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Spectroscopic parameters for 451 stars in the HARPS GTO planet search program. Stellar [Fe/H] and the frequency of exo-Neptunes
To understand the formation and evolution of solar-type stars in thesolar neighborhood, we need to measure their stellar parameters to highaccuracy. We present a catalogue of accurate stellar parameters for 451stars that represent the HARPS Guaranteed Time Observations (GTO)“high precision” sample. Spectroscopic stellar parameterswere measured using high signal-to-noise (S/N) spectra acquired with theHARPS spectrograph. The spectroscopic analysis was completed assumingLTE with a grid of Kurucz atmosphere models and the recent ARES code formeasuring line equivalent widths. We show that our results agree wellwith those ones presented in the literature (for stars in common). Wepresent a useful calibration for the effective temperature as a functionof the index color B-V and [Fe/H]. We use our results to study themetallicity-planet correlation, namely for very low mass planets. Theresults presented here suggest that in contrast to their joviancouterparts, neptune-like planets do not form preferentially aroundmetal-rich stars. The ratio of jupiter-to-neptunes is also an increasingfunction of stellar metallicity. These results are discussed in thecontext of the core-accretion model for planet formation.Based on observations collected at La Silla Observatory, ESO, Chile,with the HARPS spectrograph at the 3.6-m telescope (072.C-0488(E)). FullTables 1 and 3 are only available in electronic form at the CDS vianonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/487/373
| Metallicities and activities of southern stars
Aims. We present the results from high-resolution spectroscopicmeasurements to determine metallicities and activities of bright starsin the southern hemisphere. Methods: We measured the iron abundances([Fe/H]'s) and chromospheric emission indices (log h{R}'{HK})of 353 solar-type stars with V = 7.5-9.5. [Fe/H] abundances aredetermined using a custom χ2 fitting procedure within alarge grid of Kurucz model atmospheres. The chromospheric activitieswere determined by measuring the amount of emission in the cores of thestrong Caii HK lines. Results: Our comparison of the metallicity sampleto other [Fe/H] determinations was found to agree at the ±0.05dex level for spectroscopic values and at the ±0.1 dex level forphotometric values. The distribution of chromospheric activities isdescribed by a bimodal distribution, agreeing with the conclusions fromother works. Also an analysis of Maunder minimum status was attempted,and it was found that 6 ± 4 stars in the sample could be in aMaunder minimum phase of their evolution and hence the Sun should onlyspend a few per cent of its main sequence lifetime in Maunder minimum.Based on observations made with the ESO telescopes at the La SillaParanal observatory under programme ID's 076.C-0578(B) and077.C-0192(A). Table 4 is 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/485/571
| Pulkovo compilation of radial velocities for 35495 stars in a common system.
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| uvby-β photometry of high-velocity and metal-poor stars. XI. Ages of halo and old disk stars
New uvby-β data are provided for 442 high-velocity and metal-poorstars; 90 of these stars have been observed previously by us, and 352are new. When combined with our previous two photometric catalogues, thedata base is now made up of 1533 high-velocity and metal-poor stars, allwith uvby-β photometry and complete kinematic data, such as propermotions and radial velocities taken from the literature. Hipparcos, plusa new photometric calibration for Mv also based on theHipparcos parallaxes, provide distances for nearly all of these stars;our previous photometric calibrations give values for E(b-y) and [Fe/H].The [Fe/H], V(rot) diagram allows us to separate these stars intodifferent Galactic stellar population groups, such as old-thin-disk,thick-disk, and halo. The X histogram, where X is our stellar-populationdiscriminator combining V(rot) and [Fe/H], and contour plots for the[Fe/H], V(rot) diagram both indicate two probable components to thethick disk. These population groups and Galactic components are studiedin the (b-y)0, Mv diagram, compared to theisochrones of Bergbusch & VandenBerg (2001, ApJ, 556, 322), toderive stellar ages. The two thick-disk groups have the meancharacteristics: ([Fe/H], V(rot), Age, σW') ≈ (-0.7dex, 120 km s-1, 12.5 Gyr, 62.0 km s-1), and≈(-0.4, 160, 10.0, 45.8). The seven most metal-poor halo groups,-2.31 ≤ [Fe/H] ≤ -1.31, show a mean age of 13.0 ± 0.2(mean error) Gyr, giving a mean difference from the WMAP results for theage of the Universe of 0.7 ± 0.3 Gyr. These results for the agesand components of the thick disk and for the age of the Galactic halofield stars are discussed in terms of various models and ideas for theformation of galaxies and their stellar populations.
| Improved Astrometry and Photometry for the Luyten Catalog. II. Faint Stars and the Revised Catalog
We complete construction of a catalog containing improved astrometry andnew optical/infrared photometry for the vast majority of NLTT starslying in the overlap of regions covered by POSS I and by the secondincremental Two Micron All Sky Survey (2MASS) release, approximately 44%of the sky. The epoch 2000 positions are typically accurate to 130 mas,the proper motions to 5.5 mas yr-1, and the V-J colors to0.25 mag. Relative proper motions of binary components are measured to 3mas yr-1. The false-identification rate is ~1% for11<~V<~18 and substantially less at brighter magnitudes. Theseimprovements permit the construction of a reduced proper-motion diagramthat, for the first time, allows one to classify NLTT stars intomain-sequence (MS) stars, subdwarfs (SDs), and white dwarfs (WDs). We inturn use this diagram to analyze the properties of both our catalog andthe NLTT catalog on which it is based. In sharp contrast to popularbelief, we find that NLTT incompleteness in the plane is almostcompletely concentrated in MS stars, and that SDs and WDs are detectedalmost uniformly over the sky δ>-33deg. Our catalogwill therefore provide a powerful tool to probe these populationsstatistically, as well as to reliably identify individual SDs and WDs.
| 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.
| A Survey of Proper-Motion Stars. XVI. Orbital Solutions for 171 Single-lined Spectroscopic Binaries
We report 25,563 radial velocity measurements for 1359 single-linedstars in the Carney-Latham sample of 1464 stars selected for high propermotion. For 171 of these, we present spectroscopic orbital solutions. Wefind no obvious difference between the binary characteristics in thehalo and the disk populations. The observed frequency is the same, andthe period distributions are consistent with the hypothesis that the twosets of binaries were drawn from the same parent population. Thissuggests that metallicity in general, and radiative opacities inparticular, have little influence over the fragmentation process thatleads to short-period binaries. All the binaries with periods shorterthan 10 days have nearly circular orbits, while the binaries withperiods longer than 20 days exhibit a wide range of eccentricities and amedian value of 0.37. For the metal-poor high-velocity halo binaries inour sample, the transition from circular to eccentric orbits appears tooccur at about 20 days, supporting the conclusion that tidalcircularization on the main sequence is important for the oldestbinaries in the Galaxy. Some of the results presented here usedobservations made with the Multiple Mirror Telescope, a joint facilityof the Smithsonian Institution and the University of Arizona.
| Classification of Population II Stars in the Vilnius Photometric System. I. Methods
The methods used for classification of Population II stars in theVilnius photometric system are described. An extensive set of standardswith known astrophysical parameters compiled from the literature sourcesis given. These standard stars are classified in the Vilnius photometricsystem using the methods described. The accuracy of classification isevaluated by a comparison of the astrophysical parameters derived fromthe Vilnius photometric system with those estimated from spectroscopicstudies as well as from photometric data in other systems. For dwarfsand subdwarfs, we find a satisfactory agreement between our reddeningsand those estimated in the uvbyscriptstyle beta system. The standarddeviation of [Fe/H] deter mined in the Vilnius system is about 0.2 dex.The absolute magnitude for dwarfs and subdwarfs is estimated with anaccuracy of scriptstyle <=0.5 mag.
| A survey of proper motion stars. 12: an expanded sample
We report new photometry and radial velocities for almost 500 stars fromthe Lowell Proper Motion Catalog. We combine these results with ourprior sample and rederive stellar temperatures based on the photometry,reddening, metallicities (using chi squared matching of our 22,500 lowSignal to Noise (S/N) high resolution echelle spectra with a grid ofsynthetic spectra), distances, space motions, and Galactic orbitalparameters for 1269 (kinematics) and 1261 (metallicity) of the 1464stars in the complete survey. The frequency of spectroscopic binariesfor the metal-poor ((m/H) less than or equal to -1.2) stars with periodsshorter than 3000 days is at least 15%. The spectroscopic binaryfrequency for metal-rich stars ((m/H) greater than -0.5) appears to belower, about 9%, but this may be a selection effect. We also discussspecial classes of stars, including treatment of the double-linedspectroscopic binaries, and identification of subgiants. Four possiblenew members of the class of field blue stragglers are noted. We pointout the detection of three possible new white dwarfs, six broad-lined(binary) systems, and discuss briefly the three already knownnitrogen-rich halo dwarfs. The primary result of this paper will beavailable on CD-ROM, in the form of a much larger table.
| New subdwarfs. VI - Kinematics of 1125 high-proper-motion stars and the collapse of the Galaxy
The UVW velocity components, planar eccentricities, and angular momentaof 878 high-proper-motion stars are determined using the radial-velocitydata of Fouts and Sandage (1986) and compared with chemical abundancesand photometric parallaxes from the UBV photometry of Sandage and Kowal(1986). The results are presented, along with published data on 247additional stars, in extensive tables and graphs and characterized indetail. Two approximately equal components are differentiated: alow-velocity component identified as part of the thick disk described byGilmore and Reid (1983) and a high-velocity halo component. The data arefound to support a model of Galactic collapse (with concomitant spinupand progressive chemical enrichment) which includes a rotating bulge(the thick disk) with kinematic and metallicity properties between thoseof the old thin disk and the halo.
| New subdwarfs. V - Radial velocities for 889 high-proper-motion stars measured with the Mount Wilson 100 inch reflector
New radial velocities have been obtained from 2265 measurements of 889high-proper-motion stars taken from the subdwarf candidate list of aprevious paper. The observations were made with the Mount Wilson 100 inHooker reflector coude spectrograph with a Reticon detector, giving aninternal error of a single measurement of 4.7 km/s. From 88 stars incommon with previously known subdwarfs; the external error of the datais 6.9 km/s per measurement, and the velocity system is shown to be onthe system of the Wilson General Catalog to better than 1 km/s. Of the878 stars with nonvariable velocities in the sample, 38 have radialvelocities larger than 200 km/s, of which 22 are new. There is acorrelation between radial velocity and reduced ultraviolet excess asexpected from the previously known relations between space motion andchemical composition. The Stroemberg asymmetric drift is directlyvisible in the radial velocity and the proper-motion data separately aseach is displayed as a function of galactic longitude.
| New subdwarfs. IV - UBV photometry of 1690 high-proper-motion stars
A photometric list of 1690 stars of known high proper motion is used tosearch for potential high-velocity stars of various metallicity valuesin order to find candidates for trigonometric programs on subdwarfs andto enlarge the sample with which to study the relation between stellarkinematics and metal abundance. A list of 113 stars with tangentialspace velocities of 300 km/s or greater is obtained, the highesttangential velocity relative to the sun being 630 km/s. By using thevariation of the tangential velocity with longitude and adopting thegalactic rotation at the solar circle to be 220 km/s, the rotation ofthe subdwarf system is estimated at 0 + or - 50 km/s from the transversevelocity alone, in agreement with determinations based on other methods.
| Lowell proper motions II : proper motion survey of the Northern Hemisphere with the 13-inch photographic telescope of the Lowell Observatory
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