Extension of the ICRF for selected areas down to the 15th magnitude ^*,**

¹ Instituto de Astronomia, Geofísica e Ciências Atmosféricas da Universidade de São Paulo, Caixa Postal 3386, 01060-970 São Paulo SP, Brazil
² Observatoire de Bordeaux, UMR 5804, CNRS/INSU, BP 89, 33270 Floirac, France

Corresponding author: J. I. B. Camargo, camargo@iagusp.usp.br

Received: 19 March 2001
Accepted: 1 June 2001

Abstract

In this paper, we present our results towards the extension of the ICRF to the optical domain down to the 15th V magnitude, for some regions of special astronomical interest. This extension is given by accurate positions and proper motions in the ICRS. Present epoch positions were obtained with the CCD transit circle of the Abrahão de Moraes Observatory, in the city of Valinhos -São Paulo. Proper motion derivation is achieved by combining our meridian circle positions with those from available astrometric catalogues and SERC-J plate measurements performed with the MAMA measuring machine (Paris). The final result is presented as a catalogue containing positions, proper motions, magnitudes and cross-identifications with major catalogues for 41 721 objects. A full description of the employed data is given along with an analysis of the uncertainties on positions and proper motions in our final catalogue. On average, stars with have positional precisions better than 50 mas in both coordinates, and 100 mas at the detection limit of our instrument (). For proper motions, average precisions are better than 4 mas/year, whatever the magnitude, when . To the south of this declination, precisions become magnitude-dependent, providing figures of 3 mas/year when and reaching 17 mas/year at the detection limit. The declination dependence affects the fainter stars and reflects a feature of our main first epoch material for this magnitude range, the USNO-A2.0 catalogue. The Valinhos CCD transit circle observations cover a variety of regions of great interest. Here, we consider those containing extragalactic radio sources, mostly from ICRF, and pre-main sequence stars in southern star-forming regions (Chamaeleon, Lupus and Upper Scorpius -Ophiuchus), where positions from the SERC-J plates were employed.