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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).
| The Tokyo PMC catalog 90-93: Catalog of positions of 6649 stars observed in 1990 through 1993 with Tokyo photoelectric meridian circle
The sixth annual catalog of the Tokyo Photoelectric Meridian Circle(PMC) is presented for 6649 stars which were observed at least two timesin January 1990 through March 1993. The mean positions of the starsobserved are given in the catalog at the corresponding mean epochs ofobservations of individual stars. The coordinates of the catalog arebased on the FK5 system, and referred to the equinox and equator ofJ2000.0. The mean local deviations of the observed positions from theFK5 catalog positions are constructed for the basic FK5 stars to comparewith those of the Tokyo PMC Catalog 89 and preliminary Hipparcos resultsof H30.
| The Baade-Wesselink method and the distances to RR Lyrae stars. I - The field star VY Serpentis
The desirability and feasibility of determining distances to globularclusters, independently of field star calibrations using theBaade-Wesselink method is discussed. As a preliminary test of themethod, simultaneous, accurate photometric and radial velocity data forthe cool, lightly reddened field RR Lyrae variable VY Serpentis arepresented. The data are used to solve for the star's radius anddistance, using two versions of the Baade-Wesselink method that eachallow for the star's low metallicity and its changing gravity. For bothversions of the method, a phase difference of Delta phi approximately0.075, between the photometric and spectroscopic radii, is found. It isconcluded that the problem arises not from the method or its basicassumptions, but rather from the choice of a star with strong convectionwhich has not been properly taken into account.
| Identifications of Comparison Stars for RR Lyrae Variables
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