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On metal-deficient barium stars and their link with yellow symbiotic stars
This paper addresses the question of why metal-deficient barium starsare not yellow symbiotic stars (YSyS). Samples of (suspected)metal-deficient barium (mdBa) stars and YSyS have been collected fromthe literature, and their properties reviewed. It appears in particularthat the barium nature of the suspected mdBa stars needs to beascertained by detailed abundance analyses. Abundances are thereforederived for two of them, HD 139409 and HD 148897, which reveal that HD148897 should not be considered a barium star. HD 139409 is a mildbarium star, with overabundances observed only for elements belonging tothe first s-process peak (Y and Zr). It is only moderately metal-poor([Fe/H] = -0.4). The evidence for binarity among mdBa stars is thenreviewed, using three different methods: (i) radial-velocity variations(from CORAVEL observations), (ii) Hipparcos astrometric data, and (iii)a method based on the comparison between the Hipparcos and Tycho-2proper motions. An orbit is obtained for HIP 55852, whereas evidence forthe (so far unknown) binary nature of HIP 34795, HIP 76605, HIP 97874and HIP 107478 is presented. No conclusion regarding the binary natureof HIP 11595, HIP 25161 could be reached. Two stars with no evidence forbinarity whatsoever (HIP 58596 and BD +3°2688) are candidateslow-metallicity thermally-pulsing asymptotic giant branch stars, asinferred from their large luminosities. The reason why mdBa stars arenot YSyS is suggested to lie in their different orbital perioddistributions: mdBa stars have on average longer orbital periods thanYSyS, and hence their companion accretes matter at a lower rate, for agiven mass loss rate of the giant star. The definite validation of thisexplanation should nevertheless await the determination of the orbitalperiods for the many mdBa stars still lacking periods, in order to makethe comparison more significant.
| The Tokyo PMC catalog 90-93: Catalog of positions of 6649 stars observed in 1990 through 1993 with Tokyo photoelectric meridian circle
The sixth annual catalog of the Tokyo Photoelectric Meridian Circle(PMC) is presented for 6649 stars which were observed at least two timesin January 1990 through March 1993. The mean positions of the starsobserved are given in the catalog at the corresponding mean epochs ofobservations of individual stars. The coordinates of the catalog arebased on the FK5 system, and referred to the equinox and equator ofJ2000.0. The mean local deviations of the observed positions from theFK5 catalog positions are constructed for the basic FK5 stars to comparewith those of the Tokyo PMC Catalog 89 and preliminary Hipparcos resultsof H30.
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