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 ≤88.°3-89.°2, respectively. More RV observations are needed to determine the period and mass of the second object, and search for additional planets in this system.