The effect of stellar limb darkening values on the accuracy of the planet radii derived from photometric transit observations

Csizmadia, Sz.; Pasternacki, T.; Dreyer, C.; Cabrera, J.; Erikson, A.; Rauer, H.

doi:10.1051/0004-6361/201219888

Cited by 144 publications

(171 citation statements)

References 53 publications

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“…However, we identified that not taking into account stellar spots in the (individual) TLC analyses affected measurements of the limb darkening coefficients, the relative semi-major axis a/R S and the transit midtime. These results confirm findings and predictions from various authors (e.g., Silva-Válio 2010;SanchisOjeda et al 2011;Ballerini et al 2012;Tregloan-Reed et al 2013;Oshagh et al 2013b;Csizmadia et al 2013). For each simultaneous analysis, we additionally obtained three wavelength dependent r P /r S values for WASP-41b covering a range of about 6200-9200 Å.…”

Section: Discussionsupporting

confidence: 92%

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PyTranSpot: A tool for multiband light curve modeling of planetary transits and stellar spots

Juvan

Lendl

Cubillos

et al. 2018

A&A

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Several studies have shown that stellar activity features, such as occulted and non-occulted starspots, can affect the measurement of transit parameters biasing studies of transit timing variations and transmission spectra. We present PyTranSpot, which we designed to model multiband transit light curves showing starspot anomalies, inferring both transit and spot parameters. The code follows a pixellation approach to model the star with its corresponding limb darkening, spots, and transiting planet on a two dimensional Cartesian coordinate grid. We combine PyTranSpot with an MCMC framework to study and derive exoplanet transmission spectra, which provides statistically robust values for the physical properties and uncertainties of a transiting star-planet system. We validate PyTranSpot's performance by analyzing eleven synthetic light curves of four different star-planet systems and 20 transit light curves of the well-studied WASP-41b system. We also investigate the impact of starspots on transit parameters and derive wavelength dependent transit depth values for WASP-41b covering a range of 6200-9200 Å, indicating a flat transmission spectrum.

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Section: Discussionsupporting

confidence: 92%

“…We remark that for both scenarios, we excluded the TRAP-PIST (2011/03/21) light curve from the analysis. Csizmadia et al 2013). Especially starspots, which are located at the limb of the star, can bias the transit ingress (or egress) time of the planet.…”

Section: Impact Of Starspots On Transit Parametersmentioning

confidence: 99%

PyTranSpot: A tool for multiband light curve modeling of planetary transits and stellar spots

Juvan

Lendl

Cubillos

et al. 2018

A&A

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“…Kipping & Bakos (2011a) for Kepler-5b, also included in our analysis, and Sing (2010) for seven CoRoT targets. On the one hand these studies seem to suggest that it is necessary to fit the LDCs when modeling light curves, as already claimed by other authors (e.g., Southworth 2008;Csizmadia et al 2013); on the other hand, there are also objects which show good agreement with the theoretical LDCs (Bordé et al 2010) and one always has to keep in mind that the determined LDCs usually have rather large errors.…”

Section: Introductionsupporting

confidence: 58%

High-precision stellar limb-darkening measurements

Müller

Huber

Czesla

et al. 2013

A&A

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Context. Planetary transit light curves are influenced by a variety of fundamental parameters, such as the orbital geometry and the surface brightness distribution of the host star. Stellar limb darkening (LD) is therefore among the key parameters of transit modeling. In many applications, LD is presumed to be known and modeled based on synthetic stellar atmospheres. Aims. We measure LD in a sample of 38 Kepler planetary candidate host stars covering effective temperatures between 3000 K and 8900 K with a range of surface gravities from 3.8 to 4.7. In our study we compare our measurements to widely used theoretically predicted quadratic limb-darkening coefficients (LDCs) to check their validity. Methods. We carried out a consistent analysis of a unique stellar sample provided by the Kepler satellite. We performed a Markov chain Monte Carlo (MCMC) modeling of low-noise, short-cadence Kepler transit light curves, which yields reliable error estimates for the LD measurements in spite of the highly correlated parameters encountered in transit modeling. Results. Our study demonstrates that it is impossible to measure accurate LDCs by transit modeling in systems with high impact parameters (b 0.8). For the majority of the remaining sample objects, our measurements agree with the theoretical predictions, considering measurement errors and mutual discrepancies between the theoretical predictions. Nonetheless, theory systematically overpredicts our measurements of the quadratic LDC u 2 by about 0.07. Systematic errors of this order for LDCs would lead to an uncertainty on the order of 1% for the derived planetary parameters. Conclusions. We find that it is adequate to set the commonly used theoretical LDCs as fixed parameters in transit modeling. Furthermore, it is even indispensable to use theoretical LDCs in the case of transiting systems with a high impact parameter, since the host star's LD cannot be determined from their transit light curves.

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“…We note Csizmadia et al (2013) made a detailed study of the determinability of limb darkening coefficients. This study created 2000 light curves using the subroutines of Mandel & Agol (2002), assuming a circular orbit and adding levels of Gaussian noise to give different levels of signal to noise (S/N).…”

Section: Known Systemsmentioning

confidence: 99%