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arXiv · 2504.05480

Investigating the eccentricity distribution of transiting, long-period giant planets

Ahlam Alqasim·Teruyuki Hirano·Yasunori Hori·Daisuke Kawata·John Livingston·Steve B. Howell·Antonino F. Lanza·Andrew W. Mann·Carl Ziegler·César Briceño·Charles A. Beichman·David R. Ciardi·Ivan A. Strakhov·Michael B. Lund·Nicholas Law
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Abstract

Eccentric giant planets are predicted to have acquired their eccentricity through two major mechanisms: the Kozai-Lidov effect or planet-planet scattering, but it is normally difficult to separate the two mechanisms and determine the true eccentricity origin for a given system. In this work, we focus on a sample of 92 transiting, long-period giant planets (TLGs) as part of an eccentricity distribution study for this planet population in order to understand their eccentricity origin. Using archival high-contrast imaging observations, public stellar catalogs, precise Gaia astrometry, and the NASA Exoplanet Archive database, we explored the eccentricity distribution correlation with different planet and host-star properties of our sample. We also homogeneously characterized the basic stellar properties for all 86 host-stars in our sample, including stellar age and metallicity. We found a correlation between eccentricity and stellar metallicity, where lower-metallicity stars ([Fe/H] <= 0.1) did not host any planets beyond e > 0.4, while higher-metallicity stars hosted planets across the entire eccentricity range. Interestingly, we found no correlation between the eccentricity distribution and the presence of stellar companions, indicating that planet-planet scattering is likely a more dominant mechanism than the Kozai-Lidov effect for TLGs. This is further supported by an anti-correlation trend found between planet multiplicity and eccentricity, as well as a lack of strong tidal dissipation effects for planets in our sample, which favor planet-planet scattering scenarios for the eccentricity origin.

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Ahlam Alqasim, Teruyuki Hirano, Yasunori Hori, Daisuke Kawata, John Livingston, Steve B. Howell, Antonino F. Lanza, Andrew W. Mann, Carl Ziegler, César Briceño, Charles A. Beichman, David R. Ciardi, Ivan A. Strakhov, Michael B. Lund, Nicholas Law. 2025-04-07. Investigating the eccentricity distribution of transiting, long-period giant planets. https://doi.org/10.1093/mnras%2Fstaf418

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