Astronomy and Astrophysics – Astronomy
Scientific paper
Aug 2003
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2003basbr..23...51d&link_type=abstract
Boletim da Sociedade Astronômica Brasileira (ISSN 0101-3440), vol.23, no.1, p. 51-51
Astronomy and Astrophysics
Astronomy
Scientific paper
Astrometric positions for an evenly distributed group of 76 southern ICRF sources are presented. The positions were obtained on different representations of the Hipparcos system, namely on the ACT, the Tycho2, the UCAC-S1, and on the USNO-B1.0 frames. All optical counterparts were imaged in 5arcmin2 CCD frames from the 1.6m telescope at the Laboratório Nacional de Astrofisica, in Brazil. In general three frames per source were taken. For the USNO-B1.0 based reductions, the reference stars within the frames had their catalog coordinates corrected by proper motion towards the observation date. For the ACT, Tycho2, and UCAC1 based reductions, the reference stars were picked up from the USNO-A.20 catalog and placed on the base catalogs frame by a third degree polynomial adjustment, made on a 4deg2 neighborhood. In these cases, since the A2.0 does not contain proper motions, the base catalog frame was astrometically corrected by applying the corresponding proper motions, either towards the A2.0 plate or the observation dates. It is shown that, in the first case just a system correction, from the A2.0 frame to the base catalog frame, is achieved. Beyond this, in the second case, also the local, average proper motions of the A2.0 reference stars are modeled. The main conclusions highlight the usefulness of modeling the systematic parts of the reference stars proper motions (20mas for the Tycho2 reductions), the high quality of the astrometry made at the LNA 1.6m telescope (5mas centering error), and the accuracy that can be envisaged from the UCAC catalog (better than 100mas, using the A2.0 for the local frame stars). The results suggest a misalignment of the B1.0 from the Hipparcos system (Dd = +72+/-26mas).
Andrei Alexander H.
Assafin Marcelo
da Silva Neto Dario N.
Vieira Martins Roberto
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