Cartier, R, Sullivan, M, Firth, R, Pignata, G, Mazzali, PA, Maguire, K, Childress, MJ, Arcavi, I, Ashall, C, Bassett, B, Crawford, SM, Frohmaier, C, Galbany, L, Gal-Yam, A, Hosseinzadeh, G, Howell, DA, Inserra, C, Johansson, J, Kasai, EK, McCully, C et al, Prajs, S, Prentice, SJ, Schulze, S, Smartt, SJ, Smith, KW, Smith, M, Valenti, S and Young, DR (2017) Early observations of the nearby type Ia supernova SN 2015F. Monthly Notices of the Royal Astronomical Society, 464 (4). pp. 4476-4494. ISSN 0035-8711

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Abstract

We present photometry and time-series spectroscopy of the nearby type Ia supernova (SN Ia) SN 2015F over $-16$ days to $+80$ days relative to maximum light, obtained as part of the Public ESO Spectroscopic Survey of Transient Objects (PESSTO). SN 2015F is a slightly sub-luminous SN Ia with a decline rate of $\Delta m15(B)=1.35 \pm 0.03$ mag, placing it in the region between normal and SN 1991bg-like events. Our densely-sampled photometric data place tight constraints on the epoch of first light and form of the early-time light curve. The spectra exhibit photospheric C II $\lambda 6580$ absorption until $-4$ days, and high-velocity Ca II is particularly strong at $<-10$ days at expansion velocities of $\simeq$23000\kms. At early times, our spectral modelling with syn++ shows strong evidence for iron-peak elements (Fe II, Cr II, Ti II, and V II) expanding at velocities $>14000$ km s$^{-1}$, suggesting mixing in the outermost layers of the SN ejecta. Although unusual in SN Ia spectra, including V II in the modelling significantly improves the spectral fits. Intriguingly, we detect an absorption feature at $\sim$6800 \AA\ that persists until maximum light. Our favoured explanation for this line is photospheric Al II, which has never been claimed before in SNe Ia, although detached high-velocity C II material could also be responsible. In both cases the absorbing material seems to be confined to a relatively narrow region in velocity space. The nucleosynthesis of detectable amounts of Al II would argue against a low-metallicity white dwarf progenitor. We also show that this 6800 \AA\ feature is weakly present in other normal SN Ia events, and common in the SN 1991bg-like sub-class.

Item Type:	Article
Additional Information:	This article has been accepted for publication in Monthly Notices of the Royal Astronomical Society ©: 2016 The Authors Published by Oxford University Press on behalf of the Royal Astronomical Society. All rights reserved.
Uncontrolled Keywords:	astro-ph.SR; astro-ph.SR; astro-ph.CO
Subjects:	Q Science > QB Astronomy Q Science > QC Physics
Divisions:	Astrophysics Research Institute
Publisher:	Oxford University Press
Related URLs:	http://arxiv.org/abs/1609.04465v2
Date Deposited:	16 Dec 2016 09:12
Last Modified:	20 Apr 2022 08:34
DOI or ID number:	10.1093/mnras/stw2678
URI:	https://researchonline.ljmu.ac.uk/id/eprint/5105

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