目录
图像
上传图像
DSS Images Other Images
相关文章
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.
| Variability of the He I λ5876 Å line in early type chemically peculiar stars. II
To try to understand the behavior of helium variability in ChemicallyPeculiar stars, we continued our on-going observational campaign startedby \cite{catanzaro99}. In this paper we present a new set of timeresolved spectroscopic observations of the He I 5876 Å line for asample of 10 stars in the spectral range B3 - A2 and characterized bydifferent overabundances.This line does not show variability in two stars: HD 77350 and HD175156. It shows instead an equivalent width variation in phase with theHipparcos light curve for two stars: HD 79158 and HD 196502. Antiphasevariations have been found in 4 stars of our sample, namely: HD 35502,HD 124224, HD 129174 and HD 142990. Nothing we can say about HD 115735because of the constancy of Hipparcos photometric data, while no phaserelation has been observed for HD 90044.In the text we discuss the case of HD 175156, according to photometriccalibration and our spectroscopic observations we rule out themembership of this star to the main sequence chemically peculiar stars.We confirm the results obtained in the previous paper for which phaserelations between light, spectral and magnetic variations are notdependent on stellar spectral type or peculiarity subclass.Based on observations collected at stellar station ``M. G. Fracastoro''of the Catania Astrophysical Observatory and on observations collectedat Complejo Astrónomico El Leoncito (Casleo), which is operatedunder agreement between the Consejo Nacional de InvestigationesCientifícas y Técnicas (CONICET) and the NationalUniversities of La Plata, Córdoba and San Juan.
| Catalogue of averaged stellar effective magnetic fields. I. Chemically peculiar A and B type stars
This paper presents the catalogue and the method of determination ofaveraged quadratic effective magnetic fields < B_e > for 596 mainsequence and giant stars. The catalogue is based on measurements of thestellar effective (or mean longitudinal) magnetic field strengths B_e,which were compiled from the existing literature.We analysed the properties of 352 chemically peculiar A and B stars inthe catalogue, including Am, ApSi, He-weak, He-rich, HgMn, ApSrCrEu, andall ApSr type stars. We have found that the number distribution of allchemically peculiar (CP) stars vs. averaged magnetic field strength isdescribed by a decreasing exponential function. Relations of this typehold also for stars of all the analysed subclasses of chemicalpeculiarity. The exponential form of the above distribution function canbreak down below about 100 G, the latter value representingapproximately the resolution of our analysis for A type stars.Table A.1 and its references are only available in electronic form atthe CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/407/631 and Tables 3 to 9are only available in electronic form at http://www.edpsciences.org
| 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.
| 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
| A highly sensitive search for magnetic fields in B, A and F stars
Circular spectropolarimetric observations of 74 stars were obtained inan attempt to detect magnetic fields via the longitudinal Zeeman effectin their spectral lines. The sample observed includes 22 normal B, A andF stars, four emission-line B and A stars, 25 Am stars, 10 HgMn stars,two lambda Boo stars and 11 magnetic Ap stars. Using the Least-SquaresDeconvolution multi-line analysis approach (Donati et al.\cite{donati97etal}), high precision Stokes I and V mean signatures wereextracted from each spectrum. We find absolutely no evidence formagnetic fields in the normal, Am and HgMn stars, with upper limits onlongitudinal field measurements usually considerably smaller than anypreviously obtained for these objects. We conclude that if any magneticfields exist in the photospheres of these stars, these fields are notordered as in the magnetic Ap stars, nor do they resemble the fields ofactive late-type stars. We also detect for the first time a field in theA2pSr star HD 108945 and make new precise measurements of longitudinalfields in five previously known magnetic Ap stars, but do not detectfields in five other stars classified as Ap SrCrEu. We also report newresults for several binary systems, including a new vsin i for therapidly rotating secondary of the Am-delta Del SB2 HD 110951. Based onobservations obtained using the MuSiCoS spectropolarimeter on theBernard Lyot telescope, l'Observatoire du Pic du Midi, France.
| 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.
| 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
| Another Search for Maia Variable Stars
We have used the Hipparcos epoch photometry database, andautocorrelation analysis, to search for the elusive Maiavariables-short-period B7-A3 near-main-sequence pulsating variablestars. Of several hundred stars considered, and several dozen starsstudied in detail, only a handful are possible variables: three arepossible shallow eclipsing variables; three have possible periods in therange 0.25-0.5 day, but their amplitudes are so low that they areprobably nonvariable. The most promising are HD 29573, with a period of1.6 days (but possibly a rotating variable), and γ CrB, with aperiod of 0.9 day-a period also found spectroscopically by Lehmann andcoworkers. Sirius shows variations which are probably instrumental. Twopreviously suspected Maia stars-Maia and γ UMi-are photometricallyconstant. The Maia variables-if they exist-are very rare and veryelusive.
| 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.
| 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.
| 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 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
| Do SI stars undergo any rotational braking?
The old question of rotational braking of Ap Si stars is revisited onthe empirical side, taking advantage of the recent Hipparcos results.Field stars with various evolutionary states are considered, and it isshown that the loose correlation between their rotational period andtheir surface gravity is entirely compatible with conservation ofangular momentum. No evidence is found for any loss of angular momentumon the Main Sequence, which confirms earlier results based on lessreliable estimates of surface gravity. The importance of reliable,fundamental T_eff determinations of Bp and Ap stars is emphasized. Basedon data from the ESA Hipparcos satellite
| 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 of the mercury-manganese stars HR 89 and 33 Geminorum
Using ATLAS9 model atmospheres and two spectrograms each of themercury-manganese stars HR 89 and 33 Geminorum obtained with a 3 kpixellong CCD, camera 5 and grating A at the Kitt Peak National Observatorycoude feed telescope, we derive the elemental abundances of these stars.Both are extraordinary objects with Mn abundances similar to those of Feand marked He deficiencies. 33 Gem is the hottest known HgMn star.
| The ROSAT all-sky survey catalogue of optically bright OB-type stars.
For the detailed statistical analysis of the X-ray emission of hot starswe selected all stars of spectral type O and B listed in the Yale BrightStar Catalogue and searched for them in the ROSAT All-Sky Survey. Inthis paper we describe the selection and preparation of the data andpresent a compilation of the derived X-ray data for a complete sample ofbright OB stars.
| The Relation between Rotational Velocities and Spectral Peculiarities among A-Type Stars
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1995ApJS...99..135A&db_key=AST
| Vitesses radiales. Catalogue WEB: Wilson Evans Batten. Subtittle: Radial velocities: The Wilson-Evans-Batten catalogue.
We give a common version of the two catalogues of Mean Radial Velocitiesby Wilson (1963) and Evans (1978) to which we have added the catalogueof spectroscopic binary systems (Batten et al. 1989). For each star,when possible, we give: 1) an acronym to enter SIMBAD (Set ofIdentifications Measurements and Bibliography for Astronomical Data) ofthe CDS (Centre de Donnees Astronomiques de Strasbourg). 2) the numberHIC of the HIPPARCOS catalogue (Turon 1992). 3) the CCDM number(Catalogue des Composantes des etoiles Doubles et Multiples) byDommanget & Nys (1994). For the cluster stars, a precise study hasbeen done, on the identificator numbers. Numerous remarks point out theproblems we have had to deal with.
| 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
| A new list of effective temperatures of chemically peculiar stars. II.
Not Available
| Elemental abundance analyses with DAO spectrograms. X - The mercury-manganese stars Pi(1) Bootis, Upsilon Herculis and HR 7361
This paper presents fine analyses of three sharp-lined mercury-manganesestars: Pi(1) Bootis, Upsilon Herculis and HR 7361. The most Hg-richamong the 12 HgMn stars studied in this series is Pi(1) Boo. Both it andUpsilon Her are Fe- and Ni-poor. The greatest P and Mn overabundancesseen in the HgMn stars occur in Hr 7361; this is also the most S-poorand one of the few Ca- and Xe-rich HgMn stars. Some correlations arefound between the consistently analyzed abundances for the 12 stars.These correlations are expected if radiative diffusive processes areoperating.
| C, N, and O abundances in some CP stars
We present the results of C, N, and O abundance analysis in theatmospheres of 7 CP magnetic (Si) and nonmagnetic (Hg-Mn) stars. Thevisible lines of CII, NII, and OI were used for the analysis. The mean Cand O abundances are nearly solar, with a significant dispersion fromstar to star, while N is overabundant in the atmospheres of all magneticstars. This result does not agree with that of other works, where theauthors obtained a deficiency of C, N, and O elements by using lines ofneutral C, N, and O in the infrared. Possible reasons for such adiscrepancy are discussed.
| A catalogue of Fe/H determinations - 1991 edition
A revised version of the catalog of Fe/H determinations published by G.Cayrel et al. (1985) is presented. The catalog contains 3252 Fe/Hdeterminations for 1676 stars. The literature is complete up to December1990. The catalog includes only Fe/H determinations obtained from highresolution spectroscopic observations based on detailed spectroscopicanalyses, most of them carried out with model atmospheres. The catalogcontains a good number of Fe/H determinations for stars from open andglobular clusters and for some supergiants in the Magellanic Clouds.
| Chemical analysis of the atmosphere of the CP3 star Pi(1) Boo - Revision of a previous analysis
An analysis of the atmosphere of the CP3 star Pi(1) Boo using anLTE-blanketed model atmosphere is presented. The Ca-K line and Sr lineswere calculated under the approximate NLTE option considering partialredistribution. The adopted value of microturbulence is discussed. Aprevious atmosphere analysis is revised by including more accurategf-values and a different model atmosphere. The largest changes are instrontium, yttrium, scandium and carbon abundances derived from singlyionized lines. The elements strontium, yttrium and scandium are stronglyoverabundant while iron, titanium and calcium are underabundant; theabundance differences are in excess of 1 dex value.
| Chemical analysis of the atmosphere of CP 3 star Pi(1) Boo
The paper discusses the chemical analysis of the atmosphere of CP 3 starPi(1) Boo by the method of synthetic spectrum using an LTE modelatmosphere. The Ca II K line was calculated on the assumption of an NLTEapproximation considering partial redistribution. The selection of asuitable model atmosphere for CP 3 stars and the influence of gf-valueson the resulting abundance of elements in the atmosphere of the star arediscussed. As expected, the accuracy of the chemical analysis was muchaffected by the selection of spectral lines and atomic parameters.
| Spectrum variability of some selected bright CP stars on the main sequence
The initial findings of a survey for spectrum variations in selected CPstars is reported. It is found that almost all observedmercury-manganese stars are spectrum variables. The implications ofchemical anomalies in these stars are briefly discussed. In particular,arguments are advanced against the general assumption that CP3 stars arenonmagnetic. The observed low rotational velocities of the CP3 stars areinterpreted as rotational braking by magnetic fields mostly in thepre-main-sequence stage of evolution of these objects. The hypothesis isadvanced that high resolution spectroscopic observations of such starswould exhibit Zeeman-broadening in lines that vary in strength and arealso sensitive to the magnetic field.
| The catalogue of equivalent line widths in the spectra of A- and F-stars.
Not Available
|
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:
|
