AAS 199th meeting, Washington, DC, January 2002
Session 75. Gravitational Lensing and Cosmic Distances
Oral, Tuesday, January 8, 2002, 2:00-3:30pm, International Ballroom Center

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[75.07] Recomputing the Hipparcos Parallaxes of the Pleiades from the Hipparcos Intermediate Astrometry Data

V.V. Makarov (USRA)

The discrepancy between the mean Hipparcos parallax of the Pleiades open cluster and previous photometric, ground-based astrometric and other determinations poses a still unresolved problem for the existing stellar physics models and casts some doubts on the basic pieces of the Cosmic Distance Scale, that is the established distances to open clusters. In this paper a hypothesis is tested that the Hipparcos parallaxes of the Pleiades contain a small-scale correlated error originating in the biased along-scan attitude determinations. A method is developed to recompute the Hipparcos astrometric solutions for a selected number of stars by referencing each observation to simultaneously observed stars in the other field of view of the telescope. Astrometric parameters of 54 Pleiades members were solved for using this method. No significant error was detected in the mean parallax, but the Pleiades declinations are evidently in error by -0.6 mas.

The author(s) of this abstract have provided an email address for comments about the abstract: makarov@usno.navy.mil

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