The 2012 brightening of SN 2009ip was dominated by emission from the interaction of ejecta with the surrounding circumstellar material ( CSM ) produced by episodic mass loss from the progenitor , complicating the diagnosis of whether the underlying explosion was a true supernova or a nonterminal eruption of a massive star .
In this paper , we contribute a time series of optical photometric and spectroscopic observations for SN 2009ip from 1 to 3 years after the 2012 outburst , collected at the Las Cumbres Observatory and the Keck Observatory .
We find that the brightness of SN 2009ip continues to decline with no deviations from a linear slope of 0.0030 \pm 0.0005 mag day ^ { -1 } in the r ^ { \prime } band , and demonstrate that this is similar to both observations and models of CSM-ejecta interaction .
We show that the late-time spectra continue to be dominated by the signature features of CSM interaction , and that the large ratio of L _ { H \alpha } / L _ { H \beta } \approx 40 implies that the material remains optically thick to Balmer photons ( “ Case C ” recombination ) .
We combine our late-time photometry and spectra with early-time data for SN 2009ip and provide a comprehensive discussion that incorporates recently published models and observations for transient phenomena dominated by CSM-ejecta interaction , and conclude that the presence of broad H \alpha at early times remains among the best evidence that a terminal supernova has occurred .
Finally , we compare our late-time spectra to those of Type IIn SN and SN impostors at late phases and find that although SN 2009ip has some similarities with both types , it has more differences with late-time impostor spectra .