Comparative analysis of SN 2012dn optical spectra: days −14 to +114

MNRAS 457, 3702–3723 (2016) doi:10.1093/mnras/stw239 Advance Access publication 2016 January 29 Comparative analysis of SN 2012dn optical spectra: days −14 to +114 J. T. Parrent, 1,2,3‹ D. A. Howell, 2,4‹ R. A. Fesen, 3 S. Parker, 5 F. B. Bianco, 6 B. Dilday, 7 D. Sand, 8 S. Valenti, 2,3 J. Vink´o, 9,10 P. Berlind, 11 P. Challis, 1 D. Milisavljevic, 1 N. Sanders, 1 G. H. Marion, 10 J. C. Wheeler, 10 P. Brown, 12 M. L. Calkins, 6 B. Friesen, 13 R. Kirshner, 1 T. Pritchard, 14 R. Quimby 15,16 and P. Roming 14,17 1 Harvard–Smithsonian Center for Astrophysics, 60 Garden St, Cambridge, MA 02138, USA Cumbres Observatory Global Telescope Network, Goleta, CA 93117, USA 3 6127 Wilder Lab, Department of Physics and Astronomy, Dartmouth College, Hanover, NH 03755, USA 4 Department of Physics, U.C. Santa Barbara, Santa Barbara, CA 93117, USA 5 Backyard Observatory Supernova Search, Parkdale Observatory, Canterbury 7495, New Zealand 6 Center for Cosmology and Particle Physics, New York University, 4 Washington Place, New York, NY 10003, USA 7 Gravity Jack, 23505 E Appleway Ave #200, Liberty Lake, WA 99019, USA 8 Physics Department, Texas Tech University, Lubbock, TX 79409, USA 9 Department of Optics and Quantum Electronics, University of Szeged, D´ om t´er 9, 6720 Szeged, Hungary 10 Department of Astronomy, University of Texas, Austin, TX 78712, USA 11 F. L. Whipple Observatory, 670 Mt Hopkins Road, PO Box 97, Amado, AZ 85645, USA 12 Department of Physics and Astronomy, George P. and Cynthia Woods Mitchell Institute for Fundamental Physics and Astronomy, Texas A. & M. University, 4242 TAMU, College Station, TX 77843, USA 13 Homer L. Dodge Department of Physics and Astronomy, University of Oklahoma, 440 W Brooks, Norman, OK 73019, USA 14 Department of Astronomy and Astrophysics, Penn State University, 525 Davey Lab, University Park, PA 16802, USA 15 Department of Astronomy, San Diego State University, 5500 Campanile Drive, San Diego, CA 92182-1221, USA 16 Kavli IPMU (WPI), UTIAS, The University of Tokyo, Kashiwa, Chiba 277-8583, Japan 17 Southwest Research Institute, Department of Space Science, 6220 Culebra Road, San Antonio, TX 78238, USA 2 Las Accepted 2016 January 27. Received 2016 January 27; in original form 2015 May 31 ABSTRACT SN 2012dn is a super-Chandrasekhar mass candidate in a purportedly normal spiral (SAcd) galaxy, and poses a challenge for theories of type Ia supernova diversity. Here we utilize the fast and highly parametrized spectrum synthesis tool, SYNAPPS, to estimate relative expansion velocities of species inferred from optical spectra obtained with six facilities. As with previous studies of normal SN Ia, we find that both unburned carbon and intermediate-mass elements are spatially coincident within the ejecta near and below 14 000 km s −1 . Although the upper limit on SN 2012dn’s peak luminosity is comparable to some of the most luminous normal SN Ia, we find a progenitor mass exceeding ∼1.6 M is not strongly favoured by leading merger models since these models do not accurately predict spectroscopic observations of SN 2012dn and more normal events. In addition, a comparison of light curves and host-galaxy masses for a sample of literature and Palomar Transient Factory SN Ia reveals a diverse distribution of SN Ia subtypes where carbon-rich material remains unburned in some instances. Such events include SN 1991T, 1997br, and 1999aa where trace signatures of C III at optical wavelengths are presumably detected. Key words: supernovae: general – supernovae: individual: SN 2012dn. 1 I N T RO D U C T I O N E-mail: jparrent@cfa.harvard. edu (JTP); ahowell@lcogt.net (DAH) The progenitor systems of type Ia supernovae (SN Ia) have not been observed, although it is widely believed that some SN Ia are the product of a thermonuclear runaway in a white dwarf (WD) star with a mass near the Chandrasekhar limit, M Ch ≈ 1.38 M (Nugent et al. C 2016 The Authors Published by Oxford University Press on behalf of the Royal Astronomical Society