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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).
| Spectropolarimetry of 3CR 68.1: A Highly Inclined Quasar
We present Keck spectropolarimetry of the highly polarized radio-loudquasar 3CR 68.1 (z = 1.228, V = 19). The polarization increases from 5%in the red (4000 Angstroms rest frame) to greater than 10% in the blue(1900 Angstroms rest frame). The broad emission lines are polarized thesame as the continuum, which shows that 3CR 68.1 is not a blazar, as ithas sometimes been regarded in the past. We also present measurements ofthe emission lines and a strong, blueshifted, associated absorption linesystem as well as a detection at the emission-line redshift of Ca II Kabsorption, presumably from stars in the host galaxy. Neither a blazarnor a partially obscured radio-quiet QSO, 3CR 68.1 belongs to anobservationally rare class of highly polarized quasars. Taking intoaccount the other unusual properties of 3CR 68.1, such as its extremelyred spectral energy distribution and its extreme lobe dominance, weexplain our spectropolarimetric results in terms of unified models. Weargue that we have a dusty, highly inclined view of 3CR 68.1, withreddened scattered (polarized) quasar light diluted by even moredust-reddened quasar light reaching us directly from the nucleus.
| UBV photometry of stars whose positions are accurately known. IV
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1987A&AS...68..211O&db_key=AST
| Positions moyennes et mouvements propres de 355 etoiles DU GC de la zone de declinaison +33 +36.
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1976A&AS...26..219M&db_key=AST
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