The JCMT Transient Survey: Identifying Submillimetre Continuum Variability over Several Year Timescales Using Archival JCMT Gould Belt Survey Observations

TL;DR

This study develops methods to analyze submillimetre variability in protostars over several years, identifying 7 variable candidates and estimating their brightness changes and periodicity, thereby providing observational constraints on early star formation processes.

Contribution

It introduces a robust analysis approach for submillimetre variability using archival JCMT data, revealing the frequency and amplitude of protostellar variability over multi-year timescales.

Findings

7% of protostars show variability in 850 μm emission.

Average fractional brightness change is 4.0% per year.

EC 53 has an estimated periodicity of 567 days.

Abstract

Investigating variability at the earliest stages of low-mass star formation is fundamental in understanding how a protostar assembles mass. While many simulations of protostellar disks predict non-steady accretion onto protostars, deeper investigation requires robust observational constraints on the frequency and amplitude of variability events characterised across the observable SED. In this study, we develop methods to robustly analyse repeated observations of an area of the sky for submillimetre variability in order to determine constraints on the magnitude and frequency of deeply embedded protostars. We compare \mbox{850 $\mu$m} JCMT Transient Survey data with archival JCMT Gould Belt Survey data to investigate variability over 2-4 year timescales. Out of 175 bright, independent emission sources identified in the overlapping fields, we find 7 variable candidates, 5 of which we classify as \textit{Strong} and the remaining 2 as \textit{Extended} to indicate the latter are associated with larger-scale structure. For the \textit{Strong} variable candidates, we find an average fractional peak brightness change per year of |4.0|\% yr$^{-1}$ with a standard deviation of $2.7\%\mathrm{\:yr}^{-1}$. In total, 7\% of the protostars associated with \mbox{850 $\mu$m} emission in our sample show signs of variability. Four of the five \textit{Strong} sources are associated with a known protostar. The remaining source is a good follow-up target for an object that is anticipated to contain an enshrouded, deeply embedded protostar. In addition, we estimate the \mbox{850 $\mu$m} periodicity of the submillimetre variable source, EC 53, to be \mbox{567 $\pm$ 32 days} based on the archival Gould Belt Survey data.