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.
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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.
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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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HST/FOS Spatially Resolved Spectral Classification of Compact OB Groups in the Large Magellanic Cloud
Blue-violet spectrograms of individual components in four compact OBgroups of the Large Magellanic Cloud, obtained with the Hubble SpaceTelescope (HST) Faint Object Spectrograph (FOS), are presented anddiscussed. Two of the massive multiple systems are in the 30 Doradusperiphery, while the other two represent the core and the peripheral,triggered associations in the giant shell H II region Henize N11.Uncontaminated spectrograms of three Wolf-Rayet and two very early Ofcomponents have been obtained for the first time; they can be observedonly as composites with their close companions from the ground. Many ofthe companions have also been observed separately with the HST FOS, andseveral are of special interest in their own right. These observationsprovide information on the initial masses and ages of the peculiarobjects, and on the evolutionary relationships among different spectralcategories within the presumably coeval systems.
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Helium peculiar stars in the red spectral region
Based upon 33 A/mm dispersion spectroscopic material we examine ifequivalent widths of H and He lines can be used for the detection of newhelium-peculiar stars. The answer is affirmative and we present some newcandidates discovered this way. We have also investigated if the use ofdifferent helium lines than those of the (3) D series (4026, 4471)modifies the assignments of helium peculiar stars. This is not the case,since the use of lambda 6678 ((1) D) and lambda 7065 (3S) gives the sameresults. Based on observations obtained at the Haute ProvenceObservatory (CNRS)
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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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Kinematic signatures of violent formation of galactic OB associations from HIPPARCOS measurements
Proper motions measured by Hipparcos confirm the large anomalousvelocities of the OB associations located around the Cygnus Superbubble(Cygnus OB1, OB3, OB7, and OB9), and reveal a clearly organizedexpanding pattern in Canis Major OB1. At the distances of theseassociations, the organized velocity patterns imply LSR velocities of upto ~ 60 km s(-1) for the associations in Cygnus, and about ~ 15 km s(-1)in Canis Major OB1. The magnitude and spatial arrangement of theexpanding motions suggests that very energetic phenomena are responsiblefor the formation of the present OB associations. This is independentlysupported by observations of the associated interstellar medium carriedout in other wavelengths. The gravitational instability scenarioproposed by Comeron & Torra 1994 (ApJ 423, 652) to account for theformation of the stars in the Cygnus Superbubble region is reviewed inthe light of the new kinematic data. It is found that the energeticrequirements set by the highest velocities on the OB associationpowering the Superbubble, Cygnus OB2, are too large by orders ofmagnitude. However, the scenario can still account for the formation ofmost of the stars if, as can be reasonably expected, the stars with thehighest measured velocities are actually runaways from Cygnus OB2itself. As for Canis Major OB1, we consider their formation in asupernova remnant, as suggested by Herbst & Assousa 1977 (ApJ, 217,473). The detection of a new runaway star, HIC 35707 (=HD 57682), whosemotion is directed away from the derived center of expansion, supportsthis scenario and provides an independent age for the supernova remnant,assuming that the runaway star was the binary companion of thesupernova. Based on a number of arguments, however, we find it unlikelythat the stars are a direct consequence of instabilities in theexpanding shell. We propose instead that their formation was triggeredin preexisting clouds, accelerated and compressed by the supernovaexplosion.
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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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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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Intrinsic colour indices of O- and B- type stars in the Vilnius photometric system.
Not Available
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Anomalous Proper-Motions in the Cygnus Super Bubble Region
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1993A&AS..101...37C&db_key=AST
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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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Close binary systems in regions of open clusters. I - V448 CYG in NGC 6871
New photoelectric UBVRI' observations of the massive early-typeeclipsing system V448 Cyg in the open cluster NGC 6871 were obtained.The light curve is found to be variable in all colors. The period of thesystem is modified. New photometric elements of V448 Cyg are determinedby Lavrov's method, and absolute parameters of the system are estimated.Difficulties in interpreting the larger-size low-mass component arediscussed. The distance to V448 Cyg is estimated at 11.2 m, and its ageis 8,000,000 yr.
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A search for T Tauri's optical companion star
Speckle interferometric observations of the premain-sequence stellarsystem T Tauri at 650 and 800 nm, and at 1.6 (H) and 2.2 microns (K) inthe IR using the Palomar 200-in. telescope yield no evidence for atertiary optical companion star as reported in 1985. The presentobservations were of sufficient sensitivity to have detected the objectunambiguously if it had remained at its reported brightness and color.The IR results provide particularly stringent limits on the presence ofa third star in the system, since both the optical and southern IRcomponent are clearly resolved to the diffraction limit of the 200-in.telescope, including the H band where the southern component appearedabout 5 mag fainter than the optical primary. Possible resolutions tothe conflicting results concerning this object are discussed, and it isconcluded that if the star is bound to the T Tau system, it has dimmedby at least 1-3 mag at R, I, H, and K. The star is unlikely to be anormal M dwarf as reported, and the possibility that the star could be aHerbig-Haro object is discussed.
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A list of MK standard stars
Not Available
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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.
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H-alpha as a tracer of mass loss from OB stars
This paper investigates the use of the H-alpha emission from stellarwinds of OB stars to determine the stellar mass-loss rate. The power inH-alpha emitted by the wind can be parameterized in terms of thetemperature and the density field of the wind. A simple expression isderived which relates the observed H-alpha luminosity to the stellarmass-loss rate, the stellar radius, the velocity law, and the stellareffective temperature. This expression is calibrated for the influenceof the velocity law using a sample of Galactic OB stars with UVmass-loss rates. Consequently, the results depend on the validity of theUV rates. The derived velocity law for O stars turns out to be inagreement with the radiation-pressure-driven wind theory. There isevidence for a dependence of the velocity-law gradient on spectral type.The results for B stars, however, are more uncertain due to thedependence on the adopted mass accretion rate/L relation. Application ofthe calibrated H-alpha luminosity/mass-loss rate relation to a sample of149 galactic OB stars shows that mass accretion rate can be reliablydetermined from H-alpha. Due to the moderate amount of observing timerequired to derive mass accretion rate from H-alpha, this method may beapplied successfully to investigate mass-loss effects in extra-Galacticstars.
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A photoelectric search for variable stars in the open cluster NGC 6871.
Not Available
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Interstellar extinction curve - The profile of very broad structure
The interstellar extinction curve between 3500 and 10,500 A isdetermined from a series of two-color plots based on existing spectralscans. Very Broad Structure (VBS) covers the wavelength range from 5000to 8000 A and consists of three components centered at 5300, 5900 and6800 A. The VBS is shown to originate in the same agent as that ofcontinuous extinction.
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Observations of interstellar diffuse absorption band at 4430 A
Observations of the interstellar diffuse absorption band at 4430 A for800 O and B stars in Neckel's (1967) catalog are being carried out, and482 spectra obtained up to September 1983 have been reduced. It isconfirmed that the strength of the interstellar diffuse absorption bandat 4430 A does not simply relate to the abundance of interstellar grainson the line of sight. The relation between the color excess E(B-V) andthe equivalent width of the band to the direction of l = 130-140 deg andb = -5 to +5 deg shows that some parameter(s) other than E(B-V) is (are)needed to understand the cause of this band.
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Catalog of O-B stars observed with Tokyo Meridian Circle
A catalog of the O-B stars, selected from 'Blaauw-Parenago' list andRubin's catalog, has been compiled on the FK4 system by the observationsmade with Gautier 8-inch Meridian Circle at the Tokyo AstronomicalObservatory during the period, 1971 to 1979. It contains 1059 stars andwas compiled for the future establishment of high precision propermotions of O-B stars.
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Eclipsing binaries in open clusters. I - Preliminary study
A preliminary list of suspected eclipsing binaries in open clusters ispresented. The period, the mass ratio, the correlation between the massratio and cluster age, and the periodicity diagram are investigated.
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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.
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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.
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Catalogue of Eclipsing and Spectroscopic Binary Stars in the Regions of Open Clusters
Not Available
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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.
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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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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.
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A catalogue of stellar spectrophotometric data
A list of 378 sets of stellar energy distributions for 356 stars basedon photoelectric spectrophotometry is presented. Data from eight sourceshave been transformed to the Hayes-Latham calibration of Alpha Lyrae.The procedure follows that of Breger (1976) and the present list extendsprevious data, especially for stars of earliest and intermediatespectral types.
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Neutral hydrogen absorption in the spectra of four low-latitude pulsars
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1979A&A....77..204W&db_key=AST
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INHABITED SKY
