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Pulkovo compilation of radial velocities for 35495 stars in a common system.
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| Non-LTE abundances of magnesium, aluminum and sulfur in OB stars near the solar circle
Non-LTE abundances of magnesium, aluminum and sulfur are derived for asample of 23 low-v sin i stars belonging to six northern OBassociations of the Galactic disk within 1 kpc of the Sun. Theabundances are obtained from the fitting of synthetic line profiles tohigh resolution spectra. A comparison of our results with HII regionabundances indicates good agreement for sulfur while the cepheidabundances are higher. The derived abundances of Mg show good overlapwith the cepheid results. The aluminum abundances for OB stars aresignificantly below the cepheid values. But, the OB star results show adependence with effective temperature and need further investigation.The high Al abundances in the cepheids could be the result of mixing. Adiscussion of the oxygen abundance in objects near the solar circlesuggests that the current mean galactic oxygen abundance in this regionis 8.6-8.7 and in agreement with the recently revised oxygen abundancein the solar photosphere. Meaningful comparisons of the absolute S, Aland Mg abundances in OB stars with the Sun must await a reinvestigationof these elements with 3D hydrodynamical model atmospheres for the Sun.No abundance gradients are found within the limited range ingalactocentric distances in the present study. Such variations would beexpected only if there were large metallicity gradients in the disk.
| Chemical Abundances of OB Stars with High Projected Rotational Velocities
Elemental abundances of carbon, nitrogen, oxygen, magnesium, aluminum,and silicon are presented for a sample of 12 rapidly rotating OB star(vsini>60kms-1) members of the Cep OB2, Cyg OB3, and CygOB7 associations. The abundances are derived from spectrum synthesis,using both LTE and non-LTE calculations. As found in almost all previousstudies of OB stars, the average abundances are slightly below solar, byabout 0.1 to 0.3 dex. In the case of oxygen, even with the recentlyderived low solar abundances, the OB stars are closer to, but stillbelow, the solar value. Results for the nine Cep OB2 members in thissample can be combined with results published previously for eight CepOB2 stars with low projected rotational velocities to yield the mostcomplete set of abundances, to date, for this particular association.These abundances provide a clear picture of both the general chemicaland individual stellar evolution that has occurred within thisassociation. By placing the Cep OB2 stars studied in an HR-diagram weidentify the presence of two distinct age subgroups, with both subgroupshaving quite uniform chemical abundances. Two stars are found in theolder subgroup that show significant N/O overabundances, with both starsbeing two of the most massive, the most evolved, and the most rapidlyrotating of the members studied in Cep OB2. These characteristics ofincreased N abundances being tied to high mass, rapid rotation, and anevolved phase are those predicted from models of rotating stars thatundergo rotationally driven mixing.
| Chemical Abundances of OB Stars in the Cepheus OB2 Association
LTE and non-LTE abundances of carbon, nitrogen, oxygen, and silicon, aswell as LTE abundances of Fe, are presented from analyses of C II, N II,O II, Si III, and Fe III lines in the spectra of eight main-sequence OBstars in the Cep OB2 association. We find that the chemical compositionof the studied stars in this association is very homogeneous: theabundances of all elements analyzed do not show significant variations,and the observed abundance dispersions can be explained in terms of theuncertainties in the analysis. The abundance results indicate that thisassociation is slightly metal poor ([Fe/H]=-0.3) with the abundances ofall studied elements being subsolar by roughly the same amount.
| A HIPPARCOS Census of the Nearby OB Associations
A comprehensive census of the stellar content of the OB associationswithin 1 kpc from the Sun is presented, based on Hipparcos positions,proper motions, and parallaxes. It is a key part of a long-term projectto study the formation, structure, and evolution of nearby young stellargroups and related star-forming regions. OB associations are unbound``moving groups,'' which can be detected kinematically because of theirsmall internal velocity dispersion. The nearby associations have a largeextent on the sky, which traditionally has limited astrometricmembership determination to bright stars (V<~6 mag), with spectraltypes earlier than ~B5. The Hipparcos measurements allow a majorimprovement in this situation. Moving groups are identified in theHipparcos Catalog by combining de Bruijne's refurbished convergent pointmethod with the ``Spaghetti method'' of Hoogerwerf & Aguilar.Astrometric members are listed for 12 young stellar groups, out to adistance of ~650 pc. These are the three subgroups Upper Scorpius, UpperCentaurus Lupus, and Lower Centaurus Crux of Sco OB2, as well as VelOB2, Tr 10, Col 121, Per OB2, alpha Persei (Per OB3), Cas-Tau, Lac OB1,Cep OB2, and a new group in Cepheus, designated as Cep OB6. Theselection procedure corrects the list of previously known astrometricand photometric B- and A-type members in these groups and identifiesmany new members, including a significant number of F stars, as well asevolved stars, e.g., the Wolf-Rayet stars gamma^2 Vel (WR 11) in Vel OB2and EZ CMa (WR 6) in Col 121, and the classical Cepheid delta Cep in CepOB6. Membership probabilities are given for all selected stars. MonteCarlo simulations are used to estimate the expected number of interloperfield stars. In the nearest associations, notably in Sco OB2, thelater-type members include T Tauri objects and other stars in the finalpre-main-sequence phase. This provides a firm link between the classicalhigh-mass stellar content and ongoing low-mass star formation. Detailedstudies of these 12 groups, and their relation to the surroundinginterstellar medium, will be presented elsewhere. Astrometric evidencefor moving groups in the fields of R CrA, CMa OB1, Mon OB1, Ori OB1, CamOB1, Cep OB3, Cep OB4, Cyg OB4, Cyg OB7, and Sct OB2, is inconclusive.OB associations do exist in many of these regions, but they are eitherat distances beyond ~500 pc where the Hipparcos parallaxes are oflimited use, or they have unfavorable kinematics, so that the groupproper motion does not distinguish it from the field stars in theGalactic disk. The mean distances of the well-established groups aresystematically smaller than the pre-Hipparcos photometric estimates.While part of this may be caused by the improved membership lists, arecalibration of the upper main sequence in the Hertzsprung-Russelldiagram may be called for. The mean motions display a systematicpattern, which is discussed in relation to the Gould Belt. Six of the 12detected moving groups do not appear in the classical list of nearby OBassociations. This is sometimes caused by the absence of O stars, but inother cases a previously known open cluster turns out to be (part of) anextended OB association. The number of unbound young stellar groups inthe solar neighborhood may be significantly larger than thoughtpreviously.
| Origin and Evolution of the Cepheus Bubble
We have imaged a 10 deg x 10 deg region of the Cepheus bubble in the J =1-0 line of CO and the 21 cm line of atomic hydrogen. The CO emissiondefines a giant expanding shell 120 pc in diameter, which is similar tothat seen in the IRAS sky maps. We estimate the total gas mass in theregion to be ~4 x 10^5 M_ȯ. The total kinetic energy from theobserved spread of velocities of the molecular clouds is ~10^51 ergs. Wesuggest that the members of earlier generations of massive stars in NGC7160 are responsible for the origin of the Cepheus bubble. These starscreated an expanding compressed shell of gas that became gravitationallyunstable at an age of ~7 Myr. The members of the Cepheus OB2 associationcomprise the second, intermediate generation of stars in this regionthat formed as a consequence of this instability. The numerous colorselected IRAS point sources represent the third and youngest generationof stars in this region. Our observations suggest the great importanceof sequentially triggered star formation in the region of the Cepheusbubble.
| On the normal energy distribution in stellar spectra: O5-O8 stars
The spectral energy curves for a number of O4-O8 stars are analyzedusing measurements taken from six sources of spectrophotometric data.Based on the normal UBV color indices for O stars, these stars aredivided into three groups (O5, O6-O7, and O8), for each of which thenormal energy distribution is derived and presented. Comparison of thesedistributions indicates clear differences between the O5 and O8subclasses at UV wavelengths. A single normal distribution curve is,therefore, insufficient to characterize the O spectral class as a whole.
| A Search for Pulsar Companions to OB Runaway Stars
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1996ApJ...461..357S&db_key=AST
| 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 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
| 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.
| New spectral classifications for O-type stars in the Northern Hemisphere
In order to update the classifications of O and B stars in the vicinityof the sun, moderate-resolution spectra have been obtained in thewavelength region about 4000 A to about 5000 A of 32 O and B starswithout published luminosity classifications. Normalized spectra andrevised spectral classifications are presented. Two of the stars arefound to be members of the O3 spectral class.
| 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.
| UBV Photoelectric Photometry Catalogue (1986). III Errors and Problems on DM and HD Stars
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| X-ray observations of the runaway stars HD 206327 and 26 Cephei and of the Lambda-1 Orionis region
Observations made with the IPC on the HEAO 2 satellite (EinsteinObservatory) are reported for the runaway OB-type stars HD 206327 and 26Cephei and also of the Lambda-1 Orionis region. Only upper limits forthe X-ray emissions from the two runaway stars were determined. Assumingboth of these stars to have compact stellar companions, then theselimits, when combined with a suitable model, predict that both systemsshould have orbital periods greater than about 150 days and possiblyranging up into years. Moreover, a single imaging proportional counter(IPC) observation of the region centered on Lambda-1 Orionis has foundfive serendipitous X-ray sources. An astrometric and photometric studyof this region provides evidence that these sources are probable membersof the association. The inferred luminosities range from 5 x 10 to the30th to 5 x 10 to the 31st ergs/s. Two of the sources are identifiedwith normal OB stars, and the others are most likely pre-main-sequencestars that have evolved from T Tauri stars and will be soon burninghydrogen in their cores.
| Spectrophotometric investigation of OB stars in the region of the association CEP OB2
The results are given of spectrophotometric investigation of 39 OB starsin the region of the association Cep OB2. The blue (4000-4800 A)absolute spectrophotometric gradients, the color excesses in the UBVsystem, and the distances of these stars have been determined. Analysisof the results suggests that the absorbing material is basicallyconcentrated within the association itself.
| 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.
| 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.
| 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.
| Mean secular parallax at low galactic latitude
Very accurate relative proper motions are determined for 1332 stars in62 regions at very low galactic latitude (less than 10 deg in absolutevalue). These data are supplemented with 27 additional regions of propermotions of faint stars in the directions of open clusters, and astatistical analysis of all these motions is performed to determine theposition of the solar apex for faint stars and to calibrate the meansecular parallax at low galactic latitude. It is found that the apex forfaint stars is near the basic solar apex and that the parallaxcalibration confirms the smaller values previously obtained on the basisof a much smaller sample of proper-motion regions. This calibration isused to determine the peculiar space motions of O stars in the solarneighborhood, from which motions are computed the semimajor axes andvertex direction of the O-star velocity ellipsoid. The results show thatthe vertex direction is into the fourth velocity quadrant, that 20% ofthe O stars are runaways, and that most O stars were probably born nearthe galactic plane.
| 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
| 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
| A Spectroscopic and Photometric Investigation of the Association Cepheus OB2
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1968ApJ...154..923S&db_key=AST
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