Radial velocity confirmation of a hot super-Neptune discovered by TESS with a warm Saturn-mass companion

Abstract

We report the discovery and confirmation of the planetary system TOI-1288. This late G dwarf harbours two planets: TOI-1288 b and TOI-1288 c. We combine TESS space-borne and ground-based transit photometry with HARPS-N and HIRES high-precision Doppler measurements, which we use to constrain the masses of both planets in the system and the radius of planet b. TOI-1288~b has a period of $2.699835_{-0.000003}^{+0.000004}$ d, a radius of $5.24\pm 0.09$ R${}_{\oplus }$, and a mass of $42\pm 3$ M${}_{\oplus }$, making this planet a hot transiting super-Neptune situated right in the Neptunian desert. This desert refers to a paucity of Neptune-sized planets on short period orbits. Our 2.4-year-long Doppler monitoring of TOI-1288 revealed the presence of a Saturn-mass planet on a moderately eccentric orbit ($0.13_{-0.09}^{+0.07}$) with a minimum mass of $84\pm 7$ M${}_{\oplus }$ and a period of $443_{-13}^{+11}$ d. The 5 sectors worth of TESS data do not cover our expected mid-transit time for TOI-1288 c, and we do not detect a transit for this planet in these sectors.

16 pages, 17 figures, under review MNRAS