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Публикации по объекту
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.
| 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.
| 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.
| 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.
| Interstellar extinction in the open clusters towards galactic longitude around 130deg
In this paper we present a detailed study of the intra-cluster reddeningmaterial in the young open clusters located around l ~ 130degusing colour-excess diagrams and two-colour diagrams. The study supportsthe universality of the extinction curves for lambda >= lambdaJ, whereas for shorter wavelengths the curve depends upon thevalue of the Rcluster (total-to-selective absorption in thecluster region). The value of Rcluster in the case of NGC654, NGC 869 and NGC 884 is found to be normal, whereas the value ofRcluster in the cluster regions NGC 1502 and IC 1805indicates an anomalous reddening law in these regions. In the case ofNGC 1502 the value of Rcluster is found to be lower(2.57+/-0.27) whereas in the case of IC 1805 it is higher (3.56+/-0.29)than the normal value of 3.1. Although the intra-cluster materialindicates a higher value of Rcluster in the NGC 663 region,the error in the estimation of Rcluster is too large toconclude anything. It is also found that the extinction process in the Uband in the case of NGC 663 seems to be less efficient, whereas in thecase of NGC 869 the process is more efficient.
| 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.
| 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.
| A multicolour CCD photometric and mass function study of the distant southern open star clusters NGC 3105, NGC 3603, Melotte 105, Hogg 15, NGC 4815, Pismis 20 and NGC 6253
We derive cluster parameters and mass functions from new UBVRI CCDphotometric observations of ~3500 stars reaching down to V~20mag for thedistant southern open star clusters NGC 3105, NGC 3603, Melotte 105,Hogg 15, NGC 4815, Pismis 20 and NGC 6253. For NGC 3105 and Hogg 15, CCDdata are presented for the first time. The reddening is non-uniformacross the face of the young (age <300Myr) clusters NGC 3105, NGC3603, Melotte 105, Hogg 15 and Pismis 20, with average values ofE(B-V)=1.06, 1.44, 0.52, 1.15 and 1.20mag respectively, while it isuniform with average values of E(B-V)=0.72 and 0.20mag for the olderclusters NGC 4815 and 6253 respectively. The values of colour excessratios indicate the presence of normal interstellar reddening across thecluster regions studied here. Well-defined main sequences can be seen inall the clusters. However, main-sequence turn-off points and subgiantbranches are well defined only in the older clusters NGC 4815 and 6253.The distances to the clusters NGC 3105, NGC 3603, Melotte 105, Hogg 15,NGC 4815, Pismis 20 and NGC 6253 are 9.5+/-1.5, 7.2+/-1.2, 2.3+/-0.2,3.0+/-0.3, 2.75+/-0.2, 3.55+/-0.35 and 1.8+/-0.12kpc respectively, whilethe corresponding ages derived using theoretical convective coreovershooting stellar evolutionary isochrones are 25+/-10, 3+/-2,250+/-30, 6+/-2, 400+/-50, 6+/-2 and 2500+/-600Myr respectively. In themass range ~1-75Msolar, the mass functions of all clustersexcept for NGC 6253 have been studied. The slopes of their mass spectraagree within errors with the Salpeter value (1.35). The slope of themass function for stars more massive than 10Msolar is almostthe same as for the lower mass stars. The mass function slopes ofclusters younger than 500Myr seem to have no dependence on Galacticlongitude, Galactocentric distance and cluster age. As the inherentuncertainties in the mass function determinations of young Galactic starclusters can produce internal scatter that is larger than the externalscatter, we conclude that, above 1Msolar, the initial massfunction is universal with a slope of Salpeter value.
| 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].
| Statistical parallaxes and kinematical parameters of classical Cepheids and young star clusters
The statistical-parallax method is applied for the first time to spacevelocities of 270 classical Cepheids with proper motions adopted fromHIPPARCOS (1997) and TRC (Hog et al. 1998) catalogs and distances basedon the period-luminosity relation by Berdnikov et al. (1996). Thedistance scale of short-period Cepheids (with periods less than 9 days)is shown to require an average correction of 15-20%, whereas statisticalparallaxes of Cepheids with periods > 9 days are found to agree wellwith photometric distances. It is shown that the luminosities ofshort-period Cepheids must have been underestimated partly due to thecontamination of this subsample by a substantial (20 to 40%) fraction offirst-overtone pulsators. The statistical-parallax technique is alsoapplied for the first time to 117 open clusters younger than 100 millionyears and with proper motions reduced to the HIPPARCOS reference system.It is concluded that a 0.12-0.15 mag increase of the distance scales ofopen clusters and Cepheids would be sufficient to reconcile thestatistical-parallax results inferred for these two types of objects.Such approach leads to an LMC distance modulus of less than 18.40 mag,which agrees, within the errors, with the short distance scale for RRLyrae variables and is at variance with the conclusions by Feast andCatchpole (1998) and Feast et al. (1998), who argue that the LMCdistance modulus should be increased to 18.70 mag. The distance scalebased on the Cepheid period-luminosity relation by Berdnikov and Efremov(1985) seems to be a good compromise. Extragalactic distances, whichrely on long-period Cepheids, seem to require no substantial correction.In addition to statistical parallaxes, kinematical parameters have beeninferred for the combined sample consisting of Cepheids andopen-clusters: solar-motion components (U0 ,V0,W0) = (9, 12, 7) km/s (+/- 1 km/s); velocity-ellipsoid axes(σU; σV; σW) = (15.0,10.3, 8.5) km/s (+/- 1 km/s); the angular velocity of rotation of thesubsystem, ω0 = 28.7 +/- 1 km/s/kpc, the Oort constantA = 17.4 +/- 1.5 km/s, and the second derivative of angular velocity,⋰ω0= 1.15 +/- 0.2 km/s/kpc3.
| Absolute proper motions of 181 young open clusters.
Not Available
| On Coagulation and the Stellar Mass Spectrum
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1995ApJ...452..652A&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.
| Young open clusters as probes of the star formation process. 1: an atlas of open cluster photometry
We have obtained charge coupled device (CCD) photometry, in the UBVsystem, for 23 open clusters in order to explore the star formationhistory of the Cassiopeia region of the Perseus spiral arm of ourGalaxy. Magnitudes and colors of 35,788 stars were measured, making thisthe most comprehensive, homogeneous single study of open clusterproperties in one part of the Galaxy. This paper presents an atlas ofopen cluster photometry that serves as the database for an investigationof cluster properties such as their ages, distances, reddenings, sizes,and richnesses. This information provides insight into the spatial andtemporal formation sequence of the clusters and allows an investigationof the stellar content of the clusters to be undertaken.
| Young open clusters as probes of the star-formation process. 2: Mass and luminosity functions of young open clusters
This paper is the second in a series devoted to the use of young,optically revealed open clusters as probes of the star-formationprocess. The first paper in the series presented the dataset used forthe study, and discussed some of the results from the survey of 23 openclusters in the Cassiopeia region of the Perseus spiral arm of ourGalaxy. This paper presents an analysis of the stellar content of asubset of the clusters, including determinations of the luminosity andmass functions of 8 of the clusters to approximately 1 solar mass. Theslope of the average mass function Gamma is found to be -1.40 +/- 0.13over the mass range 1.4 less than M/solar mass less than 7.9.Significant variations from this average value are found for two of theclusters, NGC 581 and NGC 663. Possible structure in the mass functionsis discussed, as is the degree to which the initial mass function (IMF)is universal, or merely an average of many IMFs that differsubstantially on the local level.
| CCD photometric and spectroscopic observations of the young open cluster NGC 433
This paper presents the first CMD diagram and spectral types of stars inthe field of NGC 433. The cluster is rather poor, containing 12 starsdown to V = 16 in a radius of 106 arcsec around R.A. 1h 15m 07s, Dec. +60 deg 11 arcmin 11.7 arcsec (2000.0). The averaged reddening is (E(B -V)) = 0.8. The brightest stars are B5, corresponding to an age less than110 Myr. The derived cluster distance of 2.1 Kpc is compatible with aphysical association with an H I cloud detected in the clusterdirection, while the CO clouds observed in the same direction are verylikely in the foreground. Within the limits of the photometry, thecluster consists of a clump of B stars and is lacking of fainter stars.This work supports the idea that the population of disk stellar clusterscannot be sharply divided into 'true' bound open clusters and unboundstellar groups.
| A 21 centimeter line survey of a region around four outer galaxy open clusters
To investigate the role of atomic gas in the interaction of massivestars with the interstellar medium, a 21 cm survey was made of a regionsurrounding four young, outer Galaxy open clusters, NGC 281, 433, 436,and 457. A rectangular area ranging in Galactic longitude from 115 to133 deg, and in latitude from -10 to -1 deg, was observed with the NRAO140 foot telescope. Most of this region was fully sampled, resulting inspatial resolution equal to the telescope's 21 arcmin beamwidth. Thedata are presented as longitude-latitude and latitude-velocity contourmaps. A catalog of atomic gas features (e.g., clouds, filaments, andshells) is given.
| UBV photometry of open clusters in the Cassiopeia region. I - Photoelectric observations of NGC436 and 637
Abstract image available at:http://adsabs.harvard.edu/abs/1991A&AS...87..153H
| Atomic and Molecular Gas Around 4 High Z Open Clusters
Not Available
| A CO survey of regions around 34 open clusters. II - Physical properties of cataloged molecular clouds
The physical properties of the 148 molecular clouds found in a CO surveyof regions around 34 young open clusters have been examined. Expressionsare given for the cloud size spectrum and the mass spectrum. Themass-radius relation implies that clouds of all size larger than a fewpc have about the same mean volume density. Power laws with slopes of0.6 and 3 describe, respectively, the relations of CO linewidth andcloud mass to cloud size. The clouds are distinctly nonspherical andappear to be randomly oriented with respect to the Galactic plane. Theobservations can be explained by a model for molecular clouds in whichclouds are ensembles of dense clumps of gas. Based on such a model, itis shown that molecular clouds are perturbed on a time scale shortcompared to the time required for them to reestablish virialequilibrium.
| A Star-Hop in Cassiopeia
Not Available
| A CO survey of regions around 34 open clusters
Results are presented from a systematic search for CO emission fromregions around 34 young open clusters in the outer Galaxy. The clustershave well-determined distances ranging from about 1 to 5 kpc and agesnot greater than about 100 Myr. It was found that some moderately youngclusters have no associated CO emission. All the surveyed clustersyounger than about 5 Myr have associated with them at least onemolecular cloud more massive than 10,000 solar mass, while the molecularclouds associated with clusters older than about 10 Myr are not moremassive than a few thousands solar masses. It was also found thatmolecular clouds are receding from young clusters at a rate of about 10km/sec, and that they seem to be destroyed by their interaction with thestars. Sites of ongoing star formation were identified in a number ofclouds associated with young clusters.
| Component Analysis of Open Clusters
Not Available
| 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.
| The classification of open clusters by the centroid method of cluster analysis
The distribution of open clusters in the Galaxy are considered, withspace coordinates including mass, absolute magnitude, integrated colorindex, diameter, metallicity, and age. It is shown that the majority ofclusters belong to several classes which have parameter values in asufficiently narrow range. The classes form a linear sequence by age andmonotonic sequence on a color-magnitude diagram. They are not isolated,but move into each other continuously. This suggests that the process ofcluster formation contains no significant gaps. The bifurcation of theage sequence of classes depending on the mass and diameter values isfound. This bifucation makes an evolutionary interpretation possible.
| On Statistics of Star Complexes
Not Available
| 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.
| Catalog of open clusters and associated interstellar matter.
Not Available
| 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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