Post-perihelion observations of comet P/Halley. IV. r=16.6 and 18.8AU.

Deep CCD observations have been performed with the 3.58m New Technology Telescope at La Silla in the direction of comet P/Halley on April 6, 1992, at heliocentric distance r=16.6AU and on January 11, 1994, at r=18.8AU. In 1992, the comet could not be convincingly recorded; the limiting magnitude was V~25.8. In 1994, the image of the comet was clearly detected (at S/N=7) as a V=26.5 point-source, 0.9" from the predicted position. The identification is further strengthened by the observed motion, which is incompatible with that of more nearby minor bodies and perfectly matches that predicted for this comet. The observed brightness corresponds to that of the naked nucleus and no coma is detected at the 32mag per square arcsecond level, indicating a complete lack of activity. The feasibility of continued monitoring of P/Halley during the next years is discussed.