Near-infrared Spectroscopy of Supernova 2017eaw in 2017: Carbon Monoxide and Dust Formation in a Type II-P Supernova

Abstract

The origin of dust in the early Universe has been the subject of considerable debate. Core-collapse supernovae (ccSNe), which occur several million years after their massive progenitors form, could be a major source of that dust, as in the local universe several ccSNe have been observed to be copious dust producers. Here we report nine near-infrared (0.8 − 2.5 µm) spectra of the Type II-P SN 2017eaw in NGC 6946, spanning the time interval 22 − 205 days after discovery. The specta show the onset of CO formation and continuum emission at wavelengths greater than 2.1 µm from newly-formed hot dust, in addition to numerous lines of hydrogen and metals, which reveal the change in ionization as the density of much of the ejecta decreases. The observed CO masses estimated from an LTE model are typically 10 −4 M during days 124 − 205, but could be an order of magnitude larger if non-LTE conditions are present in the emitting region. The timing of the appearance of CO is remarkably consistent with chemically controlled dust models of Sarangi & Cherchneff.

SN 2017gmr: An Energetic Type II-P Supernova with Asymmetries

“…As the SN drops from the plateau phase after 100 days, additional lines of O I, Si I, He I, and other weak hydrogen series are seen. The CO overtone between 2.3 and 2.5 μm is not present in our last two spectra as has been seen for other Type II SNe (Yuan et al 2016;Rho et al 2018;Sarangi et al 2018;Tinyanont et al 2019). This may help rule out dust formation, at least in the first 150 days.…”

Near-infrared and Optical Observations of Type Ic SN 2020oi and Broad-lined Type Ic SN 2020bvc: Carbon Monoxide, Dust, and High-velocity Supernova Ejecta

“…We recently obtained a sequence of NIR spectra of the Type IIP CCSN SN 2017eaw, which shows the onset of CO formation and newly formed carbon dust (Rho et al 2018a;Szalai et al 2019;Tinyanont et al 2019). The timing of the appearance and the evolution of CO is remarkably similar to that seen in SN 1987A and is consistent with chemically controlled dust models.…”

“…(Jencson et al 2017), and SN 2007gr (Hunter et al 2009. The Fe II at 1.64 μm and Mg I lines at 1.5 μm are commonly detected in SN Ib/IIb SPIRITS 15 c (Jencson et al 2017), as well as in SN IIP SN 2017eaw (Rho et al 2018a). There is little temporal change in the spectra of SN 2020bvc from 20 to 73 days.…”

“…GNIRS was configured in its cross-dispersed mode, using its 32 line mm −1 grating and a 0 45-wide slit to provide a resolving power, R, of ∼1200 (250 km s −1 ) for the first spectrum of SN 2020oi and the SN 2020bvc spectrum and a 0 675-wide slit to nominally provide R = 800 (375 km s −1 ) for the second SN 2020oi spectrum (the seeing was much better than 0 675). The observational setup and data reduction procedures were the same as those used for SN 2017eaw as described in Rho et al (2018a). The spectra shown here have been binned such that the separation of adjacent data points, Δλ, corresponds to λ/Δλ ∼ 1000.…”

Dicarbon Formation in Collisions of Two Carbon Atoms

“…1 illustrates a sample of the experimentally observed bands (Tanabashi et al 2007;Bornhauser et al 2015;Macrae 2016;Furtenbacher et al 2016) connecting eleven singlet, triplet, and quintet states of the C 2 molecule that contribute to the overall radiative association rate coefficient for this molecule. In the ejecta of SN1987A and other core-collapse supernovae, CO and SiO were detected, see (Cherchneff & Sarangi 2011;Sarangi et al 2018), through fundamental (∆ν = 1) bands 1 of ground molecular electronic states allowing observational tests of molecular formation models (Liu et al 1992;Liu & Dalgarno 1995;Cherchneff & Sarangi 2011;Sarangi & Cherchneff 2013;Rho et al 2018)-dicarbon, however, lacks a permanent electric dipole moment and analogous vibrational transitions (fundamental bands) do not exist, making reliable theoretical predictions of rate coefficients imperative. Moreover, recent three-dimensional mapping of CO and SiO in the SN 1987A core ejecta with the Atacama Large Millimeter/submillimeter Array (ALMA) shows a clumpy mixed structure calling for improvements beyond one-dimension in hydrodynamical and chemical modeling of molecular formation (Abellán et al 2017); a reliable description of dicarbide formation might improve such future calculations.…”