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EI2GYB > ASTRO 04.01.90 15:00l 63 Lines 5858 Bytes #999 (0) @ WW
BID : 49355_EI2GYB
Subj: Study unveils the dual nature of a young stellar object
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Study unveils the dual nature of a young stellar object
Astronomers from the Aryabhatta Research Institute of Observational Sciences (ARIES) in India and elsewhere have conducted a long-term photometric and spectroscopic study of a young stellar object known as V1180 Cassiopeiae. Results of the study, published December 23 on the arXiv preprint server, unveil the dual nature of this object.
EXors, FUors, UXors: Understanding the behavior of YSOs
Young stellar objects (YSOs) are stars in the early stages of evolution; in particular, protostars and pre-main sequence (PMS) stars. They are usually observed embedded in dense molecular clumps, environments containing plenty of molecular gas and interstellar dust.
Given that episodic accretion processes occur in YSOs, these objects may experience accretion-driven outbursts. Astronomers usually divide such events into EX Lup (also known as EXors) and FU Ori outbursts (or FUors). EXors are a few magnitudes in amplitude, and last from a few months to one or two years. FUors are more extreme and rare as they can be up to 5-6 magnitudes in amplitude and last from decades to even centuries.
In contrast to EXors and FUors, there are YSOs in which changes in brightness are extrinsic-caused by circumstellar dust obscuration-known as UXors. Astronomers are also finding "hybrid" objects that show both behaviors. Hence, they have a massive accretion burst (FUor-like) but also have dust clumps that occasionally block that new light (UXor-like).
Classifying V1180 Cassiopeiae
The YSO V1180 Cassiopeiae (or V1180 Cas for short) is a variable PMS star at a distance of some 1,950 light-years. It was initially classified as an EXor-type object, based on spectrophotometric data. However, subsequent observations have found that it experiences variability typical for UXor-type sources.
Therefore, in order to verify the true nature of V1180 Cassiopeiae, a team of astronomers led by Tarak Chand of ARIES decided to comb through the available data to investigate long-term photometric and spectroscopic evolution of this star.
"We combine multiband light curves from 1999 to 2025 with over 30 epochs of optical to near-infrared spectroscopy (0.5-2.5 æm), analyzing variability patterns, color behavior, and emission line diagnostics," the scientists explained.
What did the long-term investigation find?
By analyzing the data, the astronomers found that V1180 Cassiopeiae exhibits complex photometric behavior over two decades of observations, marked by both long and short dimming events. Early brightness dips were sporadic and consistent with extinction, while more recent dips showcase quasi-periodicity and structured profiles.
According to the paper, optical color-magnitude diagrams (CMDs) show reddening during fades with blueing episodes, which is typical for UXors. Moreover, near-infrared and mid-infrared colors consistently redden, suggesting changes in thermal emission. A gradual mid-infrared brightening trend points to an evolving disk structure or heating of the inner rim.
The study revealed persistent hydrogen, calcium and hydrogen emission lines in the spectra of V1180 Cassiopeiae, as well as forbidden emission lines of oxygen and sulfur. The hydrogen lines trace accretion, with luminosities that scale with brightness. The forbidden lines turned out to be enhanced during some brightness dips, which indicates dynamic linkages between outflow and extinction.
The study also found that the most recent brightness dips show extinction-dominated behavior and reflect a true drop in accretion rate. Furthermore, a linear correlation between accretion rate and R-band magnitude was identified, supporting the scenario in which the accretion-driven changes are modulated by extinction.
A hybrid YSO
The authors of the paper concluded that the results demonstrate the dual-mode variability of V1180 Cassiopeiae driven by both variable circumstellar extinction and episodic accretion events.
"V1180 Cassiopeiae exhibits a rare hybrid of UXor- and EXor-like behaviors, where extinction, accretion, and outflow processes appear to be tightly coupled and episodic in nature," the researchers concluded.
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