My master thesis in 400 words : Dominic Couture
Dominic Couture, an iREx student at Université de Montréal, finished his master degree in 2019. Here, he summarizes the research project he carried out during his studies:
Young moving groups (YMG) are associations of stars, mainly M dwarfs, formed at the same epoch by the collapse of a molecular cloud unique to every association and located in the solar neighbourhood, that share a common kinematics. They are ideal laboratories for the study of the last steps of stellar formation and direct imaging of exoplanets. The β Pictoris YMG is one of the youngest and closest YMGs, although its age is uncertain : ages found using isochrones or the lithium depletion boundary (21 − 24 Myr) are in disagreement with kinematic ages (∼ 12 Myr) found by tracing back trajectories of stars in the association with their full kinematics up to the epoch when the size of the YMG was minimal, which coincides with the epoch of stellar formation.
In my master’s thesis, I present a new numerical method, called Traceback, capable of finding a kinematic age of a YMG by traceback with data from the Gaia DR2 Catalog. Its maximal theorical precision is calculated and two important biases are caracterized : a bias due to measurement errors (∼ −4.5 Myr) and a 0.5 km/s average bias on radial velocity measurements due to gravitational redshift (∼ −1.8 Myr). When this method is applied to a sample of 46 validated members of the β Pictoris YMG, a corrected kinematic age of 17 − 19 Myr, in agreement with isochrones and litihum depletion boundary ages, is found by minimizing the median absolute deviation, a measure of the size of the association which is robust against outliers in the data, and the X-U covariance between the X position (toward the galactic centre) and the corresponding U velocity. Futhermore, the use of a minimum spanning tree is not advantageous.