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Radiative lifetimes, branching fractions and oscillator strengths in Pd I and the solar palladium abundance
Transition probabilities have been derived for 20 5s-5p transitions ofPd I from a combination of radiative lifetime measurements for 6odd-parity levels with time-resolved laser-induced fluorescencespectroscopy and of branching fraction determination using a hollowcathode discharge lamp. Additional oscillator strengths for 18transitions have been determined from measured lifetimes and theoreticalbranching fractions obtained from configuration interaction calculationswith core-polarization effects included. These new results have allowedus to refine the palladium abundance in the solar photosphere: A_Pd =1.66 ± 0.04, in the usual logarithmic scale, a result in closeagreement with the meteoritic value.
| Improved oscillator strengths and wavelengths in Hf II, with applications to stellar elemental abundances
Aims. We present new and improved radiative lifetimes for eight levelsin Hf I and 18 levels in Hf II, along with oscillator strengths andwavelengths for 195 transitions in Hf II. With these data we determinethe abundance of hafnium in two chemically peculiar stars: the hot-Amstar HR 3383 and the HgMn star χ Lupi, and discuss the implicationsof the new data to the hafnium abundance for the Sun and the metal-poorgalactic halo stars CS 22892-052 and CS 31082-001. Methods: . Theoscillator strengths are derived by combining radiative lifetimesmeasured with the laser induced fluorescence technique and branchingfractions determined from intensity calibrated Fourier transformspectra. The hafnium abundance in the two sharp-lined peculair stars isdetermined by comparison of spectra obtained from instruments onboardthe Hubble Space Telescope with synthetic spectra, while the abundanceof hafnium in the solar photosphere and the metal-poor halo stars isdiscussed in terms of rescaling previous investigations using the new gfvalues. Results: . The abundance enhancement of hafnium has beendetermined in HR 3383 to be +1.7 dex and that for χ Lupi A is +1.3dex. In the course of the analysis we have also determined an abundanceenhancement for molybdenum in HR 3383 to be +1.2 dex, which is similarto that known for χ Lupi A. The abundances in the metal-poor halostars CS 31082-001 and CS 22892-052 were rescaled to log ɛ(Hf) =-0.75 and -0.82 respectively, with smaller 1σ uncertainty. Thishas the effect of improving the theoretical fits of r-processnucleosynthesis to abundance data for heavy elements. The change of gfvalues also implies that the hafnium abundance in the solar photosphereshould be reduced by up to 0.2 dex, thereby inducing a discrepancy withthe meteoritic hafnium abundance.
| Transition probabilities and lifetimes in neutral and singly ionized osmium and the Solar osmium abundance
Radiative lifetime measurements have been performed, with atime-resolved laser-induced fluorescence technique, for 12 levels of OsI and for 9 levels of Os II. For 9 levels of Os I and 4 levels of Os II,there were no previous experimental data available. From a comparisonwith new theoretical calculations, taking configuration interactions andcore-polarization effects into account, it has been possible to deduceoscillator strengths for 129 transitions of Os I and 137 transitions ofOs II of astrophysical interest appearing in the wavelength range180.0-870.0 nm. These results have allowed us to revise the abundance ofosmium in the solar photosphere (log \varepsilonOs = 1.25± 0.11). The newly derived oscillator strengths have been appliedas well to derive the osmium abundance in the carbon-rich metal-poorstar HD 187861.
| 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.
| Transition probabilities and lifetimes in singly ionized rhenium
Transition probabilities and radiative lifetimes have been obtained for45 transitions of ReII using a combination of radiative lifetime valuesobtained with the laser-induced fluorescence technique (seven levels)and theoretical branching fractions. This new set of results, concerningultraviolet and visible lines, will be useful in the future forinvestigating the composition of chemically peculiar stars.
| On the Ga II and Ga III Resonance Lines and the Implication for Chemical Stratification in HgMn Stars
The gallium abundance in HgMn stars has been reported to be differentfor analyses conducted from spectral lines in the optical versus thosefrom the ultraviolet. We pursue this ultraviolet-optical discrepancyfrom a line-blending perspective by investigating the Hubble SpaceTelescope (HST) Space Telescope Imaging Spectrograph (STIS) spectrum ofthe sharp-lined HgMn binary star χ Lup. Its gallium abundance isderived to be logNGa=4.5 (logNH=12) based onnonresonance Ga II lines, and we are able to demonstrate theline-blending problems associated with the abundances determined fromthe resonance lines of Ga II λ1414 and Ga III λ1495. TheHST STIS spectrum for χ Lup is also compared with a co-addedInternational Ultraviolet Explorer (IUE) spectrum to further illustratethe importance of accounting for the line blending in quantitativeabundance analyses. We have compared an IUE co-added spectrum of μLep with an LTE-based synthetic spectrum and managed to fit both Ga IIλ1414 and Ga III λ1495 with an abundance oflogNGa=7.3. However, the fitting of these lines requires adramatic change in the radiative damping constants, which may indicate abreakdown in our LTE modeling or the need to include other atmosphericeffects.
| Statistical Constraints for Astrometric Binaries with Nonlinear Motion
Useful constraints on the orbits and mass ratios of astrometric binariesin the Hipparcos catalog are derived from the measured proper motiondifferences of Hipparcos and Tycho-2 (Δμ), accelerations ofproper motions (μ˙), and second derivatives of proper motions(μ̈). It is shown how, in some cases, statistical bounds can beestimated for the masses of the secondary components. Two catalogs ofastrometric binaries are generated, one of binaries with significantproper motion differences and the other of binaries with significantaccelerations of their proper motions. Mathematical relations betweenthe astrometric observables Δμ, μ˙, and μ̈ andthe orbital elements are derived in the appendices. We find a remarkabledifference between the distribution of spectral types of stars withlarge accelerations but small proper motion differences and that ofstars with large proper motion differences but insignificantaccelerations. The spectral type distribution for the former sample ofbinaries is the same as the general distribution of all stars in theHipparcos catalog, whereas the latter sample is clearly dominated bysolar-type stars, with an obvious dearth of blue stars. We point outthat the latter set includes mostly binaries with long periods (longerthan about 6 yr).
| 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.
| Stark broadening of Cd I spectral lines
Stark broadening parameters, widths, and shifts for 33 Cd I singlets and37 triplets were calculated using the semiclassical perturbation method.The results were compared with available experimental and theoreticaldata. Also, regularity in the spectral series 5s2 ^1S-np^1P° was investigated. The influence of Stark broadening wasanalyzed in A-type stellar atmospheres.
| Heavy Element Abundances in Late-B and Early-A Stars. I. Co-Added IUE Spectra of HgMn Stars
Very heavy elements (Pt, Au, Hg, Tl, and Bi) are found to be enhanced inthe atmospheres of the chemically peculiar stars of the upper mainsequence by up to a million times the solar system levels. Suchenhancements are believed to result from atmospheric dynamics (i.e.,diffusion) rather than scenarios that dredge up nuclear-processedmaterial to the surface or transfer processed material between binarycompanions. However, the theoretical framework needs to be furtherconstrained by observations beyond the realm of the spectral types forwhich such abundance enhancements are observed at optical wavelengths.The International Ultraviolet Explorer (IUE) satellite collected spectraof bright stars for which chemical peculiarities have been derived fromground-based data. For several elements the abundance enhancements haveonly been recently measured using Hubble Space Telescope data and havetherefore not yet been exploited in the IUE data. We have initiated aprogram to analyze IUE high-dispersion spectra to more fullycharacterize the pattern of very heavy element enhancement for manymercury-manganese (HgMn) stars and to potentially extend the spectralclass (effective temperature) boundaries over which these abundanceanomalies are known to exist. The abundances of very heavy elements inchemically normal B and A-type stars provide a base level that may becompared with the solar system abundances. These early spectral typestars may therefore reveal clues for galactic chemical evolution studiessince they were formed at a later epoch than the Sun in the history ofthe Galaxy. This first paper presents the motivation for the analyses tofollow, outlines our spectral co-addition technique for IUE spectra, anddiscusses the choice of model atmospheres and the synthetic spectrumprocedures, while initiating the study by highlighting the abundance ofgold in several HgMn stars.
| Constraining the very heavy elemental abundance peak in the chemically peculiar star χ Lupi, with new atomic data for Os II and Ir II
The determination of elemental abundances plays an important role inunderstanding the atmospheric processes that lead to anomalies inspectra of chemically peculiar stars. Ongoing study of the HgMn starχ Lupi has defined much of the elemental abundance distribution butprogress is dependent upon the availability and accuracy of the atomicdata. Here we present experimentally determined wavelengths andoscillator strengths for 27 Os II and 23 Ir II transitions. Theoscillator strengths have been determined by combining radiativelifetimes measured using the laser-induced fluorescence technique withbranching fractions determined from Fourier transform spectrometeremission line intensities. The new data were used in a syntheticspectrum analysis of high-resolution ultraviolet spectra of χ Lupiobtained with the Hubble Space Telescope. Weak abundance enhancementswere determined for both elements, [Os/H] = +1.3 dex and [Ir/H] = +0.7dex, which now clearly defines the heavy element abundance peak in thisstar to be comprised of only the four elements Pt, Au, Hg, and Tl. Thisresult offers a new constraint on theoretical efforts to explain theobserved spectrum anomalies.Based in part on observations obtained with the GHRS instrument on boardthe Hubble Space Telescope.
| Beyond the iron group: Heavy metals in hot subdwarfs
We report the discovery of strong photospheric resonance lines of GaIII, Ge IV, Sn IV and Pb IV in the UV spectra of more than two dozen sdBand sdOB stars at temperatures ranging from 22 000 K to 40 000 K. Linesof other heavy elements are also detected, however in these cases moreatomic data are needed. Based on these discoveries, we present ahypothesis to explain the apparent lack of silicon in sdB stars hotterthan 32 000 K. The existence of triply ionised Ge, Sn, and Pbsuggests that rather than silicon sinking deep into the photosphere, itis removed from the star in a fractionated stellar wind. This hypothesisprovides a challenge to diffusion models of sdB stars.Based on observations made with the NASA/ESA Hubble Space Telescope,which is operated by the Association of Universities for Research inAstronomy, Inc., under NASA contract NAS 5-26555. These observations areassociated with program #8635 and #5319.
| The chemical composition of the mild barium star HD 202109
We present chemical abundances of the mild barium star HD 202109 (\zetaCyg) determined from the analysis of a spectrum obtained by using the2-m telescope at the Peak Terskol Observatory and a high-resolutionspectrometer with R=80 000, signal to noise ratio >100. We alsopresent the atmospheric parameters of the star determined using variousmethods including iron-line abundance analysis. For lineidentifications, we use whole-range synthetic spectra computed fromKurucz's database and the latest lists of spectral lines. Among thedetermined abundances of 51 elements, those of P, S, K, Cu, Zn, Ge, Rb,Sr, Nb, Mo, Ru, Rh, Pd, In, Sm, Gd, Tb, Dy, Er, Tm, Hf, Os, Ir, Pt, Tl,and Pb were not investigated previously. Assuming that the overabundancepattern of Ba stars is due to binary accretion, the observed abundancepattern of the neutron-capture process elements in HD 202109 can beexplained by combining the AGB star nucleosynthesis and the windaccretion scenario.Based on observations obtained at the 2-m telescope of Peak Terskolobservatory near Mt. Elbrus, Northern Caucasus, Russia - InternationalCenter for Astronomical, Medical and Ecological Research (ICAMER),Ukraine & Russia.
| 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
| HD 191110 a SB2 system with HgMn and Hg components. Orbital elements and abundance analysis
In this paper we present the first quantitative abundance analysis ofthe SB2 system with HgMn and Hg components HD 191110. Time-resolved(R=14 000) spectroscopic observations of this system have been obtainedduring September and October 2002 at the Catania AstrophysicalObservatory. Combining these observations with spectra (R = 50 000-110000) taken from the CFHT archive, we refined the orbital period of thissystem (P=9.34661 +/- 0.00002 d) and then we recalculated thefundamental parameters characterizing its orbit. From the fit of theHbeta profiles, obtained at different orbital phases, wedetermined the effective temperatures and surface gravities of eachcomponent and the light ratio: TeffA=11 000 K, loggA=3.60, TeffB= 10 700 K, loggB=3.90, LA/LB=1.20. Regarding thechemical composition, both components have solar abundances of sulfur,titanium and iron; magnesium and silicon are slightly underabundant;platinum and yttrium are overabundant. Manganese lines have beendetected only in the spectrum of the primary. As to rare-earths, twolines of NdIII have been identified in the secondary's spectrum. Otherlines we identified in our spectra belong to PII, CrII, NiII, SrII, ZrIIand AuII. We also discuss the isotopic structure of the HgII lambda3983.9 Å line.
| 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
| Formation scenarios for the young stellar associations between galactic longitudes l = 280degr - 360degr
We investigate the spatial distribution, the space velocities and agedistribution of the pre-main sequence (PMS) stars belonging toOphiuchus, Lupus and Chamaeleon star-forming regions (SFRs), and of theyoung early-type star members of the Scorpius-Centaurus OB association.These young stellar associations extend over the galactic longituderange from 280degr to 360degr , and are at a distance interval ofaround 100 and 200 pc. This study is based on a compilation ofdistances, proper motions and radial velocities from the literature forthe kinematic properties, and of basic stellar data for the constructionof Hertzsprung-Russel diagrams. Although there was no well-known OBassociation in Chamaeleon, the distances and the proper motions of agroup of 21 B- and A-type stars, taken from the Hipparcos Catalogue,lead us to propose that they form a young association. We show that theyoung early-type stars of the OB associations and the PMS stars of theSFRs follow a similar spatial distribution, i.e., there is no separationbetween the low and the high-mass young stars. We find no difference inthe kinematics nor in the ages of these two populations studied.Considering not only the stars selected by kinematic criteria but thewhole sample of young early-type stars, the scattering of their propermotions is similar to that of the PMS stars and all the young starsexhibit a common direction of motion. The space velocities of theHipparcos PMS stars of each SFR are compatible with the mean values ofthe OB associations. The PMS stars in each SFR span a wide range of ages(from 1 to 20 Myr). The ages of the OB subgroups are 8-10 Myr for UpperScorpius (US), and 16-20 Myr for Upper Centaurus Lupus (UCL) and forLower Centaurus Crux (LCC). Thus, our results do not confirm that UCL isolder than the LCC association. Based on these results and theuncertainties associated with the age determination, we cannot say thatthere is indeed a difference in the age of the two populations. Weanalyze the different scenarios for the triggering of large-scalestar-formation that have been proposed up to now, and argue that mostprobably we are observing a spiral arm that passes close to the Sun. Thealignment of young stars and molecular clouds and the average velocityof the stars in the opposite direction to the Galactic rotation agreewith the expected behavior of star formation in nearby spiral arms.Tables 1 to 4 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/404/913
| 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.
| On the behavior of the Cii 4267.261, 6578.052 and 6582.882 Å lines in chemically peculiar and standard stars
With the aim of investigating the possible particular behavior of carbonin a sample of chemically peculiar stars of the main sequence withoutturning to modeling, we performed spectroscopic observations of threeimportant and usually prominent single ionized carbon lines: 4267.261,6578.052 and 6582.882 Å. In addition, we observed a large numberof standard stars in order to define a kind of normality strip, usefulfor comparing the observed trend for the peculiar stars. We paidparticular attention to the problem of the determination of fundamentalatmospheric parameters, especially for the chemically peculiar stars forwhich the abundance anomalies change the flux distribution in such a waythat the classical photometric methods to infer effective temperaturesand gravities parameter cannot be applied. Regarding CP stars, we founda normal carbon abundance in Hg-Mn, Si (with some exceptions) and Hestrong stars. He weak stars are normal too, but with a large spread outof the data around the mean value. A more complicated behavior has beennoted in the group of SrCrEu stars: four out of seven show a strongoverabundance, being the others normal.
| On the infrared void in the Lupus dark clouds
Strömgren uvbyβ photometry observations obtained for 205 starsin the general direction of a void in the IRAS 100-μm emission fromthe Lupus dark cloud complex are presented and analysed. The colourexcess versus distance diagram confirms the existence of a regiondepleted from interstellar material, which is also seen in the ROSATsoft X-ray background emission map. The distance to the surroundingmaterial is estimated as being within the interval from 60 to 100pc.This result is in disagreement with previous distance estimates to thesupposed supernova that has been suggested as responsible for clearingthe region from dust. As an alternative, the data presented support thesuggestion that the void may have been produced by the detachment ofmaterial from the interface between LoopI and the Local Bubble as aconsequence of hydromagnetic instabilities. Moreover, the distributionof colour excess as a function of distance supports a value of ~150pc asthe most probable distance to the dark cloud known as Lupus1.
| The Variability of the Hg II λ3984 Line of the Mercury-Manganese Star α Andromedae
The variability of the Hg II λ3984 line in the primary of thebinary star α And was discovered through the examination ofhigh-dispersion spectra with signal-to-noise ratios greater than 500.This first definitively identified spectrum variation in anymercury-manganese star is not due to the orbital motion of thecompanion. Rather, the variation is produced by the combination of the2.38236 day period of rotation of the primary that we determined and anonuniform surface distribution of mercury that is concentrated in itsequatorial region. If the surface mercury distribution exhibitslong-term stability, then it is likely that a weak magnetic fieldoperates in its atmosphere, but if changes are observed in the lineprofile over a period of a few years, then these would constitute directevidence for diffusion.
| Ultraviolet C I Lines in the HgMn Star χ Lupi
We present non-LTE calculations for the ionization equilibrium of C Itailored to match the HgMn star χ Lupi. Comparisons are made withthe UV C I lines observed using the Hubble Space Telescope's GoddardHigh Resolution Spectrograph, as well as with Voyager far-ultraviolet(FUV) measurements of the flux between 1040 and 1200 Å, where C Iis the dominant continuum opacity source. The non-LTE models do providebetter fits to most C I line profiles than do the LTE models, but theexpected increase in the FUV continuum flux due to the non-LTEunderpopulation of the lower levels of carbon is largely masked byuncertainties in the Voyager data and in the FUV line blanketing.Realistic modeling of the C I ionization equilibrium required includingthe FUV opacity from the predicted lines of iron-group elements, and tothis end the non-LTE model atmosphere program TLUSTY was modified toinclude opacity distribution functions of Kurucz as a fixed-opacitysource. This modified code will be useful for studying non-LTE effectsin other ions in χ Lupi and similar stars.
| Light-induced drift for Hg isotopes in chemically peculiar stars
In the present paper the abundance anomalies of mercury and its isotopesin the atmospheres of HgMn stars have been studied. Observations haveshown strongly anomalous isotopic composition of Hg, Pt, Tl and He inthe atmospheres of such CP stars. Generation of elemental abundanceanomalies in quiescent atmospheres of CP stars can generally beexplained by the mechanism of diffusive segregation of elements due tooppositely directed gravitational and radiative forces. It has beenshown that the formation of the observed isotopic anomalies can besuccessfully explained by a diffusion mechanism called the light-induceddrift (LID). The observed ratios of isotopes also enable to estimate theevolutionary stages of CP stars.
| 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 laboratory analysis of Bi II and its application to the Bi-rich HgMn star HR 7775
The bismuth spectrum emitted from a hollow cathode discharge has beenrecorded with a Fourier Transform Spectrometer (FTS). Accuratewavelengths have been determined for 104 Bi Ii lines, and several newenergy levels have been found, while the accuracy of previously known BiIi level energies have been improved. The hyperfine structure of allobserved Bi Ii lines has been analyzed, yielding hyperfine constants Aand B for 56 Bi Ii levels. With the aid of the laboratory measurementsthe optical region spectrum of the HgMn star HR 7775 has been studiedfor all observable Bi Ii lines. The wavelengths and hfs constantsestablished from the laboratory work have been combined with theoreticalgf values to identify spectral lines and make an abundance estimation ofbismuth. It has been established that bismuth is present in HR 7775 atan enhancement level of approximately 5 orders of magnitude relative tothe meteoritic abundance, consistent with previous observations in theultraviolet region of this star. Astrophysical gf values are presentedfor a number of Bi Ii lines.
| The presence of Nd and Pr in HgMn stars
Optical region spectra for a number of upper main sequence chemicallypeculiar (CP) stars have been observed to study singly and doublyionized praseodymium and neodymium lines. In order to improve existingatomic data of these elements, laboratory measurements have been carriedout with the Lund VUV Fourier Transform Spectrometer (FTS). From thesemeasurements wavelengths and hyperfine structure (hfs) have been studiedfor selected Pr Ii, Pr Iii and Nd Iii lines of astrophysical interest.Radiative lifetimes for some excited states of Pr Ii have beendetermined with the aid of laser spectroscopy at the Lund Laser Center(LLC) and have been combined with branching fractions measured in thelaboratory to calculate gf values for some of the stronger optical linesof Pr Ii. With the aid of the derived gf values and laboratorymeasurements of the hfs, a praseodymium abundance was derived fromselected Pr Ii lines in the spectrum of the Am star 32 Aqr. Thisabundance was used to derive astrophysical gf values for selected Pr Iiilines in 32 Aqr, and these gf values were used to get a praseodymiumabundance for the HgMn star HR 7775. The praseodymium abundance in HR7775 was then utilized to derive astrophysical gf values for allobservable Pr Iii lines in this star. The neodymium abundance, derivedfrom unblended lines of Nd Ii in HR 7775, has been utilized to establishastrophysical gf values for observed Nd Iii lines in the optical regionof this star. Selected Pr Iii and Nd Iii lines have been identified andstudied in a number of HgMn stars and three hot Am stars. Thepraseodymium and neodymium abundance change rapidly from an approximate1-1.2 dex enhancement for the hot Am stars to 1.5-3 dex enhancement forthe cool HgMn stars, indicating a well-defined boundary between the hotAm and HgMn stars in the vicinity of 10 500 K. The enhancement ofpraseodymium and neodymium in Am and HgMn stars may be explained bydiffusive processes active in the stellar atmosphere, while the observeddiscontinuity might be explained by a thin hydrogen convection zonethought to be present for the Am stars, but absent in the HgMn stars.The absence of a convection zone would cause the diffused elements togather higher in the atmosphere of HgMn stars compared to Am stars, andexplain the observed increase in abundance.
| Rotational velocities of A-type stars. I. Measurement of v sin i in the southern hemisphere
Within the scope of a Key Programme determining fundamental parametersof stars observed by HIPPARCOS, spectra of 525 B8 to F2-type starsbrighter than V=8 have been collected at ESO. Fourier transforms ofseveral line profiles in the range 4200-4500 Å are used to derivev sin i from the frequency of the first zero. Statistical analysis ofthe sample indicates that measurement error is a function of v sin i andthis relative error of the rotational velocity is found to be about 6%on average. The results obtained are compared with data from theliterature. There is a systematic shift from standard values from\citet{Slk_75}, which are 10 to 12% lower than our findings. Comparisonswith other independent v sin i values tend to prove that those fromSlettebak et al. are underestimated. This effect is attributed to thepresence of binaries in the standard sample of Slettebak et al., and tothe model atmosphere they used. Based on observations made at theEuropean Southern Observatory (ESO), La Silla, Chile, in the frameworkof the Key Programme 5-004-43K. Table 4 is only available in electronicform at the CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.125.5)or via http://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/381/105
| An Abundance Study in the Hg-Mn Star 46 Aquilae (HD 186122) with the SUBARU/HDS
A detailed abundance analysis has been carried out for the Hg-Mn star 46Aql using high-resolution spectra in the visual region (5100--6400Å) obtained with the High Dispersion Spectrograph of the SubaruTelescope. Our attention has been mainly focused on those elements whichhave not been analyzed previously. He, C, N, and O are underabundant,while Na shows the solar abundance. We have confirmed previouslyreported underabundances of Mg, Al, and Si, and have found anoverabundances of P (+1.5 dex) and Ti (+1.0 dex) and a significantunderabundance of S (-1.8 dex). Fe is overabundant by +0.8 +/- 0.1 dexand a microturbulent velocity of 0.3 km s-1 was found from ananalysis of the FeII lines. Among a few hundred unidentified absorptionlines, we identified lines of AsII and XeII and a very large (+4.0 dex)overabundance of Xe is obtained. We have confirmed emission lines ofMnII and TiII near 6100 Å, while those of CrII cannot have beenseen.
| The Bismuth Abundance in the HGMN Stars χ Lupi and HR 7775 and Improved Atomic Data for Selected Transitions of BI I, BI II, and BI III
High-resolution spectra of the chemically peculiar HgMn stars χ Lupiand HR 7775, obtained with the Hubble Space Telescope/Goddard HighResolution Spectrograph, are investigated for their abundance of bismuthby comparison with LTE synthetic spectrum modeling. HR 7775, previouslyknown from International Ultraviolet Explorer spectra to display stronglines of Bi II, is determined to have bismuth present at an enhancementlevel of nearly 5 orders of magnitude from the lines Bi IIλλ1436, 1902 and Bi III λ1423. The bismuthenhancement for χ Lupi is found to be near a level of 1.5 dex, andan ionization anomaly between Bi+ and Bi++ isapparent. HR 7775 abundance enhancements of the heavy elements platinum,[Pt/H]=4.7 dex, and gold, [Au/H]=3.8 dex, have also been determined. Newlaboratory measurements for wavelengths and hyperfine structure patternsof Bi I/Bi II/Bi III lines are presented, as well as the results ofcalculations for hyperfine structure constants and oscillator strengthsfor selected lines of Bi II and Bi III. Based on observations with theNASA/ESA Hubble Space Telescope, obtained at the Space Telescope ScienceInstitute, which is operated by the Association of Universities forResearch in Astronomy, Inc., under NASA contract NAS5-26555.
| New results of magnetic field diagnosis in HgMn stars and normal late B-type stars
We suggested in a previous paper that three HgMn stars, HD 175640, HD178065, and HD 186122, may be suspected to possess a magnetic field thatcould be larger than 2 kG. We report here new observations of thesethree stars, three more HgMn stars, and four normal late B-type stars.The search was carried out by measuring the equivalent width of the FeII lambda 6147.7 Å line relative to the equivalent width of the FeII lambda 6149.2 Å line. The observed relative differences betweenthe equivalent widths of these Fe II lines are compared with thosederived from synthetic spectra computed by neglecting magnetic fieldeffects. To investigate the effect of oscillator strength uncertaintieson the results, we computed equivalent widths by using both Fe II loggf-values taken from Kurucz & Bell (\cite{KB95}) and Fe II loggf-values taken from Raassen & Uylings (2000). The comparison of thecomputed and observed equivalent widths based on the Kurucz & Bell(\cite{KB95}) atomic data leads us to conclude that all the stars of oursample, except HD 175640, are very likely to possess a magnetic field.On the other hand, the comparison of the computed and observedequivalent widths based on the Raassen & Uylings (2000) loggf-values suggests the possible presence of magnetic fields only inthree stars, the HgMn star HD 16717 and the two normal B-type stars HD179761 and HD 186568. The latter two are those in the sample with thelargest vsin i (15 km s-1 and 18 km s-1,respectively), so that the results for them are the most uncertain ones.
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Pozíciós és asztrometriai adatok
| Csillagkép: | Farkas |
| Rektaszcenzió: | 15h50m57.50s |
| Deklináció: | -33°37'38.0" |
| Vizuális fényesség: | 3.95 |
| Távolság: | 63.052 parszek |
| RA sajátmozgás: | -7.2 |
| Dec sajátmozgás: | -28.4 |
| B-T magnitude: | 3.902 |
| V-T magnitude: | 3.94 |
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