2008CBET.1298....2C

Chornock et al. also report an improved estimate for the equivalent width of the narrow Na I D absorption lines in the Keck ESI spectrum as reported on CBET 1290. The new measurement is about 0.18 nm, suggesting an E(B-V) reddening of about 0.5 mag. Adopting this new reddening and the other information reported on CBET 1290, the possible progenitor of SN 2008ax has an absolute magnitude of M(V) = -7.5 and colors of B-V = -0.4 and V-I = 0.1, consistent with a bright blue supergiant star. Note that the progenitor of SN 1993J (Aldering et al. 1994, A.J. 107, 662; Van Dyk et al. 2002, PASP 114, 1322) has M(V) = -7.0 and is a yellow K2 Ia supergiant, so the possible progenitor of SN 2008ax is more luminous and has a bluer color than that of SN 1993J, if the assumed reddening is correct.