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Y. L. Qiu (BAO), K. Hatano, D. Branch, E. Baron (U. Oklahoma)
We present spectroscopic observations from the Beijing Astronomical Observatory of the recent SN~1999dn in NGC~7714. This is the first well--observed Type Ib supernova since SN~1984L. Spectra of SN~1999dn beginning near maximum brightness are compared with spectra of SN~1984L. Although the spectroscopic evolution of SN~1999dn closely resembles that of SN~1984L, there are some interesting differences. We compare observed spectra of SNe~1999dn and 1984L with synthetic spectra generated with the SYNOW spectrum synthesis code. For SN~1999dn we find that lines of helium can account for most of the observed features, and that the minimum velocity of helium is at least as low as 7,000 km~s-1. The extent to which Type Ibc SNe may form a smooth sequence in terms of helium abundance is discussed.