Abstracts Astronomy & Space Science

Constraining Stellar Evolution in Young Open Clusters with NGTS

by Gareth Smith

Understanding stellar evolution is fundamental to astronomy, yet there remain significant gaps in our knowledge. Scientific progress requires testing our best explanations against observation, and open clusters act as key test sites for theories of stellar evolution. Observations of young open clusters enable theoretical models to be assessed at stages when stellar properties still reflect their initial conditions, and in regions of parameter space where constraints remain scarce. The Next Generation Transit Survey (NGTS) is a multi-telescope, ground-based, wide-field photometric survey which is well-suited to studying these environments, and its observations are at the heart of this thesis, which presents my research in the field of early-stage stellar evolution as conducted during my PhD. As a member of the NGTS consortium and, specifically, of the team focusing on open clusters and star forming regions, I have used NGTS data to analyse stellar rotation in the Orion Star-forming Complex and to characterise a low-mass eclipsing binary (EB) in a triple-star system located in the Blanco 1 open cluster. By combining NGTS observations with additional photometry and spectroscopy, and by developing a novel method for extracting radial velocities of close binary (or higher-order) systems, I derived the fundamental parameters of the Blanco 1 EB. With masses and radii measured to a precision better than 1 and 2 per cent, respectively, the newly-identified EB, NGTS J0002-29, becomes a benchmark addition to the current list of 19 well-characterised, low-mass, sub-Gyr, stellar-mass EBs, which constitute some of the strongest observational tests of stellar evolution theory at low masses and young ages. Long-baseline observations of 30 square degrees of the Orion Complex provided simultaneous photometry of thousands of stars, leading to my study of stellar rotation. I analysed cluster membership using astrometry from Gaia DR3 and built a pipeline to process light curves, producing an extensive and homogeneous dataset of more than 2000 rotation periods. I estimated interstellar extinction on a star-by-star basis by fitting broadband photometric data, and derived stellar ages using evolutionary models. I assigned the target stars to kinematic clusters, calculated their ages, and analysed rotation period distributions, finding evidence for mass-dependent evolution during the first 10 Myr, as well as corroboration for the idea that circumstellar discs play a role in regulating the evolution of angular momentum. These studies demonstrate the ability of modern ground-based photometric surveys to address questions about young-age stellar evolution, both on the scale of individual systems and on the scale of large clusters. This ability to operate at different scales facilitates rapid progress and helps to maximise the potential in our data for testing our theories.