SN 2016dsg: A Thermonuclear Explosion Involving a Thick Helium Shell

Creators: Dong, Yize; Valenti, Stefano; Polin, Abigail; Boyle, Aoife; Flörs, Andreas; Vogl, Christian; Kerzendorf, Wolfgang E.; Sand, David J.; Jha, Saurabh W.; Wyrzykowski, Łukasz; Bostroem, K. Azalee; Pearson, Jeniveve; McCully, Curtis; Andrews, Jennifer E.; Benetti, Stefano; Blondin, Stéphane; Galbany, L.; Gromadzki, Mariusz; Hosseinzadeh, Griffin; Howell, D. Andrew; Inserra, Cosimo; Jencson, Jacob E.; Lundquist, Michael; Lyman, J. D.; Magee, Mark; Maguire, Kate; Meza, Nicolas; Srivastav, Shubham; Taubenberger, Stefan; Terwel, J. H.; Wyatt, Samuel; Young, D. R.

Abstract

A thermonuclear explosion triggered by a He-shell detonation on a carbon–oxygen white-dwarf core has been predicted to have strong UV line blanketing at early times due to the iron-group elements produced during He-shell burning. We present the photometric and spectroscopic observations of SN 2016dsg, a subluminous peculiar Type I supernova consistent with a thermonuclear explosion involving a thick He shell. With a redshift of 0.04, the i-band peak absolute magnitude is derived to be around −17.5. The object is located far away from its host, an early-type galaxy, suggesting it originated from an old stellar population. The spectra collected after the peak are unusually red, show strong UV line blanketing and weak O i λ7773 absorption lines, and do not evolve significantly over 30 days. An absorption line around 9700–10500 Å is detected in the near-infrared spectrum and is likely from the unburnt He in the ejecta. The spectroscopic evolution is consistent with the thermonuclear explosion models for a sub-Chandrasekhar-mass white dwarf with a thick He shell, while the photometric evolution is not well described by existing models.

Additional Information

© 2022. The Author(s). Published by the American Astronomical Society. Original content from this work may be used under the terms of the Creative Commons Attribution 4.0 licence. Any further distribution of this work must maintain attribution to the author(s) and the title of the work, journal citation and DOI. Received 2022 March 22; revised 2022 May 16; accepted 2022 May 31; published 2022 July 28. Based on observations collected at the European Organisation for Astronomical Research in the Southern Hemisphere under ESO program 1103.D-0328. This research made use of tardis, a community-developed software package for spectral synthesis in supernovae (Kerzendorf & Sim 2014; Kerzendorf et al. 2022). The development of tardis received support from GitHub, the Google Summer of Code initiative, and from ESA's Summer of Code in Space program. tardis is a fiscally sponsored project of NumFOCUS. tardis makes extensive use of Astropy and Pyne. This work made use of the Heidelberg Supernova Model Archive (HESMA, https://hesma.h-its.org). This research has made use of the NASA/IPAC Extragalactic Database (NED), which is operated by the Jet Propulsion Laboratory, California Institute of Technology, under contract with the National Aeronautics and Space Administration. Research by Y.D., S.V., and N.M.R is supported by NSF grants AST1813176 and AST-2008108. Time domain research by D.J.S. is also supported by NSF grants AST-1821987, 1813466, 1908972, and 2108032, and by the Heising-Simons Foundation under grant #2020-1864. The SALT observations presented here were taken as part of Rutgers University program 2015-1-MLT-002 (PI: Jha). This work makes use of observations from the Las Cumbres Observatory network. The Las Cumbres Observatory team is supported by NSF grants AST-1911225 and AST-1911151, and NASA Swift grant 80NSSC19K1639. L.W. and M.G. acknowledge the Polish National Science Centre (NCN) grants Harmonia No. 2018/30/M/ST9/00311 and Daina No. 2017/27/L/ST9/03221 as well as the European Union's Horizon 2020 research and innovation program under grant agreement No. 101004719 (OPTICON-RadioNet Pilot, ORP) and MNiSW grant DIR/WK/2018/12. M.G. is supported by the EU Horizon 2020 research and innovation program under grant agreement No. 101004719. L.G. acknowledges financial support from the Spanish Ministerio de Ciencia e Innovación (MCIN), the Agencia Estatal de Investigación (AEI) 10.13039/501100011033, and the European Social Fund (ESF) "Investing in your future" under the 2019 Ramón y Cajal program RYC2019-027683-I and the PID2020-115253GA-I00 HOSTFLOWS project, from Centro Superior de Investigaciones Científicas (CSIC) under the PIE project 20215AT016, and the program Unidad de Excelencia María de Maeztu CEX2020-001058-M. J.D.L. acknowledges support from a UK Research and Innovation Fellowship (MR/T020784/1). This work was supported by the "Programme National de Physique Stellaire" (PNPS) of CNRS/INSU cofunded by CEA and CNES. This research was supported by the Excellence Cluster ORIGINS, which is funded by the Deutsche Forschungsgemeinschaft (DFG, German Research Foundation) under Germany's Excellence Strategy EXC-2094-390783311. S.B. acknowledges support from the ESO Scientific Visitor Programme in Garching. K.M. is funded by the EU H2020 ERC grant No. 758638. Facilities: Las Cumbres Observatory (Sinistro) - , SAAO:SALT (RSS) - , The New Technology Telescope (EFOSC2 - , SofI). - Software: Astropy (Astropy Collaboration et al. 2013, 2018), HOTPANTS (Becker 2015), lcogtsnpipe (Valenti et al. 2016), Matplotlib (Hunter 2007), NumPy (https://numpy.org), PYRAF, Pandas (McKinney 2010), SciPy (https://www.scipy.org), TARDIS (Kerzendorf & Sim 2014; Kerzendorf et al. 2022).

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