Contingut
Imatges
Carregar la teva Imatge
DSS Images Other Images
Articles Relacionats
The Geneva-Copenhagen survey of the solar neighbourhood. III. Improved distances, ages, and kinematics
Context: Ages, chemical compositions, velocity vectors, and Galacticorbits for stars in the solar neighbourhood are fundamental test datafor models of Galactic evolution. The Geneva-Copenhagen Survey of theSolar Neighbourhood (Nordström et al. 2004; GCS), amagnitude-complete, kinematically unbiased sample of 16 682 nearby F andG dwarfs, is the largest available sample with complete data for starswith ages spanning that of the disk. Aims: We aim to improve theaccuracy of the GCS data by implementing the recent revision of theHipparcos parallaxes. Methods: The new parallaxes yield improvedastrometric distances for 12 506 stars in the GCS. We also use theparallaxes to verify the distance calibration for uvby? photometryby Holmberg et al. (2007, A&A, 475, 519; GCS II). We add newselection criteria to exclude evolved cool stars giving unreliableresults and derive distances for 3580 stars with large parallax errorsor not observed by Hipparcos. We also check the GCS II scales of T_effand [Fe/H] and find no need for change. Results: Introducing thenew distances, we recompute MV for 16 086 stars, and U, V, W,and Galactic orbital parameters for the 13 520 stars that also haveradial-velocity measurements. We also recompute stellar ages from thePadova stellar evolution models used in GCS I-II, using the new valuesof M_V, and compare them with ages from the Yale-Yonsei andVictoria-Regina models. Finally, we compare the observed age-velocityrelation in W with three simulated disk heating scenarios to show thepotential of the data. Conclusions: With these revisions, thebasic data for the GCS stars should now be as reliable as is possiblewith existing techniques. Further improvement must await consolidationof the T_eff scale from angular diameters and fluxes, and the Gaiatrigonometric parallaxes. We discuss the conditions for improvingcomputed stellar ages from new input data, and for distinguishingdifferent disk heating scenarios from data sets of the size andprecision of the GCS.Full Table 1 is only available in electronic form at the CDS viaanonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/501/941
| Oxygen abundances in nearby stars. Clues to the formation and evolution of the Galactic disk
The abundances of iron and oxygen are homogeneously determined in asample of 523 nearby (d<150 pc) FGK disk and halo stars withmetallicities in the range -1.5<[Fe/H]<0.5. Iron abundances wereobtained from an LTE analysis of a large set of Fe I and Fe II lineswith reliable atomic data. Oxygen abundances were inferred from arestricted non-LTE analysis of the 777 nm O I triplet. We adopted theinfrared flux method temperature scale and surface gravities based onHipparcos trigonometric parallaxes. Within this framework, theionization balance of iron lines is not satisfied: the mean abundancesfrom the Fe I lines are systematically lower by 0.06 dex than those fromthe Fe II lines for dwarf stars of Teff>5500 K and[Fe/H]<0.0, and giant stars of all temperatures and metallicitiescovered by our sample. The discrepancy worsens for cooler and metal-richmain-sequence stars. We use the stellar kinematics to compute theprobabilities of our sample stars to be members of the thin disk, thickdisk, or halo of the Galaxy. We find that the majority of thekinematically-selected thick-disk stars show larger [O/Fe] ratioscompared to thin-disk stars while the rest show thin-disk abundances,which suggests that the latter are thin-disk members with unusual(hotter) kinematics. A close examination of this pattern for disk starswith ambiguous probabilities shows that an intermediate population withproperties between those of the thin and thick disks does not exist, atleast in the solar neighborhood. Excluding the stars with unusualkinematics, we find that thick-disk stars show slowly decreasing [O/Fe]ratios from about 0.5 to 0.4 in the -0.8<[Fe/H]<-0.3 range. Usinga simple model for the chemical evolution of the thick disk we show thatthis trend results directly from the metallicity dependence of the TypeII supernova yields. At [Fe/H]>-0.3, we find no obvious indication ofa sudden decrease (i.e., a "knee") in the [O/Fe] vs. [Fe/H] pattern ofthick-disk stars that would connect the thick and thin disk trends at ahigh metallicity. We conclude that Type Ia supernovae (SN Ia) did notcontribute significantly to the chemical enrichment of the thick disk.In the -0.8<[Fe/H]<+0.3 range, thin-disk stars show decreasing[O/Fe] ratios from about 0.4 to 0.0 that require a SN Ia contribution.The implications of these results for studies of the formation andevolution of the Galactic disk are discussed.Tables 4-6 are only available in electronic form at the CDS viaanonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/465/271 Partially based onobservations obtained with the Hobby-Eberly Telescope, which is a jointproject of the University of Texas at Austin, the Pennsylvania StateUniversity, Stanford University, Ludwig-Maximilians-UniversitätMünchen, and Georg-August-Universität Göttingen; and datafrom the UVES Paranal Observatory Project (ESO DDT Program ID266.D-5655).
| 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
| Hipparcos red stars in the HpV_T2 and V I_C systems
For Hipparcos M, S, and C spectral type stars, we provide calibratedinstantaneous (epoch) Cousins V - I color indices using newly derivedHpV_T2 photometry. Three new sets of ground-based Cousins V I data havebeen obtained for more than 170 carbon and red M giants. These datasetsin combination with the published sources of V I photometry served toobtain the calibration curves linking Hipparcos/Tycho Hp-V_T2 with theCousins V - I index. In total, 321 carbon stars and 4464 M- and S-typestars have new V - I indices. The standard error of the mean V - I isabout 0.1 mag or better down to Hp~9 although it deteriorates rapidly atfainter magnitudes. These V - I indices can be used to verify thepublished Hipparcos V - I color indices. Thus, we have identified ahandful of new cases where, instead of the real target, a random fieldstar has been observed. A considerable fraction of the DMSA/C and DMSA/Vsolutions for red stars appear not to be warranted. Most likely suchspurious solutions may originate from usage of a heavily biased color inthe astrometric processing.Based on observations from the Hipparcos astrometric satellite operatedby the European Space Agency (ESA 1997).}\fnmsep\thanks{Table 7 is onlyavailable in electronic form at the CDS via anonymous ftp tocdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/397/997
|
Enviar un nou article
Enllaços Relacionats
- - No s'ha trobat enllaços -
Enviar un nou enllaç
Membre dels grups següents:
|
Dades d'Observació i Astrometria
| Constel·lació: | Hydra |
| Ascensió Recta: | 08h19m15.10s |
| Declinació: | -05°37'10.2" |
| Magnitud Aparent: | 7.436 |
| Distancia: | 34.153 parsecs |
| Moviment propi RA: | -0.9 |
| Moviment propi Dec: | 41.9 |
| B-T magnitude: | 8.133 |
| V-T magnitude: | 7.494 |
Catàlegs i designacions:
|
