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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.
| Map-based trigonometric parallaxes of open clusters. II - The Hyades: 51 Tauri
The trigonometric parallax, mass, and mass ratio of 51 Tauri, a binarymember of the Hyades star cluster, are determined. The parallaxsolution, 19.4 mas with a standard error of 1.1 mas, is slightly greaterthan its generally accepted value and yields a cluster distance of 4.30+/-2.0 pc or a distance modulus equivalent of 3.16 +/- 0.10 mag, inexcellent agreement with recent photographic parallax results. Theweighted mean of all trigonometric parallax determinations of thecluster is now 22.9 +/-0.6 mas or a modulus of 3.20 +/- 0.06 mag. Thetotal mass of the 51 Tauri system was found to be 2.56 +/- 0.44 solarmasses. Adopting a magnitude difference in line with the spectral typesof the components yields individual masses of 1.61 +/- 0.28 and 0.95 +/-0.18 solar masses. This result places the mass of both the A8 V primaryand the G0 secondary stars within the errors of the measurement of themass-luminosity relation established for solar-neighborhoodmain-sequence stars.
| 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.
| Spectroscopic parallaxes of MAP region stars from UBVRI, DDO, and uvbyH-beta photometry
This paper presents the results of spectral type and luminosityclassification of reference stars in the Allegheny Observatory MAPparallax program, using broadband and intermediate-band photometry. Inaddition to the use of UBVRI and DDO photometric systems, the uvbyH-betaphotometric system was included for classification of blue (B - V lessthan 0.6) reference stars. The stellar classifications made from thephotometry are used to determine spectroscopic parallaxes. Thespectroscopic parallaxes are used in turn to adjust the relativeparallaxes measured with the MAP to absolute parallaxes. A new methodfor dereddening stars using more than one photometric system ispresented. In the process of dereddening, visual extinctions, spectraltypes, and luminosity classes are determined, as well as a measure ofthe goodness of fit. The measure of goodness of fit quantifiesconfidence in the stellar classifications. It is found that the spectraltypes are reliable to within 2.5 spectral subclasses.
| Helligkeiten und Eigenbewegungen in den Hyaden. Mit 6 Textabbildungen
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