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Vertical distribution of Galactic disk stars. IV. AMR and AVR from clump giants
We present the parameters of 891 stars, mostly clump giants, includingatmospheric parameters, distances, absolute magnitudes, spatialvelocities, galactic orbits and ages. One part of this sample consistsof local giants, within 100 pc, with atmospheric parameters eitherestimated from our spectroscopic observations at high resolution andhigh signal-to-noise ratio, or retrieved from the literature. The otherpart of the sample includes 523 distant stars, spanning distances up to1 kpc in the direction of the North Galactic Pole, for which we haveestimated atmospheric parameters from high resolution but lowsignal-to-noise Echelle spectra. This new sample is kinematicallyunbiased, with well-defined boundaries in magnitude and colours. Werevisit the basic properties of the Galactic thin disk as traced byclump giants. We find the metallicity distribution to be different fromthat of dwarfs, with fewer metal-rich stars. We find evidence for avertical metallicity gradient of -0.31 dex kpc-1 and for atransition at ~4-5 Gyr in both the metallicity and velocities. Theage-metallicity relation (AMR), which exhibits a very low dispersion,increases smoothly from 10 to 4 Gyr, with a steeper increase for youngerstars. The age-velocity relation (AVR) is characterized by thesaturation of the V and W dispersions at 5 Gyr, and continuous heatingin U.
| Abundances of neutron-capture elements in atmospheres of cool giants
We have determined the atmospheric abundances of Y, Ba, La, Ce, Pr, Nd,and Eu for a sample of 171 giants selected as clump giants withmetallicities [Fe/H] between ?0.7 and 0.3 dex, based onphotometric criteria. In our analysis, we assumed local thermodynamicequilibrium and fit the parameters of model atmospheres tohigh-resolution (R = 42 000) echelle spectra with high signal-to-noiseratios. The Ba and Eu abundances were derived using synthetic spectra,including hyperfine structure. We find no significant difference in theabundances of s-or r-process neutron-capture elements between clumpgiants and ascending-branch giants selected by us earlier. We alsoanalyze the relation between the abundances of neutron-capture elementsand [Fe/H].
| High-precision effective temperatures of 215 FGK giants from line-depth ratios
We present precise effective temperatures (Teff) of 215 FGKgiants determined using the method of line-depth ratios. For each star,we have measured the line depths and equivalent widths of a large numberof spectral lines of low and high excitation potentials and established~100 relations between Teff and their ratios. Starting withan initial value Teff, the relations are then self-calibratedby an iterative process. Our final estimates have been compared withvery accurate (1 per cent) published temperatures and show a goodagreement. Using our calibrations, we derive precise temperatures for215 giants with near-solar metallicity, from high-resolution (R = 42000)and high signal-to-noise ratio (S/N = 100-250) echelle spectra, obtainedwith the ELODIE spectrometer at the Observatoire de Haute Provence(OHP). The range of application of the method is 3500-5700K(G0III-K4III). The internal error for a single calibration is less than95K, while the combination of all 100 calibrations reduces theuncertainty to only 5-20K (1?). A big advantage of the line ratiomethod is its independence of interstellar reddening, and its modestsensitivity to spectral resolution, abundance, macroturbulence and otherfactors.
| Elemental abundances in the atmosphere of clump giants
Aims.The aim of this paper is to provide the fundamental parameters andabundances for a large sample of local clump giants with a highaccuracy. This study is a part of a big project, in which the verticaldistribution of the stars in the Galactic disc and the chemical anddynamical evolution of the Galaxy are being investigated. Methods:.The selection of clump stars for the sample group was made applying acolour-absolute magnitude window to nearby Hipparcos stars. Theeffective temperatures were estimated by the line depth ratio method.The surface gravities (log {g}) were determined by two methods (thefirst one was the method based on the ionization balance of iron and thesecond one was the method based on fitting of the wings of the Ca I6162.17 Å line). The abundances of carbon and nitrogen wereobtained from the molecular synthetic spectrum, and the Mg and Naabundances were derived using the non-LTE approximation. The "classical"models of stellar evolution without atomic diffusion androtation-induced mixing were employed. Results: .The atmosphericparameters ({T_eff}, log {g}, [Fe/H], {Vt}) and Li, C, N, O,Na, Mg, Si, Ca, and Ni abundances in 177 clump giants of the Galacticdisc were determined. The underabundance of carbon, overabundance ofnitrogen, and "normal" abundance of oxygen were detected. A small sodiumoverabundance was found. A possibility of a selection of the clumpgiants based on their chemical composition and the evolutionary trackswas explored. Conclusions: .The theoretical predictions based onthe classical stellar evolution models are in good agreement with theobserved surface variations of the carbon and nitrogen just after thefirst dredge-up episode. The giants show the same behaviour of thedependencies of O, Mg, Ca, and Si (α-elements) and Ni (iron-peakelement) abundances vs. [Fe/H] as dwarfs do. This allows us to use suchabundance ratios to study the chemical and dynamical evolution of theGalaxy.
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