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PTF11kx was a Type Ia supernova (SN Ia) that showed time-variable absorptionfeatures, including saturated Ca II H&K lines that weakened and eventually wentinto emission. The strength of the emission component of H{\alpha} increased,implying that the SN was undergoing significant interaction with itscircumstellar medium (CSM). These features were blueshifted slightly and showeda P-Cygni profile, likely indicating that the CSM was directly related to, andprobably previously ejected by, the progenitor system itself. These and otherobservations led Dilday et al. (2012) to conclude that PTF11kx came from asymbiotic nova progenitor like RS Oph. In this work we extend the spectralcoverage of PTF11kx to 124-680 rest-frame days past maximum brightness. Thesespectra of PTF11kx are dominated by H{\alpha} emission (with widths of ~2000km/s), strong Ca II emission features (~10,000 km/s wide), and a blue"quasi-continuum" due to many overlapping narrow lines of Fe II. Emission fromoxygen, He I, and Balmer lines higher than H{\alpha} is weak or completelyabsent at all epochs, leading to large observed H{\alpha}/H{\beta} intensityratios. The broader (~2000 km/s) H{\alpha} emission appears to increase instrength with time for ~1 yr, but it subsequently decreases significantly alongwith the Ca II emission. Our latest spectrum also indicates the possibility ofnewly formed dust in the system as evidenced by a slight decrease in the redwing of H{\alpha}. During the same epochs, multiple narrow emission featuresfrom the CSM temporally vary in strength. The weakening of the H{\alpha} and CaII emission at late times is possible evidence that the SN ejecta haveovertaken the majority of the CSM and agrees with models of other stronglyinteracting SNe Ia. The varying narrow emission features, on the other hand,may indicate that the CSM is clumpy or consists of multiple thin shells.

Late-Time Spectral Observations of the Strongly Interacting Type Ia Supernova PTF11kx