Brown Dwarf Companions and Background Subtraction in The Next Generation Transit Survey

Brown dwarfs are the bridge between low mass stars and giant exoplanets. Studying them provides a vast amount of information, some of which is transferable to giant exoplanets. However, their low temperatures mean they are difficult to observe with many telescopes. Chapter 1 reviews the current understanding about brown dwarfs, their characteristics and their variability. It also reviews the current understanding of the so-called ‘brown dwarf desert’ which arises due to a lack of brown dwarf companions to main sequence stars, orbiting within 3 AU. I introduce the Next Generation Transit Survey and its capabilities for studying these intriguing objects. In Chapter 2, I discuss the methods I used to discover and characterise NGTS-28Ab and TOI-2490b, two new transiting brown dwarfs within the brown dwarf desert. NGTS-28Ab and TOI-2490b, their host stars and their position in the brown dwarf desert, are discussed in Chapters 3 and 4 respectively. Chapter 5 discusses the current pipeline for NGTS and particularly, the current background subtraction and how it may be improved. Nebuliser is introduced, along with its capabilities and previous uses. Chapter 6 details the analysis I performed to test whether including Nebuliser as an extra step in the background subtraction improves the precision of the fainter objects within each field. Finally, Chapter 7 summarises this thesis and discusses any future work/observations which could be performed/taken.