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Statistical Constraints for Astrometric Binaries with Nonlinear Motion
Useful constraints on the orbits and mass ratios of astrometric binariesin the Hipparcos catalog are derived from the measured proper motiondifferences of Hipparcos and Tycho-2 (Δμ), accelerations ofproper motions (μ˙), and second derivatives of proper motions(μ̈). It is shown how, in some cases, statistical bounds can beestimated for the masses of the secondary components. Two catalogs ofastrometric binaries are generated, one of binaries with significantproper motion differences and the other of binaries with significantaccelerations of their proper motions. Mathematical relations betweenthe astrometric observables Δμ, μ˙, and μ̈ andthe orbital elements are derived in the appendices. We find a remarkabledifference between the distribution of spectral types of stars withlarge accelerations but small proper motion differences and that ofstars with large proper motion differences but insignificantaccelerations. The spectral type distribution for the former sample ofbinaries is the same as the general distribution of all stars in theHipparcos catalog, whereas the latter sample is clearly dominated bysolar-type stars, with an obvious dearth of blue stars. We point outthat the latter set includes mostly binaries with long periods (longerthan about 6 yr).
| Speckle Interferometry of New and Problem Hipparcos Binaries. II. Observations Obtained in 1998-1999 from McDonald Observatory
The Hipparcos satellite made measurements of over 9734 known doublestars, 3406 new double stars, and 11,687 unresolved but possible doublestars. The high angular resolution afforded by speckle interferometrymakes it an efficient means to confirm these systems from the ground,which were first discovered from space. Because of its coverage of adifferent region of angular separation-magnitude difference(ρ-Δm) space, speckle interferometry also holds promise toascertain the duplicity of the unresolved Hipparcos ``problem'' stars.Presented are observations of 116 new Hipparcos double stars and 469Hipparcos ``problem stars,'' as well as 238 measures of other doublestars and 246 other high-quality nondetections. Included in these areobservations of double stars listed in the Tycho-2 Catalogue andpossible grid stars for the Space Interferometry Mission.
| Four-colour and H-beta photometry of B stars in Fehrenbach and Burnage radial velocity fields at B about -30 deg
Observations in uvby and H-beta are presented for 39 stars classified asB-type in seven 4 x 4-deg fields studied by Fehrenbach and Burnage(1981, 1982) at b about -30 deg. About half the stars arephotometrically little-evolved B stars; most of the rest areintermediate A stars. Intrinsic color and absolute-magnitudecalibrations are applied: that of Hilditch et al. (1983) forintermediate A stars is estimated to be much less certain than those forother types. Maps of reddening along lines of sight indicate that littlereddening occurs within 100 pc of the sun, that essentially allreddening has occurred within z = + or - 150-200 pc, and that the totalreddening is essentially consistent with values given by the Bursteinand Heiles (1982) HI/GC method. The luminosities of some faint early Bstars cannot be usefully constrained by placing them within thereddening structure. One of the two program stars with very large radialvelocities is a horizontal branch object; the other has peculiar colors.
| A new list of 617 radial velocities in four galactic fields
Four stellar fields in the -30 deg galactic latitude have been surveyedfor radial velocities, using a 62 cm objective prism. Exact positions,spectral types, and approximate magnitudes are provided for 617 stars infour different 4 x 4 deg fields. B to F4 stars were found which haveGaussian velocity distributions.
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