Оглавление
Изображения
Загрузить ваше изображение
DSS Images Other Images
Публикации по объекту
The Geneva-Copenhagen survey of the solar neighbourhood. III. Improved distances, ages, and kinematics
Context: Ages, chemical compositions, velocity vectors, and Galacticorbits for stars in the solar neighbourhood are fundamental test datafor models of Galactic evolution. The Geneva-Copenhagen Survey of theSolar Neighbourhood (Nordström et al. 2004; GCS), amagnitude-complete, kinematically unbiased sample of 16 682 nearby F andG dwarfs, is the largest available sample with complete data for starswith ages spanning that of the disk. Aims: We aim to improve theaccuracy of the GCS data by implementing the recent revision of theHipparcos parallaxes. Methods: The new parallaxes yield improvedastrometric distances for 12 506 stars in the GCS. We also use theparallaxes to verify the distance calibration for uvby? photometryby Holmberg et al. (2007, A&A, 475, 519; GCS II). We add newselection criteria to exclude evolved cool stars giving unreliableresults and derive distances for 3580 stars with large parallax errorsor not observed by Hipparcos. We also check the GCS II scales of T_effand [Fe/H] and find no need for change. Results: Introducing thenew distances, we recompute MV for 16 086 stars, and U, V, W,and Galactic orbital parameters for the 13 520 stars that also haveradial-velocity measurements. We also recompute stellar ages from thePadova stellar evolution models used in GCS I-II, using the new valuesof M_V, and compare them with ages from the Yale-Yonsei andVictoria-Regina models. Finally, we compare the observed age-velocityrelation in W with three simulated disk heating scenarios to show thepotential of the data. Conclusions: With these revisions, thebasic data for the GCS stars should now be as reliable as is possiblewith existing techniques. Further improvement must await consolidationof the T_eff scale from angular diameters and fluxes, and the Gaiatrigonometric parallaxes. We discuss the conditions for improvingcomputed stellar ages from new input data, and for distinguishingdifferent disk heating scenarios from data sets of the size andprecision of the GCS.Full Table 1 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/501/941
| The Geneva-Copenhagen survey of the Solar neighbourhood. Ages, metallicities, and kinematic properties of 14 000 F and G dwarfs
We present and discuss new determinations of metallicity, rotation, age,kinematics, and Galactic orbits for a complete, magnitude-limited, andkinematically unbiased sample of 16 682 nearby F and G dwarf stars. Our63 000 new, accurate radial-velocity observations for nearly 13 500stars allow identification of most of the binary stars in the sampleand, together with published uvbyβ photometry, Hipparcosparallaxes, Tycho-2 proper motions, and a few earlier radial velocities,complete the kinematic information for 14 139 stars. These high-qualityvelocity data are supplemented by effective temperatures andmetallicities newly derived from recent and/or revised calibrations. Theremaining stars either lack Hipparcos data or have fast rotation. Amajor effort has been devoted to the determination of new isochrone agesfor all stars for which this is possible. Particular attention has beengiven to a realistic treatment of statistical biases and errorestimates, as standard techniques tend to underestimate these effectsand introduce spurious features in the age distributions. Our ages agreewell with those by Edvardsson et al. (\cite{edv93}), despite severalastrophysical and computational improvements since then. We demonstrate,however, how strong observational and theoretical biases cause thedistribution of the observed ages to be very different from that of thetrue age distribution of the sample. Among the many basic relations ofthe Galactic disk that can be reinvestigated from the data presentedhere, we revisit the metallicity distribution of the G dwarfs and theage-metallicity, age-velocity, and metallicity-velocity relations of theSolar neighbourhood. Our first results confirm the lack of metal-poor Gdwarfs relative to closed-box model predictions (the ``G dwarfproblem''), the existence of radial metallicity gradients in the disk,the small change in mean metallicity of the thin disk since itsformation and the substantial scatter in metallicity at all ages, andthe continuing kinematic heating of the thin disk with an efficiencyconsistent with that expected for a combination of spiral arms and giantmolecular clouds. Distinct features in the distribution of the Vcomponent of the space motion are extended in age and metallicity,corresponding to the effects of stochastic spiral waves rather thanclassical moving groups, and may complicate the identification ofthick-disk stars from kinematic criteria. More advanced analyses of thisrich material will require careful simulations of the selection criteriafor the sample and the distribution of observational errors.Based on observations made with the Danish 1.5-m telescope at ESO, LaSilla, Chile, and with the Swiss 1-m telescope at Observatoire deHaute-Provence, France.Complete Tables 1 and 2 are only available in electronic form at the CDSvia anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/418/989
| Stellar Kinematic Groups. II. A Reexamination of the Membership, Activity, and Age of the Ursa Major Group
Utilizing Hipparcos parallaxes, original radial velocities and recentliterature values, new Ca II H and K emission measurements,literature-based abundance estimates, and updated photometry (includingrecent resolved measurements of close doubles), we revisit the UrsaMajor moving group membership status of some 220 stars to produce afinal clean list of nearly 60 assured members, based on kinematic andphotometric criteria. Scatter in the velocity dispersions and H-Rdiagram is correlated with trial activity-based membership assignments,indicating the usefulness of criteria based on photometric andchromospheric emission to examine membership. Closer inspection,however, shows that activity is considerably more robust at excludingmembership, failing to do so only for <=15% of objects, perhapsconsiderably less. Our UMa members demonstrate nonzero vertex deviationin the Bottlinger diagram, behavior seen in older and recent studies ofnearby young disk stars and perhaps related to Galactic spiralstructure. Comparison of isochrones and our final UMa group membersindicates an age of 500+/-100 Myr, some 200 Myr older than thecanonically quoted UMa age. Our UMa kinematic/photometric members' meanchromospheric emission levels, rotational velocities, and scattertherein are indistinguishable from values in the Hyades and smaller thanthose evinced by members of the younger Pleiades and M34 clusters,suggesting these characteristics decline rapidly with age over 200-500Myr. None of our UMa members demonstrate inordinately low absolutevalues of chromospheric emission, but several may show residual fluxes afactor of >=2 below a Hyades-defined lower envelope. If one defines aMaunder-like minimum in a relative sense, then the UMa results maysuggest that solar-type stars spend 10% of their entire main-sequencelives in periods of precipitously low activity, which is consistent withestimates from older field stars. As related asides, we note six evolvedstars (among our UMa nonmembers) with distinctive kinematics that liealong a 2 Gyr isochrone and appear to be late-type counterparts to diskF stars defining intermediate-age star streams in previous studies,identify a small number of potentially very young but isolated fieldstars, note that active stars (whether UMa members or not) in our samplelie very close to the solar composition zero-age main sequence, unlikeHipparcos-based positions in the H-R diagram of Pleiades dwarfs, andargue that some extant transformations of activity indices are notadequate for cool dwarfs, for which Ca II infrared triplet emissionseems to be a better proxy than Hα-based values for Ca II H and Kindices.
| Catalogue of [Fe/H] determinations for FGK stars: 2001 edition
The catalogue presented here is a compilation of published atmosphericparameters (Teff, log g, [Fe/H]) obtained from highresolution, high signal-to-noise spectroscopic observations. This newedition has changed compared to the five previous versions. It is nowrestricted to intermediate and low mass stars (F, G and K stars). Itcontains 6354 determinations of (Teff, log g, [Fe/H]) for3356 stars, including 909 stars in 79 stellar systems. The literature iscomplete between January 1980 and December 2000 and includes 378references. The catalogue is made up of two tables, one for field starsand one for stars in galactic associations, open and globular clustersand external galaxies. The catalogue is distributed through the CDSdatabase. Access to the catalogue with cross-identification to othersets of data is also possible with VizieR (Ochsenbein et al.\cite{och00}). The catalogue (Tables 1 and 2) is only available inelectronic form at the 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/373/159 and VizieRhttp://vizier.u-strasbg.fr/.
| 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
| Stellar kinematic groups. I - The Ursa Major group
The Ursa Major Group (UMaG) is studied as a test case for theauthenticity of Stellar Kinematic Groups, using Coravel radialvelocities, recent compilations of astrometric data, and newspectroscopic observations. Spectroscopic age indicators, particularlyindices of the strength of chromospheric emission, are applied tosolar-type candidate members of UMaG, and it is shown that stars thatmeet the spectroscopic criteria also have kinematics that agree betterwith the space motions of the nucleus of UMaG than does the startingsample as a whole. The primary limitation on the precision of kinematicsis now parallaxes instead of radial velocities. These more restrictivekinematic criteria are then applied to other UMaG candidates and a listsummarizing membership is presented. UMaG is also examined as a cluster,confirming its traditional age of 0.3 Gyr, and a mean Fe/H of -0.08 +/-0.09 for those stars most likely to be bona fide members.
| 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.
| Lithium, age, and metallicity in open clusters
It is shown that a strong relationship exists between Li abundance andage for stars in the temperature region 5950-6350 K. The relation isderived from mean Li abundances in eight open clusters ranging in agefrom 5 x 10 to the 7th to 8 x 10 to the 9th yr. The Li declinesexponentially with t exp(-0.3). It is suggested that, in thistemperature regime, simple microscopic diffusion is the cause of the Lidepletion. It is possible that there is a metallicity term in therelation, such that higher metallicity clusters with deeper convectionzones have less Li depletion, while lower metallicity cluster undergogreater depletion. This is consistent with expectations from diffusiontheory. Furthermore, the halo stars, with even lower metallicity andshallower convection zones, would have more diffusion and more Lidepletion; this is in agreement with recent theoretical work.
| A. de Sitter's photographic polar photometry revisited; some remarks on photographic photometry with objective gratings
Not Available
| Lithium and metallicity in the Ursa Major group
The Li abundances for the UMa group F stars are reported, and the UMaLi-temperature profile is compared with that of the Hyades and the ComaBerenices clusters. The (Fe/H) abundances are determined in order toprovide a spectroscopic calibration of photometric indices and anothercriterion for UMa Group membership. The abundances are compared with themetallicity of other young clusters to study the degree of mixing in theGalactic disk in the solar neighborhood.
| Chromospheric and transition-region emission from young solar-type stars in clusters, kinematic groups, and the field
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1987AJ.....93..920S&db_key=AST
| Locations of the components of triple star systems north of +70 deg
Micrometric measurements of triple systems north of +70 deg declinationwere made with the 10.5-inch Fraunhofer refractor of Munich UniversityObservatory. Absolute positions of all measured components were derivedby using the positions of the main stars as given in the catalog AGK3and, in some cases, also in the SAO-catalog.
| Rotational studies of late-type stars. II - Ages of solar-type stars and the rotational history of the sun
Main-sequence stars later than approximately F5 have little angularmomentum. Kraft (1967) has studied the loss of angular momentum instars, taking into account late-F dwarfs with masses corresponding to1.2 solar masses. The present investigation has the objective toconsider the problem of angular momentum loss for stars as near onesolar mass as possible, and to compare the sun to similar stars. Thisobjective made it necessary to measure the small 'v sin i' valuestypical of these stars. The required techniques were discussed in thefirst part of the investigation. In the current part of theinvestigation, the v sin i values of solar-type stars are analyzed andcompared to the Li ages. It is assumed that all stars start with thesame Li abundance, and that the Li depletion rate depends only on thestellar mass. The assumption is made that the sun is typical for itsmass and age. These assumptions can be tested observationally, but muchwork remains to be done.
| Meridian observations made with the Carlsberg Automatic Meridian Circle at Brorfelde (Copenhagen University Observatory) 1981-1982
The 7-inch transit circle instrument with which the present position andmagnitude catalog for 1577 stars with visual magnitudes greater than11.0 was obtained had been equipped with a photoelectric moving slitmicrometer and a minicomputer to control the entire observationalprocess. Positions are reduced relative to the FK4 system for each nightover the whole meridian rather than the usual narrow zones. Thepositions of the FK4 stars used in the least squares solution are alsogiven in the catalog.
| Rotational studies of late-type stars. I - Rotational velocities of solar-type stars
The present investigation has the objective to obtain good rotationalvelocities for a large sample of solar-type stars, primarily for thepurpose of discussing angular momentum loss. A demonstration is providedof the technique of line profile modeling, and the factors whichcontribute to uncertainty at small v sin i's are examined. The excellentfits which can be made to solar data using simple models indicate thatsystematic errors associated with the line modeling process arenegligible. Such fits to the sun are essential for ensuring reliableresults for slow rotators. The technique of profile modeling can discerndifferences in v sin i of less than 0.3 km/s for stars rotating asslowly as the sun if the data are of very high quality.
| Visual multiples. VII - MK classifications
Classifications are given for 865 components of visual multiples; theyshow no systematic differences from the MK system, and the random errorsare one subclass in type and two-thirds of a luminosity class. It isfound that at least 1% of the F-type IV and V stars are weak-lined, 32%of the A4-F1 IV and V stars are Am, and 5% of the A0-A3 IV and V starsare early-type Am. Attention is called to the large fraction (55%) ofthe A3-A9 III-V stars that are of luminosity classes III or IV, unlikethe percentage (16%) at neighboring types.
| Spectral types in the Ursa major stream.
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1978PASP...90..429L&db_key=AST
| Catalogue des étoiles mesurées dans le système photométrique de l'Observatoire de Genève
Not Available
| Nova Herculis 1963
Not Available
| Photo-electric observations in four colours of the ultra-short-period variable SZ Lyncis
Not Available
| Three-Color Photometry of Nearby Stars.
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1957ApJ...126..113J&db_key=AST
| The color-luminosity diagram of the UMa group.
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1954AJ.....59..233M&db_key=AST
| Photographic magnitudes of stars brighter than 7m.75 between +75° and +80° declination (Errata: 11 270)
Not Available
| Yerkes actinometry. Zone +73deg to +90deg.
Not Available
|
Добавить новую статью
Внешние ссылки
- - Внешних ссылок не найдено -
Добавить внешнюю ссылку
Группы:
|
Наблюдательные данные и астрометрия
| Созвездие: | Жираф |
| Прямое восхождение: | 10h59m20.97s |
| Склонение: | +79°40'33.2" |
| Видимая звёздная величина: | 7.346 |
| Расстояние: | 62.461 парсек |
| Собственное движение RA: | 53.2 |
| Собственное движение Dec: | 41.7 |
| B-T magnitude: | 8.004 |
| V-T magnitude: | 7.401 |
Каталоги и обозначения:
|
