CONTINUED DECLINE IN THE 1-5 MU-M BRIGHTNESS OF B5-IRS1 - 1990-93

J H K L L' & nbM photometry of B5IRS1 in 1992 and 1993 shows that this low-mass YSO continues to fade in the near-infrared at an average rat e of about 0.24 mag per year, and that by 1993 September the J to K lu minosity had fallen to one-third of its 1988 December value. The chang e in luminosity continues to be virtually colour-independent between J and K, although the K-M colour is increasing with time. The changes a re consistent with an increase in extinction by a dust population depl eted of grains with radii smaller than approximately 0.4 mum, or with the short-wavelength emission (lambda less-than-or-similar-to 3 mum) b eing dominated by light scattered in a changing circumstellar geometry .