Observational properties of thermonuclear supernovae

The explosive death of a star as a supernova is one of the most dramatic events in the Universe. Supernovae have an outsized impact on many areas of astrophysics: they are major contributors to the chemical enrichment of the cosmos and significantly influence the formation of subsequent generations of stars and the evolution of galaxies. Here we review the observational properties of thermonuclear supernovaeexploding white dwarf stars resulting from the stellar evolution of lowmass stars in close binary systems. The best known objects in this class are typeIa supernovae (SNe Ia), astrophysically important in their application as standardizable candles to measure cosmological distances and the primary source of iron group elements in the Universe. Surprisingly, given their prominent role, SN Ia progenitor systems and explosion mechanisms are not fully understood; the observations we describe here provide constraints on models, not always in consistent ways. Recent advances in supernova discovery and followup have shown that the class of thermonuclear supernovae includes more than just SNe Ia, and we characterize that diversity in this review.