目录
图像
上传图像
DSS Images Other Images
相关文章
Evolution of interacting binaries with a B type primary at birth
We revisited the analytical expression for the mass ratio distributionfor non-evolved binaries with a B type primary. Selection effectsgoverning the observations were taken into account in order to comparetheory with observations. Theory was optimized so as to fit best withthe observed q-distribution of SB1s and SB2s. The accuracy of thistheoretical mass ratio distribution function is severely hindered by theuncertainties on the observations. We present a library of evolutionarycomputations for binaries with a B type primary at birth. Some liberalcomputations including loss of mass and angular momentum during binaryevolution are added to an extensive grid of conservative calculations.Our computations are compared statistically to the observeddistributions of orbital periods and mass ratios of Algols. ConservativeRoche Lobe Over Flow (RLOF) reproduces the observed distribution oforbital periods but fails to explain the observed mass ratios in therange q in [0.4-1]. In order to obtain a better fit the binaries have tolose a significant amount of matter, without losing much angularmomentum.
| 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.
| Astrometric orbits of SB^9 stars
Hipparcos Intermediate Astrometric Data (IAD) have been used to deriveastrometric orbital elements for spectroscopic binaries from the newlyreleased Ninth Catalogue of Spectroscopic Binary Orbits(SB^9). This endeavour is justified by the fact that (i) theastrometric orbital motion is often difficult to detect without theprior knowledge of the spectroscopic orbital elements, and (ii) suchknowledge was not available at the time of the construction of theHipparcos Catalogue for the spectroscopic binaries which were recentlyadded to the SB^9 catalogue. Among the 1374 binaries fromSB^9 which have an HIP entry (excluding binaries with visualcompanions, or DMSA/C in the Double and Multiple Stars Annex), 282 havedetectable orbital astrometric motion (at the 5% significance level).Among those, only 70 have astrometric orbital elements that are reliablydetermined (according to specific statistical tests), and for the firsttime for 20 systems. This represents a 8.5% increase of the number ofastrometric systems with known orbital elements (The Double and MultipleSystems Annex contains 235 of those DMSA/O systems). The detection ofthe astrometric orbital motion when the Hipparcos IAD are supplementedby the spectroscopic orbital elements is close to 100% for binaries withonly one visible component, provided that the period is in the 50-1000 drange and the parallax is >5 mas. This result is an interestingtestbed to guide the choice of algorithms and statistical tests to beused in the search for astrometric binaries during the forthcoming ESAGaia mission. Finally, orbital inclinations provided by the presentanalysis have been used to derive several astrophysical quantities. Forinstance, 29 among the 70 systems with reliable astrometric orbitalelements involve main sequence stars for which the companion mass couldbe derived. Some interesting conclusions may be drawn from this new setof stellar masses, like the enigmatic nature of the companion to theHyades F dwarf HIP 20935. This system has a mass ratio of 0.98 but thecompanion remains elusive.
| New runaway OB stars with HIPPARCOS
A Monte Carlo method for detection of runaway OB stars fromobservational data is proposed. 61 runaway OB star candidates have beendetected by an analysis of Hipparcos proper motions. The peculiartangential and total transverse velocities have been determined forthese stars. A list of the detected runaway star candidates ispresented. The evidence of a discrepancy between photometric andparallactic distances of runaway OB star candidates is presented.
| Implementing TOPbase/Iron Project: continuous absorption from FeII
We discuss implementation of TOPbase and Iron Project opacities forstellar spectral codes. We use a technique employed by Peach, where aBoltzmann-averaged cross-section is calculated for selectedtemperatures, and the opacity obtained from double interpolation intemperature and wavelength. It is straightforward to include all levelsfor which cross-sections have been calculated. Boltzmann-averagedcross-sections for FeII show a local maximum between 1700 and 2000Å. We suggest this feature arises from 3d54snl->3d54pnl transitions within FeII. IUE spectra of iron-rich CPstars show local minima in this region. Theoretical calculations of arepresentative stellar continuum demonstrate that FeII photoionizationcontributes significantly to the observed minima.
| Rotation Velocities of Red and Blue Field Horizontal-Branch Stars
We present measurements of the projected stellar rotation velocities(vsini) of a sample of 45 candidate field horizontal-branch (HB) starsspanning a wide range of effective temperatures, from red HB stars withTeff~=5000K to blue HB stars with Teff of 17,000K.Among the cooler blue HB stars (Teff=7500-11500 K), weconfirm prior studies showing that, although a majority of stars rotateat vsini<15kms-1, there exists a subset of ``fastrotators'' with vsini as high as 30-35 km s-1. All but one ofthe red HB stars in our sample have vsini<10kms-1, and noanalogous rotation bimodality is evident. We also identify anarrow-lined hot star (Teff~=16,000K) with enhancedphotospheric metal abundances and helium depletion, similar to theabundance patterns found among hot BHB stars in globular clusters, andfour other stars that may also belong in this category. We discussdetails of the spectral line fitting procedure that we use to deducevsini and explore how measurements of field HB star rotation may shedlight on the issue of HB star rotation in globular clusters.
| 3D mapping of the dense interstellar gas around the Local Bubble
We present intermediate results from a long-term program of mapping theneutral absorption characteristics of the local interstellar medium,motivated by the availability of accurate and consistent parallaxes fromthe Hipparcos satellite. Equivalent widths of the interstellar NaID-line doublet at 5890 Å are presented for the lines-of-sighttowards some 311 new target stars lying within ~ 350 pc of the Sun.Using these data, together with NaI absorption measurements towards afurther ~ 240 nearby targets published in the literature (for many ofthem, in the directions of molecular clouds), and the ~ 450lines-of-sight already presented by (Sfeir et al. \cite{sfeir99}), weshow 3D absorption maps of the local distribution of neutral gas towards1005 sight-lines with Hipparcos distances as viewed from a variety ofdifferent galactic projections.The data are synthesized by means of two complementary methods, (i) bymapping of iso-equivalent width contours, and (ii) by densitydistribution calculation from the inversion of column-densities, amethod devised by Vergely et al. (\cite{vergely01}). Our present dataconfirms the view that the local cavity is deficient in cold and neutralinterstellar gas. The closest dense and cold gas ``wall'', in the firstquadrant, is at ~ 55-60 pc. There are a few isolated clouds at closerdistance, if the detected absorption is not produced by circumstellarmaterial.The maps reveal narrow or wide ``interstellar tunnels'' which connectthe Local Bubble to surrounding cavities, as predicted by the model ofCox & Smith (1974). In particular, one of these tunnels, defined bystars at 300 to 600 pc from the Sun showing negligible sodiumabsorption, connects the well known CMa void (Gry et al. \cite{gry85}),which is part of the Local Bubble, with the supershell GSH 238+00+09(Heiles \cite{heiles98}). High latitude lines-of-sight with the smallestabsorption are found in two ``chimneys'', whose directions areperpendicular to the Gould belt plane. The maps show that the LocalBubble is ``squeezed'' by surrounding shells in a complicated patternand suggest that its pressure is smaller than in those expandingregions.We discuss the locations of several HI and molecular clouds. Usingcomparisons between NaI and HI or CO velocities, in some cases we areable to improve the constraints on their distances. According to thevelocity criteria, MBM 33-37, MBM 16-18, UT 3-7, and MBM 54-55 arecloser than ~ 100 pc, and MBM 40 is closer than 80 pc. Dense HI cloudsare seen at less than 90 pc and 85 pc in the directions of the MBM 12and MBM 41-43 clouds respectively, but the molecular clouds themselvesmay be far beyond. The above closest molecular clouds are located at theneutral boundary of the Bubble. Only one translucent cloud, G192-67, isclearly embedded within the LB and well isolated.These maps of the distribution of local neutral interstellar NaI gas arealso briefly compared with the distribution of both interstellar dustand neutral HI gas within 300 pc.Tables 1 and 2 are only available in electronic form at the CDS viaanonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or viahttp:cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/411/447
| On the elemental abundance and isotopic mixture of mercury in HgMn stars
Optical region spectra of 31 HgMn stars have been studied for theabundance and isotope mixture of mercury. In the course of theinvestigation the lines Hg I lambda 4358 and Hg Ii lambda lambda3984,6149 have been studied, with abundances established for all threelines in several HgMn stars. The mercury isotope mixture has beendetermined from high resolution spectra of the lambda 3984 line.Possible signs of an ionization anomaly have been detected by thecomparison of the abundance derived from the Hg I line and the Hg Iilines in seven of the observed HgMn stars. A possible correlation of themercury abundance with Teff has been detected. Possible signsof a weak anticorrelation of the manganese and mercury abundance in HgMnstars have been found, which could be interpreted as a sign ofinhomogeneous surface distribution of these elements. For a number ofthe HgMn stars in this study the mercury abundance and isotope mixtureare reported for the first time.
| Quantitative Stellar Spectral Classification. II. Early Type Stars
The method developed by Stock & Stock (1999) for stars of spectraltypes A to K to derive absolute magnitudes and intrinsic colors from theequivalent widths of absorption lines in stellar spectra is extended toB-type stars. Spectra of this type of stars for which the Hipparcoscatalogue gives parallaxes with an error of less than 20% were observedwith the CIDA one-meter reflector equipped with a Richardsonspectrograph with a Thompson 576×384 CCD detector. The dispersionis 1.753 Å/pixel using a 600 lines/mm grating in the first order.In order to cover the spectral range 3850 Å to 5750 Å thegrating had to be used in two different positions, with an overlap inthe region from 4800 Å to 4900 Å . A total of 116 stars wasobserved, but not all with both grating positions. A total of 12measurable absorption lines were identified in the spectra and theirequivalent widths were measured. These were related to the absolutemagnitudes derived from the Hipparcos catalogue and to the intrinsiccolors (deduced from the MK spectral types) using linear and secondorder polynomials and two or three lines as independent variables. Thebest solutions were obtained with polynomials of three lines,reproducing the absolute magnitudes with an average residual of about0.40 magnitudes and the intrinsic colors with an average residual of0.016 magnitudes.
| 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.
| Are Stellar Rotational Axes Distributed Randomly?
Stellar line widths yield values of Vsini, but the equatorial rotationalvelocities, V, cannot be determined for individual stars withoutknowledge of their inclinations, i, relative to the lines of sight. Forlarge numbers of stars we usually assume random orientations ofrotational axes to derive mean values of V, but we wonder whether thatassumption is valid. Individual inclinations can be derived only inspecial cases, such as for eclipsing binaries where they are close to90° or for chromospherically active late-type dwarfs or spotted(e.g., Ap) stars where we have independent information about therotational periods. We consider recent data on 102 Ap stars for whichCatalano & Renson compiled rotational periods from the literatureand Abt & Morrell (primarily) obtained measures of Vsini. We findthat the rotational axes are oriented randomly within the measuringerrors. We searched for possible dependence of the inclinations onGalactic latitude or longitude, and found no dependence.
| Speckle Interferometry of New and Problem Hipparcos Binaries. II. Observations Obtained in 1998-1999 from McDonald Observatory
The Hipparcos satellite made measurements of over 9734 known doublestars, 3406 new double stars, and 11,687 unresolved but possible doublestars. The high angular resolution afforded by speckle interferometrymakes it an efficient means to confirm these systems from the ground,which were first discovered from space. Because of its coverage of adifferent region of angular separation-magnitude difference(ρ-Δm) space, speckle interferometry also holds promise toascertain the duplicity of the unresolved Hipparcos ``problem'' stars.Presented are observations of 116 new Hipparcos double stars and 469Hipparcos ``problem stars,'' as well as 238 measures of other doublestars and 246 other high-quality nondetections. Included in these areobservations of double stars listed in the Tycho-2 Catalogue andpossible grid stars for the Space Interferometry Mission.
| 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
| Neon abundances in normal late-B and mercury-manganese stars
We make new non-local thermodynamic equilibrium calculations to deducethe abundances of neon from visible-region echelle spectra of selectedNei lines in seven normal stars and 20HgMn stars. We find that the beststrong blend-free Ne line that can be used at the lower end of theeffective temperature Teff range is λ6402, althoughseveral other potentially useful Nei lines are found in the red regionof the spectra of these stars. The mean neon abundance in the normalstars (logA=8.10) is in excellent agreement with the standard abundanceof neon (8.08). However, in HgMn stars neon is almost universallyunderabundant, ranging from marginal deficits of 0.1-0.3dex tounderabundances of an order of magnitude or more. In many cases, thelines are so weak that only upper limits can be established. The mostextreme example found is υ Her with an underabundance of at least1.5dex. These underabundances are qualitatively expected from radiativeacceleration calculations, which show that Ne has a very small radiativeacceleration in the photosphere, and that it is expected to undergogravitational settling if the mixing processes are sufficiently weak andthere is no strong stellar wind. According to theoretical predictions,the low Ne abundances place an important constraint on the intensity ofsuch stellar winds, which must be less than10-14Msolaryr-1 if they arenon-turbulent.
| Do the physical properties of Ap binaries depend on their orbital elements?
We reveal sufficient evidence that the physical characteristics of Apstars are related to binarity. The Ap star peculiarity [represented bythe Δ(V1-G) value and magnetic field strength] diminishes witheccentricity, and it may also increase with orbital period(Porb). This pattern, however, does not hold for largeorbital periods. A striking gap that occurs in the orbital perioddistribution of Ap binaries at 160-600d might well mark a discontinuityin the above-mentioned behaviour. There is also an interestingindication that the Ap star eccentricities are relatively lower thanthose of corresponding B9-A2 normal binaries for Porb>10d.All this gives serious support to the pioneering idea of Abt &Snowden concerning a possible interplay between the magnetism of Apstars and their binarity. Nevertheless, we argue instead in favour ofanother mechanism, namely that it is binarity that affects magnetism andnot the opposite, and suggest the presence of a newmagnetohydrodynamical mechanism induced by the stellar companion andstretching to surprisingly large Porb.
| Manganese abundances in mercury-manganese stars
We use exact curve-of-growth analysis and spectral synthesis to deducethe abundance of Mn from high signal-to-noise ratio visible-regionechelle spectra of selected Mn i and MnII lines in 24 HgMn stars. Theresults are compared with the Mn abundances derived from UV resonancelines by Smith & Dworetsky. We find excellent agreement for severalunblended Mn lines and confirm the temperature dependence of the Mnabundance found by Smith & Dworetsky. The MnII lines at lambdalambda 4206 and 4326 are much stronger than one would predict from themean Mn abundances. The lack of agreement is greatest for stars with thestrongest MnII lines. Using ad hoc multicomponent fits to the profilesof sharp-lined stars, we show that most of the discrepancies can beexplained by hyperfine structure that desaturates the lines, with fullwidths of the order of 0.06-0.09 A.
| 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
| 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.
| 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.
| 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.
| Star Streams and Galactic Structure
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1996AJ....112.1595E&db_key=AST
| 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.
| 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.
Not Available
| The late B-type stars: Refined MK classification, confrontation with stromgren photometry, and the effects of rotation
In the fourth and final of a series of papers on the late B to the earlyF type stars, we refine the Morgan Keenan (MK) spectral classificationsystem for the late B type stars and consider the effect of rotation onboth spectral classification and Stroemgren photometry of these stars.We extend the work of Morgan by establishing self-consistent sequencesof narrow and broadlined standards. We reclassify a number of Bp stars,compare these classifications with Stroemgren photometry and considerthe question of whether all Bp stars are main-sequence objects.
| Elemental abundances in normal late-B and HgMn stars from co-added IUE spectra. 3: Copper and zinc
Atmospheric abundances of copper and zinc are derived for a sample of 40normal, superficially normal, and HgMn-type main-sequence late-B starsby local thermodynamic equilibrium (LTE) spectrum-synthesis analysis ofco-added high-resolution International Ultraviolet Explorer (IUE)spectra. In the normal and superficially normal stars, the abundances ofthese elements are generally consistent with their solar values, towithin the limits of observational and analytical error. In most (butnot all) HgMn stars, copper is found to be overabundant and, moreover,exhibits a pronounced positive correlation with effective temperaturesimilar to that seen for manganese. Zinc is typically deficient in theHgMn stars with underabundances of 2 dex or more in many cases, althoughit is apparently overabundant in three program stars and present atessentially solar abundance in three others. There appears to be nocharacteristic distinguishing those HgMn stars which are zinc-rich orzinc-normal from those that are zinc-deficient. These results providefurther evidence for the existence of a sub-group of hot, mild HgMnstars characterized, in the context of this work, by relatively moderateoverabundances of copper when compared with other 'genuine' HgMn starsof similar effective temperature. While the copper abundance correlationwith effective temperature would appear to be a possible signature ofradiative diffusion in the atmospheres of HgMn stars, the inexplicablydichotomous behavior of zinc in the same objects could prove difficultto reconcile with existing parameter-free models of this mechanism.
|
提交文章
相关链接
提交链接
下列团体成员
|
观测天体数据
目录:
|
