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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.
| A method of open cluster membership determination
A new method for the determination of open cluster membership based on acumulative effect is proposed. In the field of a plate the relative xand y coordinate positions of each star with respect to all the otherstars are added. The procedure is carried out for two epochst1 and t2 separately, then one sum is subtractedfrom another. For a field star the differences in its relativecoordinate positions of two epochs will be accumulated. For a clusterstar, on the contrary, the changes in relative positions of clustermembers at t1 and t2 will be very small. On thehistogram of sums the cluster stars will gather to the left of thediagram, while the field stars will form a tail to the right. Theprocedure allows us to efficiently discriminate one group from another.The greater the distance between t1 and t2 and themore cluster stars present, the greater is the effect. The accumulationmethod does not require reference stars, determination of centroids andmodelling the distribution of field stars, necessary in traditionalmethods. By the proposed method 240 open clusters have been processed,including stars up to m<13. The membership probabilities have beencalculated and compared to those obtained by the most commonly usedVasilevskis-Sanders method. The similarity of the results acquired thetwo different approaches is satisfactory for the majority of clusters.
| 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.
| Revisiting the population of Galactic open clusters
We present results of a study of the galactic open cluster populationbased on the all-sky catalogue ASCC-2.5 (I/280A) compiled from Tycho-2,Hipparcos and other catalogues. The sample of optical clusters fromASCC-2.5 is complete up to about 850 pc from the Sun. The symmetry planeof the clusters' distribution is determined to be at Z_0=-22±4pc, and the scale height of open clusters is only 56±3 pc. Thetotal surface density and volume density in the symmetry plane areΣ= 114 kpc-2 and D(Z_0)=1015 kpc-3,respectively. We find the total number of open clusters in the Galacticdisk to be of order of 105 at present. Fluctuations in thespatial and velocity distributions are attributed to the existence offour open cluster complexes (OCCs) of different ages containing up to afew tens of clusters. Members in an OCC show the same kinematicbehaviour, and a narrow age spread. We find, that the youngest clustercomplex, OCC 1 (log t<7.9), with 19 deg inclination to the Galacticplane, is apparently a signature of Gould's Belt. The most abundant OCC2 complex has moderate age (log t≈8.45). The clusters of thePerseus-Auriga group, having the same age as OCC 2, but differentkinematics are seen in breaks between Perseus-Auriga clouds. The oldest(log t≈8.85) and sparsest group was identified due to a large motionin the Galactic anticentre direction. Formation rate and lifetime ofopen clusters are found to be 0.23±0.03 kpc-2Myr-1 and 322±31 Myr, respectively. This implies atotal number of cluster generations in the history of the Galaxy between30 to 40. We estimate that less than about 10% of the total Galacticstellar disk population has ever passed an open cluster membership.
| 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.
| Physical parameters of the Algol system CF Puppis from simultaneous analysis of Geneva 7-colour light curves
The semi-detached eclipsing binary system CF Puppis (P=7.65 days) has been analysed usingthe Wilson-Devinney program. Light curves have been obtained in theGeneva 7-colour photometric system, and radial velocity curves for bothcomponents have been measured with the cross-correlation technique. Thephysical and orbital parameters have been determined through aself-consistent simultaneous solution of light curves in seven coloursand of the radial velocity curves of both components. The absoluteelements of the components are, for the primary (mass gainer),M1=1.84+/-0.04 Msolar, R1=3.06+/-0.01Rsolar, Mbol1=1.74+/-0.02,Teff1=6671+/-27 K, and for the secondary (massloser), M2=0.38+/-0.01 Msolar, R2=5.39Rsolar, Mbol2=2.51+/-0.02,Teff2=4202+/-17 K. The semi-major axis A of therelative orbit is 21.28+/-0.15 Rsolar. The estimated spectraltypes of the components are about F3 IV (primary) and K2/3 III. CF Pup has one of the coolestcomponent A among the Algol systems. The equatorial rotationalvelocities are 24.8 (primary) and 37.0 km s-1. The secondaryis clearly synchronized, and the primary is nearly synchronized(vsyn=20.2 km s-1). The distance to CF Pup is evaluated to 506+/-16 pc, and thecolour excess E[B2-V1] to 0.033+/-0.017.
| 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.
| Deep-sky dedication.
Not Available
| 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
| 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
| Open clusters with Hipparcos. I. Mean astrometric parameters
New memberships, mean parallaxes and proper motions of all 9 openclusters closer than 300 pc (except the Hyades) and 9rich clusters between 300 and 500 pc have been computed using Hipparcosdata. Precisions, ranging from 0.2 to 0.5 mas for parallaxes and 0.1 to0.5 mas/yr for proper motions, are of great interest for calibratingphotometric parallaxes as well as for kinematical studies. Carefulinvestigations of possible biases have been performed and no evidence ofsignificant systematic errors on the mean cluster parallaxes has beenfound. The distances and proper motions of 32 more distant clusters,which may be used statistically, are also indicated. Based onobservations made with the ESA Hipparcos astrometry satellite
| 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.
| 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
| 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.
| 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
| Component Analysis of Open Clusters
Not Available
| 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.
| The classification of open clusters by the centroid method of cluster analysis
The distribution of open clusters in the Galaxy are considered, withspace coordinates including mass, absolute magnitude, integrated colorindex, diameter, metallicity, and age. It is shown that the majority ofclusters belong to several classes which have parameter values in asufficiently narrow range. The classes form a linear sequence by age andmonotonic sequence on a color-magnitude diagram. They are not isolated,but move into each other continuously. This suggests that the process ofcluster formation contains no significant gaps. The bifurcation of theage sequence of classes depending on the mass and diameter values isfound. This bifucation makes an evolutionary interpretation possible.
| 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.
| Catalogue of UBV Photometry and MK Spectral Types in Open Clusters (Third Edition)
Not Available
| 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.
| The present data situation for stars in open clusters. II
The present state of astrometric, spectroscopic, and photometric datafor stars in 63 open clusters nearer to the sun than 750 pc issummarized in tabular form. The limits of the available data arereported in terms of the apparent V magnitude. Information on theapparent V magnitude of the brightest main sequence star (Vbr) and onthe number of stars brighter than V equals 10 has been included. Thebluest spectral type on the main sequence has been used as an ageestimator.
| The frequency of peculiar A and metallic-line stars in open clusters.
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1976ApJ...205..807H&db_key=AST
| Uniform survey of clusters in the southern Milky Way.
Abstract image available at:http://adsabs.harvard.edu/abs/1975AJ.....80...11V
| The space distribution of M giants in the Warner and Swasey luminosity function field LF 15.
Abstract image available at:http://adsabs.harvard.edu/abs/1974A&AS...15..141T
| A catalogue of galactic star clusters observed in three colours
Abstract image available at:http://adsabs.harvard.edu/abs/1971A&AS....4..241B
| An atlas of open cluster colour-magnitude diagrams
Not Available
| The ages of open clusters
Not Available
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