Оглавление
Изображения
Загрузить ваше изображение
DSS Images Other Images
Публикации по объекту
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
| Coronagraphic Imaging with the Hubble Space Telescope and the Space Telescope Imaging Spectrograph
The unfiltered Space Telescope Imaging Spectrograph (STIS) CCD in tandemwith focal plane wedges and a Lyot stop provides a simple white-lightcoronagraph with a bandpass of 0.2-1.0 μm, which has been used sincelate 1998 to image nebulosity around stars in the ranges0.34<=V<=14 and -0.03<=B-V<=1.65. The residual starlightseen in STIS coronagraphic images includes diffraction spikes due to theHubble Space Telescope (HST) secondary support structure, lacks distinctAiry rings, and varies smoothly with radius from the star. Thepoint-spread function (PSF) shape is a strong function of the sourcespectral energy distribution: we find that the PSF template needs todiffer from the occulted source color by Δ(B-V)<=0.08 mag.Optimal PSF removal is achieved for contemporary template observationsmatched to HST orbital phase of the science observations. Use ofnoncontemporary PSF templates can degrade the limiting contrast by up toa factor of 10-12 at r<=2''. These systematic effects arenegligible when the nebular surface brightness is comparable to theresidual starlight, and they become progressively more important assurface brightness decreases. STIS has been used to detect circumstellarenvelopes and protoplanetary disks with surface brightnesses spanning10-4 to 10-7 per HST resolution element perFstar at 2" from the star, debris disks withFIR/Fstar>=0.001, and emission-line nebulosityassociated with bipolar outflows. The limiting contrast for single-orbitintegrations with the star placed at a location where the coronagraphicwedge is 1.0" wide is 10-8 per HST resolution element perFstar for 6<=V<=8 stars. Deeper imagery can be obtainedby placing the star off the active detector area. When the star is 5"from the detector, a limiting contrast for a single-orbit integration of2.5×10-10 per HST resolution element perFstar is reached. At this contrast level, background objectsand the stellar color variability prevent further improvement byco-adding data from multiple orbits.Based on observations made with the NASA/ESA Hubble Space Telescope,obtained at the Space Telescope Science Institute, which is operated bythe Association of Universities for Research in Astronomy, Inc., underNASA contract NAS 5-26555. This study is part of the STIS IDTprotoplanetary disk key project.
| Improved Astrometry and Photometry for the Luyten Catalog. II. Faint Stars and the Revised Catalog
We complete construction of a catalog containing improved astrometry andnew optical/infrared photometry for the vast majority of NLTT starslying in the overlap of regions covered by POSS I and by the secondincremental Two Micron All Sky Survey (2MASS) release, approximately 44%of the sky. The epoch 2000 positions are typically accurate to 130 mas,the proper motions to 5.5 mas yr-1, and the V-J colors to0.25 mag. Relative proper motions of binary components are measured to 3mas yr-1. The false-identification rate is ~1% for11<~V<~18 and substantially less at brighter magnitudes. Theseimprovements permit the construction of a reduced proper-motion diagramthat, for the first time, allows one to classify NLTT stars intomain-sequence (MS) stars, subdwarfs (SDs), and white dwarfs (WDs). We inturn use this diagram to analyze the properties of both our catalog andthe NLTT catalog on which it is based. In sharp contrast to popularbelief, we find that NLTT incompleteness in the plane is almostcompletely concentrated in MS stars, and that SDs and WDs are detectedalmost uniformly over the sky δ>-33deg. Our catalogwill therefore provide a powerful tool to probe these populationsstatistically, as well as to reliably identify individual SDs and WDs.
| Differential rotation in rapidly rotating F-stars
We obtained high quality spectra of 135 stars of spectral types F andlater and derived ``overall'' broadening functions in selectedwavelength regions utilizing a Least Squares Deconvolution (LSD)procedure. Precision values of the projected rotational velocity v \siniwere derived from the first zero of the Fourier transformed profiles andthe shapes of the profiles were analyzed for effects of differentialrotation. The broadening profiles of 70 stars rotating faster than v\sini = 45 km s-1 show no indications of multiplicity nor ofspottedness. In those profiles we used the ratio of the first two zerosof the Fourier transform q_2/q_1 to search for deviations from rigidrotation. In the vast majority the profiles were found to be consistentwith rigid rotation. Five stars were found to have flat profilesprobably due to cool polar caps, in three stars cuspy profiles werefound. Two out of those three cases may be due to extremely rapidrotation seen pole on, only in one case (v \sini = 52 km s-1)is solar-like differential rotation the most plausible explanation forthe observed profile. These results indicate that the strength ofdifferential rotation diminishes in stars rotating as rapidly as v \sini>~ 50 km s-1.Table A.1 is only available at the CDS via anonymous ftp tocdsarc.u-strasbg.fr (130.79.125.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/412/813Based on observations collected at the European Southern Observatory, LaSilla, 69.D-0015(B).
| HIPPARCOS age-metallicity relation of the solar neighbourhood disc stars
We derive age-metallicity relations (AMRs) and orbital parameters forthe 1658 solar neighbourhood stars to which accurate distances aremeasured by the HIPPARCOS satellite. The sample stars comprise 1382 thindisc stars, 229 thick disc stars, and 47 halo stars according to theirorbital parameters. We find a considerable scatter for thin disc AMRalong the one-zone Galactic chemical evolution (GCE) model. Orbits andmetallicities of thin disc stars show now clear relation each other. Thescatter along the AMR exists even if the stars with the same orbits areselected. We examine simple extension of one-zone GCE models whichaccount for inhomogeneity in the effective yield and inhomogeneous starformation rate in the Galaxy. Both extensions of the one-zone GCE modelcannot account for the scatter in age - [Fe/H] - [Ca/Fe] relationsimultaneously. We conclude, therefore, that the scatter along the thindisc AMR is an essential feature in the formation and evolution of theGalaxy. The AMR for thick disc stars shows that the star formationterminated 8 Gyr ago in the thick disc. As already reported by Grattonet al. (\cite{Gratton_et.al.2000}) and Prochaska et al.(\cite{Prochaska_et.al.2000}), thick disc stars are more Ca-rich thanthin disc stars with the same [Fe/H]. We find that thick disc stars showa vertical abundance gradient. These three facts, the AMR, verticalgradient, and [Ca/Fe]-[Fe/H] relation, support monolithic collapseand/or accretion of satellite dwarf galaxies as likely thick discformation scenarios. Tables 2 and 3 are only available in electronicform at the CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5)or via http:/ /cdsweb.u-strasbg.fr/ cgi-bin/qcat?J/ A+A/394/927
| A spectroscopic search for high azimuthal-order pulsation in broad-lined late F- and early G-stars.
During 3 consecutive nights, 13 southern F- and G-type dwarfs and giantsoutside the conventional δ Scuti instability strip were observedat high spectral (3km/s) and medium temporal (10-15min) resolution. Thestars were selected for their reported broad spectral lines(vsini>=40km/s) so that pulsation in higher azimuthal-order nonradialharmonics could, via the rotational Doppler effect, reveal itself byline profile variability. Two stars turned out to have very narrowlines, one was confirmed as a short-period double-lined binary. Lineprofile ondulations typical of pulsation with azimuthal order8<=m<=14 were detected in δ Aql and ɛ2Ara. In addition, ɛ2 Ara displayed line profiledistortions at a larger scale as they would result from a mode with m~4.The observational sampling of all three variabilities constrainspossible periods only poorly. However, if the variations are periodic,they may well be too slow for p-mode oscillations. This would suggest arelation to the new class of γ Dor variables in which g-modes seemto be excited. If so, the two stars could be the first γ Dor starswith detected higher nonradial-harmonic pulsation. While uvby photometryplaces δ Aql still just within the δ Scuti strip,ɛ2 Ara would be the reddest candidate γ Dorstar to date. For the remaining 8 stars, upper amplitude limits between2 and 6km/s were derived for nonradial mode orders 6<=m<=16 andp-modes with periods ~20minutes. In 3 stars narrow absorption lines weredetected which probably are due to a cool companion.
| Ca II H and K Filter Photometry on the UVBY System. II. The Catalog of Observations
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1995AJ....109.2828T&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.
| Optical Polarization of 1000 Stars Within 50-PARSECS from the Sun
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1993A&AS..101..551L&db_key=AST
| A narrow-band search for extraterrestrial intelligence (SETI) using the interstellar contact channel hypothesis
A search is reported for narrow spectral line emission from 176 targets(including 166 stars and seven globular clusers) at the hypothesized'interstellar communications channel' frequency of 4.462336275 GHz (= pitimes the neutral hydrogen line at 1.42 GHz) using the Parkes Radiotelescope. The frequency was Doppler corrected for the solar barycenter,target barycenter, and cosmic microwave background (CMB) referenceframes. If a 'Galactic club' of extraterrestrial civilizations exists,then the null results, down to a 3 sigma limit of 2 Jy (6 Jy in CMBframe), set an upper limit of 10 exp 8 yr on the lifetime of suchcivilizations.
| Preliminary Version of the Third Catalogue of Nearby Stars
Not Available
| Close binaries observed polarimetrically
Not Available
| An Einstein Observatory X-ray survey of main-sequence stars with shallow convection zones
The results of an X-ray survey of bright late A and early F stars on themain B-V sequence between 0.1 and 0.5 are presented. All the stars wereobserved with the Einstein Observatory for a period of at least 500seconds. The survey results show significantly larger X-ray luminositiesfor the sample binaries than for the single stars. It is suggested thatthe difference is due to the presence of multiple X-ray sources inbinaries. It is shown that the X-ray luminosities for single starsincrease rapidly with increasing color, and that the relation Lx/Lbol isequal to about 10 to the -7th does not hold for A stars. No correlationwas found between X-ray luminosity and projected equatorial rotationvelocity. It is argued on the basis of the observations that X-rayemission in the sample stars originated from coronae. The availableobservational evidence supporting this view is discussed.
| Some Cross-Reference Lists for the Catalog of Possible Nearby Stars
Not Available
| The chemical evolution of the solar neighborhood. I - A bias-free reduction technique and data sample
The possible ways of measuring the age-metallicity relation for thegalactic disk in the neighborhood of the sun are discussed. It is shownthat the use of a field star sample chosen on the basis of effectivetemperature introduces a bias which results in a monotonic increase inthe metal abundance of the disk with time. However, if theage-metallicity relation for the disk can be shown to satisfy certaincriteria, the bias introduced in such a sample can be neglected: thegalactic disk apparently satisfies the criteria. It is concluded that asample analyzed through the use of uvby and H(beta) photometry inconjunction with a self-consistent set of theoretical isochronesprovides the least biased, most accurate estimate of the age-metallicityrelation for the disk.
| Observations of short period Cepheids
Photoelectric radial velocities and BVRI photometry are presented foreight short period Cepheids. These include two low amplitude Cepheidsand a probable W Vir star. Their radii are determined and compared inthe period radius diagram.
| Observations of double-mode cepheids.
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1979MNRAS.188..595S&db_key=AST
| Possible nearby stars brighter than tenth magnitude
Basic data are compiled for 447 stars brighter than 10th visualmagnitude which may be within 25 pc of the sun and are missing from boththe Gliese (1969) and the Woolley et al. (1970) catalogs of nearbystars. The list includes 245 stars with photometric parallaxes, 17 starswith trigonometric parallaxes, and nine stars with dynamical parallaxes,all of which parallaxes are at least 0.040 arcsec, as well as 176 likelycandidates. The stars are grouped into six categories according to thereliability of absolute-magnitude estimates and ranked within each groupon the basis of calculated distance. The distance estimates incorporatea kinematic correction to the photometric parallaxes which is based onthe size of a star's proper motion. A list of stars brighter than 10thmag which appear in the Gliese but not in the Woolley et al. catalog isalso provided to facilitate cross-reference with existing catalogs ofnearby stars.
| Photometry of 5 galactic G-type supergiants
The paper examines photoelectric UBV photometry for 5 galacticsupergiants near spectral type GO. Low amplitude variations in magnitudeand color on a time scale of a few months are found in 4 of these stars,and the variability of the R Pup is confirmed. A classification of thesesupergiants in a new category of very long-period low-amplitudecepheid-like variables cannot be assessed because of the insufficienttime base of the observations, but the RV Tauri type variability canprobably be excluded. Finally, the incompleteness of statistics ofstable and low-amplitude variable galactic supergiants is noted, and thepossible coexistence of low-amplitude and large-amplitude variables inthe LMC cepheid instability strip is pointed out.
| Régions H II de l'hémisphère austral
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1970A&AS....3....1G&db_key=AST
| Stars, Parallax of : Stellar parallaxes determined photogrphically at the Cape Observatory (seventeenth list)
Not Available
|
Добавить новую статью
Внешние ссылки
- - Внешних ссылок не найдено -
Добавить внешнюю ссылку
Группы:
|
Наблюдательные данные и астрометрия
| Созвездие: | Центавр |
| Прямое восхождение: | 11h25m43.20s |
| Склонение: | -63°58'22.0" |
| Видимая звёздная величина: | 5.17 |
| Расстояние: | 27.427 парсек |
| Собственное движение RA: | -313.5 |
| Собственное движение Dec: | -65.8 |
| B-T magnitude: | 5.748 |
| V-T magnitude: | 5.224 |
Каталоги и обозначения:
|
INHABITED SKY
