|CCD BVI photometry and Coravel observations of stars in the open cluster NGC2489|
We present CCD BVI photometry for the southern open cluster NGC2489 andits surrounding field. The sample consists of 2182 stars measured in anarea of 13.6 × 13.6 arcmin2, extending down to V ~21.5. These data are supplemented with CORAVEL radial-velocityobservations for seven red giant candidates. A cluster angular radius of6.7 +/- 0.6 arcmin, equivalent to 3.5 +/- 0.3 pc, is estimated from starcounts carried out inside and outside the cluster region. The comparisonof the cluster colour-magnitude diagrams with isochrones of the Padovagroup yields E(B - V) = 0.30 +/- 0.05, E(V - I) = 0.40 +/- 0.05 and V -MV = 12.20 +/- 0.25 for log t = 8.70 (t =500+130-100 Myr) and Z = 0.019. NGC2489 is thenlocated at 1.8 +/- 0.3 kpc from the Sun and 25 pc below the Galacticplane. The analysis of the kinematical data allowed us to confirmcluster membership for six red giants, one of them being a spectroscopicbinary. A mean radial velocity of 38.13 +/- 0.33 km s-1 wasderived for the cluster red giants. The properties of a sample of openclusters aligned along the line of sight of NGC2489 are examined.
|The population in the background of open clusters: tracer of the Norma-Cygnus arm|
We present colour-magnitude diagrams of open clusters, located in therange 112° < l < 252°, manifesting stellar populations inthe background of clusters. Some of the populations are found to belocated beyond the Perseus arm and may be the part of the Norma-Cygnus(outer) arm. The outer arm seems to be continued from l ~ 120° to~235°. The background populations follow the downward warp of theGalactic plane around l ~ 240°.
|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.
|Detection of a Young Stellar Population in the Background of Open Clusters in the Third Galactic Quadrant|
We report the detection of a young stellar population (<=100 Myr) inthe background of nine young open clusters belonging to a homogenoussample of 30 star clusters in the third Galactic quadrant (at217deg<=l<=260deg). Deep and accurate UBVRIphotometry allows us to measure model-independent age and distance forthe clusters and the background population with high confidence. Thispopulation is exactly the same population (the blue plume) recentlydetected in three intermediate-age open clusters and suggested to be a<=1-2 Gyr old population belonging to the Canis Major (CMa)overdensity (Bellazzini et al.; Martínez-Delgado et al.).However, we find that the young population in those three clusters andin six clusters of our sample follows the pattern of the Norma-Cygnusspiral arm as defined by CO clouds remarkably well, while in the otherthree program clusters it lies in the Perseus arm. We finally provideone example (out of 21) of a cluster that does not show any backgroundpopulation, demonstrating that this population is not ubiquitous towardCMa.
|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.
|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.
|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.
|Open clusters in the third galactic quadrant. I. Photometry|
We have performed a photometric survey of open clusters in the thirdGalactic quadrant in order to study the star formation history andspatial structure in the Canis Major-Puppis-Vela region. In this paperwe describe a catalogue of CCD U BV RI photometry of approximately 65000 stars in the fields of 30 open clusters. The data were obtained andreduced using the same telescope, the same reduction procedures, and thesame standard photometric system, which makes this catalogue the largesthomogeneous source of open cluster photometry so far. In subsequentpapers of this series, colour-colour and colour-magnitude diagrams willbe presented which, amongst other uses, will allow the determination ofan homogeneous set of cluster reddenings, distances, and ages that willconstitute the observational basis for our studies of the spatialstructure and star formation history in the third Galactic quadrant.
|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 (220.127.116.11) or viahttp://cdsweb.u-strasbg.fr/Abstract.html
|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.
|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.
|The evolution of galactic carbon stars.|
Based on a comparison of observations with new synthetic AGB evolutioncalculations we propose a revised evolutionary scenario for carbon starsin the solar neighbourhood. From observations we derive that the lowestinitial mass from which carbon stars form is about 1.5Msun_.This constraint combined with four other constraints (the observedinitial-final mass relation, the birth rate of carbon stars, theobserved abundance ratios in planetary nebulae (PNe) and the numberratios C/M and S/C of AGB stars) are used to derive the followingparameters for the synthetic AGB evolution model. Third dredge-up occursfor core masses above 0.58Msun_ and the dredge-up efficiencyis λ=0.75. We consider a Reimers mass loss law (with a scalingfactor η_AGB_) and the mass loss rate law recently proposed byBloecker & Schoenberner (1993; with a scaling factor η_BS_). Wefind η_AGB_=4 and η_BS_=0.08. Both models fit the observationsequally well. The model predicts that stars in the range1.5Msun_<~M<~1.6Msun_ become carbon stars attheir last thermal pulse (TP) on the AGB and live only a few 10^4^yr ascarbon stars. More massive stars experience additional TPs as carbonstars (up to about 25 for a 3Msun_ star) and live up to10^6^yr. For M>4Msun_ hot-bottom burning prevents theformation of carbon stars. For M<~2Msun_, M-stars skip theS-star phase when they become carbon stars. The average lifetime of thecarbon star phase is ~3x10^5^yr. The carbon stars for which C/O ratioshave been derived in the literature (with values <~1.5) arepredominantly optical carbon stars with a 60μm excess. Yet, disk PNeare known with C/O ratios up to about 4. We predict that carbon starswith C/O ratios >1.5 are to be found among the infrared carbon stars.The model predicts that the probability that a carbon star hasC/O>1.5 is about 30%, in reasonable agreement with the observed ratioof the surface density in the galactic plane of infrared carbon stars toall carbon stars. The infrared carbon stars are predicted to be (onaverage) more massive than the optical carbon stars. The fact thatcarbon stars with C/O>1.5 apparently never reach the optical carbonstar phase (with a detached shell) is probably due to differences inevolution. If indeed infrared carbon stars are on average more massive(i.e. have larger core masses) than optical carbon stars, the interpulseperiod is shorter, and the increase in luminosity during the TP issmaller (due to the larger envelope mass). Both effects will decreasethe likelihood of a detached shell to occur. We predict that two-thirdsof all detached shells around optical carbon stars are oxygen-rich.
|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.
|UBVRI observations of stars in the fields of five open clusters with nearby carbon stars|
UBVRI photoelectric observations of stars in the fields of five openclusters with carbon stars in or very near the cluster area arereported. In three cases it is found that the carbon stars, treated asmembers of the clusters, receive absolute visual and bolometricmagnitudes within the range normally accepted for this class. In thecase of the other two clusters, the carbon stars are found to benonmembers, and at greater distances.
|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.
|Catalogue of UBV Photometry and MK Spectral Types in Open Clusters (Third Edition)|
|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.
|Yellow giants in young clusters. I - Photometric observations|
To enable a study of the properties of luminous yellow stars, a list hasbeen compiled of 84 stars which appear to be in the appropriate regionin the color-magnitude diagrams of 41 young clusters. Proper motions,radial velocities, UBV photometry, and spectral types from theliterature have been used in those cases where such data are availableto assign membership probabilities. DDO and uvby photometry have alsobeen obtained of most of the stars in the list, and these data areanalyzed to remove stars from the sample which have the wrong luminosityor the wrong color excess for cluster membership. In addition, VRIphotometry is given for many of the stars in the list. Based on thesedata, 22 of the stars (26 percent) from the original sample are likelycluster members, while 48 (57 percent) are not likely to be members. Theremainder must be studied further to determine their status, but it isprobable that some of them are also in clusters.
|Integrated Photometric Parameters of Open and Globular Clusters|
|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.
|Catalogue of Masses and Ages of Stars in 68 Open Clusters|
|Analysis of the results of MK classification of 176 stars in 37 southern open clusters|
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1979A&AS...37..345F&db_key=AST
|Age determination of open clusters|
A sample of 24 open clusters is given in order to compare the mainmethods of age determination. It turns out that, as generally agreed,the most reliable method is the isochron one, because of its moreextended consideration of data. The membership of classical Cepheids insome of the clusters is then checked by comparing the ages of theclusters and the Cepheids.
|NGC 2533 and the cepheid BN Puppis.|
Abstract image available at:http://adsabs.harvard.edu/abs/1976A&A....49..307H
|Uniform survey of clusters in the southern Milky Way.|
Abstract image available at:http://adsabs.harvard.edu/abs/1975AJ.....80...11V
|High-luminosity red stars in or near galactic clusters. Paper I|
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1974PASP...86..960E&db_key=AST
|A catalogue of galactic star clusters observed in three colours|
Abstract image available at:http://adsabs.harvard.edu/abs/1971A&AS....4..241B
|An atlas of open cluster colour-magnitude diagrams|