Spectrum analysis of the type Ib supernova SN 1999dn: Probable identifications of C II and H alpha

Low-resolution spectra of SN 1999dn at early times are presented and compar ed with synthetic spectra generated with the parameterized supernova synthe tic spectrum code SYNOW. We find that the spectra of SN 1999dn strongly res emble those of SN 1997X and SN 1984L, and hence we classify it as a Type Ib event. Line identifications are established through spectrum synthesis. St rong evidence of both H alpha and C II lambda 6580 is found. We infer that Ha appears first, before the time of maximum brightness, and then is blende d with and finally overwhelmed by the C II line after maximum; this favors a thin high-velocity hydrogen skin in this Type Ib supernova.