내용
사진
사진 업로드
DSS Images Other Images
관련 글
Pulkovo compilation of radial velocities for 35495 stars in a common system.
Not Available
| 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
| The chemical composition of the field blue stragglers.
We present the results of the spectroscopic investigation of 15 galacticfield blue stragglers and one normal F-dwarf. The analysis has shown: 1)all stars are metal deficient. The mean value of [Fe/H] for 13 stars is-0.31+/-0.13 (two stars of our sample: HD54073 and HD88923 have probablystronger iron deficiency); 2) estimated (C/H) and (O/H) ratios are closeto the solar values (i.e. these elements are slightly enhanced withrespect to iron: [C/Fe]=~[O/Fe]=~0.3dex); 3) sodium and α-elementsin the field stragglers are slightly enhanced too. Only magnesium showsa practically solar ratio: [Mg/Fe]=~0; 4) from the iron group, Sc showssolar ratio [M/Fe]. Cr and Ni are slightly overabundant; 5) the rathergreat age of the investigated stars estimated from their metallicity isin the contradiction with their locations in the evolutionary diagram.This problem can be eliminated by assuming that field stragglers are oldobjects with delayed evolution (similarly to blue stragglers of stellarclusters); 6) one of the investigated stars HD35863 (T_eff_=6700K,logg=4.0) has a rather high lithium abundance (logA_Li_=2.94), not usualfor stars with such temperature.
| Radial velocity measurements of a sample of northern metal-deficient stars
Observations of 41 northern stars with Fe/H between -1.1 and -0.3,obtained with the Coravel radial-velocity scanner on the 1-m Swisstelescope at the Observatoire de Haute Provence during 1977-1986, arereported. The data are presented in extensive tables and graphs andcharacterized in detail. Seven stars are identified as spectroscopicbinaries, and their distribution as a function of period is shown to besimilar to that for a sample of metal-rich G stars. The present radialvelocities are found to be in relatively good agreement with those ofCarney and Latham (1987), but not with those of Stryker et al. (1985).
| The binary frequency of extreme subdwarfs revisited
Spectroscopic observations of 70 extreme subdwarfs, obtained over a 4-yrperiod with the 1.8-m telescope at Dominion Astrophysical Observatory,are presented in tables and analyzed statistically along with the datareported by Abt and Levy (AL; 1969) and Crampton and Hartwick (CH;1972). The data-reduction procedures and statistical techniques employedare explained, and significance limits are established by performingsimilar analyses for known binary stars. For a subsample of 46 subdwarfswith at least three observations spanning 100 d or more, abinary-frequency lower limit of 20-30 percent and a semiamplitude limitof about 14 km/s are determined, with similar frequencies for a set of12 subdwarfs with Fe/H less than -1.5 and for the samples of AL and CH.The reasons for the discrepancy between these findings and the lowfrequencies (0-15 percent) calculated by AL and CH are examined, and alist of binary candidates for observation is provided.
| Further Studies of A-Stars and F-Stars in the Region of the North Galactic Pole - Part Four - a Catalogue of Uvbyr Photometry and Derived Quantities
Not Available
| Further Studies of A-Stars and F-Stars in the Region of the North Galactic Pole - Part Three - a Catalogue of Star Names and Positions
Not Available
| 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.
| Stars with large proper motions in the astrographic zones+ 32° and + 33° (List I)
Not Available
|
새 글 등록
관련 링크
새 링크 등록
다음 그룹에 속해있음:
|
관측 및 측정 데이터
천체목록:
|
