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Polarimetry of an intermediate-age open cluster: NGC 5617
Aims: We present polarimetric observations in the UBVRI bands of72 stars located in the direction of the medium age open cluster NGC5617. Our intention is to use polarimetry as a tool in membershipidentification, by building on previous investigations intended mainlyto determine the cluster's general characteristics rather than providemembership suitable for studies such as stellar content and metallicity,as well as study the characteristics of the dust lying between the Sunand the cluster. Methods: The obsevations were carried out usingthe five-channel photopolarimeter of the Torino Astronomical Observatoryattached to the 2.15 m telescope at the Complejo Astronómico ElLeoncito (CASLEO; Argentina). Results: We are able to add 32stars to the list of members of NGC 5617, and review the situation forothers listed in the literature. In particular, we find that five bluestraggler stars in the region of the cluster are located behind the samedust as the member stars are and we confirm the membership of two redgiants. The proposed polarimetric memberships are compared with thosederived by photometric and kinematical methods, with excellent results.Among the observed stars, we identify 10 with intrinsic polarization intheir light. NGC 5617 can be polarimetrically characterized withPmax = 4.40 % and ?v = 73.1 deg. The spreadin polarization values for the stars observed in the direction of thecluster seems to be caused by the uneven distribution of dust in frontof the cluster's face. Finally, we find that in the direction of thecluster, the interstellar medium is apparently free of dust, from theSun's position up to the Carina-Sagittarius arm, where NGC 5617 seems tobe located at its farthest border.Based on observations obtained at Complejo Astronómico ElLeoncito, operated under agreement between the Consejo Nacional deInvestigaciones Científicas y Técnicas de laRepública Argentina and the Universities of La Plata,Córdoba, and San Juan.
| New Estimates of the Solar-Neighborhood Massive Star Birthrate and the Galactic Supernova Rate
The birthrate of stars of masses >=10 Msolar is estimatedfrom a sample of just over 400 O3-B2 dwarfs within 1.5 kpc of the Sunand the result extrapolated to estimate the Galactic supernova ratecontributed by such stars. The solar-neighborhood Galactic-plane massivestar birthrate is estimated at ~176 stars kpc-3Myr-1. On the basis of a model in which the Galactic stellardensity distribution comprises a ``disk+central hole'' like that of thedust infrared emission (as proposed by Drimmel and Spergel), theGalactic supernova rate is estimated at probably not less than ~1 normore than ~2 per century and the number of O3-B2 dwarfs within the solarcircle at ~200,000.
| Catalog of Galactic OB Stars
An all-sky catalog of Galactic OB stars has been created by extendingthe Case-Hamburg Galactic plane luminous-stars surveys to include 5500additional objects drawn from the literature. This work brings the totalnumber of known or reasonably suspected OB stars to over 16,000.Companion databases of UBVβ photometry and MK classifications forthese objects include nearly 30,000 and 20,000 entries, respectively.
| Observations of OB-stars at the former Leiden Southern Station
About 700 stars, mostly OB-stars, were observed by the author at theformer Leiden Southern Station at Hartebeespoortdam, South Africa, inthe observing seasons 1965, 1968, 1969, 1974, 1977, 1978. Observationswere made in the five channels of the Walraven photometric system. Dueto weathering of the telescope mirror the W channel gave no reliableresults for the faintest stars (m = 11 mag); in these cases the U-Wcolour index is not given. The change in sensitivity in the V channel,supposedly having occurred in 1968, was not recognised. Table~5 is onlyavailable in electronic form at the CDS via anonymous ftp tocdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/369/527
| 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.
| Photoelectric and photographic photometry in the open clusters NGC 5617, TR 22 and NGC 5662.
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1978A&AS...34..417H&db_key=AST
| Spectroscopic and photometric observations of luminous stars in the Cen-Nor (l=305-340 degrees) section of the Milky Way.
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1975A&AS...19..243H&db_key=AST
| Studies of the Milky Way from Centaurus to Norma. III. OB stars.
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