The NASA-UC Eta-Earth Program: I. A Super-Earth Orbiting HD 7924

TL;DR

This paper reports the discovery of a super-Earth orbiting HD 7924, using radial velocity measurements, and confirms its planetary nature through photometry, contributing to understanding low-mass planet formation.

Contribution

First low-mass planet discovered by the NASA-UC Eta-Earth Program, demonstrating detection methods and characterizing a super-Earth in a short orbit.

Findings

Detected a super-Earth with 9.26 M_Earth in 5.398-day orbit

Confirmed the planet's existence with high statistical significance

No transits detected down to 0.5 mmag limit

Abstract

We report the discovery of the first low-mass planet to emerge from the NASA-UC Eta-Earth Program, a super-Earth orbiting the K0 dwarf HD 7924. Keplerian modeling of precise Doppler radial velocities reveals a planet with minimum mass M_P sin i = 9.26 M_Earth in a P = 5.398 d orbit. Based on Keck-HIRES measurements from 2001 to 2008, the planet is robustly detected with an estimated false alarm probability of less than 0.001. Photometric observations using the Automated Photometric Telescopes at Fairborn Observatory show that HD 7924 is photometrically constant over the radial velocity period to 0.19 mmag, supporting the existence of the planetary companion. No transits were detected down to a photometric limit of ~0.5 mmag, eliminating transiting planets with a variety of compositions. HD 7924b is one of only eight planets known with M_P sin i < 10 M_Earth and as such is a member of an emerging family of low-mass planets that together constrain theories of planet formation.