|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.
|Gamma-ray line emission from OB associations and young open clusters. II. The Cygnus region|
Gamma-ray and microwave observations of the Cygnus region reveal anintense signal of 1.809 Me line emission, attributed to radioactivedecay of 26, that is closely correlated with 53 GHz free-freeemission, originating from the ionised interstellar medium. We modelledboth emissions using a multi-wavelength evolutionary synthesis code formassive star associations that we applied to the known massive starpopulations in Cygnus. For all OB associations and young open clustersin the field, we determined the population age, distance, and richnessas well as the uncertainties in all these quantities from publishedphotometric and spectroscopic data. We propagate the populationuncertainties in model uncertainties by means of a Bayesian method. Theyoung globular cluster Cyg OB2 turns out to be the dominant26 nucleosynthesis and ionisation source in Cygnus. Our modelreproduces the ionising luminosity of the Cygnus region very well, yetit underestimates 26 production by about a factor of 2. Weattribute this underestimation to shortcomings of currentnucleosynthesis models, and suggest the inclusion of stellar rotationas possible mechanism to enhance 26 production. We alsomodelled 60Fe nucleosynthesis in the Cygnus region, yet thesmall number of recent supernova events suggests only little60Fe production. Consequently, a detection of the 1.137 Meand 1.332 Me decay lines of 60Fe from Cygnus by the upcomingINTEGRAL observatory is not expected. Appendices A and B, and Tables 1,2, and 5 are only available in electronic form athttp://www.edpsciences.org
|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 (126.96.36.199) or viahttp://cdsweb.u-strasbg.fr/Abstract.html
|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.
|On the amplitudes of the eclipsing binaries NN Lac, NR Lac, NW Lac.|
|An optical spiral arm beyond the Perseus arm|
In the second galactic quadrant, optical spiral arm tracers have beencollected in a systematic literature search. A uniform reduction of thedata led to the detection of a distinct structure (probably a spiralarm) beyond the Perseus arm that is separated by a statisticallysignificant gap from the latter.
|Component Analysis of Open Clusters|
|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.
|Properties of the open cluster system|
A system of weights corresponding to the precision of open cluster datais described. Using these weights, some properties of open clusters canbe studied more accurately than was possible earlier. It is clear thatthere are three types of objects: unbound clusters, bound clusters inthe thin disk, and older bound clusters. Galactic gradients ofmetallicity, longevity, and linear diameter are studied. Distributionsat right angles to the galactic plane are discussed in the light of thedifferent cluster types. The clumping of clusters in complexes isstudied. An estimate of the selection effects influencing the presentmaterial of open cluster data is made in order to evaluate the roleplayed by open clusters in the history of the galactic disk.
|Catalog of open clusters and associated interstellar matter.|
|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.
|Catalogue of UBV Photometry and MK Spectral Types in Open Clusters (Third Edition)|
|Star Count Integral Characteristics for 22 Open Star Clusters|
|Investigation of the initial mass spectrum of open star clusters|
The mass spectra of 228 open star clusters were derived by comparison ofcolor-magnitude diagrams with evolutionary tracks. The application tobinary stars showed the reliability of the mass determination. Thederived mass spectra were fitted by power laws as well as exponentiallaws. It could be shown that both approximate the mass spectra of openstar clusters on the same average significance level. The presentinvestigation revealed a correlation of the slope of the mass spectrawith the cluster age, whereas a detected correlation of the slope withgalactocentric distance is slight. The results suggest that the slope ofthe mass spectrum increases with increasing cluster and galactocentricdistance. These findings are discussed with respect to their reasons andprevious results concerning open clusters and field stars.
|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.
|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.
|First Supplement to the list of transit tables for star numberings in open clusters.|
|Application of the Density-Wave Theory of Spiral Structure: Shock Formation Along the Perseus Arm|
Abstract image available at:http://adsabs.harvard.edu/abs/1972ApJ...173..259R
|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|
|Distance, age and physical members of the galactic cluster NGC 7261|
|The ages of open clusters|
|Distance Moduli of Open Clusters.|
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1965ApJS...12..215H&db_key=AST
|Die räumliche Verteilung von 156 galaktischen Sternhaufen in Abhängigkeit von ihrem Alter. Mit 7 Textabbildungen|
|Photometry of stars in galactic cluster fields.|
|Galactic clusters as indicators of stellar evolution and galactic structure|