내용
사진
사진 업로드
DSS Images Other Images
관련 글
Effective temperature scale and bolometric corrections from 2MASS photometry
We present a method to determine effective temperatures, angularsemi-diameters and bolometric corrections for population I and II FGKtype stars based on V and 2MASS IR photometry. Accurate calibration isaccomplished by using a sample of solar analogues, whose averagetemperature is assumed to be equal to the solar effective temperature of5777 K. By taking into account all possible sources of error we estimateassociated uncertainties to better than 1% in effective temperature andin the range 1.0-2.5% in angular semi-diameter for unreddened stars.Comparison of our new temperatures with other determinations extractedfrom the literature indicates, in general, remarkably good agreement.These results suggest that the effective temperaure scale of FGK starsis currently established with an accuracy better than 0.5%-1%. Theapplication of the method to a sample of 10 999 dwarfs in the Hipparcoscatalogue allows us to define temperature and bolometric correction (Kband) calibrations as a function of (V-K), [m/H] and log g. Bolometriccorrections in the V and K bands as a function of T_eff, [m/H] and log gare also given. We provide effective temperatures, angularsemi-diameters, radii and bolometric corrections in the V and K bandsfor the 10 999 FGK stars in our sample with the correspondinguncertainties.
| Statistical Constraints for Astrometric Binaries with Nonlinear Motion
Useful constraints on the orbits and mass ratios of astrometric binariesin the Hipparcos catalog are derived from the measured proper motiondifferences of Hipparcos and Tycho-2 (Δμ), accelerations ofproper motions (μ˙), and second derivatives of proper motions(μ̈). It is shown how, in some cases, statistical bounds can beestimated for the masses of the secondary components. Two catalogs ofastrometric binaries are generated, one of binaries with significantproper motion differences and the other of binaries with significantaccelerations of their proper motions. Mathematical relations betweenthe astrometric observables Δμ, μ˙, and μ̈ andthe orbital elements are derived in the appendices. We find a remarkabledifference between the distribution of spectral types of stars withlarge accelerations but small proper motion differences and that ofstars with large proper motion differences but insignificantaccelerations. The spectral type distribution for the former sample ofbinaries is the same as the general distribution of all stars in theHipparcos catalog, whereas the latter sample is clearly dominated bysolar-type stars, with an obvious dearth of blue stars. We point outthat the latter set includes mostly binaries with long periods (longerthan about 6 yr).
| 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
| Detailed Analysis of Nearby Bulgelike Dwarf Stars. III. α-Element and Heavy-Element Abundances
The present sample of nearby bulgelike dwarf stars has kinematics andmetallicities characteristic of a probable inner disk or bulge origin.Ages derived by using isochrones give 10-11 Gyr for these stars, andmetallicities are in the range -0.80<=[Fe/H]<=+0.40. We calculatestellar parameters from spectroscopic data, and chemical abundances ofMg, Si, Ca, Ti, La, Ba, Y, Zr, and Eu are derived by using spectrumsynthesis. We found that [α-elements/Fe] show different patterns,depending on the element. Si/Fe, Ca/Fe, and Ti/Fe ratios declinesmoothly for increasing metallicities and essentially follow the diskpattern. O and Mg, products of massive supernovae, and also ther-process element Eu are overabundant relative to disk stars, showing asteeper decline for metallicities [Fe/H]>-0.3 dex, and[s-elements/Fe] roughly track the solar values, with no apparent trendwith metallicity for [Fe/H]<0, showing subsolar values for the metalrich stars. Both kinematical and chemical properties of the bulgelikestars indicate a distinct identity of this population when compared withdisk stars.
| 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.
| Detailed Analysis of Nearby Bulgelike Dwarf Stars. II. Lithium Abundances
Li abundances are derived for a sample of bulgelike stars withisochronal ages of 10-11 Gyr. These stars have orbits with pericentricdistances, Rp, as small as 2-3 kpc and Zmax<1kpc. The sample comprises G and K dwarf stars in the metallicity range-0.80<=[Fe/H]<=+0.40. Few data on Li abundances in old turnoffstars (>=4.5 Gyr) within the present metallicity range are available.M67 (4.7 Gyr) and NGC 188 (6 Gyr) are the oldest studied metal-rich openclusters with late-type stars. Li abundances have also been studied fora few samples of old metal-rich field stars. In the present work, a highdispersion in Li abundances is found for bulgelike stars with allmetallicity ranges, comparable with values in M67. The role ofmetallicity and age on a Li depletion pattern is discussed. The possibleconnection between Li depletion and oxygen abundance due to atmosphericopacity effects is investigated.
| Detailed Analysis of Nearby Bulgelike Dwarf Stars. I. Stellar Parameters, Kinematics, and Oxygen Abundances
High-resolution échelle spectra were obtained with the Fiber-fedExtended Range Optical Spectrograph at the 1.5 m ESO telescope for 35nearby bulgelike stars with metallicities in the range-0.8<=[Fe/H]<=+0.4. Geneva photometry, astrometric data fromHipparcos, and radial velocities from CORAVEL are available for thesestars. From Hipparcos data, it appears that the turnoff of thispopulation indicates an age of 10-11 Gyr (as stated by Grenon in 1999).Detailed analysis of the sample stars is carried out, and atmosphericparameters derived from spectroscopic and photometric determinations arepresented. Oxygen abundances are derived based on the forbidden [O I]6300.3 Å line. The results show an oxygen overabundance patternfor most of the sample stars when compared to their disk counterparts.Based on observations carried out at the European Southern Observatory,La Silla.
| Oxygen Abundances in Bulge-like Dwarf Stars
High resolution échelle spectra were obtained with the FEROSspectrograph at the 1.5m ESO telescope for 35 nearby bulge-like stars.From Hipparcos data it appears that the turn-off of this populationindicates an age of 10--11 Gyr (Grenon 2000). Oxygen abundances arecalculated using the [O I] line at 6300.3 Å. The derived resultsshow an oxygen overabundance for most of our sample stars when comparedto their disk counterparts.
| A large, complete, volume-limited sample of G-type dwarfs. I. Completion of Stroemgren UVBY photometry
Four-colour photometry of potential dwarf stars of types G0 to K2,selected from the Michigan Spectral Catalogues (Vol. 1-3), has beencarried out. The results are presented in a catalogue containing 4247uvby observations of 3900 stars, all south of δ = -26deg. Theoverall internal rms errors of one observation (transformed to thestandard system) of a program star in the interval 8.5 < V < 10.5are 0.0044, 0.0021, 0.0039, and 0.0059, respectively, in V, b-y, m_1_ ,and c_1_. The purpose of the catalogue, combined with earliercatalogues, is to allow selection of a large, complete, volume-limitedsample of G- and K-type dwarfs, investigate their metallicitydistribution, and compare it to predictions of various models ofgalactic chemical evolution. Future papers in this series will discussthese subjects.
|
새 글 등록
관련 링크
새 링크 등록
다음 그룹에 속해있음:
|
관측 및 측정 데이터
천체목록:
|
