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Near-Infrared Properties of 24 Globular Clusters in the Galactic Bulge
We present near-IR color-magnitude diagrams and physical parameters fora sample of 24 Galactic globular clusters toward the bulge. In thispaper we discuss the properties of 12 new clusters (out of the 24) inaddition to those previously studied and published by our group. Thecompilation includes measurements of the cluster reddening, distance,photometric metallicity, horizontal branch red clump, and red giantbranch morphological (e.g., mean ridgelines) and evolutionary (e.g.,bump and tip) features. The compilation is available in electronic formon the World Wide Web, and it will be updated regularly.Based on data taken at the ESO New Technology Telescope, within theobserving programs 73.D-0313, 75.D-0372, and 77.D-0757.
| 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.
| An Empirical Tool to Derive Metallicity, Reddening, and Distance for Old Stellar Populations from Near-Infrared Color-Magnitude Diagrams
We present an empirical method to derive photometric metallicity,reddening, and distance to old stellar populations by using a few majorfeatures of the red giant branch (RGB) in near-IR color-magnitudediagrams. We combine the observed RGB features with a set of equationslinking the global metallicity [M/H] to suitable RGB parameters (colors,magnitudes, and slope), as calibrated from a homogeneous sample ofGalactic globular clusters with different metallicities. This techniquecan be applied to efficiently derive the main population parameters ofold stellar systems, with the goal of using ground-based adaptive opticsand space facilities to probe the stellar content of remote galaxies.Based on observations collected at the European Southern Observatory(ESO), La Silla, Chile. Also based on observations made with the ItalianTelescopio Nazionale Galileo (TNG), operated on the island La Palma bythe Fundacion Galileo Galilei of INAF (Istituto Nazionale diAstrofisica) at the Spanish Observatorio del Roque de los Muchachos ofthe Instituto de Astrofisica de Canarias.
| An Empirical Calibration of the Mixing-Length Parameter α
We present an empirical calibration of the mixing-length free parameterα based on a homogeneous infrared database of 28 Galactic globularclusters spanning a wide metallicity range (-2.15<[Fe/H]<-0.2).Empirical estimates of the red giant effective temperatures have beenobtained from infrared colors. Suitable relations linking thesetemperatures to the cluster metallicity have been obtained and comparedto theoretical predictions. An appropriate set of models for the Sun andPopulation II giants has been computed by using both the standard solarmetallicity (Z/X)solar=0.0275 and the most recently proposedvalue (Z/X)solar=0.0177. We find that when the standard solarmetallicity is adopted, a unique value of α=2.17 can be used toreproduce both the solar radius and the Population II red gianttemperature. Conversely, when the new solar metallicity is adopted, twodifferent values of α are required: α=1.86 to fit the solarradius and α~2.0 to fit the red giant temperatures. However, itmust be noted that regardless the adopted solar reference, theα-parameter does not show any significant dependence onmetallicity.Based on observations collected at the European Southern Observatory(ESO), La Silla, Chile. Also based on observations made with the ItalianTelescopio Nazionale Galileo (TNG) operated on the island of La Palma bythe Fundacion Galileo Galilei of the INAF (Istituto Nazionale diAstrofisica) at the Spanish Observatorio del Roque de los Muchachos ofthe Instituto de Astrofisica de Canarias.
| 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.
| Infrared Photometry of NGC 6791
We present deep JHK photometry of the old and metal-rich open clusterNGC 6791. The photometry reaches below the main-sequence turnoff toK~16.5 mag. We combine our photometry with that from Stetson et al. toprovide color-magnitude diagrams showing K versus J-K, K versus V-K, andV versus V-K. We study the slope of the red giant branch in the infraredbut find that it is not a useful metallicity indicator for the cluster,nor any metal-rich cluster that lacks a well-populated red giant branch,because it is not linear, as has often been assumed, in K versus J-K.The mean color of the red horizontal-branch/red clump stars provide anestimate of the cluster reddening, E(B-V)=0.14+/-0.04 mag for[Fe/H]=+0.4+/-0.1. The mean magnitudes of these stars also provide agood distance estimate, (m-M)0=13.07+/-0.04. Finally, we findthat the isochrones of Yi et al. provide optimal fits in V versus B-Vand V-K and K versus J-K and V-K for such values if [Fe/H] lies between+0.3 and +0.5 (with a slight preference for +0.5) and ages between 9 Gyr([Fe/H]=+0.3) and 7.5 Gyr ([Fe/H]=+0.5).Based on observations made with the Mayall 4 m Telescope of the NationalOptical Astronomy Observatory.
| 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.
| Red giant branch in near-infrared colour-magnitude diagrams - II. The luminosity of the bump and the tip
We present new empirical calibrations of the red giant branch (RGB) bumpand tip based on a homogeneous near-infrared data base of 24 Galacticglobular clusters. The luminosities of the RGB bump and tip in the J, Hand K bands and their dependence on the cluster metallicity have beenstudied, yielding empirical relationships. By using recenttransformations between the observational and theoretical planes, wealso derived similar calibrations in terms of bolometric luminosity.Direct comparisons between updated theoretical models and observationsshow an excellent agreement. The empirical calibration of the RGB tipluminosity in the near-infrared passbands presented here is afundamental tool to derive distances to galaxies far beyond the LocalGroup, in view of using the new ground-based adaptive optics facilitiesand, in the near future, the James Webb Space Telescope.
| Red giant branch in near-infrared colour-magnitude diagrams - I. Calibration of photometric indices
We present new high-quality near-infrared photometry of 10 Galacticglobular clusters spanning a wide metallicity range (-2.12<=[Fe/H]<=- 0.49): five clusters belong to the halo (NGC 288, 362,6752, M15 and M30) and five (NGC 6342, 6380, 6440, 6441 and 6624) to thebulge. By combining J, H and K observations with optical data, weconstructed colour-magnitude diagrams in various planes: (K, J-K), (K,V-K), (H, J-H) and (H, V-H). A set of photometric indices (colours,magnitudes and slopes) describing the location and the morphology of thered giant branch (RGB) have been measured. We have combined this newdata set with those collected by our group over the last 5 years, andhere we present an updated calibration of the various RGB indices in theTwo-Micron All-Sky Survey photometric system, in terms of the clustermetallicity.
| HST color-magnitude diagrams of 74 galactic globular clusters in the HST F439W and F555W bands
We present the complete photometric database and the color-magnitudediagrams for 74 Galactic globular clusters observed with the HST/WFPC2camera in the F439W and F555W bands. A detailed discussion of thevarious reduction steps is also presented, and of the procedures totransform instrumental magnitudes into both the HST F439W and F555Wflight system and the standard Johnson ( B ) and ( V ) systems. We alsodescribe the artificial star experiments which have been performed toderive the star count completeness in all the relevant branches of thecolor magnitude diagram. The entire photometric database and thecompleteness function will be made available on the Web immediatelyafter the publication of the present paper. Based on observations withthe NASA/ESA Hubble Space Telescope, obtained at the Space TelescopeScience Institute, which is operated by AURA, Inc., under NASA contractNAS5-26555, and on observations retrieved from the ESO ST-ECF Archive.
| 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.
| A census with ROSAT of low-luminosity X-ray sources in globular clusters
I analyze 101 observations from the ROSAT archive to search for X-raysources in or near 55 globular clusters. New sources are found in thecores of NGC 362 (a double source), NGC 6121 (marginally significant),NGC 6139, and NGC 6266; and outside the cores of NGC 6205, NGC 6352 andNGC 6388. More accurate positions are determined for the X-ray sourcesin some ten clusters. The improved position for the source in NGC 6341excludes the suggested ultraviolet counterpart. It is shown that one ofthe two sources reported near the core of NGC 6626 is spurious, as isthe detection of a pulsar period in the PSPC data of this cluster; thecentral source is resolved in three sources. One source reportedpreviously in NGC 6304 is demoted to an upper limit. For 20 clustercores better upper limits to the X-ray luminosity are obtained. From astatistical analysis I argue that several sources outside the clustercores may well belong to the clusters. All spectral energy distributionsobserved so far are relatively soft, with bremsstrahlung temperatures =~0.9 keV; there is evidence however that bremsstrahlung spectra do notcorrectly describe the spectra. The X-ray luminosity per unit mass forthe cluster as a whole does not depend on the concentration; theluminosity per unit mass for the core may increase with the clusterconcentration.
| Astrophysical implications of gravitational microlensing of gravitational waves
Astrophysical implications of gravitational microlensing ofgravitational waves emitted by rotating neutron stars (NSs) areinvestigated. In particular, attention is focused on the followingsituations: i) NSs in the galactic bulge lensed by a central black holeof 2.6; 106 Msun or by stars and MACHOsdistributed in the galactic bulge, disk and halo between Earth and thesources; ii) NSs in globular clusters lensed by a central black hole of~ 103 Msun or by stars and MACHOs distributedthroughout the Galaxy. The detection of such kind of microlensing eventswill give a unique opportunity for the unambiguous mapping of thecentral region of the Galaxy and of globular clusters. In addition, thedetection of such events will provide a new test of the General Theoryof Relativity. Gravitational microlensing will, moreover, increase thechallenge of detecting gravitational waves from NSs.
| 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
| 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.
| Integrated spectral study of reddened globular clusters and candidates
This paper presents integrated spectra in the range 6700 - 9500Angstroms for 20 Galactic globular clusters (and candidates) in thebulge and 5 others projected on the Galactic disk (|l|>30mbox{^{\circ}}\ and |b|<5mbox {^{\circ}}). Most of them are considerablyreddened and are among those least studied in the literature. We derivereddening and metallicity from flux-calibrated spectra, thus providingindependent information of that derived through colour-magnitudestudies. For some clusters in the sample, these parameters have beendetermined for the first time, and for others a considerable revision isgiven. We indicate the globular clusters which definitely belong to thebulge metal-rich and intermediate metallicity families. Among theobjects projected on the disk, we find that the integrated spectralproperties of Lyng\aa 7, BH 176 and Palomar 10 are compatible with thoseof metal-rich globular clusters. Finally, ESO 93-SC08 is an old opencluster, and UKS 2 is an open cluster with age ~1 Gyr. Based onobservations made at the Complejo Astronómico El Leoncito(CASLEO), Argentina, and European Southern Observatory (ESO), Chile.
| V, I photometry of the bulge metal-rich globular clusters NGC 6380 and Terzan 12
We present V, I photometry of the bulge globular clusters NGC 6380 andTerzan 12, using the ESO NTT telescope. For the first timecolour-magnitude diagrams are obtained for these clusters, allowing usto derive reliable cluster parameters. From the colour-magnitude diagrammorphology both clusters result to be metal-rich. For NGC 6380 weestimate [Fe/H] ~ -0.5, a reddening of E(B-V) = 1.07 and a distancedsun= 9.8\ kpc. For Terzan 12 we obtain [Fe/H] ~ -0.5, E(B-V)= 2.06 and dsun~ 3.4\ kpc. Observations collected at theEuropean Southern Observatory - ESO, Chile; Tables 2, 3 are availableonly in electronic form at the CDS via anonymous ftp 130.79.128.5 or viahttp://cdsweb.u-strasbg.fr/Abstract.html
| 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
| The globular cluster population of low-luminosity X-ray sources.
More than thirty low-luminosity X-ray sources (withL_x_<~10^34.5^erg/s) have now been discovered in globular clusters.The nature of these sources is still unclear. One important question ishow the number of sources scales with cluster parameters such as centraldensity or cluster mass. Because the detected sample is biased towardsthe brightest sources, such an analysis must rely on knowledge of theunderlying luminosity function. We present here a statistical analysisof current observations of dim cluster X-ray sources. We determine theluminosity function to be dN/dL{prop.to}L^-1.5^, and find that thenumber of dim X-ray sources per cluster scales less steeply with coredensity than predicted by the two-body tidal capture model, just as docluster pulsars.
| 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.
| EGRET upper limits to the high-energy gamma-ray emission from the millisecond pulsars in nearby globular clusters
We report upper limits to the high-energy gamma-ray emission from themillisecond pulsars (MSPs) in a number of globular clusters. Theobservations were done as part of an all-sky survey by the energeticGamma Ray Experiment Telescope (EGRET) on the Compton Gamma RayObservatory (CGRO) during Phase I of the CGRO mission (1991 June to 1992November). Several theoretical models suggest that MSPs may be sourcesof high-energy gamma radiation emitted either as primary radiation fromthe pulsar magnetosphere or as secondary radiation generated byconversion into photons of a substantial part of the relativistic e(+/-)pair wind expected to flow from the pulsar. To date, no high-energyemission has been detected from an individual MSP. However, a largenumber of MSPs are expected in globular cluster cores where theformation rate of accreting binary systems is high. Model predictions ofthe total number of pulsars range in the hundreds for some clusters.These expectations have been reinforced by recent discoveries of asubstantial number of radio MSPs in several clusters; for example, 11have been found in 47 Tucanae (Manchester et al.). The EGRETobservations have been used to obtain upper limits for the efficiencyeta of conversion of MSP spin-down power into hard gamma rays. The upperlimits are also compared with the gamma-ray fluxes predicted fromtheoretical models of pulsar wind emission (Tavani). The EGRET limitsput significant constraints on either the emission models or the numberof pulsars in the globular clusters.
| ROSAT Observations of Nine Globular Clusters
Abstract image available at:http://adsabs.harvard.edu/abs/1994ApJ...423..633R
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