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The Luminosity Distribution of Globular Clusters in Dwarf Galaxies
The majority of the globular clusters associated with the Sagittariusdwarf galaxy are faint. In this respect it differs significantly fromthe globular cluster systems surrounding typical giant galaxies. Theobservation that most of the globular clusters in the outer halo of theGalaxy are also subluminous may be understood by assuming that theseclusters once also belonged to faint cluster-rich dwarf systems thatwere subsequently captured and destroyed by the Milky Way system.
| Where the Blue Stragglers Roam: Searching for a Link between Formation and Environment
The formation of blue stragglers is still not completely understood,particularly the relationship between formation environment andmechanism. We use a large, homogeneous sample of blue stragglers in thecores of 57 globular clusters to investigate the relationships betweenblue straggler populations and their environments. We use a consistentdefinition of ``blue straggler'' based on position in thecolor-magnitude diagram and normalize the population relative to thenumber of red giant branch stars in the core. We find that thepreviously determined anticorrelation between blue straggler frequencyand total cluster mass is present in the purely core population. We findsome weak anticorrelations with central velocity dispersion and withhalf-mass relaxation time. The blue straggler frequency does not showany trend with any other cluster parameter. Even though collisions maybe expected to be a dominant blue straggler formation process inglobular cluster cores, we find no correlation between the frequency ofblue stragglers and the collision rate in the core. We also investigatedthe blue straggler luminosity function shape and found no relationshipbetween any cluster parameter and the distribution of blue stragglers inthe color-magnitude diagram. Our results are inconsistent with somerecent models of blue straggler formation that include collisionalformation mechanisms and may suggest that almost all observed bluestragglers are formed in binary systems.
| [Fe/H] relations for c-type RR Lyrae variables based upon Fourier coefficients
[Fe/H]-φ31-P relations are found for c-type RR Lyraestars in globular clusters. The relations are analogous to that found byJurcsik & Kovács for field ab-type RR Lyrae stars, where alonger period correlates with lower metallicity values for similarvalues of the Fourier coefficient φ31. The relationsobtained here are used to determine the metallicity of field c-type RRLyrae stars, those within ωCen, the Large Magellanic Cloud andtoward the galactic bulge. The results are found to compare favourablyto metallicity values obtained elsewhere.
| 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.
| The Orbits of 48 Globular Clusters in a Milky Way-like Barred Galaxy
The effect of a barred potential (such as the one of the Milky Way) onthe Galactic orbits of 48 globular clusters for which absolute propermotions are known is studied. The orbital characteristics are comparedwith those obtained for the case of an axisymmetric Galactic potential.Tidal radii are computed and discussed for both the better knownaxisymmetric case and that including a bar. The destruction rates due tobulge and disk shocking are calculated and compared in both Galacticpotentials.
| Photometric and spectroscopic study of the Shakhbazian compact galaxy groups ShCG 254, ShCG 257, ShCG 351, and ShCG 371
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| CCD photometry of the globular cluster M2: RR Lyrae physical parameters and new variables
We report the results of CCD V and R photometry of the RR Lyrae stars inM2. The periodicities of most variables are revised and new ephemeridesare calculated. Light-curve decomposition of the RR Lyrae stars wascarried out and the corresponding mean physical parameters [Fe/H] =-1.47, Teff = 6276K, logL = 1.63Lsolar andMV = 0.71 from nine RRab and [Fe/H] = -1.61, M =0.54Msolar, Teff = 7215K, logL =1.74Lsolar and MV = 0.71 from two RRc stars werecalculated. A comparison of the radii obtained from the above luminosityand temperature with predicted radii from non-linear convective modelsis discussed. The estimated mean distance to the cluster is 10.49 +/-0.15kpc. These results place M2 correctly in the general globularcluster sequences for Oosterhoff type, mass, luminosity and temperature,all as a function of the metallicity. Mean relationships for M,logL/Lsolar, Teff and MV as a functionof [Fe/H] for a family of globular clusters are offered. These trendsare consistent with evolutionary and structural notions on thehorizontal branch. Eight new variables are reported.
| Global fitting of globular cluster age indicators
Context: .Stellar models and the methods for the age determinations ofglobular clusters are still in need of improvement. Aims: .Weattempt to obtain a more objective method of age determination based oncluster diagrams, avoiding the introduction of biases due to thepreference of one single age indicator. Methods: .We compute newstellar evolutionary tracks and derive the dependence of age indicatingpoints along the tracks and isochrone - such as the turn-off or bumplocation - as a function of age and metallicity. The same criticalpoints are identified in the colour-magnitude diagrams of globularclusters from a homogeneous database. Several age indicators are thenfitted simultaneously, and the overall best-fitting isochrone isselected to determine the cluster age. We also determine thegoodness-of-fit for different sets of indicators to estimate theconfidence level of our results. Results: .We find that ourisochrones provide no acceptable fit for all age indicators. Inparticular, the location of the bump and the brightness of the tip ofthe red giant branch are problematic. On the other hand, the turn-offregion is very well reproduced, and restricting the method to indicatorsdepending on it results in trustworthy ages. Using an alternative set ofisochrones improves the situation, but neither leads to an acceptableglobal fit. Conclusions: .We conclude that evolutionary tracks oflow-mass metal-poor stars are far from reproducing all aspects ofglobular cluster colour-magnitude diagrams and that the determination ofcluster ages still depends on the favourite method or indicator chosen.
| The new sample of giant radio sources. II. Update of optical counterparts, further spectroscopy of identified faint host galaxies, high-frequency radio maps, and polarisation properties of the sources
Our sample of giant radio-source candidates, published in Paper I, isupdated and supplemented with further radio and optical data. In thispaper we present: (i) newly detected host galaxies, their photometricmagnitude, and redshift estimate for the sample sources not identifiedyet, (ii) optical spectra and spectroscopic redshift for the hostgalaxies fainter than about R≈ 18.5 mag taken with the Apache PointObservatory 3.5 m telescope, and (iii) the VLA 4.9 GHz total-intensityand polarised-intensity radio maps of the sample members. In a few casesthey reveal extremely faint radio cores undetected before, which confirmthe previously uncertain optical identifications. The radio maps areanalysed and the polarisation properties of the sample sourcessummarised. A comparison of our updated sample with three samplespublished by other authors implies that all these four samples probe thesame part of the population of extragalactic radio sources. There is nosignificant difference between the distributions of intrinsic size andradio power among these samples. The median redshift of 0.38±0.07in our sample is the highest among the corresponding values in the foursamples, indicating that the angular size and flux-density limits in oursample, lower than those for the other three samples, result ineffective detections of more distant, giant-size galaxies compared tothose detected in the other samples. This sample and a comparison sampleof "normal"-size radio galaxies will be used in Paper III (this volume)to investigate of a number of trends and correlations in the entiredata.
| Multivariate analysis of globular cluster horizontal branch morphology: searching for the second parameter
Aims.The interpretation of globular cluster horizontal branch (HB)morphology is a classical problem that can significantly blur ourunderstanding of stellar populations. Methods: .We present a newmultivariate analysis connecting the effective temperature extent of theHB with other cluster parameters. The work is based on Hubble SpaceTelescope photometry of 54 Galactic globular clusters. Results: .The present study reveals the important role of the total mass of theglobular cluster on its HB morphology. More massive clusters tend tohave HBs more extended to higher temperatures. For a set of three inputvariables including the temperature extension of the HB, [Fe/H] and M_V,the first two eigenvectors account for 90% of the total samplevariance. Conclusions: . Possible effects of clusterself-pollution on HB morphology, stronger in more massive clusters,could explain the results derived here.
| The Field of Streams: Sagittarius and Its Siblings
We use Sloan Digital Sky Survey (SDSS) Data Release 5 (DR5) u, g, r, i,z photometry to study Milky Way halo substructure in the area around thenorth Galactic cap. A simple color cut (g-r<0.4) reveals the tidalstream of the Sagittarius dwarf spheroidal galaxy, as well as a numberof other stellar structures in the field. Two branches (A and B) of theSagittarius stream are clearly visible in an RGB composite image createdfrom three magnitude slices, and there is also evidence for a still moredistant wrap behind the A branch. A comparison of these data withnumerical models suggests that the shape of the Galactic dark halo isclose to spherical.
| The Initial Mass Functions of Four Embedded Stellar Clusters
We present near-infrared J, H, and K images of four embedded stellarclusters in the Galaxy. We find a significant fraction ofpre-main-sequence stars present in at least one of the clusters. For theclusters dominated by main-sequence stars, we determine the initial massfunction (IMF) both by using the K luminosity function and a globalextinction correction and by deriving individual extinction correctionsfor each star based on their placement in the K versus H-Kcolor-magnitude diagram. Based on our IMFs we find a significantdiscrepancy between the mean IMF derived via the different methods,suggesting that taking individual extinctions into account is necessaryto correctly derive the IMF for an embedded cluster.
| CCD Photometry of the Globular Cluster M15: RR Lyrae Fourier Decomposition and Physical Parameters
Results of CCD photometry using V and R filters are reported for 33 RRLyrae stars in M15. The periodicities of some variables have beenrevised and new ephemerides are given. The Blazhko effect, previouslyreported in V12, was not detected. Applying the approach of Fourierdecomposition of the light curves, the physical parameters of the typeRRab and RRc variables were estimated. The cluster is Oosterhoff type IIand the values for the iron content and distance are:[Fe/H]=-1.98+/-0.24 and d=8.67+/-0.41 kpc, respectively. The mean valuesof the physical parameters determined for the RR Lyrae stars place thecluster precisely into the sequences Oosterhoff type --metallicity andmetallicity-- effective temperature, valid for globular clusters.Evidences of evolution from the ZAHB are found for the RRc but not forthe RRab stars.
| 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.
| Complexity on Small Scales: The Metallicity Distribution of the Carina Dwarf Spheroidal Galaxy
The Carina dwarf spheroidal galaxy is the only galaxy of this type thatshows clearly episodic star formation separated by long pauses. Here wepresent metallicities for 437 radial velocity members of this Galacticsatellite. The metallicities and radial velocities were measured as partof a Large Programme with the Very Large Telescope at the EuropeanSouthern Observatory, Chile. We obtained medium-resolution spectroscopywith the multiobject spectrograph FLAMES. Our target red giants coverthe entire projected surface area of Carina. Our spectra are centered atthe near-infrared Ca II triplet, which is a well-established metallicityindicator for old and intermediate-age red giants. The resulting datasample provides the largest collection of spectroscopically derivedmetallicities for a Local Group dwarf spheroidal galaxy to date. Four ofour likely radial velocity members of Carina lie outside this galaxy'snominal tidal radius, supporting earlier claims of the possibleexistence of such stars beyond the main body of Carina. We find a meanmetallicity of [Fe/H]~-1.7 dex on the 1997 metallicity scale of Carrettaand Gratton for Carina. The formal FWHM of the metallicity distributionfunction is 0.92 dex, while the full range of metallicities is found tospan approximately -3.0 dex<[Fe/H]<0.0 dex. The metallicitydistribution function might be indicative of several subpopulationsdistinct in metallicity. There appears to be a mild radial gradient suchthat more metal-rich populations are more centrally concentrated,matching a similar trend for an increasing fraction of intermediate-agestars (see the 2001 work of Harbeck and coworkers). This, as well as thephotometric colors of the more metal-rich red giants, suggests thatCarina exhibits an age-metallicity relation. Indeed, the age-metallicitydegeneracy seems to conspire to form a narrow red giant branch despitethe considerable spread in metallicity and wide range of ages. Themetallicity distribution function is not well matched by a simpleclosed-box model of chemical evolution. Qualitatively better matches areobtained by chemical models that also take into account infall andoutflows. A G dwarf problem remains for all these models.Based on observations collected at the European Southern Observatory atParanal, Chile; proposal 171.B-0520(A).
| VIMOS@VLT photometric and spectroscopic survey of the Sagittarius dwarf spheroidal galaxy .
The closest neighbour of the Milky Way (MW), the Sagittarius dwarfSpheroidal Galaxy (Sgr dSph) is being tidally destroyed by theinteraction with our Galaxy, losing its stellar content along a hugestream clearly detectable within the Galactic Halo. The stellar contentand internal dynamics of Sgr dSph are poorly known due to its dimensions(about 20x5 degree2 in the sky) . We thus undertook aphotometric and spectroscopic survey of Sgr dSph with VIMOS@VLT, toderive colour - magnitude diagrams (CMD) and radial velocities acrossthe extension of the galaxy. We observed 8 fields along the major andminor axis of the galaxy (along 7 degrees and 2 degrees respectively),plus 6 globular cluster likely associated with the galaxy ( NGC 4147,Pal5, Pal12, Arp2, Ter7, Ter8 ). All of them were observed with V and Ifilters. The photometric catalogue was then used to select target forVIMOS-MOS high resolution mode. We obtained spectra for about 1200stars. 250 stars in the Sgr main body fields were established as SgrdSph members, and will now be the subject of high resolutionspectroscopy studies for the purpose of chemical analysis. Thisconstitutes one of the richest photometric and spectroscopic homogeneouscatalog of Sgr dSph stars ever realized. The survey led to discover asurprising variety in the CMDs at varying distances from the dSphcenter, with younger, more metal rich populations in the dSph nucleus,preliminary evidence for a metallicity gradient and some hint ofdishomogeneity along the major axis.
| Homogeneous Photometry. V. The Globular Cluster NGC 4147
New BVRI broadband photometry and astrometry are presented for theglobular cluster NGC 4147, based upon measurements derived from 524ground-based CCD images mostly either donated by colleagues or retrievedfrom public archives. We have also reanalyzed five exposures of thecluster obtained with WFPC2 on the Hubble Space Telescope in the F439Wand F555W (B and V) filters. We present calibrated color-magnitude andcolor-color diagrams. Analysis of the color-magnitude diagram revealsmorphological properties generally consistent with publishedmetal-abundance estimates for the cluster, and an age typical of otherGalactic globular clusters of similar metallicity. We have alsoredetermined the periods and mean magnitudes for the RR Lyrae variables,including a new c-type variable reported here for the first time. Ourdata do not show clear evidence for photometric variability in candidateV18, recently reported by Arellano Ferro et al. (2004, Rev. Mex.A&A, 40, 209). These observations also support the nonvariablestatus of candidates V5, V9, and V15. The union of our light-curve datawith those of Newburn (1957, AJ, 62, 197), Mannino (1957, Mem. Soc.Astron. Italiana, 28, 285), and Arellano Ferro et al. (op. cit.) permitsthe derivation of significantly improved periods. The mean periods andthe Bailey period-amplitude diagrams support the classification of thecluster as Oosterhoff I, despite its predominantly blue horizontalbranch. The number ratio of c- to ab-type RR Lyrae stars, on the otherhand, is unusually high for an Oosterhoff I cluster. The calibratedresults have been made available through the first author's Web site.Based in part on archival observations made with ESO telescopes at theLa Silla and Paranal Observatory under program ID 60.A-9050(A).This publication makes use of data products from the Two Micron All SkySurvey, which is a joint project of the University of Massachusetts andthe Infrared Processing and Analysis Center/California Institute ofTechnology, funded by the National Aeronautics and Space Administrationand the National Science Foundation.
| 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.
| The Century Survey Galactic Halo Project. II. Global Properties and the Luminosity Function of Field Blue Horizontal Branch Stars
We discuss a 175 deg2 spectroscopic survey for bluehorizontal branch (BHB) stars in the Galactic halo. We use the TwoMicron All Sky Survey (2MASS) and the Sloan Digital Sky Survey (SDSS) toselect BHB candidates, and we find that the 2MASS and SDSS colorselection is 38% and 50% efficient, respectively, for BHB stars. Oursamples include one likely runaway B7 star 6 kpc below the Galacticplane. The global properties of the BHB samples are consistent withmembership in the halo population: the median metallicity is[Fe/H]=-1.7, the velocity dispersion is 108 km s-1, and themean Galactic rotation of the BHB stars 3 kpc<|z|<15 kpc is-4+/-30 km s-1. We discuss the theoretical basis of thePreston, Shectman, and Beers MV-color relation for BHB starsand conclude that the intrinsic shape of the BHB MV-colorrelation results from the physics of stars on the horizontal branch. Wecalculate the luminosity function for the field BHB star samples usingthe maximum likelihood method of Efstathiou and coworkers, which isunbiased by density variations. The field BHB luminosity functionexhibits a steep rise at bright luminosities, a peak between0.8
| Shakhbazian compact galaxy groups. IV. Photometric and spectroscopic study of ShCG 8, ShCG 14 ShCG 19, ShCG 22
We present the results of a detailed spectroscopic and photometric studyof four Shakhbazian compact groups: ShCG 8, ShCG 14, ShCG 19, and ShCG22. We determined the redshifts of member galaxies and radial velocitydispersions of groups. We also studied the distribution of the surfacebrightness of member galaxies in R and determined their morphologicaltypes. The profiles of the surface brightness versus semi-major axis,the curves of isophotal twisting, and Fourier parameter a4are constructed. We found that some members of groups are in the processof interaction. We determined physical parameters of groups: virialmasses, luminosities, mass-to-luminosity ratios, and the crossing times.On the basis of the results obtained in this and our previous works, thegeneral properties of 22 ShCGs are discussed.
| Galactic Globular Cluster Relative Ages
We present accurate relative ages for a sample of 55 Galactic globularclusters. The ages have been obtained by measuring the differencebetween the horizontal branch and the turnoff in two internallyphotometrically homogeneous databases. The mutual consistency of the twodata sets has been assessed by comparing the ages of 16 globularclusters in common between the two databases. We have also investigatedthe consistency of our relative age determination within the recentstellar model framework. All clusters with [Fe/H]<-1.7 are found tobe old and coeval, with the possible exception of two objects, which aremarginally younger. The age dispersion for the metal-poor clusters is0.6 Gyr (rms), consistent with a null age dispersion.Intermediate-metallicity clusters (-1.7<[Fe/H]<-0.8) are onaverage 1.5 Gyr younger than the metal-poor ones, with an age dispersionof 1.0 Gyr (rms) and a total age range of ~3 Gyr. About 15% of theintermediate-metallicity clusters are coeval with the oldest clusters.All the clusters with [Fe/H]>-0.8 are ~1 Gyr younger than the mostmetal-poor ones, with a relatively small age dispersion, although themetal-rich sample is still too small to allow firmer conclusions. Thereis no correlation of the cluster age with the galactocentric distance.We briefly discuss the implication of these observational results forthe formation history of the Galaxy.Based on observations with the NASA/ESA Hubble Space Telescope, obtainedat the Space Telescope Science Institute, which is operated by theAssociation of Universities for Research in Astronomy, Inc., under NASAcontract NAS 5-26555, and on observations made at the European SouthernObservatory, La Silla, Chile, and with the Isaac Newton GroupTelescopes.
| Spectroscopy and photometry of ShCG 191 - Abell 1097
In the course of investigation of Shakhbazian compact groups we studiedthe group ShCG 191 which has been identified also as the Abell clusterA1097. By its richness it may be classified as a rich compact group or apoor cluster. We determined redshifts of 14 objects in the area of thecluster and found that two of the supposed members of the group arestars. Redshifts of 12 galaxies show that the system is gravitationallybound. The V and R magnitudes of 23 member galaxies and theirmorphological types are determined. We present in this paper also thesurface brightness contours of member galaxies in the central area ofthe cluster, the curves of isophotal twisting and the Fourier parametera_4. It is shown that some galaxies in the cluster are interacting witheach other. Physical parameters of the group are close to those ofShCGs.
| Photometric and Spectroscopic Study of the Shakhbazian Compact Galaxy Groups ShCG74 ShCG188, ShCG251, and ShCG348
We continue the presentation of the results of detailed spectroscopicand photometric study of Shakhbazian compact galaxy groups. They belongto the interesting class of compact groups. Because of their largenumber (the catalogue contains 377 entries) we are able to study thegroups in different stages of evolution. Here we give the results of adetailed study of five groups, ShCG4E, ShCG4W, ShCG88, ShCG51, andShCG48. We present the redshifts of individual galaxies in groups, theresults of the surface photometry in R, the contour plots of the surfacebrightness, and some physical parameters of groups, such as the radialvelocity dispersions, the crossing times, and the mass-to-luminosityratios of groups. The general properties of 18 ShCGs obtained in thisand previous works are discussed.
| Discovery of More than 200 RR Lyrae Variables in M62: An Oosterhoff I Globular Cluster with a Predominantly Blue Horizontal Branch
We report on the discovery of a large number of RR Lyrae variable starsin the moderately metal-rich Galactic globular cluster M62 (NGC 6266),which places it among the top three most RR Lyrae-rich globular clustersknown. Likely members of the cluster in our studied field, from ourpreliminary number counts, include ~130 fundamental-mode (RRab)pulsators, with =0.548 days, and ~75first-overtone (RRc) pulsators, with =0.300 days.The average periods and the position of the RRab variables withwell-defined light curves in the Bailey diagram both suggest that thecluster is of Oosterhoff type I. However, the morphology of thecluster's horizontal branch (HB) is strikingly similar to that of theOosterhoff type II globular cluster M15 (NGC 7078), with a dominant blueHB component and a very extended blue tail. Since M15 and M62 differ inmetallicity by about 1 dex, we conclude that metallicity, at a fixed HBtype, is a key parameter determining the Oosterhoff status of a globularcluster and the position of its variables in the Bailey diagram.
| Age and Metallicity Estimation of Globular Clusters from Strömgren Photometry
We present a new technique for the determination of age and metallicityin composite stellar populations using Strömgren filters. Usingprincipal component (PC) analysis on multicolor models, we isolate therange of values necessary to uniquely determine age and metallicityeffects. The technique presented here can only be applied to old(τ>3 Gyr) stellar systems composed of simple stellar populations,such as globular clusters and elliptical galaxies. Calibration using newphotometry of 40 globular clusters with spectroscopic [Fe/H] values andmain-sequence-fitted ages links the PC values to the Strömgrencolors, for an accuracy of 0.2 dex in metallicity and 0.5 Gyr in age.
| Integral field spectroscopy of the ultraluminous X-ray source Holmberg II X-1
We present optical integral field observations of the H II regioncontaining the ultraluminous X-ray source Holmberg II X-1. We confirmthe existence of an X-ray ionized nebula as the counterpart of thesource owing to the detection of an extended He II λ4686 region(21× 47 pc) at the Chandra ACIS-S position. An extended blueobject with a size of 11× 14 pc is coincident with the X-ray/He IIλ4686 region, which could indicate that it is either a youngstellar complex or a cluster. We have derived an X-ray to opticalluminosity ratio of L_X/LB≥170, and presumable it isL_X/LB300{-}400 using the recent HST ACS data. We find acomplex velocity dispersion at the position of the ULX. In addition,there is a radial velocity variation in the X-ray ionized region foundin the He II emission of ±50 km s-1 on spatial scalesof 2 3primeprime. We believe that the putative black hole notonly ionizes the surrounding HII gas, but also perturbs it dynamically(via jets or the accretion disk wind). The spatial analysis of thepublic Chandra ACIS-S data reveals a point-like X-ray source and givesmarginal indication of an extended component (ll15% of the total flux).The XMM-Newton EPIC-PN spectrum of HoII X-1 is best fitted with anabsorbed power law in addition to either a thermal thick plasma or athermal thin plasma or a multi-colour disk black body (MCD). In allcases, the thermal component shows a relatively low temperature(kT0.14{-}0.22 keV). Finally we discuss the optical/X-rayproperties of HoII X-1 with regards to the possible nature of thesource. The existence of an X-ray ionized nebula coincident with the ULXand the soft X-ray component with a cool accretion disk favours theinterpretation as an intermediate-mass black hole (IMBH). However, thecomplex velocity behaviour at the position of the ULX indicates adynamical influence of the black hole on the local HII gas.
| Chemical Abundances for Seven Giant Stars in M68 (NGC 4590): A Globular Cluster with Abnormal Silicon and Titanium Abundances
We present a detailed chemical abundance study of seven giant stars inM68, including six red giants and one post-asymptotic giant branch (AGB)star. We find significant differences in the gravities determined usingphotometry and those obtained from ionization balance, which suggeststhat non-LTE (NLTE) affects are important for these low-gravity,metal-poor stars. We adopt an iron abundance using photometric gravitiesand Fe II lines to minimize those effects, finding [Fe/H]=-2.16+/-0.02(σ=0.04). For element-to-iron ratios, we rely on neutral linesversus Fe I and ionized lines versus Fe II (except for [O/Fe]) to alsominimize NLTE effects. We find variations in the abundances of sodiumamong the program stars. However, there is no correlation (oranticorrelation) with the oxygen abundances. Furthermore, the post-AGBstar has a normal (low) abundance of sodium. Both of these facts addfurther support to the idea that the variations seen among some lightelements within individual globular clusters arise from primordialvariations and not from deep mixing. M68, like M15, shows elevatedabundances of silicon compared with other globular clusters andcomparable-metallicity field stars. But M68 deviates even more inshowing a relative underabundance of titanium. We speculate that in M68titanium is behaving like an iron-peak element rather than its morecommonly observed adherence to enhancements seen in the so-calledα-elements such as magnesium, silicon, and calcium. We interpretthis result as implying that the chemical enrichment seen in M68 mayhave arisen from contributions from supernovae with somewhat moremassive progenitors than those that contribute to abundances normallyseen in other globular clusters. The neutron capture elements barium andeuropium vary among the stars in M15, according to earlier work bySneden et al., but [Ba/Eu] is relatively constant, suggesting that bothelements arise in the same nucleosynthesis events. M68 shares the same[Ba/Eu] ratio as the stars in M15, but the average abundance ratio ofthese elements, as well as lanthanum, are lower in M68 relative to ironthan in M15, implying a slightly weaker contribution of r-processnucleosynthesis in M68.
| A brief introduction on the significance and achievements of 2MASS
2MASS has revealed the all near-IR sky with remarkable uniformity andaccuracy. Through data processing vast amount of raw data weretransformed into astronomically useful images and lists of the infraredbrightness and positions. This article briefly introduced scientificsignificance and data feature of the 2MASS project as well as some mainresearch fields using information of 2MASS.
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