Tartalom
Képek
Kép feltöltése
DSS Images Other Images
Kapcsolódó cikkek
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.
| CCD photometry of the open clusters NGC 2627, NGC 5617, Pismis 7, and Ruprecht 75
We present broad-band, optical CCD photometry of the galactic openclusters NGC 2627, NGC 5617, Pismis 7, and Ruprecht 75. By means of thecomparison between the observed cluster sequences and the theoreticalisochrones of Girardi et al. (2000, A&AS 141, 371), we derive thefollowing parameters. For NGC 2627,E(B-V)=0.04-0.02+0.10, log(age)=9.25+0.10-0.05, and (m-M)_0 =11.33±0.31; for NGC 5617,E(B-V)=0.54-0.08+0.09 , log (age)=8.15-0.15+0.25, and (m-M)_0 =11.53-0.43+0.36; for Pismis 7, E(B-V)=0.69-0.16+0.18, log (age)= 8.70±0.10, and(m-M)_0 =13.46±0.56; and for Ruprecht 75, E(B-V)=0.24-0.13+0.18, log (age)= 9.15± 0.05, and(m-M)_0 =13.16-0.57+0.60. The isochrones have beenrenormalized to the solar values (B-V)_ȯ=0.65 and M_V=4.84, alongthe lines established in Ahumada (2003, RMxAA 39, 41), and following,for instance, Twarog, Ashman & Anthony-Twarog (1997, AJ 114, 2556).Besides, a comparison is made between the isochrones by Girardi et al.(2000) and those, also renormalized, by Castellani, Degl'Innocenti &Marconi (1999, MNRAS 303, 265) in the range of ages and metallicities ofinterest. It is noted that discrepancies arise mainly for the amount ofcore overshooting incorporated into the models, which implies differentages for a given cluster.
| A multicolour CCD photometric study of the open clusters NGC 2866, Pismis 19, Westerlund 2, ESO96-SC04, NGC 5617 and NGC 6204
Accurate and deep BVI CCD photometry is presented for the core regionsof six southern compact open clusters (supplemented in one case by U andR bands), which generally have only scanty photometric data published,in some cases only photoelectric or photographic. Together with adoptionof modern reference isochrones, this has allowed us to derive improvedvalues for their distance, reddening, age and main sequence morphology.
| 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.
| 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.
| 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.
| 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].
| 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
| A Photometric and Spectroscopic Study of the Southern Open Clusters PISMIS 18, PISMIS 19, NGC 6005, and NGC 6253
CCD observations in the B, V, and I passbands have been used to generatecolor-magnitude diagrams (CMDs) for the southern open cluster candidatesPismis 18, Pismis 19, and NGC 6005, as well as for the old open clusterNGC 6253. The sample consists of about 1550 stars reaching down to V ~19 mag. From analysis of the CMDs, the physical reality of the threecluster candidates is confirmed and their reddening, distance, and ageare derived, as well as those of NGC 6253. In addition, integratedspectra for Pismis 18, Pismis 19, and NGC 6253 covering a range from3500 to 9200 Å were obtained. The reddening, age, and metallicityof these three clusters were derived from Balmer and Ca ii tripletequivalent widths by comparing the observed spectra with those oftemplate clusters. The photometric and spectroscopic results allow us toconclude that Pismis 18, Pismis 19, and NGC 6005 are intermediate-age (t~ 1 Gyr), genuine open clusters, while NGC 6253 has an age t ~ 5 Gyr.All these clusters are located approximately toward the Galactic center,between 1.5 and 2.7 kpc from the Sun. Their metallicities range overvalues that are typical of moderately metal-poor to moderatelymetal-rich open clusters.
| Absolute proper motions of 181 young open clusters.
Not Available
| 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.
| 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%.
| Reddening and age for 11 Galactic open clusters from integrated spectra
We study integrated spectra of 11 Galactic open clusters in the visibleand near-infrared. We use continuum distribution and line strengths toinfer reddening, age and, in some cases, metallicity. These parametersare derived by using different methods, mainly by employing templateintegrated spectra of Magellanic Clouds and Galactic star clusters withknown properties, as well as a grid relating the equivalent widths ofspectral absorption lines to age and metallicity spanning a wide rangeof values. The results indicate a good agreement with previous workbased mainly on color-magnitude diagrams, when available. Internalreddening is significant for very young clusters like NGC 3603 and 6611.A Wolf-Rayet star in NGC 6231 is also analyzed spectroscopically in thecluster context. Wolf-Rayet features appearing in the integrated spectraof NGC 6231 and 3603 are employed as indicators of the clusterevolutionary stage. The oldest cluster in the sample has an age of about300 Myr. The present sample considerably improves the age resolutionaround solar metallicity in the cluster spectral library for populationsynthesis.
| 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.
| Astrometric Calibration Regions with Proper Motion Membership Estimates in the Open Clusters NGC 188 and NGC 5617
Not Available
| Photometric metal abundances of high-luminosity red stars in young and intermediate-age open clusters
UBV, DDO, and Washinton photometry has been obtained for G and K starslocated in or near 22 young and intermediate-age open clusters. Nearly65 percent of the observed stars are found to have a high probability ofbeing cluster members, while the remaining 35 percent are likely to bered field stars. Five clusters (NGC 2383, NGC 3033, Ruprecht 20, NGC5168, and NGC 6249) probably do not contain any red giants. Sixteenclusters are found to be nearly solar in composition; three are slightlymetal-poor or metal-rich; one (Ruprecht 20) is moderately metal-poor(Fe/H = -0.3); and another (NGC 5617) is moderately metal-rich (Fe/H =0.3). None of the clusters with derived Washington abundances appear tobe enriched in elements of the CNO group.
| The Sagittarius-Carina Arm Structure and Parameters of Spiral Pattern
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.
| 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.
| Properties of the open cluster system
A system of weights corresponding to the precision of open cluster datais described. Using these weights, some properties of open clusters canbe studied more accurately than was possible earlier. It is clear thatthere are three types of objects: unbound clusters, bound clusters inthe thin disk, and older bound clusters. Galactic gradients ofmetallicity, longevity, and linear diameter are studied. Distributionsat right angles to the galactic plane are discussed in the light of thedifferent cluster types. The clumping of clusters in complexes isstudied. An estimate of the selection effects influencing the presentmaterial of open cluster data is made in order to evaluate the roleplayed by open clusters in the history of the galactic disk.
| 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.
| The Alpha-Centauri System
Not Available
| 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
| 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.
|
Új cikk hozzáadása
Kapcsolódó hivatkozások
- - (nincs kapcsolódó hivatkozás) -
Új link hozzáadása
Besorolás csoportokba:
|
Pozíciós és asztrometriai adatok
Katalógusok és elnevezések:
|
