HIP 8522: A Puzzling Young Solar Twin with the Lowest Detected Lithium Abundance

Abstract

We present HIP 8522, a young solar twin with the lowest detected lithium abundance, potentially a field blue straggler or the result of episodic early accretion. Its stellar parameters ( T _eff = 5729 ± 7 K, $\mathrm{log}\,g$ = 4.532 ± 0.016 dex, [Fe/H] = 0.005 ± 0.010 dex, and v _t = 1.08 ± 0.02 km s ^−1 ) and chemical composition were determined via spectroscopic equilibrium using high-resolution spectra ( R = 60,000–165,000). The age of HIP 8522 was estimated to have an upper limit of <1 Gyr through isochrone fitting and was further confirmed using chemical clocks. Spectral synthesis of the lithium line at ∼6707.8 Å yielded an upper lithium abundance limit of A (Li) < 0.8 dex. This value is unusually low for solar twins of similar age, which typically have A (Li) values ranging from 2.0 to 3.3 dex, suggesting that ∼2 dex of lithium is missing. We investigate various scenarios, such as planet engulfment, substellar mergers, and extra mixing. However, two distinct hypotheses provide plausible explanations for the significant depletion of lithium: one suggests that HIP 8522 is a field blue straggler formed by the merger of a close binary, while the other proposes that HIP 8522 experienced early episodic accretion. The young solar twin HIP 8522 presents an exceptional opportunity to rigorously test stellar evolution models and gain crucial insights into the internal mixing mechanisms responsible for the significant destruction of lithium.

Keywords

• Spectroscopy
• Stellar abundances
• Stellar atmospheres
• Fundamental parameters of stars
• Solar analogs
• Blue straggler stars