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B Star Rotational Velocities in h and χ Persei: A Probe of Initial Conditions during the Star Formation Epoch?
Projected rotational velocities (vsini) have been measured for 216 B0-B9stars in the rich, dense h and χ Persei double cluster and comparedwith the distribution of rotational velocities for a sample of fieldstars having comparable ages (t~12-15 Myr) and masses (M~4-15Msolar). For stars that are relatively little evolved fromtheir initial locations on the zero-age main sequence (ZAMS) (those withmasses M~4-5 Msolar), the mean vsini measured for the h andχ Per sample is slightly more than 2 times larger than the meandetermined for field stars of comparable mass, and the cluster and fieldvsini distributions differ with a high degree of significance. Forsomewhat more evolved stars with masses in the range 5-9Msolar, the mean vsini in h and χ Per is 1.5 times thatof the field; the vsini distributions differ as well, but with a lowerdegree of statistical significance. For stars that have evolvedsignificantly from the ZAMS and are approaching the hydrogen exhaustionphase (those with masses in the range 9-15 Msolar), thecluster and field star means and distributions are only slightlydifferent. We argue that both the higher rotation rates and the patternof rotation speeds as a function of mass that differentiatemain-sequence B stars in h and χ Per from their field analogs werelikely imprinted during the star formation process rather than a resultof angular momentum evolution over the 12-15 Myr cluster lifetime. Wespeculate that these differences may reflect the effects of the higheraccretion rates that theory suggests are characteristic of regions thatgive birth to dense clusters, namely, (1) higher initial rotationspeeds; (2) higher initial radii along the stellar birth line, resultingin greater spin-up between the birth line and the ZAMS; and (3) a morepronounced maximum in the birth line radius-mass relationship thatresults in differentially greater spin-up for stars that become mid- tolate-B stars on the ZAMS.
| Emission lines in the optical spectrum of 3 Cen A
Previously, weak emission lines had been detected at red wavelengths inthe spectra of a limited sample of mid to late B type main sequencestars. A fuller description of the occurrence and origins of these lineshas yet to be forwarded, in part due to the lack of observationsdetailing the spectral transitions involved. To address this deficiency,we present a line list of weak emission features found in the opticaland near infrared spectral region of the chemically peculiar He-weakstar 3 Cen A (HD 120709). Nearly 350 features, mostly associated withallowed transitions from high-excitation states of first ions, arecatalogued along with identifications. Prominent among the emissionlines are the spectra P II, Mn II, Fe II, Ni II and Cu II. Emissionlines from Ca II, Si II and Hg II are also evident. Abundances aredetermined for several elements from synthetic spectrum fitting, withanomalies detected for the ions O I/II, P II/III and Si II/III. The LTEsynthetic spectrum fitting also revealed that the low excitation 4s-4ptransitions of Fe II predict an abundance that is greater than thatdetermined from higher excitation 4d-4f transitions. Several of theselatter transitions have upper energy levels that are found to beassociated with emission lines. We also present empirical considerationsfor the excitation processes leading to the weak emission lines.Based on observations obtained at the European Southern Observatory, LaSilla, Chile, No. 65.L-0316 and Paranal, Chile No. 266.D-5655.Tables 2 and 3 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/418/1073
| Rotational Velocities of B Stars
We measured the projected rotational velocities of 1092 northern B starslisted in the Bright Star Catalogue (BSC) and calibrated them againstthe 1975 Slettebak et al. system. We found that the published values ofB dwarfs in the BSC average 27% higher than those standards. Only 0.3%of the stars have rotational velocities in excess of two-thirds of thebreakup velocities, and the mean velocity is only 25% of breakup,implying that impending breakup is not a significant factor in reducingrotational velocities. For the B8-B9.5 III-V stars the bimodaldistribution in V can be explained by a set of slowly rotating Ap starsand a set of rapidly rotating normal stars. For the B0-B5 III-V starsthat include very few peculiar stars, the distributions in V are notbimodal. Are the low rotational velocities of B stars due to theoccurrence of frequent low-mass companions, planets, or disks? Therotational velocities of giants originating from late B dwarfs areconsistent with their conservation of angular momentum in shells.However, we are puzzled by why the giants that originate from the earlyB dwarfs, despite having 3 times greater radii, have nearly the samerotational velocities. We find that all B-type primaries in binarieswith periods less than 2.4 days have synchronized rotational and orbitalmotions; those with periods between 2.4 and 5.0 days are rotating withina factor 2 of synchronization or are ``nearly synchronized.'' Thecorresponding period ranges for A-type stars are 4.9 and 10.5 days, ortwice as large. We found that the rotational velocities of the primariesare synchronized earlier than their orbits are circularized. The maximumorbital period for circularized B binaries is 1.5 days and for Abinaries is 2.5 days. For stars of various ages from 107.5 to1010.2 yr the maximum circularized periods are a smoothexponential function of age.
| Catalogue of Apparent Diameters and Absolute Radii of Stars (CADARS) - Third edition - Comments and statistics
The Catalogue, available at the Centre de Données Stellaires deStrasbourg, consists of 13 573 records concerning the results obtainedfrom different methods for 7778 stars, reported in the literature. Thefollowing data are listed for each star: identifications, apparentmagnitude, spectral type, apparent diameter in arcsec, absolute radiusin solar units, method of determination, reference, remarks. Commentsand statistics obtained from CADARS are given. The Catalogue isavailable in electronic form at the CDS via anonymous ftp tocdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcar?J/A+A/367/521
| Surface abundances of light elements for a large sample of early B-type stars - I. Spectral observations of 123 stars; measurements of hydrogen and helium lines; infrared photometry
High-resolution spectral observations of 123 B0-B5 stars in the mainsequence evolutionary phase were obtained at two observatories, namelythe McDonald Observatory (McDO) and the Crimean AstrophysicalObservatory (CrAO). Accurate equivalent widths W of two Balmer lines,Hβ and Hγ, and ten Hei lines were obtained for all the stars,as well as of the Heiiλ4686 line for the hottest ones. A carefulanalysis of the measured equivalent widths was performed. It is shownthat there is a very good agreement between the W values derived fromthe McDO and CrAO spectra for 14 common stars. A comparison withpublished data leads to the conclusion that the W values measuredearlier by some authors for strong Hei lines are very likely to beunderestimated. Infrared photometric observations in the J, H, and Kbands were performed for 70 programme stars. All these data will be usedin other papers: in particular for the Teff and loggdetermination and for the He, C, N and O abundance analyses.
| Search for the 3He isotope in the atmospheres of HgMn stars
No abstract submitted
| Photometric Separation of Stellar Properties Using SDSS Filters
Using synthetic photometry of Kurucz model spectra, we explore thecolors of stars as a function of temperature, metallicity, and surfacegravity with Sloan Digital Sky Survey (SDSS) filters, u'g'r'i'z'. Thesynthetic colors show qualitative agreement with the few publishedobservations in these filters. We find that the locus of synthetic starsis basically two-dimensional for 4500 < T < 8000 K, whichprecludes simultaneous color separation of the three basic stellarcharacteristics we consider. Colors including u' contain the mostinformation about normal stellar properties; measurements in this filterare also important for selecting white dwarfs. We identify two differentsubsets of the locus in which the loci separate by either metallicity orsurface gravity. For 0.5 < g' - r' < 0.8 (corresponding roughly toG stars), the locus separates by metallicity; for photometric error of afew percent, we estimate metallicity to within ~0.5 dex in this range.In the range -0.15 < g' - r' < 0.00 (corresponding roughly to Astars), the locus shows separation by surface gravity. In both cases, weshow that it is advantageous to use more than two colors whendetermining stellar properties by color. Strategic observations in SDSSfilters are required to resolve the source of a ~5% discrepancy betweensynthetic colors of Gunn-Stryker stars, Kurucz models, and externaldeterminations of the metallicities and surface gravities. The syntheticstar colors can be used to investigate the properties of any normal starand to construct analytic expressions for the photometric prediction ofstellar properties in special cases.
| The HR-diagram from HIPPARCOS data. Absolute magnitudes and kinematics of BP - AP stars
The HR-diagram of about 1000 Bp - Ap stars in the solar neighbourhoodhas been constructed using astrometric data from Hipparcos satellite aswell as photometric and radial velocity data. The LM method\cite{luri95,luri96} allows the use of proper motion and radial velocitydata in addition to the trigonometric parallaxes to obtain luminositycalibrations and improved distances estimates. Six types of Bp - Apstars have been examined: He-rich, He-weak, HgMn, Si, Si+ and SrCrEu.Most Bp - Ap stars lie on the main sequence occupying the whole width ofit (about 2 mag), just like normal stars in the same range of spectraltypes. Their kinematic behaviour is typical of thin disk stars youngerthan about 1 Gyr. A few stars found to be high above the galactic planeor to have a high velocity are briefly discussed. Based on data from theESA Hipparcos astrometry satellite and photometric data collected in theGeneva system at ESO, La Silla (Chile) and at Jungfraujoch andGornergrat Observatories (Switzerland). Tables 3 and 4 are onlyavailable in electronic form at the CDS via anonymous ftp tocdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/Abstract.html
| The ROSAT all-sky survey catalogue of optically bright OB-type stars.
For the detailed statistical analysis of the X-ray emission of hot starswe selected all stars of spectral type O and B listed in the Yale BrightStar Catalogue and searched for them in the ROSAT All-Sky Survey. Inthis paper we describe the selection and preparation of the data andpresent a compilation of the derived X-ray data for a complete sample ofbright OB stars.
| 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.
| Theoretical colours and isochrones for some Hubble Space Telescope colour systems. II
A grid of synthetic surface brightness magnitudes for 14 bandpasses ofthe Hubble Space Telescope Faint Object Camera is presented, as well asa grid of UBV, uvby, and Faint Object Camera surface brightnessmagnitudes derived from the Gunn-Stryker spectrophotometric atlas. Thesynthetic colors are used to examine the transformations between theground-based Johnson UBV and Stromgren uvby systems and the Faint ObjectCamera UBV and uvby. Two new four-color systems, similar to theStromgren system, are proposed for the determination of abundance,temperature, and surface gravity. The synthetic colors are also used tocalculate color-magnitude isochrones from the list of theoretical tracksprovided by VandenBerg and Bell (1990). It is shown that by using theappropriate filters it is possible to minimize the dependence of thiscolor difference on metallicity. The effects of interstellar reddeningon various Faint Object Camera colors are analyzed as well as theobservational requirements for obtaining data of a given signal-to-noisefor each of the 14 bandpasses.
| Empirical temperature calibrations for early-type stars
Three temperature calibrations of suitable photometric quantities havebeen derived for O and B stars. A sample of 120 stars with reliableT(eff.) determinations has been used for establishing each calibration.The different calibrations have been critically discussed and compared.Temperature determinations for 1009 program stars have been obtainedwith an accuracy of the order of 10 percent.
| Energy Distribution in the Stellar Spectra of Different Spectral Types and Luminosities - Part Five - Normal Stars
Not Available
| Nuclear stellar population of NGC 772 (Arp 78).
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1987RMxAA..14..149S&db_key=AST
| Geneva photometric boxes. V - The far-ultraviolet extinction in the solar neighbourhood
Interstellar extinction laws in the wavelength range of 0.136 to 0.274micron have been determined using data for moderately hot stars takenfrom the S2/68 ultraviolet sky survey. Golay's (1980) boxes for stars inboth the Geneva photometry and the S2/68 catalogs were used to obtainpairs of near identical stars. An upper limit to the extinction was setat E(B-V) = 0.150 in order to restrict the study to the diffuse materialin the solar neighborhood. The mean extinction law is in good agreementwith previous determinations derived from more heavily reddened stars.Variations in the shape of the curve are found implying the presence ofat least two components. The 2200 A feature appears to originate fromregions dense in elements heavier than helium.
| The abundance of Gallium in B-type chemically peculiar stars
Quantitative analyses of the Ga abundances in 27 Hg-Mn stars, 11 Si(magnetic) stars, eight He-weak stars, and seven normal stars are madewith the resonance lines of Ga II at 1414 A and Ga III at 1495 A inInternational Ultraviolet Explorer (IUE) spectra. The Ga overabundancesare confirmed as a genuine anomaly in many peculiar stars. Only upperlimits of the Ga abundance can be obtained for some stars. However,these upper limits are much lower than those inferred from visualspectra. Among the 27 Hg-Mn stars, 17 stars are distributed in a rangeof 2.0-3.8 dex of overabundances of Ga. Ten other stars show upperlimits of less than 2.1 dex. Fifteen of the 20 hotter Hg-Mn stars, withTeff greater than 11,000 K, show high overabundances in a narrow rangeof 2.6-3.8 dex, while among seven cooler Hg-Mn stars, only the star HR7775 shows the same overabundance as in the hotter 15 stars. Of 11 Sistars, nine stars have Ga overabundances ranging from 1.9 to 3.2 dex.Gallium is overabundant in five out of eight He-weak stars in the rangeof 1.7-3.2 dex, while in the three other stars the upper limits are lessthan 1.3 dex. The Ga abundances in normal stars are all upper limitswhich roughly correspond to the solar value.
| The local system of early type stars - Spatial extent and kinematics
Published uvby and H-beta photometric data and proper motions arecompiled and analyzed to characterize the structure and kinematics ofthe bright early-type O-A0 stars in the solar vicinity, with a focus onthe Gould belt. The selection and calibration techniques are explained,and the data are presented in extensive tables and graphs and discussedin detail. The Gould belt stars of age less than 20 Myr are shown togive belt inclination 19 deg to the Galactic plane and node-lineorientation in the direction of Galactic rotation, while the symmetricaldistribution about the Galactic plane and kinematic properties (purecircular differential rotation) of the belt stars over 60 Myr oldresemble those of fainter nonbelt stars of all ages. The unresolveddiscrepancy between the expansion observed in the youngest nearby starsand the predictions of simple models of expansion from a point isattributed to the inhomogeneous distribution of interstellar matter.
| Stellar spectrophotometric atlas, wavelengths from 3130 to 10800 A
Over the course of the past 10 years, a large body of homogeneousspectrophotometric data on relatively bright stars has been gathered toserve as a library with which to synthesize galaxy spectra in populationstudies. As the data might be generally useful, they are presented inthree tables. One hundred seventy-five (175) stars were selected, mostfrom the Navy photometric catalog. Covered are complete ranges ofspectral type and luminosity class. Normalized spectral energydistributions of these stars in pictorial form are provided along withtables of calculated colors, scan line and continuum indices, and someinformation on the relation of the scan colors to real photometricsystems.
| Vector Space Methods of Photometric Analysis - Part Three - the Two Components of Ultraviolet Reddening
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1980AJ.....85.1651M&db_key=AST
| Ground-based observations of some stars classified in the satellite ultraviolet with spectral particularities
Spectral classifications based on 80 A/mm plates were obtained for 48stars classified in the UV in order to examine existing discrepancies.Although reclassification generally improves the agreement, there remainseveral cases of significant disagreements.
| Helium-3 in the horizontal-branch star Feige 86
Observations of He I at the wavelength of 6678 A in the bluehorizontal-branch star Feige 86 indicate the presence of He-3 with aHe-3 to He-4 ratio of about 0.7. Feige 86 has an effective temperatureand surface gravity which are very similar to those of the Population IHe-3 stars. This result greatly strengthens the link between thePopulation I Bp stars and the He-weak blue horizontal-branch stars andargues that diffusion is responsible for the He deficiency of bothgroups of stars.
| The helium-3 stars
An investigation was conducted with the objective to examine a sample ofHe-weak stars, as well as some 'normal' stars in the same temperaturerange. A variety of other hot peculiar objects, including Si and Hg-Mnstars, were also observed. The identification of He-3 is made byaccurately measuring the small isotope shifts of the He I lines in thevisible spectrum. The expected isotope shifts for pure He-3 wereprovided by Fred et al. (1951). Definite He-3 stars include 3 CentauriA, Alpha Sculptoris, Iota Orionis B, HR 1951, HR 2306, HR 7129, HR 7467,and HD 191980. Attention is also given to probable He-3 stars, andquestions regarding the existence of He-3 in silicon stars
| Structure and age of the local association /Pleiades group/
Intermediate-band indices are used to derive luminosities for some 500early-type stars with well-determined proper motions and radialvelocities. Space motion vectors and galactic coordinates are computedfor the stars considered. It is found that the local association membersare mainly concentrated in the Sco-Cen region in the Southern Hemisphereand the Cas-Tau region in the north.
| Classification of intrinsic variables. VI - Ultrashort-period, very small amplitude B-type variables
These very young disk-population variables are found to be distributedin a very narrow instability strip, extending from M(bol) = -9 mag to -3mag and including stars with a range of at least 25 to 5 solar masses.Some new variables, for which periods are not yet available, aresuggested as possibly filling the existing gaps in the luminositydistribution and extending the instability region to still lower masses.
| Four-color and H beta photometry for the bright B8 and B9 type stars north of declination -10 degre.
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1973AJ.....78..738C&db_key=AST
| Spectral classification of the bright B8 stars.
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1972AJ.....77..750C&db_key=AST
| U, b, v, and Hβ Photometry for the Bright B8- and B9-TYPE Stars.
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1963ApJ...137..530C&db_key=AST
| Spectral Classification of 533 B8-A2 Stars and the Mean Absolute Magnitude of a0 V Stars.
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1959ApJ...130..159O&db_key=AST
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Osservazione e dati astrometrici
| Costellazione: | Cigno |
| Ascensione retta: | 19h36m56.60s |
| Declinazione: | +38°23'02.0" |
| Magnitudine apparente: | 6.5 |
| Distanza: | 386.1 parsec |
| Moto proprio RA: | 4 |
| Moto proprio Dec: | 0.3 |
| B-T magnitude: | 6.337 |
| V-T magnitude: | 6.479 |
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INHABITED SKY
