** Pierre Maxted** p.maxted@keele.ac.uk

# Comparison of the power-2 limb-darkening law from the Stagger-grid to Kepler light curves of transiting exoplanets

## Maxted

## Authors

### Abstract

Inaccurate limb-darkening models can be a significant source of error in the analysis of the light curves for transiting exoplanet and eclipsing binary star systems, particularly for high-precision light curves at optical wavelengths. The power-2 limb-darkening law, $I_\lambda(\mu) = 1 - c\left(1-\mu^{\alpha}\right)$, has recently been proposed as a good compromise between complexity and precision in the treatment of limb-darkening. I have used synthetic spectra based on the 3D stellar atmosphere models from the Stagger-grid to compute the limb-darkening for several passbands (UBVRI, CHEOPS, TESS, Kepler, etc.). The parameters of the power-2 limb-darkening laws are optimized using a least-squares fit to a simulated light curve computed directly from the tabulated $I_\lambda(\mu)$ values. I use the transformed parameters $h_1 = 1-c\left(1-2^{-\alpha}\right)$ and $h_2 = c2^{-\alpha}$ to directly compare these optimized limb-darkening parameters to the limb darkening measured from Kepler light curves of 16 transiting exoplanet systems. The posterior probability distributions (PPDs) of the transformed parameters $h_1$ and $h_2$ resulting from the light curve analysis are found to be much less strongly correlated than the PPDs for $c$ and $\alpha$. The agreement between the computed and observed values of ($h_1$, $h_2$) is generally very good but there are significant differences between the observed and computed values for Kepler-17, the only star in the sample that shows significant variability between the eclipses due to magnetic activity (star spots). The tabulation of $h_1$ and $h_2$ provided here can be used to accurately model the light curves of transiting exoplanets. I also provide estimates of the priors that should be applied to transformed parameters $h_1$ and $h_2$ based on my analysis of the Kepler light curves of 16 stars with transiting exoplanets.

Acceptance Date | Apr 21, 2018 |
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Publication Date | Aug 10, 2018 |

Journal | Astronomy & Astrophysics |

Print ISSN | 0004-6361 |

Publisher | EDP Sciences |

Pages | A39 -? |

DOI | https://doi.org/10.1051/0004-6361/201832944 |

Keywords | techniques, photometric, binaries, eclipsing, stars, fundamental parameters |

Publisher URL | http://dx.doi.org/10.1051/0004-6361/201832944 |

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