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Metallicity and age gradients in round elliptical galaxies
Aims.We probe the stellar population age and metallicity distributionsin nearby elliptical galaxies over the largest extension to date. Methods: Long-slit spectroscopy is made by using the spectrographSCORPIO of the 6-m telescope of the Special Astrophysical Observatory ofthe Russian Academy of Sciencies. The Lick indices Hβ, Mg b, Fe5270, and Fe 5335 are calculated along the slit up to radii of 1.3 to3re in 4 galaxies and up to 0.5re in the fifthone. The comparison with evolutionary synthesis models of simple stellarpopulations allows us to disentangle age and metallicity and to measureboth. Results: We have found that the mean stellar age is constantalong the radius only in one galaxy out of 5. The other 4 galaxiesdemonstrate quite different behaviour of the mean stellar age: the outerparts are older than the centres in 3 cases and younger - in one case.The metallicity gradients cannot be approximated by a single power lawover the full radial extension in 4 galaxies of 5. The inner metallicitygradients within 0.5re are all rather steep, steeper than-0.4 metallicity dex per radius dex, and are inconsistent with theorigin of the elliptical galaxies by a major merger.Based on observations collected with the 6 m telescope of the SpecialAstrophysical Observatory (SAO) of the Russian Academy of Sciences (RAS)which is operated under the financial support of Science Department ofRussia (registration number 01-43).
| 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.
| Variable Stars in Metal-Rich Globular Clusters. III. NGC 6539
We present the first CCD-based search for variable stars in themetal-rich globular cluster NGC 6539 ([Fe/H]~-0.7). Our VI photometry ofstars within 7' of the cluster center shows a color-magnitude diagramwith a normal red clump horizontal-branch morphology without theextension of blue stars seen in two globular clusters of comparablemetallicity, NGC 6388 and NGC 6441. We have discovered 13 variablestars, 12 of which are long-period variables (LPVs), and have usedinfrared photometry from the Two Micron All Sky Survey to furtherclarify their position in the color-magnitude diagram. We find thespecific frequency of these stars, SLPV=0.32, to becomparable to those found in other clusters recently surveyed. We havealso detected one RR Lyrae variable star in our data, although it isunlikely to be a cluster member. The color of this star, when comparedwith low-reddening RR Lyrae stars near the Sun, indicates aninterstellar reddening of E(V-I)=1.22 mag toward NGC 6539, in excellentagreement with estimates from the literature.
| 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.
| Near-infrared photometry and spectroscopy of NGC 6539 and UKS 1: two intermediate metallicity bulge globular clusters*
Using the `son of ISAAC' (Infrared Spectrometer And Array Camera) imagerat the European Southern Observatory New Technology Telescope and thenear-infrared spectrographs on Keck II, we have obtained J, K images andechelle spectra covering the range 1.5-1.8μm for the intermediatemetallicity bulge globular clusters NGC 6539 and UKS 1. We find[Fe/H]=-0.76 and -0.78, respectively, and an average α-enhancementof ~+0.44 and ~+0.31 dex, consistent with previous measurements ofmetal-rich bulge clusters, and favouring the scenario of rapid chemicalenrichment. We also measure very low 12C/13C ~ 4.5+/- 1 isotopic ratios in both clusters, suggesting that extra-mixingmechanisms due to cool bottom processing are at work during evolutionalong the red giant branch. Finally, we measure accurate radialvelocities of =+31 +/- 4 and=+57 +/- 6 km s-1 and velocitydispersions of ~8 and ~11 km s-1 for NGC 6539 and UKS 1,respectively,
| The Australia Telescope National Facility Pulsar Catalogue
We have compiled a new and complete catalog of the main properties ofthe 1509 pulsars for which published information currently exists. Thecatalog includes all spin-powered pulsars, as well as anomalous X-raypulsars and soft gamma-ray repeaters showing coherent pulsed emission,but excludes accretion-powered systems. References are given for alldata listed. We have also developed a new World Wide Web interface foraccessing and displaying either tabular or plotted data with the optionof selecting pulsars to be displayed via logical conditions on parameterexpressions. The Web interface has an ``expert'' mode giving access to awider range of parameters and allowing the use of custom databases. Forusers with locally installed software and database on Unix or Linuxsystems, the catalog may be accessed from a command-line interface.C-language functions to access specified parameters are also available.The catalog is updated from time to time to include new information.
| A robust method for the analysis of integrated spectra from globular clusters using Lick indices
We define a method for the analysis of the integrated spectra ofextragalactic globular clusters that provides more reliable measures ofthe age, metallicity and α-element abundance ratio than have sofar been achieved. The method involves the simultaneous fitting of up to25 Lick indices in a χ2 fitting technique that maximizesthe use of the available data. Here we compare three sets of singlestellar population (SSP) models of Lick indices to the highsignal-to-noise, integrated spectra of 20 Galactic globular clusters.The ages, [Fe/H] and α-element abundance ratios derived from theSSP models are compared with the results of resolved stellar populationstudies from the literature. We find good consistency with the publishedvalues, with an agreement of better than 0.1 dex in all three derivedparameters. The technique allows the identification of abundance ratioanomalies, such as the known nitrogen overabundance in Galactic globularclusters, and the presence of anomalous horizontal branch morphologies.It also minimizes the impact on the derived parameters of imperfectcalibration to the Lick system, and reduction errors in general. Themethod defined in this paper is therefore robust with respect to many ofthe difficulties that plague the application of SSP models in general.Consequently, it is well suited to the study of extragalactic globularcluster systems.
| Long-term timing observations of 374 pulsars
We present pulsar timing solutions for 374 pulsars. Each ephemeris wasobtained by analysing archival data stored at Jodrell Bank Observatory.This data archive contains over 5600 yr of pulsar rotational historywith individual data-spans of up to 34 yr. A new method has beendeveloped to mitigate the effects of timing noise by whitening thepulsar timing residuals. This whitening is applied before standardfitting procedures are followed to measure the astrometric anddispersion measure (DM) parameters of a pulsar. We show that the valuesobtained using this new technique are consistent with other methods, andthat the new timing solutions are, in general, significantly moreprecise than those in earlier publications. We consider the secondderivative of the frequency ν of pulsars, , and the DM gradient,d(DM)/dt, in detail. The values are obtained by fitting to timingresiduals that have not been whitened and are found to be orders ofmagnitude larger than those expected from magnetic dipole radiation; themeasured values are dominated by the effects of timing noise, andtherefore lead to braking indices that are not consistent with magneticdipole radiation. We find a dependence between |d(DM)/dt| and DM of pcyr-1, which allows DM variations to be estimated for anyradio pulsar.
| The Chemical Properties of Milky Way and M31 Globular Clusters. I. A Comparative Study
A comparative analysis is performed between high-quality integratedspectral indices of 30 M31 globular clusters, 20 Milky Way globularclusters, and a sample of field and cluster elliptical galaxies. We findthat the Lick CN indices in the M31 and Galactic clusters are enhancedrelative to the bulges of the Milky Way, M31, and elliptical spheroids,in agreement with Burstein and coworkers. Although not particularlyevident in the Lick CN indices, the near-UV cyanogen feature(λ3883) is strongly enhanced with respect to the Galacticglobular clusters at metallicities -1.5<[Fe/H]<-0.3. Carbon showssigns of varying among these two groups. For [Fe/H]>-0.8, we observeno systematic differences in the Hδ, Hγ, or Hβ indicesbetween the M31 and Galactic globular clusters, in contrast to previousstudies. The elliptical galaxy sample lies offset from the loci of theglobular clusters in both the cyanogen-[MgFe] and Balmer-line-[MgFe]planes. Six of the M31 clusters appear young and are projected onto theM31 disk. Population synthesis models suggest that these are metal-richclusters with ages 100-800 Myr, metallicities -0.20<=[Fe/H]<=0.35,and masses 0.7-~7.0×104 Msolar. Two otheryoung clusters are Hubble V in NGC 205, observed as a template, and anolder (~3 Gyr) cluster some 7 kpc away from the plane of the disk. Thesix clusters projected onto the disk show signs of rotation similar tothe H I gas in M31, and three clusters exhibit thin disk kinematics,according to Morrison and coworkers. Dynamical mass estimates anddetailed structural parameters are required for these objects todetermine whether they are massive open clusters or globular clusters.If they are the latter, our findings suggest globular clusters may tracethe buildup of galaxy disks. In either case, we conclude that theseclusters are part of a young, metal-rich disk cluster system in M31,possibly as young as 1 Gyr old.
| Pulsars in Binary Systems: Probing Binary Stellar Evolution and General Relativity
Radio pulsars in binary orbits often have short millisecond spin periodsas a result of mass transfer from their companion stars. They thereforeact as very precise, stable, moving clocks that allow us to investigatea large set of otherwise inaccessible astrophysical problems. Theorbital parameters derived from high-precision binary pulsar timingprovide constraints on binary evolution, characteristics of the binarypulsar population, and the masses of neutron stars with differentmass-transfer histories. These binary systems also test gravitationaltheories, setting strong limits on deviations from general relativity.Surveys for new pulsars yield new binary systems that increase ourunderstanding of all these fields and may open up whole new areas ofphysics, as most spectacularly evidenced by the recent discovery of anextremely relativistic double-pulsar system.
| Green Bank Telescope Discovery of Two Binary Millisecond Pulsars in the Globular Cluster M30
We report the discovery of two binary millisecond pulsars in thecore-collapsed globular cluster M30 using the Green Bank Telescope (GBT)at 20 cm. PSR J2140-2310A (M30A) is an eclipsing 11 ms pulsar in a 4 hrcircular orbit, and PSR J2140-23B (M30B) is a 13 ms pulsar in an as yetundetermined but most likely highly eccentric (e>0.5) andrelativistic orbit. Timing observations of M30A with a 20 month baselinehave provided precise determinations of the pulsar's position (within 4"of the optical centroid of the cluster) and spin and orbital parameters,which constrain the mass of the companion star to bem2>~0.1Msolar. The position of M30A iscoincident with a possible thermal X-ray point source found in archivalChandra data, which is most likely caused by emission from hot polarcaps on the neutron star. In addition, there is a faint(V555~23.8) star visible in archival Hubble Space Telescope(HST) F555W data that may be the companion to the pulsar. Eclipses ofthe pulsed radio emission from M30A by the ionized wind from the compactcompanion star show a frequency-dependent duration(~ν-α with α~0.4-0.5) and delay the pulsearrival times near eclipse ingress and egress by up to 2-3 ms. Futureobservations of M30 may allow both the measurement of post-Keplerianorbital parameters from M30B and the detection of new pulsars throughthe effects of strong diffractive scintillation.
| Keck spectroscopy and imaging of globular clusters in the lenticular galaxy NGC 524
We have obtained Keck Low-Resolution Imaging Spectrometer imaging andspectra for 29 globular clusters associated with the lenticular galaxyNGC 524. Using the empirical calibration of Brodie & Huchra we findthat our spectroscopic sample spans a metallicity range of -2.0<=[Fe/H]<= 0. We have compared the composite spectrum of themetal-poor ([Fe/H] < -1) and metal-rich clusters with stellarpopulation models in order to estimate the ages of the NGC 524 globularclusters. We conclude that the clusters are generally old, and arecoeval at the 2σ confidence level. To determine the mean[α/Fe] ratios of the globular clusters, we have employed theMilone et al. α-enhanced stellar population models. We verifiedthe reliability of these models by comparing them with highsignal-to-noise Galactic globular cluster spectra. We observe a weaktrend of decreasing [α/Fe] ratios with increasing metallicity inthe NGC 524 clusters; the metal-poor clusters possess [α/Fe]~0.3,whilst the metal-rich clusters exhibit [α/Fe] ratios closer tosolar-scaled values. Analysis of the cluster system kinematics revealsthat the full sample (excluding an outlying cluster) exhibits a rotationof 114 +/- 60 km s-1 around a position angle of 22°+/-27°, and a velocity dispersion of 186 +/- 29 km s-1 at amean radius of 89 arcsec from the galaxy centre. Subdividing theclusters into metal-poor and metal-rich subcomponents (at [Fe/H]=-1.0),we find that the metal-poor (17) clusters and metal-rich (11) clustershave similar velocity dispersions (197 +/- 40 and 169 +/- 47 kms-1, respectively). However, the metal-poor clusters dominatethe rotation in our sample with 147 +/- 75 km s-1, whilst themetal-rich clusters show no significant rotation (68 +/- 84 kms-1). We derive a virial and projected mass estimation forNGC 524 of between 4 and 13 × 1011 Msolar(depending on the assumed orbital distribution) interior to ~2 effectiveradii of this galaxy.
| An Infrared Spectroscopic Study of Eight Galactic Globular Clusters
We have obtained medium-resolution infrared K-band spectra of 44 giantsin seven heavily reddened clusters in the Galactic bulge, as well as 12giants in ω Centauri. We measure the equivalent widths of the Nadoublet, the Ca triplet, and the CO band head, and then apply the newtechnique of Frogel et al. to determine the metallicity of each star.Averaging these values, we estimate the metallicity for each cluster andcompare our new [Fe/H] values with previous determinations from theliterature. Our estimates for each cluster are NGC 6256 (-1.35), NGC6539 (-0.79), HP 1 (-1.30), Liller 1 (-0.36), Palomar 6 (-0.52), Terzan2 (-0.87), and Terzan 4 (-1.62). We briefly discuss differences betweenthe various [Fe/H] scales on which it was possible to base ourcalibration, which is found to be the largest uncertainty in using thistechnique to determine metallicities.
| 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.
| 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 Reexamination of the Distribution of Galactic Free Electrons
We present a list of 109 pulsars with independent distance informationcompiled from the literature. Since the compilation of Frail &Weisberg, there are 35 pulsars with new distance estimates and 25pulsars for which the distance or distance uncertainty have beenrevised. We used this data to fit a smooth, axisymmetric, two-disk modelof the distribution of Galactic electrons. The two exponential modelcomponents have mean local midplane densities at the solar circle of2.03×10-2 and 0.71×10-2cm-3, and scale heights of 1.07 and 0.053 kpc. The thickcomponent shows very little radial variation, while the second has aradial scale length of only a few kiloparsecs. We also examined a modelthat varies as sech2x, rather than exp(-x), in both theradial and vertical directions. We prefer this model with no midplanecusp but find that the fit parameters essentially describe the sameelectron distribution. The distances predicted by this distribution havea similar scatter to that produced by the more complex model of Taylor& Cordes. We examine the pulsars that deviate strongly from thismodel. There are two regions of enhanced dispersion measure, one ofwhich correlates well with the Sagittarius-Carina spiral arm. We findthat the scatter of the observed dispersion measure from the model isnot fitted well by either a normal or a lognormal distribution of lumpsizes but may be caused instead by the uncertainties in the distances.
| 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.
| Deep Radio Imaging of Globular Clusters and the Cluster Pulsar Population
We have obtained deep multifrequency radio observations of sevenglobular clusters using the Very Large Array and the Australia TelescopeCompact Array. Five of these, NGC 6440, NGC 6539, NGC 6544, NGC 6624,and Terzan 5, had previously been detected by Fruchter & Goss in ashallower survey for steep-spectrum radio sources in globular clusters.The sixth, the rich globular cluster Liller 1, had heretofore beenundetected in the radio, and the seventh, 47 Tucanae, was not includedin our original survey. High-resolution 6 and 20 cm images of three ofthe clusters, NGC 6440, NGC 6539, and NGC 6624, reveal only pointsources coincident with pulsars which have been discovered subsequent toour first imaging survey; 21 and 18 cm images reveal several pointsources within a few core radii of the center of 47 Tuc. Two of theseare identified pulsars, and a third, which is variable and has a steepspectrum, is also most likely a pulsar previously identified by a pulsedsurvey. However, the 6, 20, and 90 cm images of NGC 6544, Liller 1, andTerzan 5 display strong steep-spectrum emission which cannot beassociated with known pulsars. The 90 cm flux densities of Terzan 5,Liller 1, and NGC 6544 are 35, 9, and 6 mJy, respectively, implying thata number of bright pulsars in these clusters have been hidden frompulsed searches. The image of the rich cluster Terzan 5 displaysnumerous point sources within 30", or 4 core radii, of the clustercenter. The density of these objects rises rapidly toward the core,where an elongated region of emission is found. This feature may be dueto the presence of a higher density of point sources than can beresolved by the 1" resolution of our data. The brightest individualsources, as well as the extended emission, possess the steep spectraexpected of pulsars. Furthermore, the flux distribution of the sourcesagrees well with the standard pulsar luminosity function. The totalluminosity and number of objects observed suggest that Terzan 5 containsmore pulsars than any other Galactic globular cluster.
| 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
| The metal-rich globular clusters of the Milky Way
We present new (V,V-I)-photometry of the metal-rich globular clustersNGC 5927, 6316, 6342, 6441 and 6760. The clustersshow differential reddening up to delta E_{V-I}=0.32 mag, for which theCMDs are corrected via extinction maps. There are hints of a variationin the extinction law. Two different ways to determine the parametersmetallicity, reddening and distance lead to consistent results. Themetallicities of the clusters range between -0.7 <= [M/H] <= 0.0dex and the absolute reddening between 0.43 <= E_{V-I} <= 0.76mag. Taking the differential reddening into account leads to slightlyincreased distances. From the resulting parameters we conclude that theusual halo-disk-distinction in the system of globular clusters seemsquestionable.
| The evolution of short-period binary pulsars: a systematic study
We present evolutionary sequences for low-mass close binary systems inwhich a low-mass (1.0-1.5 Msolar) secondary star transfers mass to aneutron star. Roche lobe filling occurs when the secondary is a turn-offmain-sequence star (having a small helium core). We assume loss ofangular momentum owing to gravitational wave radiation and magneticbraking. We have found that the loss (and the mechanism of loss) of massand angular momentum from the system is the main factor determining thevalue of the bifurcation period (P_bif). The bifurcation periodseparates the formation of the converging systems from the divergingsystems. Variations in the initial chemical composition, and in theinitial mass of the secondary, lead only to minor changes in P_bif. Wehave also investigated how changes in the chemical composition influencethe initial orbital period (P_i) versus final orbital period (P_f)relation. The initial chemical composition has a more significant effecton this relation for shorter P_i than for longer P_i. We have foundsystematic differences for the P_f versus white dwarf mass relation forvarious chemical compositions. For converging systems, we have foundthat there is a boundary orbital period (P_b) such that if P_i
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