Dr Thomas De Boer

Research Fellow

Academic and research departments


Jethwa P, Torrealba G, Navarrete C, Carballo-Bello J.A., de Boer Thomas, Erkal Denis, Koposov S.E., Duffau S, Geisler D, Catelan M, Belokurov V (2018) Discovery of a thin stellar stream in the SLAMS survey,Monthly Notices of the Royal Astronomical Society480(4)pp. 5342-5351 Oxford University Press
We report the discovery of a thin stellar stream - which we name the Jet stream - cross- ing the constellations of Hydra and Pyxis. The discovery was made in data from the SLAMS survey, which comprises deep g and r imaging for a 650 square degree region above the Galactic disc performed by the CTIO Blanco + DECam. SLAMS photomet- ric catalogues have been made publicly available. The stream is approximately 0.18 degrees wide and 10 degrees long, though it is truncated by the survey footprint. Its colour-magnitude diagram is consistent with an old, metal-poor stellar population at a heliocentric distance of approximately 29 kpc. We corroborate this measurement by identifying a spatially coincident overdensity of likely blue horizontal branch stars at the same distance. There is no obvious candidate for a surviving stream progenitor.
de Boer T J L, Gieles M, Balbinot E, Hénault-Brunet V, Sollima A, Watkins L L, Claydon Ian (2019) Globular cluster number density profiles using Gaia DR2,Monthly Notices of the Royal Astronomical Society485(4)pp. 4906-4935 Oxford University Press (OUP)
Using data from Gaia DR2, we study the radial number density profiles of the Galactic globular cluster sample. Proper motions are used for accurate membership selection, especially crucial in the cluster outskirts. Due to the severe crowding in the centres, the Gaia data are supplemented by literature data from HST and surface brightness measurements, where available. This results in 81 clusters with a complete density profile covering the full tidal radius (and beyond) for each cluster. We model the density profiles using a set of single-mass models ranging from King and Wilson models to generalized lowered isothermal LIMEPY models and the recently introduced SPES models, which allow for the inclusion of potential escapers. We find that both King and Wilson models are too simple to fully reproduce the density profiles, with King (Wilson) models on average underestimating (overestimating) the radial extent of the clusters. The truncation radii derived from the LIMEPY models are similar to estimates for the Jacobi radii based on the cluster masses and their orbits. We show clear correlations between structural and environmental parameters, as a function of Galactocentric radius and integrated luminosity. Notably, the recovered fraction of potential escapers correlates with cluster pericentre radius, luminosity, and cluster concentration. The ratio of half mass over Jacobi radius also correlates with both truncation parameter and PE fraction, showing the effect of Roche lobe filling.