The astrometric position of T Tauri and the nature of its companion

Abstract

The optical position of T Tauri is recalculated from previous data to demonstrate that the object is actually the same as that viewed to the north of it by other investigators. Radio data at 4.885 GHz and speckle interferometric data at 2.2, 3.8, and 4.8 microns were available. The optical data were determined to be subject to systematic zero-point errors, accidental errors in the mean epoch of observation, a proper motion error, and errors due to the visible nebulosity around T Tauri. New measurements were made on the initial proper motion yellow plate from Lick Observatory and another taken with an objective grating and offset exposures. It was found that the northern component coincided with the optical component, while the strong, southern component was the same as a previous radio position. Furthermore, it was shown that the two components shared the same proper motion to within 1.1 arcsec/yr. It is suggested that an accretion disk around the object may cause some of the discrepancies.