The positions of 16 stars with confirmed or suspected radio emission were determined on the Hipparcos/ICRS reference system, as materialized by the ACT catalogue. The corresponding positions were also determined relatively to the Tycho and TAC 1.0 catalogues (15 radio stars). The level of precision is at 35 mas for right ascensions and 46 mas for declinations. For 5 of these stars there was no previous position on the Hipparcos system.
The analysis of the results for the radio stars shows that the performance of the Valinhos CCD Meridian Circle and of the observation and reduction procedures can provide positions to an accuracy better than 50 mas to the magnitude range from 9 to 13, provided that typically a minimum of 10 reference stars are present and 5 good nights of observation are used at least.
The proper motions for 14 of the studied radio stars are found, to an average precision better than 2 mas/year. The proper motions are found in general agreement with the ACT and TAC ones.
The scan drift mode of observation enabled to obtain accurate positions for many stars in the observed strips. In particular, positions at the observation epoch have been obtained for 545 ACT stars, 573 Tycho stars and 566 TAC stars. These results are available in electronic form.
As the TAC catalogue can play an all important role for the densification of the Hipparcos system, an investigation was carried out concerning its internal consistency. Naturally this investigation is limited by the number of observed strips (15) and the width of the declination belt (from -15.6 to +28.6; by average = +10.5). The internal precision of the TAC referred reductions is close to the ACT ones. An average offset of 100 mas, similar for both equatorial coordinates, in the sense Hipparcos minus FK5, is found from the position differences between the common ACT and TAC reference stars. Thus, the analysis enables to confirm the TAC 1.0 catalogue qualities, moreover that only the equatorial zone was studied here, indicating that its extension on the Hipparcos system may bring an important contribution to its densification.
In all, the results obtained show that the present
program shall be able to present reliable positions for a large number of radio stars, placed on the Hipparcos reference system.Acknowledgements
We acknowledge financial support from CAPES, CNPq and FAPESP. Also we acknowledge the suggestions made by the referee, Dr. H.G. Walter.
Copyright The European Southern Observatory (ESO)