Mutual Inclination Excitation by Stellar Oblateness. (arXiv:2001.08282v1 [astro-ph.EP])
<a href="http://arxiv.org/find/astro-ph/1/au:+Li_G/0/1/0/all/0/1">Gongjie Li</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Dai_F/0/1/0/all/0/1">Fei Dai</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Becker_J/0/1/0/all/0/1">Juliette Becker</a>

Ultra-short-period planets (USPs) provide important clues to planetary
formation and migration. Recently, it is found that the mutual inclinations of
the planetary systems are larger if the inner orbits are closer ($lesssim
5R_*$) and if the planetary period ratios are larger ($P_2/P_1 gtrsim 5$) (Dai
et al. 2018). This suggests that the USPs experienced both inclination
excitation and orbital shrinkage. Here we investigate the increase in the
mutual inclination due to stellar oblateness. We find that the stellar
oblateness (within $sim 1$Gyr) is sufficient to enhance the mutual inclination
to explain the observed signatures. This suggests that the USPs can migrate
closer to the host star in a near coplanar configuration with their planetary
companions (e.g., disk migration), before mutual inclination gets excited due
to stellar oblateness.

Ultra-short-period planets (USPs) provide important clues to planetary
formation and migration. Recently, it is found that the mutual inclinations of
the planetary systems are larger if the inner orbits are closer ($lesssim
5R_*$) and if the planetary period ratios are larger ($P_2/P_1 gtrsim 5$) (Dai
et al. 2018). This suggests that the USPs experienced both inclination
excitation and orbital shrinkage. Here we investigate the increase in the
mutual inclination due to stellar oblateness. We find that the stellar
oblateness (within $sim 1$Gyr) is sufficient to enhance the mutual inclination
to explain the observed signatures. This suggests that the USPs can migrate
closer to the host star in a near coplanar configuration with their planetary
companions (e.g., disk migration), before mutual inclination gets excited due
to stellar oblateness.

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