A recent astronomical breakthrough unveils the intriguing dynamics of the young variable star V1741 Sgr, also known as SPICY 71482 and Gaia22dtk. This celestial entity, residing in the proximity of the youthful star cluster NGC 6530, experienced an accretion outburst that caught the attention of astronomers worldwide.
First documented as a variable star in 1957, V1741 Sgr exhibited its initial outburst in mid-2022, as recorded by the European Space Agency’s Gaia satellite. The observations conducted by a team led by Michael A. Kuhn from the University of Hertfordshire, UK, using a suite of ground-based facilities and space telescopes, shed light on the nature of this cosmic phenomenon.
Classified as a classical T Tauri variable star, V1741 Sgr is believed to be in the early stages of stellar evolution, known as a young stellar object (YSO). These YSOs often undergo accretion-driven outbursts, a phenomenon divided into two categories: EX Lup (EXors) and FU Ori outbursts (FUors). EXors are moderate, lasting from months to a couple of years, while FUors are rare, extreme events lasting from decades to even centuries.
The recent outburst of V1741 Sgr falls into the EX Lup category, displaying a moderate amplitude of approximately 3.0 magnitudes in the optical and 1–2 magnitudes in the infrared spectrum. The outbursting spectrum exhibited prominent atomic and molecular emissions, along with a widespread brightening across the entire observed range.
The researchers delved into the spectral changes of V1741 Sgr, pinpointing the appearance and subsequent disappearance of titanium oxide (TiO) absorption during the fading process. This phenomenon, the team suggests, may be attributed to the cooling of circumstellar gas surrounding the star.
As the outburst began to dim in April 2023, strong TiO absorption emerged, indicating a lower temperature of approximately 3,600 K. However, once V1741 Sgr returned to its pre-outburst state in August 2023, both the TiO absorption and CO emission vanished. The authors propose that the appearance and disappearance of TiO align with the cooling and subsequent fading of circumstellar gas, leading to the reemergence of the stellar spectrum.
Analyzing the outburst light curve, Kuhn’s team identified distinct phases: a 60-day rise, a 280-day plateau, and a subsequent decay lasting about 110 days. This outburst-induced evolution caused the spectral energy distribution (SED) to shift towards bluer wavelengths below 1.6 μm and redder wavelengths above 1.6 μm.
The gathered data also facilitated the determination of V1741 Sgr’s fundamental properties. It was revealed that the star belongs to spectral type K2, possesses an age of less than 3 million years, and is situated approximately 4,100 light years away. Intriguingly, the results suggest that V1741 Sgr likely formed on the outskirts of the Lagoon Nebula, near a subcluster designated G5.9-0.9, rather than within the main cluster.