TOI-2525 b and c: A Pair of Massive Warm Giant Planets with Strong Transit Timing Variations Revealed by TESS

Abstract

The K-type star TOI-2525 has an estimated mass of M = 0.849⁺⁰.⁰²⁴ ₋₀.₀₃₃ M⊙ and radius of R = 0.785⁺⁰.⁰⁰⁷ ₋₀.₀₀₇ R⊙ observed by the TESS mission in 22 sectors (within sectors 1 and 39). The TESS light curves yield significant transit events of two companions, which show strong transit timing variations (TTVs) with a semiamplitude of ?6 hr. We performed TTV dynamical and photodynamical light-curve analysis of the TESS data combined with radial velocity measurements from FEROS and PFS, and we confirmed the planetary nature of these companions. The TOI-2525 system consists of a transiting pair of planets comparable to Neptune and Jupiter with estimated dynamical masses of m₆ = 0.088⁺⁰.⁰⁰⁵₋₀.₀₀₄ and m꜀ = 0.709⁺⁰.⁰³⁴₋₀.₀₃₃ Mⱼᵤₚ, radii of r₆ = 0.88⁺⁰.⁰²₋₀.₀₂ and r꜀ = 0.98⁺⁰.⁰²₋₀.₀₂ Rⱼᵤₚ, and orbital periods of P₆ = 23.288⁺⁰.⁰⁰¹₋₀.₀₀₂ and P꜀ = 49.260⁺⁰.⁰⁰¹₋₀.₀₀₁ days for the inner and outer planet, respectively. The period ratio is close to the 2:1 period commensurability, but the dynamical simulations of the system suggest that it is outside the mean-motion resonance (MMR) dynamical configuration. Object TOI-2525 b is among the lowest-density Neptune-mass planets known to date, with an estimated median density of P₆ = 0.174⁺⁰.⁰¹⁶₋₀.₀₁₅ g cm⁻³. The TOI-2525 system is very similar to the other K dwarf systems discovered by TESS, TOI-2202 and TOI-216, which are composed of almost identical K dwarf primaries and two warm giant planets near the 2:1 MMR.