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Na, Al, and O Abundances of Open Clusters NGC 7142, NGC 6939, and IC 4756
We present an analysis of echelle spectra of stars in three openclusters obtained with the Hydra multiobject spectrograph on the WIYN3.5 m telescope. Abundances of Fe, O, Si, Ca, Na, Al, and Ni have beendetermined via equivalent width analysis and spectrum synthesis. Meanabundances for each cluster are compared to those of previous studiesand of other clusters in the literature, with emphasis on exploring theenhancements of Na and Al seen in many open clusters. All three clustersshow enhanced values of [Na/Fe] and [Al/Fe], while the abundances of Fe,O, Si, and Ca are consistent with their ages and locations in theGalactic disk.
| CCD BV survey of 42 open clusters
Aims.We present results of a photometric survey whose aim was to derivestructural and astrophysical parameters for 42 open clusters. While oursample is definitively not representative of the total open clustersample in the Galaxy, it does cover a wide range of cluster parametersand is uniform enough to allow for simple statistical considerations. Methods: BV wide-field CCD photometry was obtained for open clusters forwhich photometric, structural, and dynamical evolution parameters weredetermined. The limiting and core radii were determined by analyzingradial density profiles. The ages, reddenings, and distances wereobtained from the solar metallicity isochrone fitting. The mass functionwas used to study the dynamical state of the systems, mass segregationeffect and to estimate the total mass and number of cluster members. Results: This study reports on the first determination of basicparameters for 11 out of 42 observed open clusters. The angular sizesfor the majority of the observed clusters appear to be several timeslarger than the catalogue data indicate. The core and limiting clusterradii are correlated and the latter parameter is 3.2 times larger onaverage. The limiting radius increases with the cluster's mass, and boththe limiting and core radii decrease in the course of dynamicalevolution. For dynamically not advanced clusters, the mass functionslope is similar to the universal IMF slope. For more evolved systems,the effect of evaporation of low-mass members is clearly visible. Theinitial mass segregation is present in all the observed young clusters,whereas the dynamical mass segregation appears in clusters older thanabout log({age}) = 8. Low-mass stars are deficient in the cores ofclusters older than log({age}) = 8.5 and not younger than one relaxationtime.Tables 1-5 are only available in electronic form at http://www.aanda.org
| On the current status of open-cluster parameters
We aim to characterize the current status of knowledge on the accuracyof open-cluster parameters such as the age, reddening and distance.These astrophysical quantities are often used to study the globalcharacteristics of the Milky Way down to the very local stellarphenomena. In general, the errors of these quantities are neglected orset to some kind of heuristic standard value. We attempt to give somerealistic estimates for the accuracy of available cluster parameters byusing the independently derived values published in the literature. Intotal, 6437 individual estimates for 395 open clusters were used in ourstatistical analysis. We discuss the error sources depending ontheoretical as well as observational methods and compare our resultswith those parameters listed in the widely used catalogue by Dias et al.In addition, we establish a list of 72 open clusters with the mostaccurate known parameters which should serve as a standard table in thefuture for testing isochrones and stellar models.
| Kinematics of the Open Cluster System in the Galaxy
Absolute proper motions and radial velocities of 202 open clusters inthe solar neighborhood, which can be used as tracers of the Galacticdisk, are used to investigate the kinematics of the Galaxy in the solarvicinity, including the mean heliocentric velocity components(u1,u2,u3) of the open cluster system,the characteristic velocity dispersions(σ1,σ2,σ3), Oortconstants (A,B) and the large-scale radial motion parameters (C,D) ofthe Galaxy. The results derived from the observational data of propermotions and radial velocities of a subgroup of 117 thin disk young openclusters by means of a maximum likelihood algorithm are:(u1,u2,u3) =(-16.1+/-1.0,-7.9+/-1.4,-10.4+/-1.5) km s-1,(σ1,σ2,σ3) =(17.0+/-0.7,12.2+/-0.9,8.0+/-1.3) km s-1,(A,B) =(14.8+/-1.0,-13.0+/-2.7) km s-1 kpc-1, and (C,D) =(1.5+/-0.7,-1.2+/-1.5) km s-1 k pc-1. A discussionon the results and comparisons with what was obtained by other authorsis given.
| UBVI CCD Photometry of the Old Open Cluster Berkeley 17
Photometric UBVI CCD photometry is presented for NGC 188 and Berkeley17. Color-magnitude diagrams (CMDs) are constructed and reach well pastthe main-sequence turnoff for both clusters. Cluster ages are determinedby means of isochrone fitting to the cluster CMDs. These fits areconstrained to agree with spectroscopic metallicity and reddeningestimates. Cluster ages are determined to be 7.0+/-0.5 Gyr for NGC 188and 10.0+/-1.0 Gyr for Berkeley 17, where the errors refer touncertainties in the relative age determinations. These ages arecompared to the ages of relatively metal-rich inner halo/thick-diskglobular clusters and other old open clusters. Berkeley 17 and NGC 6791are the oldest open clusters, with ages of 10 Gyr. They are 2 Gyryounger than the thick-disk globular clusters. These results confirm thestatus of Berkeley 17 as one of the oldest known open clusters in theMilky Way, and its age provides a lower limit to the age of the Galacticdisk.
| The Bologna Open Cluster Chemical Evolution Project: Midterm Results from the Photometric Sample
We describe a long-term project aimed at deriving information on thechemical evolution of the Galactic disk from a large sample of openclusters. The main property of this project is that all clusters areanalyzed in a homogeneous way to guarantee the robustness of the rankingin age, distance, and metallicity. Special emphasis is devoted to theevolution of the earliest phases of the Galactic disk evolution, forwhich clusters have superior reliability with respect to other types ofevolution indicators. The project is twofold: on one hand we derive theage, distance, and reddening (and indicative metallicity) byinterpreting deep and accurate photometric data with stellar evolutionmodels, and on the other hand, we derive the chemical abundances fromhigh-resolution spectroscopy. Here we describe our overall goals andapproaches and report on the midterm project status of the photometricpart, with 16 clusters already studied, covering an age interval from0.1 to 6 Gyr and galactocentric distances from 6.6 to 21 kpc. Theimportance of quantifying the theoretical uncertainties by deriving thecluster parameters with various sets of stellar models is emphasized.Stellar evolution models assuming overshooting from convective regionsappear to better reproduce the photometric properties of the clusterstars. The examined clusters show a clear metallicity dependence on thegalactocentric distance and no dependence on age. The tight relationbetween cluster age and magnitude difference between the main-sequenceturnoff and the red clump is confirmed.
| Blue Stragglers in Galactic Open Clusters and Integrated Spectral Energy Distributions
Synthetic integrated spectral properties of the old Galactic openclusters are studies in this work, in which 27 Galactic open clusters ofages >=1 Gyr are selected as the working sample. Based on thephotometric observations of these open clusters, a synthetic integratedspectrum has been made for the stellar population of each cluster. Theeffects of blue straggler (BS) stars on the conventional simple stellarpopulation (SSP) model are analyzed on an individual cluster basis. Itis shown that the BSs, whose positions in the color-magnitude diagramscannot be predicted by the current single-star evolution theory, requiresignificant modifications to the integrated properties of theoreticalSSP model. The synthesized integrated spectral energy distributions(ISEDs) of our sample clusters are dramatically different from those ofSSPs based on an isochrone only. The BS-corrected ISEDs of stellarpopulations show systematic enhancements toward shorter wavelengths inthe spectra. When measured with broadband colors in unresolvableconditions, the age of a stellar population can be seriouslyunderestimated by the conventional SSP model. Therefore, considering thecommon existence of BS components in real stellar populations, we shouldexpect considerable alterations of the conventional ISEDs when we applythe technique of evolutionary population synthesis to more complicatedstellar systems.
| Comparison of the Luminosity Functions of Open Clusters Based on USNO-A1 Data
The luminosity and mass functions of a group of Galactic open clustersare constructed by applying a statistical method to photometric datafrom the USNO-A1 catalog. Despite some limitations, this catalog can beused for statistical analyses in Galactic astronomy. Pairwisecomparisons of the derived cluster luminosity functions are performedfor five age intervals. The differences between the luminosity functionsof the open clusters are not statistically significant in most cases. Itis concluded that the luminosity functions are approximately universalthroughout a large volume in the solar neighborhood. Combined luminosityand mass functions are constructed for six age intervals. The slope ofthe mass spectrum may vary somewhat from cluster to cluster, and themean slope may be somewhat higher than the Salpetervalue.
| Interpreting the colour-magnitude diagrams of open star clusters through numerical simulations
We present detailed comparisons between high quality observationalcolour-magnitude diagrams (CMDs) of open star clusters and syntheticCMDs based on Monte Carlo numerical simulations. The comparisons accountfor all of the main parameters which determine the shape of the CMD fora stellar population. For the four clusters studied, NGC 6819, 2099(M37), 2168 (M35) and 2323 (M50), we derive reddening, distance, age,binary fraction, star formation rate and indicative metallicity bycomparing the locations and density of points in the observed CMDs tothe simulated CMDs. We estimate the uncertainties related to stellarevolution theories by adopting various sets of stellar models for all ofthe synthetic CMDs and discuss which stellar models provide thetheoretical CMDs that best reproduce the observations.
| WIYN Open Cluster Study. XX. Photometric Monitoring of the Galactic Cluster NGC 6939
A photometric monitoring program in the field of the Galactic clusterNGC 6939 was conducted using the 0.91 m WIYN and the US NavalObservatory Flagstaff Station 1.3 m and 1 m telescopes, with the primarygoal being to search for cataclysmic variables (CVs) in the cluster.Although no CVs were found during the 5 months of monitoring, a numberof short-period variables were discovered in the field of the cluster. Alarge portion of them are of the W Ursae Majoris type, whereas WOCS V7is an RR Lyrae star. Although the survey was somewhat compromised by thebright stars around the center of the cluster, it is intriguing that NGC6939 appears to be deficient in faint variables.
| UBVI photometry of the intermediate-age open cluster NGC 6939
We present CCD UBVI photometry of the nearby, intermediate-age opencluster NGC 6939. Using the synthetic colour-magnitude diagram techniquewe estimate the following parameters: age between 1.3 and 1.0 Gyr(depending on whether or not overshooting is considered), reddening 0.34<=E(B-V) <= 0.38 and distance modulus 11.3 <=(m-M)0<= 11.4.
| The age of the oldest Open Clusters
We determine ages of 71 old Open Clusters by a two-step method: we usemain-squence fitting to 10 selected clusters, in order to obtain theirdistances, and derive their ages from comparison with our own isochronesused before for Globular Clusters. We then calibrate the morphologicalage indicator δ(V), which can be obtained for all remainingclusters, in terms of age and metallicity. Particular care is taken toensure consistency in the whole procedure. The resulting Open Clusterages connect well to our previous Globular Cluster results. From theOpen Cluster sample, as well as from the combined sample, questionsregarding the formation process of Galactic components are addressed.The age of the oldest open clusters (NGC 6791 and Be 17) is of the orderof 10 Gyr. We determine a delay by 2.0±1.5 Gyr between the startof the halo and thin disk formation, whereas thin and thick disk startedto form approximately at the same time. We do not find any significantage-metallicity relationship for the open cluster sample. The cumulativeage distribution of the whole open cluster sample shows a moderatelysignificant (˜ 2σ level) departure from the predictions foran exponentially declining dissolution rate with timescale of 2.5 Gyr.The cumulative age distribution does not show any trend withgalactocentric distance, but the clusters with larger height to theGalactic plane have an excess of objects between 2-4 and 6 Gyr withrespect to their counterpart closer to the plane of the Galaxy.
| Old Open Clusters
Open clusters are among the best tracers of the Galactic disk properties(ages, distances, metallicities, etc. and their evolution in space andtime). In this framework, we are working on a long term programmededicated to the study of old Open Clusters. We are analyzingphotometric and spectroscopic data for a fair sample of Open Clusters,with the intent of determining in a precise and homogeneous way theirdistances, ages, reddenings, and detailed chemical abundances.
| TNG photometry of the open cluster NGC 6939
We present CCD UBVI photometry of the intermediate age open cluster NGC6939 for three TNG-DOLORES fields. The fields A and B cover the centerof the cluster; the third one is located about 30arcmin away, and isused for field stars decontamination.The V-I, B-V and U-B color-magnitude diagrams (CMDs), obtained joiningvery different exposures show: i) a Main Sequence (MS) extending down toV = 24, much deeper (˜ 5 magnitudes) than any previous study; ii)a clearly defined Turn Off (TO) and iii) a well populated Red GiantClump (RC) at about V = 13.
| Intermediate-age Galactic open clusters: fundamental parameters of NGC 2627
Charge-coupled device (CCD) photometry in the Johnson V, Kron-Cousins Iand Washington CMT1 systems is presented in the field of thepoorly known open cluster NGC 2627. Four independent Washingtonabundance indices yield a mean cluster metallicity of [Fe/H]=-0.12 +/-0.08, which is compatible with the existence of a radial gradient in theGalactic disc. The resultant colour-magnitude diagrams indicate that thecluster is an intermediate-age object of 1.4 Gyr. Based on the best fitsof the Geneva group's isochrones to the (V, V-I) and (T1,C-T1) diagrams, we estimate E(V-I) = 0.25 +/- 0.05 andV-MV= 11.80 +/- 0.25 for logt= 9.15, and E(C-T1) =0.23 +/- 0.07 and T1-MT1= 11.85 +/-0.25 for logt= 9.10, respectively, assuming solar metal content. Thederived reddening value E(C-T1) implies E(B-V) = 0.12 +/-0.07 and a distance from the Sun of 2.0 +/- 0.4 kpc. Using the WEBDAdata base and the available literature, we re-examined the overallproperties of all the open clusters with ages between 0.6 and 2.5 Gyr.We identified peaks of cluster formation at 0.7-0.8, 1.0-1.1, 1.6-1.7and 2.0-2.1 Gyr, separated by relative quiescent epochs of ~0.2-0.3 Gyr.We also estimated a radial abundance gradient of -0.08 +/- 0.02, whichis consistent with the most recent determinations for the Galactic disc,but no clear evidence for a gradient perpendicular to the Galactic planeis found.
| On the Galactic Disk Metallicity Distribution from Open Clusters. I. New Catalogs and Abundance Gradient
We have compiled two new open cluster catalogs. In the first one, thereare 119 objects with ages, distances, and metallicities available, whilein the second one, 144 objects have both absolute proper motion andradial velocity data, of which 45 clusters also have metallicity dataavailable. Taking advantage of the large number of objects included inour sample, we present an iron radial gradient of about -0.063+/-0.008dex kpc-1 from the first sample, which is quite consistentwith the most recent determination of the oxygen gradient from nebulaeand young stars, about -0.07 dex kpc-1. By dividing clustersinto age groups, we show that the iron gradient was steeper in the past,which is consistent with the recent result from Galactic planetarynebulae data, and also consistent with inside-out galactic diskformation scenarios. Based on the cluster sample, we also discuss themetallicity distribution, cluster kinematics, and space distribution. Adisk age-metallicity relation could be implied by those properties,although we cannot give conclusive result from the age- metallicitydiagram based on the current sample. More observations are needed formetal-poor clusters. From the second catalog, we have calculated thevelocity components in cylindrical coordinates with respect to theGalactic standard of rest for 144 open clusters. The velocitydispersions of the older clusters are larger than those of youngclusters, but they are all much smaller than that of the Galactic thickdisk stars.
| Proper Motions of Open Star Clusters and the Rotation Rate of the Galaxy
The mean proper motions of 167 Galactic open clusters withradial-velocity measurements are computed from the data of the Tycho-2catalog using kinematic and photometric cluster membership criteria. Theresulting catalog is compared to the results of other studies. The newproper motions are used to infer the Galactic rotation rate at the solarcircle, which is found to be ω0=+24.6±0.8 km s-1 kpc-1.Analysis of the dependence of the dispersion of ω0 estimates onheliocentric velocity showed that even the proper motions of clusterswith distances r>3 kpc contain enough useful information to be usedin kinematic studies demonstrating that the determination of propermotions is quite justified even for very distant clusters.
| Metallicities of Old Open Clusters
We present radial velocities and metallicities for a sample of 39 openclusters with ages greater than about 700 million years. For 24 clustersnew moderate-resolution spectroscopic data obtained with multiobjectspectrographs on the Kitt Peak National Observatory and the Cerro TololoInter-American Observatory 4 m telescopes are used to determine radialvelocities and mean cluster metallicities. These new results arecombined with data published previously by Friel & Janes to providea sample of 459 giants in 39 old open clusters, which are used toinvestigate radial abundance gradients in the Galactic disk. Based on anupdated abundance calibration of spectroscopic indices measuring Fe andFe-peak element blends, this larger sample yields an abundance gradientof -0.06+/-0.01 dex kpc-1 over a range in Galactocentricradius of 7 to 16 kpc. There is a slight suggestion of a steepening ofthe abundance gradient with increasing cluster age in this sample, butthe significance of the result is limited by the restricted distancerange for the youngest clusters. The clusters show no correlation ofmetallicity with age in the solar neighborhood. Consistent with theevidence for a steepening of the gradient with age, the clusters in theouter disk beyond 10 kpc show a suggestion at the 1.5 σ level of adependence of metallicity on age.
| CCD Observations of the Open Cluster NGC 6939
New B, V, and I CCD photometry is presented for the intermediate-ageopen cluster NGC 6939. V, B-V and V, V-I color-magnitude diagrams(CMDs), which extend 4 mag fainter than previous CMDs, have beenconstructed. The CMDs show a clearly defined turnoff and well-populatedred giant clump, suggesting a cluster age of at least 1 Gyr. Acomparison between the clump stars of this cluster and those of the opencluster NGC 752 indicate a color excess and distance modulus of0.33+/-0.07 and 12.27+/-0.41 mag, respectively. Examination of reddeningmaps and CMDs of different quadrants of the cluster suggest thatvariable reddening across the face of the cluster is present. Colorexcess values and distance moduli for four quadrants of the clusterrange from 0.29 to 0.41 mag and 12.21 to 12.39 mag. Comparison betweenthe V, B-V CMD and solar metallicity isochrones yield a cluster age of1.6+/-0.3 Gyr.
| Logarithmic Density Range and the Percentage of Stars in the Cores of Various Subsystems of the Globular Clusters M56, M12, NGC 6535, NGC 6171, NGC 5466, and M92
Lower limits for the percentages of stars with various luminosities inthe cores of six globular clusters are derived using stellar spatialdensity distributions f(r) to deep limiting B magnitudes obtainedearlier. For NGC 6535 and NGC 5466, the logarithmic density range andKholopov parameters D f and D r are also determined. These twoparameters are correlated with the mean masses of stars of varioussubsystems and the total mass (number) of stars in the cluster.
| Abundance Gradient from Open Clusters and Implications for the Galactic Disk Evolution
We compile a new sample of 89 open clusters with ages, distances andmetallicities available. We derive a radial iron gradient of about-0.099±0.008 dexkpc (unweighted) for the whole sample, which issomewhat greater than the most recent determination of oxygen gradientfrom nebulae and young stars. By dividing the clusters into age groups,we show that the iron gradient was steeper in the past and has evolvedslowly in time. Current data show a substantial scatter of the clustermetallicities indicating that the Galactic disk has undergone a veryrapid, inhomogeneous enrichment.Also, based on a simple, but quitesuccessful model of chemical evolution of the Milky Way disk, we make adetailed calculation of the iron abundance gradient and its timeevolution. The predicted current iron gradient is about -0.072 dexkpc.The model also predicts a steady flattening of the iron gradient withtime, which agrees with the result from our open cluster sample.
| A study of spatial structure of galactic open star clusters
In order to study the relation between the core and corona in galacticstar clusters, the spatial structure of 38 rich open star clusters hasbeen studied using radial density profiles derived from the photometricdata of the Digital Sky Survey. The shape of the radial density profileindicates that the corona, most probably, is the outer region around thecluster. It can exist from the very beginning of the cluster formationand dynamical evolution is not the reason for its occurrence. The studydoes not find any relation between cluster size and age but indicatesthat the clusters with galacto-centric distances >9.5 kpc have largersizes. Further, we find that the average value of the core radius is1.3+/- 0.7 pc and that of annular width of the corona is 5.6+/- 1.9 pc,while average values of densities of cluster members in the core andcorona are 15.4+/- 9.9 star/pc2 and 1.6+/- 0.99star/pc2 respectively. Average field star contaminations inthe core and corona are ~ 35% and 80% respectively. In spite of smallerdensities in the coronal region, it contains ~ 75% of the clustermembers due to its larger area in comparison to the core region. Thisclearly demonstrates the importance of the coronal region in studiesdealing with the entire stellar contents of open star clusters as wellas their dynamical evolution. In contrast to the cluster cores, thestructure of coronal regions differs significantly from one cluster toother.
| 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.
| The STACC Open Cluster Target List
Observations of variable stars offer a potential to test stellarstructure and evolution. The observations can be either of single,isolated stars, or of variable stars in clusters. The STACC group(Frandsen 1992) has for the last several years searched for openclusters with a population of delta Scuti stars. To make this searchmore efficient, we have produced a target list with a number ofpromising open clusters. The list includes parameters, finding charts,Colour-Magnitude diagrams (CM diagrams) and references for the clusters.This target list is presented here, and is thus made available toobservers interested in participating in the search for variable starsin open clusters. In this paper we describe the motivation, contents anduse of the STACC Open Cluster Target List. We also give some guidelineson how to make CCD observations of open clusters in order to search forvariable stars.
| Searching the Open Cluster NGC 6939 for Variable Stars
A high precision photometric search has found six variable stars in theopen cluster NGC 6939.
| On the Galactic disc age-metallicity relation
A comparison is made between the age-metallicity relations obtained fromfour different types of studies: F and G stars in the solarneighbourhood, analysis of open clusters, galactic structure studieswith the stellar population synthesis technique and chemical evolutionmodels. Metallicities of open clusters are corrected for the effects ofthe radial gradient, which we find to be -0.09 dex kpc^-1 and mostlikely constant in time. We do not correct for the vertical gradient,because its existence and value are not firmly established. Stars andclusters trace a similar age-metallicity relation, showing an excess ofrather metal-rich objects in the age range 5-9 Gyr. Galactic structurestudies tend to give a more metal-poor relation than chemical evolutionmodels. Neither relation explains the presence of old, relativelymetal-rich stars and clusters. This might be caused by uncertainties inthe ages of the local stars, or pre-enrichment of the disc with materialfrom the bulge, possibly as a result of a merger event in the earlyphases of the formation of our Galaxy.
| Some Revised Observational Constraints on the Formation and Evolution of the Galactic Disk
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1997AJ....114.2556T&db_key=AST
| Thirty years of research with the Baldone Schmidt Telescope
We describe the research done with the Baldone Schmidt telescope(80/120/240 cm) of the Radioastrophysical Observatory. The telescope hastwo objective prisms with reciprocal dispersions of 600 and 1130 A/mm atH-gamma. One of the main research projects is the search for andphotometric study of galactic carbon stars. The telescope has also beenused for novae studies in M 31 and stellar photometry in open clustersand fields of special interest. Comet studies, particularly during theInternational Halley Watch, proved to be another successful applicationof the telescope. The archive of the Baldone Schmidt telescope containsnearly 20,000 direct and 2000 spectral plates and films.
| LBDS 53W091: an Old, Red Galaxy at z=1.552
The weak radio source LBDS 53W091 is associated with a very faint (R ~24.5) red (R - K ~ 5.8) galaxy. Long spectroscopic integrations with theW. M. Keck telescope have provided an absorption-line redshift, z =1.552 +/- 0.002. The galaxy has a rest frame ultraviolet spectrum verysimilar to that of an F6 V star, and a single-burst old stellarpopulation that matches the IR colors, the optical energy distributionand the spectral discontinuities has a minimum age of 3.5 Gyr. Wepresent detailed population synthesis analyses of the observed spectrumin order to estimate the time since the last major epoch of starformation. We discuss the discrepancies in these estimates resultingfrom using different models, subjecting the UV spectrum of M32 to thesame tests as a measure of robustness of these techniques. The modelsmost consistent with the data tend to yield ages at z = 1.55 of >~3.5Gyr, similar to that inferred for the intermediate-age population inM32. Depending upon the assumed Hubble constant and the value of Omega0, only certain cosmological expansion times are consistent with the ageof LBDS 53W091; in particular, for Omega 0 = 1, only models with H0<~ 45 km s-1 Mpc-1 are permitted. For H0 = 50 km s-1 Mpc-1 and Omega0 = 0.2, we derive a formation redshift, zf >= 5.
| Cluster membership determinations from proper motion surveys
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