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. ...
Highlights
The improving instrumental precision and the rapidly increasing number of measurements of radial velocity (RV) target stars of different surveys are enabling the discoveries of smaller planets on longer orbits in increasing numbers (e.g. Lovis et al 2011; Mayor et al 2009, 2011)
RV signals are published in the literature as received from binned data but with no information about the binning techniques used, Article published by EDP Sciences
The Sun can exhibit activity index changes at the level of 0.005 dex over long timescales (Livingston et al 2007). This suggests that HD 10700 is exhibiting some period of sustained magnetic stability, or its orientation in space is such that it appears from our vantage point that the spot patterns on the stellar surface are of very low number and do not change considerably over the baseline of the High Accuracy Radial Velocity Planet Searcher (HARPS) measurements
Summary
The improving instrumental precision and the rapidly increasing number of measurements of radial velocity (RV) target stars of different surveys are enabling the discoveries of smaller planets on longer orbits in increasing numbers (e.g. Lovis et al 2011; Mayor et al 2009, 2011). When analysing RV data, the common strategy is to bin the measurements made within, say, intervals of an hour, and use the resulting binned data as a basis of further statistical analyses The motivation for this operation is the possibility of reducing the amount of short-term noise in the data (e.g. O’Toole et al 2009). We find the best noise models for the AAPS and HIRES RVs and use them in combination with the HARPS velocities in further analyses because signals that are not detected in any of these data sets might be available from the combined set because of its greater size and better phase-coverage relative to the individual data sets.
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