The Astrophysical Journal (Jan 2023)

The Origin and Evolution of the Normal Type Ia SN 2018aoz with Infant-phase Reddening and Excess Emission

  • Yuan Qi Ni,
  • Dae-Sik Moon,
  • Maria R. Drout,
  • Abigail Polin,
  • David J. Sand,
  • Santiago González-Gaitán,
  • Sang Chul Kim,
  • Youngdae Lee,
  • Hong Soo Park,
  • D. Andrew Howell,
  • Peter E. Nugent,
  • Anthony L. Piro,
  • Peter J. Brown,
  • Lluís Galbany,
  • Jamison Burke,
  • Daichi Hiramatsu,
  • Griffin Hosseinzadeh,
  • Stefano Valenti,
  • Niloufar Afsariardchi,
  • Jennifer E. Andrews,
  • John Antoniadis,
  • Rachael L. Beaton,
  • K. Azalee Bostroem,
  • Raymond G. Carlberg,
  • S. Bradley Cenko,
  • Sang-Mok Cha,
  • Yize Dong,
  • Avishay Gal-Yam,
  • Joshua Haislip,
  • Thomas W.-S. Holoien,
  • Sean D. Johnson,
  • Vladimir Kouprianov,
  • Yongseok Lee,
  • Christopher D. Matzner,
  • Nidia Morrell,
  • Curtis McCully,
  • Giuliano Pignata,
  • Daniel E. Reichart,
  • Jeffrey Rich,
  • Stuart D. Ryder,
  • Nathan Smith,
  • Samuel Wyatt,
  • Sheng Yang

DOI
https://doi.org/10.3847/1538-4357/aca9be
Journal volume & issue
Vol. 946, no. 1
p. 7

Abstract

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SN 2018aoz is a Type Ia SN with a B -band plateau and excess emission in infant-phase light curves ≲1 day after the first light, evidencing an over-density of surface iron-peak elements as shown in our previous study. Here, we advance the constraints on the nature and origin of SN 2018aoz based on its evolution until the nebular phase. Near-peak spectroscopic features show that the SN is intermediate between two subtypes of normal Type Ia: core normal and broad line. The excess emission may be attributable to the radioactive decay of surface iron-peak elements as well as the interaction of ejecta with either the binary companion or a small torus of circumstellar material. Nebular-phase limits on H α and He i favor a white dwarf companion, consistent with the small companion size constrained by the low early SN luminosity, while the absence of [O i ] and He i disfavors a violent merger of the progenitor. Of the two main explosion mechanisms proposed to explain the distribution of surface iron-peak elements in SN 2018aoz, the asymmetric Chandrasekhar-mass explosion is less consistent with the progenitor constraints and the observed blueshifts of nebular-phase [Fe ii ] and [Ni ii ]. The helium-shell double-detonation explosion is compatible with the observed lack of C spectral features, but current 1D models are incompatible with the infant-phase excess emission, ${B}_{\max }\mbox{--}{V}_{\max }$ color, and weak strength of nebular-phase [Ca ii ]. Although the explosion processes of SN 2018aoz still need to be more precisely understood, the same processes could produce a significant fraction of Type Ia SNe that appear to be normal after ∼1 day.

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