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

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 in 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 speed must be less than 40% 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 multi-planet 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.

HD 183579b: a warm sub-Neptune transiting a solar twin detected by TESS

“…Indeed, later work from Chambers (2010) demonstrated that the difference would disappear if adding 4 M ⊕ of Earth-like material to the solar convection zone. Additionally, alternative theories including planet ingestion (Ramírez et al 2011;Spina et al 2015;Oh et al 2018;Church, Mustill & Liu 2020) and Bedell et al (2018). HD 183579 is a member of this sample and its abundance pattern appears typical among solar twins.…”

Chemically peculiar A and F stars with enhanced s-process and iron-peak elements: stellar radiative acceleration at work

“…It has been suggested that earth-like planets could be engulfed onto the surface of a main sequence (turnoff) star, altering the observed chemical stellar surface abundances as the engulfed planet gets dissolved and mixed in the convective envelope over short time scales (a few years) (Church, Mustill & Liu 2019). To investigate if this mechanism can provide a reasonable explanation for Ba-enhanced chemically peculiar stars, we carried out rough estimates of the abundance pattern of an A/F star assuming it has engulfed a terrestrial planet with chemical composition similar to either the Earth or Mercury into its convective envelope (since the chemically peculiar stars are iron-peak enhanced, if they formed via planet engulfment, the engulfed planets would seem most plausibly terrestrial ones).…”

“…Internal atomic transport processes due to stellar evolution can both reduce the photospheric abundance of an element via gravitational setting (a process that is pertinent to old, main-sequence turnoff stars; Aller & Chapman 1960;Korn et al 2007;Önehag, Gustafsson & Korn 2014;Choi et al 2016;Gao et al 2018;Souto et al 2019) and increase the photospheric abundance of an element via radiative acceleration (which may be pertinent to relatively hot stars ;Michaud 1970;Borsenberger, Michaud & Praderie 1984;Hui-Bon-Hoa et al 2002;Vick et al 2010;Michaud, Richer & Vick 2011;Deal et al 2020). Stellar abundances can also be altered externally, polluted by material accreted from a binary companion (van den Heuvel 1968; Boffin & Jorissen 1988;Han et al 1995) or via the engulfment of a planet (Zuckerman et al 2007;Church, Mustill & Liu 2019;Turner & Wyatt 2019).…”

“…This is because the accreted material mixes rapidly within the shallow convection envelope, possibly resulting in the prominent alteration of surface abundances. Although a number of external processes have been shown to yield chemically peculiar stars (Havnes & Conti 1971;Prof-fitt & Michaud 1989;Venn & Lambert 1990;Church, Mustill & Liu 2019), their role in setting the peculiar abundances of Am/Fm stars in particular is not well understood. A recent study of how planet engulfment events can lead to the formation of chemically peculiar main-sequence (turnoff) stars (Church, Mustill & Liu 2019) further emphasizes the importance of constraining the frequency of such events.…”

“…Although a number of external processes have been shown to yield chemically peculiar stars (Havnes & Conti 1971;Prof-fitt & Michaud 1989;Venn & Lambert 1990;Church, Mustill & Liu 2019), their role in setting the peculiar abundances of Am/Fm stars in particular is not well understood. A recent study of how planet engulfment events can lead to the formation of chemically peculiar main-sequence (turnoff) stars (Church, Mustill & Liu 2019) further emphasizes the importance of constraining the frequency of such events. To make advances on this issue, a large sample of early-type chemically peculiar stars with well-determined abundances for multiple elements is crucial.…”