Calcium-rich transient SN 2019ehk in a star-forming environment: Yet another candidate for a precursor of a double neutron-star binary

Tatsuya Nakaoka, Keiichi Maeda, Masayuki Yamanaka, Masaomi Tanaka, Miho Kawabata, Takashi J. Moriya, Koji S. Kawabata, Nozomu Tominaga, Kengo Takagi, Fumiya Imazato, Tomoki Morokuma, Shigeyuki Sako, Ryou Ohsawa, Takashi Nagao, Ji An Jiang, Umut Burgaz, Kenta Taguchi, Makoto Uemura, Hiroshi Akitaya, Mahito SasadaKeisuke Isogai, Masaaki Otsuka, Hiroyuki Maehara

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12 Citations (Scopus)


We present optical and near-infrared observations of SN 2019ehk, which was initially reported as a Type Ib supernova (SN). We show that it evolved to a Ca-rich transient according to its spectral properties and evolution in late phases. However, it shows a few properties distinct from those of the canonical Ca-rich transients: a short-duration first peak in the light curve, high peak luminosity, and association with a star-forming environment. Indeed, some of these features are shared with iPTF14gqr and iPTF16hgs, which are candidates for a special class of core-collapse SNe: the so-called ultra-stripped envelope SNe, i.e., a relatively low-mass He (or C+O) star explosion in a binary as a precursor of short-period double neutron star (NS) binaries. The estimated ejecta mass (0.4Me) and explosion energy (1.7 × 1050 erg) are consistent with this scenario. The analysis of the first peak suggests the existence of dense circumstellar material in the vicinity of the progenitor, implying a CCSN origin. Based on this analysis, we suggest SN 2019ehk is another candidate for a low-mass He star explosion. It might create a double NS binary, but with a wide separation. These candidates for low-mass stripped envelope SNe, including ultra-stripped envelope SN candidates, seem to form a subpopulation among Ca-rich transients, associated with young population. We propose that the key to distinguishing this population is the early first peak in their light curves.

Original languageEnglish
Article number30
JournalAstrophysical Journal
Issue number1
Publication statusPublished - 2021 May 1


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