TOI-2525 b and c: A pair of massive warm giant planets with a strong transit timing variations revealed by TESS

Abstract

TOI-2525 is a K-type star with an estimated mass of M = 0.849${}_{-0.033}^{+0.024}$ M${}_{\odot }$ and radius of R = 0.785${}_{-0.007}^{+0.007}$ R${}_{\odot }$ 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 semi-amplitude of a $\sim$6 hours. We performed TTV dynamical, and photo-dynamical light curve analysis of the TESS data, combined with radial velocity (RV) 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 $m_{\mathrm{b}}$ = 0.088${}_{-0.004}^{+0.005}$ M${}_{Jup.}$, and $m_{\mathrm{c}}$ = 0.709${}_{-0.033}^{+0.034}$ M${}_{Jup.}$, radius of $r_b$ = 0.88${}_{-0.02}^{+0.02}$ R${}_{Jup.}$ and $r_c$ = 0.98${}_{-0.02}^{+0.02}$ R${}_{Jup.}$, and with orbital periods of $P_{\mathrm{b}}$ = 23.288${}_{-0.002}^{+0.001}$ days and $P_{\mathrm{c}}$ = 49.260${}_{-0.001}^{+0.001}$ days for the inner and the 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. TOI-2525 b is among the lowest density Neptune-mass planets known to date, with an estimated median density of $\ddot{I}{}_{\mathrm{b}}$ = 0.174${}_{-0.015}^{+0.016}$ 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 primary and two warm giant planets near the 2:1 MMR.

Accepted for publication in AJ