High-resolution spectroscopy of SN 2017hcc and its blueshifted line profiles from post-shock dust formation

Nathan Smith, Jennifer E. Andrews

Research output: Contribution to journalArticlepeer-review

Abstract

SN 2017hcc was remarkable for being a nearby and strongly polarized superluminous Type IIn supernova (SN). We obtained high-resolution Echelle spectra that we combine with other spectra to investigate its line-profile evolution. All epochs reveal narrow P Cygni components from pre-shock circumstellar material (CSM), indicating an axisymmetric outflow from the progenitor of 40-50 km s−1. Broad and intermediate-width components exhibit the classic evolution seen in luminous SNe IIn: symmetric Lorentzian profiles from pre-shock CSM lines broadened by electron scattering at early times, transitioning at late times to multicomponent, irregular profiles coming from the SN ejecta and post-shock shell. As in many SNe IIn, profiles show a progressively increasing blueshift, with a clear flux deficit in red wings of the intermediate and broad velocity components after day 200. This blueshift develops after the continuum luminosity fades, and in the intermediate-width component, persists at late times even after the SN ejecta fade. In SN 2017hcc, the blueshift cannot be explained as occultation by the SN photosphere, pre-shock acceleration of CSM, or a lopsided explosion of CSM. Instead, the blueshift arises from dust formation in the post-shock shell and in the SN ejecta. The effect has a wavelength dependence characteristic of dust, exhibiting an extinction law consistent with large grains. Thus, SN 2017hcc experienced post-shock dust formation and had a mildly bipolar CSM shell, similar to SN 2010jl. Like other superluminous SNe IIn, the progenitor lost around 10 M☉ due to extreme eruptive mass-loss in the decade before exploding.

Original languageEnglish (US)
Pages (from-to)3544-3562
Number of pages19
JournalMonthly Notices of the Royal Astronomical Society
Volume499
Issue number3
DOIs
StatePublished - Dec 1 2020

Keywords

  • Binaries: general
  • Outflows
  • Stars: evolution
  • Stars: massive
  • Stars: winds
  • Supernovae: general

ASJC Scopus subject areas

  • Astronomy and Astrophysics
  • Space and Planetary Science

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