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ABSTRACT The observed diversity in Type Ia supernovae (SNe Ia) – the thermonuclear explosions of carbon–oxygen white dwarf stars used as cosmological standard candles – is currently met with a variety of explosion models and progenitor scenarios. To help improve our understanding of whether and how often different models contribute to the occurrence of SNe Ia and their assorted properties, we present a comprehensive analysis of seven nearby SNe Ia. We obtained one to two epochs of optical spectra with Gemini Observatory during the nebular phase (>200 d past peak) for each of these events, all of which had time series of photometry and spectroscopy at early times (the first ∼8 weeks after explosion). We use the combination of early- and late-time observations to assess the predictions of various models for the explosion (e.g. double-detonation, off-centre detonation, stellar collisions), progenitor star (e.g. ejecta mass, metallicity), and binary companion (e.g. another white dwarf or a non-degenerate star). Overall, we find general consistency in our observations with spherically symmetric models for SN Ia explosions, and with scenarios in which the binary companion is another degenerate star. We also present an in-depth analysis of SN 2017fzw, a member of the subgroup of SNe Ia which appear to be transitional between the subluminous ‘91bg-like’ events and normal SNe Ia, and for which nebular-phase spectra are rare.
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Signatures of progenitors of Type Ia supernovae
Thermonuclear Supernovae (SNe Ia) are one of the building blocks of modern cosmology and laboratories for the explosion physics of White Dwarf star/s (WD) in close binary systems. The second star may be aWD(double degenerate systems, DD), or a non-degenerated star (SD) with a main sequence star, red giant or a helium star as companion (Branch et al. 1995; Nomoto et al. 2003; Wang & Han 2012). Light curves and spectra of the explosion look similar because a ’stellar amnesia’ (H¨oflich et al. 2006). Basic nuclear physics determines the progenitor structure and the explosion physics, breaking the link between progenitor evolution, and the explosion, resulting in three main classes of explosion scenarios: a) dynamical merging of two WD and a heating on time scales of seconds (Webbink 1984; Isern et al. 2011), b) surface helium detonations on top of a WD which ignite the central C/O by a detonation wave traveling inwards (Nomoto 1982; Hoeflich & Khokhlov 1996; Kromer et al. 2010); c) compressional heating in an accreting WD approaching the Chandrasekar mass on time of up to 108 years which may originated from SD and DD systems (Whelan & Iben 1973; Piersanti et al. 2003). Simulations of the explosions depend on the inital conditions at the onset of the explosions, namely the mass and angular momentum of the WD(s). For all scenarios, diversity in SNe Ia must be expected because the WD originates from a range of Main Sequence masses (MMS < 8M ) and metallicities Z. Moreover, there is growing evidence that magnetic fields B may have to be added to the ’mix’. Only with recent advances in observations ranging from X-ray to radio, high precision spectroscopy, polarimetry and photometry and in the time-domain astronomy we obtain constraints for progenitor, on the explosion scenarios and links emerge between the progenitors and their environment with LCs and spectral signatures needed for high precision cosmology. It is too early to give final answers but we present our personal view. We will give some examples from the theory point of view and discuss future prospects with upcoming ground based, ELT, GMT and space based such as JWST, Euclide and WFIRST instruments.
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- Award ID(s):
- 1715133
- PAR ID:
- 10057612
- Date Published:
- Journal Name:
- Memorie della Società astronomica italiana
- Volume:
- 88
- ISSN:
- 0037-8720
- Page Range / eLocation ID:
- 302
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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