Protoplanetary Disks around Sun-like Stars Appear to Live Longer When the Metallicity is Low

Abstract

Previous Hubble Space Telescope observations of the star-forming cluster NGC 346 in the Small Magellanic Cloud (SMC) revealed a large population of pre-main-sequence (PMS) candidates, characterized by H α excess emission in their photometry. However, without access to spectroscopy, the nature of these objects remained unclear. Using the NIRSpec instrument on board JWST, we studied a sample of these stars, with masses in the range of ∼0.9−1.8 M _⊙ , effective temperatures ( T _eff ) in the range of 4500−8000 K, and PMS ages between ∼0.1 and 30 Myr. Here, we present the first spectra of solar-mass PMS stars in the metal-poor SMC ( Z = 1/8 Z _⊙ ) and discuss the physical properties of 10 representative sources with good signal-to-noise ratio. The observations indicate that even the oldest of these PMS candidates are still accreting gas with typical rates of ∼10 ^−8 M _⊙ yr ^−1 for stars older than ∼10 Myr, confirming their PMS nature. The spectra also reveal near-infrared excess and molecular hydrogen excitation lines consistent with the presence of disks around these stars. These findings suggest that in a low-metallicity environment, circumstellar disks can live longer than previously thought.

Keywords

• Star formation
• Pre-main sequence stars
• Stellar accretion
• Young star clusters
• Small Magellanic Cloud
• Spectroscopy