Investigation on the southern part of the high density astrometric catalogs USNO B1.0, 2MASS and UCAC2 ^*

¹ Observatório do Valongo/UFRJ, Ladeira Pedro Antônio 43, Saúde. Rio de Janeiro, Brazil e-mail: dario@ov.ufrj.br
² GEA - Observatório do Valongo/UFRJ, Brazil and Observatorio Nacional/MCT, Brazil

Received: 16 June 2004
Accepted: 2 September 2004

Abstract

To access the astrometric capability of dense catalogues at southern declinations, the results from a sample of 76 ICRF sources of the observational program conducted at the 1.60m telescope of the Laboratório Nacional de Astrofísica – LNA, Brazil, are examined. The observations were taken on mean epoch 1999.76, at Johnston V filter, in fields of size 5´, with scale of 03/pixel. The astrometric reduction is made relatively to the catalogs USNO B1.0 and 2MASS. The comparison between the ICRF position and the catalogue referred measured optical counterpart position reveals both catalogs aligned to the ICRF, but for an equatorial offset of the B1.0 at 90.4 mas, to a significance level of 3.4 times the standard error. The direct comparison between catalogue and ICRF positions gives alike results. For the B1.0 there are also clumped variations on average ranging 96 mas, but reaching up to the level of 300 mas. Local corrections on the B1.0 positions were applied using the UCAC2 catalog. These were effective to remove the equatorial offset and the zonal variations, manifesting the internal consistency of the B1.0 positions. This supports the astrometric adherence of the UCAC2 catalog to the ICRS, as also shown by the 2MASS and referred results, since the systematic difference between 2MASS and UCAC2 is lowest.