A 10 mu m silicate emission feature has been discovered in the spectra
of comets P/Borrelly and P/Faye at R similar to 1.5 AU. These are the
first short period comets in which silicate emission has definitely b
een detected. The broad emission features are about 25% above the cont
inuum. No emission feature was present in the spectrum of P/Schaumasse
; it is possible that the nucleus of P/Schaumasse was directly detecte
d. If all of the observed flux originated from the nucleus, then the e
ffective radius is about 3 km; the observed color temperature is consi
stent with a rapidly rotating nucleus. We present models that show how
the shape of the silicate feature can depend on the way in which sili
cate and absorbing material are mixed in the grains. (C) 1996 Academic
Press, Inc.