A Transiting Super-Earth in the Radius Valley and an Outer Planet Candidate Around HD 307842

We report the confirmation of a TESS-discovered transiting super-Earth planet orbiting a mid-G star, HD 307842 (TOI-784). The planet has a period of 2.8 days, and the radial velocity (RV) measurements constrain the mass to be ${9.67}_{-0.82}^{+0.83}\ {M}_{\oplus }$. We also report the discovery of an additional planet candidate on an outer orbit that is most likely nontransiting. The possible periods of the planet candidate are approximately 20–63 days, with the corresponding RV semiamplitudes expected to range from 3.2 to 5.4 m s−1 and minimum masses from 12.6 to 31.1 M⊕. The radius of the transiting planet (planet b) is ${1.93}_{-0.09}^{+0.11}\ {R}_{\oplus }$, which results in a mean density of ${7.4}_{-1.2}^{+1.4}\ {\rm{g}}\,{\mathrm{cm}}^{-3}$ suggesting that TOI-784 b is likely to be a rocky planet though it has a comparable radius to a sub-Neptune. We found TOI-784 b is located at the lower edge of the so-called "radius valley" in the radius versus insolation plane, which is consistent with the photoevaporation or core-powered mass-loss prediction. The TESS data did not reveal any significant transit signal of the planet candidate, and our analysis shows that the orbital inclinations of planet b and the planet candidate are ${88.60^\circ }_{-0.86}^{+0.84}$ and ≤88fdg3–89fdg2, respectively. More RV observations are needed to determine the period and mass of the second object, and search for additional planets in this system.