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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
| 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
| Research Note Hipparcos photometry: The least variable stars
The data known as the Hipparcos Photometry obtained with the Hipparcossatellite have been investigated to find those stars which are leastvariable. Such stars are excellent candidates to serve as standards forphotometric systems. Their spectral types suggest in which parts of theHR diagrams stars are most constant. In some cases these values stronglyindicate that previous ground based studies claiming photometricvariability are incorrect or that the level of stellar activity haschanged. Table 2 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/367/297
| 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
| 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
| Corrections - Variable and Potential Variable Stars in the Bright-Star Catalogue
Not Available
| Variable and Potential Variable Stars in the Bright Star Catalogue
Not Available
| 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.
| Spectral classification of the bright F stars.
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1976PASP...88...95C&db_key=AST
| 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
| Variability of A and F main sequence stars.
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1971A&A....12..223J&db_key=AST
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Pozíciós és asztrometriai adatok
| Csillagkép: | Holló |
| Rektaszcenzió: | 12h32m36.00s |
| Deklináció: | -13°51'33.0" |
| Vizuális fényesség: | 5.74 |
| Távolság: | 36.955 parszek |
| RA sajátmozgás: | -146.1 |
| Dec sajátmozgás: | -54.3 |
| B-T magnitude: | 6.164 |
| V-T magnitude: | 5.77 |
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