Kepler-21b: A 1.6REarth Planet Transiting the Bright Oscillating F Subgiant Star HD 179070

TL;DR

This paper reports the discovery and characterization of a small, 1.6 Earth-radius exoplanet orbiting the bright, oscillating star HD 179070 using Kepler data, seismic analysis, and follow-up observations, confirming its planetary nature with high confidence.

Contribution

First detection of a small exoplanet transiting a bright, oscillating subgiant star with detailed asteroseismic and follow-up analysis confirming its properties.

Findings

Exoplanet has a radius of 1.64 Earth radii.

Orbital period is approximately 2.786 days.

Star's mass and radius are precisely measured via asteroseismology.

Abstract

We present Kepler observations of the bright (V=8.3), oscillating star HD 179070. The observations show transit-like events which reveal that the star is orbited every 2.8 days by a small, 1.6 R_Earth object. Seismic studies of HD 179070 using short cadence Kepler observations show that HD 179070 has a frequencypower spectrum consistent with solar-like oscillations that are acoustic p-modes. Asteroseismic analysis provides robust values for the mass and radius of HD 179070, 1.34{\pm}0.06 M{\circ} and 1.86{\pm}0.04 R{\circ} respectively, as well as yielding an age of 2.84{\pm}0.34 Gyr for this F5 subgiant. Together with ground-based follow-up observations, analysis of the Kepler light curves and image data, and blend scenario models, we conservatively show at the >99.7% confidence level (3{\sigma}) that the transit event is caused by a 1.64{\pm}0.04 R_Earth exoplanet in a 2.785755{\pm}0.000032 day orbit. The exoplanet is only 0.04 AU away from the star and our spectroscopic observations provide an upper limit to its mass of ~10 M_Earth (2-{\sigma}). HD 179070 is the brightest exoplanet host star yet discovered by Kepler.