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Supernovae: Physics and Cosmology in the Next Decade

Periodic Report Summary 2 - SPCND (Supernovae: Physics and Cosmology in the Next Decade)

Exploding stars, known as supernovae, impact upon many areas in astrophysics. They are particularly well-known for their key role in cosmology, leading to the discovery of the accelerating universe. Surprisingly, the supernovae that we use for this purpose, type Ia supernovae, suffer from a poor physical understanding, which in turn can limit their cosmological use. The SPCND project aims to use major new astronomical surveys to improve our knowledge of supernova Ia astrophysics in order to make a new cosmological measurement, and explore the use of other types of supernovae in a cosmological setting. These new surveys explore supernova spectra, and observe supernovae at wavelengths not before studied for large sample.

It is well known that type Ia supernovae are the thermonuclear explosions of white dwarf stars, and very likely live in binary systems (two stars orbiting each other in space). But a key question is whether type Ia supernovae originate from systems with two white dwarfs, or a white dwarf and a normal star. SPCND is addressing this question using new data from the Public ESO Spectroscopic Survey of Transient Objects (PESSTO), and its newly-approved follow-on Large Programme, extended-PESSTO (e-PESSTO). These are major time allocations on Europe's best telescopes.

SPCND is using data to examine the amount of material that surrounds the white dwarfs prior to explosion. This material, known as circumstellar material, can provide constraints on the nature and configuration of the star system that blew up. For example, the detection of hydrogen in such data would be indicative of the presence of a normal star as the companion to the white dwarf, as most normal stars are made of hydrogen. Our new data show that such systems do exist, and provide new constraints on their frequency. We are also using data to examine the core of the supernova explosion, in order to see the types of elements synthesised in the thermonuclear explosion. This provides new constraints for models that attempt to explain their origin.

SPCND has also driven the creation of the VISTA Extragalactic Infrared Legacy Survey (VEILS), a major new European Southern Observatory public survey using the VISTA telescope. This is observing distant type Ia supernovae at infrared wavelengths, which are less susceptible to dust than traditional optical measures. This will allow the project to make a new measurement of dark energy almost unaffected by dust extinction, the first measurement of its kind. This project will also use data from the highly successful Dark Energy Survey.

SPCND is also leading research on superluminous supernovae, a new type of supernova explosion some 50 times brighter than type Ia supernovae. Using data from DES, we have assembled the largest dataset of distant superlumiunous supernovae, and are using these data to investigate the physics of superluminous supernovae, and their use as cosmological standard candles (like type Ia supernovae). Their extreme brightness will allow them to be seen to much larger distances than type Ia supernovae, and thus opens up a new epoch of the universe's expansion history to study and measurement. We are also learning more about the nature of these enigmatic superluminous events: we have studied their early evolution to constrain the nature of the environments in which they explode.