Four young eruptive stellar objects discovered

By analyzing data from the SPICY catalog and NASA’s WISE spacecraft, an international team of astronomers has discovered four new young eruptive stellar objects (YSOs). The discovery was presented in a research paper published in the December issue of Journal of the Korean Astronomical Society (JKAS).

In general, YSOs are stars in the early stages of their evolution, particularly protostars and pre-main sequence (PMS) stars. They are generally detected within dense molecular clusters, abundant in molecular gases and interstellar particles.

Observations show that episodic accretion processes occur in YSOs, so these objects can experience accretion-driven explosions. Astronomers generally divide these events into EX Lup (also known as EXors) and FU Ori (or FUors) explosions. EXors have an amplitude of a few magnitudes and last from a few months to one or two years; Borers are more extreme and rarer, can reach magnitudes of 5 to 6 magnitudes, and last for decades or even centuries.

Since young eruptive stellar objects are still rare and only a few dozen such objects have been identified, a group of astronomers led by Carlos Contreras Peña of Seoul National University, South Korea, conducted a search for vibrant new YSOs. To this end, they combed through data from the Spitzer/IRAC Candidate YSO Catalog (SPICY) for the inner galactic midplane and analyzed mid-infrared photometry from the Wide-field Infrared Survey Explorer (WISE).

As a result, researchers identified four eruptive YSOs, namely: SPICY 97855, SPICY 99341, SPICY 100587, and SPICY 109331. SPICY 99341 and SPICY 100587 were classified as bona fide FUors, while SPICY 97855 is a candidate FUor, being given that its final classification is uncertain as its brilliance is still in progress.

“We found four YSOs that show similarities to the spectra of known eruptive YSOs,” the scientists wrote in the paper.

Regarding SPICY 109331, its initial classification was EXor. However, data suggests that the duration of its explosion is around five years, which is longer than expected for EXors. Overall, SPICY 109331 was classified as a V1647 Ori type source, a class between EXors and FUors, exhibiting mixed characteristics.

According to the study, all newly discovered eruptive YSOs exhibit long-term (lasting more than a year) and high-amplitude (more than 2.5 mag) explosions. They also display a strong ¹²CO emission lines in their spectra. These results indicate that all four YSOs are experiencing explosions due to significant changes in the accretion rate.

The study also found that SPICY 99341 and SPICY 109331 are located approximately 9,800 and 12,500 light years away, respectively. The distance to the other two YSOs is still uncertain and requires additional observations.

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