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arXiv 1808.07396astro-ph.SRastro-ph.EP
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重新审视恒星II的主序前演化。行星形成对恒星表面组成的影响

Revisiting the pre-main-sequence evolution of stars II. Consequences of planet formation on stellar surface composition

Masanobu Kunitomo, Tristan Guillot, Shigeru Ida, Taku Takeuchi

备注：
Accepted for publicatoin in A&A. 18 pages, 14 figures
发表信息：
A&A 618, A132 (2018)
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摘要：

我们希望利用最新的恒星演化模型来研究行星形成是如何印刻在恒星表面成分上的。我们模拟了主序前恒星的演化，作为吸积过程中热注入效率，氘质量分数和恒星质量的函数。为了简单起见，我们假设行星形成导致了零金属量气体的后期吸积，稀释了恒星表面成分作为恒星外对流区质量的函数。我们采用$150\,{\mathrm{M}_\oplus}(M_\star/\mathrm{M}_\odot)(Z/\mathrm{Z}_\odot)$作为一个不确定的，但合理的估计的重元素的质量，不吸积的恒星与巨行星，包括我们的太阳。通过结合我们的恒星演化模型，这些估计，我们评估恒星表面组成的行星形成的后果。我们发现，在第一个$\sim0.1$万年后，对流带的演化遵循经典的演化轨迹在两个因素的年龄。我们发现，行星形成应导致恒星表面成分的分散，这是大质量的恒星比低质量的恒星。我们预测具有$T_\mathrm{eff}\sim 5500\,$ K的恒星的[Fe/H]分布大约为$0.02$ dex，这与在一些带有行星的联星中观察到的金属丰度差异略有一致。具有$T_\mathrm{eff}\geq 7000\,$ K的恒星可能表现出更大的[Fe/H]亏损，亏损0.6 dex或更多，这与耐火性差的$λ$ Boo星的存在相一致。我们还发现，行星形成可以解释太阳中缺少难熔元素的原因，但前提是太阳系行星中的冰岩比小于$\approx0.4$，并且行星形成开始于太阳形成开始后的$\approx1.3$ Myr。（略）

英文摘要：

We want to investigate how planet formation is imprinted on stellar surface composition using up-to-date stellar evolution models. We simulate the evolution of pre-main-sequence stars as a function of the efficiency of heat injection during accretion, the deuterium mass fraction, and the stellar mass. For simplicity, we assume that planet formation leads to the late accretion of zero-metallicity gas, diluting the surface stellar composition as a function of the mass of the stellar outer convective zone. We adopt $150\,{\mathrm{M}_\oplus}(M_\star/\mathrm{M}_\odot)(Z/\mathrm{Z}_\odot)$ as an uncertain but plausible estimate of the mass of heavy elements that is not accreted by stars with giant planets, including our Sun. By combining our stellar evolution models to these estimates, we evaluate the consequences of planet formation on stellar surface composition. We show that after the first $\sim0.1$ Myr, the evolution of the convective zone follows classical evolutionary tracks within a factor of two in age. We find that planet formation should lead to a scatter in stellar surface composition that is larger for high-mass stars than for low-mass stars. We predict a spread in [Fe/H] of approximately $0.02$ dex for stars with $T_\mathrm{eff}\sim 5500\,$K, marginally compatible with differences in metallicities observed in some binary stars with planets. Stars with $T_\mathrm{eff}\geq 7000\,$K may show much larger [Fe/H] deficits, by 0.6 dex or more, compatible with the existence of refractory-poor $λ$ Boo stars. We also find that planet formation may explain the lack of refractory elements seen in the Sun as compared to solar twins, but only if the ice-to-rock ratio in the solar-system planets is less than $\approx0.4$ and planet formation began less than $\approx1.3$ Myr after the beginning of the formation of the Sun. (abbreviated)

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