|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.
|Inhomogeneous distribution of mercury on the surfaces of rapidly rotating HgMn stars|
Starspots are usually associated with the action of magnetic fields atstellar surfaces. However, an inhomogeneous chemical distribution ofmercury was found recently for the mercury-manganese (HgMn) star αAnd - a well-established member of a non-magnetic subclass of thechemically peculiar stars of the upper main sequence. In this study wepresent first results of the high-resolution survey of the Hg II 3984Å resonance line in the spectra of rapidly rotating HgMn starswith atmospheric parameters similar to those of α And. We usespectrum synthesis modelling and take advantage of the Dopplerresolution of stellar surfaces to probe the horizontal structure ofmercury distribution. Clear signatures of spots are found in the Hg II3984 Å line profiles of HR 1185 and HR 8723. Two observations ofthe latter star separated by two days give evidence for line profilevariability. We conclude that inhomogeneous distribution of Hg is acommon phenomenon for the rapidly rotating HgMn stars in the 13 000-13800 K effective temperature range independent of the stellarevolutionary stage. These results establish the existence of a new classof spectrum variable spotted B-type stars. It is suggested that theobserved Hg inhomogeneities arise from dynamical instabilities in thechemical diffusion processes and are unrelated to magnetic phenomena.
|Metallicities of the SPB stars from the IUE ultraviolet spectra|
We derived the stellar parameters (angular diameters, effectivetemperatures, metallicities) and interstellar reddenings for 20 SPB and34 reference stars observed during the IUE satellite mission. Theparameters were derived by means of an algorithmic procedure of fittingtheoretical flux distributions to the low-resolution IUE spectra andoptical spectrophotometric observations. Since the metallicity [m/H] hasa special importance for pulsating B type stars, we focused ourattention on that parameter. We found that the mean value of themetallicity of the considered SPB and reference stars amounts to [m/H] ~-0.20. The results only slightly depend on the reduction procedure usedfor the IUE images (NEWSIPS and INES). The metal abundances obtained inthis paper are in accordance with the average value of -0.2 dex forstars in the solar neighborhood recently reported by otherinvestigators.Tables 3-7 are 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/404/689
|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.
|Search for low-mass PMS companions around X-ray selected late B stars|
We have observed 49 X-ray-detected bright late B-type dwarfs to searchfor close low-mass pre-main sequence (PMS) companions using the EuropeanSouthern Observatory's ADONIS (Adaptive Optics Near Infrared System)instrument. We announce the discovery of 21 new companions in 9binaries, 5 triple, 4 quadruple system and 1 system consisting of fivestars. The detected new companions have K magnitudes between 6.5m and17.3m and angular separations ranging from 0.12 arcsec to 14.1 arcsec(18-2358 AU). Based on observations obtained at the European SouthernObservatory, La Silla, Chile (ESO programme No.~62.I-0477, and Swiss70~cm photometric telescope).
|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 (126.96.36.199) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcar?J/A+A/367/521
|HgMn stars as apparent X-ray emitters|
In the ROSAT all-sky survey 11 HgMn stars were detected as soft X-rayemitters. Prior to ROSAT, X-ray observations with the EinsteinObservatory had suggested that stars in the spectral range B5-A7 aredevoid of X-ray emission. Since there is no X-ray emitting mechanismavailable for these stars (also not for HgMn stars), the usual argumentin the case of an X-ray detected star of this spectral type is theexistence of an unseen low-mass companion which is responsible for theX-ray emission. The purpose of the present work is to use all availabledata for our sample of X-ray detected HgMn stars and conclude on thenature of possible companions.
|Newly discovered candidate weak-line T Tauri stars in the surrounding area of the Taurus-Auriga region|
We present results of an extensive search for weak-line T Tauri stars(WTTS) in the outskirts of the Taurus-Auriga molecular cloud on thebasis of the ROSAT All-Sky Survey Bright Source Catalog. Our surveyedregion extends from 2() h40() m to 5() h40() m in right ascension andfrom 10(deg) to 40(deg) in declination, with the central part ofTaurus-Auriga (4() h
|On the HIPPARCOS photometry of chemically peculiar B, A, and F stars|
The Hipparcos photometry of the Chemically Peculiar main sequence B, A,and F stars is examined for variability. Some non-magnetic CP stars,Mercury-Manganese and metallic-line stars, which according to canonicalwisdom should not be variable, may be variable and are identified forfurther study. Some potentially important magnetic CP stars are noted.Tables 1, 2, and 3 are available only in electronic form at the CDS viaanonymous ftp to cdsarc.u-strasbg.fr (188.8.131.52) 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.
|The photoelectric astrolabe catalogue of Yunnan Observatory (YPAC).|
The positions of 53 FK5, 70 FK5 Extension and 486 GC stars are given forthe equator and equinox J2000.0 and for the mean observation epoch ofeach star. They are determined with the photoelectric astrolabe ofYunnan Observatory. The internal mean errors in right ascension anddeclination are +/- 0.046" and +/- 0.059", respectively. The meanobservation epoch is 1989.51.
|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.
|A new list of effective temperatures of chemically peculiar stars. II.|
|A radio survey of weak T Tauri stars in Taurus-Auriga|
A multi-epoch 5 GHz survey of candidate or confirmed weak T Tauri starsin the Taurus-Auriga molecular cloud complex was conducted with the VeryLarge Array. The stars were chosen from those having detectable X-ray orchromospheric emission, and weak-emission-line pre-main-sequence starsfound by other means. Snapshots of 99 VLA fields containing 119candidate stars were obtained with a sensitivity of 0.7 mJy; most fieldswere observed on two or three dates. Nine radio sources coincident withcataloged stars were found. One may be an RS CVn binary system; theother eight are pre-main-sequence stars. Three of the detected stars -HD 283447, V410 Tau, and FK X-ray 1 - were previously known radiosources. Five new detections are Herbig's Anon 1, Hubble 4, HDE 283572,Elias 12, and HK Tau/c. At least five of the sources are variable, andno linear or circular polarization was found. Several lines of evidencesuggest that the radio-detected weak T Tauri stars are quite young,perhaps younger on average than nondetected stars.
|The ultraviolet gallium stars|
On the basis of IUE low dispersion spectra, a group of UV peculiar starsin the range of middle and late B-type stars, characterized by strong GaII 1414 A line is defined. This group has no counterpart in the optical3600-4800 A range.
|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.
|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.
|Evidence of decay of the magnetic fields of AP stars|
Data obtained in the Geneva photometric system (Rufener, 1981) andappropriate calibrations of this system in terms of surface magneticfield and gravity are used to provide, on the basis of 708 field andcluster Ap stars, observational evidence that these stars undergo decayof their magnetic field on an evolutionary timescale. Justifications aregiven for the application of a photometric gravity calibration topeculiar stars. The dependence of the photometrically estimated surfacemagnetic field on gravity is found to differ markedly from availabletheoretical calculations. HgMn stars are found to show the same trend,strengthening the impression that they might be slightly magnetic.He-weak stars do not.
|Radial velocities of northern Mercury stars|
About 200 radial velocities of 96 bright northern Hg-Mn or candidateHg-Mn stars are presented. Past and present data have been reexaminedfor periodic variability in cases that were neither previously known tobe binaries with well determined orbits nor were considered to haveconstant velocity. One definite new orbit was found (that of HR 3361)and several possible orbital solutions are given.
|Beryllium abundances in Hg-Mn stars|
The Hg-Mn stars show anomalous line strengths of many chemical elementsincluding Be. The Be II resonance doublet has been observed at 3130,3131 A at 6.7 A/mm in 43 Hg-Mn stars and 10 normal stars in the sametemperature range with the coude spectrograph of the 2.24 m Universityof Hawaii telescope at Mauna Kea. Measured equivalent widths of the twolines and/or the blend of the doublet have been compared with thepredictions from (1) LTE model atmospheres and (2) non-LTE lineformation in non-LTE model atmospheres. Overabundances of factors of20-20,000 relative to solar have been found for 75 percent of the Hg-Mnstars. The 25 percent with little or no Be are typically among thecooler Hg-Mn stars, but for the stars with Be excesses, there is onlymarginal evidence for a correlation of the size of the overabundance andtemperature. It is suggested that diffusion driven by radiation pressureis responsible for the observed Be abundance anomalies.
|Photometric properties of AP stars in the Geneva system|
An examination of the properties in some photometric diagrams of morethan 600 Ap stars measured in the Geneva photometric system confirm thatthe Balmer discontinuity is smaller than for normal stars, along withthe link between a proposed peculiarity parameter and both rotationalvelocity and effective magnetic field. It is shown that the peculiarityparameter is sensitive to interstellar reddening, and it is foundthrough examination of the standard deviations for visual magnitudesthat cool CP 2 stars without Eu peculiarity have the greatestamplitudes. Rapid rotators have a mild peculiarity, while positivecorrelation exists for Si and SrCr stars.
|Ultraviolet observations of hot stars with circumstellar dust shells|
Absolute fluxes over the wavelength range 1200-3200 A are presented for13 normal early-type stars and 12 early-type stars known to have largeIR excess; the data were obtained to study the UV spectral modificationsproduced by absorbing circumstellar dust particles. It is found that allthe Be/shell stars whose spectral types are later than B6 exhibitgreatly enhanced line absorption due to circumstellar Fe II. Thecircumstellar gaseous line absorption in stars cooler than B6 severelycomplicates the study of circumstellar dust absorption. However, those Band A stars that exhibit the circumstellar 9.7-micron emission featurehave a very large increase in circumstellar absorption for 1800 A; suchabsorption is expected from circumstellar silicate particles.
|A catalogue and bibliography of Mn-Hg stars|
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1981A&AS...44..137S&db_key=AST
|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
|The absolute magnitude of the Hg-Mn stars|
The absolute magnitude of the Hg-Mn stars has been determined usingstatistical, photometric, spectroscopic, and cluster parallaxes. Theresults of all four procedures are in excellent agreement and give anaverage absolute magnitude of 0.6m plus or minus 0.4m, which locatesthese objects above the main sequence, in agreement with spectroscopicresults.
|Surface gravity of Mn-Hg stars.|
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1979PASJ...31..473T&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.
|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
|Spectral classification from the ultraviolet line features of S2/68 spectra. II - Late B-type stars|
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1977A&AS...30...71C&db_key=AST
|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.