The JCMT Transient Survey: Four Year Summary of Monitoring the Submillimeter Variability of Protostars
Creators: name: Lee, Yong-Hee
name: Johnstone, Doug
name: Lee, Jeong-Eun
name: Herczeg, Gregory
name: Mairs, Steve
name: Contreras-Peña, Carlos
name: Hatchell, Jennifer
name: Naylor, Tim
name: Bell, Graham S.
name: Bourke, Tyler L.
name: Broughton, Colton
name: Francis, Logan
name: Gupta, Aashish
name: Harsono, Daniel
name: Liu, Sheng-Yuan
name: Park, Geumsook
name: Plovie, Spencer
name: Moriarty-Schieven, Gerald H.
name: Scholz, Aleks
name: Sharma, Tanvi
name: Teixeira, Paula Stella
name: Wang, Yao-Te
name: Aikawa, Yuri
name: Bower, Geoffrey C.
name: Chen, Huei-Ru Vivien
name: Bae, Jaehan
name: Baek, Giseon
name: Chapman, Scott
name: Chen, Wen Ping
name: Du, Fujun
name: Dutta, Somnath
name: Forbrich, Jan
name: Guo, Zhen
name: Inutsuka, Shu-ichiro
name: Kang, Miju
name: Kirk, Helen
name: Kuan, Yi-Jehng
name: Kwon, Woojin
name: Lai, Shih-Ping
name: Lalchand, Bhavana
name: Lane, James M. M.
name: Lee, Chin-Fei
name: Liu, Tie
name: Morata, Oscar
name: Pearson, Samuel
name: Pon, Andy
name: Sahu, Dipen
name: Shang, Hsien
name: Stamatellos, Dimitris
name: Tang, Shih-Yun
name: Xu, Ziyan
name: Yoo, Hyunju
Publisher: name: arXiv
Year: 2021
Subjects: subject: Solar and Stellar Astrophysics (astro-ph.SR)
subject: Astrophysics of Galaxies (astro-ph.GA)
subject: FOS: Physical sciences
subject: FOS: Physical sciences

description: We present the four-year survey results of monthly submillimeter monitoring of eight nearby ($&lt; 500 $pc) star-forming regions by the JCMT Transient Survey. We apply the Lomb-Scargle Periodogram technique to search for and characterize variability on 295 submillimeter peaks brighter than 0.14 Jy beam$^{-1}$, including 22 disk sources (Class II), 83 protostars (Class 0/I), and 190 starless sources. We uncover 18 secular variables, all of them protostars. No single-epoch burst or drop events and no inherently stochastic sources are observed. We classify the secular variables by their timescales into three groups: Periodic, Curved, and Linear. For the Curved and Periodic cases, the detectable fractional amplitude, with respect to mean peak brightness, is $\sim4$ % for sources brighter than $\sim$ 0.5 Jy beam$^{-1}$. Limiting our sample to only these bright sources, the observed variable fraction is 37 % (16 out of 43). Considering source evolution, we find a similar fraction of bright variables for both Class 0 and Class I. Using an empirically motivated conversion from submillimeter variability to variation in mass accretion rate, six sources (7 % of our full sample) are predicted to have years-long accretion events during which the excess mass accreted reaches more than 40 % above the total quiescently accreted mass: two previously known eruptive Class I sources, V1647 Ori and EC 53 (V371 Ser), and four Class 0 sources, HOPS 356, HOPS 373, HOPS 383, and West 40. Considering the full protostellar ensemble, the importance of episodic accretion on few years timescale is negligible, only a few percent of the assembled mass. However, given that this accretion is dominated by events of order the observing time-window, it remains uncertain as to whether the importance of episodic events will continue to rise with decades-long monitoring.
description: Accepted for publication in the Astrophysical Journal