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|Pre-main sequence stars in open clusters. I. The DAY-I catalogue|
Context: We present the basic ideas and first results from the projectwe are carrying out at present, the search for and characterisation ofpre-main sequence (PMS) stars among the members of Galactic youngclusters. The observations of 10 southern clusters, nine of them locatedin the Carina-Sagittarius spiral arm of the Milky Way are presented. Aims: We aim at listing candidate PMS member stars in young clusters.The catalogued stars will serve as a basis for future spectroscopicstudies of individual objects to determine the properties of stellarformation in the last phases before the main sequence stage. Propertiessuch as the presence of residual envelopes or disks, age spread amongPMS members, and the possible presence of several episodes of starformation in the clusters, are to be addressed. Methods: Multicolourphotometry in the UBVR_CIC system has been obtained for 10southern young clusters in the fourth Galactic quadrant, located betweenGalactic longitudes l = 238° and l = 310°. For six clusters inthe sample, the observations presented here provide the first publishedstudy based on CCD photometry. A quantitative comparison is performedwith post-MS isochrones, and PMS isochrones from three differentevolutionary models are used in the photometric membership analysis forpossible PMS stars. Results: The observations produce photometricindices in the Johnson-Cousins photometric systems for a total of 26 962stars. The matching of our pixel coordinates with corresponding fieldsin the 2MASS data base provides astrometric calibration for allcataloged stars and JHK 2MASS photometric indices for 60% of them.Post-MS cluster ages range from 4 to 60 Myr, whereas the photometricmembership analysis assigns PMS membership to a total of 842 stars,covering an age range between 1 and 10 Myr. This information on the PMScandidate members has been collected into a catalogue, named DAY-I,which contains 16 entries for 842 stars in the field of 10 southernclusters.Catalog is only available in electronic form at the CDS via anonymousftp to cdsarc.u-strasbg.fr (188.8.131.52) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/467/1397
|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°.
|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.
|Spiral structure of the third galactic quadrant and the solution to the Canis Major debate|
With the discovery of the Sagittarius dwarf spheroidal, a galaxy caughtin the process of merging with the Milky Way, the hunt for other suchaccretion events has become a very active field of astrophysicalresearch. The identification of a stellar ring-like structure inMonoceros, spanning more than 100°, and the detection of anoverdensity of stars in the direction of the constellation of CanisMajor (CMa), apparently associated to the ring, has led to thewidespread belief that a second galaxy being cannibalized by the MilkyWay had been found. In this scenario, the overdensity would be theremaining core of the disrupted galaxy and the ring would be the tidaldebris left behind. However, unlike the Sagittarius dwarf, which is wellbelow the Galactic plane and whose orbit, and thus tidal tail, is nearlyperpendicular to the plane of the Milky Way, the putative CMa galaxy andring are nearly co-planar with the Galactic disc. This severelycomplicates the interpretation of observations. In this Letter, we showthat our new description of the Milky Way leads to a completelydifferent picture. We argue that the Norma-Cygnus spiral arm defines adistant stellar ring crossing Monoceros and the overdensity is simply aprojection effect of looking along the nearby local arm. Our perspectivesheds new light on a very poorly known region, the third Galacticquadrant, where CMa is located.
|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.
|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.
|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.
|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.
|Discovery of three optical open clusters in the Galaxy|
We report the discovery of three optical open clusters in the Milky Way.Two clusters are in Scutum (Cluster 1 at ℓ=18.44° andb=-0.42o, and Cluster 2 at ℓ=19.60° andb=-1.02o), thus projected not far from the Galactic centerdirection, and the other is in Canis Major (Cluster 3 atℓ=235.61° and b=-4.10o), near theanti-center direction. Cluster 3 is less populous than Clusters 1 and 2,but presents evidence of being a physical system. The objects were foundoptically by inspecting maps obtained from the Guide Star Catalogue andimages from the Digitized Sky Survey. No previous identification of acluster has been reported in any of these areas so far. The analysis wascarried out with 2MASS photometry in J and H. For Cluster 1 we derive anage of t=25 ± 5 Myr, a reddening E(B-V)=2.18 ± 0.03 and adistance from the Sun dȯ=1.64 ± 0.19 kpc; forCluster 2, t=500 ± 100 Myr, E(B-V)=0.91 ± 0.03 anddȯ=2.19 ± 0.21 kpc; finally for Cluster 3,t=32-100 Myr, E(B-V)=0.94 ± 0.03 and dȯ=3.93± 0.35 kpc. Luminosity and mass functions are derived forClusters 1 and 2 which, in turn, allow us to estimate their observedmasses as 147 Mȯ and 89 Mȯ,respectively. Estimated total masses, by extrapolating the massfunctions to 0.08 Mȯ, amount to 382 Mȯand 614 Mȯ for the two clusters. Cluster 3 has anobserved mass of ˜55 Mȯ. The present resultsindicate that further searches in the optical might still reveal newopen clusters, especially in the infrared bands.
|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.
|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.
|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.|
|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.
|New list of OB associations of our galaxy.|
|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%.
|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.
|More radial-velocity measurements in young open clusters|
Further high resolution radial-velocity measurements are reported in 23young open clusters using the Kitt Peak CCD coude spectrograph on the0.9-m feed telescope. The radial velocities for the cluster stars arederived with the technique of cross correlation. The internal precisionof the velocity measurements is typically 2 km/s for early type stars.From these new data and previously published velocities, the observedstars in two clusters, NGC 663 and NGC 2287, were found to show arelatively small dispersion in the measured mean velocities. Furtherobservations of stars in young clusters will be useful in helping toestablish an early-type-star-velocity standard system.
|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.
|Some characteristics of complexes of open star clusters|
Mean coordinates and velocities, phase sizes, mean elements of galacticorbits, mean ages, and metal abundances are given for 11 complexes ofopen clusters, and correlations between these characteristics arediscussed. The possible existence of a supercomplex encompassing 9 or 10complexes, and probably a number of individual clusters, is discussed.This rotates at an angular velocity of 10 to 13 km/s kpc.
|Component Analysis of Open Clusters|
|The Guide Star Photometric Catalog.|
This paper presents data and finding charts for the Guide StarPhotometric Catalog (GSPC), which is an all-sky set of 1477pohotoelectrically determined BV sequences covering the magnitude rangefrom 9 to 15. The GSPC was created to provide photometric calibratorsfor the Guide Star Catalog, which is a catalog of approximately 2 x 10to the 7th objects needed to support the pointing of the Hubble SpaceTelescope. For declinations greater than +3 deg, the sequences generallylie near the centers of the original (Palomar Observatory-NationalGeographic Society) Sky Atlas, while for smaller declinations they lienear the centers for the ESO/SERC Southern Sky Atlas. The sequencesnominally contain (at least) six stars, each with a photometricprecision of 0.05 mag. In practice, a small number of sequences containsfewer stars, and the precisions achieved for the faintest stars are morenearly 0.1 mag.
|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.
|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.
|Kinematics of young open clusters and the rotation curve of our Galaxy|
Published observational data on a sample of 105 kinematically andspatially distinct open clusters of early spectral type (up to B3) arecompiled in tables, graphs, and diagrams and characterizedstatistically. Findings reported include (1) solar motion expanding atLSR velocity 3 km/s or less (with no noncircular motion in the directionof rotation), (2) Oort constant A = 17.0 + or - 1.5 km/s kpc andsecond-order rotation term alpha = -2.0 + or - 0.6 km/s sq kpc at R-R0between -3 and 5 kpc, (3) maximum rotation-curve deviation + or - 10km/s at R-R0 about - or + 2 kpc, and (4) nondecreasing rotationalvelocities beyond about R-R0 = 3 kpc. The rotational velocities of H IIregions and molecular clouds in the Perseus arm are found to besignificantly lower than those of the open clusters.
|Catalogue of UBV Photometry and MK Spectral Types in Open Clusters (Third Edition)|
|Membership of stars in faint galactic open clusters|
Low-dispersion spectra of the order of 1000 A/mm have been obtained forstars in several faint galactic clusters with a transmission gratingplaced in front of the photographic plate at the Cassegrain focus of theKavalur 102-cm telescope. The intensity distribution in the shorterwavelengths has been taken as the principal criterion for the spectralclassification of the individual stars in the area covered by thephotographic plate. The uncertainty in this procedure has been found tobe about two spectral subclasses. A combination of these spectralclasses with the visual magnitudes derived from the image diameters onthe Palomar Observatory Sky Survey charts provide the HR diagrams foreach cluster area. These diagrams are adequate to establish the clustermembership of any star to a first approximation. This technique has beentested on six galactic open clusters. Good agreement both in terms ofthe ages of the clusters and individual stellar membership is found.
|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.
|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
|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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