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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.
| Spectroscopic Survey of the Galactic Open Cluster NGC 6871. I. New Emission-Line Stars
We analyze spectra of 44 emission-line stars detected in alow-resolution optical spectroscopic survey of the galactic open clusterNGC 6871. The survey of 1217 stars is complete to V=14.9 and includesstars with V<16.5 between the zero-age main sequence and the107 yr pre-main-sequence (PMS) isochrone. Of the 44emission-line stars in this survey, 28 show obvious emission in Hαand 16 have weak Hα absorption (compared with Hγ). We usethe reddening to separate foreground and background stars from thecluster members; the position in the HR diagram or the presence offorbidden emission lines ([N II] and [S II]) then yields theevolutionary status of the emission-line stars. A comparison of theHα spectral index distribution in NGC 6871 with the distributionof young stars in the Taurus-Auriga molecular cloud indicates that thelate-type PMS stars in our sample may be weak-line T Tauri stars. Manyof these stars show [S II] (36%) and [N II] (45%) emission.
| Multiperiodicity and physical nature of the δ Sct star GSC 2683-3076
We present the results of a CCD Johnson V and photoelectricStrömgren uvbyβ photometric study of the recently discoveredmultiperiodic δ Sct star GSC 2683-3076. Our data set mainlyconsists of 2874 differential measurements in V together with a few datacollected into the uvbyβ system. Additional unfiltered CCDmeasurements were also carried out. A set of seven best-fittingpulsation frequencies representing the light variations of the variablehas been detected. The spectral type of the variable is found to be A9Vor F0V. Using the uvbyβ indices the following main physicalparameters for the variable have been derived: Teff=7230K,MV=1.95mag, logg=3.90, M=1.85Msolar,R=2.30Rsolar, ρ=0.16ρsolar, age=1.0Gyr,metal abundance [Me/H]=0.16 and distance modulus=8.4mag. GSC 2683-3076is found to be a Population I δ Sct star, slightly metal-enriched,evolving on its main-sequence stage. A mixture of radial and non-radialmodes seems to be present in the pulsation of this variable. This staris also known as H133 in the young open cluster NGC 6871, howeverarguments are given that address this star as a non-member of thecluster. The uvbyβ photometry available in the literature for NGC6871 is also discussed.
| 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
| Physical parameters of multiple systems like the Trapezium of early spectral types, derived from uvby-beta photometry. II.
Not Available
| 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.
| The Tokyo PMC catalog 90-93: Catalog of positions of 6649 stars observed in 1990 through 1993 with Tokyo photoelectric meridian circle
The sixth annual catalog of the Tokyo Photoelectric Meridian Circle(PMC) is presented for 6649 stars which were observed at least two timesin January 1990 through March 1993. The mean positions of the starsobserved are given in the catalog at the corresponding mean epochs ofobservations of individual stars. The coordinates of the catalog arebased on the FK5 system, and referred to the equinox and equator ofJ2000.0. The mean local deviations of the observed positions from theFK5 catalog positions are constructed for the basic FK5 stars to comparewith those of the Tokyo PMC Catalog 89 and preliminary Hipparcos resultsof H30.
| Physical parameters of multiple systems like the Trapezium of early spectral types, derived from uvby-beta photometry. I.
Not Available
| 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.
| 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
| Uvby-Beta Photometry of the Components of the Trapezium-Type Multiple Systems
Not Available
| Reliable photometric reductions to the standard UBV (or uvby) system and accurate UBV magnitudes of bright standard stars from the northern part of the international Be program
A modified method of computer reduction of UBV (or uvby) photoelectricobservations to standard systems, which combines advantages of what hasso far been achieved in this area, is described in detail. A completereduction of over 46000 UBV observations obtained at Hvar Observatorybetween 1972 and 1991, and of nearly 5000 UBV observations secured atSkalnate Pleso Observatory between 1980 and 1987, was carried out usingthe new technique. It is argued that replacing the original Johnson'sUBV values for the non-variable stars that were observed by the meanvalues based on repeated observations over several years and applyingthe new reduction technique can ensure a stable reproduction of UBVmagnitudes, obviously quite close to the standard Johnson's ones, overmany years and from observatories situated at very different altitudesabove sea level within about 0.01mag in all three UBV magnitudes. A listof new accurate mean UBV values of 191 stars which were regularlyobserved at Hvar - and a part of them also at Skalnate Pleso - ascomparison, check and standard stars in the Be- and Ap-star observingprograms, is included for future use by photometric observers in theNorthern Hemisphere. For a number of these stars, we can guaranteesecular constancy within 0.mag01 during the past 5 to 15 years.
| UVBY photometry of open clusters. II - NGC 6871
The uvby photometry on the young open cluster NGC 6871 available fromCrawford and Barnes (1974) is extended to establish more accuratecharacteristic data on the cluster and its individual members and todetermine the color excess ratio E(b-y)/E(B-V) for the cluster stars. Atrue mean distance modulus of 11.94 mag + or - 0.08 mag is obtained,equivalent to a distance of 2440 + or - 100 pc. An age of 1.2 x 120 tothe 7th yr is derived for the clusters.
| Search for variable stars in the young open cluster NGC 6871
Photoelectric uvby and H-beta observations of the brightest stars in thefield of the open cluster NGC 6871 have been performed in order todetect possible light variability of the B-type stars that are membersof the cluster. Two new variables, a Delta Scuti and a Beta Cephei star,have been discovered.
| Wolf-Rayet stars in open clusters and associations
Existing data on galactic Wolf-Rayet (WR) stars in open clusters and OBassociations have been summarized and evaluated. All WR stars withinthree cluster radii from known clusters have been studied. It was foundthat 10 - 30% of all WR stars are cluster members. It is also estimatedthat at least 50% of the WR stars are members of OB associations(including cluster members). These frequencies are in good agreementwith the corresponding figures found for O stars. Mean absolutemagnitudes for different groups of WR stars have been determined. Thereis a good correlation between mass and absolute magnitude for binary WRstars. Implications of this on different evolutionary scenarios for WRstars are briefly discussed. The distributions of WR stars in the solarneighbourhood and in LMC are compared and commented.
| The post-RLOF structure of the secondary components in close binary systems, with an application to masses of Wolf-Rayet stars
The structure of the secondary components of a close group of modelbinary systems (with initial primary masses 15-30 solar mass and initialmass ratios 0.3-0.9) after Roche-lobe overflow (RLOF) and relaxationtoward thermal equilibrium is calculated, assuming the primaries areevolving through the early B phase of mass transfer and allowing for thepossibility of mass loss from the system during RLOF. The results arepresented in graphs and tables showing the final evolutionary status,mass and mass ratio, chemical profile, and core-H burning lifetime ofthe secondary. The primary is found to evolve to a sueprnova before theexhaustion of the H core in all cases, and no WR + WR binaries areidentified. These findings are then used to estimate the masses of 10double-lined spectroscopic WR + OB binaries from observational data;most of the WR masses are in the range 8-14 solar mass and are smallerby factors as large as two than those compiled by Massey (1982).
| Mass loss rates for northern OB-stars
A mass loss survey of 44 O- and early B-type stars in northern OBassociations is presented. For 22 stars mass loss rates were derivedfrom H-alpha equivalent widths using the method of Klein and Castor(1978). For 15 stars upper limits of the mass loss rates were estimated.For the remaining 7 stars H-alpha and H-beta equivalent width values aregiven but no quantitative evaluation of M-dot was possible. The resultsare compared with present ideas concerning the relation between massloss and other basic stellar parameters.
| Observations of binaries and evolutionary implications
Visual, X-ray, and UV spectra obtained at different phases of binarysystems are used to derive radial velocity curves, construct geometricmodels, and predict mass-loss and mass-transfer parameters. The historyof binary investigations is summarized in a table, the observations usedare characterized, and the aims and methods of evolutionary modeling arereviewed. Results are presented in diagrams, graphs, and tables forAlgol binaries, the contact system SV Cen, supergiant systems,cataclysmic variables, symbiotic stars, Wolf-Rayet and OB-type binaries,massive X-ray binaries, and barium stars.
| The evolution of massive stars - The numbers and distribution of O stars and Wolf-Rayet stars
The Mv-spectral type calibration of the O and Wolf-Rayet (W-R) stars isreexamined. The actual numbers and distributions of stars and their W-Rdescendants in a volume-limited sample of stars within 2.5 kpc of thesun are compared. Evolutionary computations, with and without asimplified overshooting criterion for massive stars, are discussed inview of the observations in this sample. The following conclusions arereached: (1) Wolf-Rayet stars are descendant from stars with initialmasses greater than 40 solar masses; and (2) with conventional modelsand assuming continuous star formation, the observed number ratio of W-Rto Q stars is at least a factor of 3 larger than theoretically expected.This discrepancy can be lessened by taking account of the following: (1)the number and distribution of very luminous early-B supergiantssuggests that they are also core hydrogen burning objects, so that thesepredecessors to W-R stars must be counted among the O star statistics;(2) overshooting during the W-R core helium burning phase might beimportant, thus lengthening the lifetime of this phase; (3) starformation in the Galaxy, at least for the most massive stars, mightoccur in relatively short-lived bursts.
| A study of B-type supergiants with the uvby,beta photometric system
The applicability of the uvby,beta photometric system to theclassification and study of B-type supergiants (BTS) is investigatedusing published data on 157 BTS and observations of 17 BTS made with the36-in. reflector at McDonald Observatory. The results are presented intabular form and analyzed to produce preliminary calibrations ofluminosity class vs. beta index and of absolute magnitude (Mv) vs. beta(or delta Mv vs. delta beta) for four associations of stars. Theeffectiveness of various color indices as temperature indicators isdiscussed. It is shown that there is good correspondence between MK anduvby,beta classifications of B-type main-sequence stars, giants, andBTS, confirming the usefulness of the uvby,beta system in furtherresearch on BTS.
| 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.
| The initial mass function for massive stars
A machine readable catalog of over 750 galactic O stars with publishedphotometry, spectral types, and luminosity classes has been compiled.The catalog is probably complete to a distance of about 2.5 kpc. Fromthis volume-limited data, the initial mass function (IMF) for stars moremassive than 20 solar masses has been derived. This IMF differs fromthat of Miller and Scalo (1979) and of Lequeux (1979), in havingproportionately more O type stars and not as steep a fall-off in numberof stars with increasing mass. Dividing the sample into stars inside andoutside the solar circle, a substantial difference in the IMF of themost massive stars is found. There are proportionally more toward thegalactic center. This gradient in the IMF may be related to the observedspace density of Wolf-Rayet stars, which are descendants of O typestars.
| The optical spectrum of R136a - The central object of the 30 Doradus nebula
R136 (HD 38268) is the brightest member of the compact cluster of starsat the center of the 30 Doradus Nebula, a massive H II region in theLarge Magellanic Cloud (LMC). The far-ultraviolet luminosity isequivalent to at least 1000 ordinary O type stars. Optically, R136 is anunresolved patch corresponding to a linear extent of about 0.7 pc.Several components are known to be present, of which R136a is thebrightest. A quantitative description of the optical spectrum of R136ahas not been available in the literature. The present investigation isconcerned with the analysis of spectrograms in the visible region. It isfound that the optical spectrum of R136a shows broad but rather weakemission lines of ions which are frequently seen in early WN-type stars.The centroid of H-alpha is displaced by approximately 100 km/s redwardof the nebular H-alpha emission. The Balmer series is visible, inabsorption, up to H11.
| Structure and evolution of large groups of Massive Close Binary systems
Using the definition of four important events in the evolution ofMassive Close Binary systems, five observable evolutionary phases aredefined in the life of a Massive Close Binary system: OB plus OB, WRplus OB, C plus OB, C plus WR, and WR plus WR. A number of observablephenomena are defined and computed for large groups of Massive CloseBinaries. For one burst of star formation, the number of systems indifferent evolutionary phases is computed, along with the total massloss as functions of the time. For continuous star formation, thefraction of WR binary stars, occurring in different phases of massiveclose binary evolution, and a number of average quantities (mass, massratio) of WR binary systems are determined. The results are comparedwith observations of WR binaries in the Galaxy and in Open Clusters.
| The Wolf-Rayet star HD 193077 - Evidence for a low-mass companion and the possibility of a third body
HD 193077 is shown to probably consist of three stars: (1) a WN 6 starwith (2) a neutron star in 2.3238-day orbit, and (3) a fainter, rapidlyrotating late O main-sequence star which the first two circle in 1763days. Although this makes HD 193077 the sixth galactic W-R star whichmay contain a compact companion, it is unique in possessing a thirdbody. The effect produced on the present system by the rapid ejection ofa supernova shell in the formation of the supposed neutron star willhave been reduced by the presence of the OB star.
| Near-infrared observations of trapezium-type multiple systems Catalogue of observations and a new determination of the reddening law
Results are presented from a large scale near-infrared survey of smallsky areas of the Milky Way containing trapezium-type multiple starsystems located within young galactic clusters, H II regions or darknebulosities. Photometric maps at wavelength 2.2 microns complemented bybroadband JHKL photometry of the majority of the sources detected and ofthe star members of the systems were obtained. A number of randomlychosen comparison regions along the galactic plane were also mapped andthe results were also used, with recent semi-empirical models, todetermine the number of field stars expected for the program surveys.Analyses of the infrared two-color diagrams provide determinations ofthe values of the color excess ratios E(J-H)/E(H-K), E(H-K)/E(K-L) andE(J-K)/E(K-L). The resulting reddening law is found to differsignificantly from that in the direction of the Ophiuchus and Taurusdark clouds and possibly towards the Galactic Center.
| Absolute Proper Motions for 117 Type 0-STARS
Not Available
| H I absorption measurements of seven low-latitude pulsars
The neutral hydrogen absorption spectra of seven low-latitude pulsarsare measured and used to estimate their distances and mean electrondensities along the lines of sight. Calculations made in terms of theSchmidt (1965) galactic rotation model on the basis of the spectralobservations made using the Arecibo 305-m telescope indicate thatpulsars 1919+21 and 1929+10 are within 1.5 kpc of the earth and pulsars2016+28 and 2020+28 are further than 1.3 kpc. Considerations ofabsorption spectra, dispersion and rotation measurements and Stromgrenspheres along the line of sight indicate that PSR 0525+21 isapproximately as distant as the Crab Nebula pulsar (2 kpc), while PSR0540+23 is more distant. Absorption in PSR 0611+22 is found to besimilar to that of the nearby supernova remnant IC 443, but theresemblance may be due to the small change of velocity with distance inthe direction of the anticenter. The dispersion measured and distancesof 32 known pulsars indicates extended regions of enhanced electrondensity in the inner part of the Galaxy and the Gum Nebula, withelectron density elsewhere generally between 0.02 and 0.03/cu cm.Possible sources of the ionization include stellar UV radiation.
| Interstellar C IV and SI IV column densities toward early-type stars
Equivalent widths and deduced column densities of Si IV and C IV areexamined for 18 early-type close binaries, and physical processesresponsible for the origin of these ions in the interstellar medium areinvestigated. The available C IV/Si IV column density ratios typicallylie within a narrow range from 0.8 to 4.5, and there is evidence thatthe column density of C IV is higher than that of N V along most linesof sight, suggesting that C IV is not formed in the same hot region as OVI. In addition, the existence of regions with a narrowly defined newtemperature range around 50,000 deg K is indicated. The detection of thesemitorrid gas of Bruhweiler, Kondo, and McCluskey (1978, 1979) issubstantiated, and the relation of this gas to the observations ofcoronal gas in the galactic halo is discussed.
| Kinematics, close binary evolution, and ages of the O stars
Accurate proper motions were determined for O4-B2 stars, Wolf-Rayets,and B9-K3 supergiants. Space velocities were calculated for these starsand used to investigate the kinematics of the O stars. Observationssuggest that the group H stars were produced from mass exchange inmassive close binary (MCB) systems, and the high space velocitiestypical of these stars were caused by binary supernovae. Hence, 50% ofthe O stars were probably produced by mass accretion in MCS systems. Amodel is presented describing the evolution of a MCB system for the caseof no mass loss from the system: (1) for stars exploding as supernovae,15% of the initial stellar mass will form a collapsed remnant, (2) starswith masses at least equal to 12 solar masses will eventually explode assupernovae, and (3) the group H stars with masses greater than 45 solarmasses probably have black hole binary companions.
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Pozíciós és asztrometriai adatok
| Csillagkép: | Hattyú |
| Rektaszcenzió: | 20h05m58.71s |
| Deklináció: | +35°47'49.9" |
| Vizuális fényesség: | 7.278 |
| Távolság: | 3333.333 parszek |
| RA sajátmozgás: | -3 |
| Dec sajátmozgás: | -6.5 |
| B-T magnitude: | 7.483 |
| V-T magnitude: | 7.295 |
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