Садржај
Слике
Уплоадјуј своје слике
DSS Images Other Images
Везани чланци
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.
| Speckle Interferometry of New and Problem Hipparcos Binaries. II. Observations Obtained in 1998-1999 from McDonald Observatory
The Hipparcos satellite made measurements of over 9734 known doublestars, 3406 new double stars, and 11,687 unresolved but possible doublestars. The high angular resolution afforded by speckle interferometrymakes it an efficient means to confirm these systems from the ground,which were first discovered from space. Because of its coverage of adifferent region of angular separation-magnitude difference(ρ-Δm) space, speckle interferometry also holds promise toascertain the duplicity of the unresolved Hipparcos ``problem'' stars.Presented are observations of 116 new Hipparcos double stars and 469Hipparcos ``problem stars,'' as well as 238 measures of other doublestars and 246 other high-quality nondetections. Included in these areobservations of double stars listed in the Tycho-2 Catalogue andpossible grid stars for the Space Interferometry Mission.
| Two-colour photometry for 9473 components of close Hipparcos double and multiple stars
Using observations obtained with the Tycho instrument of the ESAHipparcos satellite, a two-colour photometry is produced for componentsof more than 7 000 Hipparcos double and multiple stars with angularseparations 0.1 to 2.5 arcsec. We publish 9473 components of 5173systems with separations above 0.3 arcsec. The majority of them did nothave Tycho photometry in the Hipparcos catalogue. The magnitudes arederived in the Tycho B_T and V_T passbands, similar to the Johnsonpassbands. Photometrically resolved components of the binaries withstatistically significant trigonometric parallaxes can be put on an HRdiagram, the majority of them for the first time. Based on observationsmade with the ESA Hipparcos satellite.
| Doppler imaging of stellar surface structure. VIII. The effectively single and rapidly-rotating G8-giant HD 51066 = CM Camelopardalis
We present first Doppler images of HD 51066 from observations in 1994,1995, 1996 and 1997, and find evidence for a vanishing polar spot inaccordance with the system's long-term brightness increase. Severalsmall spots with Delta T~500 K appear also at low latitudes. Ourcross-correlation maps indicate a latitude-dependent phase-shift patternbetween annual maps. New and continuous BVRI photometry from 1996 to1998 is presented and suggest a photometric period of 16.053+/-0.004days, that we interpret to be the stellar rotation period. Additionaloptical spectroscopy and the Hipparcos data are used to obtain absolutestellar parameters for HD 51066. A comparison with evolutionary tracksand the assumption of angular-momentum and magnetic-flux conservationsuggest that the main-sequence progenitor was a very rapidly-rotating Bpstar with a several kiloGauß\ magnetic field. We also examine theHα line profiles in this star and find some evidence that itsequivalent width is modulated with the stellar rotation period in phasewith the photospheric starspots. Our radial velocities indicate that HD51066 is likely a long-period (~10 yrs) spectroscopic binary and apreliminary orbit is presented. We emphasize that HD 51066 is aninteresting target for studies of evolutionary angular-momentum lossbecause it is effectively single, significantly evolved but stillrapidly rotating.
|
Додај нови чланак
Линкови у сродству са темом
Додај нови линк
Чланови следећих група \:
|
Посматрања и Астрометриски подаци
| Сазвежђа: | Жирафа |
| Ректацензија: | 07h00m20.92s |
| Deклинација: | +67°19'50.2" |
| Apparent магнитуда: | 6.537 |
| Даљина: | 142.45 parsecs |
| Proper motion RA: | 7.6 |
| Proper motion Dec: | -23 |
| B-T magnitude: | 7.694 |
| V-T magnitude: | 6.633 |
Каталог и designations:
|
