Investigations of the mysterious supernovae class: type IIn
Supervisors: Dr Stacey Habergham & Prof. Phil James
The final stage of a high mass (> 8 solar masses) star's lifetime is an explosion known as a core-collapse supernova (CCSN). These explosions are amongst the most energetic in the Universe and can be seen in distant galaxies due to their exceptional luminosities, which can last weeks to months. CCSNe are sub-classified into various types based upon their photometric and spectroscopic features, and comprise at least six different groups. Many questions remain unanswered about the progenitors of these explosions in terms of the differences in mass, metallicity and binarity which may contribute to the different types of explosions we observe.
One of the least understood of the sub-classifications is the type IIn, which in some cases can remain bright for years. The distinctive characteristics about this type is that the spectrum shows both hydrogen and helium, suggesting that the star held on to its outer envelope prior to explosion. It also shows narrow emission features in the spectrum which indicate that the star was surrounded by dense material, but the source of this is a mystery.
Although the class is rare, it is also one of the most researched, and the more events are detected and analysed, the less the class make sense. The class seems linked to so-called supernova 'impostors', explosions more energetic than novae, but not as bright as supernovae. These explosions are thought to be non-terminal explosions of ultra-massive stars, so could they be the progenitors of SNIIn? If so how does such a massive star maintain its hydrogen envelope right until its final demise?
This PhD project will try to answer some of these questions, and many more, by first analysing some spectra of the host environments of a sample of SNIIn, obtained from the 4.2 metre William Herschel Telescope in 2014, which will amount to the largest local environment spectroscopic analysis of SNe IIn published to date. This can be combined with photometric analysis of the environments of these supernovae in order to explore whether this is in fact a distinct group, or whether the environments of these events can help to distinguish between the intrinsic characteristics of the progenitors.
Whilst there is already data in hand to begin analysing, it is expected that this PhD will involve applying for more telescope time and hopefully going on an observing run, along with leading follow-up of new explosions with the Liverpool Telescope.
This project will be supervised by Dr Stacey Habergham and Prof. Phil James, however, collaboration with the ARI supernova group, including Dr David Bersier and Prof. Paolo Mazzali will be encouraged.