The Two Young Star Disks in the Central Parsec of the Galaxy: Properties, Dynamics, and Formation
We report the definite spectroscopic identification of ~=40 OBsupergiants, giants, and main-sequence stars in the central parsec ofthe Galaxy. Detection of their absorption lines has become possible withthe high spatial and spectral resolution and sensitivity of the adaptiveoptics integral field spectrometer SPIFFI/SINFONI on the ESO VLT.Several of these OB stars appear to be helium- and nitrogen-rich. Almostall of the ~=80 massive stars now known in the central parsec (centralarcsecond excluded) reside in one of two somewhat thick(~=0.14) rotating disks. These stellar disks have fairlysharp inner edges (R~=1'') and surface density profiles thatscale as R-2. We do not detect any OB stars outside thecentral 0.5 pc. The majority of the stars in the clockwise system appearto be on almost circular orbits, whereas most of those in the``counterclockwise'' disk appear to be on eccentric orbits. Based on itsstellar surface density distribution and dynamics, we propose that IRS13E is an extremely dense cluster(?core>~3×108 Msolarpc-3) that has formed in the counterclockwise disk. Thestellar contents of both systems are remarkably similar, indicating acommon age of ~=6+/-2 Myr. The K-band luminosity function of the massivestars suggests a top-heavy mass function and limits the total stellarmass contained in both disks to ~=1.5×104Msolar. Our data strongly favor in situ star formation fromdense gas accretion disks for the two stellar disks. This conclusion isvery clear for the clockwise disk and highly plausible for thecounterclockwise system.Based on observations with the Very Large Telescope of the EuropeanSouthern Observatory, Paranal, Chile.
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Interstellar Ca II Line Intensities and the Distances of the OB stars
We show that the equivalent widths of the well-known interstellar Ca IIH and K lines can be used to determine the distances to OB stars in ourGalaxy. The equivalent widths, measured in the spectra of 147 early-typestars, are strongly related to the Hipparcos parallaxes of thoseobjects. The lines fitted to the parallax-equivalent width data aregiven by the formulae π=1/[2.78EW(K)+95] and π=1/[4.58EW(H)+102],where π is in arcseconds and EW is in milliangstroms. The form of theformulae, yielding a finite parallax even for zero absorption, showsthat space within ~100 pc of the Sun contains very little Ca II, whichis in agreement with the known dimensions of the Local Bubble. Using CaII lines for distance determination does not require the knowledge ofthe absolute magnitude of the object; it is thus well suited for targetsfor which the absolute calibration is either not precise (OBsupergiants) or not available at all (peculiar objects). We alsodemonstrate that neither the reddening E(B-V) nor the equivalent widthsof interstellar K I and CH lines are suitable candidates for distanceestimation, their relation with parallaxes being far less tight than forCa II.
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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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A Galactic O Star Catalog
We have produced a catalog of 378 Galactic O stars with accuratespectral classifications that is complete for V<8 but includes manyfainter stars. The catalog provides cross-identifications with othersources; coordinates (obtained in most cases from Tycho-2 data);astrometric distances for 24 of the nearest stars; optical (Tycho-2,Johnson, and Strömgren) and NIR photometry; group membership,runaway character, and multiplicity information; and a Web-based versionwith links to on-line services.
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A study of RV in Galactic O stars from the 2MASS catalogue
We present new measurements of the interstellar reddening parameterRV=AV/E(B-V) towards 185 O stars, using J, H,Ks photometry from the 2MASS project. The results arecombined with data from the literature of 95 stars where RVhas been derived with the same technique, 22 of which in common with ourpresent sample from the 2MASS project catalogue. The averageRV from these 258 O stars is of 3.19 +/- 0.50. All objectswhose RV departs from this value by more than 2 sigma havebeen recognized. Ten objects have RV higher than this valueand two lower. It is found that anomalous RV can scarcely beassociated with anomalies in the general interstellar medium, e.g. withdifferent behaviour in different spiral arms. They are clearly linked tolocal cloud effect. In the Cygnus region RV values follow thebehaviour of the general interstellar medium, while in the Carina arm,in spite of the relatively larger distance, local cloud effects prevail.An explanation for this is suggested. The relatively few stars of oursample whose Hipparcos parallaxes are reliable, are found to havedistances systematically smaller than the distances derived by thespectroscopic parallaxes. We argue that this effect is consistent withthe recently claimed discovery of grey extinction towards OB stars.This publication makes use of data products from the Two Micron All SkySurvey (2MASS), which is a joint project of the University ofMassachusetts and the Infrared Processing and Analysis Center/CaliforniaInstitute of Technology, funded by the National Aeronautics and SpaceAdministration and the National Science Foundation.Tables 1 and 2 are only available in electronic form at the CDS viaanonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/410/905
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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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Digital Spectroscopy of O3-O5 and ON/OC Supergiants in Cygnus
High signal-to-noise, optical digital classification spectrograms ofthree northern very early O supergiants and four late O supergiants withCNO anomalies are illustrated and discussed. Several of theseexceptional objects either are the prototypes of their classes,originally discovered photographically, or are unique representatives ofthem in the northern hemisphere. The full blue-violet and yellow-redspectrum of the extreme ON supergiant BD +36°4063, discovered by G.Mathys with limited wavelength coverage, is shown for the first time.Extensive line identifications are provided, and the high quality ofthese data reveals numerous new absorption and emission featurescorresponding either to the high ionization in the case of the veryearly objects, or to the chemical abundance anomalies in the later ones.These data provide standards for digital classification of relatedobjects in the north and guidance for subsequent astrophysical analyseswith higher spectral resolution.
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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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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.
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A Spectral Atlas of Hot, Luminous Stars at 2 Microns
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1996ApJS..107..281H&db_key=AST
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The Peculiar Population of Hot Stars at the Galactic Center
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1996ApJ...456..206T&db_key=AST
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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 Diffuse Ionized Interstellar Medium: Structures Resulting from Ionization by O Stars
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1993ApJ...417..579M&db_key=AST
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Massive close binaries - Observations and evolutionary computations
An overview of research on massive close binary (MCB) evolution in thelate seventies and eighties is presented, and the processes involved inmassive close binaries are explained. The following aspects of the MCBevolution study are considered: definition and types; observations ofnon-evolved and evolved MCB; physical processes; and stellar wind massloss rates and convective core overshooting. A comparison between MCBobservations and evolutionary computations is made. For futuredevelopments of stellar evolution, physical studies and the determinatonof adequate abundances of carbon, oxygen and nitrogen of stars coveringthe whole massive star range are recommended.
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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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UBV photoelectric catalogue (1986). II - Analysis
The UBV photoelectric data of the stars presenting several entries inthe 1986 edition of the UBV catalog have been systematicallyintercompared, and this paper presents a discussion of the stars forwhich discrepancies larger than 0.2 mag were found. Thirty-six probablyvariable stars have been detected, among which 18 are Be stars. Sixtyfurther stars present differences in the V magnitude larger than 0.2mag. Sixteen stars already appear in the NSV catalog. Although manyproblems are probably due to poor observations, new (eclipsing) variablestars may be found in this sample. Complete disagreement is foundbetween the values published from two independent sources in 34 cases. Afirst analysis of the quality of the UBV data shows that 65 percent ofthe differences in the V magnitude and in U-B color, for respectively11,500 and 7200 stars with two sources of data, are smaller than 0.04.The scatter on the B-V index appears to be smaller, since the samepercentage reaches 79 percent.
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UBV Photoelectric Photometry Catalogue (1986). III Errors and Problems on DM and HD Stars
Not Available
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Four-colour and H-beta photometry of blue stars selected from a balloon-ultraviolet survey and other sources
New uvby and/or H-beta photometry is obtained at the Chiranhigh-altitude outstation for 105 stars. Certain of the program stars areselected from a comparison of the SCAP 2000 balloon-ultraviolet skysurvey of the Laboratoire d'Astronomie Spatiale with the correspondingblue and red prints of the Palomar Observatory sky survey. Only a smallportion of these stars turn out to be B stars, whereas, the rest of thestars, which are selected from a variety of other sources, are mostly Bstars and if of normal luminosity are in many cases many Population Iscale heights from the galactic plane. It is shown that theidentification of B stars is practicable only at a good observing siteand that if H-beta photometry is also obtained, sdOB, sdB, and hothorizontal branch B stars can be distinguished from normal stars bytheir position in the beta/c(0) diagram.
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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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Nitrogen anomalies in O-type stars - A new spectroscopic criterion
A spectroscopic analysis was performed on 95 O-type stars to detectnitrogen overabundance in an investigation of spectroscopic criteria. Itis found that the N III 4514 A line is a good indicator of the abundancevariations of N in O-type stars, and it is suggested that the ONphenomenon is a continuous one rather than a marked discontinuitybetween normal O stars and those showing nitrogen overabundance.Anomalies are investigated for several early O stars, and it isconcluded that mass transfer in close binary systems and high mass lossrates due to stellar winds are the most probable mechanisms to produceON stars.
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H-beta photometry of northern intermediate galactic latitude early-type stars and galactic structure away from the plane
Photoelectric H-beta photometry is presented for 255 early-type stars atintermediate galactic latitudes. Absolute magnitudes and distances arederived for the more luminous stars. Those with visual magnitudes lessthan or equal to 2.5 and at distances of up to 1 kpc from the galacticplane may follow the spiral structure in the plane.
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On the origin of intermediate-latitude OB stars
An attempt is made to trace the origin of early-type stars observed atappreciable distances from the galactic plane. Because uncertainties inthe proper motions make space motions and hence dynamical lifetimesrather inaccurate, a theory of oscillations normal to the plane has beenused to compute radial velocities for 138 intermediate-latitude OBstars. These theoretical values are then compared with the observedradial velocities, and it is found that the low-velocity stars wereprobably ejected from the plane some time after formation, while thehigh-velocity stars were ejected very soon after formation. Velocitiesof ejection perpendicular to the plane are computed and show a narrowdistribution with a mean absolute value of 7 km/s together with a spreadof velocities from about 40 to over 200 km/s. The data are in reasonableagreement with a 'sling' effect and 'runaway' origin for the stars inthe sample.
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The binary frequency of the OBN and OBC stars
Radial velocity measurements for a class of early-type stars havingeither enhanced carbon or nitrogen line strengths (termed OBCN stars)are undertaken to evaluate the binary frequency of the OBN and OBCsubgroups. Between 50 and 100% of the OBN stars appear to beshort-period binaries, while none of the OBC stars fall into thiscategory. Mass-transfer evolution in binary systems may thus offer areasonable explanation for the abundance anomalies exhibited by the OBNstars. The possibility that the OBN and OBC stars are kinematicallydistinct subgroups is also discussed.
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UBV photometry and MK spectral classification of northern early-type stars at intermediate galactic latitudes
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1977MNRAS.180..691H&db_key=AST
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The OBn and OBc stars.
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1976ApJ...205..419W&db_key=AST
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The CNO stars
This paper deals with those peculiar B-type stars which exhibitanomalies in the behavior of the light elements. Based upon a discussionof published and new observational material, it is shown that a largefraction exhibits evidence of changes in the spectrum. This resultthrows doubt upon the reality of a proposed subdivision of the starsinto a C-rich and an N-rich group. A summary of the spectrum variationsis provided. The analysis of the photometry, the radial velocity and therotational velocities shows that the stars are concentrated in a smallrange of U-B colors, that the generally exhibit variable radial velocityand show rotation. A discussion of related groups of stars shows thatthere exists no solution of continuity with other groups exhibitinganomalies in helium and other light elements.
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A catalogue of galactic O stars. The ionization of the low density interstellar medium by runaway stars.
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1974RMxAA...1..211C&db_key=AST
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A new determination from OB stars of the galactic rotation constants and the distance to the galactic centre.
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1974MNRAS.167..621B&db_key=AST
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A new general O type stars catalogue
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1973A&AS...12..277G&db_key=AST
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The high-luminosity boundary of the beta CEP instability strip.
Abstract image available at:http://adsabs.harvard.edu/abs/1972AJ.....77..381P
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INHABITED SKY
