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Title:
A Critical Examination of Li Pollution and Giant-Planet Consumption by a Host Star
Authors:
Sandquist, Eric L.; Dokter, Jon J.; Lin, D. N. C.; Mardling, Rosemary A.
Affiliation:
AA(Department of Astronomy, PA-210, 5500 Campanile Drive, San Diego State University, San Diego, CA 92182; , ), AB(Department of Astronomy, PA-210, 5500 Campanile Drive, San Diego State University, San Diego, CA 92182; , ), AC(Department of Astronomy and Astrophysics, 477 Clark Kerr Hall, University of California, Santa Cruz, CA 95064; ), AD(School of Mathematical Sciences, Monash University, Melbourne 3800, Australia; )
Publication:
The Astrophysical Journal, Volume 572, Issue 2, pp. 1012-1023. (ApJ Homepage)
Publication Date:
06/2002
Origin:
UCP
ApJ Keywords:
Stars: Planetary Systems, Stars: Planetary Systems: Formation, Stars: Abundances, Stars: Individual: Henry Draper Number: HD 82943
DOI:
10.1086/340452
Bibliographic Code:
2002ApJ...572.1012S

Abstract

Given the high metal contents observed for many stars with planets (SWPs), we examine the overall likelihood that the consumption of a giant planet could pollute its host star. First, we discuss 6Li and 7Li as indicators of pollution, verifying that 6Li is a strong indicator of pollution 30 Myr after star formation and showing that it strongly constrains the amount of heavy-element pollution incorporated into the star. Detection of 6Li in SWPs could also be used to distinguish between giant planet formation theories and can be used to detect the consumption of giant planets independent of planet mass. Second, we examine the probability that giant planets between 1 and 3 MJ could be destroyed in the outer convection zone of stars slightly more massive than the Sun (for which detection of a chemical signature of pollution would be easiest). We find that heated giant planets would be efficiently destroyed near the surface of the star, while the cores of cold giant planets might be able to survive a plunge through the base of the star's convection zone. Third, we examine whether dynamical processes could bring a giant planet close enough to the star to destroy it and whether the destruction of a planet would necessarily affect other planets in the system. While tidal interaction between protoplanets and their nascent disks may have led them to the proximity of their host stars, postformation star-planet interaction can lead to tidal disruption of the planet and accretion of its material or orbital decay followed by hydrodynamical interaction. Throughout, we consider the case of HD 82943, a star with a preliminary detection of 6Li that is known to have two planets. Using stellar models including diffusion, we estimate the mass of HD 82943 to be ~1.2 Msolar and its age to be ~0.5-1.5 Gyr. The observed 7Li abundance for HD 82943 is consistent with stars of similar Teff and age in the open cluster NGC 752. We describe a possible dynamical history for a hypothetical planet in the presence of the two resonant planets currently known. We present stable orbital configurations in which the hypothetical planet has low eccentricity and semimajor axis near 0.02 AU, so that it is dynamically decoupled from the resonant planets. Tidal interactions with the slowly rotating star can subsequently drag the planet into the stellar surface within the age of the star.
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