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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.
| Rotational velocities of A-type stars in the northern hemisphere. II. Measurement of v sin i
This work is the second part of the set of measurements of v sin i forA-type stars, begun by Royer et al. (\cite{Ror_02a}). Spectra of 249 B8to F2-type stars brighter than V=7 have been collected at Observatoirede Haute-Provence (OHP). Fourier transforms of several line profiles inthe range 4200-4600 Å are used to derive v sin i from thefrequency of the first zero. Statistical analysis of the sampleindicates that measurement error mainly depends on v sin i and thisrelative error of the rotational velocity is found to be about 5% onaverage. The systematic shift with respect to standard values fromSlettebak et al. (\cite{Slk_75}), previously found in the first paper,is here confirmed. Comparisons with data from the literature agree withour findings: v sin i values from Slettebak et al. are underestimatedand the relation between both scales follows a linear law ensuremath vsin inew = 1.03 v sin iold+7.7. Finally, thesedata are combined with those from the previous paper (Royer et al.\cite{Ror_02a}), together with the catalogue of Abt & Morrell(\cite{AbtMol95}). The resulting sample includes some 2150 stars withhomogenized rotational velocities. Based on observations made atObservatoire de Haute Provence (CNRS), France. Tables \ref{results} and\ref{merging} are only available in electronic form at the CDS viaanonymous ftp to cdsarc.u-strasbg.fr (130.79.125.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/393/897
| An ultra-high-resolution study of the interstellar medium towards Orion
We report ultra-high-resolution observations (R~9×105)of NaI, CaII, KI, CH and CH+ for interstellar sightlinestowards 12 bright stars in Orion. These data enable the detection ofmany more absorption components than previously recognized, providing amore accurate perspective on the absorbing medium. This is especially sofor the line of sight to the Orion nebula, a region not previouslystudied at very high resolution. Model fits have been constructed forthe absorption-line profiles, providing estimates for the columndensity, velocity dispersion and central velocity for each constituentvelocity component. A comparison between the absorption occurring insightlines with small angular separations has been used, along withcomparisons with other studies, to estimate the line-of-sight velocitystructures. Comparisons with earlier studies have also revealed temporalvariability in the absorption-line profile of ζ Ori, highlightingthe presence of small-scale spatial structure in the interstellar mediumon scales of ~10au. Where absorption from both Na0 andK0 is observed for a particular cloud, a comparison of thevelocity dispersions measured for each of these species providesrigorous limits on both the kinetic temperature and turbulent velocityprevailing in each cloud. Our results indicate the turbulent motions tobe subsonic in each case. Na0/Ca+ abundance ratiosare derived for individual clouds, providing an indication of theirphysical state.
| Rapid Temporal Variations of Interstellar Absorption Lines in the Carina Nebula
Two observations of the complex interstellar absorption-line profiles inthe UV spectrum of CPD -59°2603, obtained 22 months apart in theR~110,000 mode of the Space Telescope Imaging Spectrograph on the HubbleSpace Telescope, reveal substantial variations in the intensities ofseveral high-velocity components, including the virtual disappearance ofone of them. These are the first observations of interstellar temporalvariations in dominant ions to our knowledge. The most probableinterpretation is motion across the line of sight of discrete absorbingfeatures in the near foreground of the O-type star, within the CarinaNebula. Ground-based survey data also indicate that the extremeinterstellar profiles throughout this region originate relatively nearthe most massive stars, suggesting an origin related to their stellarwinds. The morphological similarity of these profiles to alow-ionization, narrow-line system in a quasi-stellar object (QSO)spectrum is pointed out. Time variability may provide a critical testamong different interpretations of such QSO systems. Based onobservations with the NASA/ESA Hubble Space Telescope obtained at theSpace Telescope Science Institute, which is operated by the Associationof Universities for Research in Astronomy, Inc., under NASA contractNAS5-26555.
| 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
| Evidence of Interstellar NA I Structure at Scales Down to 15 AU in Low-Density Gas
We present high-resolution Hubble Space Telescope/Space TelescopeImaging Spectrograph and multiepoch KPNO coudé feed observationsof multiple interstellar lines toward the binary system HD 32039/40.Comparisons of the Na I profiles observed over a period of 4.25 yrreveal significant temporal variation in the Na I column in at least onecomponent, implying that there is structure at scales on the order ofthe proper motion (~15-21 AU). Large differences are also observed amongmultiple components in the profiles of the neutral species between thebinary sight lines (5060 AU separation). In addition, significantdifferences in the S II profile are seen between the stars-the firstoptical/UV detection of small-scale variations in a dominant ion.Measurements of the C I fine-structure excitation in the variablecomponents suggest that the densities in these components are ~20-200cm-3, significantly lower than the densities inferred in pastH I 21 cm and Na I studies. Based on observations with the NASA/ESAHubble Space Telescope, obtained at the Space Telescope ScienceInstitute, which is operated by the Association for Research inAstronomy, Inc., under NASA contract NAS5-26555.
| An extensive Delta a-photometric survey of southern B and A type bright stars
Photoelectric photometry of 803 southern BS objects in the Deltaa-system as detection tool for magnetic chemically peculiar (=CP2) starshas been carried out and compared to published spectral types. Thestatistical yield of such objects detected by both techniques ispractically the same. We show that there are several factors whichcontaminate the search for these stars, but this contamination is onlyof the order of 10% in both techniques. We find a smooth transition fromnormal to peculiar stars. Our sample exhibits the largest fraction ofCP2 stars at their bluest colour interval, i.e. 10% of all stars in thecolour range -0.19 <= B-V < -0.10 or -0.10 <= b-y < -0.05.No peculiar stars based on the Delta a-criterion were found at bluercolours. Towards the red side the fraction of CP2 stars drops to about3% for positive values of B-V or b-y with red limits roughlycorresponding to normal stars of spectral type A5. The photometricbehaviour of other peculiar stars: Am, HgMn, delta Del, lambda Boo, Heabnormal stars, as well as Be/shell stars and supergiants shows someslight, but definite deviations from normal stars. Spectroscopic andvisual binaries are not distinguished from normal stars in their Delta abehaviour. The results of this work justify larger statistical work(e.g. in open clusters) employing more time-saving photometric methods(CCD). \newpage Based on observations obtained at the European SouthernObservatory, La Silla, Chile. This research has made use of the Simbaddatabase, operated at CDS, Strasbourg, France. Table 2 is only availablein electronic form via anonymous ftp 130.79.128.5 orhttp://cdsweb.u-strasbg.fr/Abstract.html
| Observations of Ubiquitous Small-Scale Structure in the Diffuse Interstellar Medium
We present results of a study of the Na I D interstellar absorptiontoward 17 binary and/or common proper-motion systems (including twotriples). The stars range in spectral type from O6 to A5, lie atdistances between 85 and 1200 pc, and have stellar separations between480 and 29,000 AU. We compare the Na I absorption present in each of thetwo (or three) lines of sight and find that the line strength and/orprofile varies for all 17 of the systems examined. We infer thatsmall-scale structure in clouds containing Na I is ubiquitous anddiscuss the implications of that conclusion.
| 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.
| The Relation between Rotational Velocities and Spectral Peculiarities among A-Type Stars
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1995ApJS...99..135A&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.
| UBV photometry of stars whose positions are accurately known. VI
Results are presented from UBV photometric observations of 1000 stars ofthe Bright Star Catalogue and the faint extension of the FK5.Observations were carried out between July 1987 and December 1990 withthe 40-cm Cassegrain telescope of the Kvistaberg Observatory.
| Small-scale structure in the diffuse interstellar medium
The initial results of a study to probe the small-scale structure in thediffuse interstellar medium (ISM) through IUE and optical observationsof interstellar absorption lines toward both components of resolvablebinary stars is reported. The binaries (Kappa CrA, 57 Aql, 59 And, HR1609/10, 19 Lyn, and Theta Ser) observed with IUE have projected linearseparations ranging from 5700 to 700 Au. Except for Kappa CrA, thestrengths of the interstellar absorption lines toward both components ofthese binaries agree to within 10 percent. In the case of Kappa CrA, theoptically thin interstellar Mg I and Mn II lines are about 50 percentstronger toward Kappa-2 CrA than Kappa-1 CrA. Higher resolutionobservations of interstellar Ca II show that this difference isconcentrated in the main interstellar component at V(LSR) = 9 + or - 2km/s. Interestingly, this velocity corresponds to an intervening cloudthat may be associated with the prominent Loop I shell in the local ISM.Given the separation (23 arcsec) and distance (120 pc) of Kappa CrA, theline strength variations indicate that this cloud has structure onscales of 2800 AU or less.
| 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.
| Ages and uvbybeta photometry of wide visual binaries. II
Visual magnitudes and color indices b-y, m1, c1 and beta have beenobtained for the members of 39 double or multiple systems containingstars with magnitudes greater than 4m. Relationships between stellarages, spectral types and photometric indices are given from a sample ofabout 3,500 stars. Data is presented with regard to MK spectral types,the separation, and absolute magnitudes; also tabulated are the meanvalues of photometric unreddened indices with their standard deviationfor intervals of 0.2 in log age. From calculations for each binary ofthe relative difference in the ages of the components and the differencein the effective temperatures, an increase in the relative differencesin ages with the differences in temperatures is noted.
| About the Consistency of Absolute Luminosity Calibrations
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1980A&A....82..370H&db_key=AST
| Late B-type stars - Rotation and the incidence of HgMn stars
High-dispersion spectrograms for an unbiased sample of 256 late B-typestars are examined in an attempt to determine whether slow rotation isnecessary and sufficient for the appearance of HgMn anomalies innonmagnetic stars. The peculiar stars in the sample are identified,values of v sin i are derived for all the stars observed, and theradial-velocity variations of the identified HgMn stars are analyzed.The distribution of rotational velocities for late B-type stars isobtained, and the role of rotation in producing extended envelopes isevaluated. The binary frequency and mass-ratio distribution are derivedfor systems containing HgMn components, the effect of duplicity on thedistribution of rotational velocities is estimated, and the role of suchfactors as rotation, age, and binary characteristics in determiningwhether HgMn anomalies are present is investigated. The results clearlyshow that HgMn stars occur only within a limited temperature range, thatall such stars rotate slowly, but that rotation, effective temperature,age, surface gravity, and binary properties do not serve to determinewhether a star will exhibit abundance anomalies.
| UVBY photometry of wide visual double stars with B, A and F spectral type- I.
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1978A&AS...34..453O&db_key=AST
| Is star formation bimodal ? II. The nearest early-type stars.
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1977PASP...89..187E&db_key=AST
| Rotational velocities and spectral types for a sample of binary systems.
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1975A&AS...19...91L&db_key=AST
| Statistical Studies in Stellar Rotation. II. a Method of Analyzing Rotational Coupling in Double Stars and an Introduction to its Applications
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1972ApJ...177..161B&db_key=AST
| Four-color and Hβ photometry for the brighter AO type stars
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1972A&AS....5..109C&db_key=AST
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| Sað Açýklýk: | 05h00m32.60s |
| Yükselim: | +03°36'55.0" |
| Görünürdeki Parlaklýk: | 7.03 |
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