Astro Seminar Series

Doug Johnstone received his Ph.D. degree in 1995 from Berkeley. He held an NSERC Fellowship at the Canadian Institute for Theoretical Astrophysics and then moved up a floor to become a professor at the University of Toronto. In 2001, he joined the National Research Council’s Herzberg Institute of Astronomy as a research astronomer.

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Title and Abstract for Doug's talk:

What the Sub-mm Variability of Embedded Protostars Tells Us about Accretion: Past, Present, and Future

Abstract:  We have undertaken a 4-year dedicated JCMT/SCUBA-2 monitoring program of eight nearby star-forming regions (Herczeg et al. 2017) to search for sub-mm brightness variations as a proxy of episodic accretion. In this talk I will discuss the novel methods used to reach a relative calibration of 2% (Mairs et al. 2017a) and present the first variable source found in the sub-mm with a quasi-periodic light curve, the Class I protostar EC 53 in Serpens Main (Yoo et al. 2017). The change in sub-mm brightness of EC 53 is interpreted as dust heating in the envelope, generated by a luminosity increase of the protostar. The sub-mm lightcurve resembles the historical K-band light curve, which varies by a factor of ∼6 with a 543 period and is interpreted as accretion variability excited by interactions between the accretion disk and a close companion. 

I will also discuss the results from a comparison between archival SCUBA-2 observations and the first year of our dedicated survey (Mairs et al. 2017b) and perform a statistical analysis of the first eighteen months of the survey (Johnstone et al. 2018).  From these studies, we conclude that greater than 10% of the known deeply embedded protostars are found to vary in the sub-mm.  I will close by contemplating what all this might be telling us about the inner regions of protoplanetary disks and the mass assembly of stars.