Seminar - Emily Wilson (RIT) and Mohit Bhardwaj (McGill)


Monday, November 8, 2021, 11:00am to 12:00pm



" Convection in Common Envelopes"

The common envelope (CE) phase of binary evolution is the primary theorized mechanism to produce short-period, compact binaries. The efficiency of energy transfer between the two stars of the CE, $\alpha_{CE}$, and the predicted final separations of these same systems are closely linked. Rather than using a constant ejection efficiency, we consider one that is dependent on the internal structure of the components of the binary. Specifically, we examine the effects of convection and radiative losses on $\alpha_{CE}$ and the final separations of systems which undergo a CE phase. As the companion deposits energy into the CE during inspiral, the energy can get carried by convective eddies to an optically thin surface of the primary where it can be lost from the system via radiation. This allows the companion to inspiral deeper into the CE before energy can be tapped to drive ejection. The predicted final separations given radiative losses via convection are consistent with M-dwarf+WD populations and known double white dwarf (DWD) systems.


" Discovery of local Universe FRBs by the CHIME/FRB Collaboration"

Fast radio bursts (FRBs) are one of the newest unsolved mysteries in astronomy. Though a plethora of models has been proposed to explain FRBs, the origin of these intense millisecond-duration pulses of radio emission remains a topic of intense debate, owing to the paucity of well-localized FRBs. A promising method to test the proposed FRB theories is by associating FRBs with other astronomical phenomena. By identifying their hosts and/or multiwavelength counterparts, we can narrow down potential progenitors of FRBs. Unfortunately, due to the limited sensitivity of telescopes, multi-wavelength follow-up is most promising for nearby FRBs (distance < 100 Mpc). The Canadian Hydrogen Intensity Mapping Experiment (CHIME)/FRB project has been detecting FRBs since July 2018, and many of them have sufficiently low dispersion measure (DM) suggesting a nearby origin. Even better, the localization of low-DM FRBs to a few arcminute precision using the CHIME/FRB baseband system can result in a reliable host association for nearby FRBs. In this talk, I will report on recent CHIME/FRB discoveries of local universe FRBs, including 20200120E and 20181030A, for which we identified M81 (3.6 Mpc) and NGC 3252 (20 Mpc) as the promising hosts, respectively. Lastly, I will also discuss how these localized nearby FRBs can be useful in constraining different FRB progenitor models.

See also: Seminars, 2021-22