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Long-term magnetic activity of a sample of M-dwarf stars from the HARPS program . II. Activity and radial velocity
Owing to their low mass and luminosity, M dwarfs are ideal targets ifone hopes to find low-mass planets similar to Earth using the radialvelocity (RV) method. However, stellar magnetic cycles could add noiseor even mimic the RV signal of a long-period companion. We extend ourprevious study of the correlation between activity cycles and long-termRV variations for K dwarfs to the lower-end of the main sequence. Ourobjective is to detect any correlations between long-term activityvariations and the observed RV of a sample of M dwarfs. We use a sampleof 27 M-dwarfs with a median observational timespan of 5.9 years. Thecross-correlation function (CCF) with its parameters RV, bisectorinverse slope (BIS), full width at half maximum (FWHM), and contrast arecomputed from the HARPS spectrum. The activity index is derived usingthe Na i D doublet. These parameters are compared with the activitylevel of the stars to search for correlations. We detect RV variationsup to ~5 m s-1 that we can attribute to activity cycleeffects. However, only 36% of the stars with long-term activityvariability appear to have had their RV affected by magnetic cycles, onthe typical timescale of ~6 years. Therefore, we suggest a carefulanalysis of activity data when searching for extrasolar planets usinglong-timespan RV data.Based on observations made with the HARPS instrument on the ESO 3.6-mtelescope at La Silla Observatory under programme ID072.C-0488(E).Tables with the data used for Figs. A.1-A.27 are onlyavailable at the CDS via anonymous ftp to cdsarc.u-strasbg.fr(130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/541/A9AppendixA is available in electronic form at http://www.aanda.org
| Spectroscopic stellar parameters for 582 FGK stars in the HARPS volume-limited sample. Revising the metallicity-planet correlation
To understand the formation and evolution of solar-type stars andplanets in the solar neighborhood, we need to obtain their stellarparameters with high precision. We present a catalog of precise stellarparameters for low-activity FGK single stars in a volume-limited samplefollowed by the HARPS spectrograph in the quest to identify extra-solarplanets. The spectroscopic analysis was completed assuming LTE with agrid of Kurucz atmosphere models and using the ARES code to perform anautomatic measurement of the line equivalent widths. The results arecompared with different independent methods and also with other valuesfound in the literature for common stars. Both comparisons areconsistent and illustrate the homogeneity of the parameters derived byour team. The derived metallicities of this sample reveal a somewhatdifferent distribution for the present planet hosts, but still indicatesthe already known higher frequency of planets observed for the moremetal-rich stars. We combine the results derived in this sample with theone from the CORALIE survey to present the largest homogeneousspectroscopic study of the metallicity-giant-planet relation using atotal of 1830 stars.Full Table 1 is only available in electronic form at the CDS viaanonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/533/A141
| The HARPS search for southern extra-solar planets. XXVII. Seven new planetary systems
We are conducting a planet search survey with HARPS since seven years.The volume-limited stellar sample includes all F2 to M0 main-sequencestars within 57.5 pc, where extrasolar planetary signatures aresystematically searched for with the radial-velocity technics. In thispaper, we report the discovery of new substellar companions of sevenmain-sequence stars and one giant star, detected through multipleDoppler measurements with the instrument HARPS installed on the ESO 3.6m telescope, La Silla, Chile. These extrasolar planets orbit the starsHD 1690, HD 25171, HD 33473A, HD 89839, HD 113538, HD 167677, and HD217786. The already-published giant planet around HD 72659 is alsoanalysed here, and its elements are better determined by the addition ofHARPS and Keck data. The other discoveries are giant planets in distantorbits, ranging from 0.3 to 29 MJup in mass and between 0.7and 10 years in orbital period. The low metallicity of most of these newplanet-hosting stars reinforces the current trend for long-distanceplanets around metal-poor stars. Long-term radial-velocity surveys allowprobing the outskirts of extrasolar planetary systems, althoughconfidence in the solution may be low until more than one orbital periodis fully covered by the observations. For many systems discussed in thispaper, longer baselines are necessary to refine the radial-velocity fitand derive planetary parameters. The radial-velocity time series ofstars BD -114672 and HIP 21934 are also analysed and their behaviourinterpreted in terms of the activity cycle of the star, rather thanlong-period planetary companions.Based on observations made with the HARPS instrument on the ESO 3.6 mtelescope at La Silla Observatory under programme IDs 072.C-0488(E) and085.C-0019.RV data are only available in electronic form at the CDS viaanonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/527/A63
| Bayesian inference of stellar parameters and interstellar extinction using parallaxes and multiband photometry
Astrometric surveys provide the opportunity to measure the absolutemagnitudes of large numbers of stars, but only if the individualline-of-sight extinctions are known. Unfortunately, extinction is highlydegenerate with stellar effective temperature when estimated frombroad-band optical/infrared photometry. To address this problem, Iintroduce a Bayesian method for estimating the intrinsic parameters of astar and its line-of-sight extinction. It uses both photometry andparallaxes in a self-consistent manner in order to provide anon-parametric posterior probability distribution over the parameters.The method makes explicit use of domain knowledge by employing theHertzsprung-Russell Diagram (HRD) to constrain solutions and to ensurethat they respect stellar physics. I first demonstrate this method byusing it to estimate effective temperature and extinction from BVJHKdata for a set of artificially reddened Hipparcos stars, for whichaccurate effective temperatures have been estimated from high-resolutionspectroscopy. Using just the four colours, we see the expected strongdegeneracy (positive correlation) between the temperature andextinction. Introducing the parallax, apparent magnitude and the HRDreduces this degeneracy and improves both the precision (reduces theerror bars) and the accuracy of the parameter estimates, the latter byabout 35 per cent. The resulting accuracy is about 200 K in temperatureand 0.2 mag in extinction. I then apply the method to estimate theseparameters and absolute magnitudes for some 47 000 F, G, K Hipparcosstars which have been cross-matched with Two-Micron All-Sky Survey(2MASS). The method can easily be extended to incorporate the estimationof other parameters, in particular metallicity and surface gravity,making it particularly suitable for the analysis of the 109stars from Gaia.
| Contributions to the Nearby Stars (NStars) Project: Spectroscopy of Stars Earlier than M0 within 40 pc-The Southern Sample
We are obtaining spectra, spectral types, and basic physical parametersfor the nearly 3600 dwarf and giant stars earlier than M0 in theHipparcos catalog within 40 pc of the Sun. Here we report on resultsfor 1676 stars in the southern hemisphere observed at Cerro TololoInter-American Observatory and Steward Observatory. These resultsinclude new, precise, homogeneous spectral types, basic physicalparameters (including the effective temperature, surface gravity, andmetallicity [M/H]), and measures of the chromospheric activity of ourprogram stars. We include notes on astrophysically interesting stars inthis sample, the metallicity distribution of the solar neighborhood, anda table of solar analogs. We also demonstrate that the bimodal nature ofthe distribution of the chromospheric activity parameterlogR'HK depends strongly on the metallicity, andwe explore the nature of the ``low-metallicity'' chromosphericallyactive K-type dwarfs.
| 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.
| The general catalogue of trigonometric [stellar] paralaxes
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