Graduate Research
Post-Common Envelope Binaries in Open Clusters
Collaborators: Maria Drout, Philip Muirhead, Jason Nordhaus, Joshua Speagle & Ryan Chornock
Close binary systems are the progenitors to both Type Ia supernovae and the compact object mergers that can be detected via gravitational waves. To achieve a binary with a small radial separation, it is believed that the system likely undergoes common envelope (CE) evolution. Despite its importance, CE evolution may be one of the largest uncertainties in binary evolution due to a combination of computational challenges and a lack of observed benchmarks where both the post-CE and pre-CE conditions are known. Identifying post-CE systems in star clusters can partially circumvent this second issue by providing an independent age constraint on the system. In Grondin et al. 2024b, we combined multi-band observations with a machine learning method to perform the first systematic search for white dwarf (WD) and main-sequence (MS) binary systems in Milky Way open star clusters. We identified 52 high-probability candidate WD+MS binaries in 38 open star clusters, and are currently performing targeted follow-up observations to characterize a subset of these systems. Ultimately, this work is a first step to obtaining a set of observational benchmarks to better link post-CE systems to their pre-CE progenitors. Image: Olofsson et al. (ALMA; ESO/NAOJ/NRAO).
Read Grondin, S.M. et al. (2024b) here.
Extra-tidal Stars of 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. In Grondin et al. 2023, we developed a new methodology combining unsupervised machine learning, chemodynamical tagging and a core particle-spray code (Corespray) to identify escaped stars from dynamical interactions in the cores of GCs. In Grondin et al. 2024a, we expanded upon this work by producing the catalogue of Galactic GEMS (Globular cluster Extra-tidal Mock Stars). Combining data from the GEMS catalogue with chemical and dynamical information of observed stars will allow for association of extra-tidal field stars with any Galactic globular cluster; a requisite tool for understanding population-level dynamics and evolution of clusters in the Milky Way.
Download Corespray here.
Read Grondin, S.M. et al. (2023) here.
Read Grondin, S.M. et al. (2024a) here.
Undergraduate Research
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.