Contenidos
Imágenes
Subir su imagen
DSS Images Other Images
Artículos relacionados
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
| Evolution of the 3.3-μm emission feature in the Red Rectangle
Medium-resolution infrared spectroscopic observations of the biconicalRed Rectangle nebula in the region of the 3.3-μm unidentifiedinfrared (UIR) emission band are reported. The data were recorded atUKIRT using CGS4 and have allowed the peak wavelength, width, profileand intensity of the 3.3-μm feature to be investigated as a functionof offset from the central star HD 44179. Analysis of the profile of thefeature along the north-western bicone interface shows an evolution fromType 2 to Type 1 in the classification of Tokunaga et al. The 3.3-μmband recorded on-star shows a close fit to a Lorentzian profile,possibly suggesting a single class of carriers. Subtraction of theLorentzian fit to the on-star spectrum from the spectrum at each offsetreveals a new `3.28'-μm emission feature that grows in intensityrelative to the main 3.3-μm band as a function of distance from thecentral star. The 3.28-μm emission band at large offset appears tocorrespond well in wavelength and FWHM with an absorption feature seentowards the Galactic Centre.
| Mode identification in the δ Scuti Star 1 Mon
We present new multicolour photometry and simultaneous high-dispersionspectroscopy for the δ Scuti star 1 Mon. The two mainperiodicities in the star are still present, but the third known periodis not directly detected in the new radial velocities or lightvariations. However, it is detected in the periodogram of the secondmoment of the line profile variations. We use the cross-correlationfunction as an approximation for the line profile variations. Bycomputing theoretical profiles for a given mode and comparing them withphased cross-correlation profiles, we are able to determine agoodness-of-fit criterion and estimate the most probable sphericalharmonic degree, l, the azimuthal order, m, of the pulsation and alsothe angle of inclination. We then compare the relative amplitudes andphases of the photometric variations in five wavebands and obtain thebest estimates of l for the two visible periodicities. We confirm theearlier determinations that the main periodicity is a radial mode andthat the other periodicity is probably l=1, m=-1. We show that the lineprofile variations and light variations give consistent results. Wepoint out the importance of a long wavelength range when using thephotometric mode identification technique. Finally, we attempt to matchthe two periods with unstable modes from linear, non-adiabaticcalculations. We are able to show that the principal period is wellmatched by either the fundamental or first overtone radial mode, butcould not find a satisfactory fit to the l=1 mode. We discussimplications for mode identification of δ Scuti stars based onwhat we have learned from this star.
| 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
| 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.
| Instrumental effects and the Stroemgren photometric system
The extent to which the use of different photometers can affect resultson stellar color indices was investigated by simultaneously observing asample of widely different stars with several uvby photometric systemsavailable at the ESO, La Silla, Chile. In one instance, the ESO 50-cmtelescope and the four-channel photometer at the Danish 50-cm telescopewere used simultaneously. The reductions were performed separately oneach data set, using a linear color transformation procedure. Theresults agree with theoretical investigations which showed thatsubstantial errors can arise from the nonconformity of passbands. It isemphasized that it is necessary to use separate color transformationsfor various stellar types and classes and for different interstellarreddenings.
| The oscillation modes of 1 Monocerotis
Simultaneous photoelectric radial velocities and BVRI photometry arepresented for the delta Scuti star 1 Mon. From these and other publisheddata the spherical harmonic orders of the three principal oscillationsare estimated. The strongest oscillation is found to be an overtoneradial pulsation while the two other oscillations are most probablydipole modes split by stellar rotation. The radius of 1 Mon is estimatedto be 2.2 solar units by application of a modified Wesselink techniqueto the radial mode.
| Three-dimensional motion of dwarf stars and RR Lyrae variables
A collection of 220 high-velocity dwarfs, 532 low-velocity dwarfs, and114 RR Lyrae variables is given in tables with calculations ofkinematical quantities in a three-dimensional model of galactic space. Ametal indicator, Delta-S, for RR Lyrae variables is transformed into theultraviolet excess, delta (0.6), which is utilized for a statisticalstudy of kinematics under the same metallicity classification. It isfound that the primordial Galaxy contracted by a factor of at least 20in the radial direction as compared to at least 50 in the Z direction.
| 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.
| 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
| 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
|
Enviar un nuevo artículo
Enlaces relacionados
- - No se han encontrado enlaces -
En viar un nuevo enlace
Miembro de los siguientes grupos:
|
Datos observacionales y astrométricos
| Constelación: | Unicornio |
| Ascensión Recta: | 06h05m27.00s |
| Declinación: | -10°14'34.0" |
| Magnitud Aparente: | 5.87 |
| Distancia: | 58.962 parsecs |
| Movimiento Propio en Ascensión Recta: | 21 |
| Movimiento Propio en Declinación: | 26.9 |
| B-T magnitude: | 6.286 |
| V-T magnitude: | 5.916 |
Catálogos y designaciones:
|
INHABITED SKY
