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A Survey of Stellar Families: Multiplicity of Solar-type Stars
We present the results of a comprehensive assessment of companions tosolar-type stars. A sample of 454 stars, including the Sun, was selectedfrom the Hipparcos catalog with ?>40 mas,??/? < 0.05, 0.5 <= B - V <= 1.0(~F6-K3), and constrained by absolute magnitude and color to excludeevolved stars. These criteria are equivalent to selecting all dwarf andsubdwarf stars within 25 pc with V-band flux between 0.1 and 10 timesthat of the Sun, giving us a physical basis for the term "solar-type."New observational aspects of this work include surveys for (1) veryclose companions with long-baseline interferometry at the Center forHigh Angular Resolution Astronomy Array, (2) close companions withspeckle interferometry, and (3) wide proper-motion companions identifiedby blinking multi-epoch archival images. In addition, we include theresults from extensive radial-velocity monitoring programs and evaluatecompanion information from various catalogs covering many differenttechniques. The results presented here include four new commonproper-motion companions discovered by blinking archival images.Additionally, the spectroscopic data searched reveal five new stellarcompanions. Our synthesis of results from many methods and sourcesresults in a thorough evaluation of stellar and brown dwarf companionsto nearby Sun-like stars. The overall observed fractions of single,double, triple, and higher-order systems are 56% ± 2%, 33%± 2%, 8% ± 1%, and 3% ± 1%, respectively, countingall confirmed stellar and brown dwarf companions. If all candidate,i.e., unconfirmed, companions identified are found to be real, thepercentages would change to 54% ± 2%, 34% ± 2%, 9%± 2%, and 3% ± 1%, respectively. Our completeness analysisindicates that only a few undiscovered companions remain in thiswell-studied sample, implying that the majority (54% ± 2%) ofsolar-type stars are single, in contrast to the results of priormultiplicity studies. Our sample is large enough to enable a check ofthe multiplicity dependence on various physical parameters by analyzingappropriate subsamples. Bluer, more massive stars are seen as morelikely to have companions than redder, less massive ones, consistentwith the trend seen over the entire spectral range. Systems with largerinteraction cross sections, i.e., those with more than two components orlong orbital periods, are preferentially younger, suggesting thatcompanions may be stripped over time by dynamical interactions. Weconfirm the planet-metallicity correlation (i.e., higher metallicitystars are more likely to host planets), but are unable to check it forbrown dwarfs due to the paucity of such companions, implying that thebrown dwarf desert extends over all separation regimes. We find nocorrelation between stellar companions and metallicity for B - V< 0.625, but among the redder subset, metal-poor stars ([Fe/H]<-0.3) are more likely to have companions with a 2.4?significance. The orbital-period distribution of companions is unimodaland roughly log normal with a peak and median of about 300 years. Theperiod-eccentricity relation shows the expected circularization forperiods below 12 days, caused by tidal forces over the age of theGalaxy, followed by a roughly flat distribution. The mass-ratiodistribution shows a preference for like-mass pairs, which occur morefrequently in relatively close pairs. The fraction of planet hosts amongsingle, binary, and multiple systems are statisticallyindistinguishable, suggesting that planets are as likely to form aroundsingle stars as they are around components of binary or multiple systemswith sufficiently wide separations. This, along with the preference oflong orbital periods among stellar systems, increases the space aroundstars conducive for planet formation, and perhaps life.
| UBV(RI)C JHK observations of Hipparcos-selected nearby stars
We present homogeneous, standardized UBV(RI)C photometry forover 700 nearby stars selected on the basis of Hipparcos parallaxes.Additionally, we list JHK photometry for about half of these stars, aswell as L photometry for 86 of the brightest. A number of stars withpeculiar colours or anomalous locations in various colour-magnitudediagrams are discussed.
| 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.
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