CCD BV survey of 42 open clusters
Aims.We present results of a photometric survey whose aim was to derivestructural and astrophysical parameters for 42 open clusters. While oursample is definitively not representative of the total open clustersample in the Galaxy, it does cover a wide range of cluster parametersand is uniform enough to allow for simple statistical considerations. Methods: BV wide-field CCD photometry was obtained for open clusters forwhich photometric, structural, and dynamical evolution parameters weredetermined. The limiting and core radii were determined by analyzingradial density profiles. The ages, reddenings, and distances wereobtained from the solar metallicity isochrone fitting. The mass functionwas used to study the dynamical state of the systems, mass segregationeffect and to estimate the total mass and number of cluster members. Results: This study reports on the first determination of basicparameters for 11 out of 42 observed open clusters. The angular sizesfor the majority of the observed clusters appear to be several timeslarger than the catalogue data indicate. The core and limiting clusterradii are correlated and the latter parameter is 3.2 times larger onaverage. The limiting radius increases with the cluster's mass, and boththe limiting and core radii decrease in the course of dynamicalevolution. For dynamically not advanced clusters, the mass functionslope is similar to the universal IMF slope. For more evolved systems,the effect of evaporation of low-mass members is clearly visible. Theinitial mass segregation is present in all the observed young clusters,whereas the dynamical mass segregation appears in clusters older thanabout log({age}) = 8. Low-mass stars are deficient in the cores ofclusters older than log({age}) = 8.5 and not younger than one relaxationtime.Tables 1-5 are only available in electronic form at http://www.aanda.org
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NGC 7419: a young open cluster with a number of very young intermediate mass pre-MS stars
We present a photometric and spectroscopic study of the young opencluster NGC 7419, which is known to host a large number of classical Bestars for reasons not well understood. Based on CCD photometricobservations of 327 stars in UBV passbands, we estimated the clusterparameters as, reddening [E(B - V)] = 1.65 +/- 0.15 mag and distance =2900 +/- 400 pc. The turn-off age of the cluster was estimated as 25 +/-5 Myr using isochrone fits. UBV data of the stars were combined with theJHK data from Two-Micron All-Sky Survey (2MASS) and were used to createthe near-infrared (NIR) (J - H) versus (H - K) colour-colour diagram. Alarge fraction of stars (42 per cent) was found to have NIR excess andtheir location in the diagram was used to identify them as intermediatemass pre-main-sequence (MS) stars. The isochrone fits to pre-MS stars inthe optical colour-magnitude diagram showed that the turn-on age of thecluster is 0.3-3 Myr. This indicates that there has been a recentepisode of star formation in the vicinity of the cluster.Slitless spectra were used to identify 27 stars which showed Hα inemission in the field of the cluster, of which six are newidentifications. All these stars were found to show NIR excess and arelocated closer to the region populated by Herbig Ae/Be stars in the (J -H) versus (H - K) diagram. Slit spectra of 25 stars were obtained in theregion 3700-9000 Å. The spectral features were found to be verysimilar to those of Herbig Be stars. These stars were found to be morereddened than the main-sequence stars by 0.4 mag, on an average. Thus,the emission-line stars found in this cluster are more similar to theHerbig Be-type stars where the circumstellar material is the remnant ofthe accretion disc. We conclude that the second episode of starformation has led to the formation of a large number of Herbig Be starsas well as intermediate mass pre-MS stars in the field of NGC 7419, thusexplaining the presence of emission-line stars in this cluster. Thiscould be one of the young open clusters with the largest number ofHerbig Be stars.
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Photometric survey of marginally investigated open clusters. I. Basel 11b, King 14, Czernik 43
Aims.To progress in galactic studies based on open clusters, e.g.cluster formation rate or kinematical properties, one needs to improvethe number of open clusters observed. However, only half of the 1700known galactic open clusters have been properly observed so far, makingany statistical investigation insignificant, especially at largerdistances from the Sun. Methods: .We study marginallyinvestigated or neglected open clusters with Bessell CCD BVR photometry,whose data were used to fit isochrones to the individual color-magnitudediagrams. Results: .We examined the galactic clusters Basel 11b,King 14 and Czernik 43, the last being observed for the first time tothis extent. As well as a careful comparison to available photometry,their parameters such as age, interstellar reddening, distance andapparent diameter were determined. The obtained cluster properties wereverified by near infrared 2MASS data. The three investigatedintermediate age clusters are all located in the galactic disk withdistances between 1.8 and 3.0 kpc from the Sun.
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NGC 146: a young open cluster with different ages for the low and high mass stars.
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NGC 146: a young open cluster with a Herbig Be star and intermediate mass pre-main sequence stars
We present UBV CCD photometry and low-resolution spectra of stars in thefield of the young open cluster NGC 146. UBV photometry of 434 starswere used to estimate the E(B-V) reddening of 0.55 ± 0.04 mag andBV photometry of 976 stars were used to estimate a distance modulus of(m-M)0 = 12.7 ± 0.2 mag, corresponding to a distanceof 3470+335-305 pc. We estimated 10-16 Myr as theturn-off age for the upper main sequence of the cluster using isochronesand synthetic colour magnitude diagrams. We identified two B type starswith Hα in emission and located on the MS using slit-less spectra.A higher resolution spectrum of the brighter Be star indicated thepresence of a number of emission lines, with some lines showing thesignature of gas infall. This star was found to be located in the regionof Herbig Ae/Be stars in the (J-H) vs. (H-K) colour-colour diagram.Thus, we identify this star as a Herbig Be star. On the other hand, 54stars were found to show near infrared excess, of which 17 were found tobe located in the region of Herbig Ae/Be stars and 18 stars were foundto be located in the region of Be stars in the NIR colour-colourdiagram. Thus NGC 146 is a young cluster with a large number ofintermediate mass pre-main sequence stars. The turn-on age of thecluster is found to be ~3 Myr. Though NGC 146 shows an older turn off,the bulk of stars in this cluster seems to belong to the youngerpopulation of 3 Myr.
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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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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.
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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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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.
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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.
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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].
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Absolute proper motions of 181 young open clusters.
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Probable binary open star clusters in the Galaxy.
The existence of double/binary clusters in the Magellanic Clouds isfairly well established, whereas only one such pair, h + χ Persei,is known in the Galaxy. From the catalogues of open clusters of theGalaxy, we have identified 18 probable pairs of clusters (with knowndistances), with spatial separations less than 20pc. The tidaldisruption timescales for these pairs, due to Galactic differentialrotation are calculated, using cluster data where available or byassuming typical values. In some cases, these timescales are larger thanthe average open cluster lifetime, =~10^8^yr. About 8% of open clustersappear to be members of binary systems, and hence binary cluster systemsmay not be very uncommon in the Galaxy.
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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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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.
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Numerical taxonomy for open clusters.
Abstract image available at:http://adsabs.harvard.edu/abs/1990RMxAA..21..305T
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An optical spiral arm beyond the Perseus arm
In the second galactic quadrant, optical spiral arm tracers have beencollected in a systematic literature search. A uniform reduction of thedata led to the detection of a distinct structure (probably a spiralarm) beyond the Perseus arm that is separated by a statisticallysignificant gap from the latter.
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Component Analysis of Open Clusters
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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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On Statistics of Star Complexes
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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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Catalog of open clusters and associated interstellar matter.
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Star-forming loops in the IRAS sky images
Loops containing diffuse and discrete emission are a feature of the IRASsky images. Some of these loops are limb-brightened shells resultingfrom supernovae or stellar winds acting on the interstellar medium.Secondary star formation appears to have occurred at the surface ofthese shells. A significant proportion of the early-type stars in thesolar neighborhood appear to have formed in stellar loops.
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Neutral hydrogen towards 3C 10, the remnant of Tycho's supernova
Aperture synthesis observations of neutral hydrogen towards the remnantof Tycho's supernova (AD 1572), 3C 10, have been made with the CambridgeHalf-Mile Telescope. Details of the absorption features indicate thatthe distance of 3C 10 is in the range of 1.7-3.7 kpc. The neutralhydrogen in a cloud in the local arm has a spin temperature of about 80K and an optical depth of order unity. Numerous arc and filamentarystructures are seen in emission; some have been analyzed in terms ofexpanding shells. These are found to have H I masses between 500 solarmasses and 280,000 solar masses, and H I kinetic energies between 3.5 x10 to the 40th J and 6 x 10 to the 43rd J. Stellar winds are proposed asenergy sources for two of the arcs because three open clusters are nearthe center of curvature of one, and a bright star near the center of theother. An open cluster, three 9th mag stars and two CO clouds are seento coincide with various minima in the H I emission. Two other CO cloudscoincide with bright H I emission features, as does the small H IIregion S175.
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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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Application of the Density-Wave Theory of Spiral Structure: Shock Formation Along the Perseus Arm
Abstract image available at:http://adsabs.harvard.edu/abs/1972ApJ...173..259R
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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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The ages of open clusters
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Three colour photometry and spectral classification of stars in the region of NGC133, NGC146, and K-14
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Die räumliche Verteilung von 156 galaktischen Sternhaufen in Abhängigkeit von ihrem Alter. Mit 7 Textabbildungen
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