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Hipparcos astrometry for 257 stars using Tycho-2 data
We present improved Hipparcos astrometry for 257 Hipparcos stars,resolved into 342 components. For 64 of the stars no astrometry wasobtained in the Hipparcos Catalogue, while for the remaining starsadditional components have been added by this solution or the positionshave been revised considerably. We have used the published Hipparcostransit data for the new solutions, together with results from thesecond reduction of the Tycho data for defining better initial values.Based on observations made with the ESA Hipparcos astrometry satellite.Table 3 is only available in electronic form at the CDS via anonymousftp to cdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/Abstract.html
| Construction and verification of the Tycho-2 Catalogue
The construction of the Tycho-2 Catalogue is described. The cataloguecontains astrometric positions and proper motions as well as two-colourphotometric data for 2.5 million stars. The Tycho-2 positions andmagnitudes are based on precisely the same observations as the originalTycho Catalogue (hereafter Tycho-1) collected by the sky mapper of theESA Hipparcos satellite, but Tycho-2 is much bigger and slightly moreprecise, owing to a more advanced reduction technique. Components ofdouble stars with separations down to 0.8 arcsec are included. Propermotions precise to about 2.5 mas/yr are given as derived from acomparison with the Astrographic Catalogue and 143\ other astrometriccatalogues, all reduced to the Hipparcos celestial coordinate system.Tycho-2 supersedes in most applications Tycho-1, and the ACT and TRCcatalogues based on Tycho-1. Based on observations made with the ESAHipparcos astrometry satellite.
| Dwarf K and M stars in the southern hemisphere.
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1972AJ.....77..486U&db_key=AST
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