Contingut
Imatges
Carregar la teva Imatge
DSS Images Other Images
Articles Relacionats
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.
| The Ca II infrared triplet as indicator of anomalous Ca isotopic mixture in HgMn stars
For the first time we present observational evidence for an anomalousisotopic structure of Ca II in mercury-manganese (HgMn) stars. Thecentroid wavelengths of Ca II infrared triplet lines in a number ofstars have been found redshifted with respect to the centroids of theterrestrial Ca II lines. The record holder is the star HD 175640 forwhich the measured wavelength is consistent with Ca II being present inthe atmosphere entirely in form of the heaviest stable isotope48Ca. This is a very striking result as 48Ca makesup only 0.187% of the terrestrial Ca mixture.Based on observations obtained at the European Southern Observator, LaSilla and Paranal, Chile (ESO programme Nos. 65.L-0316 and 67.D-0579).
| 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
| 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 relationship between the mercury-manganese stars and the metallic-lined stars
An HR diagram indicating the positions of the HgMn and the Am starsanalyzed by the senior author and his collaborators shows that thecoolest HgMn stars and the hottest Am stars are found on the samestellar evolutionary tracks and hence the former must evolve into thelater. The explanation of the dividing line between these two types ofnonmagnetic chemically peculiar stars where the Hg abundances suddenlychange their degree of overabundance is a major test of the theorieswhich try to explain the anomalous abundances of such stars. Some otherimportant relationships are found which can also serve as tests oftheories which purport to explain the properties of these stars.
| Weak Gravitational Lensing by a Sample of X-Ray Luminous Clusters of Galaxies. I. The Data Set
We present weak gravitational lensing mass measurements of a sample of38 highly X-ray luminous clusters of galaxies with well-definedselection criteria. The clusters were observed with either monolithic20482 CCDs, the UH8K mosaic CCD camera, or both. The weakshear caused by gravitational lensing was measured using recentlydeveloped techniques to correct for the effects of realisticpoint-spread functions and to optimally weight the contribution of eachgalaxy to the final shear estimate. The results are presented in theform of maps of the reconstructed dimensionless surface density κand plots of the radial cluster mass profiles. The κ maps arecompared to mass-traces-light predictions for κ based ontwo-color, V- and I-band galaxy photometry in the observed fields. About30% of the clusters in our sample show evidence of significant dynamicalactivity related to mergers of subclumps. More than half of the clustersshow signs of strong lensing. Our data set more than doubles the totalnumber of galaxy clusters with a detected weak lensing signal. The datafor all the clusters have been reduced and analyzed in a consistent way,and this makes our data set uniquely suitable for statistical studies ofcluster properties, which will be the subject of future papers in thisseries. Based on observations made with the Nordic Optical Telescope,operated on the island of La Palma jointly by Denmark, Finland, Iceland,Norway, and Sweden, in the Spanish Observatorio del Roque de losMuchachos of the Instituto de Astrofísica de Canarias.
| 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 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.
| The spectroscopic binaries 21 Her and gamma Gem
In the framework of a search campaign for short-term oscillations ofearly-type stars we analysed recently obtained spectroscopic andphotometric observations of the early A-type spectroscopic binaries 21Her and gamma Gem. From the radial velocities of 21 Her we derived animproved orbital period and a distinctly smaller eccentricity incomparison with the values known up to now. Moreover, fairly convincingevidence exists for an increase of the orbital period with time. Inaddition to the orbital motion we find further periods in the orbitalresiduals. The longest period of 57\fd7 is most likely due to a thirdbody which has the mass of a brown dwarf, whereas the period of 1\fd48could be related to the half rotational period of the star. For thespectral types we deduced A1 III for the primary and M for thesecondary. Two further periods of 0\fd21 and 0\fd22 give hint to theexistence of short-term pulsations in 21 Her. Their period difference isof the order of the expected rotational period so that one possibleexplanation could be rotational splitting of nonradial pulsation modes.Because of the very strong aliasing of the data this finding has to beconfirmed by observations having a more suitable time sampling, however.The analysis of photometric series and the Hipparcos photometry give nocertain evidence for periodic light variations. For gamma Gem, besidesthe orbital RV variation, no variations with amplitudes larger thanabout 100 m s-1 could be detected. The orbital elements ofgamma Gem are only slightly changed compared to the previously knownorbital solution by including our new radial velocities, but theiraccuracy is improved. For some chemical elements we determined theirabundances, NLTE values of C, O, and Na as well as LTE values of Mg, Sc,Fe, Cr, and Ti. We find the abundances to be rather close to the solarvalues, only carbon shows a little underabundance. The research is basedon spectroscopic observations made with the 2 m telescope at theThüringer Landessternwarte Tautenburg, Germany, and photometricobservations with the 0.6 m telescope of the National AstronomicalObservatory Rozhen, Bulgaria.
| Elemental abundance analyses with DAO spectrograms. XXIV. The Mercury Manganese stars upsilon Her, phi Her, and HR 7018
Elemental abundances analyses are performed for the Mercury-Manganesestars upsilon Her, phi Her, and HR 7018 consistent with previous studiesof this series using spectrograms obtained with Reticon and CCDdetectors. Comparisons of the first two analyses with those performedusing coadded photographic plates show the general consistency of thederived elemental abundances. For upsilon Her and for phi Her,abundances were newly found for O, and for Al, V, Zn, and Ce,respectively. HR 7018 is discovered to be a single-lined spectroscopicbinary. Its Sc abundance is the smallest of any class member withderived abundances and its Sr abundance the largest of any known HgMnstar. A correlation analysis of the most complete abundance sets for 20HgMn stars shows that the abundances of some elements are correlatedwith one another and some are functions of the stellar effectivetemperature. Table 6 is 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/367/597
| Sixth Catalogue of Fundamental Stars (FK6). Part III. Additional fundamental stars with direct solutions
The FK6 is a suitable combination of the results of the HIPPARCOSastrometry satellite with ground-based data, measured over a longinterval of time and summarized mainly in the FK5. Part III of the FK6(abbreviated FK6(III)) contains additional fundamental stars with directsolutions. Such direct solutions are appropriate for single stars or forobjects which can be treated like single stars. Part III of the FK6contains in total 3272 stars. Their ground-based data stem from thebright extension of the FK5 (735 stars), from the catalogue of remainingSup stars (RSup, 732 stars), and from the faint extension of the FK5(1805 stars). From the 3272 stars in Part III, we have selected 1928objects as "astrometrically excellent stars", since their instantaneousproper motions and their mean (time-averaged) ones do not differsignificantly. Hence most of the astrometrically excellent stars arewell-behaving "single-star candidates" with good astrometric data. Thesestars are most suited for high-precision astrometry. On the other hand,354 of the stars in Part III are Δμ binaries in the sense ofWielen et al. (1999). Many of them are newly discovered probablebinaries with no other hitherto known indication of binarity. The FK6gives, besides the classical "single-star mode" solutions (SI mode),other solutions which take into account the fact that hidden astrometricbinaries among "apparently single-stars" introduce sizable "cosmicerrors" into the quasi-instantaneously measured HIPPARCOS proper motionsand positions. The FK6 gives, in addition to the SI mode, the "long-termprediction (LTP) mode" and the "short-term prediction (STP) mode". TheseLTP and STP modes are on average the most precise solutions forapparently single stars, depending on the epoch difference with respectto the HIPPARCOS epoch of about 1991. The typical mean error of anFK6(III) proper motion in the single-star mode is 0.59 mas/year. This isa factor of 1.34 better than the typical HIPPARCOS errors for thesestars of 0.79 mas/year. In the long-term prediction mode, in whichcosmic errors are taken into account, the FK6(III) proper motions have atypical mean error of 0.93 mas/year, which is by a factor of about 2better than the corresponding error for the HIPPARCOS values of 1.83mas/year (cosmic errors included).
| Elemental abundance analyses with Complejo Astronomico El Leoncito REOSC echelle spectrograms. IV. Extensions of nine previous analyses
Using new CASLEO echelle spectrograms, we extended our elementalabundances of the sharp-lined Mercury-Manganese stars mu Lep, 14 Hya,kappa Cnc, HR 4487, HR 4817, 28 Her, and HR 7245, the closely relatedstar 3 Cen A, and 7 Sex an A0 V star with Population I abundances, butwith Population II star space motions. The lambda lambda 4500-6200region contains a sufficient number of lines to derive high-qualityabundances of these stars. For most stars, the new spectra provideadditional lines for the analyses which improve their quality as well ashelp fill in the periodic table. Table~5 is only available in electronicform at the CDS via anonymous ftp to cdsarc.u-strasbg.fr(130.79.128.5)or via http://cdsweb.u-strabg.fr/Abstract.html}
| Lithium in the Super-Beryllium-rich HG-MN Stars HR 6158 and HR 8915
The chemically peculiar stars that inhabit the upper main sequenceexhibit very extreme enhancements and deficiencies of several elements.In all likelihood, the primary cause of these anomalies is radiativelydriven diffusion, although other mechanisms may also be important-suchas mass loss and various kinds of mixing. Only by examining as manyelements as possible will a cohesive theory explaining these abundanceoddities materialize. To this end, we present high-resolution(R~62,500), high signal-to-noise ratio (S/N pixel^-1~120) observationsof the 6708 Å Li I resonance doublet in a pair of Hg-Mn stars. Norecord of a lithium detection has been found for this type of chemicallypeculiar star. The atmospheres of the two program stars (HR 6158=28Her=HD 149212; HR 8915=69 Peg=HD 220933) contain an inordinate amount ofberyllium (Be) in fact, the Be abundances in these stars are among thehighest known. While the LTE concentration of Be is several thousandtimes larger than cosmic [A(Be)_i~1.27] in both stars, lithium (Li) isdetected in neither HR 6158 nor HR 8915. The calculated 3 sigma (99%confidence level) upper limits place the maximum Li enhancements at 50times and 80 times cosmic [A(Li)_i~3.23] for HR 6158 and HR 8915,respectively, or ~100 times smaller than the Be overabundances. These Liupper limits, which argue against a ``nucleosynthesis'' origin for theBe surfeit, provide yet another means of constraining the physicalprocess (or processes) responsible for the Hg-Mn phenomenon in some Astars.
| Oxygen 6156-8 Angstroms Triplet in Chemically Peculiar Stars of the Upper Main Sequence: Do HgMn Stars Show an Oxygen Anomaly?
An extensive spectrum-fitting analysis in the lambda ~ 6150 Angstromsregion was performed for forty late-B and A chemically peculiar (HgMn,Ap, Am, weak-lined) and normal stars of the upper main sequence, inorder to quantitatively establish the abundance of oxygen from the O I6156-8 triplet and to study its behavior/anomaly for each peculiaritygroup, where special attention was paid to HgMn-type stars. Magnetic Apvariables (Si or SrCrEu type) generally show a remarkably large oxygendepletion (by ~ -1.6 dex to ~ -0.4 dex relative to the solar abundance),and classical Am stars also show a clear underabundance (by ~ -0.6 dexon the average). In contrast, the oxygen abundance in HgMn stars,exhibiting only a mild deficiency relative to the Sun typically by ~0.3-0.4 dex, is not markedly different from the tendency of normalstars, also showing a subsolar abundance ([O/H] =~ -0.2). In view of therecent observational implication that the present solar oxygen abundanceis enriched by ~ 0.2-0.3 dex relative to the interstellar gas (fromwhich young stars are formed), and thus unsuitable for the comparisonstandard, we concluded that the extent of the average O-deficiency inHgMn stars is appreciably reduced down to only ~ 0.1-0.2 dex (i.e., notmuch different from the initial composition), which contrasts with theirwell-known drastically large N-depletion. Yet, as can be seen from thedelicate and tight O vs. Fe anticorrelation, this marginal deficiencyshould be real, and thus some physical process simultaneously producingO-depletion/Fe-enrichment must have actually worked in the atmosphere ofHgMn stars.
| 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.
| Mercury Elemental and Isotopic Abundances in Mercury-Manganese Stars
Hg II abundances have been determined for 42 mercury-manganese (HgMn)stars by fitting synthetic spectra to observed spectra of the 3984Å Hg II line. Twenty of the stars had lines sharp enough to allowtheir Hg isotopic abundance mixes to be estimated. The Hg abundance isreported for more HgMn stars here than in any other single work. Nocorrelation was found between Hg II abundance and T_eff or the meancentral wavelength of HgMn lambda3984 stars. The mean central wavelengthof lambda3984 , an indicator of the Hg isotopic mix, is looselycorrelated with T_eff: stars with primarily heavy Hg isotopes tend to becooler, although one star, 46 Aql, has almost pure ^204Hg and T_eff inabout the middle of the temperature range for HgMn stars. We find thatthere is no evidence that any of the HgMn stars have ^196Hg or ^198Hg.For the very sharp-lined stars, the ^204Hg abundance decreases withincreasing T_eff. No correlation is seen between the mean centralwavelength and the surface gravity. No correlation was found between theprojected rotational velocity and the Hg II abundance or the centralwavelength of lambda3984, although this result may be biased by theselection of stars with low reported vsini. Hg I lambda4358 was measuredat high spectral resolution for seven HgMn stars. The isotopic shiftsare too small, and the hyperfine components are too weak to allowunambiguous isotopic abundance ratios to be found. Hg I abundancescorrelate fairly well with Hg II abundances. Some of the Hg isotopicmixtures are difficult to explain using only diffusion. HR 7245 hasapproximately equal abundances of ^199Hg, ^200Hg, ^202Hg, and ^204Hg butvery little ^201Hg, and 11 Per has Hg that is mostly ^199Hg and ^204Hg.Calculations show that hyperfine splitting of ^201Hg changes theradiative forces it feels compared with other isotopes, which may alterdiffusion of that isotope enough to explain its absence in HR 7245, butwe have found no possible explanation for the Hg isotopic mix found in11 Per. These are the first very high resolution measurements of Hg IIlambda3984 for HR 7245 and 11 Per. Although diffusion may be acting inHgMn stars, either there are one or more other mechanisms acting to helpproduce the overabundances and isotopic mixtures seen or ourunderstanding of diffusion is lacking on some important point.
| Radial velocities. Measurements of 2800 B2-F5 stars for HIPPARCOS
Radial velocities have been determined for a sample of 2930 B2-F5 stars,95% observed by the Hipparcos satellite in the north hemisphere and 80%without reliable radial velocity up to now. Observations were obtainedat the Observatoire de Haute Provence with a dispersion of 80Ä,mm(-1) with the aim of studying stellar and galactic dynamics.Radial velocities have been measured by correlation with templates ofthe same spectral class. The mean obtained precision is 3.0 km s(-1)with three observations. A new MK spectral classification is estimatedfor all stars. Based on observations made at the Haute ProvenceObservatory, France and on data from The Hipparcos Catalogue, ESA.Tables 4, 5 and 6 are only available in electronic form at the CDS viaanonymous ftp to cdsarc.u-strasbg.fr or viahttp://cdsweb.u-strasbg.fr/Abstract.htm
| 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.
| Mercury and platinum abundances in mercury-manganese stars
We report new results for the elemental and isotopic abundances of thenormally rare elements mercury and platinum in HgMn stars. Typicaloverabundances can be 4 dex or more. The isotopic patterns do not followthe fractionation model of White et al.
| 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 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.
| 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.
| 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.
| Elemental Abundance Analyses with DAO Spectrograms - Part Twelve - the Mercury / Manganese Stars HR:4072A and HR:7775 and the Metallic Lined Star HR:4072B
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1994MNRAS.266...97A&db_key=AST
| 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.
|
Enviar un nou article
Enllaços Relacionats
- - No s'ha trobat enllaços -
Enviar un nou enllaç
Membre dels grups següents:
|
Dades d'Observació i Astrometria
| Constel·lació: | Hercules |
| Ascensió Recta: | 16h32m35.70s |
| Declinació: | +05°31'16.0" |
| Magnitud Aparent: | 5.63 |
| Distancia: | 98.814 parsecs |
| Moviment propi RA: | 14 |
| Moviment propi Dec: | 0.3 |
| B-T magnitude: | 5.559 |
| V-T magnitude: | 5.612 |
Catàlegs i designacions:
|
