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.
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.
