Ýçindekiler
Görüntüler
Resim Yükleyin
DSS Images Other Images
Ýlgili Makaleler
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
| Contribution to the search for binaries among Am stars - III. HD 7119: a double-lined spectroscopic binary and a triple system
Radial velocity observations of HD 7119 with the CORAVEL instrument atObservatoire de Haute-Provence are reported. Known as anAmδδ Del metallic-line star, HD 7119 was included in ourspectroscopic survey of Am-type stars, the purpose of which was todetermine the frequency of binaries in this stellar family. This objectis found to be a double-lined spectroscopic binary with a variable valueof V0, the systematic velocity of the centre of gravity ofthe pair. The variation of this parameter is interpreted in terms of theorbital motion of an unseen third body with a much longer period. Theorbital elements were derived for both the short- and the long-periodorbits. These orbits can be considered to be well determined since theseobservations were performed on a regular basis over the 1992-1998period, covering more than 320 orbital cycles for the short-period (P=6.76 d) and 1.3 cycle for the long-period orbit (P~ 1700 d). As deducedfrom the ratio of the correlation dip areas, the magnitude difference ofthe components of the short-period system is 0.7 mag. Combined with theHipparcos data, this value leads to visual absolute magnitudes of 0.5and 1.2 for the primary and secondary components, respectively. Suchmagnitudes are consistent with evolved δ Del-type stars. The thirdbody could be a cool dwarf star with a minimum mass of 0.5Msolar, located at ~ 0.016 arcsec of the main system.Consequently, it cannot be the visual companion detected by Couteau witha separation of 3.35 arcsec. If this latter visual component were aphysical component (rather than an optical one), HD 7119 would be aquadruple system.
| Contribution to the search of binaries among Am stars. II. HD 81976 and HD 98880, double-lined spectroscopic binaries
We present the results of the observations of two Am stars of eighthmagnitude, the double-lined spectroscopic binaries HD 81976 and HD98880, carried out with the CORAVEL instrument at the Observatoire deHaute-Provence in order to determine their orbital elements. We found 1)for HD 81976: P = 5.655750 days, T = 2449785.941 HJD, omega =341.4deg, e = 0.061, K1 = 61.68 km s-1,K2 = 63.84 km s-1, V0 = 19.85 kms-1, a1 sin i = 4.788 Gm, a2 sin i =4.956 Gm, M1 sin 3 i = 0.5875 Msun,M2 sin 3 i = 0.5676 Msun, and 2) for HD98880: P = 14.20783 days, T0 = 2448682.883 HJD (ascendingnode), e = 0., K1 = 42.47 km s-1, K2 =49.16 km s-1, V0 = 2.40 km s-1,a1 sin i = 8.298 Gm, a2 sin i = 9.604 Gm,M1 sin 3 i = 0.6091 Msun, M2sin 3 i = 0.5262 Msun. The first of these twosystems, HD 81976, is formed by two quasi-identical stars, and theHipparcos data (MV, B-V) are consistent with late A stars ineffective temperature; it is likely that the components rotatesynchronised with the orbital motion. A third body may be present inthis system since (i) the orbit has a significant eccentricity despiteits short period and (ii) the systemic velocity V0 shows apossible drift. For the second system, HD 98880, we give DeltamB 1.25 and we propose a simple model based uponStrömgren photometric indices and the HR theoretical diagram ofSchaller et al (1992) in addition to orbital parameters and Hipparcosdata: Teff = 7000 K, log 10 g = 4.0, M1= 1.9 Msun, M2 = 1.6 Msun, log10(age) = 9.12. The components do not rotate synchronouslycontrary to HD 81976. Both binaries appear to be detached systemswithout possibility of eclipses. Based on observations made at theHaute-Provence Observatory, France.
| Late A-type stars: new Strömgren photometric calibrations of absolute magnitudes from HIPPARCOS
Hipparcos trigonometric parallaxes have been used to derive aphotometric absolute magnitude calibration of main-sequence late A-typestars in terms of Strömgren photometric indices - accounting fortemperature, evolution and metallicity effects - and projectedequatorial rotational velocities. The derived calibrations are valid formain-sequence normal A3-A9 and metallic Am stars, showing residuals of0.22 and 0.20 magnitudes, respectively. One of the fitting methods used(BCES) allows the derivation of the observational ZAMS in this spectralrange, showing an excellent accordance with theoretical evolutionarymodels. The evolutionary state of the Am stars is also discussed.Table~A1 is only available in electronic form from CDS via anonymous ftp130.79.128.5, and by e-mail: request to cesca@am.ub.es
| The Tokyo PMC catalog 90-93: Catalog of positions of 6649 stars observed in 1990 through 1993 with Tokyo photoelectric meridian circle
The sixth annual catalog of the Tokyo Photoelectric Meridian Circle(PMC) is presented for 6649 stars which were observed at least two timesin January 1990 through March 1993. The mean positions of the starsobserved are given in the catalog at the corresponding mean epochs ofobservations of individual stars. The coordinates of the catalog arebased on the FK5 system, and referred to the equinox and equator ofJ2000.0. The mean local deviations of the observed positions from theFK5 catalog positions are constructed for the basic FK5 stars to comparewith those of the Tokyo PMC Catalog 89 and preliminary Hipparcos resultsof H30.
| Spectroscopic tests of photoelectric stellar classification of abnormal stars
Spectroscopic classification is obtained for 169 northern A5-G0 starspredicted by Olsen (1979, 1980) to have abnormal spectra on the basis ofStromgren four-color photometry. The success in identifying reddenedearly type stars was nearly 100 percent, for Am and early type weaklined stars about 75 percent, for stars above main sequence about 50percent, for composite spectra about 25 percent, and for Ap and LambdaBoo stars 0 percent. Thus photoelectric photometry is a successful firststep in discovering stars of the more extreme spectroscopicabnormalities.
| Estimation of spectral classifications for bright northern stars with interesting Stromgren indices
The purpose of this investigation is to provide spectroscopic observerswith finding lists of potentially interesting objects. From anunpublished UVBY catalogue of 7026 northern stars (mostly brighter than8.3m) 1094 objects with interesting combinations of UVBY indices havebeen selected. Most stars with post-HD classifications have beenexcluded, as well as late F dwarfs belonging to the intermediatepopulation II. For the 792 remaining stars estimated spectralclassifications are given. The techniques and experience from a previouspaper dealing with southern stars have been utilized here. Among thepredicted spectral classifications are 40 OB stars; 262 Ap, Am, or Fmstars; 16 supergiants of types A to G; 110 bright giants of types A to K(class II); 156 double stars or objects with composite spectra; 26 lateF dwarfs; 91 weak-lined dwarf and giant stars of types F to K, includingearly F-type population II field blue stragglers; and a few possiblefield horizontal branch stars, lambda Bootis-type stars, and late-typehalo giants.
| A finding-list of stars of spectral type F2 and earlier in a north galactic pole region.
Not Available
|
Yeni bir Makale Öner
Ýlgili Baðlantýlar
Yeni Bir Baðlantý Öner
sonraki gruplarýn üyesi:
|
Gözlemler ve gökölçümü verileri
| Takýmyýldýz: | Buyuk Ayi |
| Sað Açýklýk: | 11h22m51.98s |
| Yükselim: | +44°49'28.1" |
| Görünürdeki Parlaklýk: | 8.032 |
| Uzaklýk: | 235.294 parsek |
| özdevim Sað Açýklýk: | -27.3 |
| özdevim Yükselim: | -15.7 |
| B-T magnitude: | 8.491 |
| V-T magnitude: | 8.07 |
Kataloglar ve belirtme:
|
