum final (Fe/H) is about 0.1. Since the time scale for formation and evolution of massive stars at the center of a cluster is nearly an order of magnitude less than the collapse time of the cluster, every globular cluster may have to survive a suprernova detonation. If this is the case, the minimum mass of a globular cluster is about 10 to the 4.6th solar mass.

  20. The fundamental plane correlations for globular clusters

    NASA Technical Reports Server (NTRS)

    Djorgovski, S.

    1995-01-01

    In the parameter space whose axes include a radius (core, or half-light), a surface brightness (central, or average within the half-light radius), and the central projected velocity dispersion, globular clusters lie on a two-dimensional surface (a plane, if the logarithmic quantities are used). This is analogous to the 'fundamental plane' of elliptical galaxies. The implied bivariate correlations are the best now known for globular clusters. The derived scaling laws for the core properties imply that cluster cores are fully virialized, homologous systems, with a constant (M/L) ratio. The corresponding scaling laws on the half-light scale are differrent, but are nearly identical to those derived from the 'fundamental plane' of ellipticals. This may be due to the range of cluster concentrations, which are correlated with other parameters. A similar explanation for elliptical galaxies may be viable. These correlations provide new empirical constraints for models of globular cluster formation and evolution, and may also be usable as rough distance-indicator relations for globular clusters.

  1. The fundamental plane correlations for globular clusters

    NASA Technical Reports Server (NTRS)

    Djorgovski, S.

    1995-01-01

    In the parameter space whose axes include a radius (core, or half-light), a surface brightness (central, or average within the half-light radius), and the central projected velocity dispersion, globular clusters lie on a two-dimensional surface (a plane, if the logarithmic quantities are used). This is analogous to the 'fundamental plane' of elliptical galaxies. The implied bivariate correlations are the best now known for globular clusters. The derived scaling laws for the core properties imply that cluster cores are fully virialized, homologous systems, with a constant (M/L) ratio. The corresponding scaling laws on the half-light scale are differrent, but are nearly identical to those derived from the 'fundamental plane' of ellipticals. This may be due to the range of cluster concentrations, which are correlated with other parameters. A similar explanation for elliptical galaxies may be viable. These correlations provide new empirical constraints for models of globular cluster formation and evolution, and may also be usable as rough distance-indicator relations for globular clusters.

  2. A black hole in a globular cluster.

    PubMed

    Maccarone, Thomas J; Kundu, Arunav; Zepf, Stephen E; Rhode, Katherine L

    2007-01-11

    Globular star clusters contain thousands to millions of old stars packed within a region only tens of light years across. Their high stellar densities make it very probable that their member stars will interact or collide. There has accordingly been considerable debate about whether black holes should exist in these star clusters. Some theoretical work suggests that dynamical processes in the densest inner regions of globular clusters may lead to the formation of black holes of approximately 1,000 solar masses. Other numerical simulations instead predict that stellar interactions will eject most or all of the black holes that form in globular clusters. Here we report the X-ray signature of an accreting black hole in a globular cluster associated with the giant elliptical galaxy NGC 4472 (in the Virgo cluster). This object has an X-ray luminosity of about 4 x 10(39) erg s(-1), which rules out any object other than a black hole in such an old stellar population. The X-ray luminosity varies by a factor of seven in a few hours, which excludes the possibility that the object is several neutron stars superposed.

  3. Globular cluster x-ray sources.

    PubMed

    Pooley, David

    2010-04-20

    Globular clusters and x-ray astronomy have a long and fruitful history. Uhuru and OSO-7 revealed highly luminous (> 10(36) ergs(-1)) x-ray sources in globular clusters, and Einstein and ROSAT revealed a larger population of low-luminosity (< 10(33) ergs(-1)) x-ray sources. It was realized early on that the high-luminosity sources were low-mass x-ray binaries in outburst and that they were orders of magnitude more abundant per unit mass in globular clusters than in the rest of the galaxy. However, the low-luminosity sources proved difficult to classify. Many ideas were put forth--low-mass x-ray binaries in quiescence (qLMXBs), cataclysmic variables (CVs), active main-sequence binaries (ABs), and millisecond pulsars (MSPs)--but secure identifications were scarce. In ROSAT observations of 55 clusters, about 25 low-luminosity sources were found. Chandra has now observed over 80 Galactic globular clusters, and these observations have revealed over 1,500 x-ray sources. The superb angular resolution has allowed for many counterpart identifications, providing clues to the nature of this population. It is a heterogeneous mix of qLMXBs, CVs, ABs, and MSPs, and it has been shown that the qLMXBs and CVs are both, in part, overabundant like the luminous LMXBs. The number of x-ray sources in a cluster correlates very well with its encounter frequency. This points to dynamical formation scenarios for the x-ray sources and shows them to be excellent tracers of the complicated internal dynamics. The relation between the encounter frequency and the number of x-ray sources has been used to suggest that we have misunderstood the dynamical states of globular clusters.

  4. Globular cluster x-ray sources

    PubMed Central

    Pooley, David

    2010-01-01

    Globular clusters and x-ray astronomy have a long and fruitful history. Uhuru and OSO-7 revealed highly luminous (> 1036 ergs-1) x-ray sources in globular clusters, and Einstein and ROSAT revealed a larger population of low-luminosity (< 1033 ergs-1) x-ray sources. It was realized early on that the high-luminosity sources were low-mass x-ray binaries in outburst and that they were orders of magnitude more abundant per unit mass in globular clusters than in the rest of the galaxy. However, the low-luminosity sources proved difficult to classify. Many ideas were put forth—low-mass x-ray binaries in quiescence (qLMXBs), cataclysmic variables (CVs), active main-sequence binaries (ABs), and millisecond pulsars (MSPs)—but secure identifications were scarce. In ROSAT observations of 55 clusters, about 25 low-luminosity sources were found. Chandra has now observed over 80 Galactic globular clusters, and these observations have revealed over 1,500 x-ray sources. The superb angular resolution has allowed for many counterpart identifications, providing clues to the nature of this population. It is a heterogeneous mix of qLMXBs, CVs, ABs, and MSPs, and it has been shown that the qLMXBs and CVs are both, in part, overabundant like the luminous LMXBs. The number of x-ray sources in a cluster correlates very well with its encounter frequency. This points to dynamical formation scenarios for the x-ray sources and shows them to be excellent tracers of the complicated internal dynamics. The relation between the encounter frequency and the number of x-ray sources has been used to suggest that we have misunderstood the dynamical states of globular clusters. PMID:20404204

  5. STELLAR ENCOUNTER RATE IN GALACTIC GLOBULAR CLUSTERS

    SciTech Connect

    Bahramian, Arash; Heinke, Craig O.; Sivakoff, Gregory R.; Gladstone, Jeanette C.

    2013-04-01

    The high stellar densities in the cores of globular clusters cause significant stellar interactions. These stellar interactions can produce close binary mass-transferring systems involving compact objects and their progeny, such as X-ray binaries and radio millisecond pulsars. Comparing the numbers of these systems and interaction rates in different clusters drives our understanding of how cluster parameters affect the production of close binaries. In this paper we estimate stellar encounter rates ({Gamma}) for 124 Galactic globular clusters based on observational data as opposed to the methods previously employed, which assumed 'King-model' profiles for all clusters. By deprojecting cluster surface brightness profiles to estimate luminosity density profiles, we treat 'King-model' and 'core-collapsed' clusters in the same way. In addition, we use Monte Carlo simulations to investigate the effects of uncertainties in various observational parameters (distance, reddening, surface brightness) on {Gamma}, producing the first catalog of globular cluster stellar encounter rates with estimated errors. Comparing our results with published observations of likely products of stellar interactions (numbers of X-ray binaries, numbers of radio millisecond pulsars, and {gamma}-ray luminosity) we find both clear correlations and some differences with published results.

  6. RR Lyrae Variables in Galactic Globular Clusters

    NASA Astrophysics Data System (ADS)

    Catelan, M.; Contreras, R.; Salinas, R.; Escobar, M. E.; Smith, H. A.; De Lee, N.; Pritzl, B. J.; Borissova, J.

    2004-12-01

    RR Lyrae variables are the cornerstone of the Population II distance scale, and yet our knowledge of the RR Lyrae variable star content in Galactic globular clusters is now known to be surprisingly incomplete. In the present paper, we present our new results in this area. Highlights of our work includes: i) The discovery of a vast number of variable stars in M62 (NGC 6266), making it one of the three most RR Lyrae-rich globular clusters known, and also placing it as Oosterhoff type I in spite of a blue horizontal branch morphology; ii) The determination of light curves and Oosterhoff types for globular clusters associated with the Sagittarius dSph galaxy, including NGC 5634, Arp 2, and Terzan 8; iii) A reassessment of the variable star content in the moderately metal-rich globular clusters M69 and NGC 6304; iv) The first theoretical calibration of the RR Lyrae period-luminosity-metallicity relation in I, J, and H, as well as an updated calibration of the K-band relation---along with comparisons against the empirical data, particularly in I. This project was supported in part by Proyecto Fondecyt Regular 1030954.

  7. Tidal Stripping of Globular Clusters in a Simulated Galaxy Cluster

    NASA Astrophysics Data System (ADS)

    Ramos, F.; Coenda, V.; Muriel, H.; Abadi, M.

    2015-06-01

    Using a cosmological N-body numerical simulation of the formation of a galaxy-cluster-sized halo, we analyze the temporal evolution of its globular cluster population. We follow the dynamical evolution of 38 galactic dark matter halos orbiting in a galaxy cluster that at redshift z = 0 has a virial mass of 1.71 × 1014 M⊙ h-1. In order to mimic both “blue” and “red” populations of globular clusters, for each galactic halo we select two different sets of particles at high redshift (z ≈ 1), constrained by the condition that, at redshift z = 0, their average radial density profiles are similar to the observed profiles. As expected, the general galaxy cluster tidal field removes a significant fraction of the globular cluster populations to feed the intracluster population. On average, halos lost approximately 16% and 29% of their initial red and blue globular cluster populations, respectively. Our results suggest that these fractions strongly depend on the orbital trajectory of the galactic halo, specifically on the number of orbits and on the minimum pericentric distance to the galaxy cluster center that the halo has had. At a given time, these fractions also depend on the current clustercentric distance, just as observations show that the specific frequency of globular clusters SN depends on their clustercentric distance.

  8. TIDAL STRIPPING OF GLOBULAR CLUSTERS IN A SIMULATED GALAXY CLUSTER

    SciTech Connect

    Ramos, F.; Coenda, V.; Muriel, H.; Abadi, M.

    2015-06-20

    Using a cosmological N-body numerical simulation of the formation of a galaxy-cluster-sized halo, we analyze the temporal evolution of its globular cluster population. We follow the dynamical evolution of 38 galactic dark matter halos orbiting in a galaxy cluster that at redshift z = 0 has a virial mass of 1.71 × 10{sup 14} M{sub ⊙} h{sup −1}. In order to mimic both “blue” and “red” populations of globular clusters, for each galactic halo we select two different sets of particles at high redshift (z ≈ 1), constrained by the condition that, at redshift z = 0, their average radial density profiles are similar to the observed profiles. As expected, the general galaxy cluster tidal field removes a significant fraction of the globular cluster populations to feed the intracluster population. On average, halos lost approximately 16% and 29% of their initial red and blue globular cluster populations, respectively. Our results suggest that these fractions strongly depend on the orbital trajectory of the galactic halo, specifically on the number of orbits and on the minimum pericentric distance to the galaxy cluster center that the halo has had. At a given time, these fractions also depend on the current clustercentric distance, just as observations show that the specific frequency of globular clusters S{sub N} depends on their clustercentric distance.

  9. Formation of globular clusters with multiple populations

    NASA Astrophysics Data System (ADS)

    Decressin, T.

    2017-03-01

    Spectroscopic and photometric evidences have led to a complete revision of our understanding of globular clusters with the discovery of multiple stellar populations which differ chemically. Whereas some stars have a chemical composition similar to fields stars, others show large star-to-star variations in light elements (Li to Al) while their composition in iron and heavy elements stay constant. This peculiar chemical pattern can be explained by self-pollution of the intracluster gas occurring in the early evolution of clusters. Here the possible impact from a first generation of fast rotating stars to the early evolution of globular clusters is presented. The high rotation velocity will allow the stars to rotate at the break-up velocity and release matter enrich in H-burning which in turn will produce new stars with a chemical composition in agreement with observations. The massive stars have also an important role to clear the cluster from the remaining gas left after the star formation episodes. If the gas expulsion is fast enough, the strong change in the potential well will lead to the loss of stars occupying the outer part of the cluster. As second generation stars are preferentially born in the cluster centre, the ratio of second to first generation stars will increase over time to match the present ratio determined by observations. Considerations on the properties of low-mass stars still present in globular clusters will also be presented.

  10. Primordial black holes in globular clusters

    NASA Technical Reports Server (NTRS)

    Sigurdsson, Steinn; Hernquist, Lars

    1993-01-01

    It has recently been recognized that significant numbers of medium-mass back holes (of order 10 solar masses) should form in globular clusters during the early stages of their evolution. Here we explore the dynamical and observational consequences of the presence of such a primordial black-hole population in a globular cluster. The holes initially segregate to the cluster cores, where they form binary and multiple black-hole systems. The subsequent dynamical evolution of the black-hole population ejects most of the holes on a relatively short timescale: a typical cluster will retain between zero and four black holes in its core, and possibly a few black holes in its halo. The presence of binary, triple, and quadruple black-hole systems in cluster cores will disrupt main-sequence and giant stellar binaries; this may account for the observed anomalies in the distribution of binaries in globular clusters. Furthermore, tidal interactions between a multiple black-hole system and a red giant star can remove much of the red giant's stellar envelope, which may explain the puzzling absence of larger red giants in the cores of some very dense clusters.

  11. Modelling the Milky Way's globular cluster system

    NASA Astrophysics Data System (ADS)

    Binney, James; Wong, Leong Khim

    2017-05-01

    We construct a model for the Galactic globular cluster system based on a realistic gravitational potential and a distribution function (DF) analytic in the action integrals. The DF comprises disc and halo components whose functional forms resemble those recently used to describe the stellar discs and stellar halo. We determine the posterior distribution of our model parameters using a Bayesian approach. This gives us an understanding of how well the globular cluster data constrain our model. The favoured parameter values of the disc and halo DFs are similar to values previously obtained from fits to the stellar disc and halo, although the cluster halo system shows clearer rotation than does the stellar halo. Our model reproduces the generic features of the globular cluster system, namely the density profile, the mean rotation velocity and the fraction of metal-rich clusters. However, the data indicate either incompatibility between catalogued cluster distances and current estimates of distance to the Galactic Centre, or failure to identify clusters behind the bulge. As the data for our Galaxy's components increase in volume and precision over the next few years, it will be rewarding to revisit the present analysis.

  12. Modelling the Milky Way's globular cluster system

    NASA Astrophysics Data System (ADS)

    Binney, James; Wong, Leong Khim

    2017-01-01

    We construct a model for the Galactic globular cluster system based on a realistic gravitational potential and a distribution function (DF) analytic in the action integrals. The DF comprises disc and halo components whose functional forms resemble those recently used to describe the stellar discs and stellar halo. We determine the posterior distribution of our model parameters using a Bayesian approach. This gives us an understanding of how well the globular cluster data constrain our model. The favoured parameter values of the disc and halo DFs are similar to values previously obtained from fits to the stellar disc and halo, although the cluster halo system shows clearer rotation than does the stellar halo. Our model reproduces the generic features of the globular cluster system, namely the density profile, the mean rotation velocity and the fraction of metal-rich clusters. However, the data indicate either incompatibility between catalogued cluster distances and current estimates of distance to the Galactic Centre, or failure to identify clusters behind the bulge. As the data for our Galaxy's components increase in volume and precision over the next few years, it will be rewarding to revisit the present analysis.

  13. Primordial black holes in globular clusters

    NASA Technical Reports Server (NTRS)

    Sigurdsson, Steinn; Hernquist, Lars

    1993-01-01

    It has recently been recognized that significant numbers of medium-mass back holes (of order 10 solar masses) should form in globular clusters during the early stages of their evolution. Here we explore the dynamical and observational consequences of the presence of such a primordial black-hole population in a globular cluster. The holes initially segregate to the cluster cores, where they form binary and multiple black-hole systems. The subsequent dynamical evolution of the black-hole population ejects most of the holes on a relatively short timescale: a typical cluster will retain between zero and four black holes in its core, and possibly a few black holes in its halo. The presence of binary, triple, and quadruple black-hole systems in cluster cores will disrupt main-sequence and giant stellar binaries; this may account for the observed anomalies in the distribution of binaries in globular clusters. Furthermore, tidal interactions between a multiple black-hole system and a red giant star can remove much of the red giant's stellar envelope, which may explain the puzzling absence of larger red giants in the cores of some very dense clusters.

  14. REGION OF GLOBULAR CLUSTER NGC 6397

    NASA Technical Reports Server (NTRS)

    2002-01-01

    Right A NASA Hubble Space Telescope image of a small region (1.4 light-years across) in the globular star cluster NGC 6397 shows far fewer stars than would be expected in faint red dwarf stars were abundant. 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. This observation shows the surprising cutoff point below which nature apparently doesn't make many stars smaller that 1/5 the mass of our Sun. If there were lower mass stars in the cluster, then the image would contain an estimated 500 stars. This observation provides new insights into star formation in our Galaxy. Left A ground-based sky survey photograph of the globular cluster NGC 6397, one of the nearest and densest agglomerations of stars to Earth. The cluster is located 7,200 light-years away in the southern constellation Ara, and is one of 150 such objects which orbit our Milky Way Galaxy. Globular clusters are ideal laboratories for studying the formation and evolution of stars. This visible light picture was taken on March 3, 1994 with the Wide Field Planetary Camera 2, as part of the HST parallel observing program. Credit: F. Paresce, ST ScI and ESA and NASA

  15. Globular cluster systems as clues to galaxy evolution

    NASA Technical Reports Server (NTRS)

    Zepf, Stephen E.; Ashman, Keith M.

    1993-01-01

    We investigate the properties of systems of globular clusters in light of the hypothesis that galaxy mergers play a major role in galaxy evolution. In a previous paper, we presented a model in which the formation of globular clusters occurs during galaxy interactions and mergers. We discussed several predictions of the model, including the existence of young globular clusters in currently merging galaxies and the presence of two or more metallicity peaks in the globular clusters systems of normal elliptical galaxies. Here, we present recent observational evidence which supports both of these predictions and suggests that mergers may have a significant influence on the formation and evolution of galaxies and their globular clusters.

  16. HUBBLE SPIES GLOBULAR CLUSTER IN NEIGHBORING GALAXY

    NASA Technical Reports Server (NTRS)

    2002-01-01

    Hubble Space Telescope has captured a view of a globular cluster called G1, a large, bright ball of light in the center of the photograph consisting of at least 300,000 old stars. G1, also known as Mayall II, orbits the Andromeda galaxy (M31), the nearest major spiral galaxy to our Milky Way. Located 130,000 light-years from Andromeda's nucleus, G1 is the brightest globular cluster in the Local Group of galaxies. The Local Group consists of about 20 nearby galaxies, including the Milky Way. The crisp image is comparable to ground-based telescope views of similar clusters orbiting the Milky Way. The Andromeda cluster, however, is nearly 100 times farther away. A glimpse into the cluster's finer details allow astronomers to see its fainter helium-burning stars whose temperatures and brightnesses show that this cluster in Andromeda and the oldest Milky Way clusters have approximately the same age. These clusters probably were formed shortly after the beginning of the universe, providing astronomers with a record of the earliest era of galaxy formation. During the next two years, astronomers will use Hubble to study about 20 more globular clusters in Andromeda. The color picture was assembled from separate images taken in visible and near-infrared wavelengths taken in July of 1994. CREDIT: Michael Rich, Kenneth Mighell, and James D. Neill (Columbia University), and Wendy Freedman (Carnegie Observatories), and NASA Image files in GIF and JPEG format and captions may be accessed on Internet via anonymous ftp from oposite.stsci.edu in /pubinfo.

  17. HUBBLE SPIES GLOBULAR CLUSTER IN NEIGHBORING GALAXY

    NASA Technical Reports Server (NTRS)

    2002-01-01

    Hubble Space Telescope has captured a view of a globular cluster called G1, a large, bright ball of light in the center of the photograph consisting of at least 300,000 old stars. G1, also known as Mayall II, orbits the Andromeda galaxy (M31), the nearest major spiral galaxy to our Milky Way. Located 130,000 light-years from Andromeda's nucleus, G1 is the brightest globular cluster in the Local Group of galaxies. The Local Group consists of about 20 nearby galaxies, including the Milky Way. The crisp image is comparable to ground-based telescope views of similar clusters orbiting the Milky Way. The Andromeda cluster, however, is nearly 100 times farther away. A glimpse into the cluster's finer details allow astronomers to see its fainter helium-burning stars whose temperatures and brightnesses show that this cluster in Andromeda and the oldest Milky Way clusters have approximately the same age. These clusters probably were formed shortly after the beginning of the universe, providing astronomers with a record of the earliest era of galaxy formation. During the next two years, astronomers will use Hubble to study about 20 more globular clusters in Andromeda. The color picture was assembled from separate images taken in visible and near-infrared wavelengths taken in July of 1994. CREDIT: Michael Rich, Kenneth Mighell, and James D. Neill (Columbia University), and Wendy Freedman (Carnegie Observatories), and NASA Image files in GIF and JPEG format and captions may be accessed on Internet via anonymous ftp from oposite.stsci.edu in /pubinfo.

  18. Possible systematic decreases in the age of globular clusters

    SciTech Connect

    Shi, X.; Schramm, D. N.; Dearborn, D. S.P.; Truran, J. W.

    1994-03-01

    The ages of globular clusters inferred from observations depends sensitively on assumptions like the initial helium abundance and the mass loss rate. A high helium abundance (e.g., Y\\approx0.28) or a mass loss rate of \\sim10^{-11}M_\\odot yr^{-1} near the main sequence turn-off region lowers the current age estimate from 14 Gyr to about 10--12 Gyr, significantly relaxing the constraints on the Hubble constant, allowing values as high as 60km/sec/Mpc for a universe with the critical density and 90km/sec/Mpc for a baryon-only universe. Possible mechanisms for the helium enhancement in globular clusters are discussed, as are arguments for an instability strip induced mass loss near the turn-off. Ages lower than 10 Gyr are not possible even with the operation of both of these mechanisms unless the initial helium abundance in globular clusters is >0.30, which would conflict with indirect measurements of helium abundances in globular clusters.

  19. Globular cluster formation - The fossil record

    NASA Technical Reports Server (NTRS)

    Murray, Stephen D.; Lin, Douglas N. C.

    1992-01-01

    Properties of globular clusters which have remained unchanged since their formation are used to infer the internal pressures, cooling times, and dynamical times of the protocluster clouds immediately prior to the onset of star formation. For all globular clusters examined, it is found that the cooling times are much less than the dynamical times, implying that the protoclusters must have been maintained in thermal equilibrium by external heat sources, with fluxes consistent with those found in previous work, and giving the observed rho-T relation. Self-gravitating clouds cannot be stably heated, so that the Jeans mass forms an upper limit to the cluster masses. The observed dependence of protocluster pressure upon galactocentric position implies that the protocluster clouds were in hydrostatic equilibrium after their formation. The pressure dependence is well fitted by that expected for a quasi-statically evolving background hot gas, shock heated to its virial temperature. The observations and inferences are combined with previous theoretical work to construct a picture of globular cluster formation.

  20. Globular cluster formation - The fossil record

    NASA Technical Reports Server (NTRS)

    Murray, Stephen D.; Lin, Douglas N. C.

    1992-01-01

    Properties of globular clusters which have remained unchanged since their formation are used to infer the internal pressures, cooling times, and dynamical times of the protocluster clouds immediately prior to the onset of star formation. For all globular clusters examined, it is found that the cooling times are much less than the dynamical times, implying that the protoclusters must have been maintained in thermal equilibrium by external heat sources, with fluxes consistent with those found in previous work, and giving the observed rho-T relation. Self-gravitating clouds cannot be stably heated, so that the Jeans mass forms an upper limit to the cluster masses. The observed dependence of protocluster pressure upon galactocentric position implies that the protocluster clouds were in hydrostatic equilibrium after their formation. The pressure dependence is well fitted by that expected for a quasi-statically evolving background hot gas, shock heated to its virial temperature. The observations and inferences are combined with previous theoretical work to construct a picture of globular cluster formation.

  1. The Dynamics Of Galactic Globular Cluster

    NASA Astrophysics Data System (ADS)

    Ding, Chen

    2008-10-01

    We have used the Hubble Space Telescope (HST) to measure proper motion of the globular cluster NGC 6656 (M22) with respect to the background bulge stars and its internal velocity dispersion profile. With the space velocity of (Π, Θ, W) = (184±3, 209±14, 132±15) km s-1, we also calculate the orbit of the cluster. The central velocity dispersion in both components of the proper motion of cluster stars is 16.99 km s-1. We derive the mass-to-ration (M/L)˜1.7 which is relatively higher than the past works.

  2. Pulsating White Dwarfs in Globular Clusters

    NASA Astrophysics Data System (ADS)

    Kanaan, A.; Zabot, A.; Fraga, L.

    2012-09-01

    We present our current efforts to detect pulsating white dwarfs in globular clusters and analyze the future of this area when the Extremely Large Telescope (ELT), the Giant Magellan Telescope (GMT) and the Thirty-Meter Telescope (TMT) all become operational. Today we are able to detect pulsating white dwarfs in M 4, NGC 6397 and NGC 6752. When ELT comes on line we should be able to improve the quality of data for the nearby clusters and push the limit to at least 3 magnitudes further, up to NGC 6626, increasing the number of observable clusters from 3 to 20.

  3. The Globular cluster system of M31.

    NASA Astrophysics Data System (ADS)

    Galleti, S.; Buzzoni, A.; Federici, L.; Fusi Pecci, F.

    I present here some results of the extensive revision work of M31 confirmed and candidate globular clusters. The Revised Bologna Catalog, RBC, www.bo.astro.it/M31 is currently the largest and most complete database available online. Two spectroscopic surveys are in progress to confirm RBC cluster candidates as well as newly identified candidates at large distances from the center of M31. I have also studied a subsample of bright and young (age < 2 Gyr) clusters in M31 that doesn't appear to have any counterpart in the Milky Way.

  4. Multiple populations in globular clusters: a theoretical point of view

    NASA Astrophysics Data System (ADS)

    Decressin, T.

    2010-12-01

    Globular clusters exhibit peculiar chemical patterns where Fe and heavy elements are constant inside a given cluster while light elements (Li to Al) show strong star-to-star variations. Besides precise photometric studies reveal that numerous globular clusters display multiple or broad main sequences, subgiant or giant branches. This peculiar chemical pattern can be explained by self-pollution of the intracluster gas occurring in the early evolution of clusters. Here the possible strong impact of fast rotating massive stars is reviewed. First providing they rotate initially fast enough they can reach the break-up velocity during the main sequence and a mechanical mass-loss will eject matter from the equator at low velocity. Rotation-induced mixing will also bring matter from the convective core to the surface. From this ejected matter loaded in H-burning material a second generation of stars will born. The chemical pattern of these second generation stars are similar to the one observed for stars in globular cluster with abundance anomalies in light elements. Then during the explosion as supernovae the massive stars will also clear the cluster of the remaining gas. If this gas expulsion process acts on short timescale it can strongly modify the dynamical properties of clusters by ejecting preferentially first generation stars.

  5. VARIABLES IN GLOBULAR CLUSTER NGC 5024

    SciTech Connect

    Safonova, M.; Stalin, C. S. E-mail: stalin@iiap.res.in

    2011-12-15

    We present the results of a commissioning campaign to observe Galactic globular clusters for the search of microlensing events. The central 10' Multiplication-Sign 10' region of the globular cluster NGC 5024 was monitored using the 2 m Himalayan Chandra Telescope in R-band for a period of about 8 hr on 2010 March 24. Light curves were obtained for nearly 10,000 stars using a modified Differential Image Analysis technique. We identified all known variables within our field of view and revised the periods and status of some previously reported short-period variables. We report about 70 new variable sources and present their equatorial coordinates, periods, light curves, and possible types. Out of these, 15 are SX Phe stars, 10 are W UMa-type stars, and 14 are probable RR Lyrae stars. Nine of the newly discovered SX Phe stars and one eclipsing binary belong to the blue straggler star population.

  6. Globular Cluster Systems along the Hubble Sequence

    NASA Astrophysics Data System (ADS)

    Huizinga, Edwin

    1996-07-01

    Globular Cluster Systems {GCSs} provide a powerful tool to differentiate between competing galaxy formation- and evolution scenarios. However, our current knowledge of GCS in spiral galaxies is based mainly on studies of the Galaxy and M31. Even though GCSs have been detected in other spiral galaxies, ground-based observations barely reach the peak of the Globular-Cluster luminosity function, and do not provide accurate colors. We propose a systematic study of the GCSs in 6 edge-on L* spiral galaxies beyond the Local Group, using WFPC2. These galaxies were carefully selected to meet several stringent criteria. With the new dithering techniques, it will be possible to resolve any faint background galaxies and obtain a clean sample of globular clusters for all galaxies in our sample. This will allow us to study the complete luminosity functions, {V-I} color distributions, and GCS richness for L* galaxies as a function of Hubble type {Sa, Sb, Sc}. These data will be used to study the relations between the galaxies' bulge and {thin/thick} disk properties and their GCSs. If, for example, GCS properties correlate with bulge properties, this will rule out any strong evolution along the Hubble Sequence towards earlier type spirals, from Sc to Sa, as has recently been proposed by Pfenniger et al. {1994}.

  7. HUBBLE PINPOINTS WHITE DWARFS IN GLOBULAR CLUSTER

    NASA Technical Reports Server (NTRS)

    2002-01-01

    Peering deep inside a cluster of several hundred thousand stars, NASA's Hubble Space Telescope uncovered the oldest burned-out stars in our Milky Way Galaxy. Located in the globular cluster M4, these small, dying stars - called white dwarfs - are giving astronomers a fresh reading on one of the biggest questions in astronomy: How old is the universe? The ancient white dwarfs in M4 are about 12 to 13 billion years old. After accounting for the time it took the cluster to form after the big bang, astronomers found that the age of the white dwarfs agrees with previous estimates for the universe's age. In the top panel, a ground-based observatory snapped a panoramic view of the entire cluster, which contains several hundred thousand stars within a volume of 10 to 30 light-years across. The Kitt Peak National Observatory's 0.9-meter telescope took this picture in March 1995. The box at left indicates the region observed by the Hubble telescope. The Hubble telescope studied a small region of the cluster. A section of that region is seen in the picture at bottom left. A sampling of an even smaller region is shown at bottom right. This region is only about one light-year across. In this smaller region, Hubble pinpointed a number of faint white dwarfs. The blue circles pinpoint the dwarfs. It took nearly eight days of exposure time over a 67-day period to find these extremely faint stars. Globular clusters are among the oldest clusters of stars in the universe. The faintest and coolest white dwarfs within globular clusters can yield a globular cluster's age. Earlier Hubble observations showed that the first stars formed less than 1 billion years after the universe's birth in the big bang. So, finding the oldest stars puts astronomers within arm's reach of the universe's age. M4 is 7,000 light-years away in the constellation Scorpius. Hubble's Wide Field and Planetary Camera 2 made the observations from January through April 2001. These optical observations were combined to

  8. HUBBLE PINPOINTS WHITE DWARFS IN GLOBULAR CLUSTER

    NASA Technical Reports Server (NTRS)

    2002-01-01

    Peering deep inside a cluster of several hundred thousand stars, NASA's Hubble Space Telescope uncovered the oldest burned-out stars in our Milky Way Galaxy. Located in the globular cluster M4, these small, dying stars - called white dwarfs - are giving astronomers a fresh reading on one of the biggest questions in astronomy: How old is the universe? The ancient white dwarfs in M4 are about 12 to 13 billion years old. After accounting for the time it took the cluster to form after the big bang, astronomers found that the age of the white dwarfs agrees with previous estimates for the universe's age. In the top panel, a ground-based observatory snapped a panoramic view of the entire cluster, which contains several hundred thousand stars within a volume of 10 to 30 light-years across. The Kitt Peak National Observatory's 0.9-meter telescope took this picture in March 1995. The box at left indicates the region observed by the Hubble telescope. The Hubble telescope studied a small region of the cluster. A section of that region is seen in the picture at bottom left. A sampling of an even smaller region is shown at bottom right. This region is only about one light-year across. In this smaller region, Hubble pinpointed a number of faint white dwarfs. The blue circles pinpoint the dwarfs. It took nearly eight days of exposure time over a 67-day period to find these extremely faint stars. Globular clusters are among the oldest clusters of stars in the universe. The faintest and coolest white dwarfs within globular clusters can yield a globular cluster's age. Earlier Hubble observations showed that the first stars formed less than 1 billion years after the universe's birth in the big bang. So, finding the oldest stars puts astronomers within arm's reach of the universe's age. M4 is 7,000 light-years away in the constellation Scorpius. Hubble's Wide Field and Planetary Camera 2 made the observations from January through April 2001. These optical observations were combined to

  9. RR Lyrae in Sagittarius Dwarf Globular Clusters (Poster abstract)

    NASA Astrophysics Data System (ADS)

    Pritzl, B. J.; Gehrman, T. J.; Bell, E.; Salinas, R.; Smith, H. A.; Catelan, M.

    2016-12-01

    (Abstract only) The Milky Way Galaxy was built up in part by the cannibalization of smaller dwarf galaxies. Some of them likely contained globular clusters. The Sagittarius dwarf galaxy provides a unique opportunity to study a system of globular clusters that originated outside the Milky Way. We have investigated the RR Lyrae populations in two Sagittarius globular clusters, Arp 2 and Terzan 8. The RR Lyrae are used to study the properties of the clusters and to compare this system to Milky Way globular clusters. We will discuss whether or not dwarf galaxies similar to the Sagittarius dwarf galaxy could have played a role in the formation of the Milky Way Galaxy.

  10. Understanding the Current Dynamical States of Globular Clusters

    NASA Astrophysics Data System (ADS)

    Pooley, David

    2008-09-01

    We appear to be on the verge of a major paradigm shift in our understanding of the current dynamical states of Galactic globular clusters. Fregeau (2008) brought together two recent theoretical breakthroughs as well as an observational breakthrough made possible by Chandra -- that a globular cluster's X-ray source population scales with its dynamical encounter frequency -- to persuasively argue that we have misunderstood the dynamical states of Galactic globular clusters. The observational evidence hinges on Chandra results from clusters which are classified as "core collapsed," of which there are only a handful of observations. I propose a nearly complete census with Chandra of the rest of the "core collapsed" globular clusters.

  11. Dynamics of the globular cluster NGC 362

    NASA Technical Reports Server (NTRS)

    Fischer, Philippe; Welch, Douglas L.; Mateo, Mario; Cote, Patrick

    1993-01-01

    A combination of V-band CCD images and echelle spectra of member red giants is presently used to examine the internal dynamics of the globular cluster NGC 362. A total of 285 stellar spectra were obtained of 215 stars for radial velocity determinations, and the true cluster binary fraction was determined from simulations to be 0.15 for circular orbits and 0.27 for orbits with an f(e) = e (eccentricity) distribution function. An overabundance of binaries is surmised for NGC 362 on this basis.

  12. Dynamics of the globular cluster NGC 362

    NASA Technical Reports Server (NTRS)

    Fischer, Philippe; Welch, Douglas L.; Mateo, Mario; Cote, Patrick

    1993-01-01

    A combination of V-band CCD images and echelle spectra of member red giants is presently used to examine the internal dynamics of the globular cluster NGC 362. A total of 285 stellar spectra were obtained of 215 stars for radial velocity determinations, and the true cluster binary fraction was determined from simulations to be 0.15 for circular orbits and 0.27 for orbits with an f(e) = e (eccentricity) distribution function. An overabundance of binaries is surmised for NGC 362 on this basis.

  13. The Faint Globular Cluster in the Dwarf Galaxy Andromeda I

    NASA Astrophysics Data System (ADS)

    Caldwell, Nelson; Strader, Jay; Sand, David J.; Willman, Beth; Seth, Anil C.

    2017-09-01

    Observations of globular clusters in dwarf galaxies can be used to study a variety of topics, including the structure of dark matter halos and the history of vigorous star formation in low-mass galaxies. We report on the properties of the faint globular cluster (M V -3.4) in the M31 dwarf galaxy Andromeda I. This object adds to the growing population of low-luminosity Local Group galaxies that host single globular clusters.

  14. Isolated elliptical galaxies and their globular cluster systems. II. NGC 7796 - globular clusters, dynamics, companion

    NASA Astrophysics Data System (ADS)

    Richtler, T.; Salinas, R.; Lane, R. R.; Hilker, M.; Schirmer, M.

    2015-02-01

    Context. Rich globular cluster systems, particularly the metal-poor part of them, are thought to be the visible manifestations of long-term accretion processes. The invisible part is the dark matter halo, which may show some correspondence to the globular cluster system. It is therefore interesting to investigate the globular cluster systems of isolated elliptical galaxies, which supposedly have not experienced extended accretion. Aims: We investigate the globular cluster system of the isolated elliptical NGC 7796, present new photometry of the galaxy, and use published kinematical data to constrain the dark matter content. Methods: Deep images in B and R, obtained with the VIsible MultiObject Spectrograph (VIMOS) at the VLT, form the data base. We performed photometry with DAOPHOT and constructed a spherical photometric model. We present isotropic and anisotropic Jeans-models and give a morphological description of the companion dwarf galaxy. Results: The globular cluster system has about 2000 members, so it is not as rich as those of giant ellipticals in galaxy clusters with a comparable stellar mass, but richer than many cluster systems of other isolated ellipticals. The colour distribution of globular clusters is bimodal, which does not necessarily mean a metallicity bimodality. The kinematic literature data are somewhat inconclusive. The velocity dispersion in the inner parts can be reproduced without dark matter under isotropy. Radially anisotropic models need a low stellar mass-to-light ratio, which would contrast with the old age of the galaxy. A MONDian model is supported by X-ray analysis and previous dynamical modelling, but better data are necessary for a confirmation. The dwarf companion galaxy NGC 7796-1 exhibits tidal tails, multiple nuclei, and very boxy isophotes. Conclusions: NGC 7796 is an old, massive isolated elliptical galaxy with no indications of later major star formation events as seen frequently in other isolated ellipticals. Its

  15. No energy equipartition in globular clusters

    NASA Astrophysics Data System (ADS)

    Trenti, Michele; van der Marel, Roeland

    2013-11-01

    It is widely believed that globular clusters evolve over many two-body relaxation times towards a state of energy equipartition, so that velocity dispersion scales with stellar mass as σ ∝ m-η with η = 0.5. We show here that this is incorrect, using a suite of direct N-body simulations with a variety of realistic initial mass functions and initial conditions. No simulated system ever reaches a state close to equipartition. Near the centre, the luminous main-sequence stars reach a maximum ηmax ≈ 0.15 ± 0.03. At large times, all radial bins convergence on an asymptotic value η∞ ≈ 0.08 ± 0.02. The development of this `partial equipartition' is strikingly similar across our simulations, despite the range of different initial conditions employed. Compact remnants tend to have higher η than main-sequence stars (but still η < 0.5), due to their steeper (evolved) mass function. The presence of an intermediate-mass black hole (IMBH) decreases η, consistent with our previous findings of a quenching of mass segregation under these conditions. All these results can be understood as a consequence of the Spitzer instability for two-component systems, extended by Vishniac to a continuous mass spectrum. Mass segregation (the tendency of heavier stars to sink towards the core) has often been studied observationally, but energy equipartition has not. Due to the advent of high-quality proper motion data sets from the Hubble Space Telescope, it is now possible to measure η for real clusters. Detailed data-model comparisons open up a new observational window on globular cluster dynamics and evolution. A first comparison of our simulations to observations of Omega Cen yields good agreement, supporting the view that globular clusters are not generally in energy equipartition. Modelling techniques that assume equipartition by construction (e.g. multi-mass Michie-King models) are approximate at best.

  16. Cosmic strings and the origin of globular clusters

    SciTech Connect

    Barton, Alistair; Brandenberger, Robert H.; Lin, Ling E-mail: rhb@physics.mcgill.ca

    2015-06-01

    We hypothesize that cosmic string loops are the seeds about which globular clusters accrete. Fixing the cosmic string tension by demanding that the peak in the distribution of masses of objects accreting onto string loops agrees with the peak in the observed mass distribution of globular clusters in our Milky Way galaxy, we then compute the expected number density and mass function of globular clusters, and compare with observations. Our hypothesis naturally explains why globular clusters are the oldest and most dense objects in a galaxy, and why they are found in the halo of the galaxy.

  17. Rosat Observations of Nine Globular Clusters

    NASA Technical Reports Server (NTRS)

    Rappaport, S.; Dewey, D.; Levine, A.; Macri, L.

    1994-01-01

    The ROSAT HRI was used to image fields around nine Galactic globular clusters that have central densities in the range of 10(exp 4) - 10(exp 5) solar mass pc(exp -3) and that had not previously been observed with the Einstein Observatory. We detected X-ray sources associated with Pal 2 and NGC 6304 with luminosities of 1.1 x 10(exp 34) ergs/s and 1.2 x 10(exp 33) ergs/s, respectively. No X-ray emission was detected from the source in Ter 6, thus confirming its transient nature. In all, there were 23 serendipitous sources found in the nine fields; none was apparently associated with any of the other seven clusters. The results are discussed in the context of low-luminosity cluster X-ray sources, in general.

  18. Rosat Observations of Nine Globular Clusters

    NASA Technical Reports Server (NTRS)

    Rappaport, S.; Dewey, D.; Levine, A.; Macri, L.

    1994-01-01

    The ROSAT HRI was used to image fields around nine Galactic globular clusters that have central densities in the range of 10(exp 4) - 10(exp 5) solar mass pc(exp -3) and that had not previously been observed with the Einstein Observatory. We detected X-ray sources associated with Pal 2 and NGC 6304 with luminosities of 1.1 x 10(exp 34) ergs/s and 1.2 x 10(exp 33) ergs/s, respectively. No X-ray emission was detected from the source in Ter 6, thus confirming its transient nature. In all, there were 23 serendipitous sources found in the nine fields; none was apparently associated with any of the other seven clusters. The results are discussed in the context of low-luminosity cluster X-ray sources, in general.

  19. Limits on WIMPs from globular cluster stars

    NASA Astrophysics Data System (ADS)

    Rood, R. T.; Renzini, A.

    The theoretical model proposed by Spergel and Faulkner (1988) to explain the observed solar neutrino flux is tested by applying it to detailed stellar models based on data for globular-cluster stars. In this model, nonbaryonic weakly interacting massive particles (WIMPs) act to transport energy in an isothermal central solar core, where B-8 neutrinos are produced. The potential effects of WIMPs on stellar evolution in the main sequence, the subgiant branch, near the red-giant tip, and on the horizontal branch are discussed, and effects which should be observable are identified. For the horizontal-branch stars, a diagram showing severe observational constraints on WIMP physical parameters is presented.

  20. UV Spectroscopic Indices of Galactic Globular Clusters

    NASA Astrophysics Data System (ADS)

    Morales-Hernández, J.; Chávez, M.; Bertone, E.; Buzzoni, A.; Bressan, A.

    2009-03-01

    We present the calculation of a set of 12 mid-ultraviolet (1900-3200 Å) spectroscopic indices for a sample of 15 galactic globular clusters (GGC) observed with the International Ultraviolet Explorer (IUE). We explore the dependence of the indices on age and metal abundance. We found that five indices (BL 2538, Fe II 2609, Mg II 2800, Mg I 2852 and Mg Wide) display a remarkably good correlation with [Fe/H]. With respect to age, only one index (BL 2740) shows a good correlation. Results from theoretical simple stellar populations well reproduce the global trends of indices vs. [Fe/H].

  1. Binaries in Globular Clusters Multiple Populations

    NASA Astrophysics Data System (ADS)

    Lucatello, Sara; Sollima, Antonio; Gratton, Raffaele; D'Orazi, Valentina; Vesperini, Enrico; Carretta, Eugenio; Bragaglia, Angela

    2015-08-01

    In spite of considerable theoretical and obsservational effort, the series of events that leads to the formation of Globular Clusters and their multiple populations is still unclear.One of the key matters is where the so-called second generation of stars form and its distribution at the time of its birth with respect to the first generation. Some of the latest modeling has suggested that second generation should form in a compact subsystem concentrated in the inner regions of the primordial, first generation cluster. In this scenario, loss of a large fraction of the cluster mass is expected, mostly comprised of first generation stars. This would account for the mass budget issue (one of the main problems in the self-enrichment scenario) and would imply a considerable contribution of the clusters to the formation of the Galactic Halo.Testing this prediction is hence of great importance, but not so immediate. Long-term, dynamical evolution of multiple-population clusters could blur considerably the signature of the initial different concentrations, leaving at present time some memory in the very central part (Vesperini et al. 2013), which, because of its high density, is generally not accessible to the multi-object high resolution spectrographs that yield the spectra that allow the chemical composition measurements necessary to tag the different populations.An alternative approach to test the prediction of the initial segregation of the second generations is that of determining their binary fractions. In fact, until the two populations are completely mixed, second generation stars will evolve in a denser environment where disruption will occur more rapidly, leading to a smaller binary incidence in such population (Vesperini et al 2011).I will present the results of our long-term radial velocity monitoring of 10 Galactic Globular clusters, discuss the derived binary fractions in the two populations and address the implications of our findings on our understanding of

  2. Ancient Planet in a Globular Cluster Core

    NASA Image and Video Library

    2017-09-28

    Release Date: July 10, 2003 A rich starry sky fills the view from an ancient gas-giant planet in the core of the globular star cluster M4, as imagined in this artist's concept. The 13-billion-year-old planet orbits a helium white-dwarf star and the millisecond pulsar B1620-26, seen at lower left. The globular cluster is deficient in heavier elements for making planets, so the existence of such a world implies that planet formation may have been quite efficient and common in the early universe. Object Names: B1620-26, M4 Image Type: Artwork Illustration Credit: NASA and G. Bacon (STScI) To learn more about this image go to: www.nasa.gov/centers/goddard/news/topstory/2003/0709hstss... NASA Goddard Space Flight Center is home to the nation's largest organization of combined scientists, engineers and technologists that build spacecraft, instruments and new technology to study the Earth, the sun, our solar system, and the universe.

  3. THE PRODUCTION RATE OF SN Ia EVENTS IN GLOBULAR CLUSTERS

    SciTech Connect

    Washabaugh, Pearce C.; Bregman, Joel N. E-mail: jbregman@umich.edu

    2013-01-01

    In globular clusters, dynamical evolution produces luminous X-ray emitting binaries at a rate about 200 times greater than in the field. If globular clusters also produce SN Ia at a high rate, it would account for many of the SN Ia production in early-type galaxies and provide insight into their formation. Here we use archival Hubble Space Telescope (HST) images of nearby galaxies that have hosted an SN Ia to examine the rate at which globular clusters produce these events. The location of the SN Ia is registered on an HST image obtained before the event or after the supernova (SN) faded. Of the 36 nearby galaxies examined, 21 had sufficiently good data to search for globular cluster hosts. None of the 21 SNe have a definite globular cluster counterpart, although there are some ambiguous cases. This places an upper limit to the enhancement rate of SN Ia production in globular clusters of about 42 at the 95% confidence level, which is an order of magnitude lower than the enhancement rate for luminous X-ray binaries. Even if all of the ambiguous cases are considered as having a globular cluster counterpart, the upper bound for the enhancement rate is 82 at the 95% confidence level, still a factor of several below that needed to account for half of the SN Ia events. Barring unforeseen selection effects, we conclude that globular clusters are not responsible for producing a significant fraction of the SN Ia events in early-type galaxies.

  4. LITHIUM-RICH GIANTS IN GLOBULAR CLUSTERS

    SciTech Connect

    Kirby, Evan N.; Cohen, Judith G.; Guhathakurta, Puragra; Hong, Jerry; Guo, Michelle; Guo, Rachel; Cunha, Katia

    2016-03-10

    Although red giants deplete lithium on their surfaces, some giants are Li-rich. Intermediate-mass asymptotic giant branch (AGB) stars can generate Li through the Cameron–Fowler conveyor, but the existence of Li-rich, low-mass red giant branch (RGB) stars is puzzling. Globular clusters are the best sites to examine this phenomenon because it is straightforward to determine membership in the cluster and to identify the evolutionary state of each star. In 72 hours of Keck/DEIMOS exposures in 25 clusters, we found four Li-rich RGB and two Li-rich AGB stars. There were 1696 RGB and 125 AGB stars with measurements or upper limits consistent with normal abundances of Li. Hence, the frequency of Li-richness in globular clusters is (0.2 ± 0.1)% for the RGB, (1.6 ± 1.1)% for the AGB, and (0.3 ± 0.1)% for all giants. Because the Li-rich RGB stars are on the lower RGB, Li self-generation mechanisms proposed to occur at the luminosity function bump or He core flash cannot explain these four lower RGB stars. We propose the following origin for Li enrichment: (1) All luminous giants experience a brief phase of Li enrichment at the He core flash. (2) All post-RGB stars with binary companions on the lower RGB will engage in mass transfer. This scenario predicts that 0.1% of lower RGB stars will appear Li-rich due to mass transfer from a recently Li-enhanced companion. This frequency is at the lower end of our confidence interval.

  5. Lithium-rich Giants in Globular Clusters

    NASA Astrophysics Data System (ADS)

    Kirby, Evan N.; Guhathakurta, Puragra; Zhang, Andrew J.; Hong, Jerry; Guo, Michelle; Guo, Rachel; Cohen, Judith G.; Cunha, Katia

    2016-03-01

    Although red giants deplete lithium on their surfaces, some giants are Li-rich. Intermediate-mass asymptotic giant branch (AGB) stars can generate Li through the Cameron-Fowler conveyor, but the existence of Li-rich, low-mass red giant branch (RGB) stars is puzzling. Globular clusters are the best sites to examine this phenomenon because it is straightforward to determine membership in the cluster and to identify the evolutionary state of each star. In 72 hours of Keck/DEIMOS exposures in 25 clusters, we found four Li-rich RGB and two Li-rich AGB stars. There were 1696 RGB and 125 AGB stars with measurements or upper limits consistent with normal abundances of Li. Hence, the frequency of Li-richness in globular clusters is (0.2 ± 0.1)% for the RGB, (1.6 ± 1.1)% for the AGB, and (0.3 ± 0.1)% for all giants. Because the Li-rich RGB stars are on the lower RGB, Li self-generation mechanisms proposed to occur at the luminosity function bump or He core flash cannot explain these four lower RGB stars. We propose the following origin for Li enrichment: (1) All luminous giants experience a brief phase of Li enrichment at the He core flash. (2) All post-RGB stars with binary companions on the lower RGB will engage in mass transfer. This scenario predicts that 0.1% of lower RGB stars will appear Li-rich due to mass transfer from a recently Li-enhanced companion. This frequency is at the lower end of our confidence interval. The data presented herein were obtained at the W. M. Keck Observatory, which is operated as a scientific partnership among the California Institute of Technology, the University of California and the National Aeronautics and Space Administration. The Observatory was made possible by the generous financial support of the W. M. Keck Foundation.

  6. Dynamical Formation of Black Hole Binaries in Globular Clusters

    NASA Astrophysics Data System (ADS)

    Rasio, Frederic A.; Chatterjee, Sourav; Kremer, Kyle; Rodriguez, Carl

    2017-08-01

    Theoretical predictions for black holes in field populations of binary stars are extremely sensitive to the assumptions of stellar evolution, leading, for example, to predicted merger rates for binary black holes that span several orders of magnitude. But in dense stellar environments such as globular clusters, binary black holes form by well-understood gravitational interactions. We will present an overview of recent theoretical work on the dynamical formation of black hole binaries based on realistic N-body simulations of globular clusters. By calibrating theoretical models against observed properties of globular clusters, we find that the mergers of dynamically formed binaries could eventually be detected by Advanced LIGO at a rate of at least ~ 100 per year, potentially dominating the overall detection rate of gravitational wave sources. Dynamical processes in globular clusters can also form very naturally the black hole X-ray binaries that have been tentatively identified recently in many Milky Way and extragalactic globular clusters.

  7. Globular Clusters as Cradles of Life and Advanced Civilizations

    NASA Astrophysics Data System (ADS)

    Di Stefano, Rosanne; Ray, Alak

    2016-01-01

    Globular clusters are bound groups of about a million stars and stellar remnants. They are old, largely isolated, and very dense. We consider what each of these special features can mean for the development of life, the evolution of intelligent life, and the long-term survival of technological civilizations. We find that, if they house planets, globular clusters provide ideal environments for advanced civilizations that can survive over long times. We therefore propose methods to search for planets in globular clusters. If planets are found and if our arguments are correct, searches for intelligent life are most likely to succeed when directed toward globular clusters. Globular clusters may be the first places in which distant life is identified in our own or in external galaxies.

  8. IC 1257: A New Globular Cluster in the Galactic Halo

    NASA Technical Reports Server (NTRS)

    Harris, W. E.; Phelps, R. L.; Madore, B. F.; Pevunova, O.; Skiff, B. A.; Crute, C.; Wilson, B.

    1996-01-01

    New CCD photometry of the faint, compact star cluster IC 1257 (L = 17? = +/- 15?obtained with the Palomar 5m telescope, reveals that it is a highly reddened globular cluster well beyond the Galactic center.

  9. IC 1257: A New Globular Cluster in the Galactic Halo

    NASA Technical Reports Server (NTRS)

    Harris, W. E.; Phelps, R. L.; Madore, B. F.; Pevunova, O.; Skiff, B. A.; Crute, C.; Wilson, B.

    1996-01-01

    New CCD photometry of the faint, compact star cluster IC 1257 (L = 17? = +/- 15?obtained with the Palomar 5m telescope, reveals that it is a highly reddened globular cluster well beyond the Galactic center.

  10. Lack of Energy Equipartition in Globular Clusters

    NASA Astrophysics Data System (ADS)

    Trenti, Michele

    2013-05-01

    Abstract (2,250 Maximum Characters): It is widely believed that globular clusters evolve over many two-body relaxation times toward a state of energy equipartition, so that velocity dispersion scales with stellar mass as σ∝m^{-η} with η=0.5. I will show instead that this is incorrect, using a suite of direct N-body simulations with a variety of realistic initial mass functions and initial conditions. No simulated system ever reaches a state close to equipartition. Near the center, the luminous main-sequence stars reach a maximum η_{max 0.15±0.03. At large times, all radial bins convergence on an asymptotic value η_{∞ 0.08±0.02. The development of this ``partial equipartition'' is strikingly similar across simulations, despite the range of different initial conditions employed. Compact remnants tend to have higher η than main-sequence stars (but still η< 0.5), due to their steeper (evolved) mass function. The presence of an intermediate-mass black hole (IMBH) decreases η, consistent with our previous findings of a quenching of mass segregation under these conditions. All these results can be understood as a consequence of the Spitzer instability for two-component systems, extended by Vishniac to a continuous mass spectrum. Mass segregation (the tendency of heavier stars to sink toward the core) has often been studied observationally, but energy equipartition has not. Due to the advent of high-quality proper motion datasets from the Hubble Space Telescope, it is now possible to measure η for real clusters. Detailed data-model comparisons open up a new observational window on globular cluster dynamics, structure, evolution, initial conditions, and possible IMBHs. A first comparison of my simulations to observations of Omega Cen yields good agreement, supporting the view that globular clusters are not generally in energy equipartition. Modeling techniques that assume equipartition by construction (e.g., multi-mass Michie-King models) are thus approximate

  11. Stellar Mass Loss in Globular Clusters

    NASA Astrophysics Data System (ADS)

    McDonald, Iain

    2009-10-01

    This work investigates stellar mass loss in globular clusters. It comprises of optical and infra-red photometric imaging and spectroscopy, plus radio interferometry observations. I present mid-infrared spectroscopic observations of stars in the globular clusters 47 Tucanae and ω Centauri, finding 47 Tuc V1 (and possibly V18) and ω Cen V6 surrounded by circumstellar silicate dust. ω Cen V42 may also be surrounded by carbon-rich dust. Much of this work is devoted to finding the threshold for dust production and the mass-loss rates from cluster stars with both chromospherically- and dust- or pulsation-driven winds. Using very-high-resolution optical photometry, I have identified the transition between the two driving regimes as being at earlier spectral types than in solar-metallicity stars, suggesting that pulsation and continuum-driving become the dominant wind drivers at around K5-M3, or ~1500 Lsun. In a similar vein, I have modelled spectral energy distributions of stars in ω Centauri using new photometry from the Spitzer Space Telescope and literature photometry. The total mass-loss rate for the cluster is & 1.2+/-0.6 x 10^-6 Msun yr-1, some 30% of which is from two stars - V6 and V42. This implies the cluster is being cleaned of gas and dust every ~10^5 years. Dust production appears to be efficient on both the red and asymptotic giant branches, even at the cluster's low metallicity ([Fe/H] = -1.62). I also derive a new distance to the cluster of 4850 ± 200 (statistical) ± 200 (systematic) pc with a reddening of E(B-V) = 0.08±0.02±0.02 mag and a differential reddening of delta[E(B-V)] < 0.02 mag. Finally, I also present new observations of the high velocity hydrogen cloud in the vicinity of ω Centauri, finding that it is likely not associated with the cluster.

  12. BLUE STRAGGLERS IN GLOBULAR CLUSTER 47 TUCANAE

    NASA Technical Reports Server (NTRS)

    2002-01-01

    The core of globular cluster 47 Tucanae is home to many blue stragglers, rejuvenated stars that glow with the blue light of young stars. A ground-based telescope image (on the left) shows the entire crowded core of 47 Tucanae, located 15,000 light-years away in the constellation Tucana. Peering into the heart of the globular cluster's bright core, the Hubble Space Telescope's Wide Field and Planetary Camera 2 separated the dense clump of stars into many individual stars (image on right). Some of these stars shine with the light of old stars; others with the blue light of blue stragglers. The yellow circles in the Hubble telescope image highlight several of the cluster's blue stragglers. Analysis for this observation centered on one massive blue straggler. Astronomers theorize that blue stragglers are formed either by the slow merger of stars in a double-star system or by the collision of two unrelated stars. For the blue straggler in 47 Tucanae, astronomers favor the slow merger scenario. This image is a 3-color composite of archival Hubble Wide Field and Planetary Camera 2 images in the ultraviolet (blue), blue (green), and violet (red) filters. Color tables were assigned and scaled so that the red giant stars appear orange, main-sequence stars are white/green, and blue stragglers are appropriately blue. The ultraviolet images were taken on Oct. 25, 1995, and the blue and violet images were taken on Sept. 1, 1995. Credit: Rex Saffer (Villanova University) and Dave Zurek (STScI), and NASA

  13. BLUE STRAGGLERS IN GLOBULAR CLUSTER 47 TUCANAE

    NASA Technical Reports Server (NTRS)

    2002-01-01

    The core of globular cluster 47 Tucanae is home to many blue stragglers, rejuvenated stars that glow with the blue light of young stars. A ground-based telescope image (on the left) shows the entire crowded core of 47 Tucanae, located 15,000 light-years away in the constellation Tucana. Peering into the heart of the globular cluster's bright core, the Hubble Space Telescope's Wide Field and Planetary Camera 2 separated the dense clump of stars into many individual stars (image on right). Some of these stars shine with the light of old stars; others with the blue light of blue stragglers. The yellow circles in the Hubble telescope image highlight several of the cluster's blue stragglers. Analysis for this observation centered on one massive blue straggler. Astronomers theorize that blue stragglers are formed either by the slow merger of stars in a double-star system or by the collision of two unrelated stars. For the blue straggler in 47 Tucanae, astronomers favor the slow merger scenario. This image is a 3-color composite of archival Hubble Wide Field and Planetary Camera 2 images in the ultraviolet (blue), blue (green), and violet (red) filters. Color tables were assigned and scaled so that the red giant stars appear orange, main-sequence stars are white/green, and blue stragglers are appropriately blue. The ultraviolet images were taken on Oct. 25, 1995, and the blue and violet images were taken on Sept. 1, 1995. Credit: Rex Saffer (Villanova University) and Dave Zurek (STScI), and NASA

  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. 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

  17. Most Massive Globular Cluster in Our Galaxy

    NASA Astrophysics Data System (ADS)

    1994-05-01

    Far down in the southern sky, in the constellation of Centaurus, a diffuse spot of light can be perceived with the unaided eye. It may be unimpressive, but when seen through a telescope, it turns out to be a beautiful, dense cluster of innumerable stars [1]. Omega Centauri, as this object is called, is the brightest of its type in the sky. We refer to it as a "globular cluster", due to its symmetric form. It belongs to our Milky Way galaxy and astrophysical investigations have shown that it is located at a distance of about 16,500 light-years (1 light-year = 9,460,000,000,000 km). Nobody knows for sure how many individual stars it contains, but recent estimates run into the millions. Most of these stars are more than 10,000 million years old and it is generally agreed that Omega Centauri has a similar age. Measurements of its motion indicate that Omega Centauri plows through the Milky Way in an elongated orbit. It is not easy to understand how it has managed to keep its stars together during such an extended period. MEASURING STELLAR VELOCITIES IN OMEGA CENTAURI A group of astronomers [2] have recently carried through a major investigation of Omega Centauri. After many nights of observations at the ESO La Silla observatory, they now conclude that not only is this globular cluster the brightest, it is indeed by far the most massive known in the Milky Way. The very time-consuming observations were made during numerous observing sessions over a period of no less than 13 years (1981-1993), with the photoelectric spectrometer CORAVEL mounted on the 1.5-m Danish telescope at La Silla. The CORAVEL instrument (COrelation RAdial VELocities) was built in a joint effort between the Geneva (Switzerland) and Marseilles (France) observatories. It functions according to the cross-correlation technique, by means of which the spectrum of the observed star is compared with a "standard stellar spectrum" [3]. HOW HEAVY IS OMEGA CENTAURI? In the present study, a total of 1701

  18. Chemical abundances of multiple stellar populations in massive globular clusters

    NASA Astrophysics Data System (ADS)

    Marino, Anna F.

    2017-03-01

    Multiple stellar populations in the Milky Way globular clusters manifest themselves with a large variety. Although chemical abundance variations in light elements, including He, are ubiquitous, the amount of these variations is different in different globulars. Stellar populations with distinct Fe, C+N+O and slow-neutron capture elements have been now detected in some globular clusters, whose number will likely increase. All these chemical features correspond to specific photometric patterns. I review the chemical+photometric features of the multiple stellar populations in globular clusters and discuss how the interpretation of data is being more and more challenging. Very excitingly, the origin and evolution of globular clusters is being a complex puzzle to compose.

  19. Study of Diffuse X-ray Emission in Globular Clusters

    NASA Technical Reports Server (NTRS)

    Grindlay, Jonathan E.

    1997-01-01

    This grant supported our analysis of ROSAT x-ray data on globular clusters. Although the grant title referred to our original ROSAT proposal (cycle 1) to study diffuse soft x-ray emission in three globulars (for which time was only granted in that original observing cycle for one cluster, 47 Tuc), the grant has also been maintained through several renewals and funding supplements to support our later ROSAT observations of point sources in globulars. The primary emphasis has been on the study of the dim sources, or low liuminosity globular cluster x-ray sources, which we had originally discovered with the Einstein Observatory and for which ROSAT provided the logical followup. In this Final Report, we summarize the Scientific Objectives of this investigation of both diffuse emission and dim sources in globular clusters and the Results Achieved; and finally the Papers Published.

  20. Modeling the Blue Stragglers in Globular Clusters

    NASA Astrophysics Data System (ADS)

    Chatterjee, Sourav

    2012-10-01

    Blue stragglers {BS} have been extensively observed in Galactic globular clusters {GGC}. primarily with HST. Many theoretical studies have identified BS formation channels and it is understood that dynamics in GCs modifies formation and distribution of the BSs. Despite the wealth of observational data, comprehensive theoretical models including all relevant physical processes in dynamically evolving GCs do not exist. Our dynamical cluster modeling code, developed over the past decade, includes all relevant physical processes in a GC including two-body relaxation, strong scattering, physical collisions, and stellar-evolution {single and binary}. We can model GCs with realistic N and provide star-by-star models for GCs directly comparable with the observed data. This proposed study will create realistic GC models with initial conditions from a grid spanning a large range in the multidimensional parameter space including cluster mass, binary fraction, concentration, and Galactic position. Our numerical models combined with observational constraints from existing HST data will for the first time provide explanations for the observed trends in the BS populations in GGCs, the dominant formation channel for these BSs, typical dynamical ages of the BSs, and find detailed dynamical histories of the BSs in GGCs. These models will yield valuable insight on the correlations between the BS properties and a number of cluster dynamical properties {central density, binary fraction, and binary orbital properties} which will potentially help constrain a GC's past evolutionary history. As a bonus a large set of realistic theoretical GC models will be constructed.

  1. On eccentricities of globular cluster galactocentric orbits

    NASA Astrophysics Data System (ADS)

    Ninkovic, S.

    The orbital eccentricities of 55 globular clusters are calculated and discussed. The data are taken from the study of Woltjer (1975), but include only those clusters for which reliable chemical compositions, positions, and line-of-sight velocities are given. The clusters are divided into six groups according to chemical composition and galactocentric distance, and the formulas of House and Wiegandt (1977) are employed in the calculations. The results are presented in tables and characterized individually. An LSR velocity of 225 km/sec is assumed, but some calculations using 275 km/sec are included for comparison. A general lower limit of eccentricity of 0.3 and upper limits (depending on cluster type) as high as 0.9 are estimated, with perigalactic distances not less than 1 kpc and apogalactic distances generally less than 25 but sometimes as high as 50-100 kpc. The mean orbital eccentricity of the groups is found to be better correlated to galactocentric distance than to chemical composition. The evolutionary contraction of the Galaxy is estimated to have lasted about 2-3 Gyr.

  2. What Happens to the Gas in Globular Clusters?

    NASA Astrophysics Data System (ADS)

    Thoul, A.; Jehin, E.; Magain, P.; Noels, A.; Parmentier, G.

    Observations of globular clusters show that they contain much too little gas or dust, compared to what should be present due to the mass-losing stars in the cluster. Many authors have been intrigued by the fate of the gas in globular clusters. They have suggested various mechanisms by which the gas could escape from the cluster, such as stellar UV radiation, cluster winds driven by X-ray bursters, novae, or flare-stars, relativistic winds from millisecond pulsars, condensation into stars, accretion processes drawing upon a central gas reservoir, continuous sweeping of the cluster gas by the gaseous medium of the Galactic halo dots. Recent results also show that globular cluster stars show many abundance anomalies. Accretion of interstellar gas by the cluster stars has been suggested as a plausible mechanism to explain these anomalies. It is also a major ingredient of the EASE scenario linking halo field stars to globular clusters, which we have recently developed to explain strong r-and s-elements correlations in halo field dwarf stars. Here we will briefly review the status of gas and dust detection in globular clusters, as well as the possible gas removal mechanisms. We will explore in more details the gas and dust accretion processes onto main sequence stars. In particular, we will study the efficiency of this mechanism in removing gas from the globular clusters interstellar medium.

  3. Disruption of the Globular Cluster Pal 5

    NASA Technical Reports Server (NTRS)

    Miller, R. H.; Smith, B. F.; Cuzzi, Jeffrey N. (Technical Monitor)

    1995-01-01

    Orbit calculations suggest that the sparse globular cluster, Pal 5, will pass within 7 kpc of the Galactic center the next time it crosses the plane, where it might be destroyed by tidal stresses. We study this problem, treating Pal 5 as a self-consistent dynamical system orbiting through an external potential that represents the Galaxy. The first part of the problem is to find suitable analytic approximations to the Galactic potential. They must be valid in all regions the cluster is likely to explore. Observed velocity and positional data for Pal 5 are used as initial conditions to determine the orbit. Methods we used for a different problem some 12 years ago have been adapted to this problem. Three experiments have been run, with M/L= 1, 3, and 10, for the cluster model. The cluster blew up shortly after passing through the Galactic plane (about 130 Myrs after the beginning of the run) with M/L=1. At M/L = 3 and 10 the cluster survived, although it got quite a kick in the fundamental mode on passing through the plane. But the fundamental mode oscillation died out in a couple of oscillation cycles at M/L=10. Pal 5 will probably be destroyed on its next crossing of the Galactic plane if M/L=1, but it can survive (albeit with fairly heavy damage) if NI/L=3. We haven't tried to trap the mass limits more closely than that. Pal 5 comes through pretty well unscathed at M/L=10. An interesting follow-up experiment would be to back the cluster up along its orbit to look at its previous passage through the Galactic plane, to see what kind of object it might have been at earlier times.

  4. The outer halo globular clusters of M31

    NASA Astrophysics Data System (ADS)

    Alves-Brito, Alan; Forbes, Duncan A.; Mendel, Jon T.; Hau, George K. T.; Murphy, Michael T.

    2009-05-01

    We present Keck/HIRES spectra of three globular clusters in the outer halo of M31, at projected distances beyond ~80 kpc from M31. The measured recession velocities for all three globular clusters confirm their association with the globular cluster system of M31. We find evidence for a declining velocity dispersion with radius for the globular cluster system. Their measured internal velocity dispersions, derived virial masses and mass-to-light ratios are consistent with those for the bulk of the M31 globular cluster system. We derive old ages and metallicities which indicate that all three belong to the metal-poor halo globular cluster subpopulation. We find indications that the radial gradient of the mean metallicity of the globular cluster system interior to 50 kpc flattens in the outer regions, however it is still more metal-poor than the corresponding field stars at the same (projected) radius. Based on observations obtained at the W. M. Keck Observatory, which is operated as a scientific partnership among the California Institute of Technology, the University of California and the National Aeronautics and Space Administration. E-mail: abrito@astro.swin.edu.au

  5. Globular Clusters as Cradles of Life and Advanced Civilizations

    NASA Astrophysics Data System (ADS)

    Di Stefano, R.; Ray, A.

    2016-08-01

    Globular clusters are ancient stellar populations in compact dense ellipsoids. There is no star formation and there are no core-collapse supernovae, but several lines of evidence suggest that globular clusters are rich in planets. If so, and if advanced civilizations can develop there, then the distances between these civilizations and other stars would be far smaller than typical distances between stars in the Galactic disk, facilitating interstellar communication and travel. The potent combination of long-term stability and high stellar densities provides a globular cluster opportunity. Yet the very proximity that promotes interstellar travel also brings danger, as stellar interactions can destroy planetary systems. We find, however, that large portions of many globular clusters are “sweet spots,” where habitable-zone planetary orbits are stable for long times. Globular clusters in our own and other galaxies are, therefore, among the best targets for searches for extraterrestrial intelligence (SETI). We use the Drake equation to compare the likelihood of advanced civilizations in globular clusters to that in the Galactic disk. We also consider free-floating planets, since wide-orbit planets can be ejected to travel through the cluster. Civilizations spawned in globular clusters may be able to establish self-sustaining outposts, reducing the probability that a single catastrophic event will destroy the civilization. Although individual civilizations may follow different evolutionary paths, or even be destroyed, the cluster may continue to host advanced civilizations once a small number have jumped across interstellar space. Civilizations residing in globular clusters could therefore, in a sense, be immortal.

  6. YOUNG RADIO PULSARS IN GALACTIC GLOBULAR CLUSTERS

    SciTech Connect

    Boyles, J.; Lorimer, D. R.; Turk, P. J.; Mnatsakanov, R.; Lynch, R. S.; Ransom, S. M.; Freire, P. C.; Belczynski, K.

    2011-11-20

    Currently three isolated radio pulsars and one binary radio pulsar with no evidence of any previous recycling are known in 97 surveyed Galactic globular clusters (GCs). As pointed out by Lyne et al., the presence of these pulsars cannot be explained by core-collapse supernovae, as commonly assumed for their counterparts in the Galactic disk. We apply a Bayesian analysis to the results from surveys for radio pulsars in GCs and find the number of potentially observable non-recycled radio pulsars present in all clusters to be <3600. Accounting for beaming and retention considerations, the implied birthrate for any formation scenario for all 97 clusters is <0.25 pulsars century{sup -1} assuming a Maxwellian distribution of velocities with a dispersion of 10 km s{sup -1}. The implied birthrates for higher velocity dispersions are substantially higher than inferred for such pulsars in the Galactic disk. This suggests that the velocity dispersion of young pulsars in GCs is significantly lower than those of disk pulsars. These numbers may be substantial overestimates due to the fact that the currently known sample of young pulsars is observed only in metal-rich clusters. We propose that young pulsars may only be formed in GCs with metallicities with log[Fe/H] > - 0.6. In this case, the potentially observable population of such young pulsars is 447{sup +1420}{sub -399} (the error bars give a 95% confidence interval) and their birthrate is 0.012{sup +0.037}{sub -0.010} pulsars century{sup -1}. The most likely creation scenario to explain these pulsars is the electron capture supernova of an OMgNe white dwarf.

  7. CENTRAL ROTATIONS OF MILKY WAY GLOBULAR CLUSTERS

    SciTech Connect

    Fabricius, Maximilian H.; Rukdee, Surangkhana; Saglia, Roberto P.; Bender, Ralf; Hopp, Ulrich; Thomas, Jens; Williams, Michael J.; Noyola, Eva; Opitsch, Michael

    2014-06-01

    Most Milky Way globular clusters (GCs) exhibit measurable flattening, even if on a very low level. Both cluster rotation and tidal fields are thought to cause this flattening. Nevertheless, rotation has only been confirmed in a handful of GCs, based mostly on individual radial velocities at large radii. We are conducting a survey of the central kinematics of Galactic GCs using the new Integral Field Unit instrument VIRUS-W. We detect rotation in all 11 GCs that we have observed so far, rendering it likely that a large majority of the Milky Way GCs rotate. We use published catalogs of GCs to derive central ellipticities and position angles. We show that in all cases where the central ellipticity permits an accurate measurement of the position angle, those angles are in excellent agreement with the kinematic position angles that we derive from the VIRUS-W velocity fields. We find an unexpected tight correlation between central rotation and outer ellipticity, indicating that rotation drives flattening for the objects in our sample. We also find a tight correlation between central rotation and published values for the central velocity dispersion, most likely due to rotation impacting the old dispersion measurements.

  8. Finding forming globular clusters at high redshifts

    NASA Astrophysics Data System (ADS)

    Renzini, Alvio

    2017-07-01

    The formation of globular clusters (GCs) with their multiple stellar populations remains a puzzling, unsolved problem in astrophysics. One way to gather critical insight consists in finding sizable numbers of GC progenitors (GCPs) while still near the peak of their star formation phase, at a look-back time corresponding to GC ages (˜12.5 Gyr, or z ≃ 5). This opportunity is quantitatively explored, calculating how many GCPs could be detected by deep imaging in the optical, near-IR and mid-IR bands. For concreteness, for the imaging camera performances those of NIRCam on board of James Webb Space Telescope are adopted. The number of GCPs that could be detected scales linearly with their mass, i.e. on how much more massive GCPs were compared to their GC progeny, and perspectives look promising. Besides providing direct evidence on GC formation, the detection of GCPs, their clustering, with or without a central galaxy already in place, would shed light on the relative timing of GC formation and galaxy growth and assembly. All this may be the result of dedicated observations as well as a side benefit of deep imaging meant to search for the agents of cosmic reionization.

  9. Central Rotations of Milky Way Globular Clusters

    NASA Astrophysics Data System (ADS)

    Fabricius, Maximilian H.; Noyola, Eva; Rukdee, Surangkhana; Saglia, Roberto P.; Bender, Ralf; Hopp, Ulrich; Thomas, Jens; Opitsch, Michael; Williams, Michael J.

    2014-06-01

    Most Milky Way globular clusters (GCs) exhibit measurable flattening, even if on a very low level. Both cluster rotation and tidal fields are thought to cause this flattening. Nevertheless, rotation has only been confirmed in a handful of GCs, based mostly on individual radial velocities at large radii. We are conducting a survey of the central kinematics of Galactic GCs using the new Integral Field Unit instrument VIRUS-W. We detect rotation in all 11 GCs that we have observed so far, rendering it likely that a large majority of the Milky Way GCs rotate. We use published catalogs of GCs to derive central ellipticities and position angles. We show that in all cases where the central ellipticity permits an accurate measurement of the position angle, those angles are in excellent agreement with the kinematic position angles that we derive from the VIRUS-W velocity fields. We find an unexpected tight correlation between central rotation and outer ellipticity, indicating that rotation drives flattening for the objects in our sample. We also find a tight correlation between central rotation and published values for the central velocity dispersion, most likely due to rotation impacting the old dispersion measurements. This Letter includes data taken at The McDonald Observatory of The University of Texas at Austin.

  10. The orbital eccentricities of binary millisecond pulsars in globular clusters

    NASA Technical Reports Server (NTRS)

    Rasio, Frederic A.; Heggie, Douglas C.

    1995-01-01

    Low-mass binary millisecond pulsars (LMBPs) are born with very small orbital eccentricities, typically of order e(sub i) approximately 10(exp -6) to 10(exp -3). In globular clusters, however, higher eccentricities e(sub f) much greater than e(sub i) can be induced by dynamical interactions with passing stars. Here we show that the cross section for this process is much larger than previously estimated. This is becuse, even for initially circular binaries, the induced eccentricity e(sub f) for an encounter with pericenter separation r(sub p) beyond a few times the binary semimajor axis a declines only as a power law (e(sub f) varies as (r(sub p)/a)(exp -5/2), and not as an exponential. We find that all currently known LMBPs in clusters were probably affected by interactions, with their current eccentricities typically greater than at birth by an order of magnitude or more.

  11. The orbital eccentricities of binary millisecond pulsars in globular clusters

    NASA Technical Reports Server (NTRS)

    Rasio, Frederic A.; Heggie, Douglas C.

    1995-01-01

    Low-mass binary millisecond pulsars (LMBPs) are born with very small orbital eccentricities, typically of order e(sub i) approximately 10(exp -6) to 10(exp -3). In globular clusters, however, higher eccentricities e(sub f) much greater than e(sub i) can be induced by dynamical interactions with passing stars. Here we show that the cross section for this process is much larger than previously estimated. This is becuse, even for initially circular binaries, the induced eccentricity e(sub f) for an encounter with pericenter separation r(sub p) beyond a few times the binary semimajor axis a declines only as a power law (e(sub f) varies as (r(sub p)/a)(exp -5/2), and not as an exponential. We find that all currently known LMBPs in clusters were probably affected by interactions, with their current eccentricities typically greater than at birth by an order of magnitude or more.

  12. Variable stars in the globular cluster NGC 6981.

    NASA Astrophysics Data System (ADS)

    Kadla, Z. I.; Brocato, E.; Piersimoni, A.; Gerashchenko, A. N.; Malakhova, Y. N.

    1995-10-01

    The method proposed for detecting RR Lyrae variables on photographic plates was applied to CCD observations of the globular cluster NGC 6981. In the investigated area nine previously unknown variables were discovered.

  13. THE ACCRETION OF DWARF GALAXIES AND THEIR GLOBULAR CLUSTER SYSTEMS

    SciTech Connect

    Masters, Craig E.; Ashman, Keith M. E-mail: ashmank@umkc.ed

    2010-12-10

    The question of where the low-metallicity globular clusters in early-type galaxies came from has profound implications for the formation of those galaxies. Our work supports the idea that the metal-poor globular cluster systems of giant early-type galaxies formed in dwarf galaxies that have been subsumed by the giants. To support this hypothesis, two linear relations, one involving globular cluster metallicity versus host galaxy luminosity and one involving metallicity versus velocity dispersion were studied. Tentatively, these relations show that the bright ellipticals do not obey the same trend as the dwarfs, suggesting that the low-metallicity globular clusters did not form within their parent bright ellipticals.

  14. The Nature of LSB galaxies revealed by their Globular Clusters

    NASA Astrophysics Data System (ADS)

    Kissler-Patig, Markus

    2005-07-01

    Low Surface Brightness {LSB} galaxies encompass many of the extremes in galaxy properties. Their understanding is essential to complete our picture of galaxy formation and evolution. Due to their historical under-representation on galaxy surveys, their importance to many areas of astronomy has only recently began to be realized. Globular clusters are superb tracers of the formation histories of galaxies and have been extensively used as such in high surface brightness galaxies. We propose to investigate the nature of massive LSB galaxies by studying their globular cluster systems. No globular cluster study has been reported for LSB galaxies to date. Yet, both the presence or absence of globular clusters set very strong constraints on the conditions prevailing during LSB galaxy formation and evolution. Both in dwarf and giant high surface brightness {HSB} galaxies, globular clusters are known to form as a constant fraction of baryonic mass. Their presence/absence immediately indicates similarities or discrepancies in the formation and evolution conditions of LSB and HSB galaxies. In particular, the presence/absence of metal-poor halo globular clusters infers similarities/differences in the halo formation and assembly processes of LSB vs. HSB galaxies, while the presence/absence of metal-rich globular clusters can be used to derive the occurrence and frequency of violent events {such as mergers} in the LSB galaxy assembly history. Two band imaging with ACS will allow us to identify the globular clusters {just resolved at the selected distance} and to determine their metallicity {potentially their rough age}. The composition of the systems will be compared to the extensive census built up on HSB galaxies. Our representative sample of six LSB galaxies {cz < 2700 km/s} are selected such, that a large system of globular clusters is expected. Globular clusters will constrain phases of LSB galaxy formation and evolution that can currently not be probed by other means. HST

  15. Dynamical evolution of globular-cluster systems in clusters of galaxies

    SciTech Connect

    Muzzio, J.C.

    1987-04-01

    The dynamical processes that affect globular-cluster systems in clusters of galaxies are analyzed. Two-body and impulsive approximations are utilized to study dynamical friction, drag force, tidal stripping, tidal radii, globular-cluster swapping, tidal accretion, and galactic cannibalism. The evolution of galaxies and the collision of galaxies are simulated numerically; the steps involved in the simulation are described. The simulated data are compared with observations. Consideration is given to the number of galaxies, halo extension, location of the galaxies, distribution of the missing mass, nonequilibrium initial conditions, mass dependence, massive central galaxies, globular-cluster distribution, and lost globular clusters. 116 references.

  16. Classification of stellar populations in globular clusters

    NASA Astrophysics Data System (ADS)

    Wang, Yue; Zhao, Gang; Li, Hai-Ning

    2017-04-01

    Possessing multiple stellar populations has been accepted as a common feature of globular clusters (GCs). Different stellar populations manifest themselves with different chemical features, e.g. the well-known O-Na anti-correlation. Generally, the first (primordial) population has O and Na abundances consistent with those of field stars with similar metallicity; while the second (polluted) population is identified by their Na overabundance and O deficiency. The fraction of the populations is an important constraint on the GC formation scenario. Several methods have been proposed for the classification of GC populations. Here we examine a criterion derived based on the distribution of Galactic field stars, which relies on Na abundance as a function of [Fe/H], to distinguish first and second stellar populations in GCs. By comparing the first population fractions of 17 GCs estimated by the field star criterion with those in the literature derived by methods related to individual GCs, we find that the field star criterion tends to overestimate the first population fractions. The population separation methods, which are related to an individual GC sample, are recommended because the diversity of GCs can be taken into consideration. Currently, more caution should be exercised if one wants to regard field stars as a reference for the identification of a GC population. However, further study on the connection between field stars and GCs populations is still needed.

  17. Globular clusters in the halo of M31

    SciTech Connect

    Racine, R. Canada-France-Hawaii Telescope Corp., Kamuela, HI )

    1991-03-01

    The CFHT was used to obtain high-resolution CCD images of 82 cluster candidates in the halo of M31. These data, combined with radial velocities which cover an additional 27 candidates, are used to compile a catalog of 51 bona fide M31 halo globulars. The other candidates are found to be background galaxies (54) and field stars (4). The cluster sample appears to be incomplete for V greater than 18. The projected distribution of globulars follows an 1/r-squared law for r(kpc) between values of 6 and 22 and then drops faster, suggesting a cutoff at about 40 kpc. These trends are similar to those for globular clusters in the Milky Way halo. The total populaton of globulars in M31 is estimated to be larger than in the Milky Way by a factor of 1.8 + or - 0.3. 30 refs.

  18. THE TIMING OF NINE GLOBULAR CLUSTER PULSARS

    SciTech Connect

    Lynch, Ryan S.; Freire, Paulo C. C.; Ransom, Scott M.; Jacoby, Bryan A. E-mail: pfreire@mpifr-bonn.mpg.de E-mail: bryan.jacoby@gmail.com

    2012-02-01

    We have used the Robert C. Byrd Green Bank Telescope to time nine previously known pulsars without published timing solutions in the globular clusters (GCs) M62, NGC 6544, and NGC 6624. We have full timing solutions that measure the spin, astrometric, and (where applicable) binary parameters for six of these pulsars. The remaining three pulsars (reported here for the first time) were not detected enough to establish solutions. We also report our timing solutions for five pulsars with previously published solutions, and find good agreement with other authors, except for PSR J1701-3006B in M62. Gas in this system is probably responsible for the discrepancy in orbital parameters, and we have been able to measure a change in the orbital period over the course of our observations. Among the pulsars with new solutions we find several binary pulsars with very low mass companions (members of the so-called 'black widow' class) and we are able to place constraints on the mass-to-light ratio in two clusters. We confirm that one of the pulsars in NGC 6624 is indeed a member of the rare class of non-recycled pulsars found in GCs. We have also measured the orbital precession and Shapiro delay for a relativistic binary in NGC 6544. If we assume that the orbital precession can be described entirely by general relativity, which is likely, we are able to measure the total system mass (2.57190(73) M{sub Sun }) and companion mass (1.2064(20) M{sub Sun }), from which we derive the orbital inclination (sin i = 0.9956(14)) and the pulsar mass (1.3655(21) M{sub Sun }), the most precise such measurement ever obtained for a millisecond pulsar. The companion is the most massive known around a fully recycled pulsar.

  19. Multiple Stellar Populations in Galactic Globular Clusters: General Properties

    NASA Astrophysics Data System (ADS)

    Piotto, Giampaolo

    2015-08-01

    Globular clusters are the most ancient stellar systems for which we can have a reliable age estimate, and therefore bring information on star formation processes in the early Universe. The discovery that these objects host different, distinct populations of stars drastically changed our view on their origin and evolution. Some of the most plausible scenarios able to account for the photometric and chemical properties of multiple stellar populations in globular clusters necessarily imply that these objects must have been much more massive in the past. Whether globular clusters should be considered either as remnants of massive star clusters or nuclei of former dwarf galaxies (or both of them) is an open issue. Surely, we need to better know the chemical and kinematical properties of the different populations hosted by single clusters, and their relation with the cluster parameters, in order to shed light on this problem. Determination of the basic properties of stars hosted by (young ) massive clusters, nuclear clusters, and dwarf galaxies and a comparison with the parameters characterizing multiple stellar populations in globular cluster is a complementary approach that shall be pursued.For the first time, in my talk, I will discuss the results of a large, legacy multi-wavelength, astrometric and photometric survey based on ACS and WFC3/HST observations which include UV data. A census of the presence and frequency of multiple populations in almost half of the globular clusters of our Galaxy, their chemical tagging, radial distribution and kinematics will be presented. The relation between multiple population properties and cluster parameters will be illustrated. Consequences of these observational facts on different scenarios proposed for the formation and evolution of globular cluster stars will be critically discussed. Future perspectives towards our understanding if this complex phenomenon will be highlighted.

  20. Binary interactions and multiple stellar populations in globular clusters

    NASA Astrophysics Data System (ADS)

    Jiang, Dengkai; Han, Zhanwen; Li, Lifang

    2017-03-01

    Globular clusters (GCs) have multiple stellar populations, which show star-to-star abundance variations and multiple sequences (or spreads) in the Hertzsprung-Russell diagrams. It is explained by multiple generations of star-formation in GCs. However, the observed evidence of ongoing star-formation was not found within any clusters. Here we present a binary interactions scenario for the formation of multiple stellar populations in GCs, where GC stars were born in a single burst of star formation, but some of them are members of binary systems. Binary interactions can produce peculiar stars, e.g. the merged stars and the accretor stars. They are more massive than normal single stars in the same evolutionary stage, and they are rapidly rotating stars at the moment of their formation. Rotationally induced mixing can cause the variations of their surface chemical composition. This results in the single-generation GCs showing abundance anomalies.

  1. Integrated photometry of globular clusters in the Vilnius system

    NASA Astrophysics Data System (ADS)

    Zdanavicius, K. V.

    1983-02-01

    Integrated color indices measured in the Vilnius photometric system and color excesses are given for 39 globular clusters. The integrated spectral type is not a sufficient criterion for globular clusters to have identical intrinsic colors. A study is made of the relation between the integrated color indices and parameters of the H-R diagram: the Dickens morphological type D of the horizontal branch and the slope S of the giant branch. The integrated colors of clusters with a blue horizontal branch show no correlation with either D or S. The remaining clusters have large color indices mainly because their stars are redistributed along the horizontal branch.

  2. Galactic globular cluster 47 Tucanae: new ties between the chemical and dynamical evolution of globular clusters?

    NASA Astrophysics Data System (ADS)

    Kučinskas, A.; Dobrovolskas, V.; Bonifacio, P.

    2014-08-01

    Context. It is generally accepted today that Galactic globular clusters (GGCs) consist of at least two generations of stars that are different in their chemical composition and perhaps age. However, knowledge about the kinematical properties of these stellar generations, which may provide important information for constraining evolutionary scenarios of the GGCs, is still limited. Aims: We study the connections between chemical and kinematical properties of different stellar generations in the Galactic globular cluster 47 Tuc. Methods: To achieve this goal, we used abundances of Li, O, and Na determined in 101 main sequence turn-off (TO) stars with the aid of 3D hydrodynamical model atmospheres and NLTE abundance analysis methodology. We divided our sample TO stars into three groups according to their position in the [Li/Na] - [Na/O] plane to study their spatial distribution and kinematical properties. Results: We find that there are statistically significant radial dependencies of lithium and oxygen abundances, A(Li) and A(O), as well as that of [Li/Na] abundance ratio. Our results show that first-generation stars are less centrally concentrated and dynamically hotter than stars belonging to subsequent generations. We also find a significant correlation between the velocity dispersion and O and Na abundance, and between the velocity dispersion and the [Na/O] abundance ratio.

  3. Enrichment by supernovae in globular clusters with multiple populations.

    PubMed

    Lee, Jae-Woo; Kang, Young-Woon; Lee, Jina; Lee, Young-Wook

    2009-11-26

    The most massive globular cluster in the Milky Way, omega Centauri, is thought to be the remaining core of a disrupted dwarf galaxy, as expected within the model of hierarchical merging. It contains several stellar populations having different heavy elemental abundances supplied by supernovae-a process known as metal enrichment. Although M 22 appears to be similar to omega Cen, other peculiar globular clusters do not. Therefore omega Cen and M 22 are viewed as exceptional, and the presence of chemical inhomogeneities in other clusters is seen as 'pollution' from the intermediate-mass asymptotic-giant-branch stars expected in normal globular clusters. Here we report Ca abundances for seven globular clusters and compare them to omega Cen. Calcium and other heavy elements can only be supplied through numerous supernovae explosions of massive stars in these stellar systems, but the gravitational potentials of the present-day clusters cannot preserve most of the ejecta from such explosions. We conclude that these globular clusters, like omega Cen, are most probably the relics of more massive primeval dwarf galaxies that merged and disrupted to form the proto-Galaxy.

  4. Dynamical evolution of globular clusters in dark matter halos

    NASA Astrophysics Data System (ADS)

    Breen, Phil; Varri, Anna Lisa; Penarrubia, Jorge; Heggie, Douglas C.

    2017-06-01

    The formation of globular clusters in a cosmological context is a topical open problem. One possible formation scenario is that globular clusters have formed in their own dark matter halos, and, as a result, some clusters may have retained it to the present day. In such a case, collisional processes taking place in the central regions of globulars may lead to the formation of a tenuous stellar envelope extending far beyond the tidal boundary of the parent cluster.The synergy between the astrometric mission Gaia and forthcoming multi-object spectrographs such as WEAVE will allow us to explore, with unprecedented accuracy, the outer regions of selected Galactic globular clusters, therefore it is particularly timely to consider to what extent the presence of dark matter is consistent with their dynamics and structure at large distances from the cluster centre.Driven by these motivations, we present the results of a series of direct N-body simulations where globular clusters have been evolved self-consistently in a static dark matter potential. Special attention will be given to the exploration of the effects of the dark halo on the traditional phases of the long-term evolution of collisional systems and the dynamical interplay with other fundamental physical ingredients, such as stellar-mass black holes, will be discussed.

  5. Extremely α -Enriched Globular Clusters in Early-Type Galaxies

    NASA Astrophysics Data System (ADS)

    Puzia, T. H.; Kissler-Patig, M.; Goudfrooij, P.

    2005-12-01

    We compare [α /Fe], metallicity, and age distributions of globular clusters in elliptical, lenticular, and spiral galaxies, which we derive from Lick line index measurements. We find a large number of globular clusters in elliptical galaxies that reach significantly higher [α /Fe] values ([α /Fe] >0.5) than clusters in lenticular and spiral galaxies. Most of these highly α -enriched globular clusters are old (t>8 Gyr) and exhibit relatively high metallicities up to solar values. A comparison with supernova yield models suggests that the progenitor gas clouds of these globular clusters were predominantly enriched by massive stars (⪆ 20 M⊙) with little contribution from lower-mass stars. The measured [α /Fe] ratios are also consistent with yields of very massive pair-instability supernovae ( ˜130-190 M⊙). This implies that the chemical enrichment of the progenitor gas was completed on extremely short timescales of the order of a few Myr. Given the lower [α /Fe] ratios of the diffuse stellar population in early-type galaxies, our results suggest that the extremely α -enhanced globular clusters are members of the the very first generation of star clusters formed, and that their formation epochs likely predate the formation of the majority of stars in giant early-type galaxies.

  6. Omega Centauri: Globular Cluster, Stellar Stream - Dwarf Galaxy

    NASA Astrophysics Data System (ADS)

    Marsakovv, V. A.; Borkova, T. V.

    Data from our compiled catalogs of the spectroscopic determinations of the abundances of α-elements in the stars of field and globular clusters of the Milky Way are used to investigate the chemical evolution of the ω Cen globular cluster and of the same name moving group. It is established that the dependences of the relative abundances of α-elements on the metallicity for the stars of both the ω Cen moving group and the globular cluster coincide, which with the great probability testifies as genetic connected and belonging both to dwarf galaxy-satellite galaxy, the decomposed under the action of tidal forces of the Galaxy. It is simultaneously discovered that the metallicity functions of the stream and globular cluster demonstrate identical spread, but the positions of the maximums of distributions are spread to Δ[Fe/H]≍ -0.5 (with the peak on the smaller metallicity in globular cluster). The following conclusions are made: 1. The descending branch of the "[Fe/H] - [α/Fe]" dependence of the ω Cen globular cluster is formed by the young metal-rich stars, which was captured from the parental dwarf galaxy. 2. The stars of the ω Cen globular cluster are absent in the same name moving group - are there located only the stars of their parental galaxy. 3. The star formation rate in the ω Cen dwarf galaxy was always considerably lower than in the our Galaxy, about which they testify the small metallicity of characteristic knee ("break point") to [Fe/H] ≍ -1.3 and steeply incidence in the relation [α/Fe] with further increase in the metallicity.

  7. The globular cluster system of NGC 6822

    NASA Astrophysics Data System (ADS)

    Veljanoski, J.; Ferguson, A. M. N.; Mackey, A. D.; Huxor, A. P.; Hurley, J. R.; Bernard, E. J.; Côté, P.; Irwin, M. J.; Martin, N. F.; Burgett, W. S.; Chambers, K. C.; Flewelling, H.; Kudritzki, R.; Waters, C.

    2015-09-01

    We present a comprehensive analysis of the globular cluster (GC) system of the Local Group dwarf irregular galaxy NGC 6822. Our study is based on homogeneous optical and near-IR photometry, as well as long-slit spectroscopic observations which are used to determine new radial velocities for six GCs, two of which had no previous spectroscopic information. We construct optical-near-IR colour-colour diagrams and through comparison to simple stellar population models infer that the GCs have old ages consistent with being 9 Gyr or older, while their metallicities are in the range between -1.6 ≲ [Fe/H] ≲ -0.4. We conduct a kinematic analysis of the GC population and find tentative evidence for weak net rotation of the GC system, in the same sense as that exhibited by the underlying spheroid. The most likely amplitude of rotation is ≈10 km s-1, approximately half the magnitude of the observed velocity dispersion. Finally, we use the GCs to estimate the dynamical mass of NGC 6822 within ˜11 kpc and we formally find it to be in the range between (3 and 4) × 109 M⊙. This implies an overall mass-to-light ratio in the range of ˜30-40 and indicates that NGC 6822 is highly dark-matter-dominated. The mass and the corresponding mass-to-light ratio estimates are affected by various additional systematic effects due to limitations of the data and the model that are not necessary reflected in the formal uncertainties.

  8. Globular Cluster formation in a collapsing supershell

    NASA Astrophysics Data System (ADS)

    Recchi, S.; Wünsch, R.; Palouš, J.; Dinnbier, F.

    2017-10-01

    Primordial clouds are supposed to host the so-called population III stars. These stars are very massive and completely metal-free. The final stage of the life of population III stars with masses between 130 and 260 solar masses is a very energetic hypernova explosion. A hypernova drives a shock, behind which a spherically symmetric very dense supershell forms, which might become gravitationally unstable, fragment, and form stars. In this paper we study under what conditions can an expanding supershell become gravitationally unstable and how the feedback of these supershell stars (SSSs) affects its surroundings. We simulate, by means of a 1-D Eulerian hydrocode, the early evolution of the primordial cloud after the hypernova explosion, the formation of SSSs, and the following evolution, once the SSSs start to release energy and heavy elements into the interstellar medium. Our results indicate that a shell, enriched with nucleosynthetic products from SSSs, propagates inwards, towards the center of the primordial cloud. In a time span of a few Myr, this inward-propagating shell reaches a distance of only a few parsec away from the center of the primordial cloud. Its density is extremely high and its temperature very low, thus the conditions for a new episode of star formation are achieved. We study what fraction of these two distinct populations of stars can remain bound and survive until the present day. We study also under what conditions can this process repeat and form multiple stellar populations. We extensively discuss whether the proposed scenario can help to explain some open questions of the formation mechanism of globular clusters.

  9. Determination of Globular Cluster metallicities with BUSCA

    NASA Astrophysics Data System (ADS)

    Wittlich, M.; Cordes, O.; Reif, K.

    Globular Clusters (GCs) have always been a topic of great interest probing stellar and galactic evolution. This includes both determination of age and metallicity. The stars in GCs are known to be more or less coeval and therefore considered to be formed out of the same primordial cloud, implying same chemical composition. Deriving metallicities yields indicators for primordial enrichment of the GC forming cloud. Recent studies show abundance differences among GC giants (Kraft 1994). The spread in abundances tends to be correlated with oxygen and CN-band strengths, resulting in new differing formation and evolution scenarios for GC. Strömgren photometry is known to be an adequate method for metallicity determination (Strömgren 1966). In this poster, we present preliminary results of metallicity studies in the Strömgren uvby-Hβ colour system for a sample of bright GCs. The data were obtained with BUSCA (``Bonn University Simultaneous CAmera''), the new 4k×4k CCD 4-colour imaging instrument at the 2.2m telescope at Calar Alto Observatory. The observed GC were selected relying on a wide spread in mean GC metallicities to obtain hints on their formation process. Photometric reduction was conducted using the package DAOPHOT of the IRAF program. Standard stars for calibration were chosen according to Olsen & Perry (1987). A revised Strömgren metallicity calibration for red giants proposed by Hilker (2000) was applied to the data to detect CN variations. In connection with spectroscopy from literature we are able to argue whether the CN variations are triggered by primordial abundance variations or by evolutionary mixing processes.

  10. Dark Matter Halos in Galaxies and Globular Cluster Populations

    NASA Astrophysics Data System (ADS)

    Hudson, Michael J.; Harris, Gretchen L.; Harris, William E.

    2014-05-01

    We combine a new, comprehensive database for globular cluster populations in all types of galaxies with a new calibration of galaxy halo masses based entirely on weak lensing. Correlating these two sets of data, we find that the mass ratio η ≡ M GCS/M h (total mass in globular clusters, divided by halo mass) is essentially constant at langηrang ~ 4 × 10-5, strongly confirming earlier suggestions in the literature. Globular clusters are the only known stellar population that formed in essentially direct proportion to host galaxy halo mass. The intrinsic scatter in η appears to be at most 0.2 dex we argue that some of this scatter is due to differing degrees of tidal stripping of the globular cluster systems between central and satellite galaxies. We suggest that this correlation can be understood if most globular clusters form at very early stages in galaxy evolution, largely avoiding the feedback processes that inhibited the bulk of field-star formation in their host galaxies. The actual mean value of η also suggests that about one-fourth of the initial gas mass present in protogalaxies collected into giant molecular clouds large enough to form massive, dense star clusters. Finally, our calibration of langηrang indicates that the halo masses of the Milky Way and M31 are (1.2 ± 0.5) × 1012 M ⊙ and (3.9 ± 1.8) × 1012 M ⊙, respectively.

  11. Binaries and the dynamical evolution of globular clusters

    NASA Astrophysics Data System (ADS)

    Ji, Jun

    Binaries are thought to be the primary heating source in globular clusters, since they can heat the environment of globular clusters by converting their binding energy to the kinetic energy of the incoming stars through the dynamical interactions. Even a small primordial binary fraction is sufficient to postpone globular clusters from the core collapse for many relaxation times. So the binary fraction is an essential parameter which can dramatically affect the dynamical evolution of globular clusters. In this thesis work, I determined the binary fractions for a sample of 35 Galactic globular clusters with their color-magnitude diagrams (CMDs), which covers a wide range of the dynamical ages and metallicity. Those CMDs were constructed with the PSF photometry by Dolphot (V1.2) from their HST ACS archival data. Three different methods were used to estimate the binary fractions within the core, the half-mass radius, and the whole field of view regions. The binary fractions along the cluster radial bins were also analyzed. From the results, I found that the mean binary fractions within the core and the half-mass radii are 7.0% and 5.6%, respectively. The binary fractions within the core and the half-mass radii correlate with the cluster ages, with decreasing binary fractions against time, but not with their dynamical times and metallicity. The binary fractions within the half-mass radius also correlate with the cluster absolute V magnitudes, with fainter clusters having higher binary fractions. The radial distribution of the binary fractions show a significant correlation with the cluster radii, with decreasing values outwards. This is consistent with the mass segregation effect predicted by the simulations of the dynamical evolution of globular clusters. I also compiled a catalog containing 6,004 high mass-ratio binary candidates selected from 23 Galactic globular clusters in our sample through their CMDs, which can be used to search the main

  12. Astronomers Ponder Lack of Planets in Globular Cluster

    NASA Technical Reports Server (NTRS)

    2000-01-01

    This videotape has seven segments, discussing and showing the evidence for the proposition that the galactic clusters do not have many planets. Specifically the segments show: (1) Dr. Ron Gilliland discussing the process of looking for "Hot Jupiters" (i.e., planets about the size of Jupiter, which are hotter than Jupiter) in the globular clusters, (2) a zoom into 47 Tucanae globular cluster, (3) an animation of a planet passing between the host star and the earth with a brightness graph, (4) the same animation as before without the graph, (5) Ron Gilliland of the Space Telescope Science Institute (STScI) discussing possible interpretations of his findings in the 47 Tucanae globular cluster, (6) Ron Gilliland examining the images of 47 Tucanae, and (7) images of 47 Tucanae watching for variations in brightness.

  13. 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.

  14. Astronomers Ponder Lack of Planets in Globular Cluster

    NASA Technical Reports Server (NTRS)

    2000-01-01

    This videotape has seven segments, discussing and showing the evidence for the proposition that the galactic clusters do not have many planets. Specifically the segments show: (1) Dr. Ron Gilliland discussing the process of looking for "Hot Jupiters" (i.e., planets about the size of Jupiter, which are hotter than Jupiter) in the globular clusters, (2) a zoom into 47 Tucanae globular cluster, (3) an animation of a planet passing between the host star and the earth with a brightness graph, (4) the same animation as before without the graph, (5) Ron Gilliland of the Space Telescope Science Institute (STScI) discussing possible interpretations of his findings in the 47 Tucanae globular cluster, (6) Ron Gilliland examining the images of 47 Tucanae, and (7) images of 47 Tucanae watching for variations in brightness.

  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. RETENTION OF STELLAR-MASS BLACK HOLES IN GLOBULAR CLUSTERS

    SciTech Connect

    Morscher, Meagan; Umbreit, Stefan; Farr, Will M.; Rasio, Frederic A. E-mail: s-umbreit@northwestern.edu E-mail: rasio@northwestern.edu

    2013-01-20

    Globular clusters should be born with significant numbers of stellar-mass black holes (BHs). It has been thought for two decades that very few of these BHs could be retained through the cluster lifetime. With masses {approx}10 M{sub Sun }, BHs are {approx}20 times more massive than an average cluster star. They segregate into the cluster core, where they may eventually decouple from the remainder of the cluster. The small-N core then evaporates on a short timescale. This is the so-called Spitzer instability. Here we present the results of a full dynamical simulation of a globular cluster containing many stellar-mass BHs with a realistic mass spectrum. Our Monte Carlo simulation code includes detailed treatments of all relevant stellar evolution and dynamical processes. Our main finding is that old globular clusters could still contain many BHs at present. In our simulation, we find no evidence for the Spitzer instability. Instead, most of the BHs remain well mixed with the rest of the cluster, with only the innermost few tens of BHs segregating significantly. Over the 12 Gyr evolution, fewer than half of the BHs are dynamically ejected through strong binary interactions in the cluster core. The presence of BHs leads to long-term heating of the cluster, ultimately producing a core radius on the high end of the distribution for Milky Way globular clusters (and those of other galaxies). A crude extrapolation from our model suggests that the BH-BH merger rate from globular clusters could be comparable to the rate in the field.

  17. Possible Streams of the Globular Clusters in the Galaxy

    NASA Astrophysics Data System (ADS)

    Gao, Shuang; Jiang, Bi-Wei; Zhao, Yong-Heng

    2007-02-01

    We aim to retrieve ghost streams under the assumption that all the globular clusters in our Galaxy were formed in very early merge events. Our results are based on two speculations: that the specific energy and angular momentum of the globular clusters after merge are not changed in the course of evolution and that the globular clusters with a common origin would stay in the same orbit plane as the parent galaxy. After taking into account the apogalacticum distance of the orbits, we suggest with some confidence five possible streams. The number of streams is consistent with the previous results. Three of the four well established members of the Sagittarius stream were found to be in one of our streams. Several other globular clusters in our result were also thought to come from accretion by previous researchers. The orbital parameters of the streams are derived, which provide a way to test whether these streams are true with the help of more accurate measurement of proper motions of the globular clusters.

  18. Structural and Dynamical Properties of 29 Galactic Globular Clusters

    NASA Astrophysics Data System (ADS)

    Sohn, Young-Jong; Chun, Mun-Suk; Yim, Hong-Suh; Byun, Yong-Ik

    1997-12-01

    We use B band CCD images to investigate the surface brightness distributions and dynamical properties of 29 Galactic globular clusters. Model fits suggest that 22 clusters show King type surface brightness profiles, while 7 clusters are characterized by power law cusp profiles. For the King type clusters, concentration parameters (c = log(rt =rc)) range from 1.20 to 2.10, and core radii are 0.4 to 1.9 pc. The mean value of power law slopes of 7 cuspy clusters was estimated as ¥á = 1.011 +/- 0.065. Total masses of King type globular clusters are in the range of 1.7 x 104M to 1.0 x 106M with a mean of 1.7 x 105M . A significant positive correlation between mass and mass-to-light ratio of King type globular clusters has been confirmed with a Pearson's correlation coefficient r = 0.52 and a confidence level of 99%. Our data also confirm a linear relation between total mass and absolute magnitude of King type globular clusters.

  19. 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.

  20. The Extended Globular Cluster System of NGC3923

    NASA Astrophysics Data System (ADS)

    Ahumada, Tomás; Miller, Bryan; Candlish, Graeme; McGaugh, Stacy S.; Mihos, Chris; Smith, Rory; Puzia, Thomas H.; Taylor, Matthew

    2017-01-01

    In the LambdaCMD paradigm of galaxy formation galaxy halos and their globular clusters systems build up over time by the accretion of small satellites. We can learn about this process in detail by observing systems with ongoing accretion events and comparing the data with simulations. Elliptical shell galaxies are systems that are thought to be due to ongoing or recent minor mergers. We present preliminary results of an investigation of the entire globular cluster system of the shell galaxy NGC3923 from deep DECam g and i-band imaging. Cluster candidates are selected using Principal Component Analysis of Sextractor/PSFEx parameters. We will present the 2D and radial distributions of the globular cluster candidates out to a projected radius of about 130kpc, or 26Re, making this one of the most extended cluster systems studied. We find that the bluer globular cluster candidates have a shallower radial distribution than the red cluster candidates, in agreement with many previous studies.

  1. 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).

  2. Globular Cluster Systems in Brightest Cluster Galaxies. III: Beyond Bimodality

    NASA Astrophysics Data System (ADS)

    Harris, William E.; Ciccone, Stephanie M.; Eadie, Gwendolyn M.; Gnedin, Oleg Y.; Geisler, Douglas; Rothberg, Barry; Bailin, Jeremy

    2017-01-01

    We present new deep photometry of the rich globular cluster (GC) systems around the Brightest Cluster Galaxies UGC 9799 (Abell 2052) and UGC 10143 (Abell 2147), obtained with the Hubble Space Telescope (HST) ACS and WFC3 cameras. For comparison, we also present new reductions of similar HST/ACS data for the Coma supergiants NGC 4874 and 4889. All four of these galaxies have huge cluster populations (to the radial limits of our data, comprising from 12,000 to 23,000 clusters per galaxy). The metallicity distribution functions (MDFs) of the GCs can still be matched by a bimodal-Gaussian form where the metal-rich and metal-poor modes are separated by ≃ 0.8 dex, but the internal dispersions of each mode are so large that the total MDF becomes very broad and nearly continuous from [Fe/H] ≃ ‑2.4 to solar. There are, however, significant differences between galaxies in the relative numbers of metal-rich clusters, suggesting that they underwent significantly different histories of mergers with massive gas-rich halos. Last, the proportion of metal-poor GCs rises especially rapidly outside projected radii R≳ 4 {R}{eff}, suggesting the importance of accreted dwarf satellites in the outer halo. Comprehensive models for the formation of GCs as part of the hierarchical formation of their parent galaxies will be needed to trace the systematic change in structure of the MDF with galaxy mass, from the distinctly bimodal form in smaller galaxies up to the broad continuum that we see in the very largest systems.

  3. Co-evolution of galactic nuclei and globular cluster systems

    SciTech Connect

    Gnedin, Oleg Y.; Ostriker, Jeremiah P.; Tremaine, Scott

    2014-04-10

    We revisit the hypothesis that dense galactic nuclei are formed from inspiraling globular clusters. Recent advances in the understanding of the continuous formation of globular clusters over cosmic time and the concurrent evolution of the galaxy stellar distribution allow us to construct a simple model that matches the observed spatial and mass distributions of clusters in the Galaxy and the giant elliptical galaxy M87. In order to compare with observations, we model the effects of dynamical friction and dynamical evolution, including stellar mass loss, tidal stripping of stars, and tidal disruption of clusters by the growing galactic nucleus. We find that inspiraling globular clusters form a dense central structure, with mass and radius comparable to the typical values in observed nuclear star clusters (NSCs) in late-type and low-mass early-type galaxies. The density contrast associated with the NSC is less pronounced in giant elliptical galaxies. Our results indicate that the NSC mass as a fraction of mass of the galaxy stellar spheroid scales as M{sub NSC}/M{sub ∗}≈0.0025 M{sub ∗,11}{sup −0.5}. Thus disrupted globular clusters could contribute most of the mass of NSCs in galaxies with stellar mass below 10{sup 11} M {sub ☉}. The inner part of the accumulated cluster may seed the growth of a central black hole via stellar dynamical core collapse, thereby relieving the problem of how to form luminous quasars at high redshift. The seed black hole may reach ∼10{sup 5} M {sub ☉} within ≲ 1 Gyr of the beginning of globular cluster formation.

  4. HST Imaging of the Globular Clusters in the Formax Cluster: Color and Luminosity Distributions

    NASA Technical Reports Server (NTRS)

    Grillmair, C. J.; Forbes, D. A.; Brodie, J.; Elson, R.

    1998-01-01

    We examine the luminosity and B - I color distribution of globular clusters for three early-type galaxies in the Fornax cluster using imaging data from the Wide Field/Planetary Camera 2 on the Hubble Space Telescope.

  5. MOCK OBSERVATIONS OF BLUE STRAGGLERS IN GLOBULAR CLUSTER MODELS

    SciTech Connect

    Sills, Alison; Glebbeek, Evert; Chatterjee, Sourav; Rasio, Frederic A. E-mail: e.glebbeek@astro.ru.nl E-mail: rasio@northwestern.edu

    2013-11-10

    We created artificial color-magnitude diagrams of Monte Carlo dynamical models of globular clusters and then used observational methods to determine the number of blue stragglers in those clusters. We compared these blue stragglers to various cluster properties, mimicking work that has been done for blue stragglers in Milky Way globular clusters to determine the dominant formation mechanism(s) of this unusual stellar population. We find that a mass-based prescription for selecting blue stragglers will select approximately twice as many blue stragglers than a selection criterion that was developed for observations of real clusters. However, the two numbers of blue stragglers are well-correlated, so either selection criterion can be used to characterize the blue straggler population of a cluster. We confirm previous results that the simplified prescription for the evolution of a collision or merger product in the BSE code overestimates their lifetimes. We show that our model blue stragglers follow similar trends with cluster properties (core mass, binary fraction, total mass, collision rate) as the true Milky Way blue stragglers as long as we restrict ourselves to model clusters with an initial binary fraction higher than 5%. We also show that, in contrast to earlier work, the number of blue stragglers in the cluster core does have a weak dependence on the collisional parameter Γ in both our models and in Milky Way globular clusters.

  6. Spectroscopy of the globular clusters in M87

    NASA Technical Reports Server (NTRS)

    Mould, J. R.; Oke, J. B.; Nemec, J. M.

    1986-01-01

    With a velocity dispersion of 370 + or - 50 km/sec the globular cluster system of M87 is kinematically hotter than the stars in the giant elliptical itself. This is consistent with the clusters' shallower density distribution for isotropic orbits. The mean metallicity of the 27 clusters in the sample analyzed here is no more than a factor of 2 more metal rich than the cluster system of the Milky Way, but considerably more metal poowr than the integrated starlight in the field at a radius of 1' from the center of M87. There is no evidence for the existence of young clusters in the system. The mass-radius relation between 1' and 5' required to contain the globular clusters joins on to that required to contain the hot gas around M87.

  7. Black hole binaries dynamically formed in globular clusters

    NASA Astrophysics Data System (ADS)

    Park, Dawoo; Kim, Chunglee; Lee, Hyung Mok; Bae, Yeong-Bok; Belczynski, Krzysztof

    2017-08-01

    We investigate properties of black hole (BH) binaries formed in globular clusters via dynamical processes, using directN-body simulations. We pay attention to effects of BH mass function on the total mass and mass ratio distributions of BH binaries ejected from clusters. First, we consider BH populations with two different masses in order to learn basic differences from models with single-mass BHs only. Secondly, we consider continuous BH mass functions adapted from recent studies on massive star evolution in a low metallicity environment, where globular clusters are formed. In this work, we consider only binaries that are formed by three-body processes and ignore stellar evolution and primordial binaries for simplicity. Our results imply that most BH binary mergers take place after they get ejected from the cluster. Also, mass ratios of dynamically formed binaries should be close to 1 or likely to be less than 2:1. Since the binary formation efficiency is larger for higher-mass BHs, it is likely that a BH mass function sampled by gravitational-wave observations would be weighed towards higher masses than the mass function of single BHs for a dynamically formed population. Applying conservative assumptions regarding globular cluster populations such as small BH mass fraction and no primordial binaries, the merger rate of BH binaries originated from globular clusters is estimated to be at least 6.5 yr-1 Gpc-3. Actual rate can be up to more than several times of our conservative estimate.

  8. Supra-galactic colour patterns in globular cluster systems

    NASA Astrophysics Data System (ADS)

    Forte, Juan C.

    2017-07-01

    An analysis of globular cluster systems associated with galaxies included in the Virgo and Fornax Hubble Space Telescope-Advanced Camera Surveys reveals distinct (g - z) colour modulation patterns. These features appear on composite samples of globular clusters and, most evidently, in galaxies with absolute magnitudes Mg in the range from -20.2 to -19.2. These colour modulations are also detectable on some samples of globular clusters in the central galaxies NGC 1399 and NGC 4486 (and confirmed on data sets obtained with different instruments and photometric systems), as well as in other bright galaxies in these clusters. After discarding field contamination, photometric errors and statistical effects, we conclude that these supra-galactic colour patterns are real and reflect some previously unknown characteristic. These features suggest that the globular cluster formation process was not entirely stochastic but included a fraction of clusters that formed in a rather synchronized fashion over large spatial scales, and in a tentative time lapse of about 1.5 Gy at redshifts z between 2 and 4. We speculate that the putative mechanism leading to that synchronism may be associated with large scale feedback effects connected with violent star-forming events and/or with supermassive black holes.

  9. The ACS Survey of Galactic Globular Clusters. VII. Relative Ages

    NASA Astrophysics Data System (ADS)

    Marín-Franch, Antonio; Aparicio, Antonio; Piotto, Giampaolo; Rosenberg, Alfred; Chaboyer, Brian; Sarajedini, Ata; Siegel, Michael; Anderson, Jay; Bedin, Luigi R.; Dotter, Aaron; Hempel, Maren; King, Ivan; Majewski, Steven; Milone, Antonino P.; Paust, Nathaniel; Reid, I. Neill

    2009-04-01

    The ACS Survey of Galactic globular clusters is a Hubble Space Telescope Treasury program designed to provide a new large, deep, and homogeneous photometric database. Based on observations from this program, we have measured precise relative ages for a sample of 64 Galactic globular clusters by comparing the relative position of the clusters' main-sequence (MS) turnoffs, using MS fitting to cross-compare clusters within the sample. This method provides relative ages to a formal precision of 2%-7%. We demonstrate that the calculated relative ages are independent of the choice of theoretical model. We find that the Galactic globular cluster sample can be divided into two groups—a population of old clusters with an age dispersion of ~5% and no age-metallicity relation, and a group of younger clusters with an age-metallicity relation similar to that of the globular clusters associated with the Sagittarius dwarf galaxy. These results are consistent with the Milky Way halo having formed in two phases or processes. The first one would be compatible with a rapid (<0.8 Gyr) assembling process of the halo, in which the clusters in the old group were formed. Also these clusters could have been formed before re-ionization in dwarf galaxies that would later merge to build the Milky Way halo as predicted by ΛCDM cosmology. However, the galactocentric metallicity gradient shown by these clusters seems difficult to reconcile with the latter. As for the younger clusters, it is very tempting to argue that their origin is related to their formation within Milky Way satellite galaxies that were later accreted, but the origin of the age-metallicity relation remains unclear. Based on observations with the NASA/ESA Hubble Space Telescope, obtained at the Space Telescope Science Institute, which is operated by AURA, Inc., under NASA contract NAS 5-26555, under program GO-10775 (PI: A. Sarajedini).

  10. A study of globular cluster formation in hierarchical clustering scenarios

    NASA Astrophysics Data System (ADS)

    Pellizza González, L. J.; Tissera, P. B.; García Lambas, D.; Forte, J. C.

    In this work we present preliminary results of a study of the formation of globular clusters (GCs) in hierarchical clustering scenarios. We used hydrodynamical numerical simulations which include star formation and chemical enrichment by supernovae Ia and II in a cosmological framework (Tissera, Lambas y Abadi 1997, Tissera et al. 2001, Mosconi et al. 2001) for the description of the formation of galactic-like objects (GLO) and their stellar populations. Based on these simulations we implemented a model for GC formation, which assumes that GCs are formed in high star formation efficiency periods. Hence, using the star formation history given by the simulations we determined the GC populations formed in each GLO and their astrophysical properties (age, metallicity, colour). We studied the origin of each GC population and found that it is related to violent events (e.g. collapse, mergers). We observed that the simulated GC populations are old (age >8 Gyr), consistently with observations, and that their metallicity is related to the particular kind of event (collapse, orbital decay or final fusion in a merger event). The combination of the different GC populations of a GLO shows, in some cases, a bimodal metallicity and colour distribution cualitatively similar to the ones observed in the GC systems of some galaxies. Nevertheless, the observed parameters of these distributions could not be reproduced cuantitatively. We are working on an improvement of our model (Pellizza González et al. 2003) and also on the use of higher numerical resolution simulations to study this problem.

  11. What determines the stellar mass functions in globular clusters?

    NASA Technical Reports Server (NTRS)

    Djorgovski, S.; Piotto, Giampaolo; Capaccioli, Massimo

    1993-01-01

    We analyze the dependence of stellar mass function slopes for a sample of 17 globular clusters on a variety of cluster parameters. The principal novelty of our approach is the use of appropriate multivariate statistical methods to disentangle the complex situation which is present in this problem: the slopes depend simultaneously on more than one variable, and many cluster parameters are mutually correlated. We find that the mass function slopes in the range M/M(solar) = 0.5-0.8 are largely determined by the position in the Galaxy and to a lesser extent by the cluster metallicity. Clusters closer to the Galactic center or plane have shallower mass function slopes. At a given distance to the Galactic center, clusters closer to the Galactic plane have shallower mass function slopes. At a given R(GC) and/or Z(GP), more metal-rich clusters have shallower mass function slopes. Thus, the monovariate correlations with the position or metallicity are both correct, but only partial, and in terms of slopes, biased descriptions of the situation. We present trivariate least-squares solutions where the mass function slopes can be predicted within the measurement accuracy. This relation can serve as a powerful observational constraint for theories of globular cluster formation and evolution, and it is one of the tightest correlations between globular cluster properties now known.

  12. Understanding the Variability of the First Globular Cluster Black Hole

    NASA Astrophysics Data System (ADS)

    Maccarone, Thomas; Kundu, Arunav; Zepf, Stephen; Rhode, Katherine; Steele, Matthew

    2011-02-01

    We proposed in the most recent Chandra round for a 20 kilosecond observation of the globular cluster RZ2109 in NGC 4472, along with a Gemini spectrum of 7.2 hours in duration. This proposal is for banding of the Gemini time awarded by the Chandra TAC. This globular cluster hosts the first black hole X-ray source to be umambiguosly identified in a globular cluster. While other similarly bright globular cluster X-ray sources have been seen, this is the first with strong enough variability to rule out a superposition of bright neutron star X-ray binaries. In the past Chandra cycle, we were awarded time in Feb 2010 to observe the central region of NGC 4472, and did not detect this source which had previously been bright since at least the mid 1990s. On the other hand, our recent Gemini spectra from March 2009 indicate that the cluster was still extremely bright in emission line flux at that time. Our proposed observations with Chandra and Gemini should determine whether this source has truly turned off, in which case the optical emission should fade, or merely went through an episode of very high absorption, in which case the optical emission should change little.

  13. Globular Clusters: Chemical Abundance - Integrated Colour calibration

    NASA Astrophysics Data System (ADS)

    Moyano Loyola, G.; Faifer, F. R.; Forte, J. C.

    In this work, we improve the chemical abundance - integrated colour cali- bration presented in Forte, Faifer & Geisler, 2007 (FFG07 hereafter) using a new (g-i) vs. (C-T1) colours calibration obtained from M87. Using this calibration and better values of the reddening for the galactic globulars, we found that a quadratic calibration is still enough to represent the observa- tional data, as in FFG07.

  14. What has happened in the cores of globular clusters

    NASA Astrophysics Data System (ADS)

    Lightman, A. P.

    1982-12-01

    It is found that some aspects of the observed data for globular cluster cores cannot be easily explained in terms of the existing theory of dynamical evolution. It is noted that globular clusters span only a factor of 40 in core mass, while ranging over a factor of 10 to the 6th in central density, an observation that cannot be explained as a selection effect. A strong correlation is found between the central density and the distance of a cluster from the galactic center. In addition, when cluster cores are evolved backward in time in their initial conditions, using the available theory of dynamical evolution, evidence emerges that many clusters have already undergone core collapse, for which no evolutionary theory exists. It is concluded that these results indicate the incompleteness of the theory of dynamical evolution.

  15. Far-ultraviolet radiation from disk globular clusters

    NASA Technical Reports Server (NTRS)

    Rich, R. M.; Minniti, Dante; Liebert, James

    1993-01-01

    IUE spectra obtained in a survey of the metal-rich disk system of globular clusters are presented. Significant FUV fluxes were detected in the 1200-2000-A short-wavelength (SWP) range of the IUE Observatory in several disk globular clusters. These clusters are the most metal-rich known to have an FUV flux. Three clusters show spectral energy distrbutions (SEDs) clearly rising at shorter wavelengths, not unlike the upturns observed in the bulges of metal-rich elliptical galaxies. Several others with weak SWP detections appear to have flat or uncertain spectral energy distributions. Blue stragglers provide a possible explanation for flux redder than 2000 A in clusters showing weaker flux in the SWP region, and with flat or declining SEDs.

  16. Far-ultraviolet radiation from disk globular clusters

    NASA Technical Reports Server (NTRS)

    Rich, R. M.; Minniti, Dante; Liebert, James

    1993-01-01

    IUE spectra obtained in a survey of the metal-rich disk system of globular clusters are presented. Significant FUV fluxes were detected in the 1200-2000-A short-wavelength (SWP) range of the IUE Observatory in several disk globular clusters. These clusters are the most metal-rich known to have an FUV flux. Three clusters show spectral energy distrbutions (SEDs) clearly rising at shorter wavelengths, not unlike the upturns observed in the bulges of metal-rich elliptical galaxies. Several others with weak SWP detections appear to have flat or uncertain spectral energy distributions. Blue stragglers provide a possible explanation for flux redder than 2000 A in clusters showing weaker flux in the SWP region, and with flat or declining SEDs.

  17. 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.

  18. Compact binaries in the globular cluster 47 Tucanae

    NASA Astrophysics Data System (ADS)

    Rivera Sandoval, Lilliana; Van Den Berg, Maureen; Heinke, Craig O.; Cohn, Haldan N.; Lugger, Phyllis M.; Freire, Paulo; Anderson, Jay; Cool, Adrienne; Grindlay, Jonanthan; Edmonds, Peter; Wijnands, Rudy; Ivanova, Natalia

    2017-01-01

    The high stellar interaction rates in globular clusters are ideal for studying the formation and evolution of compact binary stars. For this purpose, we have carried out a study of the cataclysmic variables (CVs) and millisecond pulsar (MSP) companions in the non core collapsed globular cluster 47 Tucanae. We used near-ultraviolet and optical (including H-alpha) images of the cluster obtained with the Hubble Space Telescope (HST), in combination with Chandra X-ray data.From this study we obtained the deepest measurements of the cluster CV luminosity function. We found that this luminosity function is different from those of core collapsed clusters. This result will help understanding how the stellar interactions affect the creation and destruction of CVs. I will discuss our results with respect to the models of formation and evolution of CVs, focusing on the predicted number of these binaries and their radial distribution in the cluster.I will also present the discovery of 2 likely He white dwarf (WD) companions to MSPs in the same cluster, as well as the confirmation of 2 tentative identifications. This represents a significant contribution to the total number of optical counterparts known in Galactic globular clusters so far. Based on our UV photometry and He WD cooling models we derived the ages, the masses and the bolometric luminosities for all the He WD companions. I will discuss these results and their implications in the context of the standard MSP formation scenario.

  19. DARK MATTER HALOS IN GALAXIES AND GLOBULAR CLUSTER POPULATIONS

    SciTech Connect

    Hudson, Michael J.; Harris, Gretchen L.; Harris, William E.

    2014-05-20

    We combine a new, comprehensive database for globular cluster populations in all types of galaxies with a new calibration of galaxy halo masses based entirely on weak lensing. Correlating these two sets of data, we find that the mass ratio η ≡ M {sub GCS}/M {sub h} (total mass in globular clusters, divided by halo mass) is essentially constant at (η) ∼ 4 × 10{sup –5}, strongly confirming earlier suggestions in the literature. Globular clusters are the only known stellar population that formed in essentially direct proportion to host galaxy halo mass. The intrinsic scatter in η appears to be at most 0.2 dex; we argue that some of this scatter is due to differing degrees of tidal stripping of the globular cluster systems between central and satellite galaxies. We suggest that this correlation can be understood if most globular clusters form at very early stages in galaxy evolution, largely avoiding the feedback processes that inhibited the bulk of field-star formation in their host galaxies. The actual mean value of η also suggests that about one-fourth of the initial gas mass present in protogalaxies collected into giant molecular clouds large enough to form massive, dense star clusters. Finally, our calibration of (η) indicates that the halo masses of the Milky Way and M31 are (1.2 ± 0.5) × 10{sup 12} M {sub ☉} and (3.9 ± 1.8) × 10{sup 12} M {sub ☉}, respectively.

  20. Globular cluster clustering around ultra compact dwarf galaxies in the halo of NGC 1399

    NASA Astrophysics Data System (ADS)

    Voggel, Karina; Hilker, Michael; Richtler, Tom

    2016-08-01

    We tested the spatial distribution of UCDs and GCs in the halo of NGC 1399 in the Fornax cluster. In particular we tried to find out if globular clusters are more abundant in the vicinity of UCDs than what is expected from their global distribution. A local overabundance of globular clusters was found around UCDs on a scale of 1 kpc compared to what is expected from the large scale distribution of globulars in the host galaxy. This effect is stronger for the metal-poor blue GCs and weaker for the red GCs. An explanation for these clustered globulars is either that they are the remains of a GC system of an ancestor dwarf galaxy before it was stripped to its nucleus, which appears as UCD today. Alternatively these clustered GCs could have been originally part of a super star cluster complex.

  1. Catalogue of variable stars in Milky Way globular clusters

    NASA Astrophysics Data System (ADS)

    Clement, Christine

    2017-09-01

    Globular cluster variable stars have been studied for more than a century. In the early investigations, more than 90% of the known variables were of the RR Lyrae type. However, in the interim, technological advances have facilitated the discovery of other types of variables. As a result, although RR Lyrae stars still dominate, they now constitute less than 70% of the known variables.

  2. BVRI CCD photometry of the globular cluster NGC 2808

    SciTech Connect

    Alcaino, G.; Liller, W.; Alvarado, F.; Wenderoth, E. )

    1990-03-01

    As a part of a continuing program, CCD color-magnitude diagrams are presented for the bright globular cluster NGC 2808 in the four colors comprising BVRI. From a comparison of four different CMDs with theoretical isochrones, an age of 16 + or - 2 Gyr is obtained, assuming a value for Fe/H near -1.3. 28 refs.

  3. Evolution of long-lived globular cluster stars. II. Sodium abundance variations on the asymptotic giant branch as a function of globular cluster age and metallicity

    NASA Astrophysics Data System (ADS)

    Charbonnel, Corinne; Chantereau, William

    2016-02-01

    evolution phases on the Na cut on the AGB: the higher the mass loss, the stronger the trends with age and metallicity. Conclusions: The theoretical trends we obtain provide, in principle, an elegant qualitative explanation to the different sodium spreads that are observed along the AGB in the Galactic globular clusters of different ages and [Fe/H] values. Although it is real, the slope with both age and metallicity is relatively flat, although it steepens when accounting for mass loss variations. Therefore, additional parameters may play a role in inducing cluster to cluster variations, that are difficult to disentangle from existing data.

  4. Spectroscopy of candidate young globular clusters in NGC 1275

    NASA Technical Reports Server (NTRS)

    Zepf, Stephen E.; Carter, Dave; Sharples, Ray M.; Ashman, Keith

    1995-01-01

    We present spectra of the brightest member of the population of compact blue objects discovered in the peculiar galaxy NGC 1275 by Holtzman et al. (1992) using Hubble Space Telescope images. These spectra show strong Balmer absorption lines like those observed in A-type stars, as expected if the object is a young globular cluster. The age estimated from the strength of the Balmer lines is about 0.5 Gyr, although ages ranging from 0.1 Gyr to 0.9 Gyr cannot be confidently excluded given current models of stellar populations. If these estimated ages are adopted for the young cluster population of NGC 1275 as a whole, the fading predicted by stellar populations models gives a luminosity function which is consistent with that of the Galactic globular cluster system convolved with the observational selection function for the NGC 1275 system. We also use the equivalent widths of the Mg b and Fe 5270 features to constrain the metallicity of the young cluster. Combining these absorption-line widths with the age estimates from the Balmer lines and stellar population models, we find a metallicity of roughly solar, based on the Mg b index, and somewhat higher for the Fe 5270 index. The radial velocity of the absorption lines of the cluster spectrum is offset from the emission lines of the galaxy spectrum at the same position by - 130 km/s, providing further evidence for the identification of the object as a global cluster and opening up the future possibility of studying the kinematics of young cluster systems. The discovery of objects with the characteristics of young globular clusters in NGC 1275, which shows evidence of a recent interaction or merger, supports the hypothesis that galaxy interactions and mergers are favorable sites for the formation of globular clusters.

  5. Spectroscopy of candidate young globular clusters in NGC 1275

    NASA Technical Reports Server (NTRS)

    Zepf, Stephen E.; Carter, Dave; Sharples, Ray M.; Ashman, Keith

    1995-01-01

    We present spectra of the brightest member of the population of compact blue objects discovered in the peculiar galaxy NGC 1275 by Holtzman et al. (1992) using Hubble Space Telescope images. These spectra show strong Balmer absorption lines like those observed in A-type stars, as expected if the object is a young globular cluster. The age estimated from the strength of the Balmer lines is about 0.5 Gyr, although ages ranging from 0.1 Gyr to 0.9 Gyr cannot be confidently excluded given current models of stellar populations. If these estimated ages are adopted for the young cluster population of NGC 1275 as a whole, the fading predicted by stellar populations models gives a luminosity function which is consistent with that of the Galactic globular cluster system convolved with the observational selection function for the NGC 1275 system. We also use the equivalent widths of the Mg b and Fe 5270 features to constrain the metallicity of the young cluster. Combining these absorption-line widths with the age estimates from the Balmer lines and stellar population models, we find a metallicity of roughly solar, based on the Mg b index, and somewhat higher for the Fe 5270 index. The radial velocity of the absorption lines of the cluster spectrum is offset from the emission lines of the galaxy spectrum at the same position by - 130 km/s, providing further evidence for the identification of the object as a global cluster and opening up the future possibility of studying the kinematics of young cluster systems. The discovery of objects with the characteristics of young globular clusters in NGC 1275, which shows evidence of a recent interaction or merger, supports the hypothesis that galaxy interactions and mergers are favorable sites for the formation of globular clusters.

  6. Globular Cluster Candidates for Hosting a Central Black Hole

    NASA Astrophysics Data System (ADS)

    Noyola, Eva

    2009-07-01

    We are continuing our study of the dynamical properties of globular clusters and we propose to obtain surface brightness profiles for high concentration clusters. Our results to date show that the distribution of central surface brightness slopes do not conform to standard models. This has important implications for how they form and evolve, and suggest the possible presence of central intermediate-mass black holes. From our previous archival proposals {AR-9542 and AR-10315}, we find that many high concentration globular clusters do not have flat cores or steep central cusps, instead they show weak cusps. Numerical simulations suggest that clusters with weak cusps may harbor intermediate-mass black holes and we have one confirmation of this connection with omega Centauri. This cluster shows a shallow cusp in its surface brightness profile, while kinematical measurements suggest the presence of a black hole in its center. Our goal is to extend these studies to a sample containing 85% of the Galactic globular clusters with concentrations higher than 1.7 and look for objects departing from isothermal behavior. The ACS globular cluster survey {GO-10775} provides enough objects to have an excellent coverage of a wide range of galactic clusters, but it contains only a couple of the ones with high concentration. The proposed sample consists of clusters whose light profile can only be adequately measured from space-based imaging. This would take us close to completeness for the high concentration cases and therefore provide a more complete list of candidates for containing a central black hole. The dataset will also be combined with our existing kinematic measurements and enhanced with future kinematic studies to perform detailed dynamical modeling.

  7. Blue Stragglers in Globular Clusters: Observations, Statistics and Physics

    NASA Astrophysics Data System (ADS)

    Knigge, Christian

    This chapter explores how we might use the observed statistics of blue stragglers in globular clusters to shed light on their formation. This means we will touch on topics also discussed elsewhere in this book, such as the discovery and implications of bimodal radial distributions and the "double sequences" of blue stragglers that have recently been found in some clusters. However, we will focus particularly on the search for a "smoking gun" correlation between the number of blue stragglers in a given globular cluster and a physical cluster parameter that would point towards a particular formation channel. As we shall see, there is little evidence for an intrinsic correlation between blue straggler numbers and stellar collision rates, even in dense cluster cores. On the other hand, there is a clear correlation between blue straggler numbers and the total (core) mass of the cluster. This would seem to point towards a formation channel involving binaries, rather than dynamical encounters. However, the correlation between blue straggler numbers and actual binary numbers—which relies on recently determined empirical binary fractions—is actually weaker than that with core mass. We explain how this surprising result may be reconciled with a binary formation channel if binary fractions depend almost uniquely on core mass. If this is actually the case, it would have significant implications for globular cluster dynamics more generally.

  8. Predictions of a population of cataclysmic variables in globular clusters

    NASA Technical Reports Server (NTRS)

    Di Stefano, R.; Rappaport, S.

    1994-01-01

    We have studied the number of cataclysmic variables (CVs) that should be active in globular clusters during the present epoch as a result of binary formation via two-body tidal capture. We predict the orbital period and luminosity distributions of CVs in globular clusters. The results arebased on Monte Carlo simulations combined with evolution calculations appropriate to each system formed during the lifetime of two specific globular clusters, omega Cen and 47 Tuc. From our study of these two clusters, which represent the range of core densities and states of mass segregation that are likely to be interesting, we extrapolate our results to the Galactic globlular cluster system. Although there is at present little direct observational evidence of CVs in globular clusters, we find that there should be a large number of active systems. We predict that there should be more than approximately 100 CVs in both 47 Tuc and omega Cen and several thousand in the Galactic globular cluster system. These numbers are based on two-body processes alone and represent a lower bound on the number of systems that may have been formed as a result of stellar interaction within globular clusters. The relation between these calculations and the paucity of optically detected CVs in globular clusters is discussed. Should future observations fail to find convincing evidence of a substantial population of cluster CVs, then the two-body tidal capture scenario is likely to be seriously constrained. Of the CVs we espect in 47 Tuc and omega Cen, approximately 45 and 20, respectively, should have accretion luminosities above 10(exp 33) ergs/s. If one utilizes a relation for converting accretion luminosity to hard X-ray luminosity that is based on observations of Galactic plane CVs, even these sources will not exhibit X-ray luminosities above 10(exp 33) ergs/s. While we cannot account directly for the most luminous subset of the low-luminosity globular cluster X-ray sources without assuming an

  9. A novel look at energy equipartition in globular clusters

    NASA Astrophysics Data System (ADS)

    Bianchini, P.; van de Ven, G.; Norris, M. A.; Schinnerer, E.; Varri, A. L.

    2016-06-01

    Two-body interactions play a major role in shaping the structural and dynamical properties of globular clusters (GCs) over their long-term evolution. In particular, GCs evolve towards a state of partial energy equipartition that induces a mass dependence in their kinematics. By using a set of Monte Carlo cluster simulations evolved in quasi-isolation, we show that the stellar mass dependence of the velocity dispersion σ(m) can be described by an exponential function σ2 ∝ exp (-m/meq), with the parameter meq quantifying the degree of partial energy equipartition of the systems. This simple parametrization successfully captures the behaviour of the velocity dispersion at lower as well as higher stellar masses, that is, the regime where the system is expected to approach full equipartition. We find a tight correlation between the degree of equipartition reached by a GC and its dynamical state, indicating that clusters that are more than about 20 core relaxation times old, have reached a maximum degree of equipartition. This equipartition-dynamical state relation can be used as a tool to characterize the relaxation condition of a cluster with a kinematic measure of the meq parameter. Vice versa, the mass dependence of the kinematics can be predicted knowing the relaxation time solely on the basis of photometric measurements. Moreover, any deviations from this tight relation could be used as a probe of a peculiar dynamical history of a cluster. Finally, our novel approach is important for the interpretation of state-of-the-art Hubble Space Telescope proper motion data, for which the mass dependence of kinematics can now be measured, and for the application of modelling techniques which take into consideration multimass components and mass segregation.

  10. Globular clusters in the far-ultraviolet: evidence for He-enriched second populations in extragalactic globular clusters?

    NASA Astrophysics Data System (ADS)

    Peacock, Mark B.; Zepf, Stephen E.; Kundu, Arunav; Chael, Julia

    2017-01-01

    We investigate the integrated far-ultraviolet (FUV) emission from globular clusters. We present new FUV photometry of M87's clusters based on archival Hubble Space Telescope (HST) Wide Field Planetary Camera 2 F170W observations. We use these data to test the reliability of published photometry based on HST space telescope imaging spectrograph FUV-MAMA observations, which are now known to suffer from significant red-leak. We generally confirm these previous FUV detections, but suggest they may be somewhat fainter. We compare the FUV emission from bright (MV < -9.0) clusters in the Milky Way, M31, M81 and M87 to each other and to the predictions from stellar populations models. Metal-rich globular clusters show a large spread in FUV - V, with some clusters in M31, M81 and M87 being much bluer than standard predictions. This requires that some metal-rich clusters host a significant population of blue/extreme horizontal branch (HB) stars. These hot HB stars are not traditionally expected in metal-rich environments, but are a natural consequence of multiple populations in clusters - since the enriched population is observed to be He enhanced and will therefore produce bluer HB stars, even at high metallicity. We conclude that the observed FUV emission from metal-rich clusters in M31, M81 and M87 provides evidence that He-enhanced second populations, similar to those observed directly in the Milky Way, may be a ubiquitous feature of globular clusters in the local Universe. Future HST FUV photometry is required to both confirm our interpretation of these archival data and provide constraints on He-enriched second populations of stars in extragalactic globular clusters.

  11. Catalogue of Galactic globular-cluster surface-brightness profiles

    NASA Technical Reports Server (NTRS)

    Trager, S. C.; King, Ivan R.; Djorgovski, S.

    1995-01-01

    We present a catalogue of surface-brightness profiles (SBPs) of 125 Galactic globular clusters, the largest such collection ever gathered. The SPBs are constructed from generally inhomogeneous data, but are based heavily on the Berkeley Global Cluster Survey of Djorgovski & King. All but four of the SBPs have photometric zero points. We derive central surface brightness, King-model concentrations, core radii, half-light, and other fraction-of-light radii where data permit, and we briefly discuss their use.

  12. Color and population gradients in globular cluster cores

    NASA Technical Reports Server (NTRS)

    Djorgovski, S.; Piotto, Giampaolo; King, Ivan R.

    1989-01-01

    New observational results on color and population gradients in the cores of several highly concentrated globular clusters are reported. The gradients are in the sense of blueing toward the cluster center, and appear to be caused mostly or entirely by population gradients in the number of blue horizontal branch and red giant branch stars. Taken at face value, such gradients would imply an inverse mass segregation, but this interpretation is not fully secure. In any case, their dynamical understanding remains a problem.

  13. A SURVEY FOR PLANETARY NEBULAE IN M31 GLOBULAR CLUSTERS

    SciTech Connect

    Jacoby, George H.; De Marco, Orsola; Lee, Myung Gyoon; Herrmann, Kimberly A.; Hwang, Ho Seong; Davies, James E.; Kaplan, Evan E-mail: rbc@astro.psu.edu E-mail: mglee@astrog.snu.ac.kr E-mail: hhwang@cfa.harvard.edu E-mail: evanskaplan@gmail.com

    2013-05-20

    We report the results of an [O III] {lambda}5007 spectroscopic survey for planetary nebulae (PNe) located within the star clusters of M31. By examining R {approx} 5000 spectra taken with the WIYN+Hydra spectrograph, we identify 3 PN candidates in a sample of 274 likely globular clusters, 2 candidates in objects which may be globular clusters, and 5 candidates in a set of 85 younger systems. The possible PNe are all faint, between {approx}2.5 and {approx}6.8 mag down the PN luminosity function, and, partly as a consequence of our selection criteria, have high excitation, with [O III] {lambda}5007 to H{beta} ratios ranging from 2 to {approx}> 12. We discuss the individual candidates, their likelihood of cluster membership, and the possibility that they were formed via binary interactions within the clusters. Our data are consistent with the suggestion that PN formation within globular clusters correlates with binary encounter frequency, though, due to the small numbers and large uncertainties in the candidate list, this study does not provide sufficient evidence to confirm the hypothesis.

  14. Globular Clusters: Low Mass Stars, Still No Brown Dwarfs!

    NASA Astrophysics Data System (ADS)

    de Marchi, Guido

    2003-06-01

    In spite of all the attempts to find them, no one has yet detected any brown dwarf in a globular cluster. Although powerful instruments such as the VLT and Advanced Camera could further push the frontiers of this search, globular clusters will probably hold tight to their secrets for a while longer. Nonetheless, the search for very low mass stars in globular clusters has taught us a lot about their original mass distribution (IMF) and its evolution in time. I shall review the results of an investigation carried out over what is presently the largest, most homogeneous sample, and discuss the reasons suggesting that: 1. dynamical evolution (internal and external) has reshaped the cluster mass function over time, but the imprint of the IMF is still visible; 2. the IMF appears to vary very little from cluster to cluster; 3. the most likely functional form of the IMF is that of a power law that rises to a peak at ˜0.3 M⊙ and tapers off at smaller masses.

  15. Globular Cluster Systems in Brightest Cluster Galaxies. II. NGC 6166

    NASA Astrophysics Data System (ADS)

    Harris, William E.; Blakeslee, John P.; Whitmore, Bradley C.; Gnedin, Oleg Y.; Geisler, Douglas; Rothberg, Barry

    2016-01-01

    We present new deep photometry of the globular cluster system (GCS) around NGC 6166, the central supergiant galaxy in Abell 2199. Hubble Space Telescope data from the Advanced Camera for Surveys and WFC3 cameras in F475W and F814W are used to determine the spatial distribution of the GCS, its metallicity distribution function (MDF), and the dependence of the MDF on galactocentric radius and on GC luminosity. The MDF is extremely broad, with the classic red and blue subpopulations heavily overlapped, but a double-Gaussian model can still formally match the MDF closely. The spatial distribution follows a Sérsic-like profile detectably to a projected radius of at least Rgc = 250 kpc. To that radius, the total number of clusters in the system is NGC = 39000 ± 2000, the global specific frequency is SN = 11.2 ± 0.6, and 57% of the total are blue, metal-poor clusters. The GCS may fade smoothly into the intracluster medium (ICM) of A2199; we see no clear transition from the core of the galaxy to the cD halo or the ICM. The radial distribution, projected ellipticity, and mean metallicity of the red (metal-richer) clusters match the halo light extremely well for {R}{gc}≳ 15 {{kpc}}, both of them varying as {σ }{MRGC}∼ {σ }{light}∼ {R}-1.8. By comparison, the blue (metal-poor) GC component has a much shallower falloff {σ }{MPGC}∼ {R}-1.0 and a more nearly spherical distribution. This strong difference in their density distributions produces a net metallicity gradient in the GCS as a whole that is primarily generated by the population gradient. With NGC 6166 we appear to be penetrating into a regime of high enough galaxy mass and rich enough environment that the bimodal two-phase description of GC formation is no longer as clear or effective as it has been in smaller galaxies.

  16. The ACS Survey of Galactic Globular Clusters. VIII. Effects of Environment on Globular Cluster Global Mass Functions

    NASA Astrophysics Data System (ADS)

    Paust, Nathaniel E. Q.; Reid, I. Neill; Piotto, Giampaolo; Aparicio, Antonio; Anderson, Jay; Sarajedini, Ata; Bedin, Luigi R.; Chaboyer, Brian; Dotter, Aaron; Hempel, Maren; Majewski, Steven; Marín-Franch, A.; Milone, Antonino; Rosenberg, Alfred; Siegel, Michael

    2010-02-01

    We have used observations obtained as part of the Hubble Space Telescope/ACS Survey of Galactic Globular Clusters to construct global present-day mass functions for 17 globular clusters utilizing multi-mass King models to extrapolate from our observations to the global cluster behavior. The global present-day mass functions for these clusters are well matched by power laws from the turnoff, ≈0.8 M sun, to 0.2-0.3 M sun on the lower main sequence. The slopes of those power-law fits, α, have been correlated with an extensive set of intrinsic and extrinsic cluster properties to investigate which parameters may influence the form of the present-day mass function. We do not confirm previous suggestions of correlations between α and either metallicity or Galactic location. However, we do find a strong statistical correlation with the related parameters central surface brightness, μ V , and inferred central density, ρ0. The correlation is such that clusters with denser cores (stronger binding energy) tend to have steeper mass functions (a higher proportion of low-mass stars), suggesting that dynamical evolution due to external interactions may have played a key role in determining α. Thus, the present-day mass function may owe more to nurture than to nature. Detailed modeling of external dynamical effects is therefore a requisite for determining the initial mass function for Galactic globular clusters.

  17. THE ACS SURVEY OF GALACTIC GLOBULAR CLUSTERS. VIII. EFFECTS OF ENVIRONMENT ON GLOBULAR CLUSTER GLOBAL MASS FUNCTIONS

    SciTech Connect

    Paust, Nathaniel E. Q.; Reid, I. Neill; Anderson, Jay E-mail: inr@stsci.edu

    2010-02-15

    We have used observations obtained as part of the Hubble Space Telescope/ACS Survey of Galactic Globular Clusters to construct global present-day mass functions for 17 globular clusters utilizing multi-mass King models to extrapolate from our observations to the global cluster behavior. The global present-day mass functions for these clusters are well matched by power laws from the turnoff, {approx}0.8 M {sub sun}, to 0.2-0.3 M {sub sun} on the lower main sequence. The slopes of those power-law fits, {alpha}, have been correlated with an extensive set of intrinsic and extrinsic cluster properties to investigate which parameters may influence the form of the present-day mass function. We do not confirm previous suggestions of correlations between {alpha} and either metallicity or Galactic location. However, we do find a strong statistical correlation with the related parameters central surface brightness, {mu} {sub V}, and inferred central density, {rho}{sub 0}. The correlation is such that clusters with denser cores (stronger binding energy) tend to have steeper mass functions (a higher proportion of low-mass stars), suggesting that dynamical evolution due to external interactions may have played a key role in determining {alpha}. Thus, the present-day mass function may owe more to nurture than to nature. Detailed modeling of external dynamical effects is therefore a requisite for determining the initial mass function for Galactic globular clusters.

  18. Formation of Globular Clusters in Hierarchical Cosmology: ART and Science

    NASA Astrophysics Data System (ADS)

    Gnedin, Oleg Y.; Prieto, José L.

    We test the hypothesis that globular clusters form in supergiant molecular clouds within high-redshift galaxies. Numerical simulations demonstrate that such large, dense, and cold gas clouds assemble naturally in current hierarchical models of galaxy formation. These clouds are enriched with heavy elements from earlier stars and could produce star clusters in a similar way to nearby molecular clouds. The masses and sizes of the model clusters are in excellent agreement with the observations of young massive clusters. Do these model clusters evolve into globular clusters that we see in our and external galaxies? In order to study their dynamical evolution, we calculate the orbits of model clusters using the outputs of the cosmological simulation of a Milky Way-sized galaxy. We find that at present the orbits are isotropic in the inner 50 kpc of the Galaxy and preferentially radial at larger distances. All clusters located outside 10 kpc from the center formed in the now-disrupted satellite galaxies. The spatial distribution of model clusters is spheroidal, with a power-law density profile consistent with observations. The combination of two-body scattering, tidal shocks, and stellar evolution results in the evolution of the cluster mass function from an initial power law to the observed log-normal distribution. However, not all initial conditions and not all evolution scenarios are consistent with the observed mass function.

  19. 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.

  20. Core-hydrogen-burning RSGs in the early globular clusters

    NASA Astrophysics Data System (ADS)

    Szécsi, Dorottya; Mackey, Jonathan; Langer, Norbert

    The first stellar generation in galactic globular clusters contained massive low-metallicity stars (Charbonnel et al. 2014). We modelled the evolution of this massive stellar population and found that such stars with masses 100-600 M⊙ evolve into cool RSGs (Szécsi et al. 2015). These RSGs spend not only the core-He-burning phase but even the last few 105 years of the core-H-burning phase on the SG branch. Due to the presence of hot massive stars in the cluster at the same time, we show that the RSG wind is trapped into photoionization confined shells (Mackey et al. 2014). We simulated the shell formation around such RSGs and find them to become gravitationally unstable (Szécsi et al. 2016). We propose a scenario in which these shells are responsible for the formation of the second generation low-mass stars in globular clusters with anomalous surface abundances.

  1. Rates of collapse and evaporation of globular clusters

    NASA Technical Reports Server (NTRS)

    Hut, Piet; Djorgovski, S.

    1992-01-01

    Observational estimates of the dynamical relaxation times of Galactic globular clusters are used here to estimate the present rate at which core collapse and evaporation are occurring in them. A core collapse rate of 2 +/- 1 per Gyr is found, which for a Galactic age of about 12 Gyr agrees well with the fact that 27 clusters have surface brightness profiles with the morphology expected for the postcollapse phase. A destruction and evaporation rate of 5 +/- 3 per Gyr is found, suggesting that a significant fraction of the Galaxy's original complement of globular clusters have perished through the combined effects of mechanisms such as relaxation-driven evaporation and shocking due to interaction with the Galactic disk and bulge.

  2. STRUCTURAL PARAMETERS OF THE MESSIER 87 GLOBULAR CLUSTERS

    SciTech Connect

    Madrid, Juan P.; Harris, William E.; Blakeslee, John P.; Gomez, MatIas

    2009-11-01

    We derive structural parameters for approx2000 globular clusters in the giant Virgo elliptical Messier 87 (M87) using extremely deep Hubble Space Telescope images in F606W (V) and F814W (I) taken with the ACS/WFC. The cluster scale sizes (half-light radii r{sub h} ) and ellipticities are determined from point-spread-function -convolved King-model profile fitting. We find that the r{sub h} distribution closely resembles the inner Milky Way clusters, peaking at r{sub h} approx = 2.5 pc and with virtually no clusters more compact than r{sub h} approx = 1 pc. The metal-poor clusters have on average an r{sub h} 24% larger than the metal-rich ones. The cluster scale size shows a gradual and noticeable increase with galactocentric distance. Clusters are very slightly larger in the bluer waveband V, a possible hint that we may be beginning to see the effects of mass segregation within the clusters. We also derived a color magnitude diagram for the M87 globular cluster system which shows a striking bimodal distribution.

  3. Kinematics of the Globular Cluster System of the Sombrero Galaxy

    NASA Astrophysics Data System (ADS)

    Windschitl, Jessica L.; Rhode, K. L.; Bridges, T. J.; Zepf, S. E.; Gebhardt, K.; Freeman, K. C.

    2013-06-01

    Using spectra from the Hydra spectrograph on the 3.5m WIYN telescope and from the AAOmega spectrograph on the 3.9m Anglo-Australian Telescope, we have measured heliocentric radial velocities for >50 globular clusters in the Sombrero Galaxy (M104). We combine these new measurements with those from previous studies to construct and analyze a total sample of >360 globular cluster velocities in M104. We use the line-of-sight velocity dispersion to determine the mass and mass-to-light ratio profiles for the galaxy using a spherical, isotropic Jeans mass model. In addition to the increased sample size, our data provide a significant expansion in radial coverage compared to previous spectroscopic studies. This allows us to reliably compute the mass profile of M104 out to ~43 kpc, nearly 14 kpc farther into the halo than previous work. We find that the mass-to-light ratio profile increases from the center to a value of ~20 at 43 kpc. We also look for the presence of rotation in the globular cluster system as a whole and within the red and blue subpopulations. Despite the large number of clusters and better radial sampling, we do not find strong evidence of rotation.

  4. A Search for Intracluster Dust of Globular Clusters

    NASA Astrophysics Data System (ADS)

    Matsunaga, N.; Mito, H.; Nakada, Y.; Fukushi, H.; Tanabé, T.; Ita, Y.; Izumiura, H.; Matsuura, M.; Ueta, T.; Yamamura, I.

    2009-12-01

    We report far-IR observations with AKARI to search for intracluster dust (ICD, hereafter) from globular clusters. We observed 12 clusters and detected both diffuse and point-like sources through our Mission Program (MP) survey. However, it is found that most of them are not associated with clusters, leaving one possible candidate of ICD cloud (Matsunaga et al. 2008). We also searched the β-1 Bright Source Catalogue of the AKARI All-Sky Survey for ICD but no likely candidate was found. This paucity suggests that the dust disappears within a lifetime shorter than 5-50 Myr depending on the dust temperature.

  5. Young globular clusters in the Milky Way Galaxy

    NASA Technical Reports Server (NTRS)

    Lin, D. N. C.; Richer, Harvey B.

    1992-01-01

    Ruprecht 106 and Pal 12 are two known globular clusters in the Milky Way that are unequivocally younger than other clusters of similar metallicity. The Galactic coordinates of Ruprecht 106 place it near to the Magellanic Stream in projection, suggesting a tidal capture from the Magellanic Clouds. It is demonstrated that a family of orbits for both clusters can be constructed that are consistent with this capture hypothesis and that these then lead to a prediction of 3 milliarcseconds per year for the proper motions of both Ruprecht 106 and Pal 12.

  6. HUBBLE SPACE TELESCOPE Photometry of the Globular Cluster M4

    NASA Astrophysics Data System (ADS)

    Ibata, Rodrigo A.; Richer, Harvey B.; Fahlman, Gregory G.; Bolte, Michael; Bond, Howard E.; Hesser, James E.; Pryor, Carlton; Stetson, Peter B.

    1999-02-01

    This paper presents a detailed description of the acquisition and processing of a large body of imaging data for three fields in the globular cluster M4 taken with the Wide Field and Planetary Camera 2 aboard the Hubble Space Telescope. Analysis with the ALLFRAME package yielded the deepest photometry yet obtained for this cluster. The resulting data set for 4708 stars (positions and calibrated photometry in V, I, and, in two fields, U) spanning approximately six cluster core radii is presented. The scientific analysis is deferred to three companion papers, which investigate the significant white dwarf population discovered and the main-sequence population.

  7. Young globular clusters in the Milky Way Galaxy

    NASA Technical Reports Server (NTRS)

    Lin, D. N. C.; Richer, Harvey B.

    1992-01-01

    Ruprecht 106 and Pal 12 are two known globular clusters in the Milky Way that are unequivocally younger than other clusters of similar metallicity. The Galactic coordinates of Ruprecht 106 place it near to the Magellanic Stream in projection, suggesting a tidal capture from the Magellanic Clouds. It is demonstrated that a family of orbits for both clusters can be constructed that are consistent with this capture hypothesis and that these then lead to a prediction of 3 milliarcseconds per year for the proper motions of both Ruprecht 106 and Pal 12.

  8. Ultraviolet fluxes for globular clusters in M31 - A rediscussion

    SciTech Connect

    Crotts, A.P.S.; Kron, R.G.; Cacciari, C.; Fusi-Pecci, F. McDonald Observatory, Austin, TX Yerkes Observatory, Williams Bay, WI Osservatorio Astronomico, Bologna Bologna Universita )

    1990-07-01

    Long-exposure observations of three bright globular clusters in M31 obtained with both the short- and long-wavelength low-resolution cameras of the International Ultraviolet Explorer satellite are discussed. All of the clusters are seen at the longer wavelengths, but only one of the clusters is seen at short wavelengths, and this detection is marginal. The ultraviolet fluxes are in fact known with only poor precision, and previous conclusions concerning the stellar population are weakened accordingly. Discrepancies between the ultraviolet fluxes obtained here and in other published work are described. 16 refs.

  9. The globular cluster system of NGC 1316. III. Kinematic complexity

    NASA Astrophysics Data System (ADS)

    Richtler, T.; Hilker, M.; Kumar, B.; Bassino, L. P.; Gómez, M.; Dirsch, B.

    2014-09-01

    Context. The merger remnant NGC 1316 (Fornax A) is one of the most important objects regarding the investigation of and thus an important object to study merger-related processes. A recent photometric study used globular clusters in NGC 1316 to constrain its star formation history, but without the knowledge of individual radial velocities. The kinematical properties of the globular cluster system in comparison with the diffuse stellar light might give more insight into the formation of NGC 1316. Of particular interest is the dark matter content. Planetary nebulae in NGC 1316 indicate a massive dark halo, and globular cluster velocities provide independent evidence. Aims: We aim at measuring radial velocities of globular clusters in NGC 1316. We use these kinematical data to investigate the global structure of NGC 1316 and to constrain the dark matter content. Methods: We perform multiobject spectroscopy with VLT/FORS2 and MXU. Out of 562 slits, we extract radial velocities for 177 globular clusters. Moreover, we measure radial velocities of the integrated galaxy light, using slits with a sufficiently bright sky. To these data, we add 20 cluster velocities from the literature. In an appendix, we identify new morphological features of NGC 1316 and its companion galaxy NGC 1317. Results: The GC sample based on radial velocities confirms the colour peaks already found in our photometric study. The bright clusters, which probably have their origin in a 2 Gyr old starburst and younger star formation events, avoid the systemic velocity. A Gaussian velocity distribution is found only for clusters fainter than about mR = 22 mag. The velocity distribution of clusters shows a pronounced peak at 1600 km s-1. These clusters populate a wide area in the south-western region which we suspect to be a disk population. Globular clusters or subsamples of them do not show a clear rotation signal. This is different from the galaxy light, where rotation along the major axis is

  10. In search of massive single-population globular clusters

    NASA Astrophysics Data System (ADS)

    Caloi, Vittoria; D'Antona, Francesca

    2011-10-01

    The vast majority of globular clusters so far examined shows the chemical signatures of hosting (at least) two stellar populations. According to recent ideas, this feature requires a two-step process, in which the nuclearly processed matter from a 'first generation' (FG) of stars gives birth to a 'second generation' (SG), bearing the fingerprint of a fully carbon-nitrogen-oxygen (CNO) cycled matter. Since, as observed, the present population of most globular clusters is made up largely of SG stars, a substantial fraction of the FG (≳90 per cent) must be lost. Nevertheless, two types of clusters dominated by a simple stellar population (FG clusters) should exist: clusters initially too small to be able to retain a cooling flow and form a second generation (FG-only clusters) and massive clusters that could retain the CNO-processed ejecta and form an SG, but were unable to lose a significant fraction of their FG (mainly-FG clusters). Identification of mainly-FG clusters may provide an estimate of the fraction of the initial mass involved in the formation of the SG. We attempt a first classification of FG clusters, based on the morphology of their horizontal branches (HBs), as displayed in the published catalogues of photometric data for 106 clusters. We select, as FG candidates, the clusters in which the HB can be reproduced by the evolution of an almost unique mass. We find that less than 20 per cent of clusters with [Fe/H] < -0.8 appear to be FG, but only ˜10 per cent probably had a mass sufficient to form at all an SG. This small percentage confirms on a wider data base the spectroscopic result that the SG is a dominant constituent of today's clusters, suggesting that its formation is an ingredient necessary for the survival of globular clusters during their dynamical evolution in the Galactic tidal field. In more detail we show that Pal 3 turns out to be a good example of FG-only cluster. Instead, HB simulations and space distribution of its components indicate

  11. THE GLOBULAR CLUSTER SYSTEM OF NGC 4636 AND FORMATION OF GLOBULAR CLUSTERS IN GIANT ELLIPTICAL GALAXIES

    SciTech Connect

    Park, Hong Soo; Lee, Myung Gyoon; Hwang, Ho Seong; Kim, Sang Chul; Arimoto, Nobuo; Yamada, Yoshihiko; Tamura, Naoyuki; Onodera, Masato E-mail: mglee@astro.snu.ac.kr E-mail: sckim@kasi.re.kr E-mail: yoshihiko.yamada@nao.ac.jp E-mail: monodera@phys.ethz.ch

    2012-11-10

    We present a spectroscopic analysis of the metallicities, ages, and alpha-elements of the globular clusters (GCs) in the giant elliptical galaxy (gE) NGC 4636 in the Virgo Cluster. Line indices of the GCs are measured from the integrated spectra obtained with Faint Object Camera and Spectrograph on the Subaru 8.2 m Telescope. We derive [Fe/H] values of 59 GCs based on the Brodie and Huchra method, and [Z/H], age, and [{alpha}/Fe] values of 33 GCs from the comparison of the Lick line indices with single stellar population models. The metallicity distribution of NGC 4636 GCs shows a hint of a bimodality with two peaks at [Fe/H] = -1.23({sigma} = 0.32) and -0.35({sigma} = 0.19). The age spread is large from 2 Gyr to 15 Gyr and the fraction of young GCs with age <5 Gyr is about 27%. The [{alpha}/Fe] of the GCs shows a broad distribution with a mean value [{alpha}/Fe] Almost-Equal-To 0.14 dex. The dependence of these chemical properties on the galactocentric radius is weak. We also derive the metallicities, ages, and [{alpha}/Fe] values for the GCs in other nearby gEs (M87, M49, M60, NGC 5128, NGC 1399, and NGC 1407) from the line index data in the literature using the same methods as used for NGC 4636 GCs. The metallicity distribution of GCs in the combined sample of seven gEs including NGC 4636 is found to be bimodal, supported by the KMM test with a significance level of >99.9%. All these gEs harbor some young GCs with ages less than 5 Gyr. The mean age of the metal-rich GCs ([Fe/H] >-0.9) is about 3 Gyr younger than that of the metal-poor GCs. The mean value of [{alpha}/Fe] of the gE GCs is smaller than that of the Milky Way GCs. We discuss these results in the context of GC formation in gEs.

  12. Globular cluster systems in nearby dwarf galaxies - III. Formation efficiencies of old globular clusters

    NASA Astrophysics Data System (ADS)

    Georgiev, Iskren Y.; Puzia, Thomas H.; Goudfrooij, Paul; Hilker, Michael

    2010-08-01

    We investigate the origin of the shape of the globular cluster (GC) system scaling parameters as a function of galaxy mass, i.e. specific frequency (SN), specific luminosity (SL), specific mass (SM) and specific number () of GCs. In the low-mass galaxy regime (MV >~ -16 mag), our analysis is based on Hubble Space Telescope/Advanced Camera for Surveys observations of GC populations of faint, mainly late-type dwarf galaxies in low-density environments. In order to sample the entire range in galaxy mass (MV = -11 to -23mag =106- 1011Lsolar), environment and morphology we augment our sample with data of spiral and elliptical galaxies from the literature, in which old GCs are reliably detected. This large data set confirms (irrespective of the galaxy type) the increase in the specific frequencies of GCs above and below a galaxy magnitude of MV ~= -20mag. Over the full mass range, the SL value of early-type galaxies is, on average, twice that of late types. To investigate the observed trends, we derive theoretical predictions of GC system scaling parameters as a function of host galaxy mass based on the models of Dekel and Birnboim in which star formation processes are regulated by stellar and supernova feedback below a stellar mass of 3 × 1010Msolar and by virial shocks above it. We find that the analytical model describes remarkably well the shape of the GC system scaling parameter distributions with a universal specific GC formation efficiency, η, which relates the total mass in GCs to the total galaxy halo mass. Early-type and late-type galaxies show a similar mean value of η = 5.5 × 10-5, with an increasing scatter towards lower galaxy masses. This can be due to the enhanced stochastic nature of the star and star-cluster formation processes for such systems. Some massive galaxies have excess η values compared to what is expected from the mean model prediction for galaxies more luminous than MV ~= -20mag (LV >~ 1010Lsolar). This may be attributed to a very

  13. Core Hydrogen Burning Red Supergiants in the Young Globular Clusters

    NASA Astrophysics Data System (ADS)

    Szecsi, Dorottya; Mackey, Jonathan; Langer, Norbert

    2015-08-01

    The first stellar generation in galactic globular clusters contained massive low metallicity stars. We modelled the evolution of this massive stellar population and found that such stars with masses 100-600 Msun evolve into red supergiants. These red supergiants are particularly interesting because they spend not only the helium burning phase but even the last few hundres tousands of years of the core hydrogen burning phase on the RSG branch. Due to the presence of hot massive stars at the same time, we show that the RSG wind is trapped into photoionization confined shells. We simulate the shell formation around such red supergiants and find them to become gravitationally unstable. We propose a scenario in which these shells are responsible for the formation of the second generation low mass stars in globular clusters with anomalous surface abundances.

  14. Globular Clusters and Dark Satellite Galaxies through the Stream Velocity

    NASA Astrophysics Data System (ADS)

    Naoz, Smadar; Narayan, Ramesh

    2014-08-01

    The formation of purely baryonic globular clusters with no gravitationally bound dark matter is still a theoretical challenge. We show that these objects might form naturally whenever there is a relative stream velocity between baryons and dark matter. The stream velocity causes a phase shift between linear modes of baryonic and dark matter perturbations, which translates to a spatial offset between the two components when they collapse. For a 2σ (3σ) density fluctuation, baryonic clumps with masses in the range 105-2.5 × 106 M ⊙ (105-4 × 106 M ⊙) collapse outside the virial radii of their counterpart dark matter halos. These objects could survive as long-lived, dark-matter-free objects and might conceivably become globular clusters. In addition, their dark matter counterparts, which were deprived of gas, might become dark satellite galaxies.

  15. Metallicity of Globular Cluster M13 from VI CCD Photometry

    NASA Astrophysics Data System (ADS)

    Shon, Young-Jong

    2000-12-01

    From the VI images of M13, obtained by using 2K CCD camera and the BOAO 1.8m telescope, we derive the (V-I)-V CMD of M13. From the shapes of red giant branch, the magnitude of horizontal branch, and the giant branch bump on the constructed CMD, we determined the metallicity of the globular cluster to be 1.74 ~<[Fe/H]~< -1.41. The good agreement between our determination of [Fe/H] and those determined by using other methods implies that the morphology of red giant and horizontal branches on (V-I)-V CMD's can be good indirect metallicity indicators of Galactic globular clusters.

  16. The Distance to the Galactic Globular Cluster, 47 Tuc

    NASA Astrophysics Data System (ADS)

    Woodley, Kristin; Goldsbury, R.; Kalirai, J.; Richer, H.; Tremblay, P.; Anderson, J.; Bergeron, P.; Dotter, A.; Esteves, L.; Fahlman, G.; Hansen, B.; Heyl, J.; Hurley, J.; Rich, R.; Shara, M.; Stetson, P.

    2012-01-01

    We present a new distance determination to the Galactic globular cluster 47 Tucanae by fitting the spectral energy distributions of its white dwarfs to pure hydrogen atmosphere white dwarf models. Our photometric data set is obtained from a 121 orbit Hubble Space Telescope program using the Wide Field Camera 3 UVIS/IR channels, capturing F390W, F606W, F110W, and F160W images. These images cover more than 60 arcmin2 and extend over a radial range of 5-13.7 arcmin (6.5-17.9 pc) within the globular cluster. Here, we present our best fitting distance modulus using a likelihood analysis. We also search the white dwarf photometry for infrared excess in the F160W filter, indicative of protoplanetary disks or low mass companions, and find no convincing cases within our sample.

  17. GLOBULAR CLUSTERS AND DARK SATELLITE GALAXIES THROUGH THE STREAM VELOCITY

    SciTech Connect

    Naoz, Smadar; Narayan, Ramesh

    2014-08-10

    The formation of purely baryonic globular clusters with no gravitationally bound dark matter is still a theoretical challenge. We show that these objects might form naturally whenever there is a relative stream velocity between baryons and dark matter. The stream velocity causes a phase shift between linear modes of baryonic and dark matter perturbations, which translates to a spatial offset between the two components when they collapse. For a 2σ (3σ) density fluctuation, baryonic clumps with masses in the range 10{sup 5}-2.5 × 10{sup 6} M {sub ☉} (10{sup 5}-4 × 10{sup 6} M {sub ☉}) collapse outside the virial radii of their counterpart dark matter halos. These objects could survive as long-lived, dark-matter-free objects and might conceivably become globular clusters. In addition, their dark matter counterparts, which were deprived of gas, might become dark satellite galaxies.

  18. Globular cluster seeding by primordial black hole population

    NASA Astrophysics Data System (ADS)

    Dolgov, A.; Postnov, K.

    2017-04-01

    Primordial black holes (PBHs) that form in the early Universe in the modified Affleck-Dine (AD) mechanism of baryogenesis should have intrinsic log-normal mass distribution of PBHs. We show that the parameters of this distribution adjusted to provide the required spatial density of massive seeds (>= 104 Msolar) for early galaxy formation and not violating the dark matter density constraints, predict the existence of the population of intermediate-mass PBHs with a number density of 0~ 100 Mpc-3. We argue that the population of intermediate-mass AD PBHs can also seed the formation of globular clusters in galaxies. In this scenario, each globular cluster should host an intermediate-mass black hole with a mass of a few thousand solar masses, and should not obligatorily be immersed in a massive dark matter halo.

  19. Helium abundance difference within globular clusters: NGC 2808.

    NASA Astrophysics Data System (ADS)

    Cacciari, C.; Pasquini, L.; Valenti, E.; Käufl, H. U.; Mauas, P.

    Multiple populations have been recently detected in most Galactic globular clusters, even with no significant spread in metallicity. Unusual features of the observed colour-magnitude diagrams can be explained by differences in the He content of the stars belonging to the sub-populations. We report on empirical evidence of He abundance spread in a few globular clusters, with particular attention to NGC 2808, where He abundance variation has been measured in a pair of otherwise identical red giant stars using the HeI 1083 nm line. A quantitative estimate of this difference has been derived by appropriate chromospheric modelling, in very good agreement with stellar evolution requirements. Partly based on observations collected at ESO VLT (Chile), under programme 384.D-0283.

  20. The kinematics of globular clusters in the Large Magellanic Cloud

    NASA Astrophysics Data System (ADS)

    Freeman, K. C.; Illingworth, G.; Oemler, A., Jr.

    1983-09-01

    Velocities have been determined for 35 globular clusters in the LMC. These data have been combined with data from other sources to give velocities for 59 clusters ranging in age from ≡108 to ≡1010 yr. Clusters younger than ≡109 yr form a flattened system having a low line-of-sight velocity dispersion (≡15 km s-1), an amplitude for their rotation of 37±5 km s-1, a galactocentric systemic velocity of 40±3 km s-1, and a line of nodes in position angle 1°±5°. The older clusters are also flattened to a disklike system with an intrinsic line-of-sight dispersion of only 17 km s-1, and a rotation amplitude of 41±4 km s-1. Surprisingly both the systemic velocity at 26±2 km s-1, and the position angle of the line of nodes at 41°±5 are very significantly different for these older clusters. This enigmatic situation resisted all attempts at a solution. The data for the oldest clusters suggest that there is no evidence for a kinematic halo population among the globular clusters in the LMC.

  1. Probing Globular Cluster Formation in Low Metallicity Dwarf Galaxies

    NASA Astrophysics Data System (ADS)

    Johnson, Kelsey E.; Hunt, Leslie K.; Reines, Amy E.

    2008-12-01

    The ubiquitous presence of globular clusters around massive galaxies today suggests that these extreme star clusters must have been formed prolifically in the earlier universe in low-metallicity galaxies. Numerous adolescent and massive star clusters are already known to be present in a variety of galaxies in the local universe; however most of these systems have metallicities of 12 + log(O/H) > 8, and are thus not representative of the galaxies in which today's ancient globular clusters were formed. In order to better understand the formation and evolution of these massive clusters in environments with few heavy elements, we have targeted several low-metallicity dwarf galaxies with radio observations, searching for newly-formed massive star clusters still embedded in their birth material. The galaxies in this initial study are HS 0822+3542, UGC 4483, Pox 186, and SBS 0335-052, all of which have metallicities of 12 + log(O/H) < 7.75. While no thermal radio sources, indicative of natal massive star clusters, are found in three of the four galaxies, SBS 0335-052 hosts two such objects, which are incredibly luminous. The radio spectral energy distributions of these intense star-forming regions in SBS 0335-052 suggest the presence of ~12,000 equivalent O-type stars, and the implied star formation rate is nearing the maximum starburst intensity limit.

  2. Results from HST Observations of Six LMC Globular Cluster Fields

    NASA Astrophysics Data System (ADS)

    Olsen, K. A. G.; Hodge, P. W.; Mateo, M.; Olszewski, E. W.; Schommer, R. A.; Suntzeff, N. B.; Walker, A. R.

    We present deep HST color-magnitude diagrams of fields centered on the six old LMC globular clusters NGC 1754, NGC 1835, NGC 1898, NGC 1916, NGC 2005, and NGC 2019. Separate cluster and field star CMDs are shown. The time of formation of the LMC is studied from an analysis of the cluster CMDs. Based on a comparison of the CMDs with sequences of the Milky Way clusters M3, M5, and M55, we suggest that the LMC formed its first stars at the same time as the Milky Way to within 1 Gyr. We derive abundances and reddenings of the clusters that agree roughly with published values. Adopting our measured abundances, we find additional evidence that these LMC globular clusters are as old as the oldest Milky Way clusters through a comparison of our data with the horizontal branch evolutionary models of Lee, Demarque, and Zinn (1994). The evolution of the LMC following its formation is studied through an analysis of the field star CMDs. Through an automated comparison with stellar evolution models, we extract the star formation histories implied by the CMDs and luminosity functions. We explore the effects of varying the reddening, distance modulus, and IMF of the field stars on the derived star formation histories. We discuss the evidence for different star formation histories among the six fields.

  3. Evolution of redback radio pulsars in globular clusters

    NASA Astrophysics Data System (ADS)

    Benvenuto, O. G.; De Vito, M. A.; Horvath, J. E.

    2017-01-01

    Context. We study the evolution of close binary systems composed of a normal, intermediate mass star and a neutron star considering a chemical composition typical of that present in globular clusters (Z = 0.001). Aims: We look for similarities and differences with respect to solar composition donor stars, which we have extensively studied in the past. As a definite example, we perform an application on one of the redbacks located in a globular cluster. Methods: We performed a detailed grid of models in order to find systems that represent the so-called redback binary radio pulsar systems with donor star masses between 0.6 and 2.0 solar masses and orbital periods in the range 0.2-0.9 d. Results: We find that the evolution of these binary systems is rather similar to those corresponding to solar composition objects, allowing us to account for the occurrence of redbacks in globular clusters, as the main physical ingredient is the irradiation feedback. Redback systems are in the quasi-RLOF state, that is, almost filling their corresponding Roche lobe. During the irradiation cycle the system alternates between semi-detached and detached states. While detached the system appears as a binary millisecond pulsar, called a redback. Circumstellar material, as seen in redbacks, is left behind after the previous semi-detached phase. Conclusions: The evolution of binary radio pulsar systems considering irradiation successfully accounts for, and provides a way for, the occurrence of redback pulsars in low-metallicity environments such as globular clusters. This is the case despite possible effects of the low metal content of the donor star that could drive systems away from redback configuration.

  4. Radial velocities of remote globular clusters - stalking the missing mass

    SciTech Connect

    Peterson, R.C.

    1985-10-01

    Measurements good to 25 km/s are presented of radial velocities of five remote galactic globular clusters, based on aperture-plate spectra of individual stars at 3.0 A resolution. Velocities with respect to the galactic rest-frame of two individual systems, Eridanus and Palomar 14, are large enough to suggest a total mass for the Galaxy of 1 trillion solar masses. A similar mass is inferred from the average of the galactocentric distance times velocity squared. 36 references.

  5. Supergiant molecular clouds and the formation of globular cluster systems

    NASA Astrophysics Data System (ADS)

    Harris, William E.; Pudritz, Ralph E.

    1994-07-01

    Data from several large elliptical and disk galaxies now show that globular clusters more massive than approximately 105 solar mass follow a power-law number distribution by mass, N approximately M-1.7, which is virtually independent of environment. Within observational uncertainty, this relation is identical to the shape of the mass distributions of giant molecular clouds (GMCs) in large spiral galaxies, the cloud cores embedded in GMCs, and giant H II regions in large spiral galaxies. We interpret this within a model whereby globular clusters formed out of dense cores within supergiant molecular clouds (SGMCs) that were present in the early protogalactic epoch. We construct a theory of pressure confined, self-gravitating, isothermal, magnetized molecular clouds and cores, based on the viral theorem and the observed mass spectra, and derive the characteristic physical properties of these parent SGMCs. These turn out to be of the right mass and density range to resemble the Searle-Zinn primordial fragments from which larger galaxies may have assembled. We suggest that the protocluster clouds were supported against gravitational collapse primarily by a combination of magnetic field pressure and Alfvenic turbulence, as is observed to be the case for contemporary molecular clouds. This approach removes the need for arbitrary external heat sources (such as long-lasting AGNs or Population III stars) to keep the clouds stable for long enough times to build up to globular-sized masses and more easily permits the global properties of the emergent clusters to be similar from one galaxy to another. By calculating lifetimes through a standard cloud growth model, we estimate that the principal epoch of globular cluster formation should have begun no earlier than a redshift of z approximately equal to 6.

  6. Formation and evolution of clumpy tidal tails in globular clusters

    NASA Astrophysics Data System (ADS)

    Di Matteo, P.; Miocchi, P.; Capuzzo Dolcetta, R.

    2004-05-01

    Numerical simulations of a globular cluster orbiting in the central region of a triaxial galaxy have been performed, in order to study the formation and subsequent evolution of tidal tails and their main features. Tails begin to form after about a quarter of the cluster orbital period and tend to lie along its orbit, with a leading tail that precedes the cluster and an outer tail that trails behind it. Tails show clumpy substructures; the most prominent ones (for a globular cluster moving on a quasi-circular orbit around the galaxy) are located at a distance from the cluster center between 50 pc and 80 pc and, after 3 orbital periods, contain about 10% of the cluster mass at that epoch. The morphology of tails and clumps will be compared with available observational data, in particular with that concerning Palomar 5, for which evident clumps in the tails have been detected. Kinematical properties of stars in the tails (line-of-sight velocities and velocity dispersion profiles) will be presented and compared to kinematical data of M15 and ω Centauri, two galactic globular clusters for which there is evidence that the velocity dispersion remains constant at large radii. All the simulations have been performed with our own implementation of a tree-code, that uses a multipolar expansion of the potential truncated at the quadrupole moment and that ran on high performance computers employing an original parallelization approach implemented via MPI routines. The time-integration of the `particles' trajectories is performed by a 2nd order leap-frog algorithm, using individual and variable time-steps. Part of this work has been done using the IBM SP4 platform located at CINECA (Bologna, Italy) thanks to the grant inarm007 obtained in the framework of INAF-CINECA agreements.

  7. The first Δa observations of three globular clusters

    NASA Astrophysics Data System (ADS)

    Paunzen, E.; Iliev, I. Kh.; Pintado, O. I.; Baum, H.; Maitzen, H. M.; Netopil, M.; Önehag, A.; Zejda, M.; Fraga, L.

    2014-09-01

    Globular clusters are main astrophysical laboratories to test and modify evolutionary models. Thought to be rather homogeneous in their local elemental distribution of members, results suggest a wide variety of chemical peculiarities. Besides different main sequences, believed to be caused by different helium abundances, peculiarities of blue horizontal-branch stars and on the red giant branch were found. This whole zoo of peculiar objects has to be explained in the context of stellar formation and evolution. The tool of Δa photometry is employed in order to detect peculiar stars in the whole spectral range. This three filter narrow-band system measures the flux distribution in the region from 4900 to 5600 Å in order to find any peculiarities around 5200 Å. It is highly efficient to detect classical chemically peculiar stars of the upper main sequence, Be/Ae, shell and metal-weak objects in the Milky Way and Magellanic Clouds. We present Δa photometry of 2266 stars from 109 individual frames for three globular clusters (NGC 104, NGC 6205, and NGC 7099). A comparison with published abundances, for three horizontal-branch stars, only, yields an excellent agreement. According to the 3σ detection limit of each globular cluster, about 3 per cent of the stars lie in abnormal regions in the diagnostic diagrams. The first observations of three widely different aggregates give very promising results, which will serve as a solid basis for follow-up observations including photometric as well as spectroscopic studies.

  8. Would a Galactic bar destroy the globular cluster system?

    NASA Technical Reports Server (NTRS)

    Long, Kevin; Ostriker, Jeremiah P.; Aguilar, Luis

    1992-01-01

    Five different dynamical Galaxy models are presented for the Galactic potential which satisfy the observed rotation curve but contain a central bar so that the 3-kpc nonintersecting streamlines have a radial velocity of 50 km/s when viewed at 45 deg to the bar axis. The effect of the central bars on the destruction rates of globular clusters in the Galaxy is investigated. The method of Aguilar et al. (1988) is applied to these barred Galaxy models. The unknown tangential velocity components of each observed cluster are drawn randomly from an assumed distribution function. The cluster's orbit is integrated, and the bulge shocking rate is calculated. The median destruction rate of the cluster is computed by sampling a large number of such orbits. The addition of the rotating bar does not strongly affect the destruction rates of globular clusters. There is a small increase in the destruction rate for those clusters within about 2.5 kpc. Thus it is not possible to rule out the existence of a rotating bar on these grounds.

  9. X-ray Sources in the Globular Cluster Terzan 1

    NASA Astrophysics Data System (ADS)

    Cackett, E. M.; Wijnands, R.; Heinke, C. O.; Pooley, D.; Lewin, W. H. G.; Grindlay, J. E.; Edmonds, P. D.; Jonker, P. G.; Miller, J. M.

    2006-06-01

    From a ˜19 ks Chandra ACIS-S observation of the globular cluster Terzan 1 we detect fourteen sources within 1.4 arcmin of the cluster center. Two of these sources are predicted to be not associated with the cluster (background AGN or foreground objects). The neutron star X-ray transient, X1732-304, has previously been observed in outburst within this globular cluster with the outburst seen to last for at least 12 years. The most likely candidate for the quiescent counterpart of the transient has a relatively soft spectrum and an unabsorbed 0.5-10 keV luminosity of 2.6 × 1032 ergs s-1, quite typical of other quiescent neutron stars. Assuming standard core cooling, from the quiescent flux of this source we predict long (>400 yr) quiescent episodes to allow the neutron star to cool. Alternatively, enhanced core cooling processes are needed to cool down the core. From the estimated stellar encounter rate of this cluster we find that the number of sources detected is significantly higher than expected by the relationship of Pooley et al. (2003), perhaps because the cluster was previously much larger and that most of the stars have been lost due to passages through the Galactic disk. EMC gratefully acknowledges support by PPARC.

  10. A spectroscopic study of the globular Cluster NGC 4147

    NASA Astrophysics Data System (ADS)

    Villanova, S.; Monaco, L.; Moni Bidin, C.; Assmann, P.

    2016-08-01

    We present the abundance analysis for a sample of 18 red giant branch stars in the metal-poor globular cluster NGC 4147 based on medium- and high-resolution spectra. This is the first extensive spectroscopic study of this cluster. We derive abundances of C, N, O, Na, Mg, Al, Si, Ca, Ti, Cr, Fe, Ni, Y, Ba, and Eu. We find a metallicity of [Fe/H] = -1.84 ± 0.02 and an α-enhancement of +0.38 ± 0.05 (errors on the mean), typical of halo globular clusters in this metallicity regime. A significant spread is observed in the abundances of light elements C, N, O, Na, and Al. In particular, we found an Na-O anticorrelation and Na-Al correlation. The cluster contains only ˜15 per cent of stars that belong to the first generation (Na-poor and O-rich). This implies that it suffered a severe mass-loss during its lifetime. Its [Ca/Fe] and [Ti/Fe] mean values agree better with the Galactic halo trend than with the trend of extragalactic environments at the cluster metallicity. This possibly suggests that NGC 4147 is a genuine Galactic object at odd with what claimed by some author that proposed the cluster to be member of the Sagittarius dwarf galaxy. An antirelation between the light s-process element Y and Na may also be present.

  11. Would a Galactic bar destroy the globular cluster system?

    NASA Technical Reports Server (NTRS)

    Long, Kevin; Ostriker, Jeremiah P.; Aguilar, Luis

    1992-01-01

    Five different dynamical Galaxy models are presented for the Galactic potential which satisfy the observed rotation curve but contain a central bar so that the 3-kpc nonintersecting streamlines have a radial velocity of 50 km/s when viewed at 45 deg to the bar axis. The effect of the central bars on the destruction rates of globular clusters in the Galaxy is investigated. The method of Aguilar et al. (1988) is applied to these barred Galaxy models. The unknown tangential velocity components of each observed cluster are drawn randomly from an assumed distribution function. The cluster's orbit is integrated, and the bulge shocking rate is calculated. The median destruction rate of the cluster is computed by sampling a large number of such orbits. The addition of the rotating bar does not strongly affect the destruction rates of globular clusters. There is a small increase in the destruction rate for those clusters within about 2.5 kpc. Thus it is not possible to rule out the existence of a rotating bar on these grounds.

  12. Luminosity Function of Faint Globular Clusters in M87

    SciTech Connect

    Waters, Christopher Z.; Zepf, Stephen E.; Lauer, Tod R.; Baltz, Edward A.; Silk, Joseph; /Oxford U.

    2006-07-14

    We present the luminosity function to very faint magnitudes for the globular clusters in M87, based on a 30 orbit Hubble Space Telescope (HST) WFPC2 imaging program. The very deep images and corresponding improved false source rejection allow us to probe the mass function further beyond the turnover than has been done before. We compare our luminosity function to those that have been observed in the past, and confirm the similarity of the turnover luminosity between M87 and the Milky Way. We also find with high statistical significance that the M87 luminosity function is broader than that of the Milky Way. We discuss how determining the mass function of the cluster system to low masses can constrain theoretical models of the dynamical evolution of globular cluster systems. Our mass function is consistent with the dependence of mass loss on the initial cluster mass given by classical evaporation, and somewhat inconsistent with newer proposals that have a shallower mass dependence. In addition, the rate of mass loss is consistent with standard evaporation models, and not with the much higher rates proposed by some recent studies of very young cluster systems. We also find that the mass-size relation has very little slope, indicating that there is almost no increase in the size of a cluster with increasing mass.

  13. The Trigonometric Parallax of the Globular Cluster M4

    NASA Astrophysics Data System (ADS)

    Rees, Richard F.; Cudworth, Kyle M.

    2017-01-01

    We have identified five stars from the Tycho-Gaia Astrometric Solution catalog as highly probable members of the globular cluster M4 (NGC 6121). A weighted average of the parallax of these five stars results in a cluster parallax of 0.55 ± 0.14 mas, corresponding to a distance of 1.82 ± 0.46 kpc and an absolute distance modulus of 11.30 ± 0.55. Examination of the Gaia DR1 astrometric validation maps of Lindegren et al. (2016) suggests that the systematic errors they identify are likely to be less than 0.1 mas for the immediate region near M4. The reddest of the five stars is also the most distant from the cluster center. This star is somewhat discrepant in both parallax and proper motion compared to the other four. Excluding this star gives a cluster parallax of 0.50 ± 0.15 mas, corresponding to a distance of 2.01 ± 0.62 kpc and an absolute distance modulus of 11.52 ± 0.67. The good agreement with previous measurements of the distance to M4 indicates that either the systematic errors are small or that diverse distance measurement techniques are seriously flawed. While the uncertainties at this point are too large to decide between the differing ground-based distance determinations, the results at this early stage bode well for future globular cluster parallaxes from Gaia. To our knowledge, this is the first measurement of the trigonometric parallax of a globular cluster.

  14. The ACS survey of Galactic globular clusters - XIV. Bayesian single-population analysis of 69 globular clusters

    NASA Astrophysics Data System (ADS)

    Wagner-Kaiser, R.; Sarajedini, A.; von Hippel, T.; Stenning, D. C.; van Dyk, D. A.; Jeffery, E.; Robinson, E.; Stein, N.; Anderson, J.; Jefferys, W. H.

    2017-06-01

    We use Hubble Space Telescope (HST) imaging from the ACS Treasury Survey to determine fits for single population isochrones of 69 Galactic globular clusters. Using robust Bayesian analysis techniques, we simultaneously determine ages, distances, absorptions and helium values for each cluster under the scenario of a 'single' stellar population on model grids with solar ratio heavy element abundances. The set of cluster parameters is determined in a consistent and reproducible manner for all clusters using the Bayesian analysis suite BASE-9. Our results are used to re-visit the age-metallicity relation. We find correlations with helium and several other parameters such as metallicity, binary fraction and proxies for cluster mass. The helium abundances of the clusters are also considered in the context of carbon, nitrogen, and oxygen abundances and the multiple population scenario.

  15. 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.

  16. Globular cluster origin of X-ray bursters

    NASA Technical Reports Server (NTRS)

    Grindlay, J. E.

    1984-01-01

    X-ray bursters and galactic bulge X-ray sources, or the most luminous X-ray sources in the Galaxy, are reasonably well constrained in their basic nature but not in their origin. It is suggested they may all have been produced by tidal capture in high density cores of globular clusters, which have now largely been disrupted by tidal stripping and shocking in the galactic plane. General arguments are presented for cluster disruption by the possible ring of giant molecular clouds in the Galaxy. Tests of the cluster disruption hypothesis are in progress and preliminary results are summarized here. The G-K star 'companions' previously noted for at least four bursters have spectra (in the two cases observed) consistent with metal-rich cluster giants. Several possibilities are discussed, including the formation of hierarchical triples in the dissolving cluster or in the galactic plane.

  17. The Newly-Discovered Outer Halo Globular Cluster System of M31

    NASA Astrophysics Data System (ADS)

    Mackey, D.; Huxor, A.; Ferguson, A.

    2012-08-01

    In this contribution we describe the discovery of a large number of globular clusters in the outer halo of M31 from the Pan-Andromeda Archaeological Survey (PAndAS). New globular clusters have also been found in the outskirts of M33, and NGC 147 and 185. Many of the remote M31 clusters are observed to preferentially project onto tidal debris streams in the stellar halo, suggesting that much of the outer M31 globular cluster system has been assembled via the accretion of satellite galaxies. We briefly discuss the global properties of the M31 halo globular cluster system.

  18. Extensive Globular Cluster Systems Associated with Ultra Diffuse Galaxies in the Coma Cluster

    NASA Astrophysics Data System (ADS)

    van Dokkum, Pieter; Abraham, Roberto; Romanowsky, Aaron J.; Brodie, Jean; Conroy, Charlie; Danieli, Shany; Lokhorst, Deborah; Merritt, Allison; Mowla, Lamiya; Zhang, Jielai

    2017-07-01

    We present Hubble Space Telescope (HST) imaging of two ultra diffuse galaxies (UDGs) with measured stellar velocity dispersions in the Coma cluster. The galaxies, Dragonfly 44 and DFX1, have effective radii of 4.7 kpc and 3.5 kpc and velocity dispersions of {47}-6+8 km s-1 and {30}-7+7 km s-1, respectively. Both galaxies are associated with a striking number of compact objects, tentatively identified as globular clusters: {N}{gc}=74+/- 18 for Dragonfly 44 and {N}{gc}=62+/- 17 for DFX1. The number of globular clusters is much higher than expected from the luminosities of the galaxies but is consistent with expectations from the empirical relation between dynamical mass and globular cluster count defined by other galaxies. Combining our data with previous HST observations of Coma UDGs we find that UDGs have a factor of {6.9}-2.4+1.0 more globular clusters than other galaxies of the same luminosity, in contrast to a recent study of a similar sample by Amorisco et al., but consistent with earlier results for individual galaxies. The Harris et al. relation between globular cluster count and dark matter halo mass implies a median halo mass of {M}{halo}˜ 1.5× {10}11 {M}⊙ for the sixteen Coma UDGs that have been observed with HST so far, with the largest and brightest having {M}{halo}˜ 5× {10}11 {M}⊙ .

  19. Dynamical Evolution of Outer-Halo Globular Clusters

    NASA Astrophysics Data System (ADS)

    Küpper, Andreas H. W.; Zonoozi, Akram H.; Haghi, Hosein; Lützgendorf, Nora; Mieske, Steffen; Frank, Matthias; Baumgardt, Holger; Kroupa, Pavel

    2017-03-01

    Outer-halo globular clusters show large half-light radii and flat stellar mass functions, depleted in low-mass stars. Using N-body simulations of globular clusters on eccentric orbits within a Milky Way-like potential, we show how a cluster's half-mass radius and its mass function develop over time. The slope of the central mass function flattens proportionally to the amount of mass a cluster has lost, and the half-mass radius grows to a size proportional to the average strength of the tidal field. The main driver of these processes is mass segregation of dark remnants. We conclude that the extended, depleted clusters observed in the Milky Way must have had small half-mass radii in the past, and that they expanded due to the weak tidal field they spend most of their lifetime in. Moreover, their mass functions must have been steeper in the past but flattened significantly as a cause of mass segregation and tidal mass loss.

  20. HST high-precision proper motions of globular clusters

    NASA Astrophysics Data System (ADS)

    Bellini, Andrea; Anderson, Jay; van der marel, roeland p.; piotto, gianpaolo; Watkins, Laura l.; Vesperini, Enrico; Milone, Antonino; Bedin, Luigi R.

    2015-08-01

    The stable environment of space makes HST an excellent astrometric tool. Its diffraction-limited resolution allows it to distinguish and measure positions and fluxes for stars all the way to the center of most globular clusters. There are now many clusters that have observations in the archive that span 13 years or more, and more observations are being taken all the time. We constructed high-precision proper-motion catalogs for over 20 clusters for which there exist two or more well-separated epochs in the archive, and we are extending the list to over 60 objects, thanks to the new observations taken within the ``HST UV Legacy Survey of Galactic Globular Clusters’’ treasury program. Each catalog contains astrometry and photometry for thousands of stars within two arcmin of the center. The catalogs are focused on the many stars within a few magnitudes of the turnoff and have typical proper-motion errors of 0.1 mas/yr, which translates to 2 km/s for the typical cluster. We are using proper motions to directly measure the clusters' anisotropy, equipartition and rotation on the plane of the sky, as well as to study internal kinematics of the different subpopulations and to probe the presence of an IMBH in their core.

  1. THE BLUE HOOK POPULATIONS OF MASSIVE GLOBULAR CLUSTERS

    SciTech Connect

    Brown, Thomas M.; Smith, Ed; Sweigart, Allen V.; Lanz, Thierry; Landsman, Wayne B.; Hubeny, Ivan E-mail: edsmith@stsci.ed E-mail: lanz@astro.umd.ed E-mail: hubeny@aegis.as.arizona.ed

    2010-08-01

    We present new Hubble Space Telescope ultraviolet color-magnitude diagrams of five massive Galactic globular clusters: NGC 2419, NGC 6273, NGC 6715, NGC 6388, and NGC 6441. These observations were obtained to investigate the 'blue hook' (BH) phenomenon previously observed in UV images of the globular clusters {omega} Cen and NGC 2808. Blue hook stars are a class of hot (approximately 35,000 K) subluminous horizontal branch stars that occupy a region of the HR diagram that is unexplained by canonical stellar evolution theory. By coupling new stellar evolution models to appropriate non-LTE synthetic spectra, we investigate various theoretical explanations for these stars. Specifically, we compare our photometry to canonical models at standard cluster abundances, canonical models with enhanced helium (consistent with cluster self-enrichment at early times), and flash-mixed models formed via a late helium-core flash on the white dwarf cooling curve. We find that flash-mixed models are required to explain the faint luminosity of the BH stars, although neither the canonical models nor the flash-mixed models can explain the range of color observed in such stars, especially those in the most metal-rich clusters. Aside from the variation in the color range, no clear trends emerge in the morphology of the BH population with respect to metallicity.

  2. An AO-assisted Variability Study of Four Globular Clusters

    NASA Astrophysics Data System (ADS)

    Salinas, R.; Contreras Ramos, R.; Strader, J.; Hakala, P.; Catelan, M.; Peacock, M. B.; Simunovic, M.

    2016-09-01

    The image-subtraction technique applied to study variable stars in globular clusters represented a leap in the number of new detections, with the drawback that many of these new light curves could not be transformed to magnitudes due to severe crowding. In this paper, we present observations of four Galactic globular clusters, M 2 (NGC 7089), M 10 (NGC 6254), M 80 (NGC 6093), and NGC 1261, taken with the ground-layer adaptive optics module at the SOAR Telescope, SAM. We show that the higher image quality provided by SAM allows for the calibration of the light curves of the great majority of the variables near the cores of these clusters as well as the detection of new variables, even in clusters where image-subtraction searches were already conducted. We report the discovery of 15 new variables in M 2 (12 RR Lyrae stars and 3 SX Phe stars), 12 new variables in M 10 (11 SX Phe and 1 long-period variable), and 1 new W UMa-type variable in NGC 1261. No new detections are found in M 80, but previous uncertain detections are confirmed and the corresponding light curves are calibrated into magnitudes. Additionally, based on the number of detected variables and new Hubble Space Telescope/UVIS photometry, we revisit a previous suggestion that M 80 may be the globular cluster with the richest population of blue stragglers in our Galaxy. 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 Hill (UNC), and Michigan State University (MSU).

  3. Effects of cosmic string velocities and the origin of globular clusters

    SciTech Connect

    Lin, Ling; Yamanouchi, Shoma; Brandenberger, Robert E-mail: shoma.yamanouchi@mail.mcgill.ca

    2015-12-01

    With the hypothesis that cosmic string loops act as seeds for globular clusters in mind, we study the role that velocities of these strings will play in determining the mass distribution of globular clusters. Loops with high enough velocities will not form compact and roughly spherical objects and can hence not be the seeds for globular clusters. We compute the expected number density and mass function of globular clusters as a function of both the string tension and the peak loop velocity, and compare the results with the observational data on the mass distribution of globular clusters in our Milky Way. We determine the critical peak string loop velocity above which the agreement between the string loop model for the origin of globular clusters (neglecting loop velocities) and observational data is lost.

  4. Spectroscopy of globular clusters in the outer halo of M81

    NASA Astrophysics Data System (ADS)

    Suwannajak, Chutipong; Sarajedini, Ata

    2017-01-01

    We present integrated spectroscopy of two globular clusters and two globular cluster candidates in the central region of the dynamically active M81 group of galaxies. These spectra were obtained from the OSIRIS instrument at the 10.4m Gran Telescopio Canarias (GTC). The target clusters are located in the halo between M81, M82, and NGC3077, which contains a significant amount of young stars and HI gas as a result of interactions between these galaxies. The spectra of the target clusters show spectral features of globular clusters, confirming their globular cluster nature. One of the two clusters is located 400 kpc away from M81, making it the most isolated globular cluster in the local universe. However, the origin of these clusters is still largely a mystery. We use their spectra to study their kinematics, ages, and metallicities to better understand the impact of galaxy interactions on the process of galaxy formation and evolution.

  5. Hunting for Optical Companions to Binary Msps in Globular Clusters

    NASA Astrophysics Data System (ADS)

    Ferraro, Francesco

    2009-07-01

    Here we present a proposal which exploits the re-newed potential of HST after the Service Mission 4 for probing the population of binary Millisecond Pulsars {MSPs} in Globular Clusters. In particular we intend to: {1} extend the search for optical counterparts in Terzan 5, by pushing the performance of the WFC3 IR channel to sample the entire MS extension down to M=0.1 Mo; {2} perform a deep multi-band search of MSP companions with the WFC3, in 3 clusters {namely NGC6440, M28 and M5}, where recent radio observations have found particularly interesting objects; {3} derive an accurate radial velocity {with STIS} of the puzzling optical companion COM6266B recently discovered by our group, to firmly assess its cluster membership.This program is the result of a large collaboration among the three major groups {lead by Freire, Ransom and Possenti} which are performing extensive MSP search in GCs in the radio bands, and our group which has a large experience in performing accurate stellar photometry in crowded environments. This collaboration has produced a number of outstanding discoveries. In fact, three of the 6 optical counterparts to binary MSP companions known to date in GCs have been discovered by our group. The observations here proposed would easily double/triple the existing sample of known MSP companions, allowing the first meaningful approach to the study of the formation, evolution and recycling process of pulsar in GCs. Moreover, since most of binary MSPs in GCs are thought to form via stellar interactions in the high density core regions, the determination of the nature of the companion and the incidence of this collisionally induced population has a significant impact on our knowledge of the cluster dynamics. Even more interesting, the study of the optical companions to NSs in GCs allows one to derive tighter constraints {than those obtainable for NS binaries in the Galactic field} on the system properties. This has, in turn, an intrisic importance for

  6. Pal 12 - A metal-rich globular cluster in the outer halo

    NASA Technical Reports Server (NTRS)

    Cohen, J. G.; Frogel, J. A.; Persson, S. E.; Zinn, R.

    1980-01-01

    New optical and infrared observations of several stars in the distant globular cluster Pal 12 show that they have CO strengths and heavy element abundances only slightly less than in M 71, one of the more metal-rich globular clusters. Pal 12 thus has a metal abundance near the high end of the range over which globular clusters exist and lies in the outer galactic halo. Its red horizontal branch is not anomalous in view of the abundance that has been found.

  7. Pal 12 - A metal-rich globular cluster in the outer halo

    NASA Technical Reports Server (NTRS)

    Cohen, J. G.; Frogel, J. A.; Persson, S. E.; Zinn, R.

    1980-01-01

    New optical and infrared observations of several stars in the distant globular cluster Pal 12 show that they have CO strengths and heavy element abundances only slightly less than in M 71, one of the more metal-rich globular clusters. Pal 12 thus has a metal abundance near the high end of the range over which globular clusters exist and lies in the outer galactic halo. Its red horizontal branch is not anomalous in view of the abundance that has been found.

  8. Structural Parameters for 10 Halo Globular Clusters in M33

    NASA Astrophysics Data System (ADS)

    Ma, Jun

    2015-05-01

    In this paper, we present the properties of 10 halo globular clusters (GCs) with luminosities L ≃ 5-7 × 105 L⊙ in the Local Group galaxy M33 using images from the Hubble Space Telescope WFPC2 in the F555W and F814W bands. We obtained the ellipticities, position angles, and surface brightness profiles for each GC. In general, the ellipticities of the M33 sample clusters are similar to those of the M31 clusters. The structural and dynamical parameters are derived by fitting the profiles to three different models combined with mass-to-light ratios (M/L values) from population-synthesis models. The structural parameters include core radii, concentration, half-light radii, and central surface brightness. The dynamical parameters include the integrated cluster mass, integrated binding energy, central surface mass density, and predicted line of sight velocity dispersion at the cluster center. The velocity dispersions of the four clusters predicted here agree well with the observed dispersions by Larsen et al. The results here showed that the majority of the sample halo GCs are better fitted by both the King model and the Wilson model than the Sérsic model. In general, the properties of the clusters in M33, M31, and the Milky Way fall in the same regions of parameter spaces. The tight correlations of cluster properties indicate a “fundamental plane” for clusters, which reflects some universal physical conditions and processes operating at the epoch of cluster formation.

  9. The Compositin of the Bulge Globular Cluster NGC 6273

    NASA Astrophysics Data System (ADS)

    Pilachowski, Catherine A.; Johnson, Christian

    2015-08-01

    Observations of red giants in the Bulge globular cluster NGC 6273 with the Michigan/Magellan Fiber System (M2FS) mounted on the Nasmyth-East port of the Magellan-Clay 6.5m telescope at Las Campanas Observatory reveal a spread in metallicity. Members have been confirmed with radial velocity. NGC 6273 has at least two populations separated by 0.2-0.3 dex in [Fe/H]. The sodium and aluminum abundances are correlated while the magnesium and aluminum abundances are anti-correlated. The cluster also shows a rise in the abundance of the s-process element lanthanum with [Fe/H] similar to other massive clusters. The cluster contains a possible 3rd population depleted in most elements by 0.3 dex.

  10. The Composition of the Bulge Globular Cluster NGC 6273

    NASA Astrophysics Data System (ADS)

    Pilachowski, C. A.; Johnson, C. I.; Rich, R. M.; Caldwell, N.; Mateo, M.; Bailey, J. I.; Crane, J. D.

    2017-03-01

    Observations of red giants in the Bulge globular cluster NGC 6273 with the Michigan/Magellan Fiber System (M2FS) mounted on the Nasmuth-East port of the Magellan-Clay 6.5-m telescope at the Las Campanas Observatory reveal a spread in metallicity. Members have been confirmed with radial velocity. NGC 6273 has at least two populations separated by 0.2-0.3 dex in [Fe/H]. The sodium and aluminum abundances are correlated while the magnesium and aluminum abundances are anti-correlated. The cluster also shows a rise in the abundance of the s-process element lanthanum with [Fe/H] similar to other massive clusters. The cluster contains a possible third population depleted in most elements by 0.3 dex.

  11. The age of the LMC globular cluster NGC 1783

    SciTech Connect

    Mould, J.; Kristian, J.; Nemec, J.; Jensen, J.; Aaronson, M.

    1989-04-01

    The age of the LMC red globular cluster NGC 1783 is estimated as 0.9 + or - 0.4 billion yr by photometry of the main-sequence turnoff. The accuracy of the estimate is limited chiefly by the uncertainty in the distance modulus of the cluster. At (m - M)0 = 18.2 the cluster is aged 1.1 + or - 0.2 Gyr; at (m - M)0 = 18.7 it is 0.7 + or - 0.2 Gyr. NGC 1783 is a sufficiently rich cluster that one can see the full development of red giants on the asymptotic giant branch from the M type, through S, to carbon-rich atmospheres. 31 refs.

  12. 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.

  13. Sulfur in the globular clusters 47 Tucanae and NGC 6752

    NASA Astrophysics Data System (ADS)

    Sbordone, L.; Limongi, M.; Chieffi, A.; Caffau, E.; Ludwig, H.-G.; Bonifacio, P.

    2009-08-01

    Context: The light elements Li, O, Na, Al, and Mg are known to show star-to-star variations in the globular clusters 47 Tuc and NGC 6752. Such variations are interpreted as coming from processing in a previous generation of stars. Aims: In this paper we investigate the abundances of the α-element sulfur, for which no previous measurements exist. In fact this element has not been investigated in any Galactic globular cluster so far. The only globular cluster for which such measurements are available is Terzan 7, which belongs to the Sgr dSph. Methods: We use high-resolution spectra of the S i Mult. 1, acquired with the UVES spectrograph at the 8.2 m VLT-Kueyen telescope, for turn-off and giant stars in the two globular clusters. The spectra were analysed making use of ATLAS static plane parallel model atmospheres and SYNTHE spectrum synthesis. We also compute 3D corrections from CO^5BOLD hydrodynamic models and apply corrections due to NLTE effects taken from the literature. Results: In the cluster NGC 6752 sulfur has been measured only in four subgiant stars. We find no significant star-to-star scatter and a mean <[S/Fe]> = +0.49 ± 0.15, consistent with what is observed in field stars of the same metallicity. In the cluster 47 Tuc we measured S in 4 turn-off and 5 subgiant stars with a mean <[S/Fe]> = +0.18 ± 0.14. While this result is compatible with no star-to-star scatter we notice a statistically significant correlation of the sulfur abundance with the sodium abundance and a tentative correlation with the silicon abundance. Conclusions: The sulfur-sodium correlation is not easily explained in terms of nucleosynthesis. An origin due to atomic diffusion can be easily dismissed. The correlation cannot be easily dismissed either, in view of its statistical significance, until better data for more stars is available. Based on observations made with the ESO VLT-Kueyen telescope at the Paranal Observatory, Chile, in the course of the ESO-Large Programme 165.L-0263.

  14. The double mode RR Lyrae stars in the globular cluster IC 4499.

    NASA Astrophysics Data System (ADS)

    Clement, C. M.; Nemec, J. M.

    The southern globular cluster IC 4499 has the highest frequency of RR Lyrae stars of any globular cluster in the Galaxy. These variables were studied by Clement, Dickens, & Bingham (1979). An inspection of their light curves shows a great deal of scatter among the long period RRc stars. Thus the cluster is a prime candidate for an investigation of double-mode pulsation.

  15. Tidal Densities of Globular Clusters and the Galactic Mass Distribution

    NASA Astrophysics Data System (ADS)

    Lee, Hyung Mok

    1990-12-01

    The tidal radii of globular clusters reflect the tidal field of the Galaxy. The mass distribution of the Galaxy thus may be obtained if the tidal fields of clusters are well known. Although large amounts of uncertainties in the determination of tidal radii have been obstacles in utilizing this method, analysis of tidal density could give independent check for the Galactic mass distribution. Recent theoretical modeling of dynamical evolution including steady Galactic tidal field shows that the observationally determined tidal radii could be systematically larger by about a factor of 1.5 compared to the theoretical values. From the analysis of entire sample of 148 globular clusters and 7 dwarf spheroidal systems compiled by Webbink(1985), we find that such reduction from observed values would make the tidal density(the mean density within the tidal radius) distribution consistent with the flat rotation curve of our Galaxy out to large distances if the velocity distribution of clusters and dwarf spheroidals with respect to the Galactic center is isotropic.

  16. 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

  17. Birth of millisecond pulsars in globular clusters

    NASA Technical Reports Server (NTRS)

    Grindlay, J. E.; Bailyn, C. D.

    1988-01-01

    It is argued here that accretion-induced collapse of white dwarfs in binaries can form millisecond pulsars directly without requiring a precursor low-mass X-ray binary stage. Ablation of the precollapse binary companion by the millisecond pulsar's radiation field, a process invoked to explain some of the characteristics of the recently discovered eclipsing millisecond pulsar, can then yield isolated neutron stars witout requiring an additional stellar encounter.

  18. Birth of millisecond pulsars in globular clusters

    NASA Technical Reports Server (NTRS)

    Grindlay, J. E.; Bailyn, C. D.

    1988-01-01

    It is argued here that accretion-induced collapse of white dwarfs in binaries can form millisecond pulsars directly without requiring a precursor low-mass X-ray binary stage. Ablation of the precollapse binary companion by the millisecond pulsar's radiation field, a process invoked to explain some of the characteristics of the recently discovered eclipsing millisecond pulsar, can then yield isolated neutron stars witout requiring an additional stellar encounter.

  19. White Dwarf Distance and Precision Age for Globular Clusters

    NASA Astrophysics Data System (ADS)

    Bragaglia, Angela

    1996-07-01

    This proposal is the natural complement of our Cycle 4 and 5 programs aimed at using the White Dwarf cooling sequence for the calibration of the globular cluster distance scale, the determination of accurate distances being a critical prerequisite for the estimate of reliable cluster ages. In Cycle 4 we obtained data on NGC6752, while in Cycle 5 we got images of 47Tuc. These two clusters will test whether there really exists a measurable age difference between the metal poor and the metal rich clusters, as has been inferred from some horizontal branch luminosity- metallicity calibration. While reducing our Cycle 4 data we have realized that a few short exposures would greatly help to accurately subtract the wings of the heavily saturated images in the field of view, hence to improve the accuracy of the faint star fotometry in the crowded field of the cluster. We therefore apply for one orbit for each of the two clusters in order to get shallow images of our Cycle 4 and 5 fields. The observed cooling sequences for the clusters {for DA and non-DA WDs} will then be fit to the corresponding FCSs to determine the cluster distance moduli. Moreover, directly fitting to each other the WD cooling sequences of the two clusters will provide very accurate relative distances {hence ages}.

  20. STRUCTURAL PARAMETERS FOR GLOBULAR CLUSTERS IN M31

    SciTech Connect

    Wang Song; Ma Jun

    2013-08-01

    In this paper, we present surface brightness profiles for 79 globular clusters in M31, using images observed with the Hubble Space Telescope, some of which are from new observations. The structural and dynamical parameters are derived from fitting the profiles to several different models for the first time. The results show that in the majority of cases, King models fit the M31 clusters just as well as Wilson models and better than Sersic models. However, there are 11 clusters best fitted by Sersic models with the Sersic index n > 2, meaning that they have cuspy central density profiles. These clusters may be the well-known core-collapsed candidates. There is a bimodality in the size distribution of M31 clusters at large radii, which is different from their Galactic counterparts. In general, the properties of clusters in M31 and the Milky Way fall in the same regions of parameter spaces. The tight correlations of cluster properties indicate a ''fundamental plane'' for clusters, which reflects some universal physical conditions and processes operating at the epoch of cluster formation.

  1. Structure and Dynamics of the Globular Cluster Palomar 13

    NASA Astrophysics Data System (ADS)

    Bradford, J. D.; Geha, M.; Muñoz, R. R.; Santana, F. A.; Simon, J. D.; Côté, P.; Stetson, P. B.; Kirby, E.; Djorgovski, S. G.

    2011-12-01

    We present Keck/DEIMOS spectroscopy and Canada-France-Hawaii Telescope/MegaCam photometry for the Milky Way globular cluster Palomar 13. We triple the number of spectroscopically confirmed members, including many repeat velocity measurements. Palomar 13 is the only known globular cluster with possible evidence for dark matter, based on a Keck/High Resolution Echelle Spectrometer 21 star velocity dispersion of σ = 2.2 ± 0.4 km s-1. We reproduce this measurement, but demonstrate that it is inflated by unresolved binary stars. For our sample of 61 stars, the velocity dispersion is σ = 0.7+0.6 -0.5 km s-1. Combining our DEIMOS data with literature values, our final velocity dispersion is σ = 0.4+0.4 -0.3 km s-1. We determine a spectroscopic metallicity of [Fe/H] = -1.6 ± 0.1 dex, placing a 1σ upper limit of σ[Fe/H] ~ 0.2 dex on any internal metallicity spread. We determine Palomar 13's total luminosity to be MV = -2.8 ± 0.4, making it among the least luminous known globular clusters. The photometric isophotes are regular out to the half-light radius and mildly irregular outside this radius. The outer surface brightness profile slope is shallower than typical globular clusters (Σvpropr η, η = -2.8 ± 0.3). Thus at large radius, tidal debris is likely affecting the appearance of Palomar 13. Combining our luminosity with the intrinsic velocity dispersion, we find a dynamical mass of M 1/2 = 1.3+2: 7 -1.3 × 103 M ⊙ and a mass-to-light ratio of M/LV = 2.4+5.0 -2.4 M ⊙/L ⊙. Within our measurement errors, the mass-to-light ratio agrees with the theoretical predictions for a single stellar population. We conclude that, while there is some evidence for tidal stripping at large radius, the dynamical mass of Palomar 13 is consistent with its stellar mass and neither significant dark matter, nor extreme tidal heating, is required to explain the cluster dynamics. The data presented herein were obtained at the W. M. Keck Observatory, which is operated as a

  2. STRUCTURE AND DYNAMICS OF THE GLOBULAR CLUSTER PALOMAR 13

    SciTech Connect

    Bradford, J. D.; Geha, M.; Munoz, R. R.; Santana, F. A.; Simon, J. D.; Cote, P.; Stetson, P. B.; Kirby, E.; Djorgovski, S. G. E-mail: marla.geha@yale.edu

    2011-12-20

    We present Keck/DEIMOS spectroscopy and Canada-France-Hawaii Telescope/MegaCam photometry for the Milky Way globular cluster Palomar 13. We triple the number of spectroscopically confirmed members, including many repeat velocity measurements. Palomar 13 is the only known globular cluster with possible evidence for dark matter, based on a Keck/High Resolution Echelle Spectrometer 21 star velocity dispersion of {sigma} = 2.2 {+-} 0.4 km s{sup -1}. We reproduce this measurement, but demonstrate that it is inflated by unresolved binary stars. For our sample of 61 stars, the velocity dispersion is {sigma} = 0.7{sup +0.6}{sub -0.5} km s{sup -1}. Combining our DEIMOS data with literature values, our final velocity dispersion is {sigma} = 0.4{sup +0.4}{sub -0.3} km s{sup -1}. We determine a spectroscopic metallicity of [Fe/H] = -1.6 {+-} 0.1 dex, placing a 1{sigma} upper limit of {sigma}{sub [Fe/H]} {approx} 0.2 dex on any internal metallicity spread. We determine Palomar 13's total luminosity to be M{sub V} = -2.8 {+-} 0.4, making it among the least luminous known globular clusters. The photometric isophotes are regular out to the half-light radius and mildly irregular outside this radius. The outer surface brightness profile slope is shallower than typical globular clusters ({Sigma}{proportional_to}r{sup {eta}}, {eta} = -2.8 {+-} 0.3). Thus at large radius, tidal debris is likely affecting the appearance of Palomar 13. Combining our luminosity with the intrinsic velocity dispersion, we find a dynamical mass of M{sub 1/2} = 1.3{sup +2:7}{sub -1.3} Multiplication-Sign 10{sup 3} M{sub Sun} and a mass-to-light ratio of M/L{sub V} = 2.4{sup +5.0}{sub -2.4} M{sub Sun }/L{sub Sun }. Within our measurement errors, the mass-to-light ratio agrees with the theoretical predictions for a single stellar population. We conclude that, while there is some evidence for tidal stripping at large radius, the dynamical mass of Palomar 13 is consistent with its stellar mass and neither

  3. Gaseous models of globular clusters with stellar evolution

    NASA Astrophysics Data System (ADS)

    Deiters, S.; Spurzem, R.

    Comparing different approaches for modelling the evolution of star clusters, gaseous models have the advantage of high "particle numbers" but --- until now --- the disadvantage of a lack of realism (Giersz & Spurzem 1994, MNRAS 269, 24 1). To improve gaseous models towards a more realistic description of globular clusters one has to take the effects of stellar evolution and many (primordial) binaries into account and add a consistent treatment of the tidal field of the galaxy (Chernoff & Weinberg 1990, ApJ 351, 121; Portegies Zwart 1998, AA in press). We want to present the first steps on our way towards more realistic gaseous models: We show results of the first implementation of stellar evolution in a spherically symmetric anisotropic gaseous model. We subdivide our model in several dynamical components, each with different stellar mass, whose stellar evolution is followed in a parameterized way. Thus we can simulate the effects of the evolution of stars of different masses in the cluster: During their evolution the stars lose a significant amount of their initial mass, which can easily escape from the cluster. Hence the binding energy of the cluster is reduced. We show several models with different initial conditions with and without the effects of stellar evolution. Their evolution is followed into core bounce and during the post-collapse phase. Dynamical properties of the clusters for the different initial conditions are compared. If time allows we will focus briefly on the treatment of a (time-independent) tidal boundary, modelling the gravitational field of the mother galaxy in our models and give an outlook on the next steps towards more realism in our models of globular clusters, e.g. the inclusion of stochastic binaries (Spurzem & Giersz 1996, MNRAS 283, 805) and stellar finite-size effects.

  4. INTERMEDIATE-MASS BLACK HOLES IN EARLY GLOBULAR CLUSTERS

    SciTech Connect

    Vesperini, Enrico; McMillan, Stephen L. W.; D'Ercole, Annibale; D'Antona, Francesca

    2010-04-10

    Spectroscopic and photometric observations show that many globular clusters host multiple stellar populations, challenging the common paradigm that globular clusters are 'simple stellar populations' composed of stars of uniform age and chemical composition. The chemical abundances of second-generation (SG) stars constrain the sources of gas out of which these stars must have formed, indicating that the gas must contain matter processed through the high-temperature CNO cycle. First-generation massive asymptotic giant branch (AGB) stars have been proposed as the source of this gas. In a previous study, by means of hydrodynamical and N-body simulations, we have shown that the AGB ejecta collect in a cooling flow in the cluster core, where the gas reaches high densities, ultimately forming a centrally concentrated subsystem of SG stars. In this Letter, we show that the high gas density can also lead to significant accretion onto a pre-existing seed black hole. We show that gas accretion can increase the black hole mass by up to a factor of 100. The details of the gas dynamics are important in determining the actual black hole growth. Assuming a near-universal seed black hole mass and small cluster-to-cluster variations in the duration of the SG formation phase, the outcome of our scenario is one in which the present intermediate-mass black hole (IMBH) mass may have only a weak dependence on the current cluster properties. The scenario presented provides a natural mechanism for the formation of an IMBH at the cluster center during the SG star formation phase.

  5. THE OUTSKIRTS OF GLOBULAR CLUSTERS AS MODIFIED GRAVITY PROBES

    SciTech Connect

    Hernandez, X.; Jimenez, M. A.

    2012-05-01

    In the context of theories of gravity modified to account for the observed dynamics of galactic systems without the need to invoke the existence of dark matter, a prediction often appears regarding low-acceleration systems: wherever a falls below a{sub 0}, one should expect a transition from the classical to the modified gravity regime. This modified gravity regime will be characterized by equilibrium velocities that become independent of distance and that scale with the fourth root of the total baryonic mass, V{sup 4}{proportional_to}M. The two conditions above are the well-known flat rotation curves and Tully-Fisher relations of the galactic regime. Recently, however, a similar phenomenology has been hinted at, at the outskirts of Galactic globular clusters, precisely in the region where a < a{sub 0}. Radial profiles of the projected velocity dispersion have been observed to stop decreasing along Keplerian expectations and to level off at constant values beyond the radii where a < a{sub 0}. We have constructed gravitational equilibrium dynamical models for a number of globular clusters for which the above gravitational anomaly has been reported, using a modified Newtonian force law that yields equilibrium velocities equivalent to modified Newtonian dynamics. We find models having an inner Newtonian region and an outer modified gravity regime, which reproduce all observational constraints, surface brightness profiles, total masses, and line-of-sight velocity dispersion profiles, can be easily constructed. Through the use of detailed single stellar population models tuned individually to each of the globular clusters in question, we derive estimates of the total masses for these systems. Interestingly, we find that the asymptotic values of the velocity dispersion profiles are consistent with scaling with the fourth root of the total masses, as expected under modified gravity scenarios.

  6. The richness of the globular cluster system of NGC 3923: Clues to elliptical galaxy formation

    NASA Technical Reports Server (NTRS)

    Zepf, Stephen E.; Geisler, Doug; Ashman, Keith M.

    1994-01-01

    We present new data on the globular cluster system of the elliptical galaxy NGC 3923 which show that it has the most globular clusters per unit luminosity of any noncluster elliptical yet observed, with S(sub N) = 6.4 +/- 1.4. NGC 3923 is also among the brightest ellipticals outside of a galaxy cluster for which the number of globular clusters has been determined. Our observation of a large number of clusters per unit luminosity (high S(sub N)-value) for a bright elliptical in a sparse environment is consistent with the suggestion of Djorgovski and Santiago that the number of globular clusters is a power-law function of the luminosity with an exponent greater than 1. We relate this higher specific frequency of globular clusters in more luminous galaxies to other observations which indicate that the physical conditions within elliptical galaxies at the time of their formation were dependent on galaxy mass.

  7. The origin of the Milky Way globular clusters

    NASA Astrophysics Data System (ADS)

    Renaud, Florent; Agertz, Oscar; Gieles, Mark

    2017-03-01

    We present a cosmological zoom-in simulation of a Milky Way-like galaxy used to explore the formation and evolution of star clusters. We investigate in particular the origin of the bimodality observed in the colour and metallicity of globular clusters, and the environmental evolution through cosmic times in the form of tidal tensors. Our results self-consistently confirm previous findings that the blue, metal-poor clusters form in satellite galaxies that are accreted on to the Milky Way, while the red, metal-rich clusters form mostly in situ, or, to a lower extent, in massive, self-enriched galaxies merging with the Milky Way. By monitoring the tidal fields these populations experience, we find that clusters formed in situ (generally centrally concentrated) feel significantly stronger tides than the accreted ones, both in the present day, and when averaged over their entire life. Furthermore, we note that the tidal field experienced by Milky Way clusters is significantly weaker in the past than at present day, confirming that it is unlikely that a power-law cluster initial mass function like that of young massive clusters, is transformed into the observed peaked distribution in the Milky Way with relaxation-driven evaporation in a tidal field.

  8. Dynamical Evolution of Rotating Globular Clusters with Embedded Black Holes

    NASA Astrophysics Data System (ADS)

    Fiestas, J.; Porth, O.; Spurzem, R.

    2008-05-01

    Evolution of self-gravitating rotating dense stellar systems (e.g. globular clusters) with embedded black holes is investigated. The interplay between velocity diffusion due to relaxation and black hole star accretion is followed together with cluster differential rotation using 2D+1 Fokker Planck numerical methods. The models can reproduce the Bahcall-Wolf f E1/4 ( r-7/4) cusp inside the zone of influence of the black hole. Angular momentum transport and star accretion processes support the development of central rotation in relaxation time scales, before re-expansion and cluster dissolution due to mass loss in the tidal field of a parent galaxy. Gravogyro and gravothermal instabilities conduce the system to a faster evolution leading to shorter collapse times with respect to models without black hole.

  9. Analysis of Globular Cluster Photometry from 2MASS

    NASA Astrophysics Data System (ADS)

    Sarajedini, Ata; Milliman, K.; Kirkpatrick, A.

    2007-12-01

    Using near-infrared color magnitude diagrams of over 30 Galactic globular clusters, we have measured the magnitude of the red giant branch (RGB) 'bump,' the level of the core-helium burning red clump, and the slope of the RGB. Our aim is to compare our values with those measured by other investigators for the same clusters as we all as to derive new relations between these quantities and cluster properties such as age and metallicity. We find a good correlation between our values and those in the literature albeit with significant scatter. This work will explore the reasons for this scatter and techniques to minimize its effects. This research was supported by an REU supplement to NSF CAREER grant AST00-94048.

  10. Intermediate-age Globular Clusters in Four Galaxy Merger Remnants

    NASA Astrophysics Data System (ADS)

    Trancho, Gelys; Miller, Bryan W.; Schweizer, François; Burdett, Daniel P.; Palamara, David

    2014-08-01

    We present the results of combining Hubble Space Telescope optical photometry with ground-based Ks -band photometry from the Gemini imagers NIRI and FLAMINGOS-I to study the globular cluster (GC) populations in four early-type galaxies that are candidate remnants of recent mergers (NGC 1700, NGC 2865, NGC 4382, and NGC 7727). These galaxies were chosen based on their blue colors and fine structure, such as shells and ripples that are indicative of past interactions. We fit the combined VIKs GC data with simple toy models of mixed cluster populations that contain three subpopulations of different age and metallicity. The fits, done via chi-squared mapping of the parameter space, yield clear evidence for the presence of intermediate-age clusters in each galaxy. We find that the ages of ~1-2 Gyr for these GC subpopulations are consistent with the previously estimated merger ages for the host galaxies.

  11. Globular cluster systems of the three Virgo ellipticals

    SciTech Connect

    Cohen, J.G.

    1988-03-01

    The globular-cluster systems (GCSs) around NGC 4406, NGC 4472, and NGC 4486 are characterized on the basis of published observational data obtained with the 5-m Hale telescope at Palomar Observatory (Cohen, 1986). The data are compiled in extensive tables and graphs and analyzed in detail. The GCS median colors (slightly redder than those for the Galaxy) and color distributions are found to be independent of the cluster luminosity and the position of the cluster in the galactic halo. The NGC 4472 and NGC 4486 GCSs are somewhat more extended than the underlying galactic halos, but all of the halo ellipticities and position angles are about equal to those of the respective GCSs. 37 references.

  12. The nonthermal stellar dynamics of the globular cluster M15

    SciTech Connect

    Peterson, R.C.; Seitzer, P.; Cudworth, K.M. Space Telescope Science Institute, Baltimore, MD Yerkes Observatory, Williams Bay, WI )

    1989-12-01

    The velocity dispersion as a function of radius in the globular cluster M15 is derived from measurements of 120 individual stars between 0.1 and 4.6 arcmin of the cluster center, and from the integrated light of the central cusp. The stellar measurements, with an individual accuracy of 1 km/s, indicate a mean cluster velocity of -107.1 + or - 0.9 km/s and a mean velocity dispersion of 9.0 + or - 0.6 km/s. The velocity dispersion inside 12 arcmin varies with radius. Except for its greater velocity gradient, the spectrum of the integrated light of the cusp is indistinguishable from that formed by superposition of the individual M15 giant spectra, demonstrating that the excess light at the center is due primarily to a normal M15 population. The findings indicate a nonthermal energy distribution with substantial heating in the central regions. 54 refs.

  13. A new look at the globular cluster M28

    SciTech Connect

    Rees, R.F.; Cudworth, K.M. )

    1991-07-01

    Reductions of PDS microdensitometer scans of 20 plates from three different telescopes over an epoch range of 92 yr have yielded proper motions and photometry for more than 250 stars down to V about 16 in the region of the poorly studied globular cluster M28 (NGC 6626). Membership probabilities for these stars, including several variables, are derived from the proper motions, and a color-magnitude diagram of probable members is presented and discussed. Strong evidence of systematic errors in previous photographic photometry is found. Some questions about the metal abundance of M28 are addressed; in particular, a dependence upon method of the derived metallicity. All previously known variables included in this study are at least possible members. Evidence is found of variability of a few stars not previously known to vary. The derivation of the cluster's absolute proper motion shows the space velocity to be surprisingly disklike for a moderately metal-poor cluster. 33 refs.

  14. Intermediate-age globular clusters in four galaxy merger remnants

    SciTech Connect

    Trancho, Gelys; Miller, Bryan W.; Schweizer, François; Burdett, Daniel P.; Palamara, David

    2014-08-01

    We present the results of combining Hubble Space Telescope optical photometry with ground-based K{sub s} -band photometry from the Gemini imagers NIRI and FLAMINGOS-I to study the globular cluster (GC) populations in four early-type galaxies that are candidate remnants of recent mergers (NGC 1700, NGC 2865, NGC 4382, and NGC 7727). These galaxies were chosen based on their blue colors and fine structure, such as shells and ripples that are indicative of past interactions. We fit the combined VIK{sub s} GC data with simple toy models of mixed cluster populations that contain three subpopulations of different age and metallicity. The fits, done via chi-squared mapping of the parameter space, yield clear evidence for the presence of intermediate-age clusters in each galaxy. We find that the ages of ∼1-2 Gyr for these GC subpopulations are consistent with the previously estimated merger ages for the host galaxies.

  15. 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).

  16. The Age of the Inner Halo Globular Cluster NGC 6652

    NASA Technical Reports Server (NTRS)

    Chaboyer, Brian; Sarajedini, Ata; Armandroff, Taft E.

    2000-01-01

    Hubble Space Telescope (HST) (V,I) photometry has been obtained for the inner halo globular cluster NGC 6652. The photometry reaches approximately 4 mag below the turn-off and includes a well populated horizontal branch (HB). This cluster is located close to the Galactic center at RGC approximately equal to 2.0 kpc with a reddening of E(V-I) = 0.15 +/- 0.02 and has a metallicity of [Fe/H] approximately equal to -0.85. Based upon DELTA V (sup SGB) (sub HB), NGC 6652 is 11.7 plus or minus 1.6 Gyr old. Using A HB precise differential ages for 47 Tuc (a thick disk globular), M107 and NGC 1851 (both halo clusters) were obtained. NGC 6652 appears to be the same age as 47 Tuc and NGC 1851 (within +/- 1.2 Gyr), while there is a slight suggestion that M107 is older than NGC 6652 by 2.3 +/- 1.5 Gyr. As this is a less than 2 sigma result, this issue needs to be investigated further before a definitive statement regarding the relative age of M107 and NGC 6652 may be made.

  17. High-resolution imaging of globular cluster cores

    NASA Technical Reports Server (NTRS)

    Weir, N.; Piotto, G.; Djorgovski, S.

    1990-01-01

    An approach based on the maximum entropy method aimed at increasing angular resolution to study globular cluster cores is presented. To perform the image restoration the Gull-Skilling (1989) MEMSYS-3 code for maximum entropy reconstruction of arbitrary data sets was used. This software was recently applied to restoration of ESO images of the R136 object in the core of the 30 Doradus nebula. It was demonstrated that the software made it possible to restore an image at subpixel spatial scales which facilitates the detection of very high-resolution structure in the restored image.

  18. Intrinsic integrated UBVRI colors of Galactic globular clusters

    NASA Technical Reports Server (NTRS)

    Reed, B. Cameron; Hesser, James E.; Shawl, Stephen J.

    1988-01-01

    Published observational data on 50 Galactic globular clusters, including spectral classifications, homogenized colors, and color excesses, are compiled in extensive tables, graphs, and diagrams and analyzed to determine the intrinsic-color/integrated-spectral-type relationship in the UBVRI system. These relationships are found to exhibit significant slopes, although the RI colors do not contribute substantially to the intrinsic-color determination. The values of a(B-V) for the northern and southern Galactic hemispheres are found to be 0.068 + or - 0.006 and 0.039 + or - 0.003 mag, respectively.

  19. High-precision HST proper motions of globular clusters

    NASA Astrophysics Data System (ADS)

    Bellini, A.

    Photometric and spectroscopic studies over the last 15 years have revolutionized our understanding of globular clusters (GCs). We now know that essentially all GCs host multiple stellar populations that can be identified along all evolutionary sequences and are characterized by differences in light elements, He, and sometimes Fe. These findings present a number of formidable challenges for the study of the formation and evolution of GCs. The internal kinematics of multiple stellar populations is a fundamental piece of the puzzle and high-precision proper motions are the key tool to shed light on many open questions regarding GCs.

  20. 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.

  1. Bayesian Analysis of Multiple Populations in Galactic Globular Clusters

    NASA Astrophysics Data System (ADS)

    Wagner-Kaiser, Rachel A.; Sarajedini, Ata; von Hippel, Ted; Stenning, David; Piotto, Giampaolo; Milone, Antonino; van Dyk, David A.; Robinson, Elliot; Stein, Nathan

    2016-01-01

    We use GO 13297 Cycle 21 Hubble Space Telescope (HST) observations and archival GO 10775 Cycle 14 HST ACS Treasury observations of Galactic Globular Clusters to find and characterize multiple stellar populations. Determining how globular clusters are able to create and retain enriched material to produce several generations of stars is key to understanding how these objects formed and how they have affected the structural, kinematic, and chemical evolution of the Milky Way. We employ a sophisticated Bayesian technique with an adaptive MCMC algorithm to simultaneously fit the age, distance, absorption, and metallicity for each cluster. At the same time, we also fit unique helium values to two distinct populations of the cluster and determine the relative proportions of those populations. Our unique numerical approach allows objective and precise analysis of these complicated clusters, providing posterior distribution functions for each parameter of interest. We use these results to gain a better understanding of multiple populations in these clusters and their role in the history of the Milky Way.Support for this work was provided by NASA through grant numbers HST-GO-10775 and HST-GO-13297 from the Space Telescope Science Institute, which is operated by AURA, Inc., under NASA contract NAS5-26555. This material is based upon work supported by the National Aeronautics and Space Administration under Grant NNX11AF34G issued through the Office of Space Science. This project was supported by the National Aeronautics & Space Administration through the University of Central Florida's NASA Florida Space Grant Consortium.

  2. A Proper Motions Study of the Globular Cluster NGC 3201

    NASA Astrophysics Data System (ADS)

    Sariya, Devesh P.; Jiang, Ing-Guey; Yadav, R. K. S.

    2017-03-01

    With a high value of heliocentric radial velocity, a retrograde orbit, and suspected to have an extragalactic origin, NGC 3201 is an interesting globular cluster for kinematical studies. Our purpose is to calculate the relative proper motions (PMs) and membership probability for the stars in the wide region of globular cluster NGC 3201. PM based membership probabilities are used to isolate the cluster sample from the field stars. The membership catalog will help address the question of chemical inhomogeneity in the cluster. Archive CCD data taken with a wide-field imager (WFI) mounted on the ESO 2.2 m telescope are reduced using the high-precision astrometric software developed by Anderson et al. for the WFI images. The epoch gap between the two observational runs is ∼14.3 years. To standardize the BVI photometry, Stetson’s secondary standard stars are used. The CCD data with an epoch gap of ∼14.3 years enables us to decontaminate the cluster stars from field stars efficiently. The median precision of PMs is better than ∼0.8 mas yr‑1 for stars having V< 18 mag that increases up to ∼1.5 mas yr‑1 for stars with 18< V< 20 mag. Kinematic membership probabilities are calculated using PMs for stars brighter than V∼ 20 mag. An electronic catalog of positions, relative PMs, BVI magnitudes, and membership probabilities in the ∼19.7 × 17 arcmin2 region of NGC 3201 is presented. We use our membership catalog to identify probable cluster members among the known variables and X-ray sources in the direction of NGC 3201. Based on observations with the MPG/ESO 2.2 m and ESO/VLT telescopes, located at La Silla and Paranal Observatory, Chile, under DDT programs 164.O-0561(F), 093.A-9028(A), and the archive material.

  3. Measuring consistent masses for 25 Milky Way globular clusters

    SciTech Connect

    Kimmig, Brian; Seth, Anil; Ivans, Inese I.; Anderton, Tim; Gregersen, Dylan; Strader, Jay; Caldwell, Nelson

    2015-02-01

    We present central velocity dispersions, masses, mass-to-light ratios (M/Ls ), and rotation strengths for 25 Galactic globular clusters (GCs). We derive radial velocities of 1951 stars in 12 GCs from single order spectra taken with Hectochelle on the MMT telescope. To this sample we add an analysis of available archival data of individual stars. For the full set of data we fit King models to derive consistent dynamical parameters for the clusters. We find good agreement between single-mass King models and the observed radial dispersion profiles. The large, uniform sample of dynamical masses we derive enables us to examine trends of M/L with cluster mass and metallicity. The overall values of M/L and the trends with mass and metallicity are consistent with existing measurements from a large sample of M31 clusters. This includes a clear trend of increasing M/L with cluster mass and lower than expected M/Ls for the metal-rich clusters. We find no clear trend of increasing rotation with increasing cluster metallicity suggested in previous work.

  4. Highlights from a Wide-field Photometric Survey of the Globular Cluster Populations of Giant Galaxies

    NASA Astrophysics Data System (ADS)

    Rhode, Katherine L.

    2014-01-01

    I will present recent results from a wide-field imaging survey of the globular cluster populations of a sample of giant galaxies, along with selected results from several spin-off projects made possible by the survey data. We use mosaic CCD cameras on the WIYN 3.5-m and Kitt Peak 4-m telescopes to image the globular cluster populations out to their full radial extent and select point-source globular cluster candidates in three filters (BVR or gri) to minimize contamination and enable analysis of the globular cluster color distributions. The ~35 galaxies observed to date for the survey have a range of morphological types (spiral, S0, elliptical), luminosities (M_V ~ -19 to -23), and environments (field, group, cluster) and each galaxy hosts anywhere from ~50 to several thousand globular clusters. I will summarize our findings regarding the total numbers,spatial distributions, and color (metallicity) distributions of the globular cluster populations of the target galaxies. I will also highlight results from several applications of the survey data, including an investigation of the possible link between supermassive black holes and globular cluster populations and follow-up spectroscopic studies that have yielded globular cluster metallicities, kinematics, and galaxy mass profiles for a subset of the galaxies so far. This work is supported by NSF FAculty Early Career Development (CAREER) award AST-0847109.

  5. The WAGGS project - I. The WiFeS Atlas of Galactic Globular cluster Spectra

    NASA Astrophysics Data System (ADS)

    Usher, Christopher; Pastorello, Nicola; Bellstedt, Sabine; Alabi, Adebusola; Cerulo, Pierluigi; Chevalier, Leonie; Fraser-McKelvie, Amelia; Penny, Samantha; Foster, Caroline; McDermid, Richard M.; Schiavon, Ricardo P.; Villaume, Alexa

    2017-07-01

    We present the WiFeS Atlas of Galactic Globular cluster Spectra, a library of integrated spectra of Milky Way and Local Group globular clusters. We used the WiFeS integral field spectrograph on the Australian National University 2.3 m telescope to observe the central regions of 64 Milky Way globular clusters and 22 globular clusters hosted by the Milky Way's low-mass satellite galaxies. The spectra have wider wavelength coverage (3300-9050 Å) and higher spectral resolution (R = 6800) than existing spectral libraries of Milky Way globular clusters. By including Large and Small Magellanic Cloud star clusters, we extend the coverage of parameter space of existing libraries towards young and intermediate ages. While testing stellar population synthesis models and analysis techniques is the main aim of this library, the observations may also further our understanding of the stellar populations of Local Group globular clusters and make possible the direct comparison of extragalactic globular cluster integrated light observations with well-understood globular clusters in the Milky Way. The integrated spectra are publicly available via the project website.

  6. The Counterparts of the Luminous, Bursting X-ray Sources in Globular Clusters-LTSA98

    NASA Technical Reports Server (NTRS)

    Anderson, Scott F.

    2003-01-01

    Under the fifth year of the LTSA, we have extended our HST and Chandra work to a number of additional globular clusters. The remarkable sensitivity and positional accuracy of the Chandra observations are enabling us to maximally exploit HST for UV/optical identifications for X-ray binaries in the cores of multiple globular clusters. The dozens of lower-luminosity X-ray sources in each globular cluster deeply examined thus far have moved us firmly into the era of studies which encompass populations of close; the large range of cluster properties we are studying have, for the first tine, established a firm empirical confirmation of the (long-suspected theoretically) high importance that close binaries play in the dynamical stability and evolution of globular clusters. The LTSA support has been a cornerstone of our success over the past 5 years in studies of globular cluster X-ray sources and their counterparts.

  7. Main Sequence Binary Fraction in Globular Cluster NGC 6397

    NASA Astrophysics Data System (ADS)

    Srinath, Srikar; Cool, A. M.; Anderson, J.

    2011-01-01

    We report preliminary results from a study of main-sequence binaries (MSBs) in the core-collapsed globular cluster NGC 6397 using the Hubble Space Telescope (HST) Advanced Camera for Surveys. We analyze images of the central regions of the cluster extending out to approximately one half-mass radius (rhm = 2.33') taken with the Wide Field Channel in the F435W and F625W filters. After removing non-members using proper motions, we construct a color-magnitude diagram (CMD) containing 15578 cluster stars. Model cluster CMDs indicate that in the range 16 < R < 22, MSBs with mass ratio (q=M2/M1) > 0.6 appear sufficiently far above and redward of the main sequence ridge line to be distinguishable from the single-star sequence. Out of 10835 stars in this magnitude range, we identify an initial set of 137 stars (with primary masses in the range 0.4-0.7 Msun) whose offset from the single-star sequence is statistically significant. A check of quality of fit to the PSF combined with close visual inspection of the images shows that 85 of these stars are well measured and unresolved and are thus good MSB candidates. The resulting upper limit on the fraction of MSBs with q > 0.6 and primaries in the range 0.4-0.7 Msun is 0.8%. We compare our measured fraction and the radial distribution of the MSB candidates to earlier findings based on HST/WFPC2 imaging and explore the significance of the results for the total binary population in NGC 6397. Keywords: binaries: general - globular clusters: individual(NGC 6397) - binary fraction - stars: main sequence binary

  8. Ultraviolet properties of hot stars in globular clusters

    SciTech Connect

    Altner, B.M.

    1988-01-01

    Most of the interesting and important stages of stellar evolution beyond the horizontal branch (HB) occur in the temperature realms best investigated by ultraviolet (UV) astronomy. In this dissertation the author studies the UV properties of hot HB and post-HB stars found in a sample of galactic globular clusters, based on spectra obtained with the International Ultraviolet Explorer (IUE). Using techniques developed specifically for the purpose, he separates the overlapping spectra of individual hot stars in the crowded central regions of the clusters. He determines the physical properties of the separated core sources by comparing them to model stellar atmospheres, Population I standards, faint blue halo stars and previously known UV-bright cluster stars, from which he attempts to better understand their evolutionary status. The majority of the more than one hundred spatially separated components turn out to be individual blue HB stars, but a few have properties similar to those of the more evolved supra-HB stars or post-asymptotic-giant-branch (post-AGB) stars, substantially increasing the number of UV-bright stars found in galactic globular clusters. Derived properties of the post-AGB stars imply, through the use of the Paczynski mass-luminosity relation, that these stars span a very narrow range in total core mass, with a mean value near 0.55 Mass of sun - somewhat smaller than that derived for central stars of planetary nebulae in the galactic disk. Several of the clusters observed to have luminous ultraviolet sources in their cores have also shown the presence of a central cusp in the visual.

  9. The globular cluster systems of NGC 3258 and NGC 3268 in the Antlia cluster

    NASA Astrophysics Data System (ADS)

    Dirsch, B.; Richtler, T.; Bassino, L. P.

    2003-09-01

    The Antlia galaxy cluster is the third nearest galaxy cluster after Virgo and Fornax. We used the wide-field MOSAIC camera of the 4-m CTIO telescope to search in the brightest cluster galaxies for globular cluster systems, which were detected in the two larger ellipticals - NGC 3258 and NGC 3268. These galaxies each contain several thousand clusters; NGC 3258 more than NGC 3268. The color distributions of the globular cluster systems are clearly bimodal. The peak colors agree with those of other ellipticals. The radial number density profiles of the globular cluster systems are indistinguishable for the two galaxies and no difference in the distribution of red and blue clusters - as observed in other elliptical galaxies - can be seen. The light profile of NGC 3268 appears to be similar to that of NGC 1399, the central galaxy of the Fornax cluster. NGC 3258 has a light profile which is steeper at large radii. Both galaxies exhibit color gradients, becoming bluer outwards. In NGC 3268, the color and morphology in the inner 3 arcsec indicate the presence of an inner dusty disk. The globular cluster systems closely trace the galaxy light in the studied radial regime. The elongation of the cluster systems of both galaxies is approximately aligned at large radii with the connecting axis of the two galaxies. We find specific frequencies within a radial range of 4 arcmin of SN=3.0+/-2.0 for NGC 3268 and SN=6.0+/-2.5 for NGC 3258. As a byproduct resulting from surveying our wide-field frames, we describe a strange absorption feature in the Antlia spiral galaxy NGC 3269, which we argue might be a tiny galactic dust cloud projected onto NGC 3269. Based on observations collected at the Cerro Tololo Inter-American Observatory (CTIO).

  10. THE FIRST CONFIRMED MICROLENS IN A GLOBULAR CLUSTER

    SciTech Connect

    Pietrukowicz, P.; Udalski, A.; Minniti, D.; Alonso-Garcia, J.; Jetzer, Ph.

    2012-01-10

    In 2000 July/August a microlensing event occurred at a distance of 2.'33 from the center of the globular cluster M22 (NGC 6656), observed against the dense stellar field of the Milky Way bulge. We have used the adaptive optics system NACO at the ESO Very Large Telescope to resolve the two objects that participated in the event: the lens and the source. The position of the objects measured in 2011 July is in agreement with the observed relative proper motion of M22 with respect to the background bulge stars. Based on the brightness of the microlens components we find that the source is a solar-type star located at a distance of 6.0 {+-} 1.5 kpc in the bulge, while the lens is a 0.18 {+-} 0.01 M{sub Sun} dwarf member of the globular cluster located at the known distance of 3.2 {+-} 0.2 kpc from the Sun.

  11. Globular clusters and the evolution of their multiple stellar populations

    NASA Astrophysics Data System (ADS)

    Chantereau, W.; Charbonnel, C.; Meynet, G.

    2017-03-01

    Our knowledge of the formation and early evolution of globular clusters (GCs) has been totally shaken with the discovery of the peculiar chemical properties of their long-lived host stars. Therefore, the interpretation of the observed Colour Magnitude Diagrams (CMD) and of the properties of the GC stellar populations requires the use of new stellar models computed with relevant chemical compositions. In this paper we use the grid of evolution models for low-mass stars computed by Chantereau et al. (2015) with the initial compositions of second-generation stars as predicted by the fast rotating massive stars scenario to build synthesis models of GCs. We discuss the implications of the assumed initial chemical distribution on 13 Gyr isochrones. We build population synthesis models to predict the fraction of stars born with various helium abundances in present day globular clusters (assuming an age of 13 Gyr). With the current assumptions, 61 % of stars on the main sequence are predicted to be born with a helium abundance in mass fraction, Yini, smaller than 0.3 and only 11 % have a Yini larger than 0.4. Along the horizontal branch, the fraction of stars with Yini inferior to 0.3 is similar to that obtained along the main sequence band (63 %), while the fraction of very He-enriched stars is significantly decreased (only 3 % with Yini larger than 0.38).

  12. The chemical evolution of globular clusters - II. Metals and fluorine

    NASA Astrophysics Data System (ADS)

    Sánchez-Blázquez, P.; Marcolini, A.; Gibson, B. K.; Karakas, A. I.; Pilkington, K.; Calura, F.

    2012-01-01

    In the first paper of this series, we proposed a new framework in which to model the chemical evolution of globular clusters. This model is predicated upon the assumption that clusters form within an interstellar medium enriched locally by the ejecta of a single Type Ia supernova and varying numbers of asymptotic giant branch stars, superimposed on an ambient medium pre-enriched by low-metallicity Type II supernovae. Paper I was concerned with the application of this model to the observed abundances of several reactive elements and so-called non-metals for three classical intermediate-metallicity clusters, with the hallmark of the work being the successful recovery of many of their well-known elemental and isotopic abundance anomalies. Here, we expand upon our initial analysis by (i) applying the model to a much broader range of metallicities (from the factor of 3 explored in Paper I, to now a factor of ˜50; i.e. essentially, the full range of Galactic globular cluster abundances; and (ii) incorporating a broader suite of chemical species, including a number of iron-peak isotopes, heavier α-elements and fluorine. While allowing for an appropriate fine-tuning of the model input parameters, most empirical globular cluster abundance trends are reproduced; our model would suggest the need for a higher production of calcium, silicon and copper in low-metallicity (or so-called 'prompt') Type Ia supernovae than predicted in current stellar models in order to reproduce the observed trends in NGC 6752, and a factor of 2 reduction in carbon production from asymptotic giant branch stars to explain the observed trends between carbon and nitrogen. Observations of heavy-element isotopes produced primarily by Type Ia supernovae, including those of titanium, iron and nickel, could support/refute unequivocally our proposed framework, although currently the feasibility of the proposed observations is well beyond current instrumental capabilities. Hydrodynamical simulations would

  13. CCD photometry of the globular cluster NGC 4147

    NASA Astrophysics Data System (ADS)

    Friel, Eileen D.; Heasley, J. N.; Christian, Carol A.

    1987-12-01

    The authors present results of CCD photometry in B and V for the globular cluster NGC 4147. The color-magnitude diagram reaches fainter than V = 22, some 3 magnitudes below the main-sequence turnoff. The morphology of the C-M diagram resembles that of a cluster of intermediate metallicity with a normal blue horizontal branch. Rough estimates of the integrated light from additional CCD data in B and I suggest, however, that the population revealed in the C-M diagram from the outer regions may not be representative of the population in the central regions of the cluster. Determination of the age of the cluster from fitting theoretical isochrones is difficult because of uncertainties in the distance modulus of the cluster. An age of 17 Gyr is implied. The revised Yale isochrones indicate an age of some 2 Gyr younger. If models with enhanced oxygen abundances are used, the ages deduced would also be 2 - 3 Gyr younger. Although determinations of the absolute age of NGC 4147 require knowledge of the absolute distance scale and choice of theoretical models, these alternative age estimates are consistent with those made for other clusters using the same models.

  14. Internal Rotation in the Globular Cluster M53

    NASA Astrophysics Data System (ADS)

    Boberg, Owen M.; Vesperini, Enrico; Friel, Eileen D.; Tiongco, Maria A.; Varri, Anna Lisa

    2017-06-01

    We present an analysis of the internal bulk rotation in the metal-poor globular cluster (GC) NGC 5024 (M53) using radial velocities (RVs) of individual cluster members. We use RV measurements from a previous abundance study of M53 done using the Hydra multi-object spectrograph on the WIYN 3.5 m telescope. The Hydra sample greatly increases the number of RVs available in the central regions of the cluster where the internal rotation is the strongest. The sample of cluster members is further increased through two previous kinematic studies of M53. The combined total sample contains 245 cluster members. With our sample, we are able to create a velocity dispersion profile of the cluster and derive a central velocity dispersion {σ }0=4.0+/- 0.3 {km} {{{s}}}-1; we find that M53 inner regions are characterized by a peak amplitude of rotation equal to 1.4+/- 0.1 {km} {{{s}}}-1 corresponding to a relatively high value of the ratio of the rotation speed to central velocity dispersion ({V}{rot}/{σ }0=0.35+/- 0.04). Our data also reveal a radial variation in the orientation of the projected rotation axis suggesting complex internal kinematics.

  15. Multivariate Analysis of the Globular Clusters in M87

    NASA Astrophysics Data System (ADS)

    Das, Sukanta; Chattopadhayay, Tanuka; Davoust, Emmanuel

    2015-11-01

    An objective classification of 147 globular clusters (GCs) in the inner region of the giant elliptical galaxy M87 is carried out with the help of two methods of multivariate analysis. First, independent component analysis (ICA) is used to determine a set of independent variables that are linear combinations of various observed parameters (mostly Lick indices) of the GCs. Next, K-means cluster analysis (CA) is applied on the independent components (ICs), to find the optimum number of homogeneous groups having an underlying structure. The properties of the four groups of GCs thus uncovered are used to explain the formation mechanism of the host galaxy. It is suggested that M87 formed in two successive phases. First a monolithic collapse, which gave rise to an inner group of metal-rich clusters with little systematic rotation and an outer group of metal-poor clusters in eccentric orbits. In a second phase, the galaxy accreted low-mass satellites in a dissipationless fashion, from the gas of which the two other groups of GCs formed. Evidence is given for a blue stellar population in the more metal rich clusters, which we interpret by Helium enrichment. Finally, it is found that the clusters of M87 differ in some of their chemical properties (NaD, TiO1, light-element abundances) from GCs in our Galaxy and M31.

  16. Globular cluster interstellar media: ionized and ejected by white dwarfs

    NASA Astrophysics Data System (ADS)

    McDonald, I.; Zijlstra, A. A.

    2015-01-01

    Ultraviolet radiation from white dwarfs can efficiently clear Galactic globular clusters (GCs) of their intracluster medium (ICM). This solves the problem of the missing ICM in clusters, which is otherwise expected to build up to easily observable quantities. To show this, we recreate the ionizing flux in 47 Tuc, following randomly generated stars through their asymptotic giant branch (AGB), post-AGB and white dwarf evolution. Each white dwarf can ionize all the material injected into the cluster by stellar winds for ˜3 Myr of its evolution: ˜40 such white dwarfs exist at any point. Every GC's ICM should be ionized. The neutral cloud in M15 should be caused by a temporary overdensity. A pressure-supported ICM will expand over the cluster's tidal radius, where it will be truncated, allowing Jeans escape. The modelled Jeans mass-loss rate approximates the total stellar mass-loss rate, allowing efficient clearing of ICM. Any cluster's ICM mass should equal the mass injected by its stars over the sound travel time between the cluster core and tidal radius. We predict ˜11.3 M⊙ of ICM within 47 Tuc, cleared over ˜4 Myr, compared to a dynamical time-scale of 4.3 Myr. We present a new mass hierarchy, discussing the transition between GCs dwarf galaxies.

  17. STRUCTURAL PARAMETERS FOR 10 HALO GLOBULAR CLUSTERS IN M33

    SciTech Connect

    Ma, Jun

    2015-05-15

    In this paper, we present the properties of 10 halo globular clusters (GCs) with luminosities L ≃ 5–7 × 10{sup 5} L{sub ⊙} in the Local Group galaxy M33 using images from the Hubble Space Telescope WFPC2 in the F555W and F814W bands. We obtained the ellipticities, position angles, and surface brightness profiles for each GC. In general, the ellipticities of the M33 sample clusters are similar to those of the M31 clusters. The structural and dynamical parameters are derived by fitting the profiles to three different models combined with mass-to-light ratios (M/L values) from population-synthesis models. The structural parameters include core radii, concentration, half-light radii, and central surface brightness. The dynamical parameters include the integrated cluster mass, integrated binding energy, central surface mass density, and predicted line of sight velocity dispersion at the cluster center. The velocity dispersions of the four clusters predicted here agree well with the observed dispersions by Larsen et al. The results here showed that the majority of the sample halo GCs are better fitted by both the King model and the Wilson model than the Sérsic model. In general, the properties of the clusters in M33, M31, and the Milky Way fall in the same regions of parameter spaces. The tight correlations of cluster properties indicate a “fundamental plane” for clusters, which reflects some universal physical conditions and processes operating at the epoch of cluster formation.

  18. A DOUBLE MAIN SEQUENCE IN THE GLOBULAR CLUSTER NGC 6397

    SciTech Connect

    Milone, A. P.; Aparicio, A.; Marino, A. F.; Piotto, G.; Bedin, L. R.; Anderson, J.; Cassisi, S.; Rich, R. M. E-mail: aparicio@iac.es E-mail: giampaolo.piotto@unipd.it E-mail: bedin@stsci.edu E-mail: rmr@astro.ucla.edu

    2012-01-20

    High-precision multi-band Hubble Space Telescope (HST) photometry reveals that the main sequence of the globular cluster NGC 6397 splits into two components, containing {approx}30% and {approx}70% of the stars. This double sequence is consistent with the idea that the cluster hosts two stellar populations: (1) a primordial population that has a composition similar to field stars, containing {approx}30% of the stars, and (2) a second generation with enhanced sodium and nitrogen, depleted carbon and oxygen, and a slightly enhanced helium abundance ({Delta}Y {approx} 0.01). We examine the color difference between the two sequences across a variety of color baselines and find that the second sequence is anomalously faint in m{sub F336W}. Theoretical isochrones indicate that this could be due to NH depletion.

  19. Soar adaptive optics observations of the globular cluster NGC 6496

    SciTech Connect

    Fraga, Luciano; Kunder, Andrea; Tokovinin, Andrei E-mail: lfraga@lna.br

    2013-06-01

    We present high-quality BVRI photometric data in the field of globular cluster NGC 6496 obtained with the SOAR Telescope Adaptive Module (SAM). Our observations were collected as part of the ongoing SAM commissioning. The distance modulus and cluster color excess as found from the red clump are (m – M) {sub V} = 15.71 ± 0.02 mag and E(V – I) = 0.28 ± 0.02 mag. An age of 10.5 ± 0.5 Gyr is determined from the difference in magnitude between the red clump and the subgiant branch. These parameters are in excellent agreement with the values derived from isochrone fitting. From the color-magnitude diagram we find a metallicity of [Fe/H] = –0.65 dex and hence support a disk classification for NGC 6496. The complete BVRI data set for NGC 6469 is made available in the electronic edition of the Journal.

  20. The Double Cooling Sequence of the Globular Cluster ω Centauri

    NASA Astrophysics Data System (ADS)

    García-Berro, E.; Sendra, L.; Torres, S.; Althaus, L. G.

    2017-03-01

    ω Centauri is a massive, old, globular cluster that has been extensively studied over the years because of its peculiar color-magnitude diagram. Specifically, the color-magnitude diagram of this cluster has evident signs of the existence of multiple populations, which are clearly seen in the morphologies of both the main sequence and of the degenerate sequence. Considerable theoretical efforts have been done so far to model the main sequence, which have led to discover several stellar populations. However, the degenerate sequence has not been hitherto modeled with sufficient detail. Here we present a population synthesis study of the white dwarf cooling sequence, and compare the properties of the modeled stellar populations with those derived from the analysis of the main-sequence number counts.

  1. Binary interactions and multiple stellar populations in globular clusters

    NASA Astrophysics Data System (ADS)

    Jiang, Dengkai

    2015-08-01

    Observations revealed the presence of multiple stellar populations in globular clusters (GCs) that exhibit wide abundance variations and multiple sequences in Hertzsprung-Russell diagram. We present a scenario for the formation of multiple stellar populations in GCs. In this scenario, initial GCs are single-generation clusters, and our model predicts that the abundance anomalous stars observed in GCs are the merged stars and the accretor stars produced by binary interactions, which are rapidly rotating stars at the moment of their formation. The stellar population with binaries can reproduce two important observational evidences of multiple stellar populations, the Na-O anticorrelation and the multiple sequences in HR diagram. This suggests that binary interactions may be a possible scenario for the formation of multiple stellar populations in GCs.

  2. Dynamical evolution and spatial mixing of multiple population globular clusters

    NASA Astrophysics Data System (ADS)

    Vesperini, Enrico; McMillan, Stephen L. W.; D'Antona, Francesca; D'Ercole, Annibale

    2013-03-01

    Numerous spectroscopic and photometric observational studies have provided strong evidence for the widespread presence of multiple stellar populations in globular clusters. In this paper, we study the long-term dynamical evolution of multiple population clusters, focusing on the evolution of the spatial distributions of the first- (FG) and second-generation (SG) stars. In previous studies, we have suggested that SG stars formed from the ejecta of FG AGB stars are expected initially to be concentrated in the cluster inner regions. Here, by means of N-body simulations, we explore the time-scales and the dynamics of the spatial mixing of the FG and the SG populations and their dependence on the SG initial concentration. Our simulations show that, as the evolution proceeds, the radial profile of the SG/FG number ratio, NSG/NFG, is characterized by three regions: (1) a flat inner part; (2) a declining part in which FG stars are increasingly dominant and (3) an outer region where the NSG/NFG profile flattens again (the NSG/NFG profile may rise slightly again in the outermost cluster regions). Until mixing is complete and the NSG/NFG profile is flat over the entire cluster, the radial variation of NSG/NFG implies that the fraction of SG stars determined by observations covering a limited range of radial distances is not, in general, equal to the SG global fraction, (NSG/NFG)glob. The distance at which NSG/NFG equals (NSG/NFG)glob is approximately between 1 and 2 cluster half-mass radii. The time-scale for complete mixing depends on the SG initial concentration, but in all cases complete mixing is expected only for clusters in advanced evolutionary phases, having lost at least 60-70 per cent of their mass due to two-body relaxation (in addition to the early FG loss due to the cluster expansion triggered by SNII ejecta and gas expulsion).The results of our simulations suggest that in many Galactic globular clusters the SG should still be more spatially concentrated than the

  3. Far-ultraviolet observation of the globular cluster NGC 6397

    NASA Astrophysics Data System (ADS)

    Dieball, A.; Rasekh, A.; Knigge, C.; Shara, M.; Zurek, D.

    2017-07-01

    We present an observational far-ultraviolet (FUV) and near-ultraviolet (NUV) study of the core region of the globular cluster (GC) NGC 6397. The observations were obtained with the Space Telescope Imaging Spectrograph (STIS, FUV) and the Wide Field Camera 3 (NUV) on board the Hubble Space Telescope. Here, we focus on the UV-bright stellar populations such as blue stragglers (BSs), white dwarfs (WDs) and cataclysmic variables (CVs). We present the first FUV - NUV colour-magnitude diagram (CMD) for this cluster. To support our classification of the stellar populations, we compare our FUV - NUV CMD with optical data from the ACS Survey of Galactic Globular Clusters. The FUV - NUV CMD indicates 16 sources located in the WD area, and 10 BSs within the 25 × 25 arcsec2 of the STIS FUV data. 18 Chandra X-ray sources are located within the FUV field of view. 13 of those have an NUV counterpart, of which 9 sources also have an FUV counterpart. Out of those, five sources are previously suggested CVs, and indeed, all five are located in the WD/CV region in our FUV - NUV CMD. Another CV has only an FUV but no NUV counterpart. We also detect an NUV (but no FUV) counterpart to the millisecond pulsar (MSP) located in the core of this cluster. The NUV light curves of the CVs and MSP show flickering behaviour typical of CVs. We found that the BSs and CVs are the most centrally concentrated populations. This might be an effect of mass segregation or it might indicate the preferred birth place of BSs and CVs via dynamical interactions in the dense core region of GCs. Horizontal branch stars are the least centrally concentrated population and absent in the innermost area of the core.

  4. Dynamical friction in multi-component evolving globular clusters

    SciTech Connect

    Alessandrini, Emiliano; Lanzoni, Barbara; Miocchi, Paolo; Ciotti, Luca; Ferraro, Francesco R.

    2014-11-10

    We use the Chandrasekhar formalism and direct N-body simulations to study the effect of dynamical friction on a test object only slightly more massive than the field stars, orbiting a spherically symmetric background of particles with a mass spectrum. The main goal is to verify whether the dynamical friction time (t {sub DF}) develops a non-monotonic radial dependence that could explain the bimodality of the blue straggler radial distributions observed in globular clusters. In these systems, in fact, relaxation effects lead to a mass and velocity radial segregation of the different mass components, so that mass-spectrum effects on t {sub DF} are expected to be dependent on radius. We find that in spite of the presence of different masses, t {sub DF} is always a monotonic function of radius, at all evolutionary times and independently of the initial concentration of the simulated cluster. This is because the radial dependence of t {sub DF} is largely dominated by the total mass density profile of the background stars (which is monotonically decreasing with radius). Hence, a progressive temporal erosion of the blue straggler star (BSS) population at larger and larger distances from the cluster center remains the simplest and the most likely explanation of the shape of the observed BSS radial distributions, as suggested in previous works. We also confirm the theoretical expectation that approximating a multi-mass globular cluster as made of (averaged) equal-mass stars can lead to significant overestimations of t {sub DF} within the half-mass radius.

  5. The Frequency of Lithium-Rich Giants in Globular Clusters

    NASA Astrophysics Data System (ADS)

    Kirby, Evan N.; Guhathakurta, Puragra; Zhang, Andrew J.; Hong, Jerry; Guo, Michelle; Guo, Rachel; Cohen, Judith G.; Cunha, Katia M. L.

    2016-01-01

    Although red giants destroy lithium, some giants are Li-rich. Intermediate-mass asymptotic giant branch (AGB) stars can generate Li through the Cameron-Fowler conveyor, but the existence of Li-rich, low-mass red giant branch (RGB) stars is puzzling. Globular clusters are the best sites to examine this phenomenon because it is straightforward to determine membership in the cluster and to identify the evolutionary state of each star. In 72 hours of Keck/DEIMOS exposures in 25 clusters, we found four Li-rich RGB and two Li-rich AGB stars. There were 1696 RGB and 125 AGB stars with measurements or upper limits consistent with normal abundances of Li. Hence, the frequency of Li-richness in globular clusters is (0.2 ± 0.1)% for the RGB, (1.6 ± 1.1)% for the AGB, and (0.3 ± 0.1)% for all giants. Because the Li-rich RGB stars are on the lower RGB, Li self-generation mechanisms proposed to occur at the luminosity function bump or He core flash cannot explain these four lower RGB stars. We propose the following origin for Li enrichment: (1) All luminous giants experience a brief phase of Li enrichment at the He core flash. (2) All post-RGB stars with binary companions on the lower RGB will engage in mass transfer. This scenario predicts that 0.1% of lower RGB stars will appear Li-rich due to mass transfer from a recently Li-enhanced companion. This frequency is at the lower end of our confidence interval.

  6. CN ANOMALIES IN THE HALO SYSTEM AND THE ORIGIN OF GLOBULAR CLUSTERS IN THE MILKY WAY

    SciTech Connect

    Carollo, Daniela; Martell, Sarah L.; Beers, Timothy C.; Freeman, Ken C. E-mail: smartell@aao.gov.au E-mail: kcf@mso.anu.edu.au

    2013-06-01

    We explore the kinematics and orbital properties of a sample of red giants in the halo system of the Milky Way that are thought to have formed in globular clusters based on their anomalously strong UV/blue CN bands. The orbital parameters of the CN-strong halo stars are compared to those of the inner- and outer-halo populations as described by Carollo et al., and to the orbital parameters of globular clusters with well-studied Galactic orbits. The CN-strong field stars and the globular clusters both exhibit kinematics and orbital properties similar to the inner-halo population, indicating that stripped or destroyed globular clusters could be a significant source of inner-halo field stars, and suggesting that both the CN-strong stars and the majority of globular clusters are primarily associated with this population.

  7. Chemical abundances in the old LMC globular cluster Hodge 11

    NASA Astrophysics Data System (ADS)

    Mateluna, R.; Geisler, D.; Villanova, S.; Carraro, G.; Grocholski, A.; Sarajedini, A.; Cole, A.; Smith, V.

    2012-12-01

    Context. The study of globular clusters is one of the most powerful ways to learn about a galaxy's chemical evolution and star formation history. They preserve a record of chemical abundances at the time of their formation and are relatively easy to age date. The most detailed knowledge of the chemistry of a star is given by high resolution spectroscopy, which provides accurate abundances for a wide variety of elements, yielding a wealth of information on the various processes involved in the cluster's chemical evolution. Aims: We studied red giant branch (RGB) stars in an old, metal-poor globular cluster of the Large Magellanic Cloud (LMC), Hodge 11 (H11), in order to measure as many elements as possible. The goal is to compare its chemical trends to those in the Milky Way halo and dwarf spheroidal galaxies in order to help understand the formation history of the LMC and our own Galaxy. Methods: We have obtained high resolution VLT/FLAMES spectra of eight RGB stars in H11. The spectral range allowed us to measure a variety of elements, including Fe, Mg, Ca, Ti, Si, Na, O, Ni, Cr, Sc, Mn, Co, Zn, Ba, La, Eu and Y. Results: We derived a mean [Fe/H] = -2.00 ± 0.04, in the middle of previous determinations. We found low [α/Fe] abundances for our targets, more comparable to values found in dwarf spheroidal galaxies than in the Galactic halo, suggesting that if H11 is representative of its ancient populations then the LMC does not represent a good halo building block. Our [Ca/Fe] value is about 0.3 dex less than that of halo stars used to calibrate the Ca IR triplet technique for deriving metallicity. A hint of a Na abundance spread is observed. Its stars lie at the extreme high O, low Na end of the Na:O anti-correlation displayed by Galactic and LMC globular clusters. Based on observations collected at the European Organisation for Astronomical Research in the Southern Hemisphere, Chile (proposal ID 082.B-0458).Table 4 is only available in electronic form at http://www.aanda.org

  8. Radial velocities in the globular cluster ω Centauri

    NASA Astrophysics Data System (ADS)

    Reijns, R. A.; Seitzer, P.; Arnold, R.; Freeman, K. C.; Ingerson, T.; van den Bosch, R. C. E.; van de Ven, G.; de Zeeuw, P. T.

    2006-01-01

    We have used the ARGUS multi-object spectrometer at the CTIO 4 m Blanco telescope to obtain 2756 radial velocity measurements for 1966 individual stars in the globular cluster ω Centauri brighter than blue photographic magnitude of about 16.5. Of these, 1589 stars are cluster members. A comparison with two independent radial velocity studies, carried out by Suntzeff & Kraft and by Mayor et al., demonstrates that the median error of our measurements is below 2 km s-1 for the stars brighter than B-magnitude 15, which constitute the bulk of the sample. The observed velocity dispersion decreases from about 15 km s-1 in the inner few arcmin to about 6 km s-1 at a radius of 25'. The cluster shows significant rotation, with a maximum amplitude of about 6 km s-1 in the radial zone between 6' and 10'. In a companion paper by van de Ven et al., we correct these radial velocities for the perspective rotation caused by the space motion of the cluster, and combine them with the internal proper motions of nearly 8000 cluster members measured by van Leeuwen et al., to construct a detailed dynamical model of ω Centauri and to measure its distance.

  9. The CCD photometry of the globular cluster Palomar 1.

    NASA Astrophysics Data System (ADS)

    Borissova, J.; Spassova, N.

    1995-04-01

    A CCD photometry of the halo cluster Palomar 1 is presented in the Thuan-Gunn photometric system. The principal sequences of the color-magnitude diagrams are delineated in different spectral bands. The color-magnitude diagrams of the cluster show a well defined red horizontal branch, a subgiant branch and a main-sequence down to about two magnitudes below the main sequence turnoff. The giant branch is absent and the brightest stars are the horizontal branch stars. The age of the cluster determined by comparison with the isochrones of Bell & Vanden Berg (1987) is consistent with an age in the interval 12-14Gyr. A distance modulus of (m-M)_g0_=15.38+/-0.15 magnitude and E(g-r)=0.16 has been derived. An estimate of the cluster structural parameters such as core radius and concentration parameter gives r_c_=1.5pc and c=1.46. A mass estimate of 1.1 10^3^Msun_ and a mass-to-light ratio of 1.79 have been obtained using King's (1966) method. The morphology of color-magnitude diagrams allows Pal 1 to be interpreted as probably a globular cluster rather than an old open one.

  10. Discovery of Remote Globular Cluster Satellites of M87

    NASA Astrophysics Data System (ADS)

    Sparkman, Lea; Guo, Rachel; Toloba, Elisa; Guhathakurta, Puragra; Peng, Eric W.; Ferrarese, Laura; Cote, Patrick; NGVS Collaboration

    2016-01-01

    We present the discovery of several tens of globular clusters (GCs) in the outer regions of the giant elliptical M87, the brightest galaxy in the Virgo Cluster. These M87 GC satellites were discovered in the course of Keck/DEIMOS spectroscopic follow up of GC candidates that were identified in the Next Generation Virgo cluster Survey (NGVS). Specifically, the primary targets of this Keck spectroscopic campaign were GC satellites of early-type dwarf (dE) galaxies. However, we found that our sample contained a subset of GCs for which M87 is the most likely host. This subset is consistent with having an r^-1 power-law surface density distribution and a radial velocity distribution both centered on M87. The remote M87 GC satellites span the radial range 140 to 900 kpc, out to about a third of the Virgo Cluster's virial radius (for comparison, M87's effective radius is only 8 kpc). These M87 GC satellites are probably former satellites of other Virgo Cluster galaxies that have subsequently been cannibalized by M87.This research was supported by the National Science Foundation and the UC Santa Cruz Science Internship Program.

  11. 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

  12. WFPC2 Observations of the Sagittarius Globular Cluster Arp 2

    NASA Astrophysics Data System (ADS)

    Dueñas, E. N.; Mighell, K. J.

    2002-12-01

    We present our preliminary analysis of archival Hubble Space Telescope WFPC2 observations in the F555W (V) and F814W (I) filters of the metal-poor globular cluster Arp 2 in the nearby Sagittarius dwarf spheroidal galaxy. The deep V vs. (V-I) color-magnitude diagram reaches 3.5 magnitudes below the main sequence turnoff with a signal-to-noise ratio of 10 or greater in both filters; it also features a well-defined subgiant branch as well as a few blue stragglers. The upper red giant branch is not analyzed due to photometric saturation. Most previous studies of Arp 2 analyzed the ground-based BV observations of Buonanno et al. (1995) or the ground-based VI observations of Sarajedini & Layden (1997). Buonanno et al. found that Arp 2 is a metal-poor, intermediate age cluster, while Layden & Sarajedini (2000) determined that it is coeval with other ancient Galactic globular clusters, e.g. 13.1 +/- 0.9 Gyr. We have analyzed our space-based observations with the Yonsei-Yale (Y2) isochrones of Yi et al. (2001) and present evidence that confirms the Layden & Sarajedini's ancient-age hypothesis for Arp 2. Dueñas was supported, in part, by awards to South Carolina State University from NASA/MU-SPIN (NCC 5-534) and NASA/OSS (NAG 5-10145), and the NOAO/KPNO REU Program, funded by the National Science Foundation. Mighell was supported by a grant from the National Aeronautics and Space Administration (NASA), S-67046-F, awarded by the Long-Term Space Astrophysics program of NASA's Office of Space Science.

  13. Globular Cluster Star Classification: Application to M13

    NASA Astrophysics Data System (ADS)

    Caimmi, R.

    2013-06-01

    Starting from recent determination of Fe, O, Na abundances on a restricted sample (N=67) of halo and thick disk stars, a natural and well motivated selection criterion is defined for the classification globular cluster stars. An application is performed to M13 using a sample (N=113) for which Fe, O, Na abundances have been recently inferred from observations. A comparison is made between the current and earlier M13 star classifications. Both O and Na empirical differential abundance distributions are determined for each class and for the whole sample (with the addition of Fe in the last case) and compared with their theoretical counterparts due to cosmic scatter obeying a Gaussian distribution whose parameters are inferred from related subsamples. The occurrence of an agreement between the empirical and theoretical distributions is interpreted as absence of significant chemical evolution and vice versa. The procedure is repeated with regard to four additional classes depending on whether oxygen and sodium abundance is above (stage CE) or below (stage AF) a selected threshold. Both O and Na empirical differential abundance distributions, related to the whole sample, exhibit a linear fit for the AF and CE stage. Within the errors, the oxygen slope for the CE stage is equal and of opposite sign with respect to the sodium slope for AF stage, while the contrary holds when dealing with the oxygen slope for the AF stage with respect to the sodium slope for the CE stage. In the light of simple models of chemical evolution applied to M13, oxygen depletion appears to be mainly turned into sodium enrichment for [O/H]≥-1.35 and [Na/H]≤-1.45, while one or more largely preferred channels occur for [O/H]<-1.35 and [Na/H]>-1.45. In addition, the primordial to the current M13 mass ratio can be inferred from the true sodium yield in units of the sodium solar abundance. Though the above results are mainly qualitative due to large (∓.5 dex) uncertainties in abundance

  14. The Sound Parameter Effect in Metal-Rich Globular Clusters

    NASA Technical Reports Server (NTRS)

    Hall, D. K

    1998-01-01

    Recent Hubble Space Telescope observations have found that the horizontal branches (HBs) in the metal-rich globular clusters NGC 6388 and NGC 6441 slope upward with decreasing B - V. Such a slope is not predicted by canonical HB models and cannot be produced by either a greater cluster age or enhanced mass loss along the red giant branch (RGB). The peculiar HB morphology in these clusters may provide an important clue for understanding the second-parameter effect. We have carried out extensive evolutionary calculations and numerical simulations in order to explore three noncanonical scenarios for explaining the sloped HBs in NGC 6388 and NGC 6441: (1) a high cluster helium abundance scenario, in which the HB evolution is characterized by long blue loops; (2) a rotation scenario, in which internal rotation during the RGB phase increases the HB core mass; and (3) a helium-mixing scenario, in which deep mixing on the RGB enhances the envelope helium abundance. All of these scenarios predict sloped HBs with anomalously bright RR Lyrae variables. We compare this prediction with the properties of the two known RR Lyrae variables in NGC 6388. Additional observational tests of these scenarios are suggested.

  15. Effect of dynamical interactions on integrated properties of globular clusters

    NASA Astrophysics Data System (ADS)

    Zhuang, Yulong; Zhang, Fenghui; Anders, Peter; Ruan, Zhifeng; Cheng, Liantao; Kang, Xiaoyu

    2015-02-01

    Globular clusters (GCs) are generally treated as natural validators of simple stellar population (SSP) models. However, there are still some differences between real GCs and SSPs. In this work, we use a direct N-body simulation code NBODY6 to study the influences of dynamical interactions, metallicity and primordial binaries on Milky Way GCs' integrated properties. Our models start with N = 100 000 stars, covering a metallicity range Z = 0.0001 ˜ 0.02, a subset of our models contain primordial binaries, resulting in a binary fraction as currently observed at a model age of GCs. Stellar evolution and external tidal field representative for an average Milky Way GC are taken into consideration. The integrated colours and Lick indices are calculated using BaSeL and Bluered stellar spectral libraries separately. By including dynamical interactions, our model clusters show integrated features (i.e. colours up to 0.01 mag bluer, Hβ up to 0.1 Å greater and [MgFe]' 0.05 Å smaller) making the clusters appear slightly younger than the model clusters without dynamical interactions. This effect is caused mainly by the preferential loss of low-mass stars which have a stronger contribution to redder passbands as well as different spectral features compared to higher mass stars. In addition, this effect is larger at lower metallicities. On the contrary, the incorporation of primordial binaries reduces this effect.

  16. The gamma-ray pulsar population of globular clusters: implications for the GeV excess

    NASA Astrophysics Data System (ADS)

    Hooper, Dan; Linden, Tim

    2016-08-01

    It has been suggested that the GeV excess, observed from the region surrounding the Galactic Center, might originate from a population of millisecond pulsars that formed in globular clusters. With this in mind, we employ the publicly available Fermi data to study the gamma-ray emission from 157 globular clusters, identifying a statistically significant signal from 25 of these sources (ten of which are not found in existing gamma-ray catalogs). We combine these observations with the predicted pulsar formation rate based on the stellar encounter rate of each globular cluster to constrain the gamma-ray luminosity function of millisecond pulsars in the Milky Way's globular cluster system. We find that this pulsar population exhibits a luminosity function that is quite similar to those millisecond pulsars observed in the field of the Milky Way (i.e. the thick disk). After pulsars are expelled from a globular cluster, however, they continue to lose rotational kinetic energy and become less luminous, causing their luminosity function to depart from the steady-state distribution. Using this luminosity function and a model for the globular cluster disruption rate, we show that millisecond pulsars born in globular clusters can account for only a few percent or less of the observed GeV excess. Among other challenges, scenarios in which the entire GeV excess is generated from such pulsars are in conflict with the observed mass of the Milky Way's Central Stellar Cluster.

  17. The gamma-ray pulsar population of globular clusters: Implications for the GeV excess

    DOE PAGES

    Hooper, Dan; Linden, Tim

    2016-08-09

    In this study, it has been suggested that the GeV excess, observed from the region surrounding the Galactic Center, might originate from a population of millisecond pulsars that formed in globular clusters. With this in mind, we employ the publicly available Fermi data to study the gamma-ray emission from 157 globular clusters, identifying a statistically significant signal from 25 of these sources (ten of which are not found in existing gamma-ray catalogs). We combine these observations with the predicted pulsar formation rate based on the stellar encounter rate of each globular cluster to constrain the gamma-ray luminosity function of millisecondmore » pulsars in the Milky Way's globular cluster system. We find that this pulsar population exhibits a luminosity function that is quite similar to those millisecond pulsars observed in the field of the Milky Way (i.e. the thick disk). After pulsars are expelled from a globular cluster, however, they continue to lose rotational kinetic energy and become less luminous, causing their luminosity function to depart from the steady-state distribution. Using this luminosity function and a model for the globular cluster disruption rate, we show that millisecond pulsars born in globular clusters can account for only a few percent or less of the observed GeV excess. Among other challenges, scenarios in which the entire GeV excess is generated from such pulsars are in conflict with the observed mass of the Milky Way's Central Stellar Cluster.« less

  18. EVIDENCE FOR AN ACCRETION ORIGIN FOR THE OUTER HALO GLOBULAR CLUSTER SYSTEM OF M31

    SciTech Connect

    Mackey, A. D.; Huxor, A. P.; Ferguson, A. M. N.; Irwin, M. J.; Chapman, S. C.; Tanvir, N. R.; McConnachie, A. W.; Ibata, R. A.; Lewis, G. F.

    2010-07-01

    We use a sample of newly discovered globular clusters from the Pan-Andromeda Archaeological Survey (PAndAS) in combination with previously cataloged objects to map the spatial distribution of globular clusters in the M31 halo. At projected radii beyond {approx}30 kpc, where large coherent stellar streams are readily distinguished in the field, there is a striking correlation between these features and the positions of the globular clusters. Adopting a simple Monte Carlo approach, we test the significance of this association by computing the probability that it could be due to the chance alignment of globular clusters smoothly distributed in the M31 halo. We find that the likelihood of this possibility is low, below 1%, and conclude that the observed spatial coincidence between globular clusters and multiple tidal debris streams in the outer halo of M31 reflects a genuine physical association. Our results imply that the majority of the remote globular cluster system of M31 has been assembled as a consequence of the accretion of cluster-bearing satellite galaxies. This constitutes the most direct evidence to date that the outer halo globular cluster populations in some galaxies are largely accreted.

  19. The gamma-ray pulsar population of globular clusters: Implications for the GeV excess

    SciTech Connect

    Hooper, Dan; Linden, Tim

    2016-08-09

    In this study, it has been suggested that the GeV excess, observed from the region surrounding the Galactic Center, might originate from a population of millisecond pulsars that formed in globular clusters. With this in mind, we employ the publicly available Fermi data to study the gamma-ray emission from 157 globular clusters, identifying a statistically significant signal from 25 of these sources (ten of which are not found in existing gamma-ray catalogs). We combine these observations with the predicted pulsar formation rate based on the stellar encounter rate of each globular cluster to constrain the gamma-ray luminosity function of millisecond pulsars in the Milky Way's globular cluster system. We find that this pulsar population exhibits a luminosity function that is quite similar to those millisecond pulsars observed in the field of the Milky Way (i.e. the thick disk). After pulsars are expelled from a globular cluster, however, they continue to lose rotational kinetic energy and become less luminous, causing their luminosity function to depart from the steady-state distribution. Using this luminosity function and a model for the globular cluster disruption rate, we show that millisecond pulsars born in globular clusters can account for only a few percent or less of the observed GeV excess. Among other challenges, scenarios in which the entire GeV excess is generated from such pulsars are in conflict with the observed mass of the Milky Way's Central Stellar Cluster.

  20. The gamma-ray pulsar population of globular clusters: Implications for the GeV excess

    SciTech Connect

    Hooper, Dan; Linden, Tim

    2016-08-09

    In this study, it has been suggested that the GeV excess, observed from the region surrounding the Galactic Center, might originate from a population of millisecond pulsars that formed in globular clusters. With this in mind, we employ the publicly available Fermi data to study the gamma-ray emission from 157 globular clusters, identifying a statistically significant signal from 25 of these sources (ten of which are not found in existing gamma-ray catalogs). We combine these observations with the predicted pulsar formation rate based on the stellar encounter rate of each globular cluster to constrain the gamma-ray luminosity function of millisecond pulsars in the Milky Way's globular cluster system. We find that this pulsar population exhibits a luminosity function that is quite similar to those millisecond pulsars observed in the field of the Milky Way (i.e. the thick disk). After pulsars are expelled from a globular cluster, however, they continue to lose rotational kinetic energy and become less luminous, causing their luminosity function to depart from the steady-state distribution. Using this luminosity function and a model for the globular cluster disruption rate, we show that millisecond pulsars born in globular clusters can account for only a few percent or less of the observed GeV excess. Among other challenges, scenarios in which the entire GeV excess is generated from such pulsars are in conflict with the observed mass of the Milky Way's Central Stellar Cluster.

  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. Long-Term Timing of Globular Cluster Pulsars

    NASA Astrophysics Data System (ADS)

    Roi Smith, Sergio; Lynch, Ryan S.

    2017-01-01

    Pulsar timing is a powerful astrophysical tool that allows us to study both pulsars and their environment. Timing models provide information about the pulsar itself, including mass, position, and orbital parameters for pulsars in binary systems. Timing models also provide information about the pulsar’s neighborhood and about the interstellar medium (ISM) between the pulsar and the Earth. We present the results of timing two millisecond globular cluster pulsars over five years, as well as steps involved in preparing the data for use in the timing model. Data was obtained using the Robert C. Byrd Green Bank Telescope (GBT) observing at 1.5 GHz between 2011 and 2015. Here, a description of the data processing procedure is given, and timing results including dispersion measure and higher order rotational period derivatives are discussed.

  3. Faint Object Camera observations of a globular cluster nova field

    NASA Technical Reports Server (NTRS)

    Margon, Bruce; Anderson, Scott F.; Downes, Ronald A.; Bohlin, Ralph C.; Jakobsen, Peter

    1991-01-01

    The Faint Object Camera onboard Hubble Space Telescope has obtained U and B images of the field of Nova Ophiuchi 1938 in the globular cluster M14 (NGC 6402). The candidate for the quiescent nova suggested by Shara et al. (1986) is clearly resolved into at least six separate images, probably all stellar, in a region of 0.5 arcsec. Although two of these objects are intriguing as they are somewhat ultraviolet, the actual nova counterpart remains ambiguous, as none of the images in the field has a marked UV excess. Many stars within the 1.4 arcsec (2 sigma) uncertainty of the nova outburst position are viable counterparts if only astrometric criteria are used for selection. The 11 x 11 arcsec frames easily resolve several hundred stars in modest exposures, implying that HST even in its current optical configuration will be unique for studies of very crowded fields at moderate (B = 22) limiting magnitudes.

  4. DO INTERMEDIATE-MASS BLACK HOLES EXIST IN GLOBULAR CLUSTERS?

    SciTech Connect

    Sun, Mou-Yuan; Jin, Ya-Ling; Gu, Wei-Min; Liu, Tong; Lin, Da-Bin; Lu, Ju-Fu

    2013-10-20

    The existence of intermediate-mass black holes (IMBHs) in globular clusters (GCs) remains a crucial problem. Searching for IMBHs in GCs reveals a discrepancy between radio observations and dynamical modelings: the upper mass limits constrained by radio observations are systematically lower than that of dynamical modelings. One possibility for such a discrepancy is that, as we suggest in this work, there exist outflows in accretion flows. Our results indicate that, for most sources, current radio observations cannot rule out the possibility that IMBHs may exist in GCs. In addition, we adopt an M-dot -L{sub R} relation to revisit this issue, which confirms the results obtained by the fundamental plane relation.

  5. Decaying globular cluster systems and galactic nuclear activity

    NASA Astrophysics Data System (ADS)

    Capuzzo-Dolcetta, R.

    Globular cluster are systems that evolve dissipatively in non symmetric galactic potentials, losing energy and angular momentum. As a consequence, the GCS radial profile in a galaxy evolves significantly, so to differ from the one of the collisionless stellar bulge phase: this can explain the observations, which indicate how the GCS distribution in galaxies is usually more extended than the underlining stellar distribution. Moreover, the GCS orbital decay implies that a significant quantity of mass is carried toward the mother galaxy's central galactic region in a time scale short compared to the Hubble time. We show that this mass can accrete a galactic nucleus and fuel its activity in early stages of galactic life.

  6. SHRINKING THE BRANEWORLD: BLACK HOLE IN A GLOBULAR CLUSTER

    SciTech Connect

    Gnedin, Oleg Y.; Maccarone, Thomas J.; Psaltis, Dimitrios; Zepf, Stephen E. E-mail: tjm@astro.soton.ac.u E-mail: zepf@pa.msu.ed

    2009-11-10

    Large extra dimensions have been proposed as a possible solution to the hierarchy problem in physics. In one of the suggested models, the RS2 braneworld model, black holes may evaporate by Hawking radiation faster than in general relativity, on a timescale that depends on the black hole mass and on the asymptotic radius of curvature of the extra dimensions. Thus the size of the extra dimensions can be constrained by astrophysical observations. Here we point out that the black hole, recently discovered in an extragalactic globular cluster, places the strongest upper limit on the size of the extra dimensions in the RS2 model, L approx< 0.003 mm. This black hole has the virtues of old age and relatively small mass. The derived upper limit is within an order of magnitude of the absolute limit afforded by astrophysical observations of black holes.

  7. FAST ROTATING BLUE STRAGGLERS IN THE GLOBULAR CLUSTER M4

    SciTech Connect

    Lovisi, L.; Mucciarelli, A.; Ferraro, F. R.; Lanzoni, B.; Dalessandro, E.; Lucatello, S.; Gratton, R.; Beccari, G.; Rood, R. T.; Sills, A.; Fusi Pecci, F.; Piotto, G.

    2010-08-20

    We have used high-resolution spectra obtained with the spectrograph FLAMES at the European Southern Observatory Very Large Telescope to determine the kinematical properties and the abundance patterns of 20 blue straggler stars (BSSs) in the globular cluster (GC) M4. We found that {approx}40% of the measured BSSs are fast rotators (with rotational velocities >50 km s{sup -1}). This is the largest frequency of rapidly rotating BSSs ever detected in a GC. In addition, at odds with what has been found in 47 Tucanae, no evidence of carbon and/or oxygen depletion has been revealed in the sample of 11 BSSs for which we were able to measure the abundances. This could be due to either low statistics, or a different BSS formation process acting in M4.

  8. Accretion onto Protoplanetary Discs: Implications for Globular Cluster Evolution

    NASA Astrophysics Data System (ADS)

    Wijnen, T. P. G.; Pols, O. R.; Pelupessy, F. I.; Zwart, S. Portegies

    2017-03-01

    In the past decade, observational evidence that Globular Clusters (GCs) harbour multiple stellar populations has grown steadily. These observations are hard to reconcile with the classical picture of star formation in GCs, which approximates them as a single generation of stars. Bastian et al. recently suggested an evolutionary scenario in which a second, chemically distinct, population is formed by the accretion of chemically enriched material onto the protoplanetary disc of low-mass stars in the initial GC population. Using assumptions that represent the (dynamical) conditions in a typical GC, we investigate whether a low-mass star surrounded by a protoplanetary disc can accrete sufficient enriched material to account for the observed abundances in `second generation' stars. We compare the outcome of two different smoothed particle hydrodynamics codes and focus on the lifetime and stability of the disc and on the gas accretion rate onto both the star and the disc.

  9. Faint Object Camera observations of a globular cluster nova field

    NASA Technical Reports Server (NTRS)

    Margon, Bruce; Anderson, Scott F.; Downes, Ronald A.; Bohlin, Ralph C.; Jakobsen, Peter

    1991-01-01

    The Faint Object Camera onboard Hubble Space Telescope has obtained U and B images of the field of Nova Ophiuchi 1938 in the globular cluster M14 (NGC 6402). The candidate for the quiescent nova suggested by Shara et al. (1986) is clearly resolved into at least six separate images, probably all stellar, in a region of 0.5 arcsec. Although two of these objects are intriguing as they are somewhat ultraviolet, the actual nova counterpart remains ambiguous, as none of the images in the field has a marked UV excess. Many stars within the 1.4 arcsec (2 sigma) uncertainty of the nova outburst position are viable counterparts if only astrometric criteria are used for selection. The 11 x 11 arcsec frames easily resolve several hundred stars in modest exposures, implying that HST even in its current optical configuration will be unique for studies of very crowded fields at moderate (B = 22) limiting magnitudes.

  10. The state of globular clusters at birth - II. Primordial binaries

    NASA Astrophysics Data System (ADS)

    Leigh, Nathan W. C.; Giersz, Mirek; Marks, Michael; Webb, Jeremy J.; Hypki, Arkadiusz; Heinke, Craig O.; Kroupa, Pavel; Sills, Alison

    2015-01-01

    In this paper, we constrain the properties of primordial binary populations in Galactic globular clusters. Using the MOCCA Monte Carlo code for cluster evolution, our simulations cover three decades in present-day total cluster mass. Our results are compared to the observations of Milone et al. using the photometric binary populations as proxies for the true underlying distributions, in order to test the hypothesis that the data are consistent with a universal initial binary fraction near unity and the binary orbital parameter distributions of Kroupa. With the exception of a few possible outliers, we find that the data are to first-order consistent with the universality hypothesis. Specifically, the present-day binary fractions inside the half-mass radius can be reproduced assuming either high initial binary fractions near unity with a dominant soft binary component as in the Kroupa distribution combined with high initial densities (104-106 M⊙ pc-3), or low initial binary fractions (˜5-10 per cent) with a dominant hard binary component combined with moderate initial densities near their present-day values (102-103 M⊙ pc-3). This apparent degeneracy can potentially be broken using the binary fractions outside the half-mass radius - only high initial binary fractions with a significant soft component combined with high initial densities can reproduce the observed anticorrelation between the binary fractions outside the half-mass radius and the total cluster mass. We further illustrate using the simulated present-day binary orbital parameter distributions and the technique first introduced in Leigh et al. that the relative fractions of hard and soft binaries can be used to further constrain both the initial cluster density and the initial mass-density relation. Our results favour an initial mass-density relation of the form r_h ∝ M_clus^{α } with α < 1/3, corresponding to an initial correlation between cluster mass and density.

  11. Where are the Dozens of Predicted Cataclysmic Variables in Globular Clusters?

    NASA Astrophysics Data System (ADS)

    Shara, Michael

    1996-07-01

    WFPC2 imaging of globular cluster cores provides us with a unique opportunity to detect erupting cataclysmic variables {CVs} because they should be relatively common in the core. Two body tidal capture theory predicts that all binary systems should be relatively common in globular clusters, up to several orders of magnitude greater in relative number than in the Galactic field. Among the most common binaries should be CVs because of the high presumed abundance of white dwarfs in globular cores. However, only a handful of confirmed CVs have been discovered in globular clusters to date. This paucity brings into question the dynamical theories which predict great numbers of CVs. We propose to image the cores of two globular clusters with WFPC2 at five epochs to detect outbursting CVs - dwarf novae {DN}. We also propose to retrieve from the archive globular cluster WFPC2 data, cycles 4 & 5, that were taken over multiple epochs to search for erupting DN. At any given time 15 to find 30 two epochs. Clusters for which we have three or more epochs should yield > 50 DN exist in the cores of globular clusters will either support present dynamical theories or strongly constrain new theories that can adequately explain these results.

  12. X-ray illumination of globular cluster puzzles. [globular cluster X ray sources as clues to Milky Way Galaxy age and evolution

    NASA Technical Reports Server (NTRS)

    Lightman, A. P.; Grindlay, J. E.

    1982-01-01

    Globular clusters are thought to be among the oldest objects in the Galaxy, and provide, in this connection, important clues for determining the age and process of formation of the Galaxy. The present investigation is concerned with puzzles relating to the X-ray emission of globular clusters, taking into account questions regarding the location of X-ray emitting clusters (XEGC) unusually near the galactic plane and/or galactic center. An adopted model is discussed for the nature, formation, and lifetime of X-ray sources in globular clusters. An analysis of the available data is conducted in connection with a search for correlations between binary formation time scales, central relaxation times, galactic locations, and X-ray emission. The positive correlation found between distance from galactic center and two-body binary formation time for globular clusters, explanations for this correlation, and the hypothesis that X-ray sources in globular clusters require binary star systems provide a possible explanation of the considered puzzles.

  13. X-ray illumination of globular cluster puzzles. [globular cluster X ray sources as clues to Milky Way Galaxy age and evolution

    NASA Technical Reports Server (NTRS)

    Lightman, A. P.; Grindlay, J. E.

    1982-01-01

    Globular clusters are thought to be among the oldest objects in the Galaxy, and provide, in this connection, important clues for determining the age and process of formation of the Galaxy. The present investigation is concerned with puzzles relating to the X-ray emission of globular clusters, taking into account questions regarding the location of X-ray emitting clusters (XEGC) unusually near the galactic plane and/or galactic center. An adopted model is discussed for the nature, formation, and lifetime of X-ray sources in globular clusters. An analysis of the available data is conducted in connection with a search for correlations between binary formation time scales, central relaxation times, galactic locations, and X-ray emission. The positive correlation found between distance from galactic center and two-body binary formation time for globular clusters, explanations for this correlation, and the hypothesis that X-ray sources in globular clusters require binary star systems provide a possible explanation of the considered puzzles.

  14. The Chemical Evolution of Heavy Elements in Globular Clusters

    NASA Astrophysics Data System (ADS)

    Shingles, Luke J.; Karakas, Amanda I.; Hirschi, Raphael

    2014-01-01

    We present preliminary results from a chemical evolution model that tracks the composition of heavy elements beyond iron in a globular cluster. The heavy elements can be used as tracers of the nucleosynthetic events that defined the formation and evolution of star clusters in the early Universe. In particular, the chemical evolution model focuses on the hypothesis that rapidly-rotating massive stars produced the heavy elements via the slow neutron-capture process and seeded the proto-cluster while the stars we see today were still forming. We compare our model with heavy element abundances in M4 and M5, and M22. Our results are strongly dependent on the highly uncertain rate of the 17O(α,γ)21Ne reaction, which determines the strength of 16O as a neutron poison. We find that the [Pb/Ba] ratio is too low to match the empirical value, which might suggest that a contribution from AGB stars is required.

  15. Dynamical evolution of rotating globular clusters with embedded black holes

    NASA Astrophysics Data System (ADS)

    Fiestas, José

    2006-02-01

    In this dissertation evolution of self-gravitating dense stellar systems (e.g. globular clusters, galactic nuclei) with embedded black holes is investigated, motivated by observational evidences of the existence of central dark objects in these systems. The interaction between the stellar and black hole component is followed in a way, different from most other investigations in this field, as flattening of the system due to differential rotation is allowed. The axisymmetric system is modelled using 2-dimensional, in energy and z-component of angular momentum, Fokker Planck numerical methods. The interplay between velocity diffusion due to relaxation and black hole star accretion is followed together with cluster rotation. The results show how angular momentum transport and star accretion support the development of central rotation in relaxation time scales. Gravogyro and gravothermal instabilities conduce the system to a faster evolution leading to shorter collapse times with respect to models without black hole, and a faster cluster dissolution in the galactic tidal field of a parent galaxy. As a further application, two-dimensional distribution (in the meridional plane) of kinematical and structural parameters (density, dispersions, rotation) are reproduced, covering a wide range of ages, rotation, concentrations and ellipticities, with the aim to enable the use of set of models for comparison with observational data.

  16. AN ECLIPSING BLUE STRAGGLER IN THE GLOBULAR CLUSTER {omega} CENTAURI

    SciTech Connect

    Li Kai; Qian Shengbang

    2012-12-01

    {omega} Centauri is the largest globular cluster in the Milky Way and hence contains the largest number of variable stars within a single cluster. The results of photometric solutions are presented for the EA-type binary V239 in this cluster. According to our analysis, V239 is a typical Algol-type binary. We obtain M = 1.20 {+-} 0.10 M{sub Sun }, R = 1.21 {+-} 0.03 R{sub Sun }, and L = 13.68 {+-} 0.63 L{sub Sun} for the primary component. The secondary component has M = 0.07 {+-} 0.02 M{sub Sun }, R = 0.90 {+-} 0.03 R{sub Sun }, and L = 2.17 {+-} 0.14 L{sub Sun }. The binary system is located in the blue straggler region on the color-magnitude diagram of {omega} Centauri and the mass of the primary component exceeds the mass of a turnoff star. Therefore, we think that V239 is a blue straggler and that V239 was formed by mass transfer from the present secondary component to the present primary.

  17. The interaction between supermassive black holes and globular clusters

    NASA Astrophysics Data System (ADS)

    Spera, Mario; Arca-Sedda, Manuel; Capuzzo-Dolcetta, Roberto

    2016-02-01

    Almost all galaxies along the Hubble sequence host a compact massive object (CMO) in their center. The CMO can be either a supermassive black hole (SMBH) or a very dense stellar cluster, also known as nuclear star cluster (NSC). Generally, heavier galaxies (mass >~ 1011 M⊙) host a central SMBH while lighter show a central NSC. Intermediate mass hosts, instead, contain both a NSC and a SMBH. One possible formation mechanisms of a NSC relies on the dry-merger (migratory) scenario, in which globular clusters (GCs) decay toward the center of the host galaxy and merge. In this framework, the absence of NSCs in high-mass galaxies can be imputed to destruction of the infalling GCs by the intense tidal field of the central SMBH. In this work, we report preliminary results of N-body simulations performed using our high-resolution, direct, code HiGPUs, to investigate the effects of a central SMBH on a single GC orbiting around it. By varying either the mass of the SMBH and the mass of the host galaxy, we derived an upper limit to the mass of the central SMBH, and thus to the mass of the host, above which the formation of a NSC is suppressed.

  18. Dynamical formation of cataclysmic variables in globular clusters

    NASA Astrophysics Data System (ADS)

    Hong, Jongsuk; Vesperini, Enrico; Belloni, Diogo; Giersz, Mirek

    2017-01-01

    The formation and evolution of X-ray sources in globular clusters is likely to be affected by the cluster internal dynamics and the stellar interactions in the cluster dense environment. Several observational studies have revealed a correlation between the number of X-ray sources and the stellar encounter rate, and provided evidence of the role of dynamics in the formation of X-ray binaries. We have performed a survey of Monte Carlo simulations aimed at exploring the connection between the dynamics and formation of cataclysmic variables (CVs) and the origin of the observed correlation between the number of these objects, Ncv, and the stellar encounter rate, Γ. The results of our simulations show a correlation between Ncv and Γ, as found in observational data, illustrate the essential role played by the dynamics, and shed light on the dynamical history behind this correlation. CVs in our simulations are more centrally concentrated than single stars with masses close to those of turn-off stars, although this trend is stronger for CVs formed from primordial binaries undergoing exchange encounters, which include a population of more massive CVs absent in the group of CVs formed from binaries not suffering any component exchange.

  19. The inhomogeneous reionization of the local intergalactic medium by metal-poor globular clusters

    NASA Astrophysics Data System (ADS)

    Griffen, B. F.; Drinkwater, M. J.; Iliev, Ilian T.; Thomas, P. A.; Mellema, Garrelt

    2013-06-01

    We present detailed radiative transfer simulations of the reionization of the Milky Way by metal-poor globular clusters. We identify potential metal-poor globular cluster candidates within the Aquarius simulation using dark matter halo velocity dispersions. We calculate the local ionization fields via a photon-conserving, three dimensional non-equilibrium chemistry code. The key feature of the model is that globular cluster formation is suppressed if the local gas is ionized. We assume that at these early times, the ionization field is dominated by the flux from metal-poor globular clusters. Our spatial treatment of the ionization field leads to drastically different numbers and spatial distributions when compared to models where globular cluster formation is simply truncated at early redshifts (z ˜ 13). The spatial distributions are more extended and more globular clusters are produced. We find that additional sources of ionization are required at later epochs (z ˜ 10) to ionize the remaining gas and recover radial distributions statistically consistent with that of the Milky Way metal-poor globular clusters. We investigate a range of plausible ionization efficiencies to determine the effect photon-rich and photon-poor models have on present-day globular cluster properties. If globular clusters do indeed form within high-redshift dark matter haloes, they produce enough photons to ionize 98 and 90 per cent local (i.e. 23 h-3 Mpc3 centred on the host galaxy) volume and mass by redshift 10, respectively. In our photon-poorest model, this contribution drops to 60 and 50 per cent. Our model therefore implies that globular clusters are important contributors to the reionization process on local scales at high-redshift until more photon-rich sources dominate the photon budget at later times. The surviving clusters in all models have a narrow average age range (mean = 13.34 Gyr, σ = 0.04 Gyr) consistent with current age estimates of the Milky Way metal-poor globular

  20. Ages of Globular Clusters from HIPPARCOS Parallaxes of Local Subdwarfs

    NASA Astrophysics Data System (ADS)

    Gratton, Raffaele G.; Fusi Pecci, Flavio; Carretta, Eugenio; Clementini, Gisella; Corsi, Carlo E.; Lattanzi, Mario

    1997-12-01

    We report here initial but strongly conclusive results for absolute ages of Galactic globular clusters (GGCs). This study is based on high-precision trigonometric parallaxes from the HIPPARCOS satellite coupled with accurate metal abundances ([Fe/H], [O/Fe], and [α/Fe]) from high-resolution spectroscopy for a sample of about thirty subdwarfs. Systematic effects due to star selection (Lutz-Kelker corrections to parallaxes) and the possible presence of undetected binaries in the sample of bona fide single stars are examined, and appropriate corrections are estimated. They are found to be small for our sample. The new data allow us to reliably define the absolute location of the main sequence (MS) as a function of metallicity. These results are then used to derive distances and ages for a carefully selected sample of nine globular clusters having metallicities determined from high-dispersion spectra of individual giants according to a procedure totally consistent with that used for the field subdwarfs. Very precise and homogeneous reddening values have also been independently determined for these clusters. Random errors for our distance moduli are +/-0.08 mag, and systematic errors are likely of the same order of magnitude. These very accurate distances allow us to derive ages with internal errors of ~12% (+/-1.5 Gyr). The main results are: 1. HIPPARCOS parallaxes are smaller than corresponding ground-based measurements, leading, in turn, to longer distance moduli (~0.2 mag) and younger ages (~2.8 Gyr). 2. The distance to NGC 6752 derived from our MS fitting is consistent with that determined using the white dwarf cooling sequence. 3. The relation between the zero-age HB (ZAHB) absolute magnitude and metallicity for the nine program clusters is MV(ZAHB)=(0.22+/-0.09)([Fe/H]+1.5)+(0.49+/-0.04) . This relation is fairly consistent with some of the most recent theoretical models. Within quoted errors, the slope is in agreement with that given by the Baade-Wesselink (BW

  1. Abundances for globular cluster giants. I. Homogeneous metallicities for 24 clusters

    NASA Astrophysics Data System (ADS)

    Carretta, E.; Gratton, R. G.

    1997-01-01

    We have obtained high resolution, high signal-to-noise ratio CCD echelle spectra of 10 bright red giants in 3 globular clusters (47 Tuc, NGC 6752 and NGC 6397) roughly spanning the whole range of metallicities of the galactic globular cluster system. The analysis of this newly acquired material reveals no significant evidence of star-to-star variation of the [Fe/H] ratio in these three clusters. Moreover, a large set of high quality literature data (equivalent widths from high dispersion CCD spectra) was re-analyzed in an homogeneous and self-consistent way to integrate our observations and derive new metal abundances for more than 160 bright red giants in 24 globular clusters (i.e. about 16% of the known population of galactic globulars). This set was then used to define a new metallicity scale for globular clusters which is the result of high quality, direct spectroscopic data, of new and updated model atmospheres from the grid of \\cite[Kurucz (1992)]{\\ref41}, and of a careful fine abundance analysis; this last, in turn, is based on a common set of both atomic and atmospheric parameters for all the stars examined. Given the very high degree of internal homogeneity, our new scale supersedes the offsets and discrepancies existing in previous attempts to obtain a metallicity scale. The internal uncertainty in [Fe/H] is very small: 0.06 dex (24 clusters) on average, and can be interpreted also as the mean precision of the c luster ranking. Compared to our system, metallicities on the widely used Zinn and West's scale are about 0.10 dex higher for [Fe/H]>-1, 0.23 dex lower for -1<[Fe/H]<-1.9 and 0.11 dex too high for [Fe/H]<-1.9. The non-linearity of the Zinn and West's scale is significant even at 3 sigma level. A quadratic transformation is given to correct older values to the new scale in the range of our calibrating clusters (-2.24 <= [Fe/H]ZW <= -0.51). A minor disagreement is found at low metallicities between the metallicity scale based on field and cluster

  2. THE GLOBULAR CLUSTER NGC 5286. II. VARIABLE STARS

    SciTech Connect

    Zorotovic, M.; Catelan, M.; Aguirre, P.; Angulo, R. E.; Aravena, M.; Assef, R. J.; Contreras, C.; Cortes, C.; De Martini, G.; Escobar, M. E.; Gonzalez, D.; Jofre, P.; Lacerna, I.; Navarro, C.; Palma, O.; Prieto, G. E.; Recabarren, E.; Trivino, J.; Smith, H. A.; Pritzl, B. J. E-mail: mcatelan@astro.puc.cl

    2010-02-15

    We present the results of a search for variable stars in the globular cluster (GC) NGC 5286, which has recently been suggested to be associated with the Canis Major dwarf spheroidal galaxy. Fifty-seven variable stars were detected, only 19 of which had previously been known. Among our detections one finds 52 RR Lyrae (22 RRc and 30 RRab), 4 long-period variables, and 1 type II Cepheid of the BL Herculis type. Periods are derived for all of the RR Lyrae as well as the Cepheid, and BV light curves are provided for all the variables. The mean period of the RRab variables is (P{sub ab} ) = 0.656 days, and the number fraction of RRc stars is N{sub c} /N {sub RR} = 0.42, both consistent with an Oosterhoff II (OoII) type-thus making NGC 5286 one of the most metal-rich ([Fe/H] = -1.67) OoII globulars known to date. The minimum period of the RRabs, namely P {sub ab,min} = 0.513 d, while still consistent with an OoII classification, falls toward the short end of the observed P {sub ab,min} distribution for OoII GCs. As was recently found in the case of the prototypical OoII GC M15 (NGC 7078), the distribution of stars in the Bailey diagram does not strictly conform to the previously reported locus for OoII stars. We provide Fourier decomposition parameters for all of the RR Lyrae stars detected in our survey, and discuss the physical parameters derived therefrom. The values derived for the RRcs are not consistent with those typically found for OoII clusters, which may be due to the cluster's relatively high metallicity-the latter being confirmed by our Fourier analysis of the ab-type RR Lyrae light curves. Using the recent recalibration of the RR Lyrae luminosity scale by Catelan and Cortes, we derive for the cluster a revised distance modulus of (m - M) {sub V} = 16.04 mag.

  3. A new point of view in the analysis of equilibrium and dynamical evolution of globular clusters .

    NASA Astrophysics Data System (ADS)

    Merafina, M.

    We develop models of globular clusters (GCs) with a different approach by applying thermodynamic principles to a Boltzmann distribution function, with an Hamiltonian function which contains an effective potential depending on the kinetic energy of the stars, due to the effect of tidal interactions induced by the hosting galaxy. The Hamiltonian function is solution of the Fokker-Planck equation solved in a different way with respect to the King approach. Interesting results implying a different caloric curve for the analysis of the evolution of GCs are presented.

  4. New Breakthroughs in the Battle of the Bulge Using Globular Clusters

    NASA Astrophysics Data System (ADS)

    Geisler, D.; Mauro, F.; Bidin, C. M.; Cohen, R.; Chené, A.; Villanova, S.; Cummings, J.; Gormaz, A.; Minniti, D.; Alonso-García, J.; Hempel, M.; VVV Team

    2015-05-01

    We present some recent work undertaken mostly at the Universidad de Concepción using bulge globular clusters to better understand this important but poorly studied Galactic component, especially based on data from the VVV Survey. This includes discovering new bulge globulars, investigating dual HBs, and obtaining Ca triplet metallicities and velocities.

  5. WFPC2 observations of the globular cluster M30

    NASA Technical Reports Server (NTRS)

    Yanny, Brian; Guhathakurta, Puragra; Schneider, Donald P.; Bachall, John N.

    1994-01-01

    We describe images of the center of the dense globular cluster M30 (NGC 7099) obtained with the Hubble Space Telescope Wide Field/Planetary Camera 2 (HST WFPC2). Data taken in the F336W, F439W, and F555W filters (approximately U, B, and V) yield a color-magnitude diagram with photometric errors of 1 sigma = 0.05 mag for stars with V less than 17.5, and 1 sigma approximately 0.1 mag at V = 20, which is 1.5 mag fainter than the main-sequence turnoff. Simulations show that the star identifications are essentially complete for stars with V less than 19.5, even in the densest regions of the cluster. The projected radial distribution of stars can be represented by a power law distribution: N(r) approximately r(exp alpha), with slope alpha = -0.4 +/- 0.15, into radii less than 0.4 sec (0.015 pc). The radial profile is also consistent with a flat core of any radius smaller than approximately 1.5 sec (0.05 pc), but inconsistent with any core radius larger than 2.5 sec (0.09 pc). A total of 30 blue straggler candidates within 20 sec of the cluster center have been identified from the three-color data. Their radial distribution is strongly centrally concentrated when compared to the horizontal branch, red giant branch, or main-sequence stars in the cluster. The abundance of blue stragglers (relative to red giants and subgiants) within r approximately less than 20 sec of the center of M30 is f(sub BS) = 0.19 =/- 0.04, about twice as high as in other dense clusters.

  6. Characterization of the velocity anisotropy of accreted globular clusters

    NASA Astrophysics Data System (ADS)

    Bianchini, P.; Sills, A.; Miholics, M.

    2017-10-01

    Galactic globular clusters (GCs) are believed to have formed in situ in the Galaxy as well as in dwarf galaxies later accreted on to the Milky Way. However, to date, there is no unambiguous signature to distinguish accreted GCs. Using specifically designed N-body simulations of GCs evolving in a variety of time-dependent tidal fields (describing the potential of a dwarf galaxy-Milky Way merger), we analyse the effects imprinted on the internal kinematics of an accreted GC. In particular, we look at the evolution of the velocity anisotropy. Our simulations show that at early phases, the velocity anisotropy is determined by the tidal field of the dwarf galaxy and subsequently the clusters will adapt to the new tidal environment, losing any signature of their original environment in a few relaxation times. At 10 Gyr, GCs exhibit a variety of velocity anisotropy profiles, namely, isotropic velocity distribution in the inner regions and either isotropy or radial/tangential anisotropy in the intermediate and outer regions. Independent of an accreted origin, the velocity anisotropy primarily depends on the strength of the tidal field cumulatively experienced by a cluster. Tangentially anisotropic clusters correspond to systems that have experienced stronger tidal fields and are characterized by higher tidal filling factor, r50/rj ≳ 0.17, higher mass-loss ≳ 60 per cent and relaxation times trel ≲ 109 Gyr. Interestingly, we demonstrate that the presence of tidal tails can significantly contaminate the measurements of velocity anisotropy when a cluster is observed in projection. Our characterization of the velocity anisotropy profiles in different tidal environments provides a theoretical benchmark for the interpretation of the unprecedented amount of three-dimensional kinematic data progressively available for Galactic GCs.

  7. A study of rotating globular clusters. The case of the old, metal-poor globular cluster NGC 4372

    NASA Astrophysics Data System (ADS)

    Kacharov, N.; Bianchini, P.; Koch, A.; Frank, M. J.; Martin, N. F.; van de Ven, G.; Puzia, T. H.; McDonald, I.; Johnson, C. I.; Zijlstra, A. A.

    2014-07-01

    Context. NGC 4372 is a poorly studied old, very metal-poor globular cluster (GC) located in the inner Milky Way halo. Aims: We present the first in-depth study of the kinematic properties and derive the structural parameters of NGC 4372 based on the fit of a Plummer profile and a rotating, physical model. We explore the link between internal rotation to different cluster properties and together with similar studies of more GCs, we put these in the context of globular cluster formation and evolution. Methods: We present radial velocities for 131 cluster member stars measured from high-resolution FLAMES/GIRAFFE observations. Their membership to the GC is additionally confirmed from precise metallicity estimates. We build a velocity dispersion profile and a systemic rotation curve using this kinematic data set. Additionally, we obtain an elliptical number density profile of NGC 4372 based on optical images using a Markov chain Monte Carlo fitting algorithm. From this, we derive the cluster's half-light radius and ellipticity as rh = 3.44' ± 0.04' and ɛ = 0.08 ± 0.01. Finally, we give a physical interpretation of the observed morphological and kinematic properties of this GC by fitting an axisymmetric, differentially rotating, dynamical model. Results: Our results show that NGC 4372 has an unusually high ratio of rotation amplitude to velocity dispersion (1.2 vs. 4.5 km s-1) for its metallicity. This puts it in line, however, with two other exceptional, very metal-poor GCs: M 15 and NGC 4590. We also find a mild flattening of NGC 4372 in the direction of its rotation. Given its old age, this suggests that the flattening is indeed caused by the systemic rotation rather than tidal interactions with the Galaxy. Additionally, we estimate the dynamical mass of the GC Mdyn = 2.0 ± 0.5 × 105M⊙ based on the dynamical model, which constrains the mass-to-light ratio of NGC 4372 between 1.4 and 2.3 M⊙/L⊙, representative of an old, purely stellar population. Based on

  8. 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.

  9. On the Globular Cluster Initial Mass Function below 1 Msolar

    NASA Astrophysics Data System (ADS)

    Paresce, Francesco; De Marchi, Guido

    2000-05-01

    Accurate luminosity functions (LFs) for a dozen globular clusters have now been measured at or just beyond their half-light radius using HST. They span almost the entire cluster main sequence (MS) below 0.75 Msolar. All these clusters exhibit LFs that rise continuously from an absolute I magnitude MI~=6 to a peak at MI~=8.5-9 and then drop with increasing MI. Transformation of the LFs into mass functions (MFs) by means of mass-luminosity (ML) relations that are consistent with all presently available data on the physical properties of low-mass, low-metallicity stars shows that all the LFs observed so far can be obtained from MFs having the shape of a lognormal distribution with characteristic mass mc=0.33+/-0.03 Msolar and standard deviation σ=0.34+/-0.04. In particular, the LFs of the four clusters in the sample that extend well beyond the peak luminosity down to close to the hydrogen-burning limit (NGC 6341, NGC 6397, NGC 6752, and NGC 6809) can only be reproduced by such distributions and not by a single power law in the 0.1-0.6 Msolar range. After correction for the effects of mass segregation, the variation of the ratio of the number of higher to lower mass stars with cluster mass or any simple orbital parameter or the expected time to disruption recently computed for these clusters shows no statistically significant trend over a range of this last parameter of more than a factor of ~100. We conclude that the global MFs of these clusters have not been measurably modified by evaporation and tidal interactions with the Galaxy and, thus, should reflect the initial distribution of stellar masses. Since the lognormal function that we find is also very similar to the one obtained independently for much younger clusters and to the form expected theoretically, the implication seems to be unavoidable that it represents the true stellar initial mass function for this type of star in this mass range. Based on observations with the NASA/ESA Hubble Space Telescope

  10. 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.

  11. 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.

  12. The Properties of Globular Cluster ESO452-SC11

    NASA Astrophysics Data System (ADS)

    Cornish, A. S. M.; Phelps, R. L.; Briley, M. M.; Friel, E. D.

    2005-12-01

    The globular cluster ESO452-SC11 has been observed using Johnson V and Cousin I filters and PSF photometry has been performed. The resulting color-magnitude diagrams were compared to theoretical isochrones to derive the cluster's age, overall chemical composition, and distance modulus. These isochrone models include those published by Girardi et al., Bergbusch & VandenBerg with BVRI color-Teff relations as described by VandenBerg & Clem, and Demarque et al. (known as the Yale isochrones). From the Yale isochrones, it is estimated that the cluster has an age 9-11 Gyr, a metallicity [Fe/H] between -1.4 and -1.0 dex, and a distance modulus (m-M)V =16.10-16.31 mag resulting in a heliocentric distance of 7.3-7.5 kpc. Using the Bergbusch & VandenBerg models, it is estimated that the cluster has an age of 11-13 Gyr, with an iron-to hydrogen ratio between -1.3 and -0.8 dex, a distance modulus (m-M)V =15.87-16.12 mag, and a heliocentric distance between 7.0-7.2 kpc. The Girardi isochrone models yield a derived age of 13-16 Gyr, metallicity between -1.3 and -0.4 dex, distance modulus (m-M)V =15.59-16.19 mag, and heliocentric distance between 6.6-7.1 kpc. The derived parameters from these models are consistent for metallicity [Fe/H] between -1.3 and -1.0 dex, reddening E(V-I) =0.70 - 0.76, and (m-M)V =16.10 - 16.12 mag. A.C. would like to acknowledge the HACU National Internship program for supporting the data analysis portion of this research.

  13. Formation of Short-Period Binary Pulsars in Globular Clusters.

    PubMed

    Rasio; Pfahl; Rappaport

    2000-03-20

    We present a new dynamical scenario for the formation of short-period binary millisecond pulsars in globular clusters. Our work is motivated by the recent observations of 20 radio pulsars in 47 Tuc. In a dense cluster such as 47 Tuc, most neutron stars acquire binary companions through exchange interactions with primordial binaries. The resulting systems have semimajor axes in the range approximately 0.1-1 AU and neutron star companion masses approximately 1-3 M middle dot in circle. For many of these systems, we find that when the companion evolves off the main sequence and fills its Roche lobe, the subsequent mass transfer is dynamically unstable. This leads to a common envelope phase and the formation of short-period neutron star-white dwarf binaries. For a significant fraction of these binaries, the decay of the orbit due to gravitational radiation will be followed by a period of stable mass transfer driven by a combination of gravitational radiation and tidal heating of the companion. The properties of the resulting short-period binaries match well those of observed binary pulsars in 47 Tuc.

  14. SOAR Adaptive Optics Observations of the Globular Cluster NGC 6496

    NASA Astrophysics Data System (ADS)

    Fraga, Luciano; Kunder, Andrea; Tokovinin, Andrei

    2013-06-01

    We present high-quality BVRI photometric data in the field of globular cluster NGC 6496 obtained with the SOAR Telescope Adaptive Module (SAM). Our observations were collected as part of the ongoing SAM commissioning. The distance modulus and cluster color excess as found from the red clump are (m - M) V = 15.71 ± 0.02 mag and E(V - I) = 0.28 ± 0.02 mag. An age of 10.5 ± 0.5 Gyr is determined from the difference in magnitude between the red clump and the subgiant branch. These parameters are in excellent agreement with the values derived from isochrone fitting. From the color-magnitude diagram we find a metallicity of [Fe/H] = -0.65 dex and hence support a disk classification for NGC 6496. The complete BVRI data set for NGC 6469 is made available in the electronic edition of the Journal. 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 Hill (UNC), and Michigan State University (MSU).

  15. The RR Lyrae variables in the globular cluster M68

    NASA Technical Reports Server (NTRS)

    Clement, Christine M.; Ferance, Stephen; Simon, Norman R.

    1993-01-01

    New observations, made with the Helen Sawyer Hogg telescope at Las Campanas, have been analyzed in a search for double-mode pulsators (RRd stars) in the metal-poor globular cluster, Messier 68. Of the 30 stars studied, nine have been identified as RRd stars; V33, which exhibited the characteristics of an RRd star in 1950, now appears to be an RRc star. Reliable periods and period ratios have been determined for six of the RRd stars. Masses for these RRd stars, calculated from fitting formulas given by Kovacs et al. (1991), range from 0.75 to 0.90 solar mass, depending on the assumed luminosity and metal abundance. These masses are in the same range as those for the RRd stars in M 15, whose RRd sample resembles that of M68 very closely. Fourier parameters determined for the light curves of the M68 variables show that the RRc stars in the two clusters are also very similar. In particular, on the plot of phase parameter phi sub 31 with period, the M15 and M68 RRc samples are virtually indistinguishable. A comparison of the new M68 observations with observations made 40 yr ago shows that the periods of some of the stars have changed, but the 40 yr interval is too short for detecting period changes caused by evolutionary effects.

  16. Accretion onto Protoplanetary Discs: Implications for Globular Cluster Evolution

    NASA Astrophysics Data System (ADS)

    Wijnen, Thomas; Pols, Onno; Portegies Zwart, Simon

    2015-08-01

    In the past decade, observational evidence that Globular Clusters (GCs) harbour multiple stellar populations has grown steadily. These observations are hard to reconcile with the classic picture of star formation in GCs, which approximates them as a single generation of stars. However, Bastian et al. recently suggested an evolutionary scenario in which a second (and higher order) population is formed by the accretion of chemically enriched material onto the low-mass stars in the initial GC population. In this early disc accretion scenario the low-mass, pre-main sequence stars sweep up gas expelled by the more massive stars of the same generation into their protoplanetary disc as they move through the cluster centre.Using assumptions that represent the (dynamical) conditions in a typical GC, we investigate whether a low-mass star surrounded by a protoplanetary disc can indeed accrete sufficient enriched material to account for the observed abundances in 'second generation' stars. We compare the outcome of two different smoothed particle hydrodynamics codes and check for consistency. In particular, we focus on the lifetime and stability of the disc and on the gas accretion rate onto both the star and the disc.

  17. RR Lyrae pulsators as helium indicators in globular clusters

    NASA Astrophysics Data System (ADS)

    Caputo, F.; Tornambe, A.; Castellani, V.

    1980-02-01

    Synthetic Horizontal Branches have been constructed adopting evolutionary horizontal branch models computed by Caputo, Castellani, and Wood for the case Z = 10-3 and assuming Y = 0.20, 0.25, and 0.30. On this basis the expected evolutionary properties of RR Lyrae pulsators in population II Clusters have been studied. It has been found that some pulsational quantities (Pminab, ¯P and ¯Pab) are strongly correlated with the original helium content Y and that, under fairly wide assumptions, they do not depend on evolutionary parameters such as mass loss and/or mass dispersion. From the above quoted RR Lyrae properties one obtains suggestions for an original He content Y ˜ 0.30 in Oosterhoff type I Globular Clusters. Some theoretical results have been found which disagree with observations. From the latter, it is inferred that in the adopted evolutionary computations lifetimes in the last phases of horizontal branch evolution are likely to be overestimated; this is tentatively confirmed by comparing with the computations of Sweigart and Gross. Pulsational properties are little affected by such an occurrence.

  18. Study of Remote Globular Cluster Satellites of M87

    NASA Astrophysics Data System (ADS)

    Sahai, Arushi; Shao, Andrew; Toloba, Elisa; Guhathakurta, Puragra; Peng, Eric W.; Zhang, Hao

    2017-01-01

    We present a sample of “orphan” globular clusters (GCs) with previously unknown parent galaxies, which we determine to be remote satellites of M87, a massive elliptical galaxy at the center of the Virgo Cluster of Galaxies. Because GCs were formed in the early universe along with their original parent galaxies, which were cannibalized by massive galaxies such as M87, they share similar age and chemical properties. In this study, we first confirm that M87 is the adoptive parent galaxy of our orphan GCs using photometric and spectroscopic data to analyze spatial and velocity distributions. Next, we increase the signal-to-noise ratio of our samples’ spectra through a process known as coaddition. We utilize spectroscopic absorption lines to determine the age and metallicity of our orphan GCs through comparison to stellar population synthesis models, which we then relate to the GCs’ original parent galaxies using a mass-metallicity relation. Our finding that remote GCs of M87 likely developed in galaxies with ~1010 solar masses implies that M87’s outer halo is formed of relatively massive galaxies, serving as important parameters for developing theories about the formation and evolution of massive galaxies.This research was funded in part by NASA/STScI and the National Science Foundation. Most of this work was carried out by high school students working under the auspices of the Science Internship Program at UC Santa Cruz.

  19. The Evolution of Globular Cluster Systems In Early-Type Galaxies

    NASA Astrophysics Data System (ADS)

    Grillmair, Carl

    1999-07-01

    We will measure structural parameters {core radii and concentrations} of globular clusters in three early-type galaxies using deep, four-point dithered observations. We have chosen globular cluster systems which have young, medium-age and old cluster populations, as indicated by cluster colors and luminosities. Our primary goal is to test the hypothesis that globular cluster luminosity functions evolve towards a ``universal'' form. Previous observations have shown that young cluster systems have exponential luminosity functions rather than the characteristic log-normal luminosity function of old cluster systems. We will test to see whether such young system exhibits a wider range of structural parameters than an old systems, and whether and at what rate plausible disruption mechanisms will cause the luminosity function to evolve towards a log-normal form. A simple observational comparison of structural parameters between different age cluster populations and between diff er ent sub-populations within the same galaxy will also provide clues concerning both the formation and destruction mechanisms of star clusters, the distinction between open and globular clusters, and the advisability of using globular cluster luminosity functions as distance indicators.

  20. 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

  1. Deep WIYN Imaging of the Globular Cluster System of the Lenticular Galaxy NGC 3607

    NASA Astrophysics Data System (ADS)

    Carr, Derrick; Rhode, Katherine L.; Jorgenson, Regina

    2017-01-01

    Globular clusters serve as relics of a galaxy’s past history, because they are thought to be among the first objects to form in a galaxy. Measuring the properties of the globular cluster population of a galaxy — in particular the total number, spatial distribution, and color distribution of the clusters — can provide important clues about the formation and evolution of that galaxy. Here we present results from the analysis of the globular cluster population of NGC 3607, an S0 galaxy with M_V = -21.9 that is ~23 Mpc away and is the brightest member of the Leo II group. We used images from the Minimosaic camera on the WIYN 3.5-m telescope with total exposure times of 6300, 6000, and 5400 seconds in the B, V, and R filters, respectively, to image the globular cluster system of NGC 3607 well past its apparent radial extent of 6.3’ (41 kpc). Point-source globular clusters are selected with three-filter photometry to help eliminate foreground stars and background galaxies. The excellent seeing in our WIYN images (0.6” to 0.9”) also helped reduce contamination in the globular cluster candidate sample. Artificial star tests yielded 50% completeness levels of B = 25.4, V=25.2, and R=24.1 and we observed approximately 41% of the galaxy’s Globular Cluster Luminosity Function. We estimate the total number of globular clusters in NGC 3607 is 1000+/-50, which translates to specific frequency values of S_N = 1.7+/-0.3 and T = 2.6+/-0.3 for this galaxy’s luminosity and stellar mass. This research was supported in part by NSF REU grant AST-1358980 and the Nantucket Maria Mitchell Association.

  2. 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.

  3. 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.

  4. Tidal evolution of globular clusters. II - The effects of Galactic tidal field and diffusion

    NASA Technical Reports Server (NTRS)

    Oh, K. S.; Lin, D. N. C.

    1992-01-01

    The tidal evolution of globular clusters subject to various degrees of the internal diffusion process is investigated. In cases of negligible diffusion, clusters are found to be tidally truncated to the theoretical tidal radius at perigalacticon. There is no apparent orbital phase dependence of the tidal radius for clusters with eccentric orbits. In clusters with moderately short two-body relaxation time scales, diffusion processes significantly modify the structure of the outer regions in such a way that the limiting radius may be comparable to the tidal radius at apogalacticon. The Galactical tidal torque induces isotropy in the velocity dispersion of the outer regions of the cluster. For relaxed clusters, the velocity dispersion may be isotropic in the core, anisotropic in the envelope and isotropic near the limiting radius. Disk shocking is also very efficient for isotropizing the orbits of stars in the outer cluster regions. Stars with direct orbits are less stable, so that prolonged tidal interaction can lead to apparent retrograde rotation in the outer regions of the cluster.

  5. Sulphur in the metal poor globular cluster NGC 6397

    NASA Astrophysics Data System (ADS)

    Koch, A.; Caffau, E.

    2011-10-01

    Sulphur (S) is a non-refractory α-element that is not locked into dust grains in the interstellar medium. Thus no correction to the measured, interstellar sulphur abundance is needed and it can be readily compared to the S content in stellar photospheres. Here we present the first measurement of sulphur in the metal poor globular cluster (GC) NGC 6397, as detected in a MIKE/Magellan high signal-to-noise, high-resolution spectrum of one red giant star. While abundance ratios of sulphur are available for a larger number of Galactic stars down to an [Fe/H] of ~ -3.5 dex, no measurements in globular clusters more metal poor than -1.5 dex have been reported so far. We find aNLTE, 3-D abundance ratio of [S/Fe] = +0.52 ± 0.20 (stat.) ± 0.08 (sys.), based on theS I, Multiplet 1 line at 9212.8 Å. This value is consistent with a Galactic halo plateau as typical of other α-elements in GCs and field stars, but we cannot rule out its membership with a second branch of increasing [S/Fe] with decreasing [Fe/H], claimed in the literature, which leads to a large scatter at metallicities around - 2 dex. The [S/Mg] and [S/Ca] ratios in this star are compatible with a Solar value to within the (large) uncertainties. Despite the very large scatter in these ratios across Galactic stars between literature samples, this indicates that sulphur traces the chemical imprints of the other α-elements in metal poor GCs. Combined with its moderate sodium abundance ([S/Na]NLTE = 0.48), the [S/Fe] ratio in this GC extends a global, positive S-Na correlation that is not seen in field stars and might indicate that proton-capture reactions contributed to the production of sulphur in the (metal poor) early GC environments. This paper includes data gathered with the 6.5 m Magellan Telescopes located at Las Campanas Observatory, Chile.

  6. Tides, Rotation Or Anisotropy? Self-consistent Nonspherical Models For Globular Clusters

    NASA Astrophysics Data System (ADS)

    Varri, Anna L.; Bertin, G.

    2011-01-01

    Spherical models of quasi-relaxed stellar systems provide a successful zeroth-order description of globular clusters. Yet, the great progress made in recent years in the acquisition of detailed information of the structure of these stellar systems calls for a renewed effort on the side of modeling. In particular, more general analytical models would allow to address the long-standing issue of the physical origin of the deviations from spherical symmetry of the globular clusters, that now can be properly measured. In fact, it remains to be established which is the cause of the observed flattening, among external tides, internal rotation, and pressure anisotropy. In this paper we focus on the first two physical ingredients. We start by briefly describing a recently studied family of triaxial models that incorporate in a self-consistent way the tidal effects of the host galaxy, as a collisionless analogue of the Roche problem (Varri & Bertin ApJ 2009). We then present two new families of axisymmetric models in which the deviations from spherical symmetry are induced by the presence of internal rotation. The first one is an extension of the well-known family of King models to the case of axisymmetric equilibria flattened by solid-body rotation. The second family is characterized by differential rotation, designed to be rigid in the center and to vanish in the outer parts, where the imposed truncation in phase space becomes effective. For possible application to globular clusters, models of interest should be those, in both families, characterized by low values of the rotation strength parameter and quasi-spherical shape. For general interest in stellar dynamics, we show that, for high values of that parameter, the differentially rotating models may exhibit unexpected morphologies, even with a toroidal core.

  7. THE DYNAMICAL EVOLUTION OF STELLAR BLACK HOLES IN GLOBULAR CLUSTERS

    SciTech Connect

    Morscher, Meagan; Pattabiraman, Bharath; Rodriguez, Carl; Rasio, Frederic A.; Umbreit, Stefan

    2015-02-10

    Our current understanding of the stellar initial mass function and massive star evolution suggests that young globular clusters (GCs) may have formed hundreds to thousands of stellar-mass black holes (BHs), the remnants of stars with initial masses from ∼20-100 M {sub ☉}. Birth kicks from supernova explosions may eject some BHs from their birth clusters, but most should be retained. Using a Monte Carlo method we investigate the long-term dynamical evolution of GCs containing large numbers of stellar BHs. We describe numerical results for 42 models, covering a broad range of realistic initial conditions, including up to 1.6 × 10{sup 6} stars. In almost all models we find that significant numbers of BHs (up to ∼10{sup 3}) are retained all the way to the present. This is in contrast to previous theoretical expectations that most BHs should be ejected dynamically within a few gigayears The main reason for this difference is that core collapse driven by BHs (through the Spitzer {sup m}ass segregation instability{sup )} is easily reverted through three-body processes, and involves only a small number of the most massive BHs, while lower-mass BHs remain well-mixed with ordinary stars far from the central cusp. Thus the rapid segregation of stellar BHs does not lead to a long-term physical separation of most BHs into a dynamically decoupled inner core, as often assumed previously. Combined with the recent detections of several BH X-ray binary candidates in Galactic GCs, our results suggest that stellar BHs could still be present in large numbers in many GCs today, and that they may play a significant role in shaping the long-term dynamical evolution and the present-day dynamical structure of many clusters.

  8. On the Density Profile of the Globular Cluster M92

    NASA Astrophysics Data System (ADS)

    Di Cecco, A.; Zocchi, A.; Varri, A. L.; Monelli, M.; Bertin, G.; Bono, G.; Stetson, P. B.; Nonino, M.; Buonanno, R.; Ferraro, I.; Iannicola, G.; Kunder, A.; Walker, A. R.

    2013-04-01

    We present new number density and surface brightness profiles for the globular cluster M92 (NGC 6341). These profiles are calculated from optical images collected with the CCD mosaic camera MegaCam at the Canada-France-Hawaii Telescope and with the Advanced Camera for Surveys on the Hubble Space Telescope. The ground-based data were supplemented with the Sloan Digital Sky Survey photometric catalog. Special care was taken to discriminate candidate cluster stars from field stars and to subtract the background contamination from both profiles. By examining the contour levels of the number density, we found that the stellar distribution becomes clumpy at radial distances larger than ~13', and there is no preferred orientation of contours in space. We performed detailed fits of King and Wilson models to the observed profiles. The best-fit models underestimate the number density inside the core radius. Wilson models better represent the observations, in particular in the outermost cluster regions: the good global agreement of these models with the observations suggests that there is no need to introduce an extra-tidal halo to explain the radial distribution of stars at large radial distances. The best-fit models for the number density and the surface brightness profiles are different, even though they are based on the same observations. Additional tests support the evidence that this fact reflects the difference in the radial distribution of the stellar tracers that determine the observed profiles (main-sequence stars for the number density, bright evolved stars for the surface brightness). Based in part on data obtained from the ST-ECF Science Archive Facility. This research used the facilities of the Canadian Astronomy Data Centre operated by the National Research Council of Canada with the support of the Canadian Space Agency.

  9. Ruprecht 106: The first single population globular cluster?

    SciTech Connect

    Villanova, S.; Geisler, D.; Muñoz, C.; Carraro, G.; Moni Bidin, C.

    2013-12-01

    All old Galactic globular clusters (GCs) studied in detail to date host at least two generations of stars, where the second is formed from gas polluted by processed material produced by massive stars of the first. This process can happen if the initial mass of the cluster exceeds a threshold above which ejecta are retained and a second generation is formed. A determination of this mass threshold is mandatory in order to understand how GCs form. We analyzed nine red giant branch stars belonging to the cluster Ruprecht 106. Targets were observed with the UVES@VLT2 spectrograph. Spectra cover a wide range and allowed us to measure abundances for light (O, Na, Mg, Al), α (Si, Ca, Ti), iron-peak (Sc, V, Cr, Mn, Fe, Co, Ni, Cu, Zn), and neutron-capture (Y, Zr, Ba, La, Ce, Pr, Nd, Sm, Eu, Dy, Pb) elements. Based on these abundances, we show that Ruprecht 106 is the first convincing example of a single-population GC (i.e., a true simple stellar population), although the sample is relatively small. This result is supported also by an independent photometric test and by the horizontal branch morphology and the dynamical state. It is old (∼12 Gyr) and, at odds with other GCs, has no α-enhancement. The material it formed from was contaminated by both s- and r-process elements. The abundance pattern points toward an extragalactic origin. Its present-day mass (M = 10{sup 4.83} M {sub ☉}) can be assumed as a strong lower limit for the initial mass threshold below which no second generation is formed. Clearly, its initial mass must have been significantly greater, but we have no current constraints on the amount of mass loss during its evolution.

  10. Ruprecht 106: The First Single Population Globular Cluster?

    NASA Astrophysics Data System (ADS)

    Villanova, S.; Geisler, D.; Carraro, G.; Moni Bidin, C.; Muñoz, C.

    2013-12-01

    All old Galactic globular clusters (GCs) studied in detail to date host at least two generations of stars, where the second is formed from gas polluted by processed material produced by massive stars of the first. This process can happen if the initial mass of the cluster exceeds a threshold above which ejecta are retained and a second generation is formed. A determination of this mass threshold is mandatory in order to understand how GCs form. We analyzed nine red giant branch stars belonging to the cluster Ruprecht 106. Targets were observed with the UVES@VLT2 spectrograph. Spectra cover a wide range and allowed us to measure abundances for light (O, Na, Mg, Al), α (Si, Ca, Ti), iron-peak (Sc, V, Cr, Mn, Fe, Co, Ni, Cu, Zn), and neutron-capture (Y, Zr, Ba, La, Ce, Pr, Nd, Sm, Eu, Dy, Pb) elements. Based on these abundances, we show that Ruprecht 106 is the first convincing example of a single-population GC (i.e., a true simple stellar population), although the sample is relatively small. This result is supported also by an independent photometric test and by the horizontal branch morphology and the dynamical state. It is old (~12 Gyr) and, at odds with other GCs, has no α-enhancement. The material it formed from was contaminated by both s- and r-process elements. The abundance pattern points toward an extragalactic origin. Its present-day mass (M = 104.83 M ⊙) can be assumed as a strong lower limit for the initial mass threshold below which no second generation is formed. Clearly, its initial mass must have been significantly greater, but we have no current constraints on the amount of mass loss during its evolution.

  11. The onset of gravothermal oscillations in globular cluster evolution

    NASA Technical Reports Server (NTRS)

    Breeden, Joseph L.; Cohn, Haldan N.; Hut, Piet

    1994-01-01

    We have carried out an extensive set of Fokker-Planck simulations of the evolution of globular clusters on very long timescales, up to 600 times the initial core collapse time t(sub cc). We consider an idealized equal mass star cluster, with a wide range of values for the total number of stars, 7000 less than N less than 2 x 10(exp 6). Our models include the heating effect of compact binaries formed in three-body encounters, which halts the initial core collapse and drives a core reexpansion. Postcollapse gravothermal oscillations of the cluster core are found to occur for all N approximately greater than or equal to 8000. For 8000 approximately less than or equal to N approximately less than or equal to 11,000, the oscillation has a simple, regular waveform with a single, well-defined period. For N approximately equals 12,000, the oscillations become nonlinear in a process resembling a period doubling. For N approximately greater than or equal to 14,000, the waveform of the oscillations becomes increasingly more irregular with increasing N, resembling chaotic behavior for N approximately greater than or equal to 15,000. During the oscillations, the core radius and core mass vary dramatically: by more than a factor of 10 for N greater than 15,000, by more than a factor of 100 for N greater than 5 x 10(exp 4), and by more than a factor of 1000 for N greater than 5 x 10(exp 5). However, even during the times of maximum expansion, the core contains only a small fraction of the cluster mass. For most N values, the maximum core mass at any time after core collapse is less than 1% of the cluster mass. The exceptions lie in the range 5 x 10(exp 4) approximately less than or equal to N approximately equal to or less than 2 x 10(exp 5), where the maximum post-collapse core mass reaches approximately 2% of the cluster mass. We discuss the observational implications of these predictions.

  12. Bayesian analysis of two stellar populations in Galactic globular clusters- III. Analysis of 30 clusters

    NASA Astrophysics Data System (ADS)

    Wagner-Kaiser, R.; Stenning, D. C.; Sarajedini, A.; von Hippel, T.; van Dyk, D. A.; Robinson, E.; Stein, N.; Jefferys, W. H.

    2016-12-01

    We use Cycle 21 Hubble Space Telescope (HST) observations and HST archival ACS Treasury observations of 30 Galactic globular clusters to characterize two distinct stellar populations. A sophisticated Bayesian technique is employed to simultaneously sample the joint posterior distribution of age, distance, and extinction for each cluster, as well as unique helium values for two populations within each cluster and the relative proportion of those populations. We find the helium differences among the two populations in the clusters fall in the range of ˜0.04 to 0.11. Because adequate models varying in carbon, nitrogen, and oxygen are not presently available, we view these spreads as upper limits and present them with statistical rather than observational uncertainties. Evidence supports previous studies suggesting an increase in helium content concurrent with increasing mass of the cluster and we also find that the proportion of the first population of stars increases with mass as well. Our results are examined in the context of proposed globular cluster formation scenarios. Additionally, we leverage our Bayesian technique to shed light on the inconsistencies between the theoretical models and the observed data.

  13. VizieR Online Data Catalog: Metallicity estimates of M31 globular clusters (Galleti+, 2009)

    NASA Astrophysics Data System (ADS)

    Galleti, S.; Bellazzini, M.; Buzzoni, A.; Federici, L.; Fusi Pecci, F.

    2010-04-01

    New empirical relations of [Fe/H] as a function of [MgFe] and Mg2 indices are based on the well-studied galactic globular clusters, complemented with theoretical model predictions for -0.2<=[Fe/H]<=+0.5. Lick indices for M31 clusters from various literature sources (225 clusters) and from new observations by our team (71 clusters) have been transformed into the Trager et al. (2000AJ....119.1645T) system, yielding new metallicity estimates for 245 globular clusters of M31. (3 data files).

  14. Photometry of the globular cluster system of the Sagittarius dwarf galaxy

    NASA Astrophysics Data System (ADS)

    Ibata, Rodrigo

    1996-07-01

    We propose to use the WFPC2 to obtain deep V {F555W} and I {F814W} band images of the globular clusters of the Sagittarius dwarf galaxy: M54 {NGC 6715}, Ter 7, Ter 8 and Arp 2. Isochrone fits to these data will yield the accurate ages of M54, Ter 8 and the Sagittarius dwarf galaxy {Sgr}. These age estimates are needed to model the dynamics and evolution of the Sgr system and its interaction with the Milky Way. Sgr is in the final stages of tidal disruption {Velazquez & White 1995}, so its globular clusters will drift away from their parent galaxy and soon disperse into the Galactic halo. Therefore at least some of the globular clusters of giant spiral galaxies like the Milky Way will have been captured from tidally destroyed dwarf galaxies. This statement has fundamental and wide ranging implications for the formation and evolution of globular clusters and spiral galaxies. It is therefore essential to conduct a detailed and accurate comparative study of the stellar populations of the Sgr and Galactic globular clusters, as we propose here. This, in turn, will allow detailed modeling of the chemical and dynamical evolution of Sgr and its globular clusters.

  15. Variable Stars in the Globular Cluster M107: The Discovery of a Probable SX Phoenicis Star

    NASA Astrophysics Data System (ADS)

    McCombs, Thayne; Reinhart, E.; Murphy, B. W.

    2013-01-01

    We used the SARA 0.9-meter telescope located at KPNO during May and June of 2012 to search for variable stars in the globular cluster M107 (NGC 6171). Pulsating variable stars in globular clusters are useful tools in determining the physical properties of stars, in particular their metallicity. Due to the close proximity of stars in globular clusters, aperture photometry is not optimal, particularly for low-amplitude variables. However, using image subtraction methods it is possible to efficiently detect variable stars in the crowded cores of globular clusters. Using V-band time-series photometry of M107 we have refined the positions and confirmed the 22 RR Lyrae variables from Clement's Catalog of Variable Stars in Globular Clusters. We have also discovered a previously unknown variable which is likely to be an SX Phoenicis star. For this SX Phe star we measured a fundamental pulsation frequency 19.01221 per day (P=0.05257 days) and a mean amplitude of 0.046 magnitudes in the V band. This variable had an average V-band magnitude of 17.72, nearly 2 magnitudes dimmer than the horizontal branch of M107, typical of SX Phoenicis stars lying beyond the main sequence turn-off in globular clusters.

  16. Galactic bulge X-ray burst sources from disrupted globular clusters?

    NASA Technical Reports Server (NTRS)

    Grindlay, J. E.; Hertz, P.

    1985-01-01

    The origin of the bright galactic bulge X-ray sources, or GX sources, is unclear despite intensive study for the past 15 years. It is suggested that the fact that many (or most) of the GX sources are X-ray burst sources (GXRBS) and are otherwise apparently identical to the luminous X-ray sources found in globular cluster cores implies that they too may have a globular cluster origin. The possibility that the compact X-ray binaries found in globulars are ejected is constrained by observations of CVs in and out of clusters. The GXRBS are instead hypothesized to have been formed by capture processes in globular clusters which have now largely been disrupted by repeated tidal stripping and shocking in the galactic plane. A statistical analysis of the 12 GXRBS which have precise positions from Einstein and/or optical (or radio) observations indicate that it is probably significant that a bright, of less than about 19, G or K star is found within the error circle (3 arcmin radius) in four cases. These may be surviving giants in a disrupted globular cluster core. Implications for globular cluster evolution and the GXRBS themselves are discussed.

  17. 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

  18. New SX Phe variables in the globular cluster NGC 288

    NASA Astrophysics Data System (ADS)

    Martinazzi, E.; Kepler, S. O.; Costa, J. E. S.; Pieres, A.; Bonatto, C.; Bica, E.; Fraga, L.

    2015-03-01

    We report the discovery of two new variable stars in the metal-poor globular cluster NGC 288, found by means of time series CCD photometry. We classified the new variables as SX Phoenicis (SX Phe) due to their characteristic fundamental mode periods (1.02 ± 0.01 and 0.69 ± 0.01 h), and refine the period estimates for other six known variables. SX Phe stars are known to follow a well-defined period-luminosity (P-L) relation and, thus, can be used for determining distances; they are more numerous than RR Lyraes in NGC 288. We obtain the P-L relation for the fundamental mode MV = (-2.59 ± 0.18) log P0(d) + (-0.34 ± 0.24) and for the first-overtone mode MV = (-2.59 ± 0.18) log P1(d) + (0.50 ± 0.25). Multichromatic isochrone fits to our UBV colour-magnitude diagrams, based on the Dartmouth Stellar Evolution Database, provide <[Fe/H]> = -1.3 ± 0.1, E(B - V) = 0.02 ± 0.01 and absolute distance modulus (m - M)0 = 14.72 ± 0.01 for NGC 288.

  19. Spectroscopy of chromospheric lines of giants in the globular cluster

    NASA Technical Reports Server (NTRS)

    Dupree, A. K.; Hartmann, Lee; Smith, Graeme H.; Rodgers, A. W.; Roberts, W. H.; Zucker, D. B.

    1994-01-01

    Spectroscopic observations of chromospheric transitions (Mg II, H-alpha, and Ca II K) from two red giants (A31 and A59) in the globular cluster NGC 6572 were made with the Goddard High Resolution Spectrograph on the Hubble Space Telescope and the coude spectrograph of the 1.9 m telescope at the Mount Stromlo Observatory. These measurements give evidence for chromospheric activity and outward motions within the atmospheres. The surface flux of the Mg II emission is comparable to that in disk population giants of similar (B-V) color. The Mg II profiles are asymmetric, which is most likely caused by absorption in an expanding stellar atmosphere and/or by possible interstellar features. Notches are found in the core of the H-alpha line of A59, which are similar to those found in Cepheids. This suggests that shocks are present in the atmosphere of A59 and indicates that hydrodynamic phenomena are influencing the levvel of chromospheric emission and producing upper atmospheric motions which may lead to mass loss.

  20. The X-Ray Globular Cluster Population in NGC 1399

    NASA Technical Reports Server (NTRS)

    Angelini, Lorella; Loewenstein, Michael; Mushotzky, Richard F.; White, Nicholas E. (Technical Monitor)

    2001-01-01

    We report on X-ray sources detected in the Chandra images of the elliptical galaxy NGC 1399 and identified with globular clusters (GCs). The 8'x 8' Chandra image shows that a large fraction of the 2-10 keV X-ray emission is resolved into point sources, with a luminosity threshold of 5 x 10 (exp 37) ergs s-1. These sources are most likely Low Mass X-ray Binaries (LMXBs). More than 70% of the X-ray sources, in a region imaged by Hubble Space Telescope (HST), are located within GCs. Many of these sources have super-Eddington luminosity (for an accreting neutron star) and their average luminosity is higher than the remaining sources. This association suggests that, in giant elliptical galaxies, luminous X-ray binaries preferentially form in GCs. The spectral properties of the GC and non-GC sources are in most cases similar to those of LMXBs in our galaxy. Two of the brightest sources, one of which is in GC, have a much softer spectra as seen in the high state black hole. The "apparent" super-Eddington luminosity in many cases may be due to multiple LMXB systems within individual GC, but with some of the most extreme luminous systems containing massive black holes.

  1. Parameters of radio pulsars in binary systems and globular clusters

    NASA Astrophysics Data System (ADS)

    Loginov, A. A.; Malov, I. F.

    2017-02-01

    The parameters of radio pulsars in binary systems and globular clusters are investigated. It is shown that such pulsars tend to have short periods (of the order of several milliseconds). Themagnetic fields of most of the pulsars considered are weak (surface fields of the order of 108-109 G). This corresponds to the generally accepted view that short-period neutron stars are spun up by angular momentum associated with the stellar wind from a companion. However, the fields at the light cylinders in these objects are two to three orders of magnitude higher than for the main population of single neutron stars. The dependence of the pulse width on the period does not differ from the corresponding dependences for single pulsars, assuming the emission is generated inside the polar cap, at moderate distances from the surface or near the light cylinder. The radio luminosities of pulsars in binary systems do not show the correlation with the rate of loss of rotational energy that is characteristic for single pulsars, probably due to the influence of accreting matter from a companion. Moreover, accretion apparently decreases the power of the emergent radiation, and can explain the observed systematic excess of the radio luminosity of single pulsars compared to pulsars in binary systems. The distributions and dependences presented in the article support generally accepted concepts concerning the processes occurring in binary systems containing neutron stars.

  2. Globular cluster abundance anomalies and the massive binary polluter scenario

    NASA Astrophysics Data System (ADS)

    Szécsi, Dorottya; González-Jímenez, Nicolas; Langer, Norbert

    2014-09-01

    Observations of globular cluster stars indicate that their material has been polluted with the nucleosynthetically processed matter of a previous generation of massive stars, but not with supernova products. The nature of the polluter is still being debated: either hot-bottom-burning AGB stars or rapidly rotating massive stars could be responsible, although both scenarios face major challenges to explain the observed abundance patterns and require fine-tuning of the most relevant parameters. An alternative scenario involves massive binary polluters: nucleosynthetically processed gas is expelled during highly non-conservative mass transfer in interacting massive binary systems. It has been shown that such systems could return enough material to form a chemically enriched second generation. However, for a detailed comparison of the chemical predictions of this scenario, binary models for a range of masses and orbital periods are needed. We have carried out detailed calculations of interacting massive binaries with various mass ratios and orbital periods. The evolution of these systems is presented. Constraints on the initial parameters are analyzed, observed abundances are compared to theoretical yields, and advantages and disadvantages of this scenario are discussed.

  3. Globular Clusters and Spur Clusters in NGC 4921, the Brightest Spiral Galaxy in the Coma Cluster

    NASA Astrophysics Data System (ADS)

    Lee, Myung Gyoon; Jang, In Sung

    2016-03-01

    We resolve a significant fraction of globular clusters (GCs) in NGC 4921, the brightest spiral galaxy in the Coma cluster. We also find a number of extended bright star clusters (star complexes) in the spur region of the arms. The latter are much brighter and bluer than those in the normal star-forming region, being as massive as 3 × 105 M⊙. The color distribution of the GCs in this galaxy is found to be bimodal. The turnover magnitudes of the luminosity functions of the blue (metal-poor) GCs (0.70 < (V - I) ≤ 1.05) in the halo are estimated V(max) = 27.11 ± 0.09 mag and I(max) = 26.21 ± 0.11 mag. We obtain similar values for NGC 4923, a companion S0 galaxy, and two Coma cD galaxies (NGC 4874 and NGC 4889). The mean value for the turnover magnitudes of these four galaxies is I(max) = 26.25 ± 0.03 mag. Adopting MI (max) = -8.56 ± 0.09 mag for the metal-poor GCs, we determine the mean distance to the four Coma galaxies to be 91 ± 4 Mpc. Combining this with the Coma radial velocity, we derive a value of the Hubble constant, H0 = 77.9 ± 3.6 km s-1 Mpc-1. We estimate the GC specific frequency of NGC 4921 to be SN = 1.29 ± 0.25, close to the values for early-type galaxies. This indicates that NGC 4921 is in the transition phase to S0s.

  4. PEERING INTO THE CORE OF A GLOBULAR CLUSTER

    NASA Technical Reports Server (NTRS)

    2002-01-01

    Astronomers have used NASA's Hubble Space Telescope to peer into the center of a dense swarm of stars called Omega Centauri. Located some 17,000 light-years from Earth, Omega Centauri is a massive globular star cluster, containing several million stars swirling in locked orbits around a common center of gravity. The stars are packed so densely in the cluster's core that it is difficult for ground-based telescopes to make out individual stars. Hubble's high resolution is able to pick up where ground-based telescopes leave off, capturing distinct points of light from stars at the very center of the cluster. Omega Centauri is so large in our sky that only a small part of it fits within the field of view of the Wide Field and Planetary Camera 2 (WFPC2) on the Hubble Space Telescope. Yet even this tiny patch contains some 50,000 stars, all packed into a region only about 13 light-years wide. For comparison, a similarly sized region centered on the Sun would contain about a half dozen stars. The vast majority of stars in this Hubble image are faint, yellow-white dwarf stars similar to our Sun. The handful of bright yellow-orange stars are red giants that have begun to exhaust their nuclear fuel and have expanded to diameters about a hundred times that of the Sun. A number of faint blue stars are also visible in the image. These are in a brief phase of evolution between the dwarf stage and the red-giant stage, during which the surface temperature is high. The stars in Omega Centauri are all very old, about 12 billion years. Stars with a mass as high as that of our Sun have already completed their evolution and have faded away as white dwarfs, too faint to be seen even in the Hubble image. The stars in the core of Omega Centauri are so densely packed that occasionally one of them will actually collide with another one. Even in the dense center of Omega Centauri, stellar collisions will be infrequent. But the cluster is so old that many thousands of collisions have occurred

  5. PEERING INTO THE CORE OF A GLOBULAR CLUSTER

    NASA Technical Reports Server (NTRS)

    2002-01-01

    Astronomers have used NASA's Hubble Space Telescope to peer into the center of a dense swarm of stars called Omega Centauri. Located some 17,000 light-years from Earth, Omega Centauri is a massive globular star cluster, containing several million stars swirling in locked orbits around a common center of gravity. The stars are packed so densely in the cluster's core that it is difficult for ground-based telescopes to make out individual stars. Hubble's high resolution is able to pick up where ground-based telescopes leave off, capturing distinct points of light from stars at the very center of the cluster. Omega Centauri is so large in our sky that only a small part of it fits within the field of view of the Wide Field and Planetary Camera 2 (WFPC2) on the Hubble Space Telescope. Yet even this tiny patch contains some 50,000 stars, all packed into a region only about 13 light-years wide. For comparison, a similarly sized region centered on the Sun would contain about a half dozen stars. The vast majority of stars in this Hubble image are faint, yellow-white dwarf stars similar to our Sun. The handful of bright yellow-orange stars are red giants that have begun to exhaust their nuclear fuel and have expanded to diameters about a hundred times that of the Sun. A number of faint blue stars are also visible in the image. These are in a brief phase of evolution between the dwarf stage and the red-giant stage, during which the surface temperature is high. The stars in Omega Centauri are all very old, about 12 billion years. Stars with a mass as high as that of our Sun have already completed their evolution and have faded away as white dwarfs, too faint to be seen even in the Hubble image. The stars in the core of Omega Centauri are so densely packed that occasionally one of them will actually collide with another one. Even in the dense center of Omega Centauri, stellar collisions will be infrequent. But the cluster is so old that many thousands of collisions have occurred

  6. The Stellar Populations of Nuclei, Globular Clusters, and Stars in dE Galaxies in Virgo and Fornax

    NASA Astrophysics Data System (ADS)

    Whitfield Miller, Bryan; Hyazinth Puzia, Thomas; Hilker, Michael; Sanchez-Janssen, Ruben; Kissler-Patig, Markus

    2015-08-01

    We present ages and metallicities for globular clusters, nuclei, and underlying stars in nucleated dwarf elliptical galaxies (dE,N) in the Virgo and Fornax Cluster based on Lick/IDS index measurements and SSP models. Gemini/GMOS spectroscopy shows that the globular clusters are mostly old and metal-poor, very similar to the globular clusters in the Milky Way halo. The nuclei and underlying stars tend to be more metal-rich than the globular clusters and have a wide range of ages. The [α/Fe] ratios for both the globular clusters and nuclei range between 0.0 and 0.3. Formation scenarios for globular clusters and nuclei will be discussed.

  7. GLOBULAR CLUSTER SYSTEMS IN BRIGHTEST CLUSTER GALAXIES: A NEAR-UNIVERSAL LUMINOSITY FUNCTION?

    SciTech Connect

    Harris, William E.; O'Halloran, Heather; Cockcroft, Robert E-mail: ohallohm@mcmaster.ca; and others

    2014-12-20

    We present the first results from our Hubble Space Telescope brightest cluster galaxy (BCG) survey of seven central supergiant cluster galaxies and their globular cluster (GC) systems. We measure a total of 48,000 GCs in all seven galaxies, representing the largest single GC database. We find that a log-normal shape accurately matches the observed the luminosity function (LF) of the GCs down to the globular cluster luminosity function turnover point, which is near our photometric limit. In addition, the LF has a virtually identical shape in all seven galaxies. Our data underscore the similarity in the formation mechanism of massive star clusters in diverse galactic environments. At the highest luminosities (L ≳ 10{sup 7} L {sub ☉}), we find small numbers of ''superluminous'' objects in five of the galaxies; their luminosity and color ranges are at least partly consistent with those of ultra-compact dwarfs. Last, we find preliminary evidence that in the outer halo (R ≳ 20 kpc), the LF turnover point shows a weak dependence on projected distance, scaling as L {sub 0} ∼ R {sup –0.2}, while the LF dispersion remains nearly constant.

  8. THE OBSERVATIONAL AND THEORETICAL TIDAL RADII OF GLOBULAR CLUSTERS IN M87

    SciTech Connect

    Webb, Jeremy J.; Sills, Alison; Harris, William E.

    2012-02-10

    Globular clusters have linear sizes (tidal radii) which theory tells us are determined by their masses and by the gravitational potential of their host galaxy. To explore the relationship between observed and expected radii, we utilize the globular cluster population of the Virgo giant M87. Unusually deep, high signal-to-noise images of M87 are used to measure the effective and limiting radii of approximately 2000 globular clusters. To compare with these observations, we simulate a globular cluster population that has the same characteristics as the observed M87 cluster population. Placing these simulated clusters in the well-studied tidal field of M87, the orbit of each cluster is solved and the theoretical tidal radius of each cluster is determined. We compare the predicted relationship between cluster size and projected galactocentric distance to observations. We find that for an isotropic distribution of cluster velocities, theoretical tidal radii are approximately equal to observed limiting radii for R{sub gc} < 10 kpc. However, the isotropic simulation predicts a steep increase in cluster size at larger radii, which is not observed in large galaxies beyond the Milky Way. To minimize the discrepancy between theory and observations, we explore the effects of orbital anisotropy on cluster sizes, and suggest a possible orbital anisotropy profile for M87 which yields a better match between theory and observations. Finally, we suggest future studies which will establish a stronger link between theoretical tidal radii and observed radii.

  9. THE RICH GLOBULAR CLUSTER SYSTEM OF ABELL 1689 AND THE RADIAL DEPENDENCE OF THE GLOBULAR CLUSTER FORMATION EFFICIENCY

    SciTech Connect

    Alamo-Martínez, K. A.; González-Lópezlira, R. A.; Blakeslee, J. P.; Côté, P.; Ferrarese, L.; Jee, M. J.; Jordán, A.; Meurer, G. R.; Peng, E. W.; West, M. J.

    2013-09-20

    We study the rich globular cluster (GC) system in the center of the massive cluster of galaxies Abell 1689 (z = 0.18), one of the most powerful gravitational lenses known. With 28 Hubble Space Telescope/Advanced Camera for Surveys orbits in the F814W bandpass, we reach a magnitude I{sub 814} = 29 with ∼>90% completeness and sample the brightest ∼5% of the GC system. Assuming the well-known Gaussian form of the GC luminosity function (GCLF), we estimate a total population of N{sup total}{sub GC}= 162,850{sup +75,450}{sub -51,310} GCs within a projected radius of 400 kpc. As many as half of the GCs may comprise an intracluster component. Even with the sizable uncertainties, which mainly result from the uncertain GCLF parameters, this system is by far the largest GC population studied to date. The specific frequency S{sub N} is high, but not uncommon for central galaxies in massive clusters, rising from S{sub N} ≈ 5 near the center to ∼12 at large radii. Passive galaxy fading would increase S{sub N} by ∼20% at z = 0. We construct the radial mass profiles of the GCs, stars, intracluster gas, and lensing-derived total mass, and we compare the mass fractions as a function of radius. The estimated mass in GCs, M{sub GC}{sup total} = 3.9 × 10{sup 10} M{sub ☉}, is comparable to ∼80% of the total stellar mass of the Milky Way. The shape of the GC mass profile appears intermediate between those of the stellar light and total cluster mass. Despite the extreme nature of this system, the ratios of the GC mass to the baryonic and total masses, and thus the GC formation efficiency, are typical of those in other rich clusters when comparing at the same physical radii. The GC formation efficiency is not constant, but varies with radius, in a manner that appears similar for different clusters; we speculate on the reasons for this similarity in profile.

  10. GALEX Grism Spectroscopy of the Globular Cluster Omega Centauri

    NASA Astrophysics Data System (ADS)

    Sweigart, Allen

    We propose to obtain GALEX FUV-only grism spectroscopy of the hot stars in omega Centauri, the most massive globular cluster in our Galaxy. Previous UIT imagery of omega Cen showed that it contains about 2000 hot horizontal branch (HB) stars, and we estimate that GALEX spectra can be obtained for about 500 of these stars in the outer regions of the cluster, including about 50 of the hot ``blue hook'' stars discovered with UIT. The blue hook stars appear to be both hotter (35,000 K) and less luminous in the UIT color-magnitude diagram than predicted by canonical HB models and, indeed, are unexplained by standard evolutionary theory. Brown et al. (2001) have suggested that the blue hook stars are the progeny of stars which mixed their surface hydrogen into their hot He-burning interior during a delayed helium flash subsequent to leaving the red giant branch. This ``flash-mixing'' results in a hot hydrogen-deficient star with a typical surface abundance of 96% He and 4% C by mass. The GALEX spectral region includes the strong lines of C III 1426, 1578 A, C IV 1550 A, and He II 1640 A which will allow this predicted carbon and helium enrichment to be detected. These observations will therefore provide a crucial test of the Brown et al. flash-mixing hypothesis and will determine if flash mixing represents a new evolutionary channel for populating the hot HB. The GALEX spectra will also address other questions concerning the hot HB in omega Cen including (1) the metallicity distribution of HB stars with 9,000 K < Teff < 11,000 K, (2) the effect of radiative levitation on the UV spectra of stars with Teff > 11,000 K, and (3) the origin of the subluminous HB stars found in the UIT photometry with 15,000K < Teff < 30,000 K.

  11. The origin of discrete multiple stellar populations in globular clusters

    NASA Astrophysics Data System (ADS)

    Bekki, K.; Jeřábková, T.; Kroupa, P.

    2017-10-01

    Recent observations have revealed that at least several old globular clusters (GCs) in the Galaxy have discrete distributions of stars along the Mg-Al anticorrelation. In order to discuss this recent observation, we construct a new one-zone GC formation model in which the maximum stellar mass (mmax) in the initial mass function of stars in a forming GC depends on the star formation rate, as deduced from independent observations. We investigate the star formation histories of forming GCs. The principal results are as follows. About 30 Myr after the formation of the first generation (1G) of stars within a particular GC, new stars can be formed from ejecta from asymptotic giant branch (AGB) stars of 1G. However, the formation of this second generation (2G) of stars can last only for [10-20] Myr because the most massive SNe of 2G expel all of the remaining gas. The third generation (3G) of stars are then formed from AGB ejecta ≈30 Myr after the truncation of 2G star formation. This cycle of star formation followed by its truncation by SNe can continue until all AGB ejecta is removed from the GC by some physical process. Thus, it is inevitable that GCs have discrete multiple stellar populations in the [Mg/Fe]-[Al/Fe] diagram. Our model predicts that low-mass GCs are unlikely to have discrete multiple stellar populations, and young massive clusters may not have massive OB stars owing to low mmax (<[20-30] M⊙) during the secondary star formation.

  12. Globular Clusters Indicate That Ultra-diffuse Galaxies Are Dwarfs

    NASA Astrophysics Data System (ADS)

    Beasley, Michael A.; Trujillo, Ignacio

    2016-10-01

    We present an analysis of archival HST/ACS imaging in the F475W (g 475), F606W (V 606), and F814W (I 814) bands of the globular cluster (GC) system of a large (3.4 kpc effective radius) ultra-diffuse galaxy (DF17) believed to be located in the Coma Cluster of galaxies. We detect 11 GCs down to the 5σ completeness limit of the imaging (I 814 = 27 mag). Correcting for background and our detection limits yields a total population of GCs in this galaxy of 27 ± 5 and a V-band specific frequency S N = 28 ± 5. Based on comparisons to the GC systems of local galaxies, we show that both the absolute number and the colors of the GC system of DF17 are consistent with the GC system of a dark-matter-dominated dwarf galaxy with virial mass ˜9.0 × 1010 M ⊙ and a dark-to-stellar mass ratio M vir/M star ˜ 1000. Based on the stellar mass growth of the Milky Way, we show that DF17 cannot be understood as a failed Milky-Way-like system, but is more similar to quenched Large-Magellanic-Cloud-like systems. We find that the mean color of the GC population, g 475-I 814 = 0.91 ± 0.05 mag, coincides with the peak of the color distribution of intracluster GCs and is also similar to those of the blue GCs in the outer regions of massive galaxies. We suggest that both the intracluster GC population in Coma and the blue peak in the GC populations of massive galaxies may be fed—at least in part—by the disrupted equivalents of systems such as DF17.

  13. 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.

  14. An updated survey of globular clusters in M 31. II. Newly discovered bright and remote clusters

    NASA Astrophysics Data System (ADS)

    Galleti, S.; Bellazzini, M.; Federici, L.; Buzzoni, A.; Fusi Pecci, F.

    2007-08-01

    Aims:We present the first results of a large spectroscopic survey of candidate globular clusters located in the extreme outskirts of the nearby M 31 galaxy. The survey is aimed at ascertaining the nature of the selected candidates to increase the sample of confirmed M 31 clusters lying more that 2° away from the center of the galaxy. Methods: We obtained low resolution spectra (λ/Δλ ≃ 800-1300) of 48 targets selected from the Extended Source Catalogue of 2MASS, as in Galleti et al. (2005, A&A, 436, 535). The observed candidates have been robustly classified according to their radial velocity and by verifying their extended/point-source nature from ground-based optical images. We have also obtained a spectrum and a radial velocity estimate for the remote M 31 globular discovered by Martin et al. (2006b, MNRAS, 371, 1983). Results: Among the 48 observed candidates clusters we found: 35 background galaxies, 8 foreground Galactic stars, and 5 genuine remote globular clusters. One of them has been already identified independently by Mackey et al. (2007, ApJ, 655, L85), their GC1; the other four are completely new discoveries: B516, B517, B518, B519. The newly discovered clusters lie at projected distance 40 kpc ≲ R_p≲ 100 kpc from the center of M 31, and have absolute integrated magnitude -9.5 ≲ MV ≲ -7.5. For all the observed clusters we have measured the strongest Lick indices and we have obtained spectroscopic metallicity estimates. Mackey-GC1, Martin-GC1, B517 and B518 have spectra typical of old and metal poor globular clusters ([Fe/H] ≲ -1.3); B519 appears old but quite metal-rich ([Fe/H]~≃ -0.5); B516 presents very strong Balmer absorption lines: if this is indeed a cluster it should have a relatively young age (likely < 2 Gyr). Conclusions: The present analysis nearly doubles the number of M 31 globulars at R_p≥ 40 kpc. At odds with the Milky Way, M 31 appears to have a significant population of very bright globular clusters in its extreme

  15. Mass evaporation rate of globular clusters in a strong tidal field

    NASA Astrophysics Data System (ADS)

    Madrid, Juan P.; Leigh, Nathan W. C.; Hurley, Jarrod R.; Giersz, Mirek

    2017-09-01

    The mass evaporation rate of globular clusters evolving in a strong Galactic tidal field is derived through the analysis of large, multimass N-body simulations. For comparison, we also study the same evaporation rates using mocca Monte Carlo models for globular cluster evolution. Our results show that the mass evaporation rate is a dynamical value, that is, far from a constant single number found in earlier analytical work and commonly used in the literature. Moreover, the evaporation rate derived with these simulations is higher than values previously published. These models also show that the value of the mass evaporation rate depends on the strength of the tidal field. We give an analytical estimate of the mass evaporation rate as a function of time and galactocentric distance ξ(RGC, t). Upon extrapolating this formula to smaller RGC values, our results provide tentative evidence for a very high ξ value at small RGC. Our results suggest that the corresponding mass-loss in the inner Galactic potential could be high and it should be accounted for when star clusters pass within it. This has direct relevance to nuclear cluster formation/growth via the infall of globular clusters through dynamical friction. As an illustrative example, we estimate how the evaporation rate increases for an ∼105 M⊙ globular cluster that decays through dynamical friction into the Galactic Centre. We discuss the findings of this work in relation to the formation of nuclear star clusters by inspiralling globular clusters.

  16. Bayesian Analysis and Characterization of Multiple Populations in Galactic Globular Clusters

    NASA Astrophysics Data System (ADS)

    Wagner-Kaiser, Rachel A.; Stenning, David; Sarajedini, Ata; von Hippel, Ted; van Dyk, David A.; Robinson, Elliot; Stein, Nathan; Jefferys, William H.; BASE-9, HST UVIS Globular Cluster Treasury Program

    2017-01-01

    Globular clusters have long been important tools to unlock the early history of galaxies. Thus, it is crucial we understand the formation and characteristics of the globular clusters (GCs) themselves. Historically, GCs were thought to be simple and largely homogeneous populations, formed via collapse of a single molecular cloud. However, this classical view has been overwhelmingly invalidated by recent work. It is now clear that the vast majority of globular clusters in our Galaxy host two or more chemically distinct populations of stars, with variations in helium and light elements at discrete abundance levels. No coherent story has arisen that is able to fully explain the formation of multiple populations in globular clusters nor the mechanisms that drive stochastic variations from cluster to cluster.We use Cycle 21 Hubble Space Telescope (HST) observations and HST archival ACS Treasury observations of 30 Galactic Globular Clusters to characterize two distinct stellar populations. A sophisticated Bayesian technique is employed to simultaneously sample the joint posterior distribution of age, distance, and extinction for each cluster, as well as unique helium values for two populations within each cluster and the relative proportion of those populations. We find the helium differences among the two populations in the clusters fall in the range of 0.04 to 0.11. Because adequate models varying in CNO are not presently available, we view these spreads as upper limits and present them with statistical rather than observational uncertainties. Evidence supports previous studies suggesting an increase in helium content concurrent with increasing mass of the cluster. We also find that the proportion of the first population of stars increases with mass. Our results are examined in the context of proposed globular cluster formation scenarios.

  17. Study of globular cluster M53: new variables, distance, metallicity

    NASA Astrophysics Data System (ADS)

    Dékány, I.; Kovács, G.

    2009-11-01

    Aims: We study the variable star content of the globular cluster M53 to compute the physical parameters of the constituting stars and the distance of the cluster. Methods: Covering two adjacent seasons in 2007 and 2008, new photometric data are gathered for 3048 objects in the field of M53. By using the OIS (optimal image subtraction) method and subsequently TFA (trend filtering algorithm), we search for variables in the full sample by using discrete Fourier transformation and box-fitting least squares methods. We select variables based on the statistics related to these methods combined with visual inspection. Results: We identified 12 new variables (2 RR Lyrae stars, 7 short periodic stars - 3 of them are SX Phe stars - and 3 long-period variables). No eclipsing binaries were found in the present sample. Except for the 3 (hitherto unknown) Blazhko RR Lyrae (two RRab and an RRc) stars, no multiperiodic variables were found. We showed that after proper period shift, the PLC (period-luminosity-color) relation for the first overtone RR Lyrae sample tightly follows the one spanned by the fundamental stars. Furthermore, the slope is in agreement with that derived from other clusters. Based on the earlier Baade-Wesselink calibration of the PLC relations, the derived reddening-free distance modulus of M53 is 16.31±0.04 mag, corresponding to a distance modulus of 18.5 mag for the Large Magellanic Cloud. From the Fourier parameters of the RRab stars we obtained an average iron abundance of -1.58± 0.03 (error of the mean). This is ~0.5 dex higher than the overall abundance of the giants as given in the literature and derived in this paper from the three-color photometry of giants. We suspect that the source of this discrepancy (observable also in other, low-metallicity clusters) is the lack of a sufficient number of low-metallicity objects in the calibrating sample of the Fourier method. Table 1 is only available in electronic form at http://www.aanda.org Photometric data

  18. On the Absolute Age of the Globular Cluster M92

    NASA Astrophysics Data System (ADS)

    Di Cecco, A.; Becucci, R.; Bono, G.; Monelli, M.; Stetson, P. B.; Degl’Innocenti, S.; Prada Moroni, P. G.; Nonino, M.; Weiss, A.; Buonanno, R.; Calamida, A.; Caputo, F.; Corsi, C. E.; Ferraro, I.; Iannicola, G.; Pulone, L.; Romaniello, M.; Walker, A. R.

    2010-09-01

    We present precise and deep optical photometry of the globular M92. Data were collected in three different photometric systems: Sloan Digital Sky Survey (g‧, r‧, i‧, and z‧ MegaCam at CFHT), Johnson-Kron-Cousins (B, V, and I; various ground-based telescopes), and Advanced Camera for Surveys (ACS) Vegamag (F475W, F555W, and F814W; Hubble Space Telescope). Special attention was given to the photometric calibration, and the precision of the ground-based data is generally better than 0.01 mag. We computed a new set of α-enhanced evolutionary models accounting for the gravitational settling of heavy elements at fixed chemical composition ([α/Fe] = +0.3, [Fe/H] = -2.32 dex, and Y = 0.248). The isochrones—assuming the same true distance modulus (μ = 14.74 mag), the same reddening [E(B - V) = 0.025 ± 0.010 mag], and the same reddening law—account for the stellar distribution along the main sequence and the red giant branch in different color-magnitude diagrams (i‧, g‧ - i‧ i‧, and g‧ - r‧ i‧, g‧ - z‧ I, and B - I and F814W and F475W–F814W). The same outcome applies to the comparison between the predicted zero-age horizontal-branch (ZAHB) and the HB stars. We also found a cluster age of 11 ± 1.5 Gyr, in good agreement with previous estimates. The error budget accounts for uncertainties in the input physics and the photometry. To test the possible occurrence of CNO-enhanced stars, we also computed two sets of α- and CNO-enhanced (by a factor of 3) models, both at fixed total metallicity ([M/H] = -2.10 dex) and at fixed iron abundance. We found that the isochrones based on the former set give the same cluster age (11 ± 1.5 Gyr) as the canonical α-enhanced isochrones. The isochrones based on the latter set also give a similar cluster age (10 ± 1.5 Gyr). These findings support previous results concerning the weak sensitivity of cluster isochrones to CNO-enhanced chemical mixtures. This paper makes use of data obtained from the Isaac

  19. Evidence for an Accretion Origin for the Outer Halo Globular Cluster System of M31

    NASA Astrophysics Data System (ADS)

    Mackey, A. D.; Huxor, A. P.; Ferguson, A. M. N.; Irwin, M. J.; Tanvir, N. R.; McConnachie, A. W.; Ibata, R. A.; Chapman, S. C.; Lewis, G. F.

    2010-07-01

    We use a sample of newly discovered globular clusters from the Pan-Andromeda Archaeological Survey (PAndAS) in combination with previously cataloged objects to map the spatial distribution of globular clusters in the M31 halo. At projected radii beyond ≈30 kpc, where large coherent stellar streams are readily distinguished in the field, there is a striking correlation between these features and the positions of the globular clusters. Adopting a simple Monte Carlo approach, we test the significance of this association by computing the probability that it could be due to the chance alignment of globular clusters smoothly distributed in the M31 halo. We find that the likelihood of this possibility is low, below 1%, and conclude that the observed spatial coincidence between globular clusters and multiple tidal debris streams in the outer halo of M31 reflects a genuine physical association. Our results imply that the majority of the remote globular cluster system of M31 has been assembled as a consequence of the accretion of cluster-bearing satellite galaxies. This constitutes the most direct evidence to date that the outer halo globular cluster populations in some galaxies are largely accreted. Based on observations obtained with MegaPrime/MegaCam, a joint project of CFHT and CEA/DAPNIA, at the Canada-France-Hawaii Telescope (CFHT) which is operated by the National Research Council (NRC) of Canada, the Institut National des Science de l'Univers of the Centre National de la Recherche Scientifique (CNRS) of France, and the University of Hawaii.

  20. Globular Clusters at the Centre of the Fornax Cluster: Tracing Interactions Between Galaxies

    NASA Astrophysics Data System (ADS)

    Bassino, Lilia P.; Richtler, Tom; Faifer, Favio R.; Forte, Juan C.; Dirsch, Boris; Geisler, Doug; Schuberth, Ylva

    We present the combined results of two investigations: a large-scale study of the globular cluster system (GCS) around NGC 1399, the central galaxy of the Fornax cluster, and a study of the GCSs around NGC 1374, NGC 1379 and NGC 1387, three low-luminosity early-type galaxies located close to the centre of the same cluster. In both cases, the data consist of images from the wide-field MOSAIC Imager of the CTIO 4-m telescope, obtained with Washington C and Kron-Cousins R filters, which provide good metallicity resolution. The colour distributions and radial projected densities of the GCSs are analyzed. We focus on the properties of the GCSs that trace possible interaction processes between the galaxies, such as tidal stripping of globular clusters (GCs). For the blue GCs, we find tails between NGC 1399 and neighbouring galaxies in the azimuthal projected distribution, and the three low-luminosity galaxies show low specific frequencies and a low proportion of blue GCs.

  1. Multiple Populations in M31 Globular Clusters: Clues from Infrared High Resolution Integrated Light Spectroscopy

    NASA Astrophysics Data System (ADS)

    Sakari, Charli; APOGEE Team

    2017-01-01

    Abundance variations are a common feature of Milky Way globular clusters. The globular clusters in M31 are too distant for detailed abundance studies of their individual stars; however, cluster abundances can be determined through high resolution, integrated light (IL) spectroscopy. In this talk, I discuss how IL abundances can be interpreted in the context of multiple populations. In particular, I will present new infrared abudances of 25 M31 globular clusters, derived from IL spectra from the Apache Point Observatory Galactic Evolution Experiment (APOGEE). These H band spectra allow determinations of C, N, and O from molecular features, and Fe, Na, Mg, Al, Si, Ca, Ti, and K from atomic features. The integrated abundance ratios are then investigated with cluster [Fe/H] and mass.

  2. Bright Stars and Metallicity Spread in the Globular Cluster omega Centauri

    NASA Astrophysics Data System (ADS)

    Ortolani, Sergio; Covino, Stefano; Carraro, Giovanni

    The globular cluster omega Centauri (NGC~5139) is the most massive and brightest cluster in our Galaxy. It has also a moderately high mass to light ratio (3.6) and an anomalous flattening (0.83) for a globular cluster. This cluster is also very interesting because it is one of a few examples of globular clusters with a measurable spread in the metal abundance (see Da Costa & Willumsen 1981, Norris et al. 1996, and Suntzeff and Kraft 1996 and references therein) and then it offers a unique, big sample of nearby stars having all the same distance and reddening but showing different metallicity (and age ?) effects. A recent paper by Norris et al. (1997) shows also an interesting correlation between kinematics and metal abundance.

  3. Evolution of X-ray Binary Populations of Globular Clusters: A Boltzmann study

    NASA Astrophysics Data System (ADS)

    Ghosh, Pranab; Banerjee, S.

    2008-03-01

    We present a Boltzmann scheme for studying evolution of compact-binary populations of globular clusters, including dynamical formation and destruction processes, and binary hardening processes. For those processes which are stochastic (e.g., tidal formation, collisional destruction, and collisional hardening), we study the continuous limit first. We then introduce our stochastic model, showing that the continuous limit is an excellent representation of the average of many "realizations" of stochastic processes. We explore the scaling of the number of X-ray binaries in a globular cluster with two essential cluster parameters measuring star-star and star-binary encounter rates, which we call Verbunt parameters. We show that our computed scalings are in good agreement with CHANDRA data on Galactic globular cluster X-ray binaries. We discuss ways of extending our scheme, and of handling evolution of the cluster background.

  4. Collisions of Free-floating Planets with Evolved Stars in Globular Clusters

    NASA Astrophysics Data System (ADS)

    Soker, Noam; Rappaport, Saul; Fregeau, John

    2001-12-01

    We estimate the rate of collisions between stars and free-floating planets (FFPs) in globular clusters, in particular, the collision of FFPs with red giant branch (RGB) stars. Recent dynamical simulations imply that the density of such objects could exceed ~106 pc-3 near the cores of rich globular clusters. We show that in these clusters ~5%-10% of all RGB stars near the core would suffer a collision with an FFP and that such a collision can spin up the RGB star's envelope by an order of magnitude. In turn, the higher rotation rates may lead to enhanced mass-loss rates on the RGB, which could result in bluer horizontal branch (HB) stars. Hence, it is plausible that the presence of a large population of FFPs in a globular cluster can influence the distribution of stars on the HB of that cluster to a detectable degree.

  5. ON THE BIRTH MASSES OF THE ANCIENT GLOBULAR CLUSTERS

    SciTech Connect

    Conroy, Charlie

    2012-10-10

    All globular clusters (GCs) studied to date show evidence for internal (star-to-star) variation in their light-element abundances (including Li, C, N, O, F, Na, Mg, Al, and probably He). These variations have been interpreted as evidence for multiple star formation episodes within GCs, with secondary episodes fueled, at least in part, by the ejecta of asymptotic giant branch (AGB) stars from a first generation of stars. A major puzzle emerging from this otherwise plausible scenario is that the fraction of stars associated with the second episode of star formation is observed to be much larger than expected for a standard initial mass function. The present work investigates this tension by modeling the observed anti-correlation between [Na/Fe] and [O/Fe] for 20 Galactic GCs. If the abundance pattern of the retained AGB ejecta does not depend on GC mass at fixed [Fe/H], then a strong correlation is found between the fraction of current GC stellar mass composed of pure AGB ejecta, f{sub p} , and GC mass. This fraction varies from 0.20 at low masses (10{sup 4.5} M{sub Sun }) to 0.45 at high masses (10{sup 6.5} M{sub Sun }). The fraction of mass associated with pure AGB ejecta is directly related to the total mass of the cluster at birth; the ratio between the initial and present mass in stars can therefore be derived. Assuming a star formation efficiency of 50%, the observed Na-O anti-correlations imply that GCs were at least 10-20 times more massive at birth, a conclusion that is in qualitative agreement with previous work. These factors are lower limits because any mass-loss mechanism that removes first- and second-generation stars equally will leave f{sub p} unchanged. The mass dependence of f{sub p} probably arises because lower mass GCs are unable to retain all of the AGB ejecta from the first stellar generation. Recent observations of elemental abundances in intermediate-age Large Magellanic Cloud clusters are re-interpreted and shown to be consistent with this

  6. Competition of supermassive black holes and galactic spheroids in the destruction of globular clusters

    NASA Technical Reports Server (NTRS)

    Charlton, Jane C.; Laguna, Pablo

    1995-01-01

    The globular clusters that we observe in galaxies may be only a fraction of the initial population. Among the evolutionary influences on the population is the destruction of globular clusters by tidal forces as the cluster moves through the field of influence of a disk, a bulge, and/or a putative nuclear component (black hole). We have conducted a series of N-body simulations of globular clusters on bound and marginally bound orbits through poetentials that include black hole and speroidal components. The degree of concentration of the spheroidal component can have a considerable impact on the extent to which a globular cluster is disrupted. If half the mass of a 10(exp 10) solar mass spheroid is concentrated within 800 pc, then only black holes with masses greater than 10(exp 9) solar mass can have a significant tidal influence over that already exerted by the bulge. However, if the matter in the spheroidal component is not so strongly concentrated toward the center of the galaxy, a more modest central black hole (down to 10(exp 8) solar mass) could have a dominant influence on the globular cluster distribution, particularly if many of the clusters were initially on highly radial orbits. Our simulations show that the stars that are stripped from a globular cluster follow orbits with roughly the same eccentricity as the initial cluster orbit, spreading out along the orbit like a 'string of pearls.' Since only clusters on close to radial orbits will suffer substantial disruption, the population of stripped stars will be on orbits of high eccentricity.

  7. 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.

  8. INITIAL SIZE DISTRIBUTION OF THE GALACTIC GLOBULAR CLUSTER SYSTEM

    SciTech Connect

    Shin, Jihye; Kim, Sungsoo S.; Yoon, Suk-Jin; Kim, Juhan

    2013-01-10

    Despite the importance of their size evolution in understanding the dynamical evolution of globular clusters (GCs) of the Milky Way, studies that focus specifically on this issue are rare. Based on the advanced, realistic Fokker-Planck (FP) approach, we theoretically predict the initial size distribution (SD) of the Galactic GCs along with their initial mass function and radial distribution. Over one thousand FP calculations in a wide parameter space have pinpointed the best-fit initial conditions for the SD, mass function, and radial distribution. Our best-fit model shows that the initial SD of the Galactic GCs is of larger dispersion than today's SD, and that the typical projected half-light radius of the initial GCs is {approx}4.6 pc, which is 1.8 times larger than that of the present-day GCs ({approx}2.5 pc). Their large size signifies greater susceptibility to the Galactic tides: the total mass of destroyed GCs reaches 3-5 Multiplication-Sign 10{sup 8} M {sub Sun }, several times larger than previous estimates. Our result challenges a recent view that the Milky Way GCs were born compact on the sub-pc scale, and rather implies that (1) the initial GCs were generally larger than the typical size of the present-day GCs, (2) the initially large GCs mostly shrank and/or disrupted as a result of the galactic tides, and (3) the initially small GCs expanded by two-body relaxation, and later shrank by the galactic tides.

  9. Far-ultraviolet photometry of the globular cluster omega Cen

    NASA Technical Reports Server (NTRS)

    Whitney, Jonathan H.; O'Connell, Robert W.; Rood, Robert T.; Dorman, Ben; Landsman, Wayne B.; Cheng, K.-P.; Bohlin, Ralph C.; Hintzen, Paul M. N.; Roberts, Morton S.; Smith, Andrew M.

    1994-01-01

    We present far-ultraviolet images of the globular cluster omega Centauri obtained with the Ultraviolet Imaging Telescope (UIT) during the 1990 December Astro-1 mission. A total of 1957 sources are detected at 1620 A to a limiting ultraviolet (UV) magnitude of 16.4 in the central 24 min diameter region of the field and a limit of 15.6 over the remainder of the 40 min diameter field. Over 1400 of these sources are matched with stars on a Stroemgren u band charge coupled devices (CCD) frame obtained with the Cerro Tololo Inter-American Observatory (CTIO) 0.9 m telescope to produce a (far-UV, u) color-magnitude diagram (CMD). Completeness of the sample and error estimates are determined by photometry of artificial stars added to the images. The horizontal branch (HB) of the CMD is heavily populated hotter than 9000 K. A large number of 'extreme HB' stars are found hotter than a conspicuous break in the HB at T(sub e) approximately 16000 K. There is also a significant population of stars above the HB, the brightest of which is 4 mag brighter than the HB. Most of the hotter of these appear to be 'AGB-manque' or 'Post-Early Asymptotic Giant Branch' stars. We compare the observations to recent theoretical evolutionary tracks for the zero-age HB and subsequent phases. The tracks match the data well, with the exception of the hotter HB stars, many of which fall below the zero-age horizontal branch. It is unclear as yet whether these are a special population or an artifact of errors in the models or photometry. We identify 33 stars with T(sub e) greater than or approximately = 50000 K, which are hotter than zero-age HB stars with envelope masses of 0.003 solar mass.

  10. Far-ultraviolet photometry of the globular cluster omega Cen

    NASA Technical Reports Server (NTRS)

    Whitney, Jonathan H.; O'Connell, Robert W.; Rood, Robert T.; Dorman, Ben; Landsman, Wayne B.; Cheng, K.-P.; Bohlin, Ralph C.; Hintzen, Paul M. N.; Roberts, Morton S.; Smith, Andrew M.

    1994-01-01

    We present far-ultraviolet images of the globular cluster omega Centauri obtained with the Ultraviolet Imaging Telescope (UIT) during the 1990 December Astro-1 mission. A total of 1957 sources are detected at 1620 A to a limiting ultraviolet (UV) magnitude of 16.4 in the central 24 min diameter region of the field and a limit of 15.6 over the remainder of the 40 min diameter field. Over 1400 of these sources are matched with stars on a Stroemgren u band charge coupled devices (CCD) frame obtained with the Cerro Tololo Inter-American Observatory (CTIO) 0.9 m telescope to produce a (far-UV, u) color-magnitude diagram (CMD). Completeness of the sample and error estimates are determined by photometry of artificial stars added to the images. The horizontal branch (HB) of the CMD is heavily populated hotter than 9000 K. A large number of 'extreme HB' stars are found hotter than a conspicuous break in the HB at T(sub e) approximately 16000 K. There is also a significant population of stars above the HB, the brightest of which is 4 mag brighter than the HB. Most of the hotter of these appear to be 'AGB-manque' or 'Post-Early Asymptotic Giant Branch' stars. We compare the observations to recent theoretical evolutionary tracks for the zero-age HB and subsequent phases. The tracks match the data well, with the exception of the hotter HB stars, many of which fall below the zero-age horizontal branch. It is unclear as yet whether these are a special population or an artifact of errors in the models or photometry. We identify 33 stars with T(sub e) greater than or approximately = 50000 K, which are hotter than zero-age HB stars with envelope masses of 0.003 solar mass.

  11. Photometric and kinematic studies of extragalactic globular cluster systems

    NASA Astrophysics Data System (ADS)

    Dowell, Jessica

    Globular clusters (GCs) are old, luminous, compact collections of stars found in galaxy halos that formed during the early stages of galaxy formation. Because of this, GCs serve as excellent tracers of the formation, structure, and merger history of their host galaxies. My dissertation will examine both the photometric and kinematic properties of GC systems and their relationship to their host galaxies. In the first section, I will present the analysis of the GC systems of two spiral galaxies, NGC 891 and NGC 1055. I will discuss the photometric methods used to detect GCs using wide-field BVR imaging and to quantify the global properties of the system such as the total number of GCs and their radial distribution. My results for these two GC systems were compared to those of other galaxies. I will also present the results of spectroscopic follow-up for two giant galaxies: the S0 galaxy NGC 4594 (M104), and the elliptical galaxy NGC 3379 (M105). I measured the radial velocities of GCs in these two galaxies, and combined them with published results to determine the mass distribution and mass-to-light (M/L) ratio profile for each galaxy out to large effective radius (7-9 Re). For both galaxies, I found that the M/L profiles increase with radius and do not flatten, which suggests that the dark matter halos in these galaxies extend to the edge of my data. I also looked for evidence of rotation in the GC systems, and found that neither system exhibits significant rotation around the host galaxy. I examined the velocity dispersion profile of each GC system and found kinematic differences between the red and blue GC subpopulations. Finally, I compared my results to mass estimates for these galaxies from other kinematic tracers and considered them in the context of galaxy formation models.

  12. MANGANESE ABUNDANCES IN THE GLOBULAR CLUSTER {omega} CENTAURI

    SciTech Connect

    Cunha, Katia; Smith, Verne V.; Bergemann, Maria; Suntzeff, Nicholas B.; Lambert, David L.

    2010-07-01

    We present manganese abundances in 10 red giant members of the globular cluster {omega} Centauri; eight stars are from the most metal-poor population (RGB MP and RGB MInt1) while two targets are members of the more metal-rich groups (RGB MInt2 and MInt3). This is the first time Mn abundances have been studied in this peculiar stellar system. The LTE values of [Mn/Fe] in {omega} Cen overlap those of Milky Way stars in the metal-poor {omega} Cen populations ([Fe/H] {approx}-1.5 to -1.8), however unlike what is observed in Milky Way halo and disk stars, [Mn/Fe] declines in the two more metal-rich RGB MInt2 and MInt3 targets. Non-LTE calculations were carried out in order to derive corrections to the LTE Mn abundances. The non-LTE results for {omega} Cen in comparison with the non-LTE [Mn/Fe] versus [Fe/H] trend obtained for the Milky Way confirm and strengthen the conclusion that the manganese behavior in {omega} Cen is distinct. These results suggest that low-metallicity supernovae (with metallicities {<=} -2) of either Type II or Type Ia dominated the enrichment of the more metal-rich stars in {omega} Cen. The dominance of low-metallicity stars in the chemical evolution of {omega} Cen has been noted previously in the s-process elements where enrichment from metal-poor asymptotic giant branch stars is indicated. In addition, copper, which also has metallicity-dependent yields, exhibits lower values of [Cu/Fe] in the RGB MInt2 and MInt3 {omega} Cen populations.

  13. Abundance analysis of the outer halo globular cluster Palomar 14

    NASA Astrophysics Data System (ADS)

    Çalışkan, Ş.; Christlieb, N.; Grebel, E. K.

    2012-01-01

    We determine the elemental abundances of nine red giant stars belonging to Palomar 14 (Pal 14). Pal 14 is an outer halo globular cluster (GC) at a distance of ~70 kpc. Our abundance analysis is based on high-resolution spectra and one-dimensional stellar model atmospheres. We derived the abundances for the iron peak elements Sc, V, Cr, Mn, Co, Ni, the α-elements O, Mg, Si, Ca, Ti, the light odd element Na, and the neutron-capture elements Y, Zr, Ba, La, Ce, Nd, Eu, Dy, and Cu. Our data do not permit us to investigate light element (i.e., O to Mg) abundance variations. The neutron-capture elements show an r-process signature. We compare our measurements with the abundance ratios of inner and other outer halo GCs, halo field stars, GCs of recognized extragalactic origin, and stars in dwarf spheroidal galaxies (dSphs). The abundance pattern of Pal 14 is almost identical to those of Pal 3 and Pal 4, the next distant members of the outer halo GC population after Pal 14. The abundance pattern of Pal 14 is also similar to those of the inner halo GCs, halo field stars, and GCs of recognized extragalactic origin, but differs from what is customarily found in dSphs field stars. The abundance properties of Pal 14, as well as those of the other outer halo GCs, are thus compatible with an accretion origin from dSphs. Whether or not GC accretion played a role, it seems that the formation conditions of outer halo GCs and GCs in dSphs were similar. Based on observations collected at the European Southern Observatory, Chile (Program IDs 077.B-0769).Tables A.1 and A.2 are only available at the CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/537/A83

  14. Identification of Hard X-ray Sources in Galactic Globular Clusters: Simbol-X Simulations

    NASA Astrophysics Data System (ADS)

    Servillat, M.

    2009-05-01

    Globular clusters harbour an excess of X-ray sources compared to the number of X-ray sources in the Galactic plane. It has been proposed that many of these X-ray sources are cataclysmic variables that have an intermediate magnetic field, i.e. intermediate polars, which remains to be confirmed and understood. We present here several methods to identify intermediate polars in globular clusters from multiwavelength analysis. First, we report on XMM-Newton, Chandra and HST observations of the very dense Galactic globular cluster NGC 2808. By comparing UV and X-ray properties of the cataclysmic variable candidates, the fraction of intermediate polars in this cluster can be estimated. We also present the optical spectra of two cataclysmic variables in the globular cluster M 22. The HeII (4868 Å) emission line in these spectra could be related to the presence of a magnetic field in these objects. Simulations of Simbol-X observations indicate that the angular resolution is sufficient to study X-ray sources in the core of close, less dense globular clusters, such as M 22. The sensitivity of Simbol-X in an extended energy band up to 80 keV will allow us to discriminate between hard X-ray sources (such as magnetic cataclysmic variables) and soft X-ray sources (such as chromospherically active binaries).

  15. Two stellar-mass black holes in the globular cluster M22.

    PubMed

    Strader, Jay; Chomiuk, Laura; Maccarone, Thomas J; Miller-Jones, James C A; Seth, Anil C

    2012-10-04

    Hundreds of stellar-mass black holes probably form in a typical globular star cluster, with all but one predicted to be ejected through dynamical interactions. Some observational support for this idea is provided by the lack of X-ray-emitting binary stars comprising one black hole and one other star ('black-hole/X-ray binaries') in Milky Way globular clusters, even though many neutron-star/X-ray binaries are known. Although a few black holes have been seen in globular clusters around other galaxies, the masses of these cannot be determined, and some may be intermediate-mass black holes that form through exotic mechanisms. Here we report the presence of two flat-spectrum radio sources in the Milky Way globular cluster M22, and we argue that these objects are black holes of stellar mass (each ∼10-20 times more massive than the Sun) that are accreting matter. We find a high ratio of radio-to-X-ray flux for these black holes, consistent with the larger predicted masses of black holes in globular clusters compared to those outside. The identification of two black holes in one cluster shows that ejection of black holes is not as efficient as predicted by most models, and we argue that M22 may contain a total population of ∼5-100 black holes. The large core radius of M22 could arise from heating produced by the black holes.

  16. FORS2/VLT survey of Milky Way globular clusters. II. Fe and Mg abundances of 51 Milky Way globular clusters on a homogeneous scale

    NASA Astrophysics Data System (ADS)

    Dias, B.; Barbuy, B.; Saviane, I.; Held, E. V.; Da Costa, G. S.; Ortolani, S.; Gullieuszik, M.; Vásquez, S.

    2016-05-01

    Context. Globular clusters trace the formation and evolution of the Milky Way and surrounding galaxies, and outline their chemical enrichment history. To accomplish these tasks it is important to have large samples of clusters with homogeneous data and analysis to derive kinematics, chemical abundances, ages and locations. Aims: We obtain homogeneous metallicities and α-element enhancement for 51 Galactic bulge, disc, and halo globular clusters that are among the most distant and/or highly reddened in the Galaxy's globular cluster system. We also provide membership selection based on stellar radial velocities and atmospheric parameters. The implications of our results are discussed. Methods: We observed R ~ 2000 spectra in the wavelength interval 456-586 nm for over 800 red giant stars in 51 Galactic globular clusters. We applied full spectrum fitting with the code ETOILE together with libraries of observed and synthetic spectra. We compared the mean abundances of all clusters with previous work and with field stars. We used the relation between mean metallicity and horizontal branch morphology defined by all clusters to select outliers for discussion. Results: [Fe/H], [Mg/Fe], and [α/Fe] were derived in a consistent way for almost one-third of all Galactic globular clusters. We find our metallicities are comparable to those derived from high-resolution data to within σ = 0.08 dex over the interval -2.5< [Fe/H] < 0.0. Furthermore, a comparison of previous metallicity scales with our values yields σ< 0.16 dex. We also find that the distribution of [Mg/Fe] and [α/Fe] with [Fe/H] for the 51 clusters follows the general trend exhibited by field stars. It is the first time that the following clusters have been included in a large sample of homogeneous stellar spectroscopic observations and metallicity derivation: BH 176, Djorg 2, Pal 10, NGC 6426, Lynga 7, and Terzan 8. In particular, only photometric metallicities were available previously for the first three

  17. The Chemical Properties of Milky Way and M31 Globular Clusters. II. Stellar Population Model Predictions

    NASA Astrophysics Data System (ADS)

    Beasley, Michael A.; Brodie, Jean P.; Strader, Jay; Forbes, Duncan A.; Proctor, Robert N.; Barmby, Pauline; Huchra, John P.

    2005-03-01

    We derive ages, metallicities, and abundance ratios ([α/Fe]) from the integrated spectra of 23 globular clusters in M31 by employing multivariate fits to two different stellar population models. We also perform a parallel analysis on 21 Galactic globular clusters as a consistency check and in order to facilitate a differential analysis. Our analysis shows that the M31 globular clusters separate into three distinct components in age and metallicity; we identify an old, metal-poor group (seven clusters), an old, metal-rich group (10 clusters), and an intermediate-age (3-6 Gyr), intermediate-metallicity ([Z/H]~-1) group (six clusters). This third group is not identified in the Galactic globular cluster sample. We also see evidence that the old, metal-rich Galactic globular clusters are 1-2 Gyr older than their counterparts in M31. The majority of globular clusters in both samples appear to be enhanced in α-elements, but the degree of enhancement is rather model-dependent. The intermediate-age globular clusters appear to be the most enhanced, with [α/Fe]~0.4. These clusters are clearly depressed in CN with respect to the models and the bulk of the M31 and Milky Way sample. Compared with the bulge of M31, M32, and NGC 205, these clusters most resemble the stellar populations in NGC 205 in terms of age, metallicity, and CN abundance. We infer horizontal branch morphologies for the M31 clusters using the Rose Ca II index and demonstrate that blue horizontal branches are not leading to erroneous age estimates in our analysis. We discuss and reject as unlikely the hypothesis that these objects are in fact foreground stars contaminating the optical catalogs. The intermediate-age clusters have generally higher velocities than the bulk of the M31 cluster population. Spatially, three of these clusters are projected onto the bulge region, and the remaining three are distributed at large radii. We discuss these objects within the context of the build-up of the M31 halo and

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

    NASA Astrophysics Data System (ADS)

    Bekki, Kenji

    2017-05-01

    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 on to 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] × 105 M⊙ can accrete more than 105 M⊙ gas from AGB stars of the SCC. We suggest that merging of hierarchical SSCs can play key roles in stellar halo formation around GCs and self-enrichment processes in the early phase of GC formation.

  19. Comparing the properties of local globular cluster systems: implications for the formation of the Galactic halo

    NASA Astrophysics Data System (ADS)

    Mackey, A. D.; Gilmore, G. F.

    2004-12-01

    We investigate the hypothesis that some fraction of the globular clusters presently observed in the Galactic halo formed in external dwarf galaxies. This is done by means of a detailed comparison between the `old halo', `young halo' and `bulge/disc' subsystems defined by Zinn and the globular clusters in the Large Magellanic Cloud, Small Magellanic Cloud, and Fornax and Sagittarius dwarf spheroidal galaxies. We first use high-quality photometry from Hubble Space Telescope images to derive a complete set of uniform measurements of horizontal branch (HB) morphology in the external clusters. We also compile structural and metallicity measurements for these objects and update the data base of such measurements for the Galactic globular clusters, including new calculations of HB morphology for 11 objects. Using these data together with recent measurements of globular cluster kinematics and ages we examine the characteristics of the three Galactic cluster subsystems. Each is quite distinct in terms of their spatial and age distributions, age-metallicity relationships, and typical orbital parameters, although we observe some old halo clusters with ages and orbits more similar to those of young halo objects. In addition, almost all of the Galactic globular clusters with large core radii fall into the young halo subsystem, while the old halo and bulge/disc ensembles are characterized by compact clusters. We demonstrate that the majority of the external globular clusters are essentially indistinguishable from the Galactic young halo objects in terms of HB morphology, but ~20-30 per cent of external clusters have HB morphologies most similar to the Galactic old halo clusters. We further show that the external clusters have a distribution of core radii which very closely matches that for the young halo objects. The old halo distribution of core radii can be very well represented by a composite distribution formed from ~83-85 per cent of objects with structures typical of bulge

  20. Multiple populations in the Sagittarius nuclear cluster M 54 and in other anomalous globular clusters

    NASA Astrophysics Data System (ADS)

    Milone, A. P.

    2016-08-01

    M 54 is the central cluster of the Sagittarius dwarf galaxy. This stellar system is now in process of being disrupted by the tidal interaction with the Milky Way and represents one of the building blocks of the Galactic Halo. Recent discoveries, based on the synergy of photometry and spectroscopy have revealed that the color-magnitude diagram (CMD) of some massive, anomalous, Globular Clusters (GCs) host stellar populations with different content of heavy elements. In this paper, I use multi-wavelength Hubble Space Telescope (HST) photometry to detect and characterize multiple stellar populations in M 54. I provide empirical evidence that this GC shares photometric and spectroscopic similarities with the class of anomalous GCs. These findings make it tempting to speculate that, similarly to Sagittarius nuclear cluster M 54, other anomalous GCs were born in an extra-Galactic environment.

  1. ACS Photometry of Extended, Luminous Globular Clusters in the Outskirts of M31

    NASA Astrophysics Data System (ADS)

    Mackey, A. D.; Huxor, A.; Ferguson, A. M. N.; Tanvir, N. R.; Irwin, M.; Ibata, R.; Bridges, T.; Johnson, R. A.; Lewis, G.

    2006-12-01

    A new population of extended, luminous globular clusters has recently been discovered in the outskirts of M31. These objects have luminosities typical of classical globular clusters, but much larger half-light radii. We report the first results from deep ACS imaging of four such clusters, one of which is a newly discovered example lying at a projected distance of ~60 kpc from M31. Our F606W, F814W color-magnitude diagrams extend ~3 mag below the horizontal branch level, and clearly demonstrate, for the first time, that all four clusters are composed of >~10 Gyr old, metal-poor stellar populations. No evidence for multiple populations is observed. From a comparison with Galactic globular cluster fiducials we estimate metallicities in the range -2.2<~[Fe/H]<~-1.8. The observed horizontal branch morphologies show a clear second parameter effect between the clusters. Preliminary radial luminosity profiles suggest integrated magnitudes in the range -7.7<~MV<~-6.6, near the median value of the globular cluster luminosity function. Our results confirm that these four objects are bona fide old, metal-poor globular clusters, albeit with combined structures and luminosities unlike those observed for any other globular clusters in the Local Group or beyond. Based on observations made with the NASA/ESA Hubble Space Telescope, obtained at the Space Telescope Science Institute (STScI), 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 10394.

  2. Multiple populations in more metal-rich galactic globular clusters

    NASA Astrophysics Data System (ADS)

    Cordero, Maria J.

    In this thesis we present chemical abundances for bright stars in the intermediate metallicity globular cluster (GC) M5, and the relatively metal-rich GCs M71 and 47 Tuc with the goal of improving the understanding of chemical evolution in the metallicity regime sampled by these three GCs. The first chapter presents a brief historical overview in light element abundance variations in globular clusters. In the second chapter we present the results obtained for 47 Tuc, the most-metal rich cluster of my sample. 47 Tuc is an ideal target to study chemical evolution and GC formation in massive more metal-rich GCs since it is the closest massive GC. Chemical abundances for O, Na, Al, Si, Ca, Ti, Fe, Ni, La, and Eu were determined for 164 red giant branch (RGB) stars in 47 Tuc using spectra obtained with both the Hydra multi-fiber spectrograph at the Blanco 4-m telescope and the FLAMES multi-object spectrograph at the ESO Very Large Telescope. The average [Fe/H]= --0.79+/-0.09 dex is consistent with literature values, as well as over-abundances of alpha-elements ([alpha/Fe] ~ 0.3 dex). The n-capture process elements indicate that 47 Tuc is r-process dominated ([Eu/La]=+0.24), and the light elements O, Na, and Al exhibit star-to-star variations. The Na-O anti-correlation, a signature typically seen in Galactic GCs, is present in 47 Tuc, and extends to include a small number of stars with [O/Fe] ~ --0.5. Additionally, the [O/Na] ratios of our sample reveal that the cluster stars can be separated into three distinct populations. A KS-test demonstrates that the O-poor/Na-rich stars are more centrally concentrated than the O-rich/Na-poor stars. The observed number and radial distribution of 47 Tuc's stellar populations, as distinguished by their light element composition, agrees closely with the results obtained from photometric data. We do not find evidence supporting a strong Na-Al correlation in 47 Tuc, which is consistent with current models of AGB nucleosynthesis yields

  3. GLOBULAR CLUSTERS AND SPUR CLUSTERS IN NGC 4921, THE BRIGHTEST SPIRAL GALAXY IN THE COMA CLUSTER

    SciTech Connect

    Lee, Myung Gyoon; Jang, In Sung E-mail: isjang@astro.snu.ac.kr

    2016-03-01

    We resolve a significant fraction of globular clusters (GCs) in NGC 4921, the brightest spiral galaxy in the Coma cluster. We also find a number of extended bright star clusters (star complexes) in the spur region of the arms. The latter are much brighter and bluer than those in the normal star-forming region, being as massive as 3 × 10{sup 5} M{sub ⊙}. The color distribution of the GCs in this galaxy is found to be bimodal. The turnover magnitudes of the luminosity functions of the blue (metal-poor) GCs (0.70 < (V − I) ≤ 1.05) in the halo are estimated V(max) = 27.11 ± 0.09 mag and I(max) = 26.21 ± 0.11 mag. We obtain similar values for NGC 4923, a companion S0 galaxy, and two Coma cD galaxies (NGC 4874 and NGC 4889). The mean value for the turnover magnitudes of these four galaxies is I(max) = 26.25 ± 0.03 mag. Adopting M{sub I} (max) = −8.56 ± 0.09 mag for the metal-poor GCs, we determine the mean distance to the four Coma galaxies to be 91 ± 4 Mpc. Combining this with the Coma radial velocity, we derive a value of the Hubble constant, H{sub 0} = 77.9 ± 3.6 km s{sup −1} Mpc{sup −1}. We estimate the GC specific frequency of NGC 4921 to be S{sub N} = 1.29 ± 0.25, close to the values for early-type galaxies. This indicates that NGC 4921 is in the transition phase to S0s.

  4. A NEW DISTANT MILKY WAY GLOBULAR CLUSTER IN THE PAN-STARRS1 3π SURVEY

    SciTech Connect

    Laevens, Benjamin P. M.; Martin, Nicolas F.; Sesar, Branimir; Rix, Hans-Walter; Schlafly, Edward F.; Bernard, Edouard J.; Ferguson, Annette M. N.; Slater, Colin T.; Bell, Eric F.; Burgett, William S.; Chambers, Kenneth C.; Denneau, Larry; Kaiser, Nicholas; Kudritzki, Rolf-Peter; Magnier, Eugene A.; Morgan, Jeffrey S.; Sweeney, William E.; Draper, Peter W.; Metcalfe, Nigel; Price, Paul A.; and others

    2014-05-01

    We present a new satellite in the outer halo of the Galaxy, the first Milky Way satellite found in the stacked photometric catalog of the Panoramic Survey Telescope and Rapid Response System 1 (Pan-STARRS1) Survey. From follow-up photometry obtained with WFI on the MPG/ESO 2.2 m telescope, we argue that the object, located at a heliocentric distance of 145 ± 17 kpc, is the most distant Milky Way globular cluster yet known. With a total magnitude of M{sub V} = –4.3 ± 0.2 and a half-light radius of 20 ± 2 pc, it shares the properties of extended globular clusters found in the outer halo of our Galaxy and the Andromeda galaxy. The discovery of this distant cluster shows that the full spatial extent of the Milky Way globular cluster system has not yet been fully explored.

  5. NO EVIDENCE FOR INTERMEDIATE-MASS BLACK HOLES IN GLOBULAR CLUSTERS: STRONG CONSTRAINTS FROM THE JVLA

    SciTech Connect

    Strader, Jay; Chomiuk, Laura; Maccarone, Thomas J.; Miller-Jones, James C. A.; Seth, Anil C.; Heinke, Craig O.; Sivakoff, Gregory R.

    2012-05-10

    With a goal of searching for accreting intermediate-mass black holes (IMBHs), we report the results of ultra-deep Jansky Very Large Array radio continuum observations of the cores of three Galactic globular clusters: M15, M19, and M22. We reach rms noise levels of 1.5-2.1 {mu}Jy beam{sup -1} at an average frequency of 6 GHz. No sources are observed at the center of any of the clusters. For a conservative set of assumptions about the properties of the accretion, we set 3{sigma} upper limits on IMBHs from 360 to 980 M{sub Sun }. These limits are among the most stringent obtained for any globular cluster. They add to a growing body of work that suggests either (1) IMBHs {approx}> 1000 M{sub Sun} are rare in globular clusters or (2) when present, IMBHs accrete in an extraordinarily inefficient manner.

  6. Impact of the Low Solar Abundance on the Ages of Globular Clusters

    NASA Astrophysics Data System (ADS)

    Yi, Sukyoung K.; Kim, Yong-Cheol

    2010-08-01

    We present the result of our investigation on the impact of the low Solar abundance of Asplund and collaborators (2004) on the derived ages for the oldest star clusters based on isochrone fittings. We have constructed new stellar models and corresponding isochrones using this new solar mixture with a proper Solar calibration. We have found that the use of the Asplund et al. (2004) metallicity causes the typical ages for old globular clusters in the Milky Way to be increased roughly by 10%. Although this may appear small, it has a significant impact on the interpretation for the formation epoch of Milky Way globular clusters.The tet{asp04} abundance may not necessarily threaten the current concordance cosmology but would suggest that Milky Way globular clusters formed before the reionization epoch and before the main galaxy body starts to build up. This is in contrast to the current understanding on the galaxy formation.

  7. Binary Black Hole Mergers from Globular Clusters: Implications for Advanced LIGO.

    PubMed

    Rodriguez, Carl L; Morscher, Meagan; Pattabiraman, Bharath; Chatterjee, Sourav; Haster, Carl-Johan; Rasio, Frederic A

    2015-07-31

    The predicted rate of binary black hole mergers from galactic fields can vary over several orders of magnitude and is extremely sensitive to the assumptions of stellar evolution. But in dense stellar environments such as globular clusters, binary black holes form by well-understood gravitational interactions. In this Letter, we study the formation of black hole binaries in an extensive collection of realistic globular cluster models. By comparing these models to observed Milky Way and extragalactic globular clusters, we find that the mergers of dynamically formed binaries could be detected at a rate of ∼100 per year, potentially dominating the binary black hole merger rate. We also find that a majority of cluster-formed binaries are more massive than their field-formed counterparts, suggesting that Advanced LIGO could identify certain binaries as originating from dense stellar environments.

  8. HST observations of globular clusters in M 31. 1: Surface photometry of 13 objects

    NASA Technical Reports Server (NTRS)

    Pecci, F. Fusi; Battistini, P.; Bendinelli, O.; Bonoli, F.; Cacciari, C.; Djorgovski, S.; Federici, L.; Ferraro, F. R.; Parmeggiani, G.; Weir, N.

    1994-01-01

    We present the initial results of a study of globular clusters in M 31, using the Faint Object Camera (FOC) on the Hubble Space Telescope (HST). The sample of objects consists of 13 clusters spanning a range of properties. Three independent image deconvolution techniques were used in order to compensate for the optical problems of the HST, leading to mutually fully consistent results. We present detailed tests and comparisons to determine the reliability and limits of these deconvolution methods, and conclude that high-quality surface photometry of M 31 globulars is possible with the HST data. Surface brightness profiles have been extracted, and core radii, half-light radii, and central surface brightness values have been measured for all of the clusters in the sample. Their comparison with the values from ground-based observations indicates the later to be systematically and strongly biased by the seeing effects, as it may be expected. A comparison of the structural parameters with those of the Galactic globulars shows that the structural properties of the M 31 globulars are very similar to those of their Galactic counterparts. A candidate for a post-core-collapse cluster, Bo 343 = G 105, has been already identified from these data; this is the first such detection in the M 31 globular cluster system.

  9. 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.

  10. 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.

  11. 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.

  12. THE SIZE DIFFERENCE BETWEEN RED AND BLUE GLOBULAR CLUSTERS IS NOT DUE TO PROJECTION EFFECTS

    SciTech Connect

    Webb, Jeremy J.; Harris, William E.; Sills, Alison

    2012-11-10

    Metal-rich (red) globular clusters in massive galaxies are, on average, smaller than metal-poor (blue) globular clusters. One of the possible explanations for this phenomenon is that the two populations of clusters have different spatial distributions. We test this idea by comparing clusters observed in unusually deep, high signal-to-noise images of M87 with a simulated globular cluster population in which the red and blue clusters have different spatial distributions, matching the observations. We compare the overall distribution of cluster effective radii as well as the relationship between effective radius and galactocentric distance for both the observed and simulated red and blue sub-populations. We find that the different spatial distributions does not produce a significant size difference between the red and blue sub-populations as a whole or at a given galactocentric distance. These results suggest that the size difference between red and blue globular clusters is likely due to differences during formation or later evolution.

  13. Abundances of Local Group Globular Clusters Using High Resolution Integrated Light Spectroscopy

    NASA Astrophysics Data System (ADS)

    Sakari, Charli; McWilliam, A.; Venn, K.; Shetrone, M. D.; Dotter, A. L.; Mackey, D.

    2014-01-01

    Abundances and kinematics of extragalactic globular clusters provide valuable clues about galaxy and globular cluster formation in a wide variety of environments. In order to obtain such information about distant, unresolved systems, specific observational techniques are required. An Integrated Light Spectrum (ILS) provides a single spectrum from an entire stellar population, and can therefore be used to determine integrated cluster abundances. This dissertation investigates the accuracy of high resolution ILS analysis methods, using ILS (taken with the Hobby-Eberly Telescope) of globular clusters associated with the Milky Way (47 Tuc, M3, M13, NGC 7006, and M15) and then applies the method to globular clusters in the outer halo of M31 (from the Pan-Andromeda Archaeological Survey, or PAndAS). Results show that: a) as expected, the high resolution method reproduces individual stellar abundances for elements that do not vary within a cluster; b) the presence of multiple populations does affect the abundances of elements that vary within the cluster; c) certain abundance ratios are very sensitive to systematic effects, while others are not; and d) certain abundance ratios (e.g. [Ca/Fe]) can be accurately obtained from unresolved systems. Applications of ILABUNDS to the PAndAS clusters reveal that accretion may have played an important role in the formation of M31's outer halo.

  14. Observing globular cluster RR Lyraes with the BYU West Mountain Observatory

    NASA Astrophysics Data System (ADS)

    Jeffery, E. J.; Joner, M. D.; Walton, R. S.

    2016-05-01

    We have utilized the 0.9-meter telescope of the Brigham Young University West Mountain Observatory to secure data on six northern hemi- sphere globular clusters. Here we present observations of RR Lyrae stars located in these clusters. We compare light curves produced using both DAOPHOT and ISIS software packages. Light curve fitting is done with FITLC.

  15. Distances, Ages, and Epoch of Formation of Globular Clusters

    NASA Astrophysics Data System (ADS)

    Carretta, Eugenio; Gratton, Raffaele G.; Clementini, Gisella; Fusi Pecci, Flavio

    2000-04-01

    We review the results on distances and absolute ages of Galactic globular clusters (GCs) obtained after the release of the Hipparcos catalog. Several methods aimed at the definition of the Population II local distance scale are discussed, and their results compared, exploiting new results for RR Lyraes in the Large Magellanic Cloud (LMC). We find that the so-called short distance and long distance scales may be reconciled whether or not a consistent reddening scale is adopted for Cepheids and RR Lyrae variables in the LMC. Emphasis is given in the paper to the discussion of distances and ages of GCs derived using Hipparcos parallaxes of local subdwarfs. We find that the selection criteria adopted to choose the local subdwarfs, as well as the size of the corrections applied to existing systematic biases, are the main culprit for the differences found among the various independent studies that first used Hipparcos parallaxes and the subdwarf fitting technique. We also caution that the absolute age of M92 (usually considered one of the oldest clusters) still remains uncertain due to the lack of subdwarfs of comparable metallicity with accurate parallaxes. Distances and ages for the nine clusters discussed in a previous paper by Gratton et al. are rederived using an enlarged sample of local subdwarfs, which includes about 90% of the metal-poor dwarfs with accurate parallaxes (Δπ/π<=0.12) in the whole Hipparcos catalog. On average, our revised distance moduli are decreased by 0.04 mag with respect to Gratton et al. The corresponding age of the GCs is t=11.5+/-2.6 Gyr, where the error bars refer to the 95% confidence range. The relation between the zero-age horizontal branch (ZAHB) absolute magnitude and metallicity for the nine program clusters turns out to be MV(ZAHB)=(0.18+/-0.09)([Fe/H]+1.5)+(0.53+/-0.12) Thanks to Hipparcos the major contribution to the total error budget associated with the subdwarf fitting technique has been moved from parallaxes to photometric

  16. The Globular Cluster Relative Ages and the Milky Way Formation Time Scale

    NASA Astrophysics Data System (ADS)

    Aparicio, Antonio; Marín-Franch, Antonio; Piotto, Giampaolo; Rosenberg, Alfred; Chaboyer, Brian; Sarajedini, Ata; Siegel, Michael; Anderson, Jay; Bedin, Luigi R.; Dotter, Aaron; Hempel, Maren; King, Ivan; Majewski, Steven; Milone, Antonino P.; Paust, Nathaniel; Reid, I. Neill

    2009-05-01

    The ACS Survey of Galactic Globular Clusters is a Hubble Space Telescope (HST) Treasury program designed to provide a new large, deep and homogeneous photometric database. Based on observations from this program, we have measured precise relative ages for a sample of 64 Galactic globular clusters by comparing the relative position of the clusters' main sequence turn offs, using main-sequence fitting to cross-compare clusters within the sample. This method provides relative ages to a formal precision of 2-7%. We demonstrate that the calculated relative ages are independent of the choice of theoretical model. We find that the Galactic globular cluster sample can be divided into two groups-a population of old clusters with an intrinsic age dispersion of ~3% and no age-metallicity relation, and a group of younger clusters with an age-metallicity relation similar to that of the globular clusters associated with the Sagittarius dwarf galaxy. These results are consistent with the Milky Way halo having formed in two phases. The first phase would be compatible with a rapid (<0.8 Gyr) assembling process of the halo, in which the clusters in the old group were formed. The second phase lasted much longer in time and resulted in a group of globular clusters with a clear age-metallicity relation. It is very tempting to argue that the origin of this second group of clusters is related to the accretion of Milky Way satellite galaxies, but the origin of the age-metallicity relation remains unclear.

  17. FURTHER DEFINITION OF THE MASS-METALLICITY RELATION IN GLOBULAR CLUSTER SYSTEMS AROUND BRIGHTEST CLUSTER GALAXIES

    SciTech Connect

    Cockcroft, Robert; Harris, William E.; Wehner, Elizabeth M. H.; Whitmore, Bradley C.; Rothberg, Barry E-mail: harris@physics.mcmaster.ca E-mail: whitmore@stsci.edu

    2009-09-15

    We combine the globular cluster (GC) data for 15 brightest cluster galaxies and use this material to trace the mass-metallicity relations (MMRs) in their globular cluster systems (GCSs). This work extends previous studies which correlate the properties of the MMR with those of the host galaxy. Our combined data sets show a mean trend for the metal-poor subpopulation that corresponds to a scaling of heavy-element abundance with cluster mass Z {approx} M {sup 0.30{+-}}{sup 0.05}. No trend is seen for the metal-rich subpopulation which has a scaling relation that is consistent with zero. We also find that the scaling exponent is independent of the GCS specific frequency and host galaxy luminosity, except perhaps for dwarf galaxies. We present new photometry in (g',i') obtained with Gemini/GMOS for the GC populations around the southern giant ellipticals NGC 5193 and IC 4329. Both galaxies have rich cluster populations which show up as normal, bimodal sequences in the color-magnitude diagram. We test the observed MMRs and argue that they are statistically real, and not an artifact caused by the method we used. We also argue against asymmetric contamination causing the observed MMR as our mean results are no different from other contamination-free studies. Finally, we compare our method to the standard bimodal fitting method (KMM or RMIX) and find our results are consistent. Interpretation of these results is consistent with recent models for GC formation in which the MMR is determined by GC self-enrichment during their brief formation period.

  18. RR Lyrae Stars and the Instability Strip of 4 Globular Clusters: a Survey at Behlen Observatory

    NASA Astrophysics Data System (ADS)

    Young, Todd Scott

    This investigation reports on observations taken for 4 globular clusters (NGC 5466, NGC 6934, NGC 6426, and NGC 7006) with the 30-inch reflecting telescope at Behlen Observatory. These globular clusters had few previous observations collected using CCD photometry, the IRAF/DAOPHOT algorithms, and no observations through Cousins R and I filters. This was the first globular cluster investigation for Behlen Observatory. Observations concentrated on the central 2.8'×4.6' region (dictated by the size of the CCD chip) of each globular cluster. Behlen Observatory performed admirably with some limitations: a limiting magnitude of 17.5 in R for 300 second exposures; a mechanical error in the tracking of the telescope that prevented exposures much longer than 6 minutes; and a location and night sky that usually offered a seeing value not much better than 2 arcseconds. For the data reduction of the crowded fields, the IRAF/DAOPHOT algorithms displayed an inability to reduce the extremely crowded core of a globular cluster or stars located near bad pixels on the CCD chip. This inability often produced subtle photometric errors throughout the results that were difficult to recognize. For NGC 5466, this investigation determined a horizontal branch magnitude of 16.3 in R and confirmed an external reddening of approximately zero. Eleven of twelve previous variables within the field were detected with four period corrections, and one additional variable was found. One variable, V25, showed evidence of being another anomalous Cepheid for the cluster. For NGC 6934, this investigation determined a horizontal branch magnitude of 16.5 in R and recommends an external reddening of 0.06. Thirteen of thirty-nine previous variables within the field were detected with 2 period corrections, and 5 additional variables were found. NGC 6426 and NGC 7006 both produced unreliable results due to the proximity of the limiting magnitude to their horizontal branch magnitudes. Possible improvements for

  19. THE GLOBULAR CLUSTER SYSTEM OF THE VIRGO GIANT ELLIPTICAL GALAXY NGC 4636. II. KINEMATICS OF THE GLOBULAR CLUSTER SYSTEM

    SciTech Connect

    Lee, Myung Gyoon; Park, Hong Soo; Hwang, Ho Seong; Arimoto, Nobuo; Tamura, Naoyuki; Onodera, Masato E-mail: hspark@astro.snu.ac.k E-mail: masato.onodera@cea.f E-mail: naoyuki@subaru.naoj.or

    2010-02-01

    We present a kinematic analysis of the globular cluster (GC) system in the giant elliptical galaxy (gE) NGC 4636 in the Virgo cluster. Using the photometric and spectroscopic database of 238 GCs (108 blue GCs and 130 red GCs) at the galactocentric radius 0.'39 < R < 15.'43, we have investigated the kinematics of the GC system. The NGC 4636 GC system shows weak overall rotation, which is dominated by the red GCs. However, both the blue GCs and red GCs show some rotation in the inner region at R < 4.'3 (=2.9R{sub eff} = 18.5 kpc). The velocity dispersion for all the GCs is derived to be sigma{sub p} = 225{sup +12}{sub -9} km s{sup -1}. The velocity dispersion for the blue GCs (sigma{sub p} = 251{sup +18}{sub -12} km s{sup -1}) is slightly larger than that for the red GCs (sigma{sub p} = 205{sup +11}{sub -13} km s{sup -1}). The velocity dispersions for the blue GCs about the mean velocity and about the best-fit rotation curve have a significant variation depending on the galactocentric radius. Comparison of observed stellar and GC velocity dispersion profiles (VDPs) with the VDPs calculated from the stellar mass profile shows that the mass-to-light ratio should increase as the galactocentric distance increases, indicating the existence of an extended dark matter halo. From the comparison of the observed GC VDPs and the VDPs calculated for the X-ray mass profiles in the literature, we find that the orbit of the GC system is tangential, and that the orbit of the red GCs is slightly more tangential than that of the blue GCs. We compare the GC kinematics of NGC 4636 with those of other six gEs, finding that the kinematic properties of the GCs are diverse among gEs. We find several correlations between the kinematics of the GCs and the global parameters of their host galaxies. We discuss the implication of the results for the formation models of the GC system in gEs, and suggest a mixture scenario for the origin of the GCs in gEs.

  20. Clues on the missing sources of reionization from self-consistent modelling of Milky Way and dwarf galaxy globular clusters

    NASA Astrophysics Data System (ADS)

    Katz, Harley; Ricotti, Massimo

    2014-11-01

    Globular clusters are unique tracers of ancient star formation. We determine the formation efficiencies of globular clusters across cosmic time by modelling the formation and dynamical evolution of the globular cluster population of a Milky Way type galaxy in hierarchical cosmology, using the merger tree from the Via Lactea II simulation. All of the models are constrained to reproduce the observed specific frequency and initial mass function of globular clusters in isolated dwarfs. Globular cluster orbits are then computed in a time varying gravitational potential after they are either accreted from a satellite halo or formed in situ, within the Milky Way halo. We find that the Galactocentric distances and metallicity distribution of globular clusters are very sensitive to the formation efficiencies of globular clusters as a function of redshift and halo mass. Our most accurate models reveal two distinct peaks in the globular cluster formation efficiency at z ˜ 2 and 7-12 and prefer a formation efficiency that is mildly increasing with decreasing halo mass, the opposite of what expected for feedback-regulated star formation. This model accurately reproduces the positions, velocities, mass function, metallicity distribution, and age distribution of globular clusters in the Milky Way and predicts that ˜40 per cent formed in situ, within the Milky Way halo, while the other ˜60 per cent were accreted from about 20 satellite dwarf galaxies with vcir > 30 km s-1, and about 29 per cent of all globular clusters formed at redshifts z > 7. These results further strengthen the notion that globular cluster formation was an important mode of star formation in high-redshift galaxies and likely played a significant role in the reionization of the intergalactic medium.

  1. 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.

  2. Tidal stripping stellar substructures around four metal-poor globular clusters in the galactic bulge

    SciTech Connect

    Chun, Sang-Hyun; Kang, Minhee; Jung, DooSeok; Sohn, Young-Jong

    2015-01-01

    We investigate the spatial density configuration of stars around four metal-poor globular clusters (NGC 6266, NGC 6626, NGC 6642, and NGC 6723) in the Galactic bulge region using wide-field deep J, H, and K imaging data obtained with the Wide Field Camera near-infrared array on the United Kingdom Infrared Telescope. A statistical weighted filtering algorithm for the stars on the color–magnitude diagram is applied in order to sort cluster member candidates from the field star contamination. In two-dimensional isodensity contour maps of the clusters, we find that all four of the globular clusters exhibit strong evidence of tidally stripped stellar features beyond the tidal radius in the form of tidal tails or small density lobes/chunks. The orientations of the extended stellar substructures are likely to be associated with the effect of dynamic interaction with the Galaxy and the cluster's space motion. The observed radial density profiles of the four globular clusters also describe the extended substructures; they depart from theoretical King and Wilson models and have an overdensity feature with a break in the slope of the profile at the outer region of clusters. The observed results could imply that four globular clusters in the Galactic bulge region have experienced strong environmental effects such as tidal forces or bulge/disk shocks of the Galaxy during the dynamical evolution of globular clusters. These observational results provide further details which add to our understanding of the evolution of clusters in the Galactic bulge region as well as the formation of the Galaxy.

  3. Tidal Stripping Stellar Substructures Around Four Metal-Poor Globular Clusters in the Galactic Bulge

    NASA Astrophysics Data System (ADS)

    Chun, Sang-Hyun; Kang, Minhee; Jung, DooSeok; Sohn, Young-Jong

    2015-01-01

    We investigate the spatial density configuration of stars around four metal-poor globular clusters (NGC 6266, NGC 6626, NGC 6642, and NGC 6723) in the Galactic bulge region using wide-field deep J, H, and K imaging data obtained with the Wide Field Camera near-infrared array on the United Kingdom Infrared Telescope. A statistical weighted filtering algorithm for the stars on the color-magnitude diagram is applied in order to sort cluster member candidates from the field star contamination. In two-dimensional isodensity contour maps of the clusters, we find that all four of the globular clusters exhibit strong evidence of tidally stripped stellar features beyond the tidal radius in the form of tidal tails or small density lobes/chunks. The orientations of the extended stellar substructures are likely to be associated with the effect of dynamic interaction with the Galaxy and the cluster's space motion. The observed radial density profiles of the four globular clusters also describe the extended substructures; they depart from theoretical King and Wilson models and have an overdensity feature with a break in the slope of the profile at the outer region of clusters. The observed results could imply that four globular clusters in the Galactic bulge region have experienced strong environmental effects such as tidal forces or bulge/disk shocks of the Galaxy during the dynamical evolution of globular clusters. These observational results provide further details which add to our understanding of the evolution of clusters in the Galactic bulge region as well as the formation of the Galaxy.

  4. Optical, X-ray and gamma-ray observations of compact objects in globular clusters

    NASA Technical Reports Server (NTRS)

    Grindlay, J. E.

    1993-01-01

    In the past three years, a new era of study of globular clusters has begun with multiwavelength observations from the current generation of astronomical telescopes in space. We review the recent results obtained from our studies of compact binaries and x-ray sources in globulars with ROSAT and Hubble Space Telescope (HST) as well as our balloon-borne hard x-ray telescope EXITE (Energetic X-ray Imaging Telescope Experiment) and ground-based observations (CTIO). With ROSAT, we have obtained the most sensitive high resolution soft x-ray images of clusters which show multiple low luminosity sources in cluster cores that are likely indicative of the long-sought population of cataclysmic variables (CVs). We have obtained deep H-alpha images of two clusters with HST and found CV candiates for 3 of the ROSAT sources in the core of NGC 6397. New CTIO imaging and spectroscopy of two 'dim source' fields in omega-Cen are also described. With EXITE we carried out the first hard x-ray imaging observations of the cluster 47 Tuc; such studies can ultimately limit the populations of millisecond pulsars and pulsar emission mechanisms. A long ROSAT exposure on 47 Tuc also shows probable cluster diffuse emission, possibly due to hot gas from ablating millisecond pulsars. Multiwavelength studies of globular clusters may provide new constraints on problems as diverse as the origin of CVs and low mass X-ray binaries (LMXBs) and the origin of hot gas in globulars.

  5. Photometric and Kinematic Studies of Extragalactic Globular Cluster Systems

    NASA Astrophysics Data System (ADS)

    Windschitl-Dowell, Jessica L.

    2015-01-01

    Globular clusters (GCs) are compact, luminous collections of stars created during the early stages of galaxy formation. As a result, the properties of GC systems provide important clues about the formation, merger history, and structure of their host galaxies. In particular, kinematic studies of GCs can be used to investigate the dark matter distribution in galaxy halos and provide observational evidence that can be used to constrain models of galaxy formation. I will present our study of the GC systems of two spiral galaxies, NGC 891 and NGC 1055, and show how we used wide-field BVR imaging from the WIYN 3.5-m telescope to detect the GC population and measure the global properties of the system. We quantified the radial distribution of the GC system and total number of GCs in these galaxies and compared the results to those of other galaxies.I will also present the results of spectroscopic follow-up for two giant galaxies: the S0 galaxy NGC 4594 (M104), and the elliptical galaxy NGC 3379 (M105). Using spectra taken with AAT/AAOmega, WIYN/HYDRA, and MMT/Hectospec, I measured the radial velocities of GCs, and combined them with published results to determine the mass distribution and V-band mass-to-light (M/LV) ratio profile for each galaxy out to large effective radius (7-9 Re). I compared our results to mass estimates from other kinematic tracers and also considered them in the context of galaxy formation models. For both galaxies, I found that the M/LV profiles increase with radius and do not flatten, which suggests that the dark matter halos in these galaxies extend to the edge of our data. I also looked for evidence of rotation within the GC systems, and found that neither system exhibits significant rotation around the host galaxy. Finally, I examined the velocity dispersion of each GC system as a function of radius and found kinematic differences between the red, metal-rich and blue, metal-poor GC subpopulations.

  6. Globular cluster systems associated with cD galaxies in poor clusters

    NASA Astrophysics Data System (ADS)

    Bridges, Terry J.; Hanes, David A.

    1994-08-01

    We present an analysis of direct charge coupled devices (CCD) images of the central dominant (cD) galaxies of four poor clusters (Albert, White, & Morgan 1977; Morgan, Kayser, & White 1975) obtained at the prime focus of the Canada-France-Hawaii Telescope. A globular cluster system (GCS) is detected in only one of the galaxies: NGC 4073 (MKW 4); it has a specific frequency of SN approximately equal 4 + or - 4, a value typical for an 'average' elliptical of no particular distinction (Harris 1991). In the other three clusters, upper limits of SN less than 5-10 can be set on the specific frequency of any attendant GCS. These findings strongly suggest that mergers are not important in the generation of extremely populous GCSs, since the central galaxies in poor clusters presumably have more active merging histories than do their counterparts in richer surroundings. It is noted that MKW 4 has a moderate cooling flow, which may play some role in the formation of its GCS; the other poor clusters studied have neither the cooling flow nor the detected GCS. Finally, we note that the GCS associated with NGC 4073, the cD galaxy in MKW 4, is among the least centrally concentrated of any studied to date. This supports a suggestion by Harris (1991) that the degree of central concentration of a GCS is a function of the luminosity of the parent galaxy, with the most luminous galaxies having the most distended cluster systems.

  7. Gaps in globular cluster streams: giant molecular clouds can cause them too

    NASA Astrophysics Data System (ADS)

    Amorisco, Nicola C.; Gómez, Facundo A.; Vegetti, Simona; White, Simon D. M.

    2016-11-01

    As a result of their internal dynamical coherence, thin stellar streams formed by disrupting globular clusters (GCs) can act as detectors of dark matter (DM) substructure in the Galactic halo. Perturbations induced by close flybys amplify into detectable density gaps, providing a probe both of the abundance and of the masses of DM subhaloes. Here, we use N-body simulations to show that the Galactic population of giant molecular clouds (GMCs) can also produce gaps (and clumps) in GC streams, and so may confuse the detection of DM subhaloes. We explore the cases of streams analogous to the observed Palomar 5 and GD1 systems, quantifying the expected incidence of structure caused by GMC perturbations. Deep observations should detect such disturbances regardless of the substructure content of the Milky Way's halo. Detailed modelling will be needed to demonstrate that any detected gaps or clumps were produced by DM subhaloes rather than by molecular clouds.

  8. Implications of intermediate mass black hole in globular cluster G1 on dark matter detection.

    SciTech Connect

    Zaharijas, G.; High Energy Physics

    2008-07-01

    Recently there has been growing evidence in favor of the presence of an intermediate mass black hole in the globular cluster G1, in Andromeda Galaxy. Under the assumption that formation of this globular cluster occurred within a dark matter halo, we explore whether the presence of a black hole could result in an observable gamma ray signal due to dark matter annihilation in this globular cluster. Starting from an initial Navarro-Frenk-White matter profile, with density parameters consistent with G1 observations, we find that indeed, if the spike in the density has been formed and has survived until the present, the signal could be observed by GLAST and current atmospheric Cerenkov telescope detectors.

  9. POSSIBLE SUBGROUPS OF GLOBULAR CLUSTERS AND PLANETARY NEBULAE IN NGC 5128

    SciTech Connect

    Woodley, Kristin A.; Harris, William E. E-mail: harris@physics.mcmaster.ca

    2011-01-15

    We use recently compiled position and velocity data for the globular cluster and planetary nebula subsystems in NGC 5128, the nearby giant elliptical, to search for evidence of past dwarf-satellite accretion events. Beyond a 10' ({approx}11 kpc) radius in galactocentric distance, we find tentative evidence for four subgroups of globular clusters and four subgroups of planetary nebulae. These each have more than four members within a search radius of 2' and internal velocity dispersion of {approx}<40 km s{sup -1}, typical parameters for a dwarf galaxy. In addition, two of the globular cluster groupings overlap with two of the planetary nebulae groupings, and two subgroupings also appear to overlap with previously known arc and shell features in the halo light. Simulation tests of our procedure indicate that the probability of finding false groups due to chance is <1%.

  10. The SLUGGS survey: calcium triplet-based spectroscopic metallicities for over 900 globular clusters

    NASA Astrophysics Data System (ADS)

    Usher, Christopher; Forbes, Duncan A.; Brodie, Jean P.; Foster, Caroline; Spitler, Lee R.; Arnold, Jacob A.; Romanowsky, Aaron J.; Strader, Jay; Pota, Vincenzo

    2012-10-01

    Although the colour distribution of globular clusters in massive galaxies is well known to be bimodal, the spectroscopic metallicity distribution has been measured in only a few galaxies. After redefining the calcium triplet index-metallicity relation, we use our relation to derive the metallicity of 903 globular clusters in 11 early-type galaxies. This is the largest sample of spectroscopic globular cluster metallicities yet assembled. We compare these metallicities with those derived from Lick indices finding good agreement. In six of the eight galaxies with sufficient numbers of high-quality spectra we find bimodality in the spectroscopic metallicity distribution. Our results imply that most massive early-type galaxies have bimodal metallicity as well as colour distributions. This bimodality suggests that most massive early-type galaxies experienced two periods of star formation.

  11. The Structural Parameters of the Globular Clusters in M31 with PAndAS

    NASA Astrophysics Data System (ADS)

    Woodley, Kristin; Pan-Andromeda Archaeological Survey (PAndAS), The

    2012-05-01

    The Pan-Andromeda Archaeological Survey (PAndAS) has obtained images with the Canada France Hawaii Telescope using the instrument MegaCam, covering over 400 square degrees in the sky and extending beyond 150 kpc in radius from the center of M31. With this extensive data set, we have measured the structural parameters of all confirmed globular clusters in M31 as well as for a large fraction of the candidate globular clusters in the Revised Bologna Catalog V.4 (Galleti et al. 2004, A&A, 416, 917). In this paper, we present their parameters, including their core-, effective (half-light)-, and tidal radii, as well as their ellipticities measured in a homogeneous manner with ISHAPE (Larsen 1999, A&AS, 139, 393). We examine these parameters as functions of radial position, luminosity, color, metallicity, and age. We also use our measurements as an additional parameter to help constrain the candidacy of the unconfirmed globular clusters.

  12. The pollution of the interstellar medium from AGB stars in Globular Clusters

    NASA Astrophysics Data System (ADS)

    Ventura, Paolo; Carini, Roberta

    2015-03-01

    We discuss the yields from Asymptotic Giant Branch stars, depending on their mass and metallicity. In agreement with previous investigations, we find that the extent of Hot Bottom Burning increases with mass. The yields of models with chemistry typical of high-metallicity Globular Clusters, i.e. Z = 0.008, show only a modest depletion of magnesium, and an oxgen depletion of ~ 0.4 dex. Low-metallicity yields show a much stronger magnesium depletion, and a dramatic drop in the oxygen content, ~ 1.2dex smaller than the initial value. We suggest that the Globular Cluster NGC 2419 is a possible target to the hypothesis of the self-enrichment scenario of Globular Clusters by the winds of Asymptotic Giant Branch stars.

  13. A population of gamma-ray emitting globular clusters seen with the Fermi Large Area Telescope

    DOE PAGES

    Abdo, A. A.

    2010-11-24

    Context. Globular clusters with their large populations of millisecond pulsars (MSPs) are believed to be potential emitters of high-energy gamma-ray emission. The observation of this emission provides a powerful tool to assess the millisecond pulsar population of a cluster, is essential for understanding the importance of binary systems for the evolution of globular clusters, and provides complementary insights into magnetospheric emission processes. Aims. Our goal is to constrain the millisecond pulsar populations in globular clusters from analysis of gamma-ray observations. Methods. We use 546 days of continuous sky-survey observations obtained with the Large Area Telescope aboard the Fermi Gamma-ray Spacemore » Telescope to study the gamma-ray emission towards 13 globular clusters. Results. Steady point-like high-energy gamma-ray emission has been significantly detected towards 8 globular clusters. Five of them (47 Tucanae, Omega Cen, NGC 6388, Terzan 5, and M 28) show hard spectral power indices (0.7 < Γ < 1.4) and clear evidence for an exponential cut-off in the range 1.0 - 2.6 GeV, which is the characteristic signature of magnetospheric emission from MSPs. Three of them (M 62, NGC 6440 and NGC 6652) also show hard spectral indices (1.0 < Γ < 1.7), however the presence of an exponential cut-off can not be unambiguously established. Three of them (Omega Cen, NGC 6388, NGC 6652) have no known radio or X-ray MSPs yet still exhibit MSP spectral properties. From the observed gamma-ray luminosities, we estimate the total number of MSPs that is expected to be present in these globular clusters. We show that our estimates of the MSP population correlate with the stellar encounter rate and we estimate 2600 - 4700 MSPs in Galactic globular clusters, commensurate with previous estimates. Conclusions. The observation of high-energy gamma-ray emission from globular clusters thus provides a reliable independent method to assess their millisecond pulsar populations.« less

  14. The outer halo globular cluster system of M31 - II. Kinematics

    NASA Astrophysics Data System (ADS)

    Veljanoski, J.; Mackey, A. D.; Ferguson, A. M. N.; Huxor, A. P.; Côté, P.; Irwin, M. J.; Tanvir, N. R.; Peñarrubia, J.; Bernard, E. J.; Fardal, M.; Martin, N. F.; McConnachie, A.; Lewis, G. F.; Chapman, S. C.; Ibata, R. A.; Babul, A.

    2014-08-01

    We present a detailed kinematic analysis of the outer halo globular cluster system of the Andromeda galaxy (M31). Our basis for this is a set of new spectroscopic observations for 78 clusters lying at projected distances between Rproj ˜ 20-140 kpc from the M31 centre. These are largely drawn from the recent Pan-Andromeda Archaeological Survey globular cluster catalogue; 63 of our targets have no previous velocity data. Via a Bayesian maximum likelihood analysis, we find that globular clusters with Rproj > 30 kpc exhibit coherent rotation around the minor optical axis of M31, in the same direction as more centrally located globular clusters, but with a smaller amplitude of 86 ± 17 km s-1. There is also evidence that the velocity dispersion of the outer halo globular cluster system decreases as a function of projected distance from the M31 centre, and that this relation can be well described by a power law of index ≈ -0.5. The velocity dispersion profile of the outer halo globular clusters is quite similar to that of the halo stars, at least out to the radius up to which there is available information on the stellar kinematics. We detect and discuss various velocity correlations amongst subgroups of globular clusters that lie on stellar debris streams in the M31 halo. Many of these subgroups are dynamically cold, exhibiting internal velocity dispersions consistent with zero. Simple Monte Carlo experiments imply that such configurations are unlikely to form by chance, adding weight to the notion that a significant fraction of the outer halo globular clusters in M31 have been accreted alongside their parent dwarf galaxies. We also estimate the M31 mass within 200 kpc via the Tracer Mass Estimator (TME), finding (1.2-1.6) ± 0.2 × 1012 M⊙. This quantity is subject to additional systematic effects due to various limitations of the data, and assumptions built in into the TME. Finally, we discuss our results in the context of formation scenarios for the M31 halo.

  15. Globular cluster formation from gravitational tidal effects of merging and interacting galaxies

    NASA Astrophysics Data System (ADS)

    Bekki, K.; Forbes, Duncan A.; Beasley, M. A.; Couch, W. J.

    2002-10-01

    We investigate the spatial, kinematic and chemical properties of globular cluster systems formed in merging and interacting galaxies using N-body-smoothed particle hydrodynamics (SPH) simulations. Although we cannot resolve individual clusters in our simulation, we assume that they form in collapsing molecular clouds when the local external gas pressure exceeds 105kB (where kB is the Boltzmann constant). Several simulations are carried out for a range of initial conditions and galaxy mass ratios. The input model spirals are given a halo globular cluster system similar to those observed for the Milky Way and M31. Gravitational tidal effects during galaxy merging and interaction lead to a dramatic increase in gas pressure, which exceeds our threshold and hence triggers new globular cluster formation. We investigate the properties of the globular cluster system in the remnant galaxy, such as the number density, the specific frequency, kinematic properties and the metallicity distribution. Different orbital conditions and mass ratios give rise to a range in globular cluster properties, particularly for the interaction models. Our key results are the following: the newly formed metal-rich clusters are concentrated at the centre of the merger remnant elliptical, whereas the metal-poor ones are distributed to the outer parts because of strong angular momentum transfer. The dissipative merging of present-day spirals, including chemical evolution, results in metal-rich clusters with a mean metallicity that is super-solar, i.e. much higher than is observed in elliptical galaxies. If elliptical galaxies form by dissipative major mergers, then they must do so at very early epochs when their discs contained low-metallicity gas. Our simulations show that the specific frequency can be increased in a dissipative major merger. However, when this occurs it results in a ratio of metal-poor to metal-rich clusters that is less than one, contrary to the ratio observed in many elliptical

  16. CCD photometry of the globular cluster NGC 5897 - Morphology of the color-magnitude diagram

    NASA Technical Reports Server (NTRS)

    Sarajedini, Ata

    1992-01-01

    The paper presents CCD photometry in the B and V bands of the Galactic globular cluster NGC 5897. The color-magnitude diagram (CMD) obtained for this cluster is used to examine the properties of the cluster and to compare the NGC 5897 to the well-known globular cluster M3. It was found that the metallicity of the NGC 5897 is in the range of the metallicity of M3 and that the age of NGC 5897 is about 2 Gyr greater than that of M3. The CMD for NGC 5897 also reveals a significant population of blue straggler stars (BSS) more massive than the cluster subgiant branch stars. A pseudomain sequence is constructed for NGC 5897 and the previously studied (Sarajedini and Da Costa, 1991) global cluster 6101, which includes the BSS and extends to the faintest regions of the unevolved main sequence.

  17. APOGEE chemical abundances of globular cluster giants in the inner Galaxy

    NASA Astrophysics Data System (ADS)

    Schiavon, Ricardo P.; Johnson, Jennifer A.; Frinchaboy, Peter M.; Zasowski, Gail; Mészáros, Szabolcs; García-Hernández, D. A.; Cohen, Roger E.; Tang, Baitian; Villanova, Sandro; Geisler, Douglas; Beers, Timothy C.; Fernández-Trincado, J. G.; García Pérez, Ana E.; Lucatello, Sara; Majewski, Steven R.; Martell, Sarah L.; O'Connell, Robert W.; Prieto, Carlos Allende; Bizyaev, Dmitry; Carrera, Ricardo; Lane, Richard R.; Malanushenko, Elena; Malanushenko, Viktor; Muñoz, Ricardo R.; Nitschelm, Christian; Oravetz, Daniel; Pan, Kaike; Roman-Lopes, Alexandre; Schultheis, Matthias; Simmons, Audrey

    2017-04-01

    We report chemical abundances obtained by Sloan Digital Sky Survey (SDSS)-III/Apache Point Observatory Galactic Evolution Experiment for giant stars in five globular clusters located within 2.2 kpc of the Galactic Centre. We detect the presence of multiple stellar populations in four of those clusters (NGC 6553, NGC 6528, Terzan 5 and Palomar 6) and find strong evidence for their presence in NGC 6522. All clusters with a large enough sample present a significant spread in the abundances of N, C, Na and Al, with the usual correlations and anticorrelations between various abundances seen in other globular clusters. Our results provide important quantitative constraints on theoretical models for self-enrichment of globular clusters, by testing their predictions for the dependence of yields of elements such as Na, N, C and Al on metallicity. They also confirm that, under the assumption that field N-rich stars originate from globular cluster destruction, they can be used as tracers of their parental systems in the high-metallicity regime.

  18. 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.

  19. A carbon-rich Mira variable in a globular cluster: a stellar merger

    NASA Astrophysics Data System (ADS)

    Feast, Michael W.; Menzies, John W.; Whitelock, Patricia A.

    2013-01-01

    The membership of Matsunaga's variable 1, a carbon-rich, mass-losing, Mira variable, in the globular cluster Lynga 7 is discussed on the basis of radial velocities. We conclude that it is a member, the first known C-Mira in a globular cluster. Since such a variable is expected to have an age of ˜1-2 Gyr and an initial mass of ˜1.5 M⊙, we conclude that this star must be the product of a stellar merger.

  20. NO HEAVY-ELEMENT DISPERSION IN THE GLOBULAR CLUSTER M92

    SciTech Connect

    Cohen, Judith G.

    2011-10-20

    Although there have been recent claims that there is a large dispersion in the abundances of the heavy neutron capture elements in the old Galactic globular cluster M92, we show that the measured dispersion for the absolute abundances of four of the rare earth elements within a sample of 12 luminous red giants in M92 ({<=}0.07 dex) does not exceed the relevant sources of uncertainty. As expected from previous studies, the heavy elements show the signature of the r-process. Their abundance ratios are essentially identical to those of M30, another nearby globular cluster of similar metallicity.

  1. Star Clusters in M31. VII. Global Kinematics and Metallicity Subpopulations of the Globular Clusters

    NASA Astrophysics Data System (ADS)

    Caldwell, Nelson; Romanowsky, Aaron J.

    2016-06-01

    We carry out a joint spatial-kinematical-metallicity analysis of globular clusters (GCs) around the Andromeda Galaxy (M31), using a homogeneous, high-quality spectroscopic data set. In particular, we remove the contaminating young clusters that have plagued many previous analyses. We find that the clusters can be divided into three major metallicity groups based on their radial distributions: (1) an inner metal-rich group ([Fe/H] > -0.4); (2) a group with intermediate metallicity (with median [Fe/H] = -1) and (3) a metal-poor group, with [Fe/H] < -1.5. The metal-rich group has kinematics and spatial properties like those of the disk of M31, while the two more metal-poor groups show mild prograde rotation overall, with larger dispersions—in contrast to previous claims of stronger rotation. The metal-poor GCs are the least concentrated group; such clusters occur five times less frequently in the central bulge than do clusters of higher metallicity. Despite some well-known differences between the M31 and Milky Way GC systems, our revised analysis points to remarkable similarities in their chemodynamical properties, which could help elucidate the different formation stages of galaxies and their GCs. In particular, the M31 results motivate further exploration of a metal-rich GC formation mode in situ, within high-redshift, clumpy galactic disks.

  2. Wide-Field Survey of Globular Clusters in M31. II. Kinematics of the Globular Cluster System

    NASA Astrophysics Data System (ADS)

    Lee, Myung Gyoon; Hwang, Ho Seong; Kim, Sang Chul; Park, Hong Soo; Geisler, Doug; Sarajedini, Ata; Harris, William E.

    2008-02-01

    We present a kinematic analysis of the globular cluster (GC) system in M31, using the velocity data for 504 GCs including those for 150 GCs in our wide-field survey. The all GC system shows strong rotation, with rotation amplitude of vrot ~ 190 km s-1, and weak rotation persists even for the outermost samples at | Y| >= 5 kpc, where Y represents the projected distance from the major axis. The rotation-corrected velocity dispersion for the GC system is estimated to be σp,r ~ 130 km s-1, and it increases from σp,r ~ 120 km s-1 at | Y| < 1 kpc to σp,r ~ 150 km s-1 at | Y| >= 5 kpc. These results are very similar to those for the metal-poor GCs. This shows that there is a dynamically hot halo in M31 that is rotating but primarily pressure-supported. We have identified 50 "friendless" GCs, and they appear to rotate around the major axis of M31. Both metal-rich GCs and metal-poor GCs show strong rotation in the inner region. The rotation for the faint GCs is stronger than that for the bright GCs. We have identified 56 GCs and GC candidates with X-ray detection including 39 GCs with measured velocities. The majority of X-ray-emitting GCs follow the disk rotation. We have derived a rotation curve of M31 using the GCs at | Y| <= 0.6 kpc. We have estimated the dynamical mass of M31 using "Projected Mass Estimator (PME)" and "Tracer Mass Estimator (TME)" as MPME = 5.5+ 0.4-0.3 × 1011 M⊙ out to a radius of ~55 kpc and MTME = 19.2+ 1.4-1.3 × 1011 M⊙ for a radius of ~100 kpc, respectively. We finally discuss the implication of these results and compare the kinematics of GCs with that of planetary nebulae in M31. Based on observations with the Kitt Peak National Observatory, National Optical Astronomy Observatory, which is operated by the Association of Universities for Research in Astronomy (AURA), Inc., under cooperative agreement with the National Science Foundation.

  3. Globular clusters as tracers of stellar bimodality in elliptical galaxies: the case of NGC 1399

    NASA Astrophysics Data System (ADS)

    Forte, Juan C.; Faifer, Favio; Geisler, Doug

    2005-02-01

    Globular cluster systems (GCSs) frequently show a bimodal distribution of cluster integrated colours. This work explores the arguments to support the idea that the same feature is shared by the diffuse stellar population of the galaxy they are associated with. The particular case of NGC 1399, one of the dominant central galaxies in the Fornax cluster, for which a new B surface brightness profile and (B-RKC) colours are presented, is discussed taking advantage of a recently published wide-field study of its GCS. The results show that the galaxy brightness profile and colour gradient, as well as the behaviour of the cumulative globular cluster specific frequency, are compatible with the presence of two dominant stellar populations, associated with the so-called `blue' and `red' globular cluster families. These globular families are characterized by different intrinsic specific frequencies (defined in terms of each stellar population): Sn= 3.3 +/- 0.3 in the case of the red globulars and Sn= 14.3 +/- 2.5 for the blue ones. We stress that this result does not necessarily conflict with recent works that point out a clear difference between the metallicity distribution of (resolved) halo stars and globulars when comparing their number statistics. The region within 0.5arcmin of the centre shows a deviation from the model profile (in both surface brightness and colour) that may be explained in terms of the presence of a bulge-like high-metallicity component. Otherwise, the model gives an excellent fit up to 12arcmin (or 66.5Kpc) from the centre, the galactocentric limit of our blue brightness profile. The inferred specific frequencies imply that, in terms of their associated stellar populations, the formation of the blue globulars took place with an efficiency about six times higher than that corresponding to their red counterparts. The similarity of the spatial distribution of the blue globulars with that inferred for dark matter, as well as with that of the X

  4. The globular cluster system of NGC 1316. IV. Nature of the star cluster complex SH2

    NASA Astrophysics Data System (ADS)

    Richtler, T.; Husemann, B.; Hilker, M.; Puzia, T. H.; Bresolin, F.; Gómez, M.

    2017-05-01

    Context. The light of the merger remnant NGC 1316 (Fornax A) is dominated by old and intermediate-age stars. The only sign of current star formation in this big galaxy is the Hii region SH2, an isolated star cluster complex with a ring-like morphology and an estimated age of 0.1 Gyr at a galactocentric distance of about 35 kpc. A nearby intermediate-age globular cluster, surrounded by weak line emission and a few more young star clusters, is kinematically associated. The origin of this complex is enigmatic. Aims: We want to investigate the nature of this star cluster complex. The nebular emission lines permit a metallicity determination which can discriminate between a dwarf galaxy or other possible precursors. Methods: We used the Integral Field Unit (IFU) of the VIMOS instrument at the Very Large Telescope of the European Southern Observatory in high dispersion mode to study the morphology, kinematics, and metallicity employing line maps, velocity maps, and line diagnostics of a few characteristic spectra. Results: The line ratios of different spectra vary, indicating highly structured Hii regions, but define a locus of uniform metallicity. The strong-line diagnostic diagrams and empirical calibrations point to a nearly solar or even super-solar oxygen abundance. The velocity dispersion of the gas is highest in the region offset from the bright clusters. Star formation may be active on a low level. There is evidence for a large-scale disk-like structure in the region of SH2, which would make the similar radial velocity of the nearby globular cluster easier to understand. Conclusions: The high metallicity does not fit to a dwarf galaxy as progenitor. We favour the scenario of a free-floating gaseous complex having its origin in the merger 2 Gyr ago. Over a long period the densities increased secularly until finally the threshold for star formation was reached. SH2 illustrates how massive star clusters can form outside starbursts and without a considerable field

  5. 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.

  6. Globular clusters in the inner regions of NGC 5128 (CENTAURUS A)

    SciTech Connect

    Minniti, D. |; Alonso, M.V.; Goudfrooij, P.; Jablonka, P.; Meylan, G.

    1996-08-01

    We have identified 26 new globular cluster candidates in the inner 3 kpc of NGC 5128 (Centaurus A), the nearest known large galaxy that is the probable product of a merger. The clusters are selected on the basis of their structural parameters (observed core diameters and ellipticities), as measured from archival Wide Field Planetary Camera (WFPC) {ital Hubble} {ital Space} {ital Telescope} ({ital HST}) images. IR photometry obtained with IRAC2B at the ESO/MPI 2.2 m telescope is combined with the optical HST photometry. Most of these clusters have normal colors typical of old globular clusters like those found in the Milky Way and M31. We estimate their metal abundances based on the {ital R}{minus}{ital K}{sub 0} color, confirming the existence of a metallicity gradient in the inner regions of NGC 5128. The presence of metal-rich globular clusters suggests that one of the colliding galaxies was a bulge-dominated galaxy ({ital E} or early {ital S}). A few clusters have colors and magnitudes similar to intermediate-age clusters containing carbon stars in the Magellanic Clouds. If the intermediate-age clusters were formed during a merger, then this episode must have occurred a few gigayears ago. Alternatively, we are looking at the cluster members of one of the colliding galaxies, which would then have been a late-type disk galaxy. {copyright} {ital 1996 The American Astronomical Society.}

  7. An updated survey of globular clusters in M 31. I. Classification and radial velocity for 76 candidate clusters

    NASA Astrophysics Data System (ADS)

    Galleti, S.; Federici, L.; Bellazzini, M.; Buzzoni, A.; Fusi Pecci, F.

    2006-09-01

    Aims.We present the first results of a large spectroscopic survey of globular clusters and candidate globular clusters in the nearby M 31 galaxy. The survey is aimed at the classification of known candidate M 31 clusters and at the study of their kinematic properties. Methods: .We obtained low-resolution spectroscopy (λ/Δλ ≃ 800-1300) for 133 targets, including 76 yet-to-be-confirmed candidate clusters (i.e. with no previous spectroscopic information), 55 already-confirmed genuine M 31 clusters, and 2 uncertain candidates. Our observations allowed a reliable estimate of the target radial velocity, within a typical accuracy of ~± 20 km s-1. The observed candidates have been robustly classified according to their radial velocity and shape parameters that allowed us to confidently discriminate between point sources and extended objects even from low-spatial-resolution imagery. Results: .In our set of 76 candidate clusters we found: 42 newly-confirmed bona-fide M 31 clusters, 12 background galaxies, 17 foreground Galactic stars, 2 Hii regions belonging to M 31 and 3 unclassified (possibly M 31 clusters or foreground stars) objects. The classification of a few other candidates not included in our survey has been also reassessed on various observational bases. All the sources of radial velocity estimates for M 31 known globular clusters available in the literature have been compared and checked, and a homogeneous general list has been obtained for 349 confirmed clusters with radial velocity. Conclusions: .Our results suggest that a significant number of genuine clusters (≳100) is still hidden among the plethora of known candidates proposed by various authors. Hence our knowledge of the globular cluster system of the M 31 galaxy is still far from complete even in terms of simple membership.

  8. 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.

  9. Young accreted globular clusters in the outer halo of M31

    NASA Astrophysics Data System (ADS)

    Mackey, A. D.; Huxor, A. P.; Ferguson, A. M. N.; Irwin, M. J.; Veljanoski, J.; McConnachie, A. W.; Ibata, R. A.; Lewis, G. F.; Tanvir, N. R.

    2013-02-01

    We report on observations of two newly discovered globular clusters in the outskirts of M31 made using the Gemini Multi-Object Spectrograph (GMOS) instrument on Gemini North. These objects, PAndAS-7 (PA-7) and PAndAS-8 (PA-8), lie at a galactocentric radius of ≈87 kpc and are projected, with separation ≈19 kpc, on to a field halo substructure known as the South-West Cloud. We measure radial velocities for the two clusters which confirm that they are almost certainly physically associated with this feature. Colour-magnitude diagrams reveal strikingly short, exclusively red horizontal branches in both PA-7 and PA-8; both also have photometric [Fe/H] = -1.35 ± 0.15. At this metallicity, the morphology of the horizontal branch is maximally sensitive to age, and we use the distinctive configurations seen in PA-7 and PA-8 to demonstrate that both objects are very likely to be at least 2 Gyr younger than the oldest Milky Way globular clusters. Our observations provide strong evidence for young globular clusters being accreted into the remote outer regions of M31 in a manner entirely consistent with the established picture for the Milky Way, and add credence to the idea that similar processes play a central role in determining the composition of globular cluster systems in large spiral galaxies in general.

  10. DISCOVERY OF THE MOST ISOLATED GLOBULAR CLUSTER IN THE LOCAL UNIVERSE

    SciTech Connect

    Jang, In Sung; Lim, Sungsoon; Park, Hong Soo; Lee, Myung Gyoon E-mail: slim@astro.snu.ac.kr E-mail: mglee@astro.snu.ac.kr

    2012-05-20

    We report the discovery of two new globular clusters in the remote halos of M81 and M82 in the M81 Group based on Hubble Space Telescope archive images. They are brighter than typical globular clusters (M{sub V} = -9.34 mag for GC-1 and M{sub V} = -10.51 mag for GC-2), and much larger than known globular clusters with similar luminosity in the Milky Way Galaxy and M81. Radial surface brightness profiles for GC-1 and GC-2 do not show any features of tidal truncation in the outer part. They are located much farther from both M81 and M82 in the sky, compared with previously known star clusters in these galaxies. Color-magnitude diagrams of resolved stars in each cluster show a well-defined red giant branch (RGB), indicating that they are metal-poor and old. We derive a low metallicity with [Fe/H] Almost-Equal-To -2.3 and an old age {approx}14 Gyr for GC-2 from the analysis of the absorption lines in its spectrum in the Sloan Digital Sky Survey in comparison with the simple stellar population models. The I-band magnitude of the tip of the RGB for GC-2 is 0.26 mag fainter than that for the halo stars in the same field, showing that GC-2 is {approx}400 kpc behind the M81 halo along our line of sight. The deprojected distance to GC-2 from M81 is much larger than any other known globular clusters in the local universe. This shows that GC-2 is the most isolated globular cluster in the local universe.

  11. SUPERNOVAE AND THEIR EXPANDING BLAST WAVES DURING THE EARLY EVOLUTION OF GALACTIC GLOBULAR CLUSTERS

    SciTech Connect

    Tenorio-Tagle, Guillermo; Silich, Sergiy; Muñoz-Tuñón, Casiana; Cassisi, Santi E-mail: cmt@iac.es

    2015-11-20

    Our arguments deal with the early evolution of Galactic globular clusters and show why only a few of the supernovae (SNe) products were retained within globular clusters and only in the most massive cases (M ≥ 10{sup 6} M{sub ⊙}), while less massive clusters were not contaminated at all by SNe. Here, we show that SN blast waves evolving in a steep density gradient undergo blowout and end up discharging their energy and metals into the medium surrounding the clusters. This inhibits the dispersal and the contamination of the gas left over from a first stellar generation. Only the ejecta from well-centered SNe that evolve into a high-density medium available for a second stellar generation (2SG) in the most massive clusters would be retained. These are likely to mix their products with the remaining gas, eventually leading in these cases to an Fe-contaminated 2SG.

  12. THE GLOBULAR CLUSTER MASS FUNCTION AS A REMNANT OF VIOLENT BIRTH

    SciTech Connect

    Elmegreen, Bruce G.

    2010-04-01

    The log-normal shape of the mass function for metal-poor halo globular clusters is proposed to result from an initial M {sup -2} power law modified rapidly by evaporation, collisions with clouds, and mutual cluster interactions in the dense environment of a redshift z {approx} 5-15 disk galaxy. Galaxy interactions subsequently spray these clusters into the galaxy group environment, where they fall into other growing galaxies and populate their halos. Clusters forming later in z {approx} 2-5 galaxies, and those formed during major mergers, produce metal-rich globulars. Monte Carlo models of evolving cluster populations demonstrate the early formation of a log-normal mass function for typical conditions in high-redshift galaxies.

  13. Galactic evolution of sulphur as traced by globular clusters

    NASA Astrophysics Data System (ADS)

    Kacharov, N.; Koch, A.; Caffau, E.; Sbordone, L.

    2015-05-01

    Context. Sulphur is an important volatile α element, but its role in the Galactic chemical evolution is still uncertain, and more observations constraining the sulphur abundance in stellar photospheres are required. Aims: We derive the sulphur abundances in red giant branch (RGB) stars in three Galactic halo globular clusters (GC) that cover a wide metallicity range (-2.3 < [Fe/H] < -1.2): M 4 (NGC 6121), M 22 (NGC 6656), and M 30 (NGC 7099). The halo field stars show a large scatter in the [S/Fe] ratio in this metallicity span, which is inconsistent with canonical chemical evolution models. To date, very few measurements of [S/Fe] exist for stars in GCs, which are good tracers of the chemical enrichment of their environment. However, some light and α elements show star-to-star variations within individual GCs, and it is as yet unclear whether the α element sulphur also varies between GC stars. Methods: We used the infrared spectrograph CRIRES to obtain high-resolution (R ~ 50 000), high signal-to-noise (S/N ~ 200 per px) spectra in the region of the S I multiplet 3 at 1045 nm for 15 GC stars selected from the literature (six stars in M 4,six stars in M 22, and three stars in M 30). Multiplet 3 is better suited for S abundance derivation than the more commonly used lines of multiplet 1 at 920 nm, since its lines are not blended by telluric absorption or other stellar features at low metallicity. Results: We used spectral synthesis to derive the [S/Fe] ratio of the stars assuming local thermodynamic equilibrium (LTE). We find mean [S/Fe]LTE = 0.58 ± 0.01 ± 0.20 dex (statistical and systematic error) for M 4, [S/Fe]LTE = 0.57 ± 0.01 ± 0.19 dex for M 22, and [S/Fe]LTE = 0.55 ± 0.02 ± 0.16 dex for M 30. The negative NLTE corrections are estimated to be in the order of the systematic uncertainties. We do not detect star-to-star variations of the S abundance in any of the observed GCs, with the possible exception of two individual stars, one in M 22 and one in M

  14. The Helium Content of Globular Clusters: NGC 6121 (M4)

    NASA Astrophysics Data System (ADS)

    Villanova, S.; Geisler, D.; Piotto, G.; Gratton, R. G.

    2012-03-01

    In the context of the multiple stellar population scenario in globular clusters, helium (He) has been proposed as a key element to interpret the observed multiple main sequences, subgiant branches, and red giant branches, as well as the complex horizontal branch (HB) morphology. In particular, second-generation stars belonging to the bluer part of the HB are thought to be more He-rich (ΔY = 0.03 or more) but also more Na-rich/O-poor than those located in the redder part that should have Y equal to the cosmological value. Up to now this hypothesis was only partially confirmed in NGC 6752, where stars of the redder zero-age HB showed an He content of Y = 0.25 ± 0.01, fully compatible with the primordial He content of the universe, and were all Na-poor/O-rich. Here we study hot blue horizontal branch (BHB) stars in the GC NGC 6121 (M4) to measure their He plus O/Na content. Our goal is to complete the partial results obtained for NGC 6752, focusing our attention on targets located on the bluer part of the HB of M4. We observed six BHB stars using the VLT2/UVES spectroscopic facility. Spectra of signal-to-noise ratio ~ 150 were obtained and the very weak He line at 5875 Å measured for all our targets. We compared this feature with synthetic spectra to obtain He abundances. In addition O, Na, and Fe abundances were estimated. Stars turned out to be all Na-rich and O-poor and to have a homogeneous He content with a mean value of Y = 0.29 ± 0.01(random) ± 0.01(systematic), which is enhanced by ΔY ~ 0.04 with respect to the most recent measurements of the primordial He content of the universe (Y ~ 0.24/0.25). The high He content of blue HB stars in M4 is also confirmed by the fact that they are brighter than red HB stars (RHB). Theoretical models suggest the BHB stars are He-enhanced by Δ(Y) = 0.02/0.03 with respect to the RHB stars. The whole sample of stars has a metallicity of [Fe/H] = -1.06 ± 0.02 (internal error), in agreement with other studies available in

  15. THE HELIUM CONTENT OF GLOBULAR CLUSTERS: NGC 6121 (M4)

    SciTech Connect

    Villanova, S.; Geisler, D.; Piotto, G.; Gratton, R. G. E-mail: dgeisler@astro-udec.cl E-mail: raffaele.gratton@oapd.inaf.it

    2012-03-20

    In the context of the multiple stellar population scenario in globular clusters, helium (He) has been proposed as a key element to interpret the observed multiple main sequences, subgiant branches, and red giant branches, as well as the complex horizontal branch (HB) morphology. In particular, second-generation stars belonging to the bluer part of the HB are thought to be more He-rich ({Delta}Y = 0.03 or more) but also more Na-rich/O-poor than those located in the redder part that should have Y equal to the cosmological value. Up to now this hypothesis was only partially confirmed in NGC 6752, where stars of the redder zero-age HB showed an He content of Y = 0.25 {+-} 0.01, fully compatible with the primordial He content of the universe, and were all Na-poor/O-rich. Here we study hot blue horizontal branch (BHB) stars in the GC NGC 6121 (M4) to measure their He plus O/Na content. Our goal is to complete the partial results obtained for NGC 6752, focusing our attention on targets located on the bluer part of the HB of M4. We observed six BHB stars using the VLT2/UVES spectroscopic facility. Spectra of signal-to-noise ratio {approx} 150 were obtained and the very weak He line at 5875 A measured for all our targets. We compared this feature with synthetic spectra to obtain He abundances. In addition O, Na, and Fe abundances were estimated. Stars turned out to be all Na-rich and O-poor and to have a homogeneous He content with a mean value of Y = 0.29 {+-} 0.01(random) {+-} 0.01(systematic), which is enhanced by {Delta}Y {approx} 0.04 with respect to the most recent measurements of the primordial He content of the universe (Y {approx} 0.24/0.25). The high He content of blue HB stars in M4 is also confirmed by the fact that they are brighter than red HB stars (RHB). Theoretical models suggest the BHB stars are He-enhanced by {Delta}(Y) = 0.02/0.03 with respect to the RHB stars. The whole sample of stars has a metallicity of [Fe/H] = -1.06 {+-} 0.02 (internal error), in

  16. Intermediate Mass Black Holes in Globular Clusters - Comparison of Monte Carlo Cluster Models with Observations

    NASA Astrophysics Data System (ADS)

    Umbreit, Stefan; Rasio, F. A.

    2009-01-01

    Decades after first predicting Intermediate Mass Black Holes (IMBHs) in Globular Clusters (GCs) there is still no unambiguous observational evidence for their existence. The most promising signatures for IMBHs are found in the cores of GCs, where the evidence now comes from both the stellar velocity distribution and the surface brightness profile near the cluster center. However, interpretation of the data and, in particular, constraints on central IMBH masses, require the use of detailed cluster dynamical models. Here we present results from simulations of GCs that harbor IMBHs. These simulations have been carried out with our Monte Carlo cluster code which now includes all relevant physical processes, including both stellar dynamics and stellar evolution, making direct and detailed comparisons with observations possible. We compare our predicted velocity and surface brightness profiles with observations and derive constraints on the masses of possible central IMBHs for several candidate GCs. This work is supported by NASA through grant HST-AR-11779.01 from the Space Telescope Science Institute.

  17. A POPULATION OF NON-RECYCLED PULSARS ORIGINATING IN GLOBULAR CLUSTERS

    SciTech Connect

    Lynch, Ryan S.; Lorimer, Duncan R.; Boyles, Jason; Ransom, Scott M.

    2012-09-01

    We explore the enigmatic population of long-period, apparently non-recycled pulsars in globular clusters, building on recent work by Boyles et al. This population is difficult to explain if it formed through typical core-collapse supernovae, leading many authors to invoke electron capture supernovae. While Boyles et al. dealt only with non-recycled pulsars in clusters, we focus on the pulsars that originated in clusters but then escaped into the field of the Galaxy due to the kicks they receive at birth. The magnitude of the kick induced by electron capture supernovae is not well known, so we explore various models for the kick velocity distribution and size of the population. The most realistic models are those where the kick velocity is {approx}< 10 km s{sup -1} and where the number of pulsars scales with the luminosity of the cluster (as a proxy for cluster mass). This is in good agreement with other estimates of the electron capture supernovae kick velocity. We simulate a number of large-area pulsar surveys to determine if a population of pulsars originating in clusters could be identified as being separate from normal disk pulsars. We find that the spatial and kinematical properties of the population could be used, but only if large numbers of pulsars are detected. In fact, even the most optimistic surveys carried out with the future Square Kilometer Array are likely to detect <10% of the total population, so the prospects for identifying these as a separate group of pulsars are presently poor.

  18. The extended stellar substructures of four metal-poor globular clusters in the galactic bulge

    NASA Astrophysics Data System (ADS)

    Chun, Sang-Hyun; Sohn, Young-Jong

    2015-08-01

    We investigated stellar spatial density distribution around four metal-poor globular clusters (NGC 6266, NGC 6626, NGC 6642 and NGC 6723) in order to find extended stellar substructures. Wide-field deep J, H, and K imaging data were taken using the WFCAM near-infrared array on United Kingdom Infrared Telescope (UKIRT). The contamination of field stars around clusters was minimised by applying a statistical weighted filtering algorithm for the stars on the color-magnitude diagram. In two-dimensional isodensity contour map, we find that all four of the globular clusters shows tidal stripping stellar features in the form of tidal tails (NGC 6266 and NGC 6723) or small density lobes/chunk (NGC 6642 and NGC 6723). The stellar substructures extend toward the Galactic centre or anticancer, and the proper motion direction of the clusters. The radial density profiles of the clusters also depart from theoretical King and Wilson models and show overdensity feature with a break in a slope of profile at the outer region of clusters. The observed results indicate that four globular clusters in the Galactic bulge have experienced strong tidal force or bulge/disk shock effect of the Galaxy. These observational results provide us further constraints to understand the evolution of clusters in the Galactic bulge region as well as the formation of the Galaxy.

  19. A Science Portal and Archive for Extragalactic Globular Cluster Systems Data

    NASA Astrophysics Data System (ADS)

    Young, Michael; Rhode, Katherine L.; Gopu, Arvind

    2015-01-01

    For several years we have been carrying out a wide-field imaging survey of the globular cluster populations of a sample of giant spiral, S0, and elliptical galaxies with distances of ~10-30 Mpc. We use mosaic CCD cameras on the WIYN 3.5-m and Kitt Peak 4-m telescopes to acquire deep BVR imaging of each galaxy and then analyze the data to derive global properties of the globular cluster system. In addition to measuring the total numbers, specific frequencies, spatial distributions, and color distributions for the globular cluster populations, we have produced deep, high-quality images and lists of tens to thousands of globular cluster candidates for the ~40 galaxies included in the survey.With the survey nearing completion, we have been exploring how to efficiently disseminate not only the overall results, but also all of the relevant data products, to the astronomical community. Here we present our solution: a scientific portal and archive for extragalactic globular cluster systems data. With a modern and intuitive web interface built on the same framework as the WIYN One Degree Imager Portal, Pipeline, and Archive (ODI-PPA), our system will provide public access to the survey results and the final stacked mosaic images of the target galaxies. In addition, the astrometric and photometric data for thousands of identified globular cluster candidates, as well as for all point sources detected in each field, will be indexed and searchable. Where available, spectroscopic follow-up data will be paired with the candidates. Advanced imaging tools will enable users to overlay the cluster candidates and other sources on the mosaic images within the web interface, while metadata charting tools will allow users to rapidly and seamlessly plot the survey results for each galaxy and the data for hundreds of thousands of individual sources. Finally, we will appeal to other researchers with similar data products and work toward making our portal a central repository for data

  20. Hubble Space Telescope Proper Motion (HSTPROMO) Catalogs of Galactic Globular Cluster. II. Kinematic Profiles and Maps

    NASA Astrophysics Data System (ADS)

    Watkins, Laura L.; van der Marel, Roeland P.; Bellini, Andrea; Anderson, Jay

    2015-04-01

    We present kinematical analyses of 22 Galactic globular clusters using the Hubble Space Telescope proper motion catalogs recently presented in Bellini et al. For most clusters, this is the first proper-motion study ever performed, and, for many, this is the most detailed kinematic study of any kind. We use cleaned samples of bright stars to determine binned velocity-dispersion and velocity-anisotropy radial profiles and two-dimensional velocity-dispersion spatial maps. Using these profiles, we search for correlations between cluster kinematics and structural properties. We find the following: (1) more centrally concentrated clusters have steeper radial velocity-dispersion profiles; (2) on average, at 1σ confidence in two dimensions, the photometric and kinematic centers of globular clusters agree to within ˜1″, with a cluster-to-cluster rms of 4″(including observational uncertainties); (3) on average, the cores of globular clusters have isotropic velocity distributions to within 1% ({{σ }t}/{{σ }r}=0.992+/- 0.005), with a cluster-to-cluster rms of 2% (including observational uncertainties); (4) clusters generally have mildly radially anisotropic velocity distributions ({{σ }t}/{{σ }r}≈ 0.8-1.0) near the half-mass-radius, with bigger deviations from isotropy for clusters with longer relaxation times; and (5) there is a relation between {{σ }minor}/{{σ }major} and ellipticity, such that the more flattened clusters in the sample tend to be more anisotropic, with {{σ }minor}/{{σ }major}≈ 0.9-1.0. Aside from these general results and correlations, the profiles and maps presented here can provide a basis for detailed dynamical modeling of individual globular clusters. Given the quality of the data, this is likely to provide new insights into a range of topics concerning globular cluster mass profiles, structure, and dynamics. Based on proprietary and archival observations with the NASA/ESA Hubble Space Telescope, obtained at the Space Telescope Science