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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 open cluster NGC 3293 and the OB complex in Carina
Photoelectric measures in UBVRI of 46 stars in and around the opencluster NGC 3293 are presented. A distance modulus of V(0) - M(v) equals12.1 plus or minus 0.15 (s.d.), corresponding to 2.6 kpc, was derivedfrom the photometric data for 34 member stars. This is similar todistances found for other young groups in the Carina region. One Msupergiant and one Be star are members of the cluster. The brighteststars on the main sequence are of type B1. Several stars that haveevolved away from the upper main sequence have been classified as giantsand supergiants. The age of the cluster is about 7-million years. Thestar HD 91824 (no. 1), spectral type O7 V((f)), is not a member of thegroup. The insterstellar reddening is normal in front of this cluster.
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