The optical light curve of SN 1985f in NGC 4618.

The optical (λ ≈ 4930 Å) light curve of the bizarre supernova 1985f in NGC 4618 is presented. It covers a six-month interval from the date of discovery (28 February 1985 UT) through the beginning of September 1985, after which the object was near the Sun for two months and also very faint. Great effort is made to eliminate contamination by bright underlying H II regions. The light curve is well approximated by a constant decline of 0.0153 mag day^-1, close to the average decay rate observed in normal Type I supernovae (SNe Ia) three to 13 months after maximum light (≡0.016 mag day^-1). Recent spectroscopic work by Gaskell et al. (1986) suggests that SN 1985f was a Type Ib object, probably discovered ≡8 or 9 months past maximum brightness. The observations reported here represent the first well-determined light curve of a SN Ib at late times, and provide a good standard against which future SNe Ib can be compared.