Article open access publication

Evidence for a Chandrasekhar-mass explosion in the Ca-strong 1991bg-like type Ia supernova 2016hnk

Astronomy & Astrophysics, EDP Sciences, ISSN 0004-6361

Volume 630, 2019

DOI:10.1051/0004-6361/201935537, Dimensions: pub.1120558244,



  1. (1) University of Granada, grid.4489.1
  2. (2) University of Pittsburgh, grid.21925.3d
  3. (3) Florida State University, grid.255986.5
  4. (4) University of Lisbon, grid.9983.b
  5. (5) European Southern Observatory, grid.424907.c
  6. (6) Max Planck Institute for Astrophysics, grid.452596.9
  7. (7) Aarhus University, grid.7048.b, AU
  8. (8) Liverpool John Moores University, grid.4425.7
  9. (9) University of Oklahoma, grid.266900.b
  10. (10) Laboratoire d’Astrophysique de Marseille, grid.463707.1
  11. (11) University of Chile, grid.443909.3
  12. (12) Peking University, grid.11135.37
  13. (13) Stockholm University, grid.10548.38
  14. (14) Las Cumbres Observatory Global Telescope Network, grid.436159.c
  15. (15) University of California, Santa Barbara, grid.133342.4
  16. (16) Carnegie Observatories, grid.432988.c
  17. (17) Cerro Tololo Inter-American Observatory, grid.440541.0
  18. (18) Capodimonte Observatory, INAF-Naples, Salita Moiariello 16, 80131 Naples, Italy
  19. (19) Astrophysics Science Division, grid.468494.3
  20. (20) University of Southampton, grid.5491.9
  21. (21) University of Turku, grid.1374.1
  22. (22) Harvard-Smithsonian Center for Astrohysics, 60 Garden Street, Cambridge, MA 02138, USA
  23. (23) University of California, San Diego, grid.266100.3
  24. (24) Cardiff University, grid.5600.3
  25. (25) University of California, Berkeley, grid.47840.3f
  26. (26) Rutgers, The State University of New Jersey, grid.430387.b
  27. (27) Space Telescope Science Institute, grid.419446.a
  28. (28) Heidelberg Institute for Theoretical Studies, grid.424699.4
  29. (29) Heidelberg University, grid.7700.0
  30. (30) University of Warwick, grid.7372.1
  31. (31) Trinity College Dublin, grid.8217.c
  32. (32) Queen's University Belfast, grid.4777.3
  33. (33) The University of Texas at Austin, grid.89336.37
  34. (34) Purdue University West Lafayette, grid.169077.e
  35. (35) European Southern Observatory, grid.440369.c
  36. (36) University of Arizona, grid.134563.6
  37. (37) University of Hawaii at Manoa, grid.410445.0
  38. (38) Department of Physics, BITS Pilani K.K. Birla Goa Campus, India
  39. (39) Vanderbilt University, grid.152326.1
  40. (40) University of California, Davis, grid.27860.3b
  41. (41) Massachusetts Institute of Technology, grid.116068.8
  42. (42) Tsinghua University, grid.12527.33
  43. (43) Chinese Academy of Sciences, grid.9227.e
  44. (44) Yunnan Observatories, grid.458483.6


Aims . We present a comprehensive dataset of optical and near-infrared photometry and spectroscopy of type Ia supernova (SN) 2016hnk, combined with integral field spectroscopy (IFS) of its host galaxy, MCG -01-06-070, and nearby environment. Our goal with this complete dataset is to understand the nature of this peculiar object. Methods . Properties of the SN local environment are characterized by means of single stellar population synthesis applied to IFS observations taken two years after the SN exploded. We performed detailed analyses of SN photometric data by studying its peculiar light and color curves. SN 2016hnk spectra were compared to other 1991bg-like SNe Ia, 2002es-like SNe Ia, and Ca-rich transients. In addition, we used abundance stratification modeling to identify the various spectral features in the early phase spectral sequence and also compared the dataset to a modified non-LTE model previously produced for the sublumnious SN 1999by. Results . SN 2016hnk is consistent with being a subluminous ( M B = −16.7 mag, s B V =0.43 ± 0.03), highly reddened object. The IFS of its host galaxy reveals both a significant amount of dust at the SN location, residual star formation, and a high proportion of old stellar populations in the local environment compared to other locations in the galaxy, which favors an old progenitor for SN 2016hnk. Inspection of a nebular spectrum obtained one year after maximum contains two narrow emission lines attributed to the forbidden [Ca  II ] λ λ 7291,7324 doublet with a Doppler shift of 700 km s −1 . Based on various observational diagnostics, we argue that the progenitor of SN 2016hnk was likely a near Chandrasekhar-mass ( M Ch ) carbon-oxygen white dwarf that produced 0.108 M ⊙ of 56 Ni. Our modeling suggests that the narrow [Ca  II ] features observed in the nebular spectrum are associated with 48 Ca from electron capture during the explosion, which is expected to occur only in white dwarfs that explode near or at the M Ch limit.


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