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CCD astrometry of a sample of southern very low-mass (VLM) stars, obtained on the 2.2-m telescope at the European Southern Observatory, La Silla, is presented. Trigonometric parallaxes have been determined for 13 stars, and proper motions for a further two stars. Photometry in the I and K passbands is also presented for the astrometric programme stars, and is used to construct an MK:I — K colour-magnitude diagram. Astrometric observations have been made of the canonical very late M dwarf VB10 through a narrow-band (Δλ = 90 Å) filter. These data confirm that the effects of differential colour refraction can be substantially reduced by the use of such filters, without compromising astrometric precision.
C. G. Tinney (Thu,) studied this question.