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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
| Pulkovo compilation of radial velocities for 35495 stars in a common system.
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| 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 CORALIE survey for southern extra-solar planets. IX. A 1.3-day period brown dwarf disguised as a planet
In this article we present the case of HD 41004 AB, a system composed ofa K0V star and a 3.7-mag fainter M-dwarf companion. We have obtained 86CORALIE spectra of this system with the goal of obtaining preciseradial-velocity measurements. Since HD 41004 A and B are separated byonly 0.5\arcsec, in every spectrum taken for the radial-velocitymeasurement, we are observing the blended spectra of the two stars. Ananalysis of the measurements has revealed a velocity variation with anamplitude of about 50 m s-1 and a periodicity of 1.3 days.This radial-velocity signal is consistent with the expected variationinduced by the presence of a companion to either HD 41004 A or HD 41004B, or to some other effect due to e.g. activity related phenomena. Inparticular, such a small velocity amplitude could be the signature ofthe presence of a very low mass giant planetary companion to HD 41004 A,whose light dominates the spectra. The radial-velocity measurements werethen complemented with a photometric campaign and with the analysis ofthe bisector of the CORALIE Cross-Correlation Function (CCF). While theformer revealed no significant variations within the observationalprecision of ~ 0.003-0.004 mag (except for an observed flare event), thebisector analysis showed that the line profiles are varying in phasewith the radial-velocity. This latter result, complemented with a seriesof simulations, has shown that we can explain the observations byconsidering that HD 41004 B has a brown-dwarf companion orbiting withthe observed 1.3-day period. As the spectrum of the fainter HD 41004 B``moves'' relative to the one of HD 41004 A (with an amplitude of a fewkm s-1), the relative position of the spectral lines of thetwo spectra changes, thus changing the blended line-profiles. Thisvariation is large enough to explain the observed radial-velocity andbisector variations, and is compatible with the absence of anyphotometric signal. If confirmed, this detection represents the firstdiscovery of a brown dwarf in a very short period (1.3-day) orbit aroundan M dwarf. Finally, this case should be taken as a serious warningabout the importance of analyzing the bisector when looking for planetsusing radial-velocity techniques. Based on observations collected at theLa Silla Observatory, ESO (Chile), with the CORALIE spectrograph at the1.2-m Euler Swiss telescope and with the Strömgren AutomaticTelescope (SAT).
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Osservazione e dati astrometrici
| Costellazione: | Pittore |
| Ascensione retta: | 05h52m30.02s |
| Declinazione: | -49°05'04.2" |
| Magnitudine apparente: | 8.38 |
| Distanza: | 118.064 parsec |
| Moto proprio RA: | 34.8 |
| Moto proprio Dec: | -53.3 |
| B-T magnitude: | 9.474 |
| V-T magnitude: | 8.471 |
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