|CCD photometric search for peculiar stars in open clusters. VIII. King 21, NGC 3293, NGC 5999, NGC 6802, NGC 6830, Ruprecht 44, Ruprecht 115, and Ruprecht 120|
Context: We continue our survey of magnetic chemically peculiar (CP2)stars in galactic open clusters to shed more light on their origin andevolution. Aims: To study the group of CP2 stars, it is essential tofind these objects in different galactic environments and at a widerange of evolutionary stages. The knowledge of open cluster ages andmetallicities can help for finding a correlation between theseparameters and the (non-)presence of peculiarities, which has to betaken into account in stellar evolution models. Methods: Theintermediate band Δ a photometric system samples the depth of the5200 Å flux depression by comparing the flux at the centre withthe adjacent regions with bandwidths of 110 Å to 230 Å. Itis capable of detecting magnetic CP2 and CP4 stars with high efficiency,but also the groups of (metal-weak) λ Bootis and classicalBe/shell stars can be successfully investigated. In addition, it allowsthe age, reddening, and distance modulus to be determined withappropriate accuracy by fitting isochrones. Results: From the 1677observed members of the eight open clusters, one Ae and twenty-five CP2stars were identified. Furthermore nineteen deviating stars aredesignated as questionable for several reasons. The estimated age,reddening, and distance for the programme clusters were compared withpublished values of the literature and discussed in this context. Conclusions: .The current paper shows that CP2 stars are continuouslypresent in very young (7 Myr) to intermediate age (500 Myr) openclusters at distances greater than 2 kpc from the Sun.Based on observations at CASLEO, CTIO (Proposal 2003A-0057), and OSN.The Observatorio de Sierra Nevada is operated by the Consejo Superior deInvestigaciones Científicas through the Instituto deAstrofísica de Andalucía (Granada, Spain). Photometricdata are only avaialable in electronic form at the CDS via anonymous ftpto cdsarc.u-strasbg.fr (184.108.40.206) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/462/591 Full Fig. [seefull textsee full textsee full textsee full textsee full text], Tables[see full textsee full textsee full textsee full textsee full text] and[see full textsee full textsee full textsee full textsee full text] areonly available in electronic form at http://www.aanda.org
|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.
|Close binary systems in regions of OB-associations. II. AT Vulpeculae in Vul OB1 and EV Vulpeculae in Vul OB4.|
|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.
|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 (220.127.116.11) or viahttp://cdsweb.u-strasbg.fr/Abstract.html
|Absolute proper motions of 181 young open clusters.|
|Estimates of geometric and dynamic parameters of star-gas complexes in the Galaxy|
Parameters of geometric models of 11 gas-star complexes (GSCs) wereobtained. We used information about GSC projections onto the celestialsphere and the Galactic plane and about GSC extension along the line ofsight. GSCs were represented as triaxial ellipsoids. To estimate thesemiminor axis of the GSC ellipsoidal model and GSC slope angle to theGalactic plane, we used data on spatial location of open stellarclusters (OSCs) entering GSCs. GSC slopes to the Galactic plane varybetween 2.5 and 20.5 deg. Their semiminor axes are between 11 and 164pc. GSC total masses are estimated from GSC tidal effect on OSCs thatare members of the corresponding GSCs. The effect manifests itself insmaller sizes of young OSCs as compared to their tidal sizes in theforce field of the Galaxy. We used studies of stability of an OSC movingin the joint force field of the Galaxy and spheroidal stationary GSC, aswell as studies of evolution of a virialized cluster located at thecenter of a nonstationary ellipsoidal GSC. Estimated total masses fordifferent GSCs lie between 0.65 x 10 exp 5 solar masses and 11.5 x 10exp 7 solar masses.
|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.
|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%.
|Gamma rays from globular clusters|
Globular clusters are known to contain a relatively large number ofpulsars whose individual and collective emission in the X-ray andgamma-ray energy bands may be detectable by the instruments on board theCompton Gamma-Ray Observatory (CGRO), ROSAT, and possibly SIGMA. Wediscuss the several types of high-energy emission expected from isolatedand interacting binary pulsars in globular clusters. Individual orcollective high-energy emission from isolated pulsars is expected to betoo low to be detected with current instruments. However, a class ofhigh-luminosity hidden millisecond pulsars enshrouded in the evaporatingmaterial from irradiated companion stars can produce unpulsed shockemission detectable by the high-sensitivity instruments of ROSAT andCGRO. Establishing upper limits of high-energy emission from globularclusters will be valuable in constraining models for the formation ofcluster millisecond pulsars.
|Physical parameters of the cluster NGC 6823|
A new selection of NGC 6823 cluster members is performed by a methodbased on the kinematic and photometric data, as well as on the spectraldata available for the majority of stars. The number of cluster membersgiven in previous studies is shown to be overestimated by a factor oftwo, because stars of the star formation region 1 Vul are taken asmembers. The cluster luminosity function was determined; the slope ofthe mass function is x = -1.59 +/- 0.36 in the stellar mass range of12-50 solar masses. The total cluster mass is 2800 solar masses.
|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.
|Groups of open clusters with common motion in the Galaxy|
A method of identifying star groups with common motion in space isapplied to a sample of 66 open clusters with known space velocitycomponents. Eight groups are obtained; out of these, five are probablyreal. It is shown that the motions of the cepheids and the open clustersare analogous in the vicinity of the sun.
|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 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.
|Catalog of open clusters and associated interstellar matter.|
|A catalog of some observational data and elements of the galactic orbits of open star clusters|
|A Possible Rotation of the System of Open Cluster Complexes|
|BU-Arecibo HI Galactic Survey Progress Report|
|Catalogue of UBV Photometry and MK Spectral Types in Open Clusters (Third Edition)|
|Search for B-Type Variable Stars in Open Clusters|
|The absolute masses of 72 galactic clusters and 12 OB associations|
The Reddish (1978) relative masses for 72 open clusters and 12 OBassociations are presently converted to absolute masses, within an errormargin of about 25 percent, using three calibration clusters of knownmass whose average mass is 300 solar masses. The Reddish techniqueassumes the initial stellar mass distribution function to be valid forall aggregates, together with a universal relationship between stellarmass and stellar luminosity.
|Integrated Photometric Parameters of Open and Globular Clusters|