תוכן
תמונות
הוסף תמונה שלך
DSS Images Other Images
מאמרים קשורים
Rotation and Lithium Surface Abundances, Revisited
For giants in the Hertzsprung gap, the relations betweenTeff, vsini, and lithium surface abundances arereinvestigated and compared with the relations found for Hyadesmain-sequence F stars. For the Hyades main-sequence F stars, the vsinidecrease steeply around Teff~6450 K. At the same temperaturethe lithium surface abundances show a narrow, deep dip. For most giantsthere is also a steep decrease of vsini for Teff around 6450K. At this temperature the lithium surface abundances of the giants alsodecrease steeply and remain low for Teff<6400 K. Thechanges in rotation and Li surface abundances occur over a temperatureinterval of less than 300 K, which for a 2 Msolar giantcorresponds to an age interval of about 106 yr. Thesimultaneous steep decreases of rotation velocities and Li surfaceabundances indicate that for the giants these changes are due to thesame cause, which we suggest to be deep mixing. It then seems ratherlikely that for the Hyades main-sequence F5 V stars the decrease ofrotation and Li surface abundance is also caused by deep mixing. Wesuggest that in both cases the changes are related to the merging of thehydrogen and helium convection zones.
| Observational constraints for lithium depletion before the RGB
Precise Li abundances are determined for 54 giant stars mostly evolvingacross the Hertzsprung gap. We combine these data with rotationalvelocity and with information related to the deepening of the convectivezone of the stars to analyse their link to Li dilution in the referredspectral region. A sudden decline in Li abundance paralleling the onealready established in rotation is quite clear. Following similarresults for other stellar luminosity classes and spectral regions, thereis no linear relation between Li abundance and rotation, in spite of thefact that most of the fast rotators present high Li content. The effectsof convection in driving the Li dilution is also quite clear. Stars withhigh Li content are mostly those with an undeveloped convective zone,whereas stars with a developed convective zone present clear sign of Lidilution.Based on observations collected at ESO, La Silla, Chile, and at theObservatoire de Haute Provence, France, operated by the Centre Nationalde la Recherche Scientifique (CNRS).
| High resolution spectroscopy over lambda lambda 8500-8750 Å for GAIA. IV. Extending the cool MK stars sample
A library of high resolution spectra of MK standard and reference stars,observed in support to the GAIA mission, is presented. The aim of thispaper is to integrate the MK mapping of Paper I of this series as wellas to consider stars over a wider range of metallicities. Radialvelocities are measured for all the target stars.The spectra are available in electronic form (ASCII format) at CDS viaanonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/406/995 and from the webpage http://ulisse.pd.astro.it/MoreMK/, where further bibliographicalinformation for the target stars is given.
| The Rotation of Binary Systems with Evolved Components
In the present study we analyze the behavior of the rotational velocity,vsini, for a large sample of 134 spectroscopic binary systems with agiant star component of luminosity class III, along the spectral regionfrom middle F to middle K. The distribution of vsini as a function ofcolor index B-V seems to follow the same behavior as their singlecounterparts, with a sudden decline around G0 III. Blueward of thisspectral type, namely, for binary systems with a giant F-type component,one sees a trend for a large spread in the rotational velocities, from afew to at least 40 km s-1. Along the G and K spectral regionsthere are a considerable number of binary systems with moderate tomoderately high rotation rates. This reflects the effects ofsynchronization between rotation and orbital motions. These rotatorshave orbital periods shorter than about 250 days and circular or nearlycircular orbits. Except for these synchronized systems, the largemajority of binary systems with a giant component of spectral type laterthan G0 III are composed of slow rotators.
| A catalog of rotational and radial velocities for evolved stars
Rotational and radial velocities have been measured for about 2000evolved stars of luminosity classes IV, III, II and Ib covering thespectral region F, G and K. The survey was carried out with the CORAVELspectrometer. The precision for the radial velocities is better than0.30 km s-1, whereas for the rotational velocity measurementsthe uncertainties are typically 1.0 km s-1 for subgiants andgiants and 2.0 km s-1 for class II giants and Ib supergiants.These data will add constraints to studies of the rotational behaviourof evolved stars as well as solid informations concerning the presenceof external rotational brakes, tidal interactions in evolved binarysystems and on the link between rotation, chemical abundance and stellaractivity. In this paper we present the rotational velocity v sin i andthe mean radial velocity for the stars of luminosity classes IV, III andII. Based on observations collected at the Haute--Provence Observatory,Saint--Michel, France and at the European Southern Observatory, LaSilla, Chile. Table \ref{tab5} also available in electronic form at CDSvia anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/Abstract.html
| The Tokyo PMC catalog 90-93: Catalog of positions of 6649 stars observed in 1990 through 1993 with Tokyo photoelectric meridian circle
The sixth annual catalog of the Tokyo Photoelectric Meridian Circle(PMC) is presented for 6649 stars which were observed at least two timesin January 1990 through March 1993. The mean positions of the starsobserved are given in the catalog at the corresponding mean epochs ofobservations of individual stars. The coordinates of the catalog arebased on the FK5 system, and referred to the equinox and equator ofJ2000.0. The mean local deviations of the observed positions from theFK5 catalog positions are constructed for the basic FK5 stars to comparewith those of the Tokyo PMC Catalog 89 and preliminary Hipparcos resultsof H30.
| 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.
| The lithium content and other properties of F2-G5 giants in the Hertzsprung Gap
As stars of 2-5 solar mass evolve across the Hertzsprung Gap they shouldfirst deplete their surface lithium by convective dilution and then,when convection penetrates deeper, begin to bring CN processed materialto their surfaces. To investigate this process we have observed 52giants, 25 of which have known C/N ratios, for their Li abundances.After eliminating four stars that may actually be dwarfs and includingthe two components of Capella analyzed by Pilachowski and Sowell we havecompared our (Li/Fe) ratios with models of Swenson. For stars showing vsin i greater than 50 km/s we find (Li/Fe) to be unaffected by mixingfor B - V less than 0.7 as predicted. For stars cooler than B - V = 0.7both v sin i and (Li/Fe) drop to smaller values. For the sharp linedstars (v sin i less than 50 km/s) we find a drop in Li between B - V =0.45 and 0.60 which cannot be understood in terms of dilution byconvection. Various possible causes of such an early depletion ordilution of surface Li are discussed including diffusion at the base ofthe convection zone, mass loss possibly enhanced by pulsation, andmagnetic activity as in the magnetic A and B type stars. The models ofRicher & Michaud (1993) with diffusion point toward a satisfactorysolution. A few giants with low v sin i values stand out with muchhigher than expected (Li/Fe) values despite their cool effectivetemperatures. We do not understand why those stars have not depletedtheir lithium as have most giants of similar color. The correlation of(N/C) with (Li/Fe) follows expectations in so far as almost all starswith enhanced (N/C) have depleted their Li as well.
| Improved Mean Positions and Proper Motions for the 995 FK4 Sup Stars not Included in the FK5 Extension
Not Available
| The composite nature of the peculiar star HR 6560 (HD 159870)
Ground-based high-dispersion photographic spectra and ultravioletspectra obtained with the IUE satellite are described and employed todetermine the nature of the peculiar star HR 6560 (HD 159870).Previously this object had been described as both a composite system andas a strong Fm star. The UBVRI, Stromgren, and ultraviolet colors of HR6560 are compared with objects classified composite from the Bright StarCatalogue and normal dwarfs and giants. The colors of HR 6560 are notunusual for a composite and are consistent with a late-A dwarf, combinedwith a late-G or early-K giant. The ultraviolet satellite clearly showsthe presence of an A component, but its precise spectral type isdifficult to assign. The IUE and TD-1 data suggest that the ultravioletis dominated by light from an A5 V secondary and the visual from a GOIII primary. This does not agree well with the most plausible model thatfits the visual photometry. The peculiar nature of HR 6560's spectrum ismost likely due to its composite nature.
| The near-IR NA I doublet and CA II triplet in late-type stars and the determination of stellar atmosphere parameters
CCD spectroscopic observations in the near-IR (7990-8680 A) for a sampleof 144 late type stars are presented. The dependence of the Na I doublet(8183 and 8194 A) and the Ca II triplet (8498, 8542 and 8662 A) onstellar atmospheric parameters is investigated. It is confirmed in starsof spectral types later than G0 a dependence of line strength oneffective temperature, surface gravity, and metallicity in goodagreement with previous studies. However, the present sample containsmany more very late type stars than previous studies, and these starsshow a strong dependence of Ca-II triplet strength on temperature. Theselines, together with the (R - I) color index which is known to be a goodtemperature indicator, were used to estimate the metal abundance and thesurface gravity of the present program stars.
| The rotational break for G giants
New high-resolution spectroscopic observations have been obtained for 73G giants. Fourier analysis of their spectral lines yields rotationvelocities and macroturbulence dispersions. Combined with data from anearlier study, total of 86 analyses of luminosity class III giants isnow available. The existence of a rotational discontinuity forluminosity class III giants is confirmed, but it is found to be near G0III rather than G5 III, as indicated in the earlier work. Evidence forrotation being a single-valued function of spectral type isstrengthened. The observations are interpreted in terms of adynamo-generated magnetic brake and a 'rotostat' phenomenon.
| Spectral classification of middle-type supergiants in the photographic infrared
A semiquantitative spectral classification scheme for middle-typesupergiant stars is presented which is wholly dependent on data in thenear infrared. The method involves the measurement of central depths asindicators of the strengths of the Paschen hydrogen lines 12 through 16,the Ca II infrared triplet and the 7774-A blend of O I, and was testedon slit spectrograms of previously classified stars of spectral types B8through G2. Results for the 142 stars considered are found to agree wellwith the MK spectral types determined previously, particularly inspectral types A5 through G0 and luminosity classes Ia through II.
| Pulsation in peculiar A stars.
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1975AJ.....80..698P&db_key=AST
| Catalog of Indidual Radial Velocities, 0h-12h, Measured by Astronomers of the Mount Wilson Observatory
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1970ApJS...19..387A&db_key=AST
|
הכנס מאמר חדש
לינקים קשורים
הכנס לינק חדש
משמש של הקבוצה הבאה
|
תצפית ומידע אסטרומטרי
| קבוצת-כוכבים: | ג'ירף |
| התרוממות ימנית: | 08h02m30.81s |
| סירוב: | +63°05'25.1" |
| גודל גלוי: | 6.082 |
| תנועה נכונה: | -9.9 |
| תנועה נכונה: | -14 |
| B-T magnitude: | 6.913 |
| V-T magnitude: | 6.151 |
קטלוגים וכינוים:
|
