Sixteen month decline in the 850 micron continuum brightness of the young stellar object HOPS 358 in NGC 2068

ATel #11583; Steve Mairs (East Asian Observatory), Graham S. Bell (East Asian Observatory), Doug Johnstone (NRC Herzberg Astronomy and Astrophysics, University of Victoria), Gregory J. Herczeg (Kavli Institute for Astronomy and Astrophysics), Geoffrey C. Bower (Academia Sinica Institute of Astronomy and Astrophysics), Yuri Aikawa (University of Tokyo), Jeong-Eun Lee (Kyung Hee University), Huei-Ru Vivien Chen (National Tsing Hua University), Jennifer Hatchell (University of Exeter), Miju Kang (Korea Astronomy and Space Science Institute), Carlos Contreras Pena (University of Exeter), Alexander Scholz (University of St Andrews), Tim Naylor (University of Exeter)
on 27 Apr 2018; 21:56 UT
Credential Certification: Steve Mairs (s.mairs@eaobservatory.org)

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As part of our young stellar object (YSO) sub-mm monthly monitoring programme, the JCMT Transient Survey (Herczeg et al. 2017 ApJ, 849, 43; Johnstone et al. 2018 ApJ, 854, 31), we have uncovered a steady sixteen-month decline in the 850 micron peak brightness of YSO HOPS 358 (R.A. 05:46:07.2, Dec. -00:13:30.9) in NGC 2068 (d=388 pc). Our 850 micron sub-mm continuum monitoring of this source with SCUBA2 on the James Clerk Maxwell Telescope (JCMT) revealed no evidence of variability during the first nine epochs, December 26, 2015 through November 26, 2016. Over this time the mean peak brightness of the source within the JCMT (15" beam) was 1.47 +/- 0.03 Jy/bm. The most recent twelve epochs show a steep roughly linear decline in sub-mm brightness through the most recent measurement on March 31, 2018, where the peak brightness was 1.16 +/- 0.04 Jy/bm (see light curve and finder chart at this URL). Thus, HOPS 358 has dimmed in the sub-mm by 25% over sixteen months. While the absolute calibration of the JCMT is typically uncertain by about 10%, the relative calibration of the JCMT Transient Survey between epochs is significantly better, roughly 2% (Mairs et al. 2017 ApJ, 843, 55). The YSO HOPS 358 (Furlan et al. 2016, ApJS, 224, 5) is classified based on Herschel Space Observatory continuum observations as a PACS Bright Red Source (PBRS, Stutz et al. 2013 ApJ, 767, 36). Based on this classification, it is thought to be among the youngest and most deeply embedded YSOs in NGC 2068.  HOPS 358 is embedded within the dense core HH25 MMS (Bontemps et al. 1995, A&A, 297, 98) and has a KVN-measured deuterium fractionation no higher than typical protostars (Kang et al. 2015, ApJ, 814,31). At higher angular resolution, using the SMA, HH25 MMS breaks into three sub-mm peaks separated by ~10", with HOPS 358 associated with the most northern peak SMM1 (Chen et al. 2013, ApJ, 768, 110). The much fainter source HOPS 316, located 6.9" north of HOPS 358, may contaminate the peak beam. Difference maps between the most recent epochs and the earlier measurements show clearly that the decrease in flux is coincident with the position of HOPS 358. Follow-up observations in the infrared, submm/mm, and radio are highly encouraged.

Hops 358 850 Micron Light Curve and Location