Chinese astronomers conducting a blind search for large-amplitude mid-infrared variables in the Wide Infrared Sky Explorer (WISE) archive have accidentally discovered a giant mid-infrared flare from a distant young stellar object labeled J064722.95+031644.6. The finding was reported in an article published on the preprint server on September 20. arXiv.

Young stellar objects (YSOs) are stars in early stages of evolution, including protostars and proto-main sequence stars. They are usually observed in dense molecular clusters, in environments containing large amounts of molecular gas and interstellar dust.

Considering that intermittent accumulation processes occur in YSOs, these objects may experience accumulation-induced flares. Astronomers generally divide such events into EX Lup (also known as EXor) and FU Ori (or FUors) flares. The amplitude of EXs is several orders of magnitude and lasts from several months to a year or two; Fuors are more extreme and rare, can have amplitudes of up to five to six orders of magnitude and last from decades to even centuries.

J064722.95+031644.6 (or J0647 for short) was first identified as an infrared source near the star-forming region in the constellation Monoceros. The true nature of J0647 was unknown until a team of astronomers led by Tinggui Wang from the University of Science and Technology of China in Hefei conducted a new study.

Wang’s team recently examined mid-infrared light curves from the W1 and W2 bands of the AllWISE and NEOWISE photometric database with a single exposure at the Infrared Science Archive (IRSA) within 6 arcseconds from ALLWISE’s location. They discovered that J0647 is a YSO that displays a giant mid-infrared flare.

“In this paper, we report the serendipitous discovery of a giant explosion in the mid-infrared at a previously unknown YSO (RA = 06:47:22.95, DEC = +03:16:44.56),” the researchers write. According to the study, J0647 is a deeply embedded Class I YSO (has a disk and an envelope) with a residual luminosity of approximately 9.0 solar luminosity. The mass of J0647 is estimated to be in the range of 0.58 to 1.3 solar masses.

Astronomers found that during the mid-infrared burst, J0647 gradually increased by a factor of 5 from 2014 to 2016, followed by a dramatic increase of more than 100-fold in 2017. Thus, YSO showed a 500-fold increase in brightness. an increase in mid-infrared brightness over a period of two years, followed by a slow decrease. This burst amplitude is the second largest among all known mid-infrared YSO bursts.

Based on the light curve alone, astronomers classified J0647 as a medium-type YSO with exceptional amplitude. They noted that the near-infrared spectrum differs from classical FUors in YSOs, EXs, or many other known intermediate type flares due to the absence of absorption or emission lines other than diatomic hydrogen (H2). Source