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The Peculiar Ca-rich SN2019ehk: Evidence for a Type IIb Core-collapse Supernova from a Low-mass Stripped Progenitor

De, Kishalay and Fremling, U. Christoffer and Gal-Yam, Avishay and Yaron, Ofer and Kasliwal, Mansi M. and Kulkarni, S. R. (2021) The Peculiar Ca-rich SN2019ehk: Evidence for a Type IIb Core-collapse Supernova from a Low-mass Stripped Progenitor. Astrophysical Journal Letters, 907 (1). Art. No. L18. ISSN 2041-8213. doi:10.3847/2041-8213/abd627.

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The nature of the peculiar "Ca-rich" SN 2019ehk in the nearby galaxy M100 remains unclear. Its origin has been debated as either a stripped core-collapse supernova or a thermonuclear helium detonation event. Here, we present very late-time photometry of the transient obtained with the Keck I telescope at ≈280 days from peak light. Using the photometry to perform accurate flux calibration of a contemporaneous nebular phase spectrum, we measure an [O I] luminosity of (0.19–1.08) × 10³⁸ erg s⁻¹ and [Ca II] luminosity of (2.7–15.6) × 10³⁸ erg s⁻¹ over the range of the uncertain extinction along the line of sight and distance to the host galaxy. We use these measurements to derive lower limits on the synthesized oxygen mass of ≈0.004–0.069 M_⊙. The oxygen mass is a sensitive tracer of the progenitor mass for core-collapse supernovae, and our estimate is consistent with explosions of very low-mass CO cores of 1.45–1.5 M_⊙, corresponding to He core masses of ≈1.8–2.0 M_⊙. We present high-quality peak light optical spectra of the transient and highlight features of hydrogen in both the early ("flash") and photospheric phase spectra that suggest the presence of ≳0.02 M_⊙ of hydrogen in the progenitor at the time of explosion. The presence of H, together with the large [Ca II]/[O I] ratio (≈10–15) in the nebular phase, is consistent with SN 2019ehk being a Type IIb core-collapse supernova from a stripped low-mass (≈9–9.5 M_⊙) progenitor, similar to the Ca-rich SN IIb iPTF 15eqv. These results provide evidence for a likely class of "Ca-rich" core-collapse supernovae from stripped low-mass progenitors in star-forming environments, distinct from the thermonuclear Ca-rich gap transients in old environments.

Item Type:Article
Related URLs:
URLURL TypeDescription Paper
De, Kishalay0000-0002-8989-0542
Fremling, U. Christoffer0000-0002-4223-103X
Gal-Yam, Avishay0000-0002-3653-5598
Yaron, Ofer0000-0002-0301-8017
Kasliwal, Mansi M.0000-0002-5619-4938
Kulkarni, S. R.0000-0001-5390-8563
Alternate Title:The Peculiar Ca-rich SN 2019ehk: Evidence for a Type IIb Core-collapse Supernova from a Low-mass Stripped Progenitor
Additional Information:© 2021 The American Astronomical Society. Received 2020 August 31; revised 2020 December 20; accepted 2020 December 22; published 2021 January 21. We thank S. Hachinger for providing the model spectral sequences used in this work. We thank the anonymous referee for a careful reading of the manuscript that significantly improved the quality of the paper. We thank W. Jacobson-Galan for providing the spectral sequence of SN 2019ehk. We thank J. Sollerman and C. Fransson for constructive comments on this manuscript. We thank L. Bildsten and A. Polin for valuable discussions. We thank D. Perley for assistance with lpipe. M.M.K. acknowledges generous support from the David and Lucille Packard Foundation. This work was supported by the GROWTH (Global Relay of Observatories Watching Transients Happen) project funded by the National Science Foundation under PIRE grant No. 1545949. Some of the data presented herein were obtained at the W.M. Keck Observatory, which is operated as a scientific partnership among the California Institute of Technology, the University of California and the National Aeronautics and Space Administration. The Observatory was made possible by the generous financial support of the W.M. Keck Foundation. The authors wish to recognize and acknowledge the very significant cultural role and reverence that the summit of Maunakea has always had within the indigenous Hawaiian community. We are most fortunate to have the opportunity to conduct observations from this mountain. A.G.Y.'s research is supported by the EU via ERC grant No. 725161, the ISF GW excellence center, an IMOS space infrastructure grant and BSF/Transformative and GIF grants, as well as The Benoziyo Endowment Fund for the Advancement of Science, the Deloro Institute for Advanced Research in Space and Optics, The Veronika A. Rabl Physics Discretionary Fund, Paul and Tina Gardner, Yeda-Sela and the WIS-CIT joint research grant; A.G.Y. is the recipient of the Helen and Martin Kimmel Award for Innovative Investigation.
Group:Astronomy Department
Funding AgencyGrant Number
David and Lucile Packard FoundationUNSPECIFIED
W. M. Keck FoundationUNSPECIFIED
European Research Council (ERC)725161
Israel Science FoundationUNSPECIFIED
Ministry of Science (Israel)UNSPECIFIED
Binational Science Foundation (USA-Israel)UNSPECIFIED
German-Israeli Foundation for Research and DevelopmentUNSPECIFIED
Benoziyo Endowment Fund for the Advancement of ScienceUNSPECIFIED
Deloro Institute for Advanced Research in Space and OpticsUNSPECIFIED
Veronika A. Rabl Physics Discretionary FundUNSPECIFIED
Paul and Tina GardnerUNSPECIFIED
Weizmann Institute of ScienceUNSPECIFIED
Helen and Martin Kimmel AwardUNSPECIFIED
Subject Keywords:Core-collapse supernovae ; Oxygen burning ; Nucleosynthesis ; Massive stars
Issue or Number:1
Classification Code:Unified Astronomy Thesaurus concepts: Core-collapse supernovae (304); Oxygen burning (1193); Nucleosynthesis (1131); Massive stars (732)
Record Number:CaltechAUTHORS:20200916-112851135
Persistent URL:
Official Citation:Kishalay De et al 2021 ApJL 907 L18
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:105412
Deposited By: George Porter
Deposited On:21 Sep 2020 20:45
Last Modified:16 Nov 2021 18:42

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