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Mairs, Steve,Johnstone, Doug,Kirk, Helen,Lane, James,Bell, Graham S.,Graves, Sarah,Herczeg, Gregory J.,Scicluna, Peter,Bower, Geoffrey C.,Chen, Huei-Ru Vivien,Hatchell, Jennifer,Aikawa, Yuri,Chen, Wen American Astronomical Society 2017 The Astrophysical journal Vol.849 No.2
<P>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 characterized across the observable SED. In this study, we develop methods to robustly analyze repeated observations of an area of the sky for submillimeter variability in order to determine constraints on the magnitude and frequency of deeply embedded protostars. We compare 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 seven variable candidates, five of which we classify as Strong, and the remaining two we classify as Extended to indicate that the latter are associated with larger-scale structure. For the 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% yr(-1). In total, 7% of the protostars associated with 850 mu m emission in our sample show signs of variability. Four of the five 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 850 mu m periodicity of the submillimeter variable source, EC 53, to be 567 +/- 32 days, based on the archival Gould Belt Survey data.</P>
Herczeg, Gregory J.,Johnstone, Doug,Mairs, Steve,Hatchell, Jennifer,Lee, Jeong-Eun,Bower, Geoffrey C.,Chen, Huei-Ru Vivien,Aikawa, Yuri,Yoo, Hyunju,Kang, Sung-Ju,Kang, Miju,Chen, Wen-Ping,Williams, Jo American Astronomical Society 2017 The Astrophysical Journal Vol.849 No.1
<P>Most protostars have luminosities that are fainter than expected from steady accretion over the protostellar lifetime. The solution to this problem may lie in episodic mass accretion -- prolonged periods of very low accretion punctuated by short bursts of rapid accretion. However, the timescale and amplitude for variability at the protostellar phase is almost entirely unconstrained. In 'A JCMT/SCUBA-2 Transient Survey of Protostars in Nearby Star Forming Regions', we are monitoring monthly with SCUBA-2 the sub-mm emission in eight fields within nearby (<500 pc) star forming regions to measure the accretion variability of protostars. The total survey area of similar to 1.6 sq.deg. includes similar to 105 peaks with peaks brighter than 0.5 Jy/beam (43 associated with embedded protostars or disks) and 237 peaks of 0.125-0.5 Jy/beam (50 with embedded protostars or disks). Each field has enough bright peaks for flux calibration relative to other peaks in the same field, which improves upon the nominal flux calibration uncertainties of sub-mm observations to reach a precision of similar to 2-3% rms, and also provides quantified confidence in any measured variability. The timescales and amplitudes of any sub-mm variation will then be converted into variations in accretion rate and subsequently used to infer the physical causes of the variability. This survey is the first dedicated survey for sub-mm variability and complements other transient surveys at optical and near-IR wavelengths, which are not sensitive to accretion variability of deeply embedded protostars.</P>
Yoo, Hyunju,Lee, Jeong-Eun,Mairs, Steve,Johnstone, Doug,Herczeg, Gregory J.,Kang, Sung-ju,Kang, Miju,Cho, Jungyeon American Astronomical Society 2017 The Astrophysical Journal Vol.849 No.1
<P>During the protostellar phase of stellar evolution, accretion onto the star is expected to be variable, but this suspected variability has been difficult to detect because protostars are deeply embedded. In this paper, we describe a submillimeter luminosity burst of the Class I protostar EC 53 in Serpens Main, the first variable found during our dedicated JCMT/SCUBA-2 monitoring program of eight nearby star-forming regions. EC. 53 remained quiescent for the first six months of our survey, from 2016 February to August. The submillimeter emission began to brighten in 2016 September, reached a peak brightness of 1.5 times the faint state, and has been decaying slowly since 2017 February. The change in submillimeter brightness is interpreted as dust heating in the envelope, generated by a luminosity increase of the protostar of a factor of >= 4 The 850 mu m light curve resembles the historical K-band light curve, which varies by a factor of similar to 6 with a 543 period and is interpreted as accretion variability excited by interactions between the accretion disk and a close binary system. The predictable detections of accretion variability observed at both near-infrared and submillimeter wavelengths make the system a unique test-bed, enabling us to capture the moment of the accretion burst and to study the consequences of the outburst on the protostellar disk and envelope.</P>
A modest outburst and emission structure of very young protostar HOPS 373
Sung-Yong Yoon,Gregory J. Herczeg,Jeong-Eun Lee,Ho-Gyu Lee,Doug Johnstone,Watson Varricatt,John J. Tobin,Carlos Contreras Peña,Steve Mairs,Klaus Hodapp,P. Manoj,Mayra Osorio,S. Thomas Megeath,the JCM 한국천문학회 2022 天文學會報 Vol.47 No.2