Late-time spectroscopy of SN 2002hh: A continued visible light echo with no shock interaction yet

TL;DR

This study presents late-time spectra of SN 2002hh, revealing a persistent light echo without signs of shock interaction, challenging expectations based on its circumstellar dust shell's size.

Contribution

It provides the first deep late-time spectral analysis of SN 2002hh, showing continued light echo and no shock interaction despite predictions.

Findings

No clear signs of shock interaction detected

Persistent light echo observed similar to peak luminosity spectrum

Circumstellar dust shell's expected interaction not observed

Abstract

Supernova (SN) 2002hh was unusual among core-collapse SNe because it was highly reddened, and displayed a bright infrared (IR) excess due to radiatively heated dust in its circumstellar medium (CSM). Estimates for the mass of dust responsible for the IR echo suggested the presence of a massive shell within 0.26 pc of the star. For a velocity of 5000 - 10000 km/s, this material should be hit by the SN blast wave at late times, starting at roughly 12 years post-explosion. We have obtained deep late-time spectra with the MMT Blue Channel spectrograph to search for any spectral signatures of ongoing shock interaction. Interaction with a strength comparable to SN 1987A's collision with the equatorial ring would be detected in our data. However, in the spectra reported here, we do not detect clear signs of strong CSM interaction, contrary to expectations based on the reported radii of the dust shell. We do, however, detect emission associated with the old SN, and we find that the broad lines in the spectrum indicate a continuation of an ongoing reflected light echo, which appears similar to the spectrum at peak luminosity for this Type II-P event.