We present a new maximum-light optical spectrum of the the extremely low
luminosity and exceptionally low energy Type Ia supernova (SN Ia) 2008ha,
obtained one week before the earliest published spectrum. Previous observations
of SN 2008ha were unable to distinguish between a massive star and white dwarf
origin for the SN. The new maximum-light spectrum, obtained one week before the
earliest previously published spectrum, unambiguously shows features
corresponding to intermediate mass elements, including silicon, sulfur, and
carbon. Although strong silicon features are seen in some core-collapse SNe,
sulfur features, which are a signature of carbon/oxygen burning, have always
been observed to be weak in such events. It is therefore likely that SN 2008ha
was the result of a thermonuclear explosion of a carbon-oxygen white dwarf.
Carbon features at maximum light show that unburned material is present to
significant depths in the SN ejecta, strengthening the case that SN 2008ha was
a failed deflagration. We also present late-time imaging and spectroscopy that
are consistent with this scenario.Comment: ApJL, accepted. 5 pages, 3 figure
