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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).
A catalog of precise reference star positions for the astrometry network of the international comet P/Halley compaign Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1987A&AS...71..525D&db_key=AST
Micrometer Observations of Double Stars and New Pairs - Part Ten Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1980ApJS...44..111H&db_key=AST
Mesures d'étoiles doubles visuelles Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1970A&AS....3...71M&db_key=AST
Mesures d'etoiles doubles faites AU refracteur de 38cm de l'Observatoire de Nice. Not Available
Mesures d'étoiles doubles faites au réfracteur de 38 cm de l'Observatoire de Nice Not Available

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Observation and Astrometry data

Constellation:	Pisces
Right ascension:	00^h09^m57.43^s
Declination:	+08Â°34'36.9"
Apparent magnitude:	8.774
Distance:	172.414 parsecs
Proper motion RA:	-73.6
Proper motion Dec:	-44.4
B-T magnitude:	9.495
V-T magnitude:	8.834

Catalogs and designations:

Proper Names	(Edit)
HD 1989	HD 542
TYCHO-2 2000	TYC 594-354-1
USNO-A2.0	USNO-A2 0975-00035854
HIP	HIP 807

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