Two planetary companions around the K7 dwarf GJ 221 : a hot super-Earth and a candidate in the sub-Saturn desert range

TL;DR

This paper reports the discovery of two low-mass planetary companions orbiting the nearby K7 dwarf GJ 221, including a hot super-Earth and a candidate in the sub-Saturn desert, based on re-analyzed HARPS and Magellan/PFS data.

Contribution

It presents the first detection of two low-mass planets around GJ 221, including a sub-Saturn desert candidate, demonstrating planet formation around slightly metal-poor stars.

Findings

GJ 221b: 125-day period, 53.2 Earth masses

GJ 221c: 3.87-day period, 6.5 Earth masses

Presence of low-mass planets around a metal-poor star

Abstract

We report two low mass companions orbiting the nearby K7 dwarf GJ 221 that have emerged from re-analyzing 4.4 years of publicly available HARPS spectra complemented with 2 years of high precision Doppler measurements with Magellan/PFS. The HARPS measurements alone contain the clear signal of a low mass companion with a period of 125 days and a minimum mass of 53.2 \mearth (GJ 221b), falling in a mass range where very few planet candidates have been found (sub-Saturn desert). The addition of 17 PFS observations allow the confident detection of a second low mass companion (6.5 \mearth) in a hot orbit (3.87 days period, GJ 221c). Spectrocopic and photometric calibrations suggest that GJ 221 is slightly depleted ([Fe/H]$\sim$ -0.1) compared to the Sun so the presence of two low mass companions in the system confirms the trend that slightly reduced stellar metallicity does not prevent the formation of planets in the super-Earth to sub-Saturn mass regime.