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

TL;DR

This paper confirms a super-Earth transiting a G star with a 2.8-day orbit, and reports a potential outer planet candidate, providing insights into planetary composition and the radius valley phenomenon.

Contribution

It presents the first confirmation of a transiting super-Earth in the radius valley around HD 307842 and suggests a possible outer non-transiting planet candidate, expanding understanding of planetary system architectures.

Findings

The transiting planet has a radius of 1.93 Earth radii and a density indicating a rocky composition.

The planet is located at the lower edge of the radius valley, supporting mass loss theories.

An outer planet candidate with an estimated period between 20 and 63 days was identified.

Abstract

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+0.83/-0.82 [Earth Masses]. We also report the discovery of an additional planet candidate on an outer orbit that is most likely non-transiting. The possible periods of the planet candidate are approximately 20 to 63 days, with the corresponding RV semi-amplitudes expected to range from 3.2 to 5.4 m/s and minimum masses from 12.6 to 31.1 [Earth Masses]. The radius of the transiting planet (planet b) is 1.93+0.11/-0.09 [Earth Radii], which results in a mean density of 7.4+1.4/-1.2 g/cm^3 suggesting that TOI-784b is likely to be a rocky planet though it has a comparable radius to a sub-Neptune. We found TOI-784b is located at the lower edge of the so-called ``radius valley'' in the radius vs. 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+0.84/-0.86 degrees and <= 88.3-89.2 degrees, respectively. More RV observations are needed to determine the period and mass of the second object, and search for additional planets in this system.