TY - JOUR
T1 - Kronos and Krios
T2 - Evidence for Accretion of a Massive, Rocky Planetary System in a Comoving Pair of Solar-type Stars
AU - Oh, Semyeong
AU - Price-Whelan, Adrian M.
AU - Brewer, John M.
AU - Hogg, David W.
AU - Spergel, David N.
AU - Myles, Justin
N1 - Publisher Copyright:
© 2018. The American Astronomical Society. All rights reserved.
PY - 2018/2/20
Y1 - 2018/2/20
N2 - We report and discuss the discovery of a significant difference in the chemical abundances of a comoving pair of bright solar-type stars, HD 240430 and HD 240429. The two stars have an estimated 3D separation of ≈0.6 pc (≈0.01 pc projected) at a distance of r ≈ 100 pc with nearly identical 3D velocities, as inferred from Gaia TGAS parallaxes and proper motions, and high-precision radial velocity measurements. Stellar parameters determined from high-resolution spectra obtained with the High Resolution Echelle Spectrometer (HIRES) at the Keck Observatory indicate that the two stars are ∼4 Gyr old. The more metal-rich of the two, HD 240430, shows an enhancement of refractory (TC > 1200 K) elements by ≈0.2 dex and a marginal enhancement of (moderately) volatile elements (TC < 1200 K; C, N, O, Na, and Mn). This is the largest metallicity difference found in a wide binary pair to date. Additionally, HD 240430 shows an anomalously high surface lithium abundance (A(Li) = 2.75), higher than its cooler companion by 0.5 dex. The proximity in phase-space and ages between the two stars suggests that they formed together with the same composition, which is at odds with the observed differences in metallicity and abundance patterns. We therefore suggest that the star HD 240430, "Kronos," accreted 15 M⊕ of rocky material after birth, selectively enhancing the refractory elements as well as lithium in its surface and convective envelope.
AB - We report and discuss the discovery of a significant difference in the chemical abundances of a comoving pair of bright solar-type stars, HD 240430 and HD 240429. The two stars have an estimated 3D separation of ≈0.6 pc (≈0.01 pc projected) at a distance of r ≈ 100 pc with nearly identical 3D velocities, as inferred from Gaia TGAS parallaxes and proper motions, and high-precision radial velocity measurements. Stellar parameters determined from high-resolution spectra obtained with the High Resolution Echelle Spectrometer (HIRES) at the Keck Observatory indicate that the two stars are ∼4 Gyr old. The more metal-rich of the two, HD 240430, shows an enhancement of refractory (TC > 1200 K) elements by ≈0.2 dex and a marginal enhancement of (moderately) volatile elements (TC < 1200 K; C, N, O, Na, and Mn). This is the largest metallicity difference found in a wide binary pair to date. Additionally, HD 240430 shows an anomalously high surface lithium abundance (A(Li) = 2.75), higher than its cooler companion by 0.5 dex. The proximity in phase-space and ages between the two stars suggests that they formed together with the same composition, which is at odds with the observed differences in metallicity and abundance patterns. We therefore suggest that the star HD 240430, "Kronos," accreted 15 M⊕ of rocky material after birth, selectively enhancing the refractory elements as well as lithium in its surface and convective envelope.
KW - binaries: visual
KW - planet-star interactions
KW - stars: abundances
KW - stars: formation
KW - stars: individual (HD 240430, HD 240429)
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U2 - 10.3847/1538-4357/aaab4d
DO - 10.3847/1538-4357/aaab4d
M3 - Article
AN - SCOPUS:85042708943
SN - 0004-637X
VL - 854
JO - Astrophysical Journal
JF - Astrophysical Journal
IS - 2
M1 - 138
ER -