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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.
| Searching for links between magnetic fields and stellar evolution. I. A survey of magnetic fields in open cluster A- and B-type stars with FORS1
Context: .About 5% of upper main sequence stars are permeated by astrong magnetic field, the origin of which is still matter of debate. Aims: . With this work we provide observational material to studyhow magnetic fields change with the evolution of stars on the mainsequence, and to constrain theory explaining the presence of magneticfields in A and B-type stars. Methods: . Using FORS1 inspectropolarimetric mode at the ESO VLT, we have carried out a survey ofmagnetic fields in early-type stars belonging to open clusters andassociations of various ages. Results: . We have measured themagnetic field of 235 early-type stars with a typical uncertainty of 100 G. In our sample, 97 stars are Ap or Bp stars. For thesetargets, the median error bar of our field measurements was 80 G.A field has been detected in about 41 of these stars, 37 of which werenot previously known as magnetic stars. For the 138 normal A and B-typestars, the median error bar was 136 G, and no field was detected in anyof them.
| 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.
| On the Galactic Disk Metallicity Distribution from Open Clusters. I. New Catalogs and Abundance Gradient
We have compiled two new open cluster catalogs. In the first one, thereare 119 objects with ages, distances, and metallicities available, whilein the second one, 144 objects have both absolute proper motion andradial velocity data, of which 45 clusters also have metallicity dataavailable. Taking advantage of the large number of objects included inour sample, we present an iron radial gradient of about -0.063+/-0.008dex kpc-1 from the first sample, which is quite consistentwith the most recent determination of the oxygen gradient from nebulaeand young stars, about -0.07 dex kpc-1. By dividing clustersinto age groups, we show that the iron gradient was steeper in the past,which is consistent with the recent result from Galactic planetarynebulae data, and also consistent with inside-out galactic diskformation scenarios. Based on the cluster sample, we also discuss themetallicity distribution, cluster kinematics, and space distribution. Adisk age-metallicity relation could be implied by those properties,although we cannot give conclusive result from the age- metallicitydiagram based on the current sample. More observations are needed formetal-poor clusters. From the second catalog, we have calculated thevelocity components in cylindrical coordinates with respect to theGalactic standard of rest for 144 open clusters. The velocitydispersions of the older clusters are larger than those of youngclusters, but they are all much smaller than that of the Galactic thickdisk stars.
| 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.
| Proper motions of open clusters within 1 kpc based on the TYCHO2 Catalogue
We present mean absolute proper motions of 112 open clusters, determinedusing the data from the Tycho2 Catalogue. For 28 clusters, this is thefirst determination of proper motion. The measurements made use of alarge number of stars (usually several tens) for each cluster. The totalnumber of stars studied in the fields of the 164 open clusters is 5016,of which 4006 were considered members. The mean proper motions of theclusters and membership probability of individual stars were obtainedfrom the proper motion data by applying the statistical method proposedby Sanders (\cite{Sanders71}). Based on observations of the ESAHipparcos satellite. Tables 1, 2 and 5 to 117 are only available inelectronic form at the CDS via anonymous ftp to cdsarc.u-strasbg.fr(130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/376/441
| 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].
| From the Top to the Bottom of the Main Sequence: A Complete Mass Function of the Young Open Cluster M35
We present very deep and accurate photometry of the open cluster M35. Wehave observed this association in the Cousins R, I filters, togetherwith the Johnson V filter. We have covered a region of 27.5×27.5square arcmin, equivalent to a fifth of the total area of the cluster.The data range from Ic=12.5 to 23.5 mag, and the colorintervals are 0.4<=(V-I)c<=3.0,0.5<=(R-I)c<=2.5. Roughly, these values span from 1.6Msolar down to the substellar limit, in the case of clustermembers. By using the location of the stars on color-magnitude andcolor-color diagrams, we have selected candidate members of thiscluster. We have merged our sample with previously published data andobtained a color-magnitude diagram for the complete stellar populationof the cluster, covering the spectral range early B-mid M. Based on thedistribution of field and cluster stars in color-magnitude andcolor-color diagrams, we estimate that two-thirds of these candidatesare likely to be true members of M35. These stars approximately doublethe number of stars identified as candidate members of this cluster(~2700). We provide the photometry and accurate positions of thesestars. The deep photometry has allowed us to study the mass segregationwithin the cluster, the luminosity function, and mass function. We showthat in the magnitude range 13<=Ic<=22 there is areduced mass segregation, in opposition to what happens to higher massstars, where the mass segregation is stronger. The luminosity functionbehaves essentially as the one characteristic of the Pleiades,presenting a peak at Ic~19 mag (MI~9). Combiningour photometry with previous data corresponding to more massive stars,we find that the mass function increases monotonically, when plotted ina log-log form, until it reaches ~0.8 Msolar (α=2.59).It remains shallower for less massive stars (α=0.81 for 0.8-0.2Msolar), whereas a decrease is observed for stars close tothe substellar regime. These different behaviors suggest that at leastthree mechanisms play a role in the formation of stellar and substellarobjects. The total mass of the cluster is ~1600 Msolar in thearea covered by this study.
| 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
| Search for Low-Instability Strip Variables in the Young Open Cluster NGC 2516
In this paper we revise and complete the photometric survey of theinstability strip of the southern open cluster NGC 2516 published byAntonello & Mantegazza. No variable stars with amplitudes largerthan 0.02 mag were found. However, by means of an accurate analysisbased on a new statistical method, two groups of small-amplitudevariables have been disentangled: one with periods of less than 0.25days (probably delta Scuti stars) and one with periods of greater than0.025 days. The position in the H-R diagram and the apparent timescalemay suggest that the stars of the second group belong to a recentlydiscovered new class of variables, named gamma Dor variables. Theycertainly deserve further study. We also present a comparison betweenthe results of the photometric survey and the available pointed ROSATobservations of this cluster.
| The spur-like radio feature in Centaurus
We present a study of the radio emission of the Centaurus region atgalactic latitudes 2(deg) <= b <= 18(deg) , using pre-existing408MHz continuum data and results of new 1.42GHz continuum and neutralhydrogen line observations. It is shown that the extensive spur-likeradio feature visible in this region has a non-thermal nature and isactually formed by several previously unidentified individual sources.Five new supernova remnant (SNR) candidates have been detected atrelatively high latitudes. Three of them, as well as two formercandidates reported by Duncan et al. (1995), were confirmed through thecomputation of their spectral indices. One of the new SNRs, G315.4+12.9,might be associated with the open cluster NGC 5460.
| Geneva photometry in the young open cluster NGC 6231.
We present photoelectric (127 stars) and CCD (168 stars) Genevaphotometry for the very young open cluster NGC 6231. We have searchedfor new cluster members out to a distance of ~13['arc], extending theSeggewiss area (~8['arc]), and we found at least 64 new probable membersin this extended field. Differential reddening is clearly measuredacross the cluster area. We determine the cluster distance (1800 pc) andage (3.8+/-0.6x10^6^yr). The probable presence of PMS stars and theconsequence of this population on the cluster formation history isanalysed. We also found that the O8.5III star S161 is a long termvariable and we present its light curve extending over more than 20years. Finally we discuss the existence of Ap stars in the cluster.
| 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
| BV(RI)_KC_ CCD photometry of the core of the young open cluster, NGC 5460.
We present CCD photometry on the BV(RI)_KC_ (Cape) photometric system ofthe core of the young open cluster, NGC 5460, to a magnitude limitV=~19, R=~19.5. We give photometry for 353 stars and identify 25 ascluster members along with a further 27 as possible members based ontheir positions in individual colour-magnitude diagrams. We estimate thereddening to the cluster and redefine its distance and age. Four starsare identified as possible variables and their nature discussed.
| 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.
| Further observations of stars in the open cluster NGC 5460
New photoelectric UBV photometry in the open cluster NGC 5460 ispresented for 155 stars brighter than 14.0 mag. In addition, sixcomparatively bright red stars in the cluster field were observed in theDDO and Washington systems. Nearly 40 percent of the observed stars arefound to be members or probable members. The analysis of the new datayields E(B-V) = 0.12 +/- 0.03 and V(0) - M(v) = 9.34 +/- 0.20 (740 +/-68 pc) for the cluster reddening and true distance modulus,respectively. An age of 1.1 x 10 exp 8 yr was derived, which places thiscluster within the NGC 2516 age group. NGC 5460 does not probablycontain any red giant.
| New dating of galactic open clusters
A new set of isochrones for solar metallicity computed from modelstaking into account mass loss and moderate overshooting and using therecent opacity tables by Rogers and Iglesias (1992) has been used todetermine the ages of 30 galactic open clusters covering an interval ofage from 4 million to 9.5 billion years. The clusters collected hereconstitute an ensemble of homogeneous and accurate data, well discussedfor distance, reddening, membership and binarity, and thus they providea basic reference for age determinations. The present set of isochronesfits the observed color-magnitude diagrams of the clusters veryaccurately, and may thus be expected to provide reliable ages. Analyticrelations between several characteristics of the isochrones and the ageare given and can be used for further age calibrations consistent withthis homogeneous scale.
| South for the Winter
Not Available
| 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.
| Liste des étoiles Ap et Am dans les amas ouverts (Edition révisée)
Not Available
| 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.
| Catalog of AP and AM stars in open clusters
The previous results of Raab (1922), Markarian (1951), and Collinder(1931) have been used to catalog Ap and Am stars that are in the fieldof open clusters. Tabular data are presented for the clusterdesignation, the HD or HDE number, the right ascension (1900), thedeclination (1900), and the magnitude. Also listed are the spectraltypes and, for certain stars, the probability of cluster membership.
| 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.
| Absolute Magnitude Calibration from H-Beta Photometry of Open Star Clusters
Not Available
| 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.
| 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
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