The progenitor of SN 2004dj in a star cluster

The progenitor of Type II- P ( P p plateau) supernova SN 2004dj is identified with a supergiant in a compact star cluster known as Sandage's star 96 ( S96) in the nearby spiral galaxy NGC 2403, which was fortuitously imaged as part of the Beijing- Arizona- Taiwan- Connecticut ( BATC) Multicolor Sky Survey from 1995 February to 2003 December prior to SN 2004dj. The superior photometry of BATC images for S96, taken with 14 intermediate- band filters covering 3000 - 10000 angstrom, unambiguously establishes the star cluster nature of S96, with an age of similar to 20 Myr, a reddening of mag, and a total mass of similar to 96,000 M-circle dot. The compact star E( B - V) similar to 0.35 cluster nature of S96 is also consistent with the lack of light variations in the past decade. The SN progenitor is estimated to have a main- sequence mass of similar to 12 M-circle dot. The comparison of our intermediate- band data of S96 with the postoutburst photometry obtained as the SN significantly dims with time may hopefully conclusively establish the nature of the progenitor.