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Colloquium with Kathryn Neugent and Ziggy Pleunis

The Binary Fraction of Red Supergiants … and Beyond! — by Kathryn Neugent

The binary fraction of massive main-sequence OB stars is thought to be as high as 70% or greater. However, until recently, only around a dozen binary red supergiants (RSGs) had been identified, despite the fact that these stars are the evolved descendants of a large portion of OB stars. My PhD research focused on searching for these “missing” binary RSGs. As dictated by stellar evolution, binary RSGs will likely have B-type companions and such systems will have unique photometric signatures due to the shape of their spectral energy distributions. After observing candidate RSG+B star binaries spectroscopically in the Local Group galaxies of M31, M33 and the Magellanic Clouds, we’ve discovered over 250 new systems. In this talk I’ll discuss how these results have allowed us to place constraints on the binary fraction of RSGs as a function of metallicity, and also mention the work I’m doing as a new Dunlap Fellow to better understand both massive star evolution and the creation of gravitational wave events.

The repetition and morphology of fast radio bursts — by Ziggy Pleunis 
Fast radio bursts (FRBs) are millisecond-duration extragalactic radio transients of elusive origin that were first discovered in 2007. The bursts exhibit a variety of time-frequency structures, shaped by an unknown emission mechanism and transformed by propagation through an ionized and inhomogeneous medium. More than twenty FRBs have been observed to repeat, which has ruled out a cataclysmic origin for these sources and allows for detailed multi-wavelength follow-up observations. It is as-of-yet unclear whether all FRBs repeat and if there are multiple populations of FRBs. The CHIME/FRB experiment has recently released a first catalog of >500 FRBs, 62 of which are bursts from 18 different repeater sources, detected in the 400-800 MHz octave, all detected with the same instrument and a similar selection function. With this first catalog, we confirm that repeater bursts, on average, have larger widths and we show, for the first time, that repeater bursts, on average, are narrower in bandwidth. This difference could be due to a beaming or propagation effect, or it can be intrinsic to the populations. I will also present the lowest-frequency FRBs, detected down to 110 MHz with the LOFAR telescope by following up CHIME/FRB-discovered repeating sources. Finally, I will point out how an updated sample of repeaters and other observables can help reveal if we are observing one continuum or multiple populations of FRBs.
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Dr. Kathryn Neugent and Dr. Ziggy Pleunis

October 20, 2021
2:00 pm - 3:00 pm