2026-06-15 ミシガン大学
An artist’s conception of a star engulfing a planet. The blue lines traces the path of the planet as it spirals toward the star and ultimately collides with it (the planet is partially as it crashes into the left-hand side of the star). Image credit: NASA, ESA, CSA, Ralf Crawford (STScI)
＜関連情報＞
- https://news.umich.edu/you-just-ate-that-planet-didnt-you/
- https://iopscience.iop.org/article/10.3847/1538-4357/ae71bb
褐色矮星を伴星とする準巨星におけるリチウム濃縮：惑星の飲み込み候補 Lithium Enrichment in a Subgiant Star with a Brown Dwarf Companion: A Planetary Engulfment Candidate
Brooke Kotten, Melinda Soares-Furtado, Ricardo Yarza, Andrew C. Nine, Seth A. Jacobson, Noah Vowell, Olivia Maynard, Allyson Bieryla, Andrew Vanderburg, Jack Schulte,…
The Astrophysical Journal Published: 2026 June 15
DOI:10.3847/1538-4357/ae71bb
Abstract
Theoretical models predict that subgiants within a narrow mass regime can retain detectable lithium enrichment signatures from planetary engulfment. We test this prediction using TOI-5882, selected because it occupies this favorable subgiant parameter space and hosts a massive brown dwarf (22 MJ, P = 7.1 days) companion capable of dynamically perturbing inner planets. We investigate whether (1) TOI-5882 exhibits lithium enhancement among similar subgiants, (2) planetary material would be deposited in the convective zone, and (3) the required engulfed mass lies within a plausible range for planetary engulfment. Using spectra from the Tillinghast Reflector Echelle Spectrograph, we measured a Li I equivalent width of 75.39 ± 3.58 mÅ and an abundance of A(Li) = 2.49 ± 0.12 dex. Comparing these values to a control sample of 61 subgiants from the GALactic Archaeology with HERMES (GALAH)DR4 survey, we find that TOI-5882 ranks in the 98.4th percentile in both metrics, confirming significant lithium enrichment. We evaluate the engulfment scenario by modeling convective zone deposition and estimating the mass required to reproduce the observed enhancement relative to the control sample. We perform an estimate of the engulfed planetary mass incorporating CI chondritic Li abundances, as planets formed via core accretion are enriched in heavy elements and lithium partitions with these metals. This yields a required engulfed mass of 9–95 M⊕—an order of magnitude lower than the 5.6 MJ implied by protosolar assumptions. TOI-5882’s lithium excess can plausibly result from the ingestion of a super-Earth to Neptune-mass planet, motivating further studies to test this scenario.
