Ultra Short Period Planets in K2 with companions: a double transiting system for EPIC 220674823

TL;DR

This paper reports the discovery of a double transiting planetary system around EPIC 220674823, featuring an ultra-short-period planet and a longer-period companion, providing insights into the formation of extreme planetary systems.

Contribution

It presents the first detailed characterization of a system with an ultra-short-period planet accompanied by another planet, expanding understanding of such rare systems.

Findings

First ultra-short-period planet with a companion in K2 data.

Follow-up observations show no stellar companions.

System adds to the small sample of similar extreme systems.

Abstract

Two transiting planets have been identified orbiting K2 target EPIC 220674823. One object is an ultra-short-period planet (USP) with a period of just 0.57 days (13.7 hours), while the other has a period of 13.3 days. Both planets are small, with the former having a radius of R_p1=1.5 R_E and the latter R_p2=2.5 R_E. Follow-up observations, including radial velocity (with uncertainties of 110 m/s) and high-resolution adaptive optics imagery, show no signs of stellar companions. EPIC 220674823 is the 12th confirmed or validated planetary system in which an ultra-short-period planet (i.e., having an orbital period less than 1 day) is accompanied by at least one additional planet, suggesting that such systems may be common and must be accounted for in models for the formation and evolution of such extreme systems.