Papers › TOI-2015b: A Warm Neptune with Transit Timing Variations Orbiting an Active mid M Dwarf
TOI-2015b: A Warm Neptune with Transit Timing Variations Orbiting an Active mid M Dwarf
Sinclaire E. Jones, Gudmundur Stefansson, Kento Masuda, Jessica E. Libby-Roberts, Cristilyn N. Gardner, Rae Holcomb, Corey Beard, Paul Robertson, Caleb I. Cañas, Suvrath Mahadevan, Shubham Kanodia, Andrea S. J. Lin, Henry A. Kobulnicky, Brock A. Parker, Chad F. Bender, William D. Cochran, Scott A. Diddams, Rachel B. Fernandes, Arvind F. Gupta, Samuel Halverson, Suzanne L. Hawley, Fred R. Hearty, Leslie Hebb, Adam Kowalski, Jack Lubin, Andrew Monson, Joe P. Ninan, Lawrence Ramsey, Arpita Roy, Christian Schwab, Ryan C. Terrien, John Wisniewski
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We report the discovery of a close-in (P_(orb) = 3.349 days) warm Neptune with clear transit timing variations (TTVs) orbiting the nearby (d=47.3 pc) active M4 star, TOI-2015. We characterize the planet's properties using TESS photometry, precise near-infrared radial velocities (RV) with the Habitable-zone Planet Finder (HP) Spectrograph, ground-based photometry, and high-contrast imaging. A joint photometry and RV fit yields a radius Rₚ = 3.37_(-0.20)^(+0.15) R_⊕, mass mₚ = 16.4_(-4.1)^(+4.1) M_⊕, and density ρₚ = 2.32_(-0.37)^(+0.38) g cm⁻³ for TOI-2015b, suggesting a likely volatile-rich planet. The young, active host star has a rotation period of Pᵣₒₜ = 8.7 ± 0.9 days and associated rotation-based age estimate of 1.1 ± 0.1 Gyr. Though no other transiting planets are seen in the TESS data, the system shows clear TTVs of super period Pₛᵤₚ ≈ 430 days and amplitude $\sim$$100\:\mathrm{minutes}$. After considering multiple likely period ratio models, we show an outer planet candidate near a 2:1 resonance can explain the observed TTVs while offering a dynamically stable solution. However, other possible two-planet solutions -- including 3:2 and 4:3 resonance -- cannot be conclusively excluded without further observations. Assuming a 2:1 resonance in the joint TTV-RV modeling suggests a mass of m_b = 13.3_(-4.5)^(+4.7) M_⊕ for TOI-2015b and m_c = 6.8_(-2.3)^(+3.5) M_⊕ for the outer candidate. Additional transit and RV observations will be beneficial to explicitly identify the resonance and further characterize the properties of the system.
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