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Integrated-Light Two Micron All Sky Survey Infrared Photometry of Galactic Globular Clusters
We have mosaicked Two Micron All Sky Survey (2MASS) images to derivesurface brightness profiles in J, H, and Ks for 104 Galacticglobular clusters. We fit these with King profiles and show that thecore radii are identical to within the errors for each of these IRcolors and are identical to the core radii at V in essentially allcases. We derive integrated-light colors V-J, V-H, V-Ks, J-H,and J-Ks for these globular clusters. Each color shows areasonably tight relation between the dereddened colors and metallicity.Fits to these are given for each color. The IR - IR colors have verysmall errors, due largely to the all-sky photometric calibration of the2MASS survey, while the V-IR colors have substantially largeruncertainties. We find fairly good agreement with measurements ofintegrated-light colors for a smaller sample of Galactic globularclusters by M. Aaronson, M. Malkan, and D. Kleinmann from 1977. Ourresults provide a calibration for the integrated light of distantsingle-burst old stellar populations from very low to solarmetallicities. A comparison of our dereddened measured colors withpredictions from several models of the integrated light of single-burstold populations shows good agreement in the low-metallicity domain forV-Ks colors but also shows an offset at a fixed [Fe/H] of~0.1 mag in J-Ks, which we ascribe to photometric systemtransformation issues. Some of the models fail to reproduce the behaviorof the integrated-light colors of the Galactic globular clusters nearsolar metallicity.
| Globular cluster system and Milky Way properties revisited
Aims.Updated data of the 153 Galactic globular clusters are used toreaddress fundamental parameters of the Milky Way, such as the distanceof the Sun to the Galactic centre, the bulge and halo structuralparameters, and cluster destruction rates. Methods: .We build areduced sample that has been decontaminated of all the clusters youngerthan 10 Gyr and of those with retrograde orbits and/or evidence ofrelation to dwarf galaxies. The reduced sample contains 116 globularclusters that are tested for whether they were formed in the primordialcollapse. Results: .The 33 metal-rich globular clusters([Fe/H]≥-0.75) of the reduced sample basically extend to the Solarcircle and are distributed over a region with the projected axial-ratiostypical of an oblate spheroidal, Δ x:Δ y:Δz≈1.0:0.9:0.4. Those outside this region appear to be related toaccretion. The 81 metal-poor globular clusters span a nearly sphericalregion of axial-ratios ≈1.0:1.0:0.8 extending from the central partsto the outer halo, although several clusters in the external regionstill require detailed studies to unravel their origin as accretion orcollapse. A new estimate of the Sun's distance to the Galactic centre,based on the symmetries of the spatial distribution of 116 globularclusters, is provided with a considerably smaller uncertainty than inprevious determinations using globular clusters, R_O=7.2±0.3 kpc.The metal-rich and metal-poor radial-density distributions flatten forR_GC≤2 kpc and are represented well over the full Galactocentricdistance range both by a power-law with a core-like term andSérsic's law; at large distances they fall off as R-3.9. Conclusions: .Both metallicity components appearto have a common origin that is different from that of the dark matterhalo. Structural similarities between the metal-rich and metal-poorradial distributions and the stellar halo are consistent with a scenariowhere part of the reduced sample was formed in the primordial collapseand part was accreted in an early period of merging. This applies to thebulge as well, suggesting an early merger affecting the central parts ofthe Galaxy. The present decontamination procedure is not sensitive toall accretions (especially prograde) during the first Gyr, since theobserved radial density profiles still preserve traces of the earliestmerger(s). We estimate that the present globular cluster populationcorresponds to ≤23±6% of the original one. The fact that thevolume-density radial distributions of the metal-rich and metal-poorglobular clusters of the reduced sample follow both a core-likepower-law, and Sérsic's law indicates that we are dealing withspheroidal subsystems at all scales.
| Nearby Spiral Globular Cluster Systems. I. Luminosity Functions
We compare the near-infrared (JHK) globular cluster luminosity functions(GCLFs) of the Milky Way, M31, and the Sculptor Group spiral galaxies.We obtained near-infrared photometry with the Persson's AuxiliaryNasmyth Infrared Camera on the Baade Telescope for 38 objects (mostlyglobular cluster candidates) in the Sculptor Group. We also havenear-infrared photometry from the Two Micron All Sky Survey (2MASS)-6Xdatabase for 360 M31 globular cluster candidates and aperture photometryfor 96 Milky Way globular cluster candidates from the 2MASS All-Sky andSecond Incremental Release databases. The M31 6X GCLFs peak at absolutereddening-corrected magnitudes of MJ0=-9.18,MH0=-9.73, and MK0=-9.98.The mean brightness of the Milky Way objects is consistent with that ofM31 after accounting for incompleteness. The average Sculptor absolutemagnitudes (correcting for relative distance from the literature andforeground reddening) are MJ0=-9.18,MH0=-9.70, and MK0=-9.80.NGC 300 alone has absolute foreground-dereddened magnitudesMJ0=-8.87, MH0=-9.39, andMK0=-9.46 using the newest Gieren et al. distance.This implies either that the NGC 300 GCLF may be intrinsically fainterthan that of the larger galaxy M31 or that NGC 300 may be slightlyfarther away than previously thought. Straightforward application of ourM31 GCLF results as a calibrator gives NGC 300 distance moduli of26.68+/-0.14 using J, 26.71+/-0.14 using H, and 26.89+/-0.14 using K.Data for this project were obtained at the Baade 6.5 m telescope, LasCampanas Observatory, Chile.
| RR Lyrae-based calibration of the Globular Cluster Luminosity Function
We test whether the peak absolute magnitude MV(TO) of theGlobular Cluster Luminosity Function (GCLF) can be used for reliableextragalactic distance determination. Starting with the luminosityfunction of the Galactic Globular Clusters listed in Harris catalogue,we determine MV(TO) either using current calibrations of theabsolute magnitude MV(RR) of RR Lyrae stars as a function ofthe cluster metal content [Fe/H] and adopting selected cluster samples.We show that the peak magnitude is slightly affected by the adoptedMV(RR)-[Fe/H] relation, with the exception of that based onthe revised Baade-Wesselink method, while it depends on the criteria toselect the cluster sample. Moreover, grouping the Galactic GlobularClusters by metallicity, we find that the metal-poor (MP) ([Fe/H]<-1.0, <[Fe/H]>~-1.6) sample shows peak magnitudes systematicallybrighter by about 0.36mag than those of the metal-rich (MR) ([Fe/H]>-1.0, (<[Fe/H]>~-0.6) one, in substantial agreement with thetheoretical metallicity effect suggested by synthetic Globular Clusterpopulations with constant age and mass function. Moving outside theMilky Way, we show that the peak magnitude of the MP clusters in M31appears to be consistent with that of Galactic clusters with similarmetallicity, once the same MV(RR)-[Fe/H] relation is used fordistance determination. As for the GCLFs in other external galaxies,using Surface Brightness Fluctuations (SBF) measurements we giveevidence that the luminosity functions of the blue (MP) GlobularClusters peak at the same luminosity within ~0.2mag, whereas for the red(MR) samples the agreement is within ~0.5mag even accounting for thetheoretical metallicity correction expected for clusters with similarages and mass distributions. Then, using the SBF absolute magnitudesprovided by a Cepheid distance scale calibrated on a fiducial distanceto Large Magellanic Cloud (LMC), we show that the MV(TO)value of the MP clusters in external galaxies is in excellent agreementwith the value of both Galactic and M31 ones, as inferred by an RR Lyraedistance scale referenced to the same LMC fiducial distance. Eventually,adopting μ0(LMC) = 18.50mag, we derive that the luminosityfunction of MP clusters in the Milky Way, M31, and external galaxiespeak at MV(TO) =-7.66 +/- 0.11, - 7.65 +/- 0.19 and -7.67 +/-0.23mag, respectively. This would suggest a value of -7.66 +/- 0.09mag(weighted mean), with any modification of the LMC distance modulusproducing a similar variation of the GCLF peak luminosity.
| Resolved Massive Star Clusters in the Milky Way and Its Satellites: Brightness Profiles and a Catalog of Fundamental Parameters
We present a database of structural and dynamical properties for 153spatially resolved star clusters in the Milky Way, the Large and SmallMagellanic Clouds, and the Fornax dwarf spheroidal. This databasecomplements and extends others in the literature, such as those ofHarris and Mackey & Gilmore. Our cluster sample comprises 50 ``youngmassive clusters'' in the LMC and SMC, and 103 old globular clustersbetween the four galaxies. The parameters we list include central andhalf-light-averaged surface brightnesses and mass densities; core andeffective radii; central potentials, concentration parameters, and tidalradii; predicted central velocity dispersions and escape velocities;total luminosities, masses, and binding energies; central phase-spacedensities; half-mass relaxation times; and ``κ-space'' parameters.We use publicly available population-synthesis models to computestellar-population properties (intrinsic B-V colors, reddenings, andV-band mass-to-light ratios) for the same 153 clusters plus another 63globulars in the Milky Way. We also take velocity-dispersionmeasurements from the literature for a subset of 57 (mostly old)clusters to derive dynamical mass-to-light ratios for them, showing thatthese compare very well to the population-synthesis predictions. Thecombined data set is intended to serve as the basis for futureinvestigations of structural correlations and the fundamental plane ofmassive star clusters, including especially comparisons between thesystemic properties of young and old clusters.The structural and dynamical parameters are derived from fitting threedifferent models-the modified isothermal sphere of King; an alternatemodified isothermal sphere based on the ad hoc stellar distributionfunction of Wilson; and asymptotic power-law models withconstant-density cores-to the surface-brightness profile of eachcluster. Surface-brightness data for the LMC, SMC, and Fornax clustersare based in large part on the work of Mackey & Gilmore, but includesignificant supplementary data culled from the literature and importantcorrections to Mackey & Gilmore's V-band magnitude scale. Theprofiles of Galactic globular clusters are taken from Trager et al. Weaddress the question of which model fits each cluster best, finding inthe majority of cases that the Wilson models-which are spatially moreextended than King models but still include a finite, ``tidal'' cutoffin density-fit clusters of any age, in any galaxy, as well as or betterthan King models. Untruncated, asymptotic power laws often fit about aswell as Wilson models but can be significantly worse. We argue that theextended halos known to characterize many Magellanic Cloud clusters maybe examples of the generic envelope structure of self-gravitating starclusters, not just transient features associated strictly with youngage.
| Comparing the properties of local globular cluster systems: implications for the formation of the Galactic halo
We investigate the hypothesis that some fraction of the globularclusters presently observed in the Galactic halo formed in externaldwarf galaxies. This is done by means of a detailed comparison betweenthe `old halo', `young halo' and `bulge/disc' subsystems defined by Zinnand the globular clusters in the Large Magellanic Cloud, SmallMagellanic Cloud, and Fornax and Sagittarius dwarf spheroidal galaxies.We first use high-quality photometry from Hubble Space Telescope imagesto derive a complete set of uniform measurements of horizontal branch(HB) morphology in the external clusters. We also compile structural andmetallicity measurements for these objects and update the data base ofsuch measurements for the Galactic globular clusters, including newcalculations of HB morphology for 11 objects. Using these data togetherwith recent measurements of globular cluster kinematics and ages weexamine 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, althoughwe observe some old halo clusters with ages and orbits more similar tothose of young halo objects. In addition, almost all of the Galacticglobular clusters with large core radii fall into the young halosubsystem, while the old halo and bulge/disc ensembles are characterizedby compact clusters. We demonstrate that the majority of the externalglobular clusters are essentially indistinguishable from the Galacticyoung halo objects in terms of HB morphology, but ~20-30 per cent ofexternal clusters have HB morphologies most similar to the Galactic oldhalo clusters. We further show that the external clusters have adistribution of core radii which very closely matches that for the younghalo objects. The old halo distribution of core radii can be very wellrepresented by a composite distribution formed from ~83-85 per cent ofobjects with structures typical of bulge/disc clusters, and ~15-17 percent of objects with structures typical of external clusters. Takentogether our results fully support the accretion hypothesis. We concludethat all 30 young halo clusters and 15-17 per cent of the old haloclusters (10-12 objects) are of external origin. Based on cluster numbercounts, we estimate that the Galaxy may have experienced approximatelyseven merger events with cluster-bearing dwarf-spheroidal-type galaxiesduring its lifetime, building up ~45-50 per cent of the mass of theGalactic stellar halo. Finally, we identify a number of old halo objectswhich have properties characteristic of accreted clusters. Several ofthe clusters associated with the recently proposed dwarf galaxy in CanisMajor fall into this category.
| Globular Clusters as Candidates for Gravitational Lenses to Explain Quasar-Galaxy Associations
We argue that globular clusters (GCs) are good candidates forgravitational lenses in explaining quasar-galaxy associations. Thecatalog of associations (Bukhmastova 2001) compiled from the LEDAcatalog of galaxies (Paturel 1997) and from the catalog of quasars(Veron-Cetty and Veron 1998) is used. Based on the new catalog, we showthat one might expect an increased number of GCs around irregulargalaxies of types 9 and 10 from the hypothesis that distant compactsources are gravitationally lensed by GCs in the halos of foregroundgalaxies. The King model is used to determine the central surfacedensities of 135 GCs in the Milky Way. The distribution of GCs incentral surface density was found to be lognormal.
| Variable Stars in Galactic Globular Clusters
Based on a search of the literature up to 2001 May, the number of knownvariable stars in Galactic globular clusters is approximately 3000. Ofthese, more than 2200 have known periods and the majority (approximately1800) are of the RR Lyrae type. In addition to the RR Lyrae population,there are approximately 100 eclipsing binaries, 120 SX Phoenicisvariables, 60 Cepheids (including Population II Cepheids, anomalousCepheids and RV Tauri), and 120 SR/red variables. The mean period of thefundamental mode RR Lyrae variables is 0.585 days, for the overtonevariables it is 0.342 days (0.349 days for the first-overtone pulsatorsand 0.296 days for the second-overtone pulsators) and approximately 30%are overtone pulsators. These numbers indicate that about 65% of RRLyrae variables in Galactic globular clusters belong to Oosterhoff typeI systems. The mean period of the RR Lyrae variables in the Oosterhofftype I clusters seems to be correlated with metal abundance in the sensethat the periods are longer in the more metal poor clusters. Such acorrelation does not exist for the Oosterhoff type II clusters. Most ofthe Cepheids are in clusters with blue horizontal branches.
| Globular Cluster Subsystems in the Galaxy
Data from the literature are used to construct a homogeneous catalog offundamental astrophysical parameters for 145 globular clusters of theMilky Way Galaxy. The catalog is used to analyze the relationshipsbetween chemical composition, horizontal-branch morphology, spatiallocation, orbital elements, age, and other physical parameters of theclusters. The overall globular-cluster population is divided by a gap inthe metallicity function at [Fe/H]=-1.0 into two discrete groups withwell-defined maxima at [Fe/H]=-1.60±0.03 and -0.60±0.04.The mean spatial-kinematic parameters and their dispersions changeabruptly when the metallicity crosses this boundary. Metal-poor clustersoccupy a more or less spherical region and are concentrated toward theGalactic center. Metal-rich clusters (the thick disk subsystem), whichare far fewer in number, are concentrated toward both the Galacticcenter and the Galactic plane. This subsystem rotates with an averagevelocity of V rot=165±28 km/s and has a very steep negativevertical metallicity gradient and a negligible radial gradient. It is,on average, the youngest group, and consists exclusively of clusterswith extremely red horizontal branches. The population ofspherical-subsystem clusters is also inhomogeneous and, in turn, breaksup into at least two groups according to horizontal-branch morphology.Clusters with extremely blue horizontal branches occupy a sphericalvolume of radius 9 kpc, have high rotational velocities (Vrot=77±33 km/s), have substantial and equal negative radial andvertical metallicity gradients, and are, on average, the oldest group(the old-halo subsystem). The vast majority of clusters withintermediate-type horizontal branches occupy a more or less sphericalvolume ≈18 kpc in radius, which is slightly flattened perpendicularto the Z direction and makes an angle of ≈30° to the X-axis. Onaverage, this population is somewhat younger than the old-halo clusters(the young-halo subsystem), and exhibits approximately the samemetallicity gradients as the old halo. As a result, since theirGalactocentric distance and distance from the Galactic plane are thesame, the young-halo clusters have metallicities that are, on average,Δ[Fe/H] ≈0.3 higher than those for old-halo clusters. Theyoung-halo subsystem, which apparently consists of objects captured bythe Galaxy at various times, contains many clusters with retrogradeorbits, so that its rotational velocity is low and has large errors, Vrot=-23±54 km/s. Typical parameters are derived for all thesubsystems, and the mean characteristics of their member globularclusters are determined. The thick disk has a different nature than boththe old and young halos. A scenario for Galactic evolution is proposedbased on the assumption that only the thick-disk and old-halo subsystemsare genetically associated with the Galaxy. The age distributions ofthese two subsystems do not overlap. It is argued that heavy-elementenrichment and the collapse of the proto-Galactic medium occurred mainlyin the period between the formation of the old-halo and thick-disksubsystems.
| Foreground and background dust in star cluster directions
This paper compares reddening values E(B-V) derived from the stellarcontent of 103 old open clusters and 147 globular clusters of the MilkyWay with those derived from DIRBE/IRAS 100 mu m dust emission in thesame directions. Star clusters at |b|> 20deg showcomparable reddening values between the two methods, in agreement withthe fact that most of them are located beyond the disk dust layer. Forvery low galactic latitude lines of sight, differences occur in thesense that DIRBE/IRAS reddening values can be substantially larger,suggesting effects due to the depth distribution of the dust. Thedifferences appear to arise from dust in the background of the clustersconsistent with a dust layer where important extinction occurs up todistances from the Plane of ~ 300 pc. For 3 % of the sample asignificant background dust contribution might be explained by higherdust clouds. We find evidence that the Milky Way dust lane and higherdust clouds are similar to those of several edge-on spiral galaxiesrecently studied in detail by means of CCD imaging.
| B and V photometry of the metal-rich bulge globular cluster NGC 6304
We present B and V photometry of the bulge globular cluster NGC 6304. Wederive a reddening E(B-V) ~ 0.5 and a distance from the Sundsun ~ 6 kpc. From the red giant branch morphology weestimate that the metallicity of NGC 6304 is intermediate between thoseof 47 Tuc and NGC 6528. The cluster is foreground to the bulk of thebulge population and the reddenings are comparable. Evidence of a hotstellar component belonging to the cluster is found. These hot starscould correspond to a blue extended horizontal branch and/or bluestragglers. Observations collected at the European Southern Observatory-- ESO, Chile, proposal no. 61.E-0335
| Blue horizontal branch globular clusters towards the bulge: Terzan 9, NGC 6139 and NGC 6453
We present V and I photometry of the globular clusters Terzan 9 and NGC6453 for the first time, and also of NGC 6139. The three clusters areprojected towards the bulge. The Colour-Magnitude Diagram morphologiesreveal that the sample clusters have blue horizontal branches. Thischaracterizes an important fraction of the clusters projected on thebulge, with implications on the early Galaxy history. From thecolour-magnitude diagrams we derive reddenings of E(B-V) = 1.95, 0.77,0.70 and distances dsun~ 4.9, 9.4, 8.5 kpc respectively forTerzan 9, NGC 6139 and NGC 6453. We conclude that these metal-poorclusters are within the bulge volume. Observations collected at theEuropean Southern Observatory - ESO, Chile, proposal No. 61.E-0335.
| The metal-rich bulge globular cluster NGC 6401
We present V and I photometry for the bulge globular cluster NGC 6401for the first time. The Colour-Magnitude Diagram reveals a redhorizontal branch, and the cluster is metal-rich ([Fe/H] ~ -0.7). NGC6401 is located at 5.3(deg) from the Galactic center, turning out to bean interesting target to trace the extent of the bulge. A reddeningE(B-V) = 0.53+/-0.15 and a distance from the Sun dsun ~12.0+/-1.0 kpc are derived. The cluster is slightly behind the bulk ofthe bulge population in that direction, but still within the bulgevolume. Since the number of clusters with Horizontal Branch informationhas increased enormously in the later years for the central 20(deg)x20(deg), we present a discussion on the distribution of red and bluehorizontal branch clusters and their possible relation to bulge and/orhalo. Observations collected at the European Southern Observatory --ESO, Chile, proposal no. 61.E-0335
| Kinematics of the Galactic Globular Cluster System: New Radial Velocities for Clusters in the Direction of the Inner Galaxy
The High-Resolution Echelle Spectrometer (HIRES) on the Keck I telescopehas been used to measure the first radial velocities for stars belongingto 11 heavily reddened globular clusters in the direction of the innerGalaxy. The sample consists of the clusters Terzan 3, NGC 6256, IC 1257,NGC 6380 (=Ton 1), Ton 2 (=Pismis 26), Djorg 1, NGC 6540 (=Djorg 3), IC1276 (=Pal 7), Terzan 12, NGC 6749, and Pal 10. Candidate clustermembers were selected from a combination of previously publishedcolor-magnitude diagrams (CMDs) and new instrumental CMDs obtained withthe Palomar 1.5 m telescope. The systemic velocities of Djorg 1 and Pal10 should be considered provisional, since velocities are available foronly two stars. For the remaining nine clusters, we have measured radialvelocities for three to nine member stars. Using our HIRES spectra, weestimate metallicities of [Fe/H]~=-0.75 for both Terzan 3 and IC 1276,two clusters lacking previous metallicity estimates. The question ofkinematic substructuring among the Galactic globular clusters isinvestigated using an updated catalog of globular cluster distances,metallicities, and velocities. It is found that the population ofmetal-rich globular clusters shows significant rotation at allGalactocentric radii. For the metal-rich clusters within 4 kpc of theGalactic center, the measured rotation velocity and line-of-sightvelocity dispersion are similar to those of bulge field stars. Weinvestigate claims that the metal-rich clusters are associated with thecentral Galactic bar by comparing the kinematics of the innermostclusters to that of the atomic hydrogen in the inner Galaxy. Thelongitude-velocity diagram of both metal-rich and metal-poor clustersbears a remarkable similarity to that of the gas, including the samenoncircular motions that have traditionally been interpreted as evidencefor a Galactic bar, or, alternatively, a nonaxisymmetric bulge. However,uncertainties in the existing three-dimensional Galactocentric positionsfor most of the clusters do not yet allow an unambiguous discriminationbetween the competing scenarios of membership in a rigidly rotating baror in a bulge that is an oblate isotropic rotator. We conclude that themajority of metal-rich clusters within the central ~4 kpc of the Galaxyare probably associated with the bulge/bar, and not the thick disk.
| Terzan 3 and IC 1276 (Palomar 7): Two metal-rich bulge globular clusters uncovered
{Colour magnitude diagrams of Terzan 3 and IC 1276 are presented for thefirst time. The morphology of the horizontal and red giant branchesindicates that they are metal rich ([Fe/H] ~ -0.7). They areconsiderably reddened, with E(B-V) = 0.72 (Terzan 3) and E(B-V) = 1.16(IC 1276). Terzan 3 is located at a distance from the Sundsun ~ 6.5 kpc, and IC 1276 at dsun ~ 4.0 kpc.Both clusters are in the Galactic Bulge. The photometries attain themain sequence turnoff regions, and a discussion of ages is given ascompared to other bulge and halo globular clusters. } Observationscollected at the European Southern Observatory - ESO, Chile.
| Some Integrated Properties of Galactic Globular Clusters
Abstract image available at:http://adsabs.harvard.edu/abs/1996AJ....112.2634V
| A Catalog of Parameters for Globular Clusters in the Milky Way
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1996AJ....112.1487H&db_key=AST
| A Search for Radio Pulsars in Globular Clusters, Supernova Remnants and Transient X-Ray Sources
We present the results of a targeted search for radio pulsars inglobular clusters, supernova remnants (SNRs) and transient X-raysources. 85 globular clusters, 29 SNRs and three transient X-ray sourceswere observed in the course of the search, during which four pulsarswere found. For each object searched, the sensitivity limit is given.The four new pulsars discovered were all in globular clusters, namelyPSR B1620-26 in M4, PSR B1718-19 in NGC6342, and PSR B1820-30A andB1820-30B in NGC6624. While PSR B1620-26 provides strong support for thebinary evolution hypothesis for the formation of millisecond pulsars,PSR B1718-19 and B1820-30A are somewhat anomalous as they are apparentlyrelatively young, the former pulsar and PSR B1820-30B have high magneticfields, and all are located in old globular clusters (ages ~10^10yr).Not surprisingly, the well-known pulsar PSR B0531+21 was detected in theCrab nebula SNR. The number of pulsars detected was probably limited bythe finite size of pulsar emission beams, as in any survey. Otherfactors such as large distance, low pulsar luminosity and orbital motionmay have inhibited the detection of other pulsars in globular clusters.Pulsars in SNRs and transient X-ray sources are probably less affectedby these factors. Our inability to detect the former is probably due tothe relatively high level of emission from the SNRs, the limited areathat we observed within each target and possibly the high birth velocityof pulsars which carries them away from the centres of their remnants.Processes concerning the accretion discs of transient X-ray sourcesprobably thwarted the detection of any potential radio pulsars in thesesystems.
| Microlensing effects in globular star clusters
Not Available
| Faint balls of fire.
Not Available
| Perigalactic Distances of Globular Clusters
Abstract image available at:http://adsabs.harvard.edu/abs/1995AJ....110.1171V
| The ROSAT XRT Sky Survey of X-ray sources in globular clusters.
We present data obtained on globular clusters during the Rosat XRT +PSPC Sky Survey. Sources were detected in the 0.5-2.5keV range in 11globular clusters. In Ter 6 a previously unknown sources was detected byRosat ; the source H1825-331 was confirmed to be in the cluster NGC6652; the persistent flux of the known burst source in Ter 5 was alsodetected for the first time. The sources in Ter 5 and NGC 6652 aretransients, seen by Rosat in their bright state. Improved positions areobtained for the sources in NGC 6652, Ter 5, and Ter 6. From ouranalysis of the area surrounding ω Cen, we suggest that only oneof the five sources detected by Einstein is related to the globularcluster. One source was detected in the 0.07-0.5keV band only, in NGC5272. A fit of a blackbody to the spectrum of the source in NGC 5272gives a temperature of ~45eV, and a bolometric luminosity of~1.3x10^35^erg/s. Upper limits of sources in clusters for which onlyHEAO-1 observations were available have been improved by factors ten tohundred, and indicate that most clusters do not contain sources withluminosities L_x_(0.5-2.5keV)>3x10^32^erg/s.
| Catalogue of Galactic globular-cluster surface-brightness profiles
We present a catalogue of surface-brightness profiles (SBPs) of 125Galactic globular clusters, the largest such collection ever gathered.The SPBs are constructed from generally inhomogeneous data, but arebased heavily on the Berkeley Global Cluster Survey of Djorgovski &King. All but four of the SBPs have photometric zero points. We derivecentral surface brightness, King-model concentrations, core radii,half-light, and other fraction-of-light radii where data permit, and webriefly discuss their use.
| A project for investigation of the stellar population of the galactic disk.
Not Available
| Space distribution and metallicities of globular clusters: The distance to the galactic centre
The system of globular clusters in the Galaxy is used in order to locatethe position of the galactic centre and, consequently, to determine thegalacto-centric distance of the Sun, R0. The spacedistribution and metallicities of the whole sample of known globularclusters are taken in to account, and the obtained results indicate that8.6 greater than R0 (kpc) greater than 6.4. Analysis of aselected sample of clusters further suggests that R0 equals7.6 +/- 0.4 kpc.
| Infrared Study of Globular Clusters Near the Galactic Center
The study of globular clusters near the galactic center is important toour understanding of the dynamics and chemical evolution of the Galaxyas well as our understanding of the evolution of low-mass stars. Becausethese bulge clusters are heavily obscured by interstellar dust, opticalobservations are difficult or even impossible. Using the UCLA 256x256infrared camera (KCAM) and also infrared cameras at Kitt Peak and IRTFwe have obtained IR images for a set of clusters which are located closeto the galactic center, including Terzan 1, Terzan 2, Terzan 4, Terzan5, Terzan 6, Terzan 9, Terzan 10, and UKS 1. Some of these clusters areobscured by up to 10 magnitudes in visual extinction. In addition, wehave also obtained K band and R band images for eight globular clusterswhich are located in the bulge of the Galaxy and therefore havesignificant but less reddening than the former sample. They are NGC6366, NGC 6402, NGC 6517, NGC 6539, NGC 6544, IC 1276, NGC 6712, and NGC6749. For both samples profile fitting photometry is performed on theimages to derive infrared magnitudes that allow us to construct infraredcolor-magnitude diagrams for giant branch stars in these clusters. Forsome of the observed clusters, the derived CMDs include cluster starsfainter than the horizontal branch. These observations allow improved orin some cases the only estimates of structural parameters, reddening,metallicity, horizontal branch morphology, and distances for theseclusters. These observations will also eventually be used to constrainmodels for the evolution of low-mass stars with near solar abundances.
| Dynamical masses for Galactic globular clusters
Dynamical masses have been determined for 147 Galactic globular clustersare found to be between 260 and 2.4 x 10 exp 6 solar masses, with a meanof 1.9 x 10 exp 5 solar masses. The mass-to-light ratios of the sampleof 32 cluster range from 0.66 to 2.9, with a mean of 1.21. It is shownthat some clusters of low and intermediate mass lie outside the survivalzone in the (log M - log rb) diagram. This is considered to be evidencefor rapid mass loss through stellar evaporation. It is also found thatthe M/L(v) ratio is most likely dependent on the cluster mass, with themost massive clusters having the largest M/L(v) ratios. A comparisonbetween the masses obtained with single-component and multicomponentKing models show that the mass-luminosity relations for both types ofmodels are parallel within uncertainties, and that the multicomponentmasses are about twice as large as the single-component ones.
| Metal abundances of RR Lyrae variables in selected Galactic star fields. V - The Lick Astrographic fields at intermediate Galactic latitudes
Metal abundances are derived for 60 newly discovered RR Lyraes in threeLick Astrographic Survey fields at three Galactic altitudes (l,b): (86deg, +35 deg), (52 deg, +35 deg), and (18 deg, +25 deg). In addition,Delta S values were obtained for five nearby field RR Lyraes which haveno previous records, and improved Delta S values were obtained for 24nearby RR Lyraes. These values, in conjunction with data from previousLick surveys and those obtained by Saha and Oke (1985), were used tostudy the nature of the Galactic halo in the galactocentric distancerange 4-30 kpc, based on 171 Lyraes. It was found that the Galactic haloundergoes a change in the behavior of the Fe/H ratio at the position ofthe solar circle.
| An IRAS search for dust in globular clusters
The IRAS Point-Source Catalog, Small-Scale Structure Catalog, and HCON1Sky Brightness Images were searched for sources of emission that werespatially coincident with any of 144 globular clusters. The purpose wasto measure or place upper limits on the amount of thermal dust emissionfrom the clusters, which would lead to estimates and upper limits to themass of intraglobular dust. Sputtering by hot gas in the galactic halocan destroy dust grains and thus possibly explain the absence of dust inglogular clusters.
| The pulsar content of globular clusters
Recent surveys of Galactic globular clusters have been very effective atdiscovering radio pulsars. By a careful analysis of selection effects inthe various surveys, and after estimating the relative efficiency ofpulsar production in the individual clusters, a census of the clusterpopulation of pulsars is obtained. It is found that there are about10,000 pulsars in the Galactic globular clusters, subject touncertainties in pulsar beaming and binarity. Such a large populationposes severe problems for the standard model of pulsar production inclusters, unless the uncertain factors due to beaming and binary arepushed to values inconsistent with the present expectations. Thissuggests the need for a substantial modification of the standard model,either by including accretion-induced collapse of massive white dwarfsor by increasing the retention of primordial neutron stars in theclusters.
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