Super-Earth ingestion can explain the anomalously high metal abundances of M67 Y2235

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Abstract

We investigate the hypothesis that ingestion of a terrestrial or super-Earth planet could cause the anomalously high metal abundances seen in a turn-off star in the open cluster M67, when compared to other turn-off stars in the same cluster. We show that the mass of the convective envelope of the star is likely only 3.45 × 10-3 M, and hence 5.2 M of rock is required to obtain the observed 0.128 dex metal enhancement. Rocky planets dissolve entirely in the convective envelope if they enter it with sufficiently tangential orbits: we find that the critical condition for dissolution is that the planet's radial velocity must be less than 40 per cent of its total velocity at the stellar surface; or, equivalently, the impact parameter must be greater than about 0.9. We model the delivery of rocky planets to the stellar surface both by planet-planet scattering in a realistic multiplanet system, and by Lidov-Kozai cycles driven by a more massive planetary or stellar companion. In both cases almost all planets that are ingested arrive at the star on grazing orbits and hence will dissolve in the surface convection zone. We conclude that super-Earth ingestion is a good explanation for the metal enhancement in M67 Y2235, and that a high-resolution spectroscopic survey of stellar abundances around the turn-off and main sequence of M67 has the potential to constrain the frequency of late-time dynamical instability in planetary systems.

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Research areas and keywords

Subject classification (UKÄ) – MANDATORY

  • Astronomy, Astrophysics and Cosmology

Keywords

  • Methods: numerical, Open clusters and associations: individual: M67, Planet, Planetary systems, Star interactions, Stars: evolution
Original languageEnglish
Pages (from-to)2391-2402
Number of pages12
JournalMonthly Notices of the Royal Astronomical Society
Volume491
Issue number2
Publication statusPublished - 2020 Jan
Publication categoryResearch
Peer-reviewedYes