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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.
| Radial-velocity measurements. V - Ground support of the HIPPARCOS satellite observation program
The paper presents data on 1070 radial velocity measurements of starsdistributed in 39 fields measuring 4 deg x 4 deg. The PPO series ofFehrenbach et al. (1987) and Duflot et al. (1990) is continued using theFehrenbach objective prism method.
| 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.
| MAP determinations of the parallaxes of stars in the regions of HD 2665, BD +68.946 deg, and Lambda Ophiuchi
The Multichannel Astrometic Photometer and new optical system of theAllegheny Observatory have been used to obtain parallaxes of stars inthe regions of HD 2665, BD +68.946 deg, and Lambda Ophiuchi. HD 2665 isfound to have an absolute visual magnitude of 1.6 + or - 0.4 and adistance of 149 + or - 28 pc. It is shown that the Lambda Ophiuchisystem has a parallax of 23.5 + or - 2.1 mas and that its A0 V and A4 Vcomponents have masses of 2.7 + or - 0.7 and 1.5 + or - 0.4 solarmasses, respectively.
| The multichannel astrometric photometer and atmospheric limitations in the measurement of relative positions
The operational Multichannel Astrometric Photometer (MAP) now in use inthe Allegheny Observatory astrometric program is the culmination of adecade of design and development effort. A detailed description of thesystem and its related software is followed by analysis of data acquiredin four stellar regions. The study indicates an accuracy (in the senseof conformity to the best model), per night, for stars of the eighthmagnitude or brighter, of 0.003 arcsec or better. These data points eachhave approximately twice the precision of the annual normal pointsobtained in our photographic program. Accuracy is shown to depend on:(1) the photon-count rate of the target star (it follows that the numberof photons from the reference frame is also in important factor), (2)the duration of the observation, (3) the angular size of the referenceframe, and (4) the quality of the astronomical seeing. Since (4) and, toa lesser extent, (1) involve the atmospheric characteristics at the timeof observation, the probable performance at more favorable sites isdiscussed briefly.
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