tex2html_wrap_inlineuvbyb#beta; Photoelectric Photometry of the Open Cluster NGC823
Absolute uvby beta photoelectric photometry of the brightest stars inthe direction of the Open Cluster NGC823 has been secured and ispresented. From the data analysis, reddening, distance, temperature andgravity are determined for the B, A, F stars and, from these, reddeningand a mean distance modulus ( 12.475+/-0.414) to the cluster aredetermined. Also, their membership in the cluster has been establishedand a numerical value of the age is determined through direct comparisonwith theoretical models. A brief analysis of the short period variablestars in the direction of NGC823 is made. We have concluded that theymight not be pre-MS delta Scuti stars.
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The total-to-selective extinction ratio determined from near IR photometry of OB stars
The paper presents an extensive list of the total to selectiveextinction ratios R calculated from the infrared magnitudes of 597 O andB stars using the extrapolation method. The IR magnitudes of these starswere taken from the literature. The IR colour excesses are determinedwith the aid of "artificial standards" - Wegner (1994). The individualand mean values of total to selective extinction ratios R differ in mostcases from the average value R=3.10 +/-0.05 - Wegner (1993) in differentOB associations. The relation between total to selective extinctionratios R determined in this paper and those calculated using the "methodof variable extinction" and the Cardelli et al. (1989) formulae isdiscussed. The R values presented in this paper can be used to determineindividual absolute magnitudes of reddened OB stars with knowntrigonometric parallaxes.
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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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UBV beta Database for Case-Hamburg Northern and Southern Luminous Stars
A database of photoelectric UBV beta photometry for stars listed in theCase-Hamburg northern and southern Milky Way luminous stars surveys hasbeen compiled from the original research literature. Consisting of over16,000 observations of some 7300 stars from over 500 sources, thisdatabase constitutes the most complete compilation of such photometryavailable for intrinsically luminous stars around the Galactic plane.Over 5000 stars listed in the Case-Hamburg surveys still lackfundamental photometric data.
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Derivation of the Galactic rotation curve using space velocities
We present rotation curves of the Galaxy based on the space-velocitiesof 197 OB stars and 144 classical cepheids, respectively, which rangeover a galactocentric distance interval of about 6 to 12kpc. Nosignificant differences between these rotation curves and rotationcurves based solely on radial velocities assuming circular rotation arefound. We derive an angular velocity of the LSR of{OMEGA}_0_=5.5+/-0.4mas/a (OB stars) and {OMEGA}_0_=5.4+/-0.5mas/a(cepheids), which is in agreement with the IAU 1985 value of{OMEGA}_0_=5.5mas/a. If we correct for probable rotations of the FK5system, the corresponding angular velocities are {OMEGA}_0_=6.0mas/a (OBstars) and {OMEGA}_0_=6.2mas/a (cepheids). These values agree betterwith the value of {OMEGA}_0_=6.4mas/a derived from the VLA measurementof the proper motion of SgrA^*^.
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The Initial Mass Function and Massive Star Evolution in the OB Associations of the Northern Milky Way
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1995ApJ...454..151M&db_key=AST
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The Henry Draper Extension Charts: A catalogue of accurate positions, proper motions, magnitudes and spectral types of 86933 stars
The Henry Draper Extension Charts (HDEC), published in the form offinding charts, provide spectral classification for some 87000 starsmostly between 10th and 11th magnitude. This data, being highlyvaluable, as yet was practically unusable for modern computer-basedastronomy. An earlier pilot project (Roeser et al. 1991) demonstrated apossibility to convert this into a star catalogue, using measurements ofcartesian coordinates of stars on the charts and positions of theAstrographic Catalogue (AC) for subsequent identification. We presenthere a final HDEC catalogue comprising accurate positions, propermotions, magnitudes and spectral classes for 86933 stars of the HenryDraper Extension Charts.
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Galactic OB associations in the northern Milky Way Galaxy. I - Longitudes 55 deg to 150 deg
The literature on all OB associations was reviewed, and their IRAS pointsource content was studied, between galactic longitude 55 and 150 deg.Only one third of the 24 associations listed by Ruprecht et al. (1981)have been the subject of individual studies designed to identify thebrightest stars. Distances to all of these were recomputed using themethod of cluster fitting of the B main sequence stars, which makes itpoossible to reexamine the absolute magnitude calibration of the Ostars, as well as for the red supergiant candidate stars. Also examinedwas the composite HR diagram for these associations. Associations withthe best defined main sequences, which also tend to contain very youngclusters, referred to here as OB clusters, have extremely few evolved Band A or red supergiants. Associations with poorly defined mainsequences and few OB clusters have many more evolved stars. They alsoshow an effect in the upper HR diagram referred to as a ledge byFitzpatrick and Garmany (1990) in similar data for the Large MagellanicCloud. It is suggested that the differences in the associations are notjust observational selection effects but represent real differences inage and formation history.
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Photoelectric photometry of OB stars in the Vilnius system
Not Available
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Hydrogenated amorphous carbon-coated silicate particles as a source of interstellar extinction
A new model for interstellar grains has recently been proposed in whichlarge and small silicate grains are mantled with thin layers ofhydrogenated amorphous carbon (HAC or a-C:H) and amorphous carbon (a-C).A complete description of the grain model is presented for the firsttime. The optical properties of small inhomogenous particles arediscussed and new expressions for carbon depletion, bump strength andalbedo are derived. It is shown, in particular, that the wide variety ofinterstellar extinction curves can be explained by variations in carbondepletion, and model fits to normal and extreme cases of extinction arepresented. The model enables a direct measurement of carbon depletion tobe made from the extinction data and implies that carbon depletion in aninterstellar cloud is determined by the recent history of that cloud.Thus, on this model, grains respond to and react with their environment,rather than being immutable, inert entities in the interstellar gas.
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Surface distribution of the luminous and early-type emission stars in the OB Vulpecula associations
The surface distribution of the luminous and early-type emission starsin a Milky Way region in Vulpecula is obtained. The results show adiscrepancy between the places of greatest concentration of such kindsof stars and those indicated in literature as positions of OBassociations.
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The interstellar 217 NM band - A third catalogue of equivalent widths
A catalog of equivalent widths of the 217 nm interstellar absorptionband as well as other parameters characterizing the extinction curve inthe ultraviolet has been compiled for 790 O and B stars. A relativelytight correlation between the equivalent width of the 217 nm band andE(B-V) indicates that the absorber of this band is connected with thepopulation of larger interstellar grains responsible for the visualextinction. The parameter characterizing the amount of extinction in thefar UV is only weakly correlated with E(B-V), a result in accord withthe assumption that a second population of very small grains causes therapid increase of the far-UV extinction.
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The variation of galactic interstellar extinction in the ultraviolet
It has been found that the wavelength dependence of interstellarextinction is not the same for all stars in the Galaxy. The presentinvestigation is concerned with a further demonstration of the degree ofvariation of interstellar extinction in the UV, taking into account newextinction measurements toward 29 early-type stars. The stars do notrepresent a random sample. Approximately 15 of them were chosen becausethey have either an unusually large or an unusually small ratio of thestrength of the diffuse interstellar band at 4430 A to the color excessE(B-V). Five stars have a ratio of these quantities near average andnine additional stars are illuminating reflection nebulae. Attention isgiven to the deviation from the average galactic extinction law, denseversus diffuse cloud environments, and the galactic longitudedependence.
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New UBVRI photometry for 900 supergiants
A description is presented of the results obtained in connection with asystematic program of supergiant photometry on the Johnson UBVRI system.During the eight years after the start of the program, almost 1000 starshave been observed, about 400 three or more times each. The originalselection of stars used the spectral type catalog of Jaschek et al.(1964) to choose supergiants. Since observations were possible from bothChile and Canada, no declination limits were imposed, and no particularselection criteria were imposed other than to eliminate carbon stars.These are so red as to require enormous extrapolations of thetransformation equations.
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Studies of luminous stars in nearby galaxies. I. Supergiants and O stars in the Milky Way.
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1978ApJS...38..309H&db_key=AST
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Infrared colors and the diffuse interstellar bands
Broad-band infrared photometric measurements have been gathered for 105stars which exhibit diffuse interstellar bands in their spectra. Allnormal stars obey a single reddening law, and a value of R equal to 3.08+ or - 0.15 is derived. This value is consistent with other recentdeterminations of R. The diffuse band indicators, the central depth ofthe 4430-A feature and the equivalent widths of the 5780-A and 6284-Afeatures, show as large a scatter with the infrared color excesses asthey do with E(B - V). No single-valued relation between the colorexcesses and the diffuse band strengths appears to exist. This castsdoubt on whether dust grains which produce the visual and infraredextinctions are the carriers for the diffuse interstellar features.
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The abundance of negative hydrogen in small hot interstellar clouds
The observed intensities of the diffuse interstellar absorption band at4430 A have minimum values, for given stellar distances, that areequivalent to the reddening caused by the small Ambarzumian-type cloudsstudied by Stromgren (1972). This indicates that there is no negativehydrogen present between these clouds, which are then identified withthe hot H I phase of interstellar matter. The equilibrium density of H-inside such clouds is calculated from mean densities of neutral hydrogenatoms and free electrons, derived from radio observations for the localregion outside the large Orion-arm clouds. The filling factor of thesmall clouds is taken to be the same as that preserved in the structureof the Gum Nebula from before its ionization. An electron temperature of3375 K corresponding to the local degree of ionization of thesmall-cloud hydrogen then leads to a mean density of negative hydrogenequal to 20 trillions per sq cm per kpc, in agreement with the observeddiffuse-band intensities.
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Wavelength dependence of interstellar polarization and ratio of total to selective extinction
A multichannel polarimeter-photometer which uses dichroic filters toseparate the (UBVR) spectral regions is described. The instrument wasused with a 24-inch rotatable tube telescope for polarimetricobservation of nearby stars. Polarization data for 364 nearby stars aretabulated, together with the wavelength dependence of linear andinterstellar polarization.
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Red Supergiants and Neutrino Emission. II
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1972ApJ...175..717S&db_key=AST
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UBV photoelectric photometry of early type stars in the direction of the association VUL OB1 and VUL OB4.
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1971A&A....13..274T&db_key=AST
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Vitesses radiales et distances des regions HII galactiques.
Not Available
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The space distribution and kinematics of supergiants
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1970AJ.....75..602H&db_key=AST
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Correlation Between the Regional Variations in Wavelength Dependence of Interstellar Extinction and Polarization
Abstract image available at:http://adsabs.harvard.edu/abs/1968ApJ...154..115S
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Spectral Types and Hγ Observations for Stars in Eight Associations
Not Available
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Photoelectric 4430 A observations of 506 O, B and A stars.
Not Available
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Polarization of Galactic Clusters M25, NGC 869, 884, 1893, 2422, 6823, 6871, and Association VI Cygni.
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1965ApJ...141.1340S&db_key=AST
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Radial Velocities of Distant OB Stars.
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1964ApJ...140..162M&db_key=AST
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Polarisation de la lumièe des étoiles dans le système U, B, V, R
Not Available
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Photoelectric measures of the 4430 A diffuse interstellar band
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1963MNRAS.125..141W&db_key=AST
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On the Radio Emission from HII Clouds
Abstract image available at:http://adsabs.harvard.edu/abs/1960PASJ...12..203M
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INHABITED SKY
