Optical Spectra of Supernovae

Abstract

The temporal evolution of the optical spectra of various types of supernovae (SNe) is illustrated, in part to aid observers classifying supernova candidates. Type II SNe are defined by the presence of hydrogen, and they exhibit a very wide variety of photometric and spectroscopic properties. Among hydrogen-deficient SNe (Type I), three subclasses are now known: those whose early-time spectra show strong Si II (Ia), prominent He I (Ib), or neither Si II nor He I (Ic). The late-time spectra of SNe Ia consist of a multitude of blended emission lines of iron-group elements; in sharp contrast, those of SNe Ib and SNe Ic (which are similar to each other) are dominated by several relatively unblended lines of intermediatemass elements. Although SNe Ia, which result from the thermonuclear runaway of white dwarfs, constitute a rather homogeneous subclass, important variations in their photometric and spectroscopic properties are undeniably present. SNe Ib/Ic probably result from core collapse in massive stars largely stripped of their hydrogen (Ib) and helium (Ic) envelopes, and hence they are physically related to SNe II. Indeed, the progenitors of some SNe II seem to have only a low-mass skin of hydrogen; their spectra gradually evolve to resemble those of SNe Ib. In addition to the two well-known photometric subclasses (linear and plateau) of SNe II, which may exhibit minor spectroscopic differences, there is a new subclass (SNe IIn) distinguished by relatively narrow emission lines with little or no P Cygni absorption component and slowly declining light curves. These objects probably have unusually dense circumstellar gas with which the ejecta interact.

Observational probes of cosmic acceleration

“…Type Ia supernovae, defined observationally by the absence of hydrogen and presence of SiII in their early-time spectra (Filippenko, 1997), are thought to arise from thermonuclear explosions of white dwarfs, though the evolutionary sequence or sequences that lead to these explosions remains poorly understood. The two broad classes of progenitor models are "single degenerate," in which a white dwarf accreting from a binary companion is pushed over the Chandrasekhar mass limit, and "double degenerate," in which gravitational radiation causes an orbiting pair of white dwarfs to merge and exceed the Chandrasekhar mass.…”

Type Ia Supernovae Strongly Interacting with Their Circumstellar Medium

“…LOSS also showed that SNe IIP/IIL have an overlapping range of peak absolute magnitudes (−17 mag M R −15 mag; Smith et al 2011b), but the spectra of SNe IIP/IIL differ significantly from those of SNe IIn or SNe Ia-CSM (the former consisting of broad P-Cygni profiles of H Balmer lines; e.g., Filippenko 1997). On the less luminous end, luminous blue variable star (LBV) outbursts and the so-called SN impostors (which are spectroscopically similar to SNe IIn and SNe Ia-CSM) have peak absolute magnitudes −16 mag M R (Smith et al 2011b).…”

“…These "hybrid" objects resemble Type IIn SNe (SNe IIn) and have been dubbed SNe Ia/IIn, Ian, IIa, and IIan. Under the standard SN classification scheme (e.g., Filippenko 1997), any SN with hydrogen features in its optical spectrum is considered an SN II and the subset of these showing relatively narrow emission lines are referred to as SNe IIn. Objects with relatively narrow hydrogen emission lines that are further linked (spectroscopically) to SNe Ia could be denoted "Type IIna," though this moniker is somewhat cumbersome and obfuscating.…”

Optical Light Curves of Supernovae

“…Light curves are discussed in [37,51,56,80,81]. Reviews concentrating more specifically on SNIa light curves can be found in [57,58,73,107], while the light curves of core-collapse supernovae have mostly been summarized in relation to SN1987A [4,72].…”