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The HARPS search for southern extra-solar planets . XXII. Multiple planet systems from the HARPS volume limited sample
We present the detections of three multiple systems within the HARPSvolume-limited sample. Among the six planets discussed in this paper, wehave identified a "super-Earth" planet with a minimum mass of 6.6MEarth and a "Neptune" planet with minimum mass of 18MEarth, both orbiting their parent stars within a distance of0.05 AU and a period of approximately four days. These detectionsstrengthen the argument that low-mass planets are primarily found inmultiple-planetary systems.Based on observations made with the HARPS instrument on the ESO 3.6 mtelescope at La Silla (Chile), under the GTO program ID 072.C-0488.RVtables are only available in electronic form at the CDS via anonymousftp to cdsarc.u-strasbg.fr (130.79.128.5) or via http://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/512/A48
| K dwarfs and the chemical evolution of the solar cylinder
K dwarfs have lifetimes older than the present age of the Galactic disc,and are thus ideal stars for investigating the chemical evolution of thedisc. We have developed several photometric metallicity indicators for Kdwarfs, based on a sample of accurate spectroscopic metallicities for 34disc and halo G and K dwarfs. The photometric metallicities lead us todevelop a metallicity index for K dwarfs based only on their position inthe colour-absolute-magnitude diagram. Metallicities have beendetermined for 431 single K dwarfs drawn from the Hipparcos catalogue,selecting the stars by absolute magnitude and removing multiple systems.The sample is essentially a complete reckoning of the metal content innearby K dwarfs. We use stellar isochrones to mark the stars by mass,and select a subset of 220 of the stars, which is complete within anarrow mass interval. We fit the data with a model of the chemicalevolution of the solar cylinder. We find that only a modest cosmicscatter is required to fit our age-metallicity relation. The modelassumes two main infall episodes for the formation of the halo-thickdisc and thin disc, respectively. The new data confirm that the solarneighbourhood formed on a long time-scale of the order of 7 Gyr.
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