The HD 60779 Planetary System: A Transiting Sub-Neptune on a 30-day Orbit and a More Massive Outer World

TL;DR

This paper reports the discovery and characterization of a two-planet system around the bright star HD 60779, including a transiting sub-Neptune and a more massive outer planet, highlighting its suitability for atmospheric studies.

Contribution

It presents the first detailed characterization of the HD 60779 system, including mass, radius, and orbital parameters of both planets, and identifies it as an ideal target for atmospheric escape observations.

Findings

HD 60779 b is a 3.25 Earth radii sub-Neptune with a 30-day orbit.

An outer planet, HD 60779 c, has a minimum mass of 27.7 Earth masses and a 104-day orbit.

Both planets likely have circular orbits, indicating a dynamically quiet system.

Abstract

We present the discovery of the planetary system orbiting the bright (V = 7.2), nearby (35 pc), Sun-like star HD 60779, which has a mass of 1.050 +/- 0.044 solar masses and a radius of 1.129 +/- 0.013 solar radii. We report two TESS transits and a subsequent CHEOPS transit of HD 60779 b, a sub-Neptune with a radius of 3.250 (+0.100 / -0.098) Earth radii on a 29.986175 (+0.000030 / -0.000033) day orbit. Additionally, 286 HARPS-N radial velocity measurements reveal the mass of planet b (14.7 +1.1 / -1.0 Earth masses) and the presence of an outer planet, HD 60779 c, with an orbital period of 104.25 (+0.30 / -0.29) days and a minimum mass (m sin i) of 27.7 +/- 1.6 Earth masses. Both planets' orbits are consistent with being circular, suggesting that they have a dynamically quiet history. The data are not sufficient to determine whether planet c transits. HD 60779's uniquely high systemic radial velocity (129.75 +/- 0.12 km/s) allows its Lyman-alpha emission to avoid absorption by the interstellar medium, making it a prime candidate for probing atmospheric escape from HD 60779 b. HD 60779 is also the third-brightest host of a sub-Neptune with orbital period greater than 25 days and with both mass and radius measured, distinguishing it in terms of accessibility to spectroscopic characterization.