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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).
| Photoelectric observations of lunar occultations. XIV
Observations of 314 events between March 1982 and March 1983 arepresented in the same form as in previous papers in this series. Theresults include 18 cases of duplicity of which 12 appear to be newdiscoveries. Unluckily, few cases of possible large angular diametersoccurred, and in no case can the results derived be accepted withoutreserve, these having been observed at very low altitudes withconsequent severe corruption by seeing effects. A remark on theincidence of doubles in the Hyades and its possible consequences forestimates of stellar distances is appended.
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