People powered planet hunting with TESS

To date, over 5000 exoplanets have been confirmed, and studies of their characteris- tics have unveiled an extremely wide range of masses, sizes, system architectures, and orbital periods. More than two-thirds of these known planets were identified using dedicated planet detection algorithms that search for transit events in data obtained by space-based survey satellites, such as the Transiting Exoplanet Survey Satellite (TESS). These automated transit detection algorithms are, however, strongly biased towards the detection of short-period planets. For example, 90% of the pipeline- detected TESS planet candidates known to date have orbital periods shorter than 27 days. In this thesis, I show that we can address this period bias by visually inspecting TESS data with the help of a global community of over 30 000 volunteers.
I present the Planet Hunters TESS (PHT) citizen science project that I designed, built, and continue to manage. Throughout this thesis I demonstrate that with visual vetting we are sensitive to detecting both short- and longer-period planets. This makes PHT an effective tool to help populate under-explored regions of parameter space that have limited prospects for being studied by automated searches that typically require a minimum of two transit events for detection. To that end, the PHT planet sample can benefit studies of planet occurrence rates, as well as inform theories of physical processes involved with the formation and evolution of different types of exoplanets. I also present LATTE; a new open-source vetting suite that includes numerous diagnostic tests to aid in the detection and characterisation of planetary and stellar signals. The tool, which is regularly used by both professional astronomers and citizen scientists, forms part of the PHT pipeline and helps identify promising candidates for ground-based follow-up.
The large-scale visual vetting with PHT, combined with the LATTE vetting suite, has led to the discovery of 139 new planet candidates in the two-minute cadence data from the first three years of TESS data alone. In addition to discussing this ensemble sample of new planet candidates, I present a detailed analysis of two of these systems. First, I discuss a Saturn-sized planet orbiting around a bright subgiant on an ~84-day orbit. The planet’s relatively long orbital period combined with the evolved nature of the host star places this planet in a relatively under explored region of parameter space and is, therefore, an exciting target for further characterisation. Second, I present a two-planet system orbiting around a bright G dwarf. Preliminary mass estimates derived from ground-based radial velocity observations, combined with detailed transit modelling, suggest that both planets in this second system have low bulk densities and therefore extended H/He atmospheres. This makes both planets prime candidates for future atmospheric characterisation and comparative planetology.
Finally, I show that visual inspection of large amounts of data via PHT yields many scientifically valuable by-products, including the identification of 4584 eclipsing binary candidates and multi-stellar systems. I discuss one of these systems - a massive compact hierarchical triple star system - in more detail and present a dynamical analysis of its past, present, and future. Overall, this thesis demonstrates the scientific value of citizen science for identifying unique signals that are often missed by automated searches and, therefore, shows that people-powered planet hunting can play an important role in a world that is becoming increasingly automated.

Keywords: citizen science
exoplanets
stars--multiples
planet detection
Advisor: Lintott, C
Aigrain, S