|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.
|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 (18.104.22.168) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcar?J/A+A/367/521
|Research Note Hipparcos photometry: The least variable stars|
The data known as the Hipparcos Photometry obtained with the Hipparcossatellite have been investigated to find those stars which are leastvariable. Such stars are excellent candidates to serve as standards forphotometric systems. Their spectral types suggest in which parts of theHR diagrams stars are most constant. In some cases these values stronglyindicate that previous ground based studies claiming photometricvariability are incorrect or that the level of stellar activity haschanged. Table 2 is only available in electronic form at the CDS viaanonymous ftp to cdsarc.u-strasbg.fr (22.214.171.124) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/367/297
|Sixth Catalogue of Fundamental Stars (FK6). Part III. Additional fundamental stars with direct solutions|
The FK6 is a suitable combination of the results of the HIPPARCOSastrometry satellite with ground-based data, measured over a longinterval of time and summarized mainly in the FK5. Part III of the FK6(abbreviated FK6(III)) contains additional fundamental stars with directsolutions. Such direct solutions are appropriate for single stars or forobjects which can be treated like single stars. Part III of the FK6contains in total 3272 stars. Their ground-based data stem from thebright extension of the FK5 (735 stars), from the catalogue of remainingSup stars (RSup, 732 stars), and from the faint extension of the FK5(1805 stars). From the 3272 stars in Part III, we have selected 1928objects as "astrometrically excellent stars", since their instantaneousproper motions and their mean (time-averaged) ones do not differsignificantly. Hence most of the astrometrically excellent stars arewell-behaving "single-star candidates" with good astrometric data. Thesestars are most suited for high-precision astrometry. On the other hand,354 of the stars in Part III are Δμ binaries in the sense ofWielen et al. (1999). Many of them are newly discovered probablebinaries with no other hitherto known indication of binarity. The FK6gives, besides the classical "single-star mode" solutions (SI mode),other solutions which take into account the fact that hidden astrometricbinaries among "apparently single-stars" introduce sizable "cosmicerrors" into the quasi-instantaneously measured HIPPARCOS proper motionsand positions. The FK6 gives, in addition to the SI mode, the "long-termprediction (LTP) mode" and the "short-term prediction (STP) mode". TheseLTP and STP modes are on average the most precise solutions forapparently single stars, depending on the epoch difference with respectto the HIPPARCOS epoch of about 1991. The typical mean error of anFK6(III) proper motion in the single-star mode is 0.59 mas/year. This isa factor of 1.34 better than the typical HIPPARCOS errors for thesestars of 0.79 mas/year. In the long-term prediction mode, in whichcosmic errors are taken into account, the FK6(III) proper motions have atypical mean error of 0.93 mas/year, which is by a factor of about 2better than the corresponding error for the HIPPARCOS values of 1.83mas/year (cosmic errors included).
|Rotational Velocity Determinations for 164 Be and B Stars|
Rotational velocities, v sin i, have been obtained for 96 Be and 68normal B stars by measurements of the FWHM of the He I lambda-4471 line(for spectral types B0-B4.5) and Mg II lambda-4481 (for types B5-B9.5).The consistency of various published sources is examined. (SECTION:Stars)
|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.
|The local distribution of NA I interstellar gas|
We present high-resolution absorption measurements (lambda/Delta lambdaapproximately 75,000) of the interstellar Na I D lines at 5890 A toward80 southern hemisphere early-type stars located in the localinterstellar medium (LISM). Combining these results with other sodiummeasurements taken from the literature, we produce galactic maps of thedistribution of neutral sodium column density for a total of 293 starsgenerally lying within approximately 250 pc of the Sun. These mapsreveal the approximate shape of the mid-plane contours of the rarefiedregion of interstellar space termed the Local Bubble. Its shape is seenas highly asymmetric, with a radius ranging from 30 to 300 pc, and withan average radius of 60 pc. Similar plots of the Galactic mid-planedistribution of sources emitting extreme ultraviolet radiation show thatthey also trace out similar contours of the Local Bubble derived from NaI absorption measurements. We conclude that the Local Bubble absorptioninterface can be represented by a hydrogen column density,NuETA = 2 x 1019 cm-2, which explainsboth the local distribution of Na I absorption and the observed galacticdistribution of extreme ultraviolet sources. The derived mid-planecontours of the Bubble generally reproduce the large-scale featurescarved out in the interstellar medium by several nearby galactic shellstructures.
|Improved Mean Positions and Proper Motions for the 995 FK4 Sup Stars not Included in the FK5 Extension|
|The distribution of interstellar dust in the solar neighborhood|
We surveyed the IRAS data base at the positions of the 1808 O6-B9.5stars in The Bright Star Catalog for extended objects with excessemission at 60 microns, indicating the presence of interstellar dust atthe location of the star. Within 400 pc the filling factor of theinterstellar medium, for dust clouds with a density greater than 0.5/cucm is 14.6 + or - 2.4%. Above a density of 1.0/cu cm, the densitydistribution function appears to follow a power law index - 1.25. Whenthe dust clouds are mapped onto the galactic plane, the sun appears tobe located in a low-density region of the interstellar medium of widthabout 60 pc extending at least 500 pc in the direction of longitudes 80deg - 260 deg, a feature we call the 'local trough'.
|High-resolution CA II observations of the local interstellar medium|
High-resolution absorption measurements of the interstellar Ca II K lineobserved toward 46 early-type stars in the local ISM (LISM) arepresented. Ca II was detected in 36 of the 46 stars with 82 individualcloud components identified. Ca II was detected to most of the starscloser than 50 pc, except in the region of the Galactic quadrant l =180-270 degrees which also contains the empty line of sight to B CMa at220 pc. The mean local standard of rest velocity of the 82 Ca IIcomponents implies that the LISM clouds are associated with the motionof the solar neighborhood and not the sun. If the present data arecombined with other nearby Ca II component velocities taken from theliterature, then a cloud centered approximately at l = 90 deg, b = -40deg moving coherently with the local interstellar wind vector issupported at a significance level of 99 percent. The Ca II data havebeen combined with Na I data for the same stars to produce a N(NaI)/N(Ca II) ratio for each identified absorption feature. This ratioplotted against the local standard of rest velocities of the cloudsshows that the Routly-Spitzer effect exists down to +/- 10 km/s, whichsupports grain desorption/destruction models that are efficient atreturning calcium to the gas phase at these low velocities.
|Intrinsic Energy Distributions in Spectra of Early Type Stars|
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1990MNRAS.246..408P&db_key=AST
|The frequency and formation mechanism of B2-B5 main-sequence binaries|
Twenty coude spectra were obtained for each of the 74 B2-B5 IV or Vstars, and the results of their radial velocities were combined withthose of a previous study of 42 similar stars, to examine the frequencyand the formation mechanism of these binaries. New improved orbitalelements are listed for nine known double-lined and 26 single-linedspectroscopic binaries. It is found that, systems with periods of 0.01yr to 100,000 yrs, have secondary frequencies that fit the Salpeter(1955) luminosity function (but not the van Rhijn function), indicatingthat these systems were formed primarily by capture. For systems withperiods shorter than 0.01 yr, the separations of components are only afew stellar radii, suggesting that these systems have undergone masstransfer; their secondary masses have no direct information concerningthe formation mechanism.
|High-resolution sodium absorption-line observations of the local interstellar medium|
High-resolution observations of the sodium D1 and D2 interstellarabsorption lines have been made toward 19 stars in the local ISM atdistances ranging from 20 to 220 pc. A least-squares absorptionline-fitting analysis is carried out on 10 of the stars that showdetectable sodium. The velocity structure, velocity dispersions, andcolumn densities of the various interstellar cloud components arederived. For the majority of stars, the best-fit dispersion parameter isabout 2 km/s, corresponding to an upper limit for the kinetictemperature of the interstellar gas of about 5500 K. No sodium isdetected toward stars with distances less than 42 pc, placing an upperlimit 2.5 x 10 to the 18th/sq cm to the hydrogen column density in theselines of sight.
|Third preliminary catalogue of stars observed with the photoelectric astrolabe of the Beijing Astronomical Observatory.|
|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.
|Observations of interstellar diffuse absorption band at 4430 A|
Observations of the interstellar diffuse absorption band at 4430 A for800 O and B stars in Neckel's (1967) catalog are being carried out, and482 spectra obtained up to September 1983 have been reduced. It isconfirmed that the strength of the interstellar diffuse absorption bandat 4430 A does not simply relate to the abundance of interstellar grainson the line of sight. The relation between the color excess E(B-V) andthe equivalent width of the band to the direction of l = 130-140 deg andb = -5 to +5 deg shows that some parameter(s) other than E(B-V) is (are)needed to understand the cause of this band.
|Catalog of O-B stars observed with Tokyo Meridian Circle|
A catalog of the O-B stars, selected from 'Blaauw-Parenago' list andRubin's catalog, has been compiled on the FK4 system by the observationsmade with Gautier 8-inch Meridian Circle at the Tokyo AstronomicalObservatory during the period, 1971 to 1979. It contains 1059 stars andwas compiled for the future establishment of high precision propermotions of O-B stars.
|A catalog of ultraviolet interstellar extinction excesses for 1415 stars|
Ultraviolet interstellar extinction excesses are presented for 1415stars with spectral types B7 and earlier. The excesses with respect to Vare derived from Astronomical Netherlands Satellite (ANS) 5-channel UVphotometry at central wavelengths of approximately 1550, 1800, 2500, and3300 A. A measure of the excess extinction in the 2200-A extinction bumpis also given. The data are valuable for investigating the systematicsof peculiar interstellar extinction and for studying the character of UVinterstellar extinction in the general direction of stars for which theextinction-curve shape is unknown.
|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.
|Be stars in binaries|
The known companions to 80 Be stars and 355 B stars listed in the BrightStar Catalogue in the range B1-B7 III-V and north of delta = -30 deg areconsidered. The known near-absence of Be binaries with periods less than1/10 yr is confirmed. For longer periods up to the limit of 10,000 AU ofthis survey, the Be and B stars do not differ in binary frequencies.This result implies that during pre-main-sequence contraction, the tidalbraking in binaries wider than 0.5 AU was inadequate to prevent theformation of stars with nearly the break-up rotational velocities. Thefraction of Be and B stars that have companions is higher in clustersand associations (38 percent) than among field stars (25 percent),confirming that escapees from clusters tend to be single stars. There issome evidence that the companions of Be stars that occur in the sameluminosity range tend also to be Be stars; that result was expectedbecause in visual binaries there is a known tendency for rapidlyrotating primaries to have rapidly rotating secondaries.
|Space velocities and ages of nearby early-type stars|
Photometric distances and space velocities have been calculated for 458B0-A0 stars with apparent magnitudes not exceeding 6.5. UsingStromgren's ubvy-beta photometry the effective temperature and theposition in bolometric magnitude over the zero-age main sequence of thestars were derived. These quantities were used to obtain age and massfor 423 of the stars by interpolation in the models of stellar evolutionfor the chemical composition (X Z) = (0.7, 0.03). A relation forderiving interstellar reddening for normal stars in the intermediategroup is given.
|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.
|Catalogue of early-type stars measured in a narrow-band photometric system|
A compilation of the photoelectric measurements in the Barbier-Morguleffsystem is presented. The catalogue includes data for 773 stars ofspectral type 08 to F6. 706 stars have been measured at least twice.
|Ultra-violet photometry of early type stars from TD I satellite observations.|
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1973MNRAS.163....1H&db_key=AST
|Four-color, Hbeta, and UBV photometry for bright B-type stars in the northern hemisphere|
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1971AJ.....76.1058C&db_key=AST
|Narrow-band photometry of early-type stars.|
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1971A&A....12....5H&db_key=AST
|Observations of the 21-CM Hydrogen Line Toward High-Latitude Stars|
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1969ApJ...157.1101G&db_key=AST
|The Kinematics of the Gould Belt: an Expanding Group?|
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1968ApJS...17..371L&db_key=AST