Characterising 4 sub-Neptunes transiting the K dwarf TOI-1246

We report the discovery and confirmation of 4 transiting planets orbiting TOI 1246, a K dwarf (V=11.6) observed in 12 sectors of TESS. Using TESS photometry and ground-based radial velocity measurements collected on Keck/HIRES, we measure the planet masses and characterize the system. We investigate four sub-Neptune planets: TOI 1246.01 (P=18.65d, R=3.31+0.83R_Earth), TOI 1246.02 (P=4.31d, R=2.92±1.21R_Earth), TOI 1246.03 (P=5.9d, R=2.77±0.28R_Earth), and TOI 1246.04 (P=37.9d, R=3.32±1.60R_Earth) orbiting the host star. Insolation fluxes in the system range from 10.8 to 196 S_Earth. TOIs 1246.01 and 1246.04 lie near the 2:1 resonance, and the other two planets in the system (1246.02 and 1246.03) are tightly packed inner planets. While all four planets are similar in size, their masses and densities are substantially more diverse. This system is thus a particularly interesting testing ground for mass loss and formation hypotheses due to the number of planets and their varied masses.