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Proper motion determination of open clusters based on the UCAC2 catalogue
We present the kinematics of hundreds of open clusters, based on theUCAC2 Catalogue positions and proper motions. Membership probabilitieswere obtained for the stars in the cluster fields by applying astatistical method uses stellar proper motions. All open clusters withknown distance were investigated, and for 75 clusters this is the firstdetermination of the mean proper motion. The results, including the DSSimages of the cluster's fields with the kinematic members marked, areincorporated in the Open Clusters Catalogue supported on line by ourgroup.
| Astrophysical parameters of Galactic open clusters
We present a catalogue of astrophysical data for 520 Galactic openclusters. These are the clusters for which at least three most probablemembers (18 on average) could be identified in the ASCC-2.5, a catalogueof stars based on the Tycho-2 observations from the Hipparcos mission.We applied homogeneous methods and algorithms to determine angular sizesof cluster cores and coronae, heliocentric distances, mean propermotions, mean radial velocities, and ages. For the first time we derivedistances for 200 clusters, radial velocities for 94 clusters, and agesof 196 clusters. This homogeneous new parameter set is compared withearlier determinations, where we find, in particular, that the angularsizes were systematically underestimated in the literature.
| Morphology of Galactic Open Clusters
We analyzed the shapes of Galactic open clusters by the star-countingtechnique with the Two Micron All Sky Survey star catalog database.Morphological parameters such as the ellipticity and size have beenderived via stellar density distribution, weighed by clusteringprobability. We find that most star clusters are elongated, even for theyoungest star clusters of a few million years old, which are locatednear the Galactic disk. The shapes of young star clusters must reflectthe conditions in the parental molecular clouds and during the clusterformation process. As an open cluster ages, stellar dynamics cause theinner part of the cluster to circularize, but the overall radius getslarger and the stellar density becomes sparser. We discuss how theinternal relaxation process competes with Galactic external perturbationduring cluster evolution.
| New variable stars in open clusters. I. Methods and results for 20 open clusters
We present high precision CCD photometry of 1791 objects in 20 openclusters with an age of 10 Myr to 1 Gyr. These observations wereperformed within the Δ a photometric system which is primarilyused to detect chemically peculiar stars of the upper main sequence.Time bases range from 30 min up to 60 days with data from severalnights. We describe the time series analysis reaching a detection limitof down to 0.006 mag for apparent variability. In total, we havedetected 35 variable objects of which four are not members of theircorresponding clusters. The variables cover the entireHertzsprung-Russell diagram, hence they are interesting targets forfollow-up observations.Based on observations obtained at Complejo Astronómico elLeoncito (CASLEO), operated under the agreement between the ConsejoNacional de Investigaciones Científicas y Técnicas de laRepública Argentina and the National Universities of La Plata,Córdoba y San Juan; ESO-La Silla and UTSO-Las Campanas.
| Theoretical isochrones for the Delta a photometric system
We have calculated theoretical isochrones for the photometric Delta asystem to derive astrophysical parameters such as the age, reddening anddistance modulus for open clusters. The Delta a system samples the fluxdepression at 520 nm which is highly efficient to detect chemicallypeculiar (CP) objects of the upper main sequence. The evolutionarystatus of CP stars is still a matter of debate and very important totest, for example, the dynamo and diffusion theories. In fact, thedynamo or fossil origin of the magnetic fields present in this kind ofstar is still not clear. Using the stellar evolutionary models by Claret(\cite{Cla95}), a grid of isochrones with different initial chemicalcompositions for the Delta a system was generated. The published dataof 23 open clusters were used to fit these isochrones with astrophysicalparameters (age, reddening and distance modulus) from the literature. Asan additional test, isochrones with the same parameters for Johnson UBVdata of these open clusters were also considered. The fits show a goodagreement between the observations and the theoretical grid. We findthat the accuracy of fitting isochrones to Delta a data without theknowledge of the cluster parameters is between 5 and 15%.
| Metallicity distribution on the galactic disk
Depending mainly on UBVCCD data, the metallicities of 91 open starclusters nearby the galactic disk have been estimated using Cameron's[A&A 147 (1985b) 39] method. The metallicity radial gradient alongthe galactic plane is found to be -0.09 dex/kpc; which is in a very goodagreement with Panagia and Tosi [A&A 96 (1981) 306] and Carraro etal. [MNRAS 296 (1998) 1045]. Vertically on the galactic disk, withinabout 800 pc, the metallicity gradient is found to be so trivial. Anaverage age-metallicity relation has been examined, which confirms theprevious suggestion that the metallicity of a cluster depending mainlyon its position on the galactic disk more than its age.
| 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.
| Morphological analysis of open clusters' propertiesII. Relationships projected onto the galactic plane
A morphological analysis study of open clusters' properties has beenachieved for a sample of 160 UBVCCD open star clusters of approximately128,000 stars near the galactic plane. The data was obtained and reducedfrom using the same reduction procedures, which makes this catalogue thelargest homogeneous source of open clusters' parameters.
| Proper motions of open clusters based on the TYCHO2 Catalogue. II. Clusters farther than 1 kpc
We determined the mean absolute proper motion of 94 open clusterssituated farther than 1 kpc from the Sun. The results are derived fromthe stellar proper motion data given in the Tycho2 Catalogue. The meanproper motion of the clusters and membership probability of individualstars were obtained from the proper motion data by applying thestatistical method proposed by Sanders (\cite{Sanders1971}). Themeasurements made use of a large number of stars, usually several tens,for each cluster. The total number of stars investigated in the fieldsof the clusters is 4864 of which 2021 were considered members. For 55clusters, this is the first determination of the proper motion. Based onobservations of the ESA Hipparcos satellite. Tables 1 to 95 are onlyavailable in electronic form at the CDS via anonymous ftp tocdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/388/168
| Integrated photometric characteristics of galactic open star clusters
Integrated UBVRI photometric parameters of 140 galactic open clustershave been computed. Integrated I(V-R)0 and I(V-I)0colours as well as integrated parameters for 71 star clusters have beenobtained for the first time. These, in combination with published data,altogether 352 objects, are used to study the integrated photometriccharacteristics of the galactic open clusters. The I(MV)values range from -9.0 to -1.0 mag corresponding to a range in totalmass of the star clusters from ~ 25 to 4*E4 Msun.The integrated colours have a relatively narrow range, e.g., I(B-V){_0}varies from -0.4 to 1.2 mag. The scatter in integrated colours at agiven integrated magnitude can be understood in terms of differences infraction of red giants/supergiants in the clusters. The observedintegrated magnitudes and colours agree with the synthetic ones, exceptthe dependences of I(V-R)0 and I(V-I)0 colours forclusters younger than ~ 100 Myrs and also of the integrated magnitudesof oldest clusters. The large sample provides the most accurate agedependence of integrated magnitudes and colours determined so far. Theluminosity function of the I(MV) has a peak around -3.5 magand its slope indicates that only ~ 1% of the open clusters in thegalactic disc are brighter than I(MV)=-11 mag. No variationhas been found of integrated magnitude with galactocentric distance andmetallicity.
| 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.
| Morphological analysis of open clusters' propertiesI. Properties' estimations
A sample of 160 UBVCCD observations of open star clusters near thegalactic plane has been studied, and a catalogue of their propertiesobtained. The main photometrical properties have been re-estimated selfconsistently and the results have been compared with those of Lynga[Lynga, G., 1987. Catalog of Open Cluster Data, 5th Edition, StellarData Centers, Observatoire de Strasbourg, France].
| CCD photometric search for peculiar stars in open clusters. II. NGC 2489, NGC 2567, NGC 2658, NGC 5281 and NGC 6208
High accurate photometric data in the three filter, narrow-band Deltaa-system for five open clusters (NGC 2489, NGC 2567, NGC 2658, NGC 5281and NGC 6208) are presented permitting one to detect apparent chemicallypeculiar stars. The ages and distances are wide spread to improve thestatistics of peculiar stars in our Milky Way. A total of 235 starswithin these clusters have been observed. We have detected ten apparentpeculiar objects (six with significant positive and four with negativeDelta a-values) in four open clusters. Although three of them within theboundaries of NGC 2567 are probably not members of this cluster. Sinceno Strömgren uvbybeta data are available from the literature,Johnson UBV photometry was used to test and calibrate our photometricdata. The results from a comparison of both systems are excellent. Basedon observations at ESO-La Silla and UTSO-Las Campanas. Tables 4 to 8 areonly available at the CDS via anonymous ftp to cdsarc.u-strasbg.fr(130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/373/153 Figure 1 is onlyavailable in electronic form at http://www.edpsciences.org
| Absolute proper motions of open clusters. I. Observational data
Mean proper motions and parallaxes of 205 open clusters were determinedfrom their member stars found in the Hipparcos Catalogue. 360 clusterswere searched for possible members, excluding nearby clusters withdistances D < 200 pc. Members were selected using ground basedinformation (photometry, radial velocity, proper motion, distance fromthe cluster centre) and information provided by Hipparcos (propermotion, parallax). Altogether 630 certain and 100 possible members werefound. A comparison of the Hipparcos parallaxes with photometricdistances of open clusters shows good agreement. The Hipparcos dataconfirm or reject the membership of several Cepheids in the studiedclusters. Tables 1 and 2 are only available in electronic form at theCDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/Abstract.html
| 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
| Red giants in open clusters. VI. Orbits of ten spectroscopic binaries.
We present new orbits for ten (single-lined) spectroscopic binaries inseven open clusters: NGC 2489, 2567, 3033, 5822, 6134, 6664 and IC 2488based on 243 individual radial velocities obtained with the southernCORAVEL scanner. The orbital periods range from 98.5 to 3566 days. Theshortest-period orbit is circular, as expected. Seven of the binariesare confirmed cluster members, one is a possible member, and two areclearly non-members. Maximum masses from photometric separation andminimum masses from the spectroscopic orbits define the mass of thesecondaries within an interval of M_max_-M_min_=0.5Msun_. NGC6664 #54 seems to have a rather massive secondary(M>3Msun_), but the UBV colours appear normal for aluminous red giant, while significantly bluer (B-V) and (U-B) colourswould be expected. It could be a triple system, the secondary beingitself a short period binary. This paper brings the number of orbitspublished in this programme to 53, 45 of which are confirmed red-giantcluster members and 8 are non-members.
| Chemical Evolution of the Galactic Disk: Evidence for a Gradient Perpendicular to the Galactic Plane
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1995AJ....110.2813P&db_key=AST
| Catalogue of blue stragglers in open clusters.
An extensive survey of blue straggler candidates in galactic openclusters of both hemispheres is presented. The blue stragglers wereselected considering their positions in the cluster colour-magnitudediagrams.They were categorized according to the accuracy of thephotometric measurements and membership probabilities. An amount of 959blue straggler candidates in 390 open clusters of all ages wereidentified and classified. A set of basic data is given for everycluster and blue straggler. The information is arranged in the form of acatalogue. Blue stragglers are found in clusters of all ages. Thepercentage of clusters with blue stragglers generally grows with age andrichness of the clusters. The mean ratio of the number of bluestragglers to the number of cluster main sequence stars is approximatelyconstant up to a cluster age of about 10^8.6^ yr and rises for olderclusters. In general, the blue stragglers show a remarkable degree ofcentral concentration.
| CCD observations in 7 open clusters - NGC2421, NGC2439, NGC2489, NGC2567, NGC2627, NGC2658 and NGC2910
Photometric UBVIc data are presented for the open clusters NGC2439,NGC2489, NGC2567, NGC2627, NGC2658, and NGC2910. From a combination ofthe new BVIc technique and the analysis of the CMDs, the color excessE(B-V), the distance modulus, and approximate age are given for theseclusters and NGC2421.
| An improved metal abundance calibration for the Washington system
The determination of metal abundances for individual giants fromWashington photometry is revised, with several significant improvementsincorporated. The solar-abundance two-color relations are revamped withthe inclusion of new observations of a large sample of solar-abundancegiants with small reddenings, especially those with late-K spectraltypes. The new relations are very similar to the original ones derivedin C76 except for a zero-point offset. A new temperature index, M-T2, isinvestigated, as well as a new abundance index, C-T1, in addition to thestandard indices. The M-T2 index has a much broader baseline and thus amuch larger range than T1-T2, and is therefore less susceptible tophotometric errors. The significant decrease in abundance sensitivityfor cooler stars, suspected by previous investigations, is confirmed byincluding observations of a number of giants with a range in temperaturein each of a large sample of open and globular clusters. A procedure forcorrecting the abundance indices for cool stars is derived whichsignificantly improves the metallicity determination.
| An observational age-metallicity relation for the Galaxy
An observational Age-Metallicity Diagram for the Galaxy has beenconstructed on the base of star cluster data available in theliterature. This diagram exhibits two independent and simultaneousmetallicity enhancement processes identified with two dynamical galacticsubstructures: the thin and the thick disks. Within the observationaluncertainties both these processes can be satisfactory approximated byInfall-Inflow models of the chemical evolution with different high,although rapidly decaying with time, Star Formation and Infall Rates.The comparison of the galactic age-metallicity relations with that forthe Large Magellanic Cloud shows some similarities between processes ofthe chemical enhancement in the Large Magellanic Cloud and the Thin Disksubsystem in the Galaxy.
| Metallicities of open clusters
An examination is conducted of available metallicity data on openclusters, gathering the largest possible set of homogeneous estimationsof this parameter and determining whether open cluster metallicities arerelated to the spatial and age distributions of such objects. The'composite' C-M diagrams for the two metallicity groups discussedexhibit interesting morphological differences which may be characterizedas the presence of numbered blue stragglers at the two metal-richclusters and a lack of such members in two metal-poor ones.
| Two populations of open clusters
The paper proposes a division of the local open clusters into twodifferent dislike subpopulations on the base of the metallicityenhancement history, spatial distribution in the Galaxy and morphologyof their C-M diagrams. The thin disk population objects exhibit highermetallicities and are more closely concentrated to the center and thedisk of the Galaxy than the thick disk clusters. The former contain alsofrequently blue stragglers while the later exhibit the presence of Clumpgiant members, typical for the thick disk globular clusters. Kinematicalproperties of the two considered open cluster subpopulations remainunknown due to the lack of observational data.
| Young stellar-gas complexes in the Galaxy
It is found that about 90 percent of OB-associations and o-b2 clusterssituated within 3 kpc of the sun can be united into complexes withdiameters of 150-700 pc. Almost all of these clusters contain giantmolecular clouds with a mass greater than about 100,000 solar masses. Anumber of complexes are associated with giant H I clouds; a few of thesmall complexes are situated in the HI caverns. The concentration ofOB-associations and young clusters in star complexes attests to theircommon origin in the supergiant gaseous clouds.
| A cluster analysis of young open clusters
Cluster analysis methods are used to consider the galactic distributionof 224 open clusters with an age up to 10 to the 8th yrs. Most of theseclusters enter condensations with characteristic dimensions of a fewhundred parsecs. Some condensations are so similar in terms of the age,integrated color, and radial velocity of their components, that thiscannot be considered a coincidence. This suggests that each condensationis a physical entity consisting of clusters apparently linked by acommon origin.
| Yellow evolved stars in open clusters
This paper describes a program in which Galactic cluster post-AGBcandidates were first identified and then analyzed for clustermembership via radial velocities, monitored for possible photometricvariations, examined for evidence of mass loss, and classified ascompletely as possible in terms of their basic stellar parameters. Theintrinsically brightest supergiants are found in the youngest clusters.With increasing cluster age, the absolute luminosities attained by thesupergiants decline. It appears that the evolutionary tracks ofluminosity class II stars are more similar to those of class I than ofclass III. Only two superluminous giant star candidates are found inopen clusters.
| Mass-losing red giants in open clusters
Mass-losing stars in open clusters with main-sequence turn-offs atintermediate mass have been searched for by using the IRAS data base.The absence of many strong 60 micron sources in open clusters impliesthat intermediate-mass stars lose much of their mass during an intensewind phase of rather short duration. For stars of about seven solarmasses, this phase, if it exists at all, lasts for not much more than100,000 yr. For stars of about four solar masses, the intense wind phaseappears to last considerably less than 10 million yr; it may well lastfor less than a million yr.
| Age distribution of open clusters as a function of their linear diameter and age-dependence of cluster masses
From the well-observed data of star clusters, the age distribution ofgalactic clusters is obtianed as a function of their linear diameter andit is concluded that the observed age distribution of clusters fordifferent linear diameter intervals within 1500 pc, is not seriouslyaffected by the selection effects. If we assume that the rate offormation of clusters is constant, the lifetimes r112 of the clustersfor different linear diameter intervals have been obtained and it isfound that the clusters with a linear diameter in the range 0-1.9 Pchave longer lifetimes than the clusters having linear diameters largerthan 2.0 Pc. Total masses of 57 clusters have been obtained using thecatalogues of Piskunov (1983) and Myakutin et al. (1984). A study ofage-dependence of cluster masses, based on the total masses of theclusters obtained in the present study and the cluster masses given byBruch and Sanders (1983) and Lynga (1983b), shows that there is adecreasing trend in the total mass with the age, however, there is anincreasing trend after the age of about 108 yr. It is also concludedthat the initial rate of formation of rich clusters was relativelyhigher than the present rate of formation
| Catalogue of UBV Photometry and MK Spectral Types in Open Clusters (Third Edition)
Not Available
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