EMISSION FROM COBALT IN TYPE IA SUPERNOVAE

Nebular spectra of Type Ia supernovae are modelled by including the fo rbidden lines of cobalt ions for which the radiative transition probab ilities and effective collision strengths have recently been calculate d. As a result, the agreement between the synthetic and observed spect ra is significantly improved in the early nebular phase when cobalt is as abundant as iron in the supernovae. Strong cobalt emission lines a re identified in the supernova spectra, which provides a direct spectr oscopic evidence for the radioactive decay of Ni-56-->Co-56-->Fe-56 th at powers the supernovae.