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Rotation- and temperature-dependence of stellar latitudinal differential rotation
More than 600 high resolution spectra of stars with spectral type F andlater were obtained in order to search for signatures of differentialrotation in line profiles. In 147 stars the rotation law could bemeasured, with 28 of them found to be differentially rotating.Comparison to rotation laws in stars of spectral type A reveals thatdifferential rotation sets in at the convection boundary in theHR-diagram; no star that is significantly hotter than the convectionboundary exhibits the signatures of differential rotation. Four lateA-/early F-type stars close to the convection boundary and at v sin{i}≈ 100 km s-1 show extraordinarily strong absolute shear atshort rotation periods around one day. It is suggested that this is dueto their small convection zone depth and that it is connected to anarrow range in surface velocity; the four stars are very similar inTeff and v sin{i}. Detection frequencies of differentialrotation α = ΔΩ/Ω > 0 were analyzed in starswith varying temperature and rotation velocity. Measurable differentialrotation is more frequent in late-type stars and slow rotators. Thestrength of absolute shear, ΔΩ, and differential rotationα are examined as functions of the stellar effective temperatureand rotation period. The highest values of ΔΩ are found atrotation periods between two and three days. In slower rotators, thestrongest absolute shear at a given rotation rateΔΩmax is given approximately byΔΩmax ∝ P-1, i.e.,αmax ≈ const. In faster rotators, bothαmax and ΔΩmax diminish lessrapidly. A comparison with differential rotation measurements in starsof later spectral type shows that F-stars exhibit stronger shear thancooler stars do and the upper boundary in absolute shear ΔΩwith temperature is consistent with the temperature-scaling law found inDoppler Imaging measurements.
| 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
| 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).
| 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).
| The ROSAT all-sky survey catalogue of optically bright main-sequence stars and subgiant stars
We present X-ray data for all main-sequence and subgiant stars ofspectral types A, F, G, and K and luminosity classes IV and V listed inthe Bright Star Catalogue that have been detected as X-ray sources inthe ROSAT all-sky survey; several stars without luminosity class arealso included. The catalogue contains 980 entries yielding an averagedetection rate of 32 percent. In addition to count rates, sourcedetection parameters, hardness ratios, and X-ray fluxes we also listX-ray luminosities derived from Hipparcos parallaxes. The catalogue isalso available in electronic form via anonymous ftp tocdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/Abstract.html
| 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.
| The Stellar Content of Star Stream I
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1996AJ....111.1615E&db_key=AST
| 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.
| Chromospheric Activity in Galactic Open Clusters
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1993ApJ...417..157B&db_key=AST
| Fifth fundamental catalogue. Part 2: The FK5 extension - new fundamental stars
The mean positions and proper motions for 3117 new fundamental starsessentially in the magnitude range about 4.5 to 9.5 are given in thisFK5 extension. Mean apparent visual magnitude is 7.2 and is on average2.5 magnitudes fainter then the basic FK5 which has a mean magnitude of4.7. (The basic FK5 gives the mean positions and proper motions for theclassical 1535 fundamental stars). The following are discussed: theobservational material, reduction of observations, star selection, andthe system for the FK5 extension. An explanation and description of thecatalog are given. The catalog of 3117 fundamental stars for the equinoxand epoch J2000.0 and B1950.0 is presented. The parallaxes and radialvelocities for 22 extension stars with large forecasting effects aregiven. Catalogs used in the compilation of the FK5 fundamental catalogare listed.
| Magnetic structure in cool stars. XV - The evolution of rotation rates and chromospheric activity of giants
For cool giants and subgiants the observed dependence of rotationalvelocity and Ca II H and K line-core emission on color B-V isinterpreted in terms of changes in the moment of inertia by stellarevolution. Modeling of the rotational velocity during the evolution ofcool giants with masses between 2.0 and 3.0 solar masses, by taking intoaccount the change in the moment of inertia and assuming rigid-bodyrotation and conservation of angular momentum, describes the observeddecrease of v sin i with B-V. The computed evolution of the rotationalvelocity, together with the empirical relation between the Ca IIline-core emission and the rotation rate, explain the observed drop inthe Ca II line-core emission for giants at B-V = about 0.95. Forsubgiants with masses of about 1.5 solar mass, the change in the momentof inertia by itself cannot explain the observed v sin i distribution:there are indications of loss of angular momentum, presumably bymagnetic braking.
| Starlight polarization in the direction of two H I complexes
Upper limits to the gas/dust ratio in the direction of two complexes arederived based on 21-cm line observations and starlight polarizationmeasurements. Elongated H I structures parallel to the galactic magneticfield suggest that the gas and dust comprise a common cloud or cloudsystem. Dust producing the starlight polarization is mixed with the H Igas, aiding in estimating the distance for the two H I complexes.Distances of 100 pc for the filament at low velocities and of 200 pc foran intermediate-velocity cloud complex (IVC) are established frompolarimetric data, and possible origins for the filaments and IVC aresuggested.
| 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.
| Absolute luminosity calibration of F stars
Luminosity calibrations are performed for a restricted sample of 706F-type field stars of all luminosity classes and a similarly restrictedsample of 251 main-sequence F stars. The samples are restricted withrespect to values of photometric and metallicity indices, propermotions, radial velocities, and apparent magnitudes. Both linear andsecond-order relations between absolute magnitude and the photometricindices beta, /c1/ or (b-y), /c1/ are considered.These relations are calibrated by the statistical parallax method basedon the principle of maximum likelihood. The possible effect ofinterstellar absorption on the calibration results is investigated alongwith an effect of a photometric correction to the absolute magnitudes.The results obtained are compared with those of Crawford (1975) as wellas with the trigonometric parallaxes. The coefficients of thecalibration relations are derived from the trigonometric parallaxes, andpoor agreement is indicated. It is concluded that the trigonometricparallaxes must be used very carefully and only for nearby stars.
| UBV Photometry of 500 Southern Stars [erratum: 1973MNSSA..32...48C]
Not Available
| Four-colour and H BET photometry of some bright southern stars- II.
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1972MNRAS.160..155S&db_key=AST
| Four-colour and H BET photometry of some bright southern stars.
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1972MNRAS.159..165S&db_key=AST
| Luminosities and Motions of the F-Type Stars. I. Luminosity and Metal Abundance Indices for Disk Population Stars
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1971PASP...83..741E&db_key=AST
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Наблюдательные данные и астрометрия
| Созвездие: | Хамелеон |
| Прямое восхождение: | 09h24m09.10s |
| Склонение: | -80°47'13.0" |
| Видимая звёздная величина: | 5.36 |
| Расстояние: | 56.529 парсек |
| Собственное движение RA: | -138.7 |
| Собственное движение Dec: | 136 |
| B-T magnitude: | 5.861 |
| V-T magnitude: | 5.39 |
Каталоги и обозначения:
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INHABITED SKY
