Following the recent discovery and classification of 2021yfj (Schulze et al. 2024, submitted), whose spectra show prominent narrow emission lines (including narrow P-Cygni profiles) of highly ionized silicon (Si III/IV) and sulphur (S III/IV), and some argon (Ar III), but almost completely lacking lines of carbon/oxygen, hydrogen and helium, we tentatively propose to use a new spectroscopic SN type - SN Ien - to refer to such objects.
We propose to continue the existing SN classification sequence of types IIn, Ibn and Icn -- events showing spectra that are dominated by narrow emission lines of hydrogen, helium and C/O, respectively, likely reflecting H-rich, He-rich and C/O-rich CSM. Moving inward along the expected shell structure of massive stars with progressively heavier compositions, CSM stripped from such inner layers is theoretically predicted to be composed of O/Ne/Mg and later O/Si/S/Ar.
Continuing the accepted relation between SN spectroscopic classification and massive star shell structures, material from such inner layers should naturally correspond to SN Types Id and Ie; and events with narrow CSM lines would then be denoted by Idn and Ien.
This topic should be re-examined once additional relevant examples are discovered.
(To clarify, we have added now only the definition for SN Ien, leaving the potential additional types for future discussion and implementation.)
| Catalog | Name | Reported RA | Reported DEC | Reported Obj-Type | Reported Redshift | Host Name | Host Redshift | Remarks | TNS RA | TNS DEC | TNS Obj-Type | TNS Redshift |
|---|---|---|---|---|---|---|---|---|---|---|---|---|
| TNS | 2021yfj [ZTF21abzbmhz] | 01:37:46.171 | -01:15:17.78 | SN Ien | 0.13865 | SDSS J013746.19-011518.6 | 01:37:46.171 | -01:15:17.78 | SN Ien | 0.13865 |