Evidence for a high-velocity carbon-rich layer in the Type Ia SN 1990N

We use a parameterized spectrum-synthesis code to make a direct analysis of a high quality spectrum of the Type Ia SN 1990N that was obtained by Leibundgut et al. 14 days before the time of optical maximum. We suggest that the absorption feature observed near 6040 Angstrom, which has been attributed to blueshifted lambda 6355 of Si II, actually was produced by blueshifted lambda 6580 of C II, in a high-velocity (upsilon > 26, 000 km s(-1)) carbon-rich region. Implications for SN Ia explosion models are briefly discussed.