Photometric and Coravel observations of red giant candidates in three open clusters: membership, binarity, reddening and metallicity
Aims.We present new CORAVEL radial-velocity observations andphotoelectric photometry in the UBV and DDO systems for a sample ofpotential members of the red-giant branches of NGC 6192, NGC 6208 andNGC 6268, three open clusters projected close to the Galactic centerdirection. We also examine the properties of a sample of 42 inner diskopen clusters projected towards almost the same direction as the threeclusters. Methods: .Cluster members and red field giants werediscriminated by using the CORAVEL radial-velocity data and by applyingtwo photometric criteria. Interstellar reddening and metal content ofthe clusters were derived from combined BV and DDO data. Results:.Cluster membership for five red giants in NGC 6192, three in NGC 6208and three in NGC 6268 has been confirmed by the analysis of thephotometric and kinematic data. Photometric membership probabilitiesshow very good agreement with those obtained from CORAVEL radialvelocities. Three new spectroscopic binaries were discovered among thered giants of NGC 6192 and NGC 6208. Mean radial velocities and E(B-V)colour excesses were derived. Conclusions: .The overallmetallicities were found to be nearly solar for NGC 6208 and above solarfor NGC 6192 and NGC 6268. Most of the clusters located closer than 2kpc from the Sun in the considered direction are slightly more reddenedthan the absorption resulting from the Baade's window absorption law.
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The Evolutionary Status of Be Stars: Results from a Photometric Study of Southern Open Clusters
Be stars are a class of rapidly rotating B stars with circumstellardisks that cause Balmer and other line emission. There are threepossible reasons for the rapid rotation of Be stars: they may have beenborn as rapid rotators, spun up by binary mass transfer, or spun upduring the main-sequence (MS) evolution of B stars. To test the variousformation scenarios, we have conducted a photometric survey of 55 openclusters in the southern sky. Of these, five clusters are probably notphysically associated groups and our results for two other clusters arenot reliable, but we identify 52 definite Be stars and an additional 129Be candidates in the remaining clusters. We use our results to examinethe age and evolutionary dependence of the Be phenomenon. We find anoverall increase in the fraction of Be stars with age until 100 Myr, andBe stars are most common among the brightest, most massive B-type starsabove the zero-age main sequence (ZAMS). We show that a spin-up phase atthe terminal-age main sequence (TAMS) cannot produce the observeddistribution of Be stars, but up to 73% of the Be stars detected mayhave been spun-up by binary mass transfer. Most of the remaining Bestars were likely rapid rotators at birth. Previous studies havesuggested that low metallicity and high cluster density may also favorBe star formation. Our results indicate a possible increase in thefraction of Be stars with increasing cluster distance from the Galacticcenter (in environments of decreasing metallicity). However, the trendis not significant and could be ruled out due to the intrinsic scatterin our data. We also find no relationship between the fraction of Bestars and cluster density.
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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.
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A CCD BVI Photometric Study of the Young, Highly Reddened Open Cluster NGC 6318
We present CCD BVI photometry for the southern open cluster NGC 6318.The sample consists of 9876 stars measured in an area of13.6m×13.6m, extending down to V~21.5 mag. Star countscarried out within and outside the cluster region allowed us to estimatethe cluster angular radius as ~8'. The comparison of the clustercolor-magnitude diagrams with isochrones of the Geneva group yieldsE(B-V)=1.20+/-0.05, E(V-I)=1.55+/-0.10, and V-MV=15.45+/-0.35for logt=8.20 (t=160 Myr) and Z=0.020. NGC 6318 is then located at2.1+/-0.5 kpc from the Sun and 30 pc below the Galactic plane. Using theWEBDA open cluster database, we examined the structure of the Galacticdisk along the line of sight of NGC 6318. Among the known clusters inthis direction, HM 1 and BH 222 are the farthest ones, while thoselocated between 1 and 2 kpc of the Sun appear to be more absorbed thanthose expected to follow a quasi-linear extinction law.
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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.
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Spectroscopic Binaries in Young Open Clusters
We have analysed the binarity and multiplicity characteristics of 120O-type stars in 22 very young open clusters and found marked differencesbetween the "rich" (N >= 6 O-type stars and primaries) and "poor" (N= 1) clusters. In the rich clusters, the binary frequencies vary between14% (1 SB among 7 stars) and 80% (8 SBs among 10 stars). Multiplesystems seem not to be frequent and stars are spread all over thecluster area. In poor clusters, the binary frequency of the O-typeobjects is nearly 100%, with orbital periods around 3 days. Severalbinaries are also eclipsing. Additional companions are always present.They form either hierarchical multiple stars or trapezium systems. Thesemassive multiple systems are generally found close to the clustercenter, although there are exceptions.
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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
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Diffuse X-Ray Emission in Three Poor Clusters of Galaxies
We report on ROSAT PSPC soft X-ray observations of three poor clustersof galaxies at distances above 100 Mpc (cz>8000 km s-1). Inall three cases the emission is centered on the dominant member of thecluster, i.e., NGC 4104, NGC 6269, and NGC 6329, respectively. X-rayemission was detected out to radii of 400-600 kpc. The bolometric X-rayluminosities range from 2.6 to 8.6x1042 ergs s-1.The soft X-ray emission characteristics and the physical propertiesdeduced from our observations of all three poor clusters resemble thoseof downscaled rich clusters. In each case, the soft X-ray spectrum iswell represented by a thermal model with kT~=1.1-1.3 keV and near-solarmetallicity in the center, increasing to kT~=1.4-1.6 keV toward theouter boundaries while the metallicity, Z, decreases to about 0.1 solar.Equally good fits can be achieved if the metallicity is left at thesolar value and an additional gas component with kT~=0.5 keV isintroduced. The central electron densities in all three poor clustersstudied here are enhanced with respect to a King profile by factors of2-6. This, together with the results of the spectral fits, can beinterpreted as either indicating the presence of cooling flows or of atwo-phase medium in the central areas. The spatial electron densitydistribution in the outer regions of each cluster can be fitted by Kingprofiles with core radii of 17-60 kpc and exponents of β=0.38-0.44.Using the derived radial temperature and density distributions, thetotal gravitating mass is obtained. We deriveMtot=3.7+/-0.7x1013 Msolar within aradius of 300 kpc for each of the three systems, as opposed to1014-1015 Msolar for rich clusters. Wefind that the LX versus kT relation found by A. C. Edge andG. C. Stewart (1991) for rich clusters of galaxies scales into thedomain of poor clusters and groups of galaxies. The spectral fits of thecentral regions show that none of the first-ranking galaxies of thethree poor clusters hosts a Seyfert 1 active galactic nucleus thatcontributes significantly to the emission in the ROSAT band (0.1-2.4keV).
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Absolute proper motions of 181 young open clusters.
Not Available
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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.
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The young open clusters in the galaxy.
Abstract image available at:http://adsabs.harvard.edu/abs/1994RMxAA..29..141F
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Integrated photometric properties of open clusters
Galactic open clusters provide an abundant sample of stellar aggregatesof various sizes, ages and metal abundances, apt to constitute atemplate for comparison with star systems in other galaxies. In thispaper we present and discuss a standard methodology to synthesize U,B,Vfluxes and colours, and apply it to a set of 138 open clusters. Resultsare compared with previous ones available in the literature. We wereable to calibrate a mass-luminosity relation by which we evaluated themass of ~400 open clusters, leading to a well defined present-day massfunction. The number-complete sample of galactic open clusters presentedin Battinelli & Capuzzo-Dolcetta (1991) is enlarged of a 15%.
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Topography of the Galactic disk - Z-structure and large-scale star formation
A 3D morphological description of the Galactic disk defined by the youngstellar population is delineated using a sample of young open clusterswith cataloged distances and treated with Kriging techniques. The valuesof the positional variable Z for the cluster sample are considered asprospectings of the displacement of the Galactic disk in respect to theequator in the plane. The Kriging technique is described with emphasison its application to the automatic cartography problem. A view of theGalactic disk in a region of about 3 kpc around the sun emerges fromthis treatment and shows a trough-peak structure with four maindepressions as the more striking features. The most prominentdepression, named Big Dent, is apparent at about 1.8 kpc in anapproximately 240-deg direction. It has an elliptical shape with axissizes of 1.5 and 3 kpc, reaching a Z value of 200 pc below the formalGalactic plane. Two-dimensional sections across some selected directionsof the topography show profiles in good agreement with previousobservational studies based on different object samples.
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Formation and evolutionary properties of the Galactic open cluster system
Results are reported from a statistical analysis of observational dataon 100 open clusters within 2 kpc of the sun, selected from the catalogof Lynga (1987). The selection criteria and the completeness of thesample are discussed; the data are compiled in a table; and the analysisresults are presented in a series of graphs and characterized in detail.A cluster formation rate of 0.45 clusters/kpc Myr is found,significantly lower than the rates determined previously (using clusterswithin 1 kpc of the sun) and corresponding to a cluster star-formationefficiency of 0.0063. The low average cluster lifetime (about 10 Myr)suggests that clusters are formed as unstable systems.
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Initial masses of WR stars in open clusters.
Abstract image available at:http://adsabs.harvard.edu/abs/1990RMxAA..21..346V
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Component Analysis of Open Clusters
Not Available
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Description of a Database for Stars in Open Clusters
Not Available
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Supernova rates and bursts of star formation
A new analysis of supernova (SN) rates in spiral and irregular galaxiesis presented. It is shown that the concept of a single average SN ratefor all 'normal' galaxies has to be abandoned. Normal galaxies belong totwo distinct classes with regard to the formation of SN II progenitors:most galaxies are rather inactive while a small percentage of galaxiesin a 'burst' phase is producing these massive stars vigorously. Theinitial mass function during such bursts must be notably different fromthat determined in the solar neighborhood. It has to be strongly biasedtoward stars with masses above about eight solar. The formation ofmassive stars follows a pattern fundamentally different from that of lowand intermediate-mass stars. It occurs episodically and apparently overentire disks of spirals, in particular Sc galaxies.
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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.
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A cluster analysis of open clusters
The Galactic distribution of 361 open clusters is studied using acluster analysis method. It is shown that more than half of the clustersenter groups with characteristic dimensions of several hundred parsecs.To distinguish physical clusters from random condensations, criteriabased on age similarity, the color of the main-sequence blue end, andthe integrated color and radial velocity of the clusters are used. Theproximity of these values suggests a physical unity and common origin ofclusters in a group.
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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.
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Catalogue of UBV Photometry and MK Spectral Types in Open Clusters (Third Edition)
Not Available
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Investigation of the initial mass spectrum of open star clusters
The mass spectra of 228 open star clusters were derived by comparison ofcolor-magnitude diagrams with evolutionary tracks. The application tobinary stars showed the reliability of the mass determination. Thederived mass spectra were fitted by power laws as well as exponentiallaws. It could be shown that both approximate the mass spectra of openstar clusters on the same average significance level. The presentinvestigation revealed a correlation of the slope of the mass spectrawith the cluster age, whereas a detected correlation of the slope withgalactocentric distance is slight. The results suggest that the slope ofthe mass spectrum increases with increasing cluster and galactocentricdistance. These findings are discussed with respect to their reasons andprevious results concerning open clusters and field stars.
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Integrated Photometric Parameters of Open and Globular Clusters
Not Available
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Open clusters and galactic structure
A total of 610 references to 434 clusters are employed in thecompilation of a catalog of open clusters with color-magnitude diagramson the UBV or RGU systems. Estimates of reddening, distance modulus, ageand number of cluster members are included. Although the sample isconsidered representative of the discoverable clusters in the galaxy,the observed distribution is nonuniform because of interstellarobscuration. Cluster distribution in the galactic plane is found to bedominated by the locations of dust clouds rather than by spiralstructure. The distributions of clusters as a function of age andrichness class show that the lifetimes of poor clusters are much shorterthan rich ones, and that clusters in the outer disk survive longer thanthose in the inner disk. An outer disk age which is only about 50% theage of the globular clusters is indicated by cluster statistics. Thethickening of the galactic disk with increasing galactocentric distancemay be due to either a younger dynamical age or a lower gravitationalpotential in the outer regions.
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Analysis of UBV Data in Open Clusters
Not Available
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A catalogue of galactic clusters observed in three colours
This catalogue contains photometric data for 190 galactic clusters, allobserved in UBV or RGU. The distances of the young clusters (with spless than b3) have been calculated or recalculated according to method Aof Becker (1963). The galactic distribution of these clusters confirmstheir role of being good spiral tracers.
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Observational tests on star formation. I - Size variation of very young clusters through the Galaxy
Study of the linear dimensions of very young open star clusters (ageless than 15 my) shows that in the observable part of the Galaxy thediameter of clusters increases on the average with distance from thegalactic center, the variation being especially pronounced around adistance from the galactic center of 11 kpc. Both the direction and thesize of the observed increase may be interpreted in terms of the changeof the Jeans critical radius throughout the Galaxy. The requiredincrease of the Jeans radius with distance from the galactic center maybe accounted for by the decrease in the mean gas density throughout theGalaxy and by the decrease in the compression effects of the galacticshock waves or whatever other mechanism initiates star formation.
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Southern open star clusters VI. UBV-Hbeta photometry of 18 clusters from Centaurus to Sagittarius.
Abstract image available at:http://adsabs.harvard.edu/abs/1975A&AS...20..155M
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A catalogue of galactic star clusters observed in three colours
Abstract image available at:http://adsabs.harvard.edu/abs/1971A&AS....4..241B
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INHABITED SKY
