Signals embedded in the radial velocity noise. Periodic variations in the tau Ceti velocities

TL;DR

This study analyzes radial velocity data of tau Ceti to characterize stellar noise and search for low-mass exoplanets, using Bayesian methods to distinguish signals from stellar jitter and instrumental effects.

Contribution

It provides a comprehensive Bayesian analysis of stellar jitter in tau Ceti's radial velocities and introduces methods to better detect low-amplitude planetary signals amidst noise.

Findings

Identification of periodic variations linked to stellar activity.

Quantification of noise components affecting radial velocity measurements.

Detection limits for low-mass exoplanets around tau Ceti.

Abstract

The abilities of radial velocity exoplanet surveys to detect the lowest-mass extra-solar planets are currently limited by a combination of instrument precision, lack of data, and "jitter". Jitter is a general term for any unknown features in the noise, and reflects a lack of detailed knowledge of stellar physics (asteroseismology, starspots, magnetic cycles, granulation, and other stellar surface phenomena), as well as the possible underestimation of instrument noise. We study an extensive set of radial velocities for the star HD 10700 ($\tau$ Ceti) to determine the properties of the jitter arising from stellar surface inhomogeneities, activity, and telescope-instrument systems, and perform a comprehensive search for planetary signals in the radial velocities. We perform Bayesian comparisons of statistical models describing the radial velocity data to quantify the number of significant signals and the magnitude and properties of the excess noise in the data. We reach our goal by adding artificial signals to the "flat" radial velocity data of HD 10700 and by seeing which one of our statistical noise models receives the greatest posterior probabilities while still being able to extract the artificial signals correctly from the data. We utilise various noise components to assess properties of the noise in the data and analyse the HARPS, AAPS, and HIRES data for HD 10700 to quantify these properties and search for previously unknown low-amplitude Keplerian signals. ...