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We present Hubble Space Telescope (HST) and ground-based optical andnear-infrared observations of SN 2005hk and SN 2008A, typical members of theType Iax class of supernovae (SNe). Here we focus on late-time observations,where these objects deviate most dramatically from all other SN types. Insteadof the dominant nebular emission lines that are observed in other SNe at latephases, spectra of SNe 2005hk and 2008A show lines of Fe II, Ca II, and Fe Imore than a year past maximum light, along with narrow [Fe II] and [Ca II]emission. We use spectral features to constrain the temperature and density ofthe ejecta, and find high densities at late times, with n_e >~ 10^9 cm^-3. Suchhigh densities should yield enhanced cooling of the ejecta, making theseobjects good candidates to observe the expected "infrared catastrophe," ageneric feature of SN Ia models. However, our HST photometry of SN 2008A doesnot match the predictions of an infrared catastrophe. Moreover, our HSTobservations rule out a "complete deflagration" that fully disrupts the whitedwarf for these peculiar SNe, showing no evidence for unburned material at latetimes. Deflagration explosion models that leave behind a bound remnant canmatch some of the observed properties of SNe Iax, but no published model isconsistent with all of our observations of SNe 2005hk and 2008A.

Hubble Space Telescope and Ground-Based Observations of the Type Iax Supernovae SN 2005hk and SN 2008A