Insert an entry for Cas A into the table of models. Need to specify the
    year of the observations to account for the time variation of Cas A's
    emission.

def init_cas_a (year):
    """Insert an entry for Cas A into the table of models. Need to specify the
    year of the observations to account for the time variation of Cas A's
    emission.

    """
    year = float (year)
    models['CasA'] = lambda f: cas_a (f, year)