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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).
| An IUE survey of interstellar H I LY alpha absorption. 1: Column densities
We measure Galactic interstellar neutral hydrogen column densities byanalyzing archival interstellar Ly alpha absorption line data toward 554B2 and hotter stars observed at high resolution with the IUE satellite.This study more than doubles the number of lines of sight with measuresof N(H I) based on Ly alpha. We have included the scattered lightbackground correction algorithm of Bianchi and Bohlin in our datareduction. We use the correlation between the Balmer discontinuity(c1) index and the stellar Ly alpha absorption in order toassess the effects of stellar Ly alpha contamination. Approximately 40%of the B stars with measured (c1) index, exhibit seriousstellar Ly alpha contamination. One table contains the derived values ofthe interstellar N(H I) for 393 stars with at most small amounts ofstellar contamination. Another lists the observed values of total N(H I)for 161 stars with suspected stellar Ly alpha contamination and/oruncertain stellar parameters.
| Optical eclipses and precession effects in the X-ray binary system HD 77581=4U 0900-40
Results of an analysis of multiyear series of photometric observationsof the X-ray binary system HD 77581 are presented. It is shown that thesystem is an eclipsing variable in the optical range and displaysregular long-period variability in the shape and amplitude of theoptical light curves with a period of 93.3 days, which may be connectedwith phenomena in the system. It is also shown that the amplitude of theellipsoidality effect of the visible star is about 0.04 mag in the HD77581 system, with the total amplitude of optical variability reaching0.09 mag. The eclipses are caused by gas streams and by the accretionstructure, whose orientation in the binary system varies with theprecession period of the visible star. The relatively small amplitude ofthe ellipsoidality effect corresponds to the incomplete filling of itsRoche lobe by the visible star. The mass of the neutron star isestimated at 1.6 + or - 0.3 solar masses.
| UBV Photometry of 500 Southern Stars [erratum: 1973MNSSA..32...48C]
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