Chemical Disparity in Binary System HD 81809 Points to Recent Planet Engulfment
English summary
Astronomers studying the 10-billion-year-old binary system HD 81809, located 113 light-years away, found that the two G-type stars have a 3.7-fold difference in iron abundance, far beyond typical binary evolution. The main-sequence star HD 81809B exhibits unusually high lithium levels, a strong signature of recent planetary engulfment for an old low-mass star. Modeling suggests it must have swallowed 25 to 75 Earth masses of metal-rich material, equivalent to the metal core mass between Neptune and Saturn. This system provides direct observational evidence of a star consuming its planets in a co-eval binary.
Chinese summary
天文学家研究年龄约100亿年、距离113光年的双星系统HD 81809，发现两颗G型恒星的铁丰度相差约3.7倍，超出通常双星演化范围。主序星HD 81809B还显示异常高的锂含量，这是老年低质量恒星近期吞噬行星的关键迹象。模型表明它必须吞没了25至75地球质量的富金属物质，相当于海王星至土星金属核的质量。该系统为同龄双星中恒星吞噬行星提供了直接的观测证据。
Key points
Binary system HD 81809 consists of two co-eval G-type stars with a 3.7x difference in iron abundance.
双星系统HD 81809由两颗同龄G型恒星组成，铁丰度相差3.7倍。
HD 81809B shows high lithium levels, anomalous for an old low-mass star, indicating recent planet engulfment.
HD 81809B显示高锂含量，这对于老年低质量恒星极不正常，是近期行星吞噬的明确迹象。
The engulfed material is estimated at 25–75 Earth masses, matching the metal core mass between Neptune and Saturn.
估计被吞噬的物质质量为25至75地球质量，相当于海王星到土星之间的金属核质量。
This discovery provides direct chemical evidence of planet eating in a coeval binary system.
这一发现为同龄双星系统中的行星吞噬现象提供了直接的化学证据。