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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Kinematics and binaries in young stellar aggregates. II. NGC 6913 ≡ M 29
Between 1996 and 2003 we obtained 226 high resolution spectra of 16stars in the field of the young open cluster NGC 6913, to constrain itsmain properties and study its internal kinematics. Twelve of the programstars turned out to be members, one of them probably unbound. Nine arebinaries (one eclipsing and another double lined) and for seven of themthe observations allowed us to derive the orbital elements. All but twoof the nine discovered binaries are cluster members. In spite of theyoung age (a few Myr), the cluster already shows signs that could beinterpreted as evidence of dynamical relaxation and mass segregation.However, they may be also the result of an unconventional formationscenario. The dynamical (virial) mass as estimated from the radialvelocity dispersion is larger than the cluster luminous mass, which maybe explained by a combination of the optically thick interstellar cloudthat occults part of the cluster, the unbound state or undetected verywide binary orbit of some of the members that inflate the velocitydispersion and a high inclination for the axis of possible clusterangular momentum. All the discovered binaries are hard enough to surviveaverage close encounters within the cluster and do not yet show signs ofrelaxation of the orbital elements to values typical of field binaries.Table 2 is only available in electronic form athttp://www.edpsciences.orgTable 4 is only available in electronic form at the CDS via anonymousftp to cdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/415/145
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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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Vilnius Photometry and Reddening of the Young Open Cluster NGC 6913
87 stars in the NGC 6913 field with both UBV and Vilnius photometry areselected to be the sample. The membership probability of the stars isgreater than 50%. The correlation among Vilnius photometry, UBVphotometry and reddening in the cluster is reviewed. It is found thatthe photometry in the Vilnius X, Y and Z bands can be used to make roughspectral classification. The values of E(B-V) are well correlated withthe Vilnius colors of X-Y, Y-Z, Z-V and V-S in NGC 6913. The ratio of(V-S)/(Y-Z) of the MPCM (Most Possible Cluster Members) is a constant(1.30 ~ ± 0.06), and has no effect on the values of E(B-V), (B-V)_0and V_0. Comparing with the observational data of all the stars of NGC6913 region, we propose that the value of (V-S)/(Y-Z) can probably beused to select the preliminary candidates of one open cluster. Inaddition, 12 variable stars are discovered in the NGC 6913 region, inwhich star #155 has a variation with an amplitude of 4.25 mag.
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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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Spectral classification and reddening in the young open cluster NGC 6913
Spectroscopic observations have been made for the young open cluster NGC6913. In total, the spectra of 100 stars of the cluster, havingmembership probability greater than 50%, have been obtained andclassified. Reddening is estimated on the basis of spectralclassification. The variable extinction across NGC 6913 is analyzed anddiscussed. From the spectroscopic observations, it is found that thespectral type distribution in our sample covers from O7 to K3. There areonly 2 O-type stars in this OB association. 40 and 33 percent of thetotal stars are B and A type stars respectively, and the F, G, K starsamount to 25 percent. An extreme variation of extinction is found acrossthe young open cluster NGC 6913. The distribution of extinction in theregion is correlated with the effective temperature of the stars forstars earlier than F8. It is found that extinction in the cluster centeris relatively homogeneous, but very large. The north and south of thiscluster have the largest extinction. The eastern and western parts seemto be low reddening regions. A mean distance modulus of 10.17+/-0.14mag. is derived for the cluster, which corresponds to a distance of 1.08kpc. A large part of the values of interstellar reddening of the starsin NGC 6913 from spectral classification are quite different from thosetaken from photometry (especially for early B and F type stars); thelargest discrepancy amounts to 1.48 mag.. Depending on a reddeningmethod, a total amount of 30% of the stars with membership probabilitygreater than 50% can be evaluated to be probable ``non-members" of thecluster. In addition, some interesting objects are found in this study.Further observations for these stars will be made in the future.
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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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More radial-velocity measurements in young open clusters
Further high resolution radial-velocity measurements are reported in 23young open clusters using the Kitt Peak CCD coude spectrograph on the0.9-m feed telescope. The radial velocities for the cluster stars arederived with the technique of cross correlation. The internal precisionof the velocity measurements is typically 2 km/s for early type stars.From these new data and previously published velocities, the observedstars in two clusters, NGC 663 and NGC 2287, were found to show arelatively small dispersion in the measured mean velocities. Furtherobservations of stars in young clusters will be useful in helping toestablish an early-type-star-velocity standard system.
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The upper main sequence of OB associations. II - The single-lined O stars: Spectral classification of northern stars and lines of C and N
The properties of the stars close to the upper main sequence of OBassociations are studied in order to provide constraints on the theoryof evolution of massive stars. The spectral classification of northernsingle-lined O stars, most of them belonging to the associations CygOB1, Per OB1 and Cas OB6, is presented. The classification is performedaccording to Conti's classification scheme for O stars, amended byMathys (1988). The behavior of the C and N lines of the stars isstudied, in order to determine whether CNO-processed material is visibleat their surface. Three new ON stars have been discovered: BD + 36 deg4063 (O9.71), HD 13268 (O8V), and HD 110360 (O7V).
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Radial-velocity measurements in 20 young open clusters
The further results of a program to determine the radial velocities ofyoung open clusters are presented. Using the KPNO coude spectrographcoupled with the 1-m feed and 2.1-m telescopes, radial velocities havebeen measured for nearly one hundred stars, most of which are ofspectral type B and A, in 20 young clusters. The combination ofinstruments and the use of cross-correlation techniques show that radialvelocities of B and A type stars as faint as 10th magnitude can bedetermined with an internal precision of less than about 2 km/s. Asexpected, the uncertainties in the velocity determination for the youngclusters are dominated by spectroscopic binary stars in these clusters.A third of the stars in the sample are found to be spectroscopicbinaries, but with a large variation in the frequency of binaries fromcluster to cluster. Because the time coverage is still limited, thisshould be considered a lower limit to the binary frequency. Clustervelocities are determined after eliminating binaries and known nonmemberstars. The new velocities are compared with a model galactic rotationcurve, as well as with previous velocity determinations.
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Not Available
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Photoelectric Photometry of Stars in the Vilnius System in the Region of the Open Cluster NGC6913 = M29
Not Available
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Distribution of OB stars and absorbing matter in the region around P CYG
The results of spectrophotometric observations of 277 OB stars in a 7 x7-deg region around P Cyg, obtained in 8-sec, 45-sec, and 8-minexposures on ORWO ZU-21 plates with a 4-deg 272-A/mm-dispersionobjective prism on the 40-in. Schmidt telescope at BiurakanAstrophysical Observatory on October 14-19, 1979, are presented intables and graphs and characterized. Data reported include 400-480-nmabsolute spectrophotometric gradients, color excesses, and distances. Itis found that concentrations of OB stars with associated absorbingmatter exist toward the associations Cyg OB9 (two concentrations at 800and 1800 pc), Cyg OB3 (three concentrations at 1.4, 2.5, and 3.7 kpc),OB1 (at 1.6 kpc), Cyg OB8 (at 1.5 kpc), and over the entire observedregion at a distance of about 500 pc.
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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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Photometry of the open cluster NGC 6913
Photoelectric UBV magnitudes and colors have been determined for 103stars in the field of NGC 6913. The reddening across the cluster isvariable. The distance modulus to the cluster is estimated at 10.85 + or- 0.15 mag. It is found that cluster stars have ages between 0.3 and1.75 Myr.
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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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Four-color and H-beta photometry of open clusters. XII - NGC 6910 and NGC 6913
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1977AJ.....82..606C&db_key=AST
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Evolved stars in open clusters.
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1976ApJS...30..451H&db_key=AST
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Membership of the open cluster NGC 6913 (M29)
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1973A&AS....9..221S&db_key=AST
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Variable Stars in the Galactic Cluster NGC 6913
Not Available
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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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Hot Stars with Excess Reddening in the Cluster NGC 6913.
Not Available
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Spectral Types and Hγ Observations for Stars in Eight Associations
Not Available
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Distance Moduli of Open Clusters.
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1965ApJS...12..215H&db_key=AST
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Kinematic studies of early-type stars. I. Photometric survey, space motions, and comparison with radio observations.
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1962AJ.....67..491R&db_key=AST
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Photometry of stars in galactic cluster fields.
Not Available
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INHABITED SKY
