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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.
| The Indo-US Library of Coudé Feed Stellar Spectra
We have obtained spectra for 1273 stars using the 0.9 m coudéfeed telescope at Kitt Peak National Observatory. This telescope feedsthe coudé spectrograph of the 2.1 m telescope. The spectra havebeen obtained with the no. 5 camera of the coudé spectrograph anda Loral 3K×1K CCD. Two gratings have been used to provide spectralcoverage from 3460 to 9464 Å, at a resolution of ~1 Å FWHMand at an original dispersion of 0.44 Å pixel-1. For885 stars we have complete spectra over the entire 3460 to 9464 Åwavelength region (neglecting small gaps of less than 50 Å), andpartial spectral coverage for the remaining stars. The 1273 stars havebeen selected to provide broad coverage of the atmospheric parametersTeff, logg, and [Fe/H], as well as spectral type. The goal ofthe project is to provide a comprehensive library of stellar spectra foruse in the automated classification of stellar and galaxy spectra and ingalaxy population synthesis. In this paper we discuss thecharacteristics of the spectral library, viz., details of theobservations, data reduction procedures, and selection of stars. We alsopresent a few illustrations of the quality and information available inthe spectra. The first version of the complete spectral library is nowpublicly available from the National Optical Astronomy Observatory(NOAO) via ftp and http.
| Variability of the He I λ5876 Å line in early type chemically peculiar stars. II
To try to understand the behavior of helium variability in ChemicallyPeculiar stars, we continued our on-going observational campaign startedby \cite{catanzaro99}. In this paper we present a new set of timeresolved spectroscopic observations of the He I 5876 Å line for asample of 10 stars in the spectral range B3 - A2 and characterized bydifferent overabundances.This line does not show variability in two stars: HD 77350 and HD175156. It shows instead an equivalent width variation in phase with theHipparcos light curve for two stars: HD 79158 and HD 196502. Antiphasevariations have been found in 4 stars of our sample, namely: HD 35502,HD 124224, HD 129174 and HD 142990. Nothing we can say about HD 115735because of the constancy of Hipparcos photometric data, while no phaserelation has been observed for HD 90044.In the text we discuss the case of HD 175156, according to photometriccalibration and our spectroscopic observations we rule out themembership of this star to the main sequence chemically peculiar stars.We confirm the results obtained in the previous paper for which phaserelations between light, spectral and magnetic variations are notdependent on stellar spectral type or peculiarity subclass.Based on observations collected at stellar station ``M. G. Fracastoro''of the Catania Astrophysical Observatory and on observations collectedat Complejo Astrónomico El Leoncito (Casleo), which is operatedunder agreement between the Consejo Nacional de InvestigationesCientifícas y Técnicas (CONICET) and the NationalUniversities of La Plata, Córdoba and San Juan.
| Catalogue of averaged stellar effective magnetic fields. I. Chemically peculiar A and B type stars
This paper presents the catalogue and the method of determination ofaveraged quadratic effective magnetic fields < B_e > for 596 mainsequence and giant stars. The catalogue is based on measurements of thestellar effective (or mean longitudinal) magnetic field strengths B_e,which were compiled from the existing literature.We analysed the properties of 352 chemically peculiar A and B stars inthe catalogue, including Am, ApSi, He-weak, He-rich, HgMn, ApSrCrEu, andall ApSr type stars. We have found that the number distribution of allchemically peculiar (CP) stars vs. averaged magnetic field strength isdescribed by a decreasing exponential function. Relations of this typehold also for stars of all the analysed subclasses of chemicalpeculiarity. The exponential form of the above distribution function canbreak down below about 100 G, the latter value representingapproximately the resolution of our analysis for A type stars.Table A.1 and its references are only available in electronic form atthe CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/407/631 and Tables 3 to 9are only available in electronic form at http://www.edpsciences.org
| STELIB: A library of stellar spectra at R ~ 2000
We present STELIB, a new spectroscopic stellar library, available athttp://webast.ast.obs-mip.fr/stelib. STELIB consists of an homogeneouslibrary of 249 stellar spectra in the visible range (3200 to 9500Å), with an intermediate spectral resolution (la 3 Å) andsampling (1 Å). This library includes stars of various spectraltypes and luminosity classes, spanning a relatively wide range inmetallicity. The spectral resolution, wavelength and spectral typecoverage of this library represents a substantial improvement overprevious libraries used in population synthesis models. The overallabsolute photometric uncertainty is 3%.Based on observations collected with the Jacobus Kaptein Telescope,(owned and operated jointly by the Particle Physics and AstronomyResearch Council of the UK, The Nederlandse Organisatie voorWetenschappelijk Onderzoek of The Netherlands and the Instituto deAstrofísica de Canarias of Spain and located in the SpanishObservatorio del Roque de Los Muchachos on La Palma which is operated bythe Instituto de AstrofÃsica de Canarias), the 2.3 mtelescope of the Australian National University at Siding Spring,Australia, and the VLT-UT1 Antu Telescope (ESO).Tables \ref{cat1} to \ref{cat6} and \ref{antab1} to A.7 are onlyavailable in electronic form at http://www.edpsciences.org. The StellarLibrary STELIB library is also available at the CDS, via anonymous ftpto cdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/402/433
| New periodic variables from the Hipparcos epoch photometry
Two selection statistics are used to extract new candidate periodicvariables from the epoch photometry of the Hipparcos catalogue. Theprimary selection criterion is a signal-to-noise ratio. The dependenceof this statistic on the number of observations is calibrated usingabout 30000 randomly permuted Hipparcos data sets. A significance levelof 0.1 per cent is used to extract a first batch of candidate variables.The second criterion requires that the optimal frequency be unaffectedif the data are de-trended by low-order polynomials. We find 2675 newcandidate periodic variables, of which the majority (2082) are from theHipparcos`unsolved' variables. Potential problems with theinterpretation of the data (e.g. aliasing) are discussed.
| On the Periods of the Magnetic CP Stars
An HR diagram annotated to show several ranges of photometericallydetermined periods has been constructed for the magnetic CP stars whoseperiods have been determined by the author and his collaborators. Thedistribution of periods reflects both the initial conditions as well asthe subsequent stellar histories. Since the stellar magnetic field doesnot penetrate the convective core, eventually a shear zone near thecore-radiative envelope boundary may develop which produces turbulenceand modifies the field. Many, but not all, of the most rapidly rotatingmCP stars are close to the ZAMS and some of the least rapidly rotatingmCP stars are the furthest from 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.
| 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
| The proper motions of fundamental stars. I. 1535 stars from the Basic FK5
A direct combination of the positions given in the HIPPARCOS cataloguewith astrometric ground-based catalogues having epochs later than 1939allows us to obtain new proper motions for the 1535 stars of the BasicFK5. The results are presented as the catalogue Proper Motions ofFundamental Stars (PMFS), Part I. The median precision of the propermotions is 0.5 mas/year for mu alpha cos delta and 0.7mas/year for mu delta . The non-linear motions of thephotocentres of a few hundred astrometric binaries are separated intotheir linear and elliptic motions. Since the PMFS proper motions do notinclude the information given by the proper motions from othercatalogues (HIPPARCOS, FK5, FK6, etc.) this catalogue can be used as anindependent source of the proper motions of the fundamental stars.Catalogue (Table 3) is only available at the CDS via anonymous ftp tocdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strastg.fr/cgi-bin/qcat?J/A+A/365/222
| UVBY photometry of the magnetic CP stars HD 36668, 36 Lyncis, HD 86592, and HR 8861
Differential Strömgren uvby photometric observations from the FourCollege Automated Photoelectric Telescope (FCAPT) are presented for themagnetic CP stars HD 36668, 36 Lyn, HD 86592, and HR 8861. Using theFCAPT values, North's period for HD 36668 is refined to 2.11884 days.The 3.834 day period of Shore et al. for 36 Lyn, which was found frommagnetic field measurements, is confirmed by photometry. The FCAPTobservations also support the 2.8867 day period of Babel & North forHD 86592, demonstrate that this star is a large amplitude variable in v(0.13 mag.), and show that y varies crudely out of phase from u, v, andb which are in phase with one another. The variability of HR 8861appears to be correlated with the meridional passages of regions of Siover- and underabundance as found by Piskunov et al. Tables~2, 3, 4 and5 are only available 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
| Sixth Catalogue of Fundamental Stars (FK6). Part I. Basic fundamental stars with direct solutions
The FK6 is a suitable combination of the results of the HIPPARCOSastrometry satellite with ground-based data, measured over more than twocenturies and summarized in the FK5. Part I of the FK6 (abbreviatedFK6(I)) contains 878 basic fundamental stars with direct solutions. Suchdirect solutions are appropriate for single stars or for objects whichcan be treated like single stars. From the 878 stars in Part I, we haveselected 340 objects as "astrometrically excellent stars", since theirinstantaneous proper motions and 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,199 of the stars in Part I 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(I) proper motion in the single-star mode is 0.35 mas/year. This isabout a factor of two better than the typical HIPPARCOS errors for thesestars of 0.67 mas/year. In the long-term prediction mode, in whichcosmic errors are taken into account, the FK6(I) proper motions have atypical mean error of 0.50 mas/year, which is by a factor of more than 4better than the corresponding error for the HIPPARCOS values of 2.21mas/year (cosmic errors included).
| A Second Catalog of Orbiting Astronomical Observatory 2 Filter Photometry: Ultraviolet Photometry of 614 Stars
Ultraviolet photometry from the Wisconsin Experiment Package on theOrbiting Astronomical Observatory 2 (OAO 2) is presented for 614 stars.Previously unpublished magnitudes from 12 filter bandpasses withwavelengths ranging from 1330 to 4250 Å have been placed on thewhite dwarf model atmosphere absolute flux scale. The fluxes wereconverted to magnitudes using V=0 for F(V)=3.46x10^-9 ergs cm^-2 s^-1Å^-1, or m_lambda=-2.5logF_lambda-21.15. This second catalogeffectively doubles the amount of OAO 2 photometry available in theliterature and includes many objects too bright to be observed withmodern space observatories.
| Gallium abundances in mercury-manganese stars
There is a widespread assertion in the literature that the optical Galines give much higher abundances than the UV lines. We have determinedGa abundances in HgMn stars taking the observed hyperfine structure ofthe optical Ga II lines into account. This reduces these abundances towithin 0.2 dex of the values from the resonance lines.
| 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 (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/Abstract.html
| Effective temperatures of AP stars
A new method of determination of the effective temperatures of Ap starsis proposed. The method is based on the fact that the slopes of theenergy distribution in the Balmer continuum near the Balmer jump for``normal" main sequence stars and chemically peculiar stars with thesame Teff are identical. The effective temperaturecalibration is based on a sample of main sequence stars with well knowntemperatures (\cite[Sokolov 1995]{sokolov}). It is shown that theeffective temperatures of Ap stars are derived by this method in goodagreement with those derived by the infrared flux method and by themethod of \cite[Stepien & Dominiczak (1989)]{stepien}. On the otherhand, the comparison of obtained Teff with Teffderived from the color index (B2-G) of Geneva photometry shows a largescatter of the points, nevertheless there are no systematicaldifferences between two sets of the data.
| Delta a and Stroemgren photometry of stars in the Renson-catalogue of AP and AM stars
We have observed 131 stars of \cite[Renson's (1991)]{re91} catalogue ofAp and Am stars both in the Stroemgren & Maitzen's (1976) Delta asystem as a contribution to the photometric studies of the lambda 5200broad band flux depression feature in chemically peculiar stars. Withfew exceptions the probability grouping of Renson for membership in theCP2 group of peculiar stars is nicely reflected by peculiar values ofDelta a. Comparison with already available Delta a values yieldsslightly larger values due to a minor shift in the filter g_1 samplingthe depression. As found by \cite[Maitzen & Vogt (1983)]{ma83} theGeneva system peculiarity parameters correlate well with Delta a. Thisstudy demonstrates the advantageous performance of a photoelectricphotometer with a rapidly rotating filter wheel moving in a stop and gomode. Tables 3 and 4 are also available in electronic form at the CDSvia anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/Abstract.html
| The observed periods of AP and BP stars
A catalogue of all the periods up to now proposed for the variations ofCP2, CP3, and CP4 stars is presented. The main identifiers (HD and HR),the proper name, the variable-star name, and the spectral type andpeculiarity are given for each star as far as the coordinates at 2000.0and the visual magnitude. The nature of the observed variations (light,spectrum, magnetic field, etc.) is presented in a codified way. Thecatalogue is arranged in three tables: the bulk of the data, i.e. thosereferring to CP2, CP3, and CP4 stars, are given in Table 1, while thedata concerning He-strong stars are given in Table 2 and those foreclipsing or ellipsoidal variables are collected in Table 3. Notes arealso provided at the end of each table, mainly about duplicities. Thecatalogue contains data on 364 CP stars and is updated to 1996, October31. This research has made use of the SIMBAD database, operated at CDS,Strasbourg, France.
| Helium peculiar stars in the red spectral region
Based upon 33 A/mm dispersion spectroscopic material we examine ifequivalent widths of H and He lines can be used for the detection of newhelium-peculiar stars. The answer is affirmative and we present some newcandidates discovered this way. We have also investigated if the use ofdifferent helium lines than those of the (3) D series (4026, 4471)modifies the assignments of helium peculiar stars. This is not the case,since the use of lambda 6678 ((1) D) and lambda 7065 (3S) gives the sameresults. Based on observations obtained at the Haute ProvenceObservatory (CNRS)
| 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 gallium problem in HgMn stars
Previous studies of visible-region high-excitation lines of ion{Ga}{ii}in HgMn stars have usually concluded that these lines (lambda lambda4251-4262 and lambda 6334) yield abundance estimates for gallium ~1 dexgreater than the UV resonance lines. Of the explanations proposed in theliterature, we find that the presence of hyperfine structure (hfs) inthe lines is the most likely. We analyse Lick Hamilton Echelle CCDspectra by spectrum synthesis with the code UCLSYN. Using the Bidelman& Corliss (bidelman) measurements of hfs in ion{Ga}{ii}, and thecalculations given by Lanz et al. (lanz), with the oscillator strengthsby Ryabchikova & Smirnov (rya, b), we determine a difference inabundance (visual-UV) of only 0.2 dex. Of this difference, about 0.1 dexcan be explained by the simplified approximation to the true hfs, whichcan be estimated theoretically, and the remaining 0.1 dex can probablybe accounted for by the stratification of Ga found by Smith (smith, b.,smith, d.). We conclude that the visible-region and UV abundances are inagreement within the errors of the determinations, and that the anomalypreviously found by several investigations is an artifact of thesimplified atomic line structures assumed, or results from the use ofvery different gf-values from those adopted here.
| The Tokyo PMC catalog 90-93: Catalog of positions of 6649 stars observed in 1990 through 1993 with Tokyo photoelectric meridian circle
The sixth annual catalog of the Tokyo Photoelectric Meridian Circle(PMC) is presented for 6649 stars which were observed at least two timesin January 1990 through March 1993. The mean positions of the starsobserved are given in the catalog at the corresponding mean epochs ofobservations of individual stars. The coordinates of the catalog arebased on the FK5 system, and referred to the equinox and equator ofJ2000.0. The mean local deviations of the observed positions from theFK5 catalog positions are constructed for the basic FK5 stars to comparewith those of the Tokyo PMC Catalog 89 and preliminary Hipparcos resultsof H30.
| Study of the Element Distribution on the Surface of the He-weak star 36 lyn
Not Available
| A catalogue of [Fe/H] determinations: 1996 edition
A fifth Edition of the Catalogue of [Fe/H] determinations is presentedherewith. It contains 5946 determinations for 3247 stars, including 751stars in 84 associations, clusters or galaxies. The literature iscomplete up to December 1995. The 700 bibliographical referencescorrespond to [Fe/H] determinations obtained from high resolutionspectroscopic observations and detailed analyses, most of them carriedout with the help of model-atmospheres. The Catalogue is made up ofthree formatted files: File 1: field stars, File 2: stars in galacticassociations and clusters, and stars in SMC, LMC, M33, File 3: numberedlist of bibliographical references The three files are only available inelectronic form at the Centre de Donnees Stellaires in Strasbourg, viaanonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5), or viahttp://cdsweb.u-strasbg.fr/Abstract.html
| Elemental abundances in normal late-B and HgMn stars from co-added IUE spectra V. Mercury.
Atmospheric mercury abundances are derived for a sample of 40main-sequence, late-B stars, of which 14 are classified normal, and 26are known chemically peculiar stars of HgMn or related He-weak types.The observational material for this study comprises co-added,short-wavelength IUE spectra encompassing the HgII λ1942resonance line, coupled with a selection of new and publishedmeasurements (equivalent widths and centroid wavelengths) of the opticalHgII λ3984 and HgI λ4358 lines. The analysis includes anexplicit treatment of the isotopic and hyperfine structure of theselines, and allows for star-to-star variations in the isotopiccomposition of mercury within the framework of an assumed,mass-dependent fractionation model. The relative isotopic abundances ofmercury (as defined by a dimensionless mix parameter, q) are determinedusing the graphical method pioneered by White et al. In agreement withprevious studies, q is found to be strongly anti-correlated witheffective temperature, in the sense that the coolest stars are dominatedby the heaviest isotopes (e.g., ^202^Hg and ^204^Hg). New isotopic-mixparameters for three programme stars - 87 Psc (q=0.3), 28 Her (q=2.8),and HR 7775 (q=1.5) - reinforce that anti-correlation. Syntheticreconstruction of the λ3984 line in those programme stars forwhich high-resolution spectra are available tends to confirm theisotopic mixtures derived using the graphical method, and lends validityto the mass-dependent fractionation model in general. However, theλ3984 feature observed in the cool HgMn star HR 7775 can only besatisfactorily reproduced by using a tailored isotopic mixture, whichdeparts significantly from that predicted by the q-formalism. Theλ1942 resonance line is detected in 10 normal B stars, for whichthe mean isotope-summed mercury abundance of 1.96+/-0.34dex (on thescale where logN(H)=12) exceeds the meteoritic value by nearly 3σ.The mercury abundances derived for the HgMn stars vary between ~5 and7dex, except for two objects (53 Tau and HR 2676) in which theabundances are consistent with those observed in the normal stars. TheHe-weak stars in the programme (33 Gem, HR 6000, 36 Lyn, and 46 Aql)appear to be mildly enriched in mercury, but to an extent rendereduncertain by unknown isotopic-mix parameters. The abundances obtainedfrom the optical and ultraviolet lines agree to within their estimatederrors, which lends weight to the view that the metastable lower levelof λ3984 (5d^9^6s^2^^2^D_5/2_) is not overpopulated with respectto its LTE value. The isotope-summed mercury abundances are notcorrelated with the effective temperatures, surface gravities, or degreeof isotopic fractionation of the programme stars; nor is there evidencefor systematic changes in the surface mercury abundances of HgMn starsalong evolutionary tracks in the H-R diagram.
| 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.
| Elemental abundances in normal late-B and HgMn stars from co-added IUE spectra. IV. Gallium.
An analysis is presented of the ultraviolet gallium resonance lines inInternational Ultraviolet Explorer (IUE) spectra of 40 normal,superficially normal, and HgMn-type late-B stars. Gallium abundances arederived by fitting the GaIIλ1414, and GaIIIλλ1495,1534 lines with synthetic spectra computed under the conventionalassumptions of local thermodynamic equilibrium (LTE) and atmosphericchemical homogeneity. We find that the derived upper limits on thegallium abundances of the normal and superficially normal stars areconsistent with the solar value. However, gallium is overabundant inessentially all HgMn stars, including the cooler examples such as HR4072, χ Lup, and ι CrB, where the enhancements are relativelymoderate and unambiguous identification of the resonance lines dependscritically on newly available laboratory wavelengths. Furthermore, thegallium overabundances in the HgMn stars exhibit a loose correlationwith effective temperature, similar in most respects to those identifiedfor manganese and copper in the same stars except for the presence ofthe anomalously Ga-rich, cool HgMn star HR 7775. We show that asystematic discrepancy between the abundances derived from the Ga^+^ andGa^2+^ ions in the hotter HgMn stars (T_eff_>12000K) can be explainedby radiative transfer effects in the presence of a stratification ofgallium at optical depths above logτ_0_=~0. This `stratificationmodel' can also account for the anomalously shaped Gaiii λ1495profiles observed in the extreme cases of μ Lep, HR 2844, and HR 7143(as demonstrated in a previous paper), and is consistent with publishedpredictions of radiative diffusion theory for non-magnetic 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.
| Radio continuum emission from stars: a catalogue update.
An updated version of my catalogue of radio stars is presented. Somestatistics and availability are discussed.
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Membre dels grups següents:
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Dades d'Observació i Astrometria
| Constel·lació: | Lynx |
| Ascensió Recta: | 09h13m48.20s |
| Declinació: | +43°13'04.0" |
| Magnitud Aparent: | 5.32 |
| Distancia: | 175.747 parsecs |
| Moviment propi RA: | 0 |
| Moviment propi Dec: | 0 |
| B-T magnitude: | 5.116 |
| V-T magnitude: | 5.261 |
Catàlegs i designacions:
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