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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.
| Correlation of the HIPPARCOS and Allegheny Observatory Parallax Catalogs
No significant difference is found between the systems of the Hipparcosand Allegheny Observatory MAP parallax catalogs. The correlation of theparallaxes of 63 stars common to both programs is 0.9995 +/- 0.0001,with an average standard deviation of the difference of 0.0023". Whilethere is no indication of systematic difference in the two programs, ourstudy suggests that the formal errors in one or both catalogs aresomewhat underestimated.
| Multichannel astrometric photometer parallax studies in the regions of Groombridge 1618, Zeta Bootis, and Sigma Draconis
Improved trigonometric parallaxes are reported for stars in the regionsof Groombridge 1618, Zeta Bootis, and Sigma Draconis which differ fromgenerally accepted parallaxes by two to five standard deviations. Theweighted mean parallax of Groombridge 1618 becomes 0.2079 +/- 0.0013arcsec, indicating a distance modulus of -1.59 +/- 0.014 and yielding anabsolute magnitude of this K7 V star of 8.20 +/- 0.017. The parallaxdetermined for the visual binary Zeta Bootis is 0.0202 +/- 0.0010 arcsecand implies an average absolute visual magnitude of 1.067 +/- 0.12 forthe spectroscopically similar components. The weighted mean parallax ofSigma Draconis becomes 0.1747 +/- 0.0010 arcsec, indicating a distancemodulus of -1.210 +/- 0.012 and yielding an absolute visual magnitude of5.90 +/- 0.012 for this K0 V star. The absolute visual magnitudes of thehigh velocity star Roman 336 and of the subdwarf star AO 1187 are foundto be + 4.0 +/- 0.13 and + 5.9 +/- 0.17, respectively.
| Photometry of astrometric reference stars
UBVRI, DDO, and uvby, H-beta photometry of astrometric reference starsis presented. Spectral types and luminosity classifications made fromthe colors are used to determine their spectroscopic parallaxes. In thispaper, colors for 309 stars in 25 regions are given, and classificationsfor 210 stars have been made. These stars form reference frames in theAllegheny Observatory Multichannel Astrometric Photometer astrometricprogram, and in the Praesepe cluster reduced by Russell (1976). It isfound that the present photometric spectral types are reliable to within2.5 spectral subclasses.
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