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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 (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/467/1397
| 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.
| 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.
| On the determination of age and mass functions of stars in young open star clusters from the analysis of their luminosity functions
We construct the observed luminosity functions of the remote young openclusters NGC 2383, 2384, 4103, 4755, 7510 and Hogg 15 from CCDobservations of them. The observed LFs are corrected for field starcontamination determined with the help of a Galactic star count model.In the case of Hogg 15 and NGC 2383 we also consider the additionalcontamination from neighbouring clusters NGC 4609 and 2384,respectively. These corrections provide a realistic pattern of clusterLF in the vicinity of the main-sequence (MS) turn-on point and atfainter magnitudes reveal the so-called H-feature arising as a result ofthe transition of the pre-MS phase to the MS, which is dependent on thecluster age. The theoretical LFs are constructed representing a clusterpopulation model with continuous star formation for a short time-scaleand a power-law initial mass function (IMF), and these are fitted to theobserved LF. As a result, we are able to determine for each cluster aset of parameters describing the cluster population (the age, durationof star formation, IMF slope and percentage of field starcontamination). It is found that in spite of the non-monotonic behaviourof observed LFs, cluster IMFs can be described as power-law functionswith slopes similar to Salpeter's value. The present main-sequenceturn-on cluster ages are several times lower than those derived from thefitting of theoretical isochrones to the turn-off region of the uppermain sequences.
| 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.
| 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.
| 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].
| Photometric and kinematic studies of open star clusters. III. NGC 4103, NGC 5281, and NGC 4755
We present CCD photometry and proper motion studies of the three openstar clusters NGC 4103, NGC 5281, and NGC 4755 (kappa Cru). By fittingisochrones to the colour magnitude diagrams, we found that all threeobjects are young open star clusters with ages of at most t=45 Myr. Theyare located at distances from approx. 1600 pc to 2200 pc, derived fromdistance moduli (m-M)_0 ranging from 11 mag to 12 mag. We combinedmembership determinations based on proper motions and statistical fieldstar subtraction to derive the initial mass function (IMF) of theclusters. The shape of the IMFs could be represented by power laws withexponents of Gamma =-1.46 +/- 0.22 for NGC 4103, Gamma =-1.60 +/- 0.50for NGC 5281, and Gamma =-1.68 +/- 0.14 for NGC 4755, when - as areference - Salpeter's (\cite{salpeter}) value would be Gamma =-1.35.These results agree well with other IMF studies of open star clusters.Partly based on observations from ESO, La Silla.
| 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
| Upper main sequence and blue stragglers in galactic open clusters.
Not Available
| Multicolour deep CCD photometric study of the moderately young southern open star clusters NGC 3228, NGC 4103, NGC 5662 and NGC 6087
CCD observations in the U, B, V, R and I passbands have been used togenerate colour-colour and deep colour-magnitude diagrams for the youngopen star clusters NGC 3228, NGC 4103, NGC 5662 and NGC 6087. The sampleconsists of about 2000 stars reaching down to V = 20 mag. Theinterstellar extinction across the face of the imaged cluster regionsseems to be uniform with average values of E(B-V) = 0.31, 0.34 and 0.22mag for NGC 4103, NGC 5662 and NGC 6087 respectively. The distances tothe clusters NGC 3228, NGC 4103, NGC 5662 and NGC 6087 have beenestimated as 0.5 +/- 0.05, 2.0 +/- 0.3, 0.8 +/- 0.1 and 1.0 +/- 0.1 kpcrespectively, while the corresponding ages estimated from thetheoretical stellar evolutionary isochrones fitted to the bright propermotion cluster members are ~ 100, 30, 80 and 65 Myr respectively.Present data are consistent with the membership of the Cepheid variableV Cen to NGC 5662 and of S Norm to NGC 6087. Heavy contamination byforeground and background field stars has unfortunately made itimpossible to reach definite conclusions about the faint luminosityfunction, and the data do not reach faint enough limits to investigatepre-main sequence stars. Tables 6 to 9 only available in electronic format CDS.
| Parameters of open star clusters from uvby-beta photometry.
Not Available
| Another "normal" cluster : no age spread or low-mass star deficit in NGC 4103.
Not Available
| Determination of absolute proper motions for stars in 21 open clusters.
Not Available
| A deep UBVRI CCD photometric study of the moderately young southern open star cluster NGC 4755 = κ Crucis.
CCD observations in U, B, V, R and I passbands have been used togenerate (U-B), (B-V) colour-colour and deep V, (B-V); V, (U-B) and V,(V-I) colour-magnitude diagrams for the young open cluster NGC 4755. Thesample consists of 813 stars reaching down to V~20mag. There appears tobe non-uniform extinction over the face of the cluster with a mean valueof E(B-V)=0.41mag and a range of about 0.05mag. The true distancemodulus to the cluster has been estimated as 11.6+/-0.2mag. An age of~10Myr has been assigned to the post-main sequence (MS) cluster members.Ages of the post-MS and pre-MS stars indicate that massive(M>10Msun_) and low mass (M<2Msun_) stars inthe cluster are formed nearly at the same time from a molecular cloudwhich might have existed for a minimum period of about 6-7Myr.
| 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.
| 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.
| The Gould plates
Most of the 1200 photographs of southern galactic star clusters anddouble stars taken by Benjamin A. Gould at Cordoba, Argentina, in1872-1882 are in the Harvard College Observatory plate collection. Arecent evaluation of these plates shows many to be in usable condition.Details of the characteristics of Gould's plates of galactic clusters,including limiting magnitudes, are presented.
| Internal kinematics of open star clusters
Proper motion measurements are employed to investigate the internalkinematics of eight open star clusters. In most of the clustersconsidered, no dependence of the intrinsic dispersion in proper motionon stellar mass and radial distance from the cluster center is noted.Velocity isotropy is found in all of the clusters except NGC 2516.
| Integrated parameters of open clusters
Integrated magnitudes and colors of population I synthetic clusters havebeen derived using theoretical evolutionary tracks and an age-dependedntinitial mass function. A comparison of the theoretically obtainedintegrated parameters with the observational data of open clusters inthe Milky Way and clusters in the LMC has also been made. It is foundthat the observed dependences show a better agreement with thetheoretical dependences obtained in the present work than thetheoretical dependences obtained by earlier authors. It is alsoconcluded that the clusters in the LMC in general show a mean reddeningof E(B-V) = 0.12 mag.
| The velocity field of the outer Galaxy in the southern hemisphere. III - Determination of distances to O, B, and A type stars in the Walraven photometric system
The Walraven photometric system has been used to derive distances tostars of spectral types earlier than A7. The details of the observingprocedure are given, and the way the data were analyzed is described.The accuracy of the data is discussed, and the results are compared withthose of Gathier et al. (1986). The observational results for stars ineight well-studied star cluster are presented, compared with theliterature, and discussed.
| 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 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 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.
| Mass-losing red giants in open clusters
Mass-losing stars in open clusters with main-sequence turn-offs atintermediate mass have been searched for by using the IRAS data base.The absence of many strong 60 micron sources in open clusters impliesthat intermediate-mass stars lose much of their mass during an intensewind phase of rather short duration. For stars of about seven solarmasses, this phase, if it exists at all, lasts for not much more than100,000 yr. For stars of about four solar masses, the intense wind phaseappears to last considerably less than 10 million yr; it may well lastfor less than a million yr.
| The velocity field of the outer Galaxy in the Southern Hemisphere. II - CO observations of galactic nebulae
CO observations of 308 objects (77 percent) from a catalogue (Brand etal., 1985) of galactic emission and reflection nebulae are presented; COwas detected in the direction of 234 nebulae (76 percent). For 194 ofthese objects (63 percent) the emission could actually be associatedwith the nebula. Fifteen objects (5 percent) have associated CO emissionwith velocity in excess of 50 km/s (VLSR). These objects areof crucial importance as they are potentially very distant, and nearlyall of them have been newly identified. In the course of this surveyseveral sources with interesting line profiles were found. Eighteen ofthem exhibit wings and/or plateaus and are potential CO outflow sources.
| Catalogue of UBV Photometry and MK Spectral Types in Open Clusters (Third Edition)
Not Available
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