A new reduction of the raw Hipparcos data

Astrophysics, abstract
astro-ph/0505432

From: Floor van Leeuwen [view email]

Date: Fri, 20 May 2005 09:19:26 GMT   (399kb)

We present an outline of a new reduction of the Hipparcos astrometric data,
the justifications of which are described in the accompanying paper. The
emphasis is on those aspects of the data analysis that are fundamentally
different from the ones used for the catalogue published in 1997. The new
reduction uses a dynamical modelling of the satellite’s attitude. It
incorporates provisions for scan-phase discontinuities and hits, most of which
have now been identified. Solutions for the final along-scan attitude (the
reconstruction of the satellite’s scan phase), the abscissa corrections and the
instrument model, originally solved simultaneously in the great-circle
solution, are now de-coupled. This is made possible by starting the solution
iterations with the astrometric data from the published catalogue. The
de-coupling removes instabilities that affected great-circle solutions for
short data sets in the published data. The modelling-noise reduction implies
smaller systematic errors, which is reflected in a reduction of the
abscissa-error correlations by about a factor 40. Special care is taken to
ensure that measurements from both fields of view contribute significantly to
the along-scan attitude solution. This improves the overall connectivity of the
data and rigidity of the reconstructed sky, which is of critical importance to
the reliability of the astrometric data. The changes in the reduction process
and the improved understanding of the dynamics of the satellite result in
considerable formal-error reductions for stars brighter than 8th magnitude.

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SLAC-SPIRES HEP (refers to ,
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