March
2026
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2026AJ....171..135W
Authors
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Wang, Mu-Tian
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Dai, Fei
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Liu, Hui-Gen
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Masuda, Kento
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Howard, Andrew W.
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Halverson, Samuel
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Isaacson, Howard
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Zhang, Elina Y.
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Goldberg, Max
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Teng, Huan-Yu
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Rubenzahl, Ryan A.
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Fulton, Benjamin
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Petigura, Erik A.
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Giacalone, Steven
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Handley, Luke
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Latham, David W.
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Bieryla, Allyson
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Baker, Ashley
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Edelstein, Jerry
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Gibson, Steven R.
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Rider, Kodi
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Roy, Arpita
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Smith, Chris
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Walawender, Josh
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Rapetti, David
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Jenkins, Jon M.
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Winn, Joshua N.
Abstract
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We report the discovery of a sub-Neptune and a Neptune-like planet (R b=2.48−0.10+0.14 R⊕, R c=4.03−0.15+0.23 R⊕) orbiting the F-type star TOI-4495. The planets have orbital periods of 2.567 and 5.185 days, lying close to a 2:1 mean-motion resonance (MMR). Our photodynamical analysis of the TESS light curves constrains the planetary masses to Mb = 7.7 ± 1.4 M⊕and Mc = 23.2 ± 4.7 M⊕. The measured masses and radii indicate the presence of volatile-rich gaseous envelopes on both planets. The Rossiter─McLaughlin effect and the Doppler shadow of TOI-4495 c reveal a well-aligned orbit with a projected stellar obliquity of λ=−2.3−7.8+8.3° . Combined with the low mutual inclination constrained by the photodynamical analysis (∆I < 8.7°), the planetary orbits are likely coplanar and aligned with the host star's spin axis. We show that the planets are near, but not in, the 2:1 MMR, with a circulating resonant angle. We also find substantial free eccentricity for the inner planet, TOI-4495 b ( eb=0.078−0.013+0.02 ). Given the observed proximity to the 2:1 resonance and the more massive outer planet, TOI-4495 b and c are particularly susceptible to resonant overstability, which in turn can explain the observed eccentricity by converting resonantly excited eccentricity into free eccentricity. However, additional mechanisms (e.g., planetesimal scattering) may be required to further excite the eccentricity by ∼4%. To prevent tidal damping from reducing the eccentricity below the observed level over the star's lifetime (1.9 Gyr), the reduced tidal quality factor of TOI-4495 b must be Q'≳105 , consistent with the presence of a thick envelope on the planet.
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