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HD 181581


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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 Coronal Spectrum of the July 20, 1963 Eclipse
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Datos observacionales y astrométricos

Constelación:Sagitario
Ascensión Recta:19h21m53.54s
Declinación:-21°38'39.3"
Magnitud Aparente:8.603
Distancia:130.378 parsecs
Movimiento Propio en Ascensión Recta:57
Movimiento Propio en Declinación:-5.4
B-T magnitude:9.065
V-T magnitude:8.642

Catálogos y designaciones:
Nombres Propios   (Edit)
HD 1989HD 181581
TYCHO-2 2000TYC 6309-2318-1
USNO-A2.0USNO-A2 0675-32787878
HIPHIP 95193

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