Li, W. and Wang, X. and Vinkó, J. and Mo, J. and Hosseinzadeh, G. and Sand, D. J. and Zhang, J. and Lin, H. and Zhang, T. and Wang, L. and Zhang, J. and Chen, Z. and Xiang, D. and Rui, L. and Huang, F. and Li, X. and Zhang, X. and Li, L. and Baron, E. and Derkacy, J. M. and Zhao, X. and Sai, H. and Zhang, K. and Wang, L. and Howell, D. A. and McCully, C. and Arcavi, I. and Valenti, S. and Hiramatsu, D. and Burke, J. and Rest, A. and Garnavich, P. and Tucker, B. E. and Narayan, G. and Shaya, E. and Margheim, S. and Zenteno, A. and Villar, A. and Dimitriadis, G. and Foley, R. J. and Pan, Y.-C. and Coulter, D. A. and Fox, O. D. and Jha, S. W. and Jones, D. O. and Kasen, D. N. and Kilpatrick, C. D. and Piro, A. L. and Riess, A. G. and Rojas-Bravo, C. and Shappee, B. J. and Holoien, T. W.-S. and Stanek, K. Z. and Drout, M. R. and Auchettl, K. and Kochanek, C. S. and Brown, J. S. and Bose, S. and Bersier, D. and Brimacombe, J. and Chen, P. and Dong, S. and Holmbo, S. and Muñoz, J. A. and Mutel, R. L. and Post, R. S. and Prieto, J. L. and Shields, J. and Tallon, D. and Thompson, T. A. and Vallely, P. J. and Villanueva, S., Jr. and Smartt, S. J. and Smith, K. W. and Chambers, K. C. and Flewelling, H. A. and Huber, M. E. and Magnier, E. A. and Waters, C. Z. and Schultz, A. S. B. and Bulger, J. and Lowe, T. B. and Willman, M. and Sárneczky, K. and Pál, A. and Wheeler, J. C. and Bódi, A. and Bognár, Zs. and Csák, B. and Cseh, B. and Csörnyei, G. and Hanyecz, O. and Ignácz, B. and Kalup, Cs. and Könyves-Tóth, R. and Kriskovics, L. and Ordasi, A. and Rajmon, I. and Sódor, A. and Szabó, R. and Szakáts, R. and Zsidi, G. and Milne, P. and Andrews, J. E. and Smith, N. and Bilinski, C. and Brown, P. J. and Nordin, J. and Williams, S. C. and Galbany, L. and Palmerio, J. and Hook, I. M. and Inserra, C. and Maguire, K. and Cartier, Régis and Razza, A. and Gutiérrez, C. P. and Hermes, J. J. and Reding, J. S. and Kaiser, B. C. and Tonry, J. L. and Heinze, A. N. and Denneau, L. and Weiland, H. and Stalder, B. and Barentsen, G. and Dotson, J. and Barclay, T. and Gully-Santiago, M. and Hedges, C. and Cody, A. M. and Howell, S. and Coughlin, J. and Van Cleve, J. E. and Cardoso, J. Vinícius de Miranda and Larson, K. A. and McCalmont-Everton, K. M. and Peterson, C. A. and Ross, S. E. and Reedy, L. H. and Osborne, D. and McGinn, C. and Kohnert, L. and Migliorini, L. and Wheaton, A. and Spencer, B. and Labonde, C. and Castillo, G. and Beerman, G. and Steward, K. and Hanley, M. and Larsen, R. and Gangopadhyay, R. and Kloetzel, R. and Weschler, T. and Nystrom, V. and Moffatt, J. and Redick, M. and Griest, K. and Packard, M. and Muszynski, M. and Kampmeier, J. and Bjella, R. and Flynn, S. and Elsaesser, B. (2019) Photometric and Spectroscopic Properties of Type Ia Supernova 2018oh with Early Excess Emission from the $Kepler$ 2 Observations. The Astrophysical Journal, 870 (1). ISSN 0004-637X
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Abstract
Supernova (SN) 2018oh (ASASSN-18bt) is the first spectroscopically-confirmed type Ia supernova (SN Ia) observed in the $Kepler$ field. The $Kepler$ data revealed an excess emission in its early light curve, allowing to place interesting constraints on its progenitor system (Dimitriadis et al. 2018, Shappee et al. 2018b). Here, we present extensive optical, ultraviolet, and near-infrared photometry, as well as dense sampling of optical spectra, for this object. SN 2018oh is relatively normal in its photometric evolution, with a rise time of 18.3$\pm$0.3 days and $\Delta$m$_{15}(B)=0.96\pm$0.03 mag, but it seems to have bluer $B - V$ colors. We construct the "uvoir" bolometric light curve having peak luminosity as 1.49$\times$10$^{43}$erg s$^{-1}$, from which we derive a nickel mass as 0.55$\pm$0.04M$_{\odot}$ by fitting radiation diffusion models powered by centrally located $^{56}$Ni. Note that the moment when nickel-powered luminosity starts to emerge is +3.85 days after the first light in the Kepler data, suggesting other origins of the early-time emission, e.g., mixing of $^{56}$Ni to outer layers of the ejecta or interaction between the ejecta and nearby circumstellar material or a non-degenerate companion star. The spectral evolution of SN 2018oh is similar to that of a normal SN Ia, but is characterized by prominent and persistent carbon absorption features. The C II features can be detected from the early phases to about 3 weeks after the maximum light, representing the latest detection of carbon ever recorded in a SN Ia. This indicates that a considerable amount of unburned carbon exists in the ejecta of SN 2018oh and may mix into deeper layers.