Understanding eccentric temperate giants: an in-depth study of the architecture and stellar obliquity of the TOI-2134 system

Abstract

We revisit the TOI-2134 planetary system with three new high-cadence TESS sectors and 98 more spectra. This new analysis confirms the two orbiting planets by simultaneously modelling a total of eight sectors of corrected TESS photometry and 280 HARPS-N and SOPHIE radial velocities: an inner mini-Neptune in a near-circular $9.229198\pm 0.000003$ days orbit, and an outer temperate sub-Saturn orbiting with a $95.852840\pm 0.000042$ days period and eccentricity of $0.31\pm 0.01$. The masses and radii of the planets were computed to be $9.37\pm 0.54$ Me and $2.735\pm 0.068$ Re for planet b, and $58.3\pm 1.9$ Me and $7.35\pm 0.18$ Re for planet c. The new data not only improves the detection significance and precisions on the planetary orbits, but also breaks the original multimodality in the eccentricity solution for the outer planet. We also detect a long-term trend in the radial velocity data, which we attribute to a stellar magnetic cycle. We investigate the spin-orbit alignment of the system via observations of the Rossiter-McLaughlin effect for TOI-2134~b with EXPRES and TOI-2134~c with PARAS-2. No RM effect was detected for planet b, but we find a 4.7$\ddot{I}ƒ$ detection of a $59\pm 31^{\circ }$ obliquity for planet c. Finally, we examine the architecture of the system, assess its completeness, investigate the planetary interior, and their suitability for follow-up atmospheric analysis.

26 pages, accepted at MNRAS