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Rotational and Radial Velocities for a Sample of 761 HIPPARCOS Giants and the Role of Binarity
We present rotational and radial velocities for a sample of 761 giantsselected from the Hipparcos Catalogue to lie within 100 pc of the Sun.Our original goal was to examine stellar rotation in field giants usingspectroscopic line broadening to look for evidence of excess rotationthat could be attributed to planets that were engulfed as the parentstars expanded. Thus we were obliged to investigate other sources ofline broadening, including tidal coupling in close binaries andmacroturbulence. For all the binaries in our sample with periods shorterthan 20 days the orbits have been circularized, while about half theorbits with periods in the range 20-100 days still show significanteccentricity. All our primaries in orbits shorter than 30 days show linebroadening consistent with synchronized rotation, while about half theprimaries with periods in the range 30-120 days are synchronized. Tostudy the dependence of rotation on stellar evolution when tidal effectsare not important, we used a subsample of single stars and members inwide binaries. We found evidence to suggest that the first dredge-up mayplay a role in speeding up the rotation of the observable outer layersof giants and that the rotational velocity of horizontal branch stars islarger by a few km s-1 than that of first-ascent giants withsimilar mass, effective temperature, and radius. Finally, we found threegiants that rotate more rapidly than expected. We conjecture that theyacquired their excess angular momentum by ingesting planets.Some of the results presented here used observations made with theMultiple Mirror Telescope, a joint facility of the SmithsonianInstitution and the University of Arizona.
| Effective temperature scale and bolometric corrections from 2MASS photometry
We present a method to determine effective temperatures, angularsemi-diameters and bolometric corrections for population I and II FGKtype stars based on V and 2MASS IR photometry. Accurate calibration isaccomplished by using a sample of solar analogues, whose averagetemperature is assumed to be equal to the solar effective temperature of5777 K. By taking into account all possible sources of error we estimateassociated uncertainties to better than 1% in effective temperature andin the range 1.0-2.5% in angular semi-diameter for unreddened stars.Comparison of our new temperatures with other determinations extractedfrom the literature indicates, in general, remarkably good agreement.These results suggest that the effective temperaure scale of FGK starsis currently established with an accuracy better than 0.5%-1%. Theapplication of the method to a sample of 10 999 dwarfs in the Hipparcoscatalogue allows us to define temperature and bolometric correction (Kband) calibrations as a function of (V-K), [m/H] and log g. Bolometriccorrections in the V and K bands as a function of T_eff, [m/H] and log gare also given. We provide effective temperatures, angularsemi-diameters, radii and bolometric corrections in the V and K bandsfor the 10 999 FGK stars in our sample with the correspondinguncertainties.
| Mean absolute magnitude of the blue stars at high galactic latitude.
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1962AJ.....67..740K&db_key=AST
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