Extra-tidal Stars in Galactic Globular Clusters

Collaborators: Jeremy Webb, Nathan Leigh, Joshua Speagle & Reem Khalifeh

Globular clusters (GCs) are some of the most ancient structures in the Milky Way. The dense nature of these groups of hundreds of thousands to millions of stars makes them ideal systems to probe how different dynamical processes can influence GCs and the Galaxy over time (van den Bergh 2008). Recently, we developed a new methodology consisting of high-dimensional analysis and a core particle-spray code (Corespray) to identify extra-tidal stars generated from three-body interactions in the cores of GCs (Grondin et al. 2022). While this method finds 10 new high-probability extra-tidal candidates of M3, it can be applied to search for new extra-tidal stars of any GC in the Milky Way. Image: Piotto et al. (HST; NASA/ESA)

Download corespray here.
Read Grondin, S.M. et al. (2022) here.

Post-Common Envelope Evolution in Open Clusters

Collaborators: Maria Drout, Philip Muirhead & Jason Nordhaus

Close binary systems are the progenitors to compact object mergers that produce both Type Ia supernovae and gravitational waves. To achieve a binary with a small radial separation, it is believed that the system must undergo common envelope (CE) evolution — an unstable form of mass transfer that occurs when both components of a binary overflow their Roche lobes and thus orbit exclusively inside a “common envelope”. Although a large fraction of binary systems will undergo CE evolution at some point, modelling CE evolution is extremely difficult. To help resolve the main challenges in modelling CE evolution, we have been searching for white-dwarf and main-sequence post-CE binaries throughout the Milky Way. Image: Olofsson et al. (ALMA; ESO/NAOJ/NRAO).

Massive White Dwarfs in Young Open Clusters

Advisors: Harvey Richer & Jeremy Heyl (UBC)

White dwarfs (WDs) can be born with velocity kicks, causing them to be located off cluster centre or appear to be missing from star clusters entirely. As WDs provide insight into the final evolutionary phase for over 98% of stars in our Galaxy, understanding their creation mechanisms is crucial. For my undergraduate thesis, I investigated white dwarf kicks using Gaia DR2. Examining WD cluster radial distributions and fitting stellar isochrones to colour magnitude diagrams allowed me to compute the expected number of WDs in hundreds of clusters. In turn, this provided evidence on whether clusters were missing WDs (i.e. a WD deficit due to kicks). In the process, I also derived new ages for dozens of star clusters. Image: Jeff Johnson.

Read Richer, H.B. et al. (incl. Grondin, S.M.) (2021) here.

RRAT and FRB Pulse Comparison with CHIME

Advisor: Cherry Ng (Dunlap Institute; UofT)

Rotating radio transients (RRATs) and fast radio bursts (FRBs) are both short bursts of radio emission, making it hard to distinguish between the two phenomena. Currently, the only way to determine if a transient radio burst is a RRAT or FRB is whether it originates from inside (RRATs) or outside (FRBs) the Galaxy. To better understand the differences between RRATs and FRBs, I performed a systematic analysis of over 350 pulses from 12 RRATs with the CHIME telescope. Comparing pulse widths and bandwidth occupancies, this project was one of the first times anyone had directly compared the two radio populations. Image: Andre Renard (CHIME).

Pulsar Timing Systematics with the Double Pulsar

Advisor: Ingrid Stairs (UBC)

Since their discovery in 1967, pulsars have acted as impressive cosmic laboratories that have allowed us to test the limits of general relativity. In this project, I utilized the only known double pulsar binary system to develop a computational pipeline to improve pulse time of arrivals (TOAs). By designing an image correction procedure, I was able to lower pulse TOA residuals for two bandwidths of the visible pulsar. This work was used in part of a 16-year study to precisely test Einstein’s theory of general relativity (Kramer et al. 2021). Relativistic effects like delay, deflection of light due to the curvature of spacetime and change in orbit due to mass loss of the pulsar were measured to ultra-high precision. Image: Michael Kramer (MPIfR).

Read Kramer, M. et al. (incl. Grondin, S.M.) (2021) here.

Read media coverage by UBC PHAS here.