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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.
| The Solar Neighborhood. VII. Discovery and Characterization of Nearby Multiples in the CTIO Parallax Investigation
We report the discovery of eight new multiple star systems among 191stellar systems targeted for parallax determinations in the RECONS(Research Consortium on Nearby Stars) southern parallax program, CTIOPI(Cerro Tololo Inter-American Observatory Parallax Investigation). Theeight new companions have separations of 1.42" to 14.90" andinstrumental magnitude differences at VRI of 0.06-6.07 mag. Orbitalmotion has not been detected in any of these systems. These newcompanions increase the multiplicity fraction of this sample, made upprimarily of nearby (less than 25 pc) M dwarfs, to 15%. Comparison withsamples that have been more completely scrutinized for companionsindicates that probably only half of all multiples have so far beendiscovered. Given the large number of frames acquired for theastrometric series, the eight new systems and 16 known multiples havebeen searched for variability at VRI during the 3 year duration ofCTIOPI. A flare has been detected in the secondary of the RX J1132-264system, while at least one component in the GJ 2006 system is a probablelong-term variable. Variables were detected in only 9% of the systemssearched, primarily as a result of the restrictive 0.05 mag thresholdrequired for variability confirmation.
| Hipparcos astrometry for 257 stars using Tycho-2 data
We present improved Hipparcos astrometry for 257 Hipparcos stars,resolved into 342 components. For 64 of the stars no astrometry wasobtained in the Hipparcos Catalogue, while for the remaining starsadditional components have been added by this solution or the positionshave been revised considerably. We have used the published Hipparcostransit data for the new solutions, together with results from thesecond reduction of the Tycho data for defining better initial values.Based on observations made with the ESA Hipparcos astrometry satellite.Table 3 is only available in electronic form at the CDS via anonymousftp to cdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/Abstract.html
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