Quasi-periodic Gaussian processes for stellar activity: From physical to kernel parameters

Article


Nicholson, B. A. and Aigrain, S. 2022. "Quasi-periodic Gaussian processes for stellar activity: From physical to kernel parameters." Monthly Notices of the Royal Astronomical Society. 515 (4), pp. 5251-5266. https://doi.org/10.1093/mnras/stac2097
Article Title

Quasi-periodic Gaussian processes for stellar activity: From physical to kernel parameters

ERA Journal ID1074
Article CategoryArticle
AuthorsNicholson, B. A. and Aigrain, S
Journal TitleMonthly Notices of the Royal Astronomical Society
Journal Citation515 (4), pp. 5251-5266
Number of Pages16
Year18 Aug 2022
PublisherOxford University Press
Place of PublicationUnited Kingdom
ISSN0035-8711
1365-2966
Digital Object Identifier (DOI)https://doi.org/10.1093/mnras/stac2097
Web Address (URL)https://academic.oup.com/mnras/article/515/4/5251/6651396
Abstract

In recent years, Gaussian Process (GP) regression has become widely used to analyse stellar and exoplanet time-series data sets. For spotted stars, the most popular GP covariance function is the quasi-periodic (QP) kernel, whose hyperparameters of the GP have a plausible interpretation in terms of physical properties of the star and spots. In this paper, we test the reliability of this interpretation by modelling data simulated using a spot model using a QP GP, and the recently proposed quasi-periodic plus cosine (QPC) GP, comparing the posterior distributions of the GP hyperparameters to the input parameters of the spot model. We find excellent agreement between the input stellar rotation period and the QP and QPC GP period, and very good agreement between the spot decay time-scale and the length scale of the squared exponential term. We also compare the hyperparameters derived from light and radial velocity (RV) curves for a given star, finding that the period and evolution time-scales are in good agreement. However, the harmonic complexity of the GP, while displaying no clear correlation with the spot properties in our simulations, is systematically higher for the RV than for the light-curve data. Finally, for the QP kernel, we investigate the impact of noise and time-sampling on the hyperparameters in the case of RVs. Our results indicate that good coverage of rotation period and spot evolution time-scales is more important than the total number of points, and noise characteristics govern the harmonic complexity.

Keywordsmethods: data analysis; techniques: photometric; techniques: radial velocities; stars: activity
ANZSRC Field of Research 2020510109. Stellar astronomy and planetary systems
Byline AffiliationsUniversity of Oxford, United Kingdom
Centre for Astrophysics
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