Optical polarimetric study of open clusters: distribution of interstellar matter towards NGC 654
We present new B,V and R linear polarimetric observations for 61 starstowards the region of the young open cluster NGC 654. In this study wefound evidence for the presence of at least two layers of dust along theline of sight to the cluster. The distances to the two dust layers areestimated to be ~200 pc and ~1 kpc which are located much closer to theSun than the cluster (~2.4 kpc). Both the dust layers have their localmagnetic field orientation nearly parallel to the direction of theGalactic plane. The foreground dust layer is found to have a ringmorphology with the central hole coinciding with the centre of thecluster. The foreground dust grains are suggested to be mainlyresponsible for both the observed differential reddening and thepolarization towards the cluster.
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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.
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Stellar contents of two young open clusters: NGC 663 and 654
UBVRI CCD photometry in a wide field around two young open clusters, NGC663 and 654, has been carried out. Hα and polarimetricobservations for the cluster NGC 654 have also been obtained. We use thephotometric data to construct colour-colour and colour-magnitudediagrams, from which we can investigate the reddening, age, mass andevolutionary states of the stellar contents of the these clusters. Thereddening across the cluster regions is found to be variable. There isevidence for anomalous reddening law in both clusters; however, moreinfrared and polarimetric data are needed to conclude about thereddening law. Both clusters are situated at about a distance of 2.4kpc. Star formation in both clusters is found to be a continuousprocess. In the case of NGC 663, star formation seems to have takenplace sequentially, in the sense that formation of low-mass starsprecedes the formation of most massive stars. Whereas, in the case ofNGC 654, formation of low-mass stars did not cease after the formationof most massive stars in the cluster.
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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.
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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
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Spectroscopic observations of young open clusters: IC 1805, NGC 654 and NGC 6823
Spectroscopic observations were made for a sample of 263 stars fromthree young open clusters IC 1805, NGC 654 and NGC 6823 with CCDdetectors in the blue and yellow-red spectral regions. MKK types wereproperly determined for these stars by carefully comparing spectra ofprogram stars with those of a complete grid of MKK standards, which wereobserved with the same instruments as the program stars. For most of theobserved stars precise MKK types were assigned for the first time. A fewof early-type emission-line stars were discovered or confirmed. Thepresence of Be stars in the studied clusters is discussed. Spectra ofthe observed MKK standards also reveal lots of features showingtemperature or luminosity effect in the yellow-red region, which helpedin our stellar spectral classification.
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Vitesses radiales. Catalogue WEB: Wilson Evans Batten. Subtittle: Radial velocities: The Wilson-Evans-Batten catalogue.
We give a common version of the two catalogues of Mean Radial Velocitiesby Wilson (1963) and Evans (1978) to which we have added the catalogueof spectroscopic binary systems (Batten et al. 1989). For each star,when possible, we give: 1) an acronym to enter SIMBAD (Set ofIdentifications Measurements and Bibliography for Astronomical Data) ofthe CDS (Centre de Donnees Astronomiques de Strasbourg). 2) the numberHIC of the HIPPARCOS catalogue (Turon 1992). 3) the CCDM number(Catalogue des Composantes des etoiles Doubles et Multiples) byDommanget & Nys (1994). For the cluster stars, a precise study hasbeen done, on the identificator numbers. Numerous remarks point out theproblems we have had to deal with.
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JHK photometric study of the variable interstellar extinction in the direction of open star cluster NGC 654
JHK magnitudes have been determined for 18 stars in the field of NGC654. Study of the interstellar extinction law in the cluster directionindicates an anomalous distribution of interstellar grains causing moreextinction in U and B pass-bands compared to that obtained from thecolor excesses E(V-J), E(V-H) and E(V-K) using a normal reddening law.This implies a small shift in the grain-size distribution towardssmaller than normal-sized particles. Patchy distribution of interstellarmatter seems to be responsible for the nonuniform extinction in thecluster region.
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Photometry of the open cluster NGC 654
A reddening which varies from 0.74 to 1.16 mag across the cluster isdetermined by a photoelectric UBV study of NGC 654. The true distancemodulus is estimated to be 10.85 mag. A discussion is presented of theage of the cluster stars and NGC 654's position on the HR diagram. Anevolutionary effect in the cluster stars is observable. Almost all ofthe stars have reached the main sequence.
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Membership in the young open cluster NGC 654
Relative proper motions with an average standard error of + or 0.07arcsec/century in each coordinate have been determined for 186 stars inthe region of the young open cluster NGC 654. Of these stars 60 arefound to be probable members, including the A0 Ib supergiant BD +61 deg315. The F5 Ia MK standard HD 10494 tentatively appears to be a probablemember. With an adopted absorption ratio of 3.0, the corrected distancemodulus is 11.9 + or - 0.3 magnitudes or a distance of 2400 pc. Derivedabsolute visual magnitudes and intrinsic (B-V) colors for thesupergiants are given. Three additional bright stars are presented aspossible B-A Ib supergiants. The known variable reddening across thecluster is probably due to foreground dust rather than to dust left overfrom the period of star formation.
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La mesure des vitesses radiales au prisme objectif. IX - 3e liste de vitesses radiales déterminées au prisme objectif à vision directe
Not Available
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Stellar Spectra and Colors in a Milky way Region in Cassiopeia.
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1955ApJS....2..123F&db_key=AST
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