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Physical parameters of pre-main sequence stars in open clusters
Aims: The aims are twofold: we search and analyse pre-mainsequence (PMS) stars in Galactic young open clusters (YOCs) to determinethe ages, masses, and spatial distribution of PMS members in YOCs, andto check and compare the performances of different model isochrones. Methods: We compare UBVRI photometric observations to theoreticalisochrones in the photometric diagrams. The comparison simultaneouslyprovides membership assignments for both main sequence (MS) and PMSstars and estimates for the physical properties of the cluster candidatemembers: masses, ages, and spatial distribution inside the cluster. Results: The photometric measurement of an average (U - V) excess,supposedly indicative of accretion disks, is considered prior tomembership assignment. This photometric excess is correlated withcluster age, suggesting that disks able to show up in (U - V) excessvanish at ages around 5 Myr. We find that comparing photometry to modelsin the colour-magnitude (CM) diagram leads to better results for themasses than performing the comparison in the theoretical HR plane. Theobtained cluster mass functions show a marginal steepening with clusterage. Significant variations in the mass function slopes are found withthe models used in member selection. The clusters NGC3293 and NGC 2362 are found to have massfunctions flatter than the Salpeter slope for all models considered. Therelation between the calculated dispersion of PMS age and thecharacteristic clustering scale of the cluster shows interestingagreement with previous findings in star-forming regions in a wide rangeof scales. Finally, the ratio of characteristic clustering scales forPMS candidate members in different mass ranges can be interpreted assuggesting mass segregation, in the sense of a relatively wider spatialdistribution for the lower mass members in older clusters. Conclusions: The relations between the different cluster parameters showthat the procedure applied to assign cluster membership and to measurephysical parameters for the selected members is well founded.The photometric catalogue is available in electronic form at the CDS viaanonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or via http://cdsweb.u-strasbg.fr/cgi-viz/qcat?J/A+A/531/A141
| 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
| 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 open cluster TR 18
UBVRI photoelectric photometry was obtained in the field of the opencluster Tr 18. From the analysis of the data it is confirmed thatseveral distant OB stars were wrongly assumed as cluster members inprevious investigations. The true distance modulus of the cluster is10.95 equivalent to a distance of 1550 pc with the adopted age of (9.0 +or - 1.0) x 10 to the 7th yr. The GH Carinae Cepheid variable star isvery much probably a cluster member in view of its spatial position andthe average absolute magnitude. However, some arguments are given tosuggest that the reality of this cluster is still an open question.
| Southern open star clusters .V. UBV Hbet photometry of 20 clusters in Car.
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1975A&AS...20..125M&db_key=AST
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Observation and Astrometry data
| Constellation: | Τρόπις |
| Right ascension: | 11h11m27.08s |
| Declination: | -60°40'42.0" |
| Apparent magnitude: | 9.147 |
| Proper motion RA: | -8.7 |
| Proper motion Dec: | -0.7 |
| B-T magnitude: | 9.186 |
| V-T magnitude: | 9.151 |
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