Where Are the Stars of Yesteryear?: A Reflection on Astrophysical Transience

Abstract

This thesis concerns a number of kinds of astrophysical transients, including interacting supernovae (SNe), gap transients and tidal-disruption events. There are three papers included and they address differing phenomena, each of which has implications for stellar evolution more broadly.

The first paper is a detailed study of the long-lived slowly evolving type IIn SN, SN 2017hcc. The paper covers a five-year follow-up campaign, with extensive optical and near-infrared imaging and spectroscopy. The object was very bright, peaking at −20.78 ± 0.01 mag in ATLAS band after an eight-week rise, suggesting significant interaction between the ejecta and circumstellar material. The paper also covers evidence for pre-existing dust as well as new dust formation. The second paper is a study of the intermediate-luminosity red transient (ILRT), AT 2022fnm. This ILRT displayed certain features consistent with luminous red novae (LRNe) and the overlapping observational features of ILRTs and LRNe are discussed. The third paper concerns the fast-evolving transient SN 2017fwm/Gaia17byh. This object had an extremely fast rise time (≲5 days) as well as a small ejecta mass (0.01 M⊙). One particularly interesting feature of this object is that it displayed a peculiar velocity of approximately −5000 km/s. A number of origin scenarios for SN 2017fwm are explored in the paper, including its being an ultrastripped SN and its resulting from the tidal disruption of a white dwarf.

Additionally, upcoming astronomical surveys are discussed as well as the future of astronomical modelling and multi-messenger astronomy.