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J/A+A/616/A39       Power-2 limb-darkening law from STAGGER-grid  (Maxted, 2018)

Comparison of the power-2 limb-darkening law from the STAGGER-grid to Kepler light curves of transiting exoplanets. Maxted P.F.L. <Astron. Astrophys. 616, A39 (2018)> =2018A&A...616A..39M (SIMBAD/NED BibCode)
ADC_Keywords: Binaries, eclipsing ; Stars, normal ; Models, atmosphere Keywords: techniques: photometric - binaries: eclipsing - stars: fundamental parameters 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, Iλ(µ)=1-c(1-µα), has recently been proposed as a good compromise between complexity and precision in the treatment of limb-darkening. My aim is to develop a practical implementation of the power-2 limb-darkening law and to quantify the accuracy of this implementation. 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 Iλ(µ) values. I use the transformed parameters h1=1-c(1-2(-α)) and h2=c2(-α) 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 h1 and h2 resulting from the light curve analysis are found to be much less strongly correlated than the PPDs for c and α. The agreement between the computed and observed values of (h1, h2) 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 h1 and h2 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 h1 and h2 based on my analysis of the Kepler light curves of 16 stars transiting exoplanets. Description: The power-2 limb-darkening law can be recommended for the analysis of light curves for transiting exoplanet systems and binary stars for stars with Teff, logg and [Fe/H] within the model grid range studied here. Tabulations of the parameters of the power-2 limb-darkening law have been provided and tested against very high-quality observations of transiting exoplanet systems obtained with Kepler. These observations have been used to quantify the uncertainties in the parameters h1 and h2 for dwarf stars with [Fe/H]≥0 showing weak magnetic activity. There may be a small bias in the computed values of h1 and h2 compared to the best-fit values for magneticically active stars, but this needs further investigation. Further work is also needed to quantify the uncertainties in h1 and h2 for metal poor stars and red giants. File Summary:
FileName Lrecl Records Explanations
ReadMe 80 . This file table1.dat 89 2800 Specific intensity as function of mu table2.dat 41 2800 Optimized power-2 limb-darkening law parameters
See also: J/A+A/573/A90 : STAGGER-grid of 3D stellar models. IV. (Magic+, 2015) Byte-by-byte Description of file: table1.dat
Bytes Format Units Label Explanations
1- 2 A2 --- X Bandpass 4- 9 F6.1 K Teff Effective temperature 11- 13 F3.1 [cm/s2] logg Logarithm of surface gravity 15- 18 F4.1 --- [Fe/H] Metallicity [Fe/H] 20- 22 F3.1 --- I(0.00) Specific intensity Iλ(µ=0.00) 24- 29 F6.4 --- I(0.01) Specific intensity Iλ(µ=0.01) 31- 36 F6.4 --- I(0.05) Specific intensity Iλ(µ=0.05) 38- 43 F6.4 --- I(0.10) Specific intensity Iλ(µ=0.10) 45- 50 F6.4 --- I(0.20) Specific intensity Iλ(µ=0.20) 52- 57 F6.4 --- I(0.30) Specific intensity Iλ(µ=0.30) 59- 64 F6.4 --- I(0.50) Specific intensity Iλ(µ=0.50) 66- 71 F6.4 --- I(0.70) Specific intensity Iλ(µ=0.70) 73- 78 F6.4 --- I(0.80) Specific intensity Iλ(µ=0.80) 80- 85 F6.4 --- I(0.90) Specific intensity Iλ(µ=0.90) 87- 89 F3.1 --- I(1.00) Specific intensity Iλ(µ=1.00)
Byte-by-byte Description of file: table2.dat
Bytes Format Units Label Explanations
1- 2 A2 --- X Bandpass 4- 9 F6.1 K Teff Effective temperature 11- 13 F3.1 [cm/s2] logg Logarithm of surface gravity 15- 18 F4.1 --- [Fe/H] Metallicity [Fe/H] 20- 24 F5.3 --- c c parameter 26- 30 F5.3 --- alpha α parameter 32- 36 F5.3 --- h1 h1 (=1-c(1-2(-α)) parameter 38- 41 F4.2 --- h2 h2 (=c2(-α) parameter
Acknowledgements: Pierre F.L. Maxted, p.maxted(at)keele.ac.uk
(End) Pierre F.L. Maxted [Univ. Keele], Patricia Vannier [CDS] 25-Apr-2018
The document above follows the rules of the Standard Description for Astronomical Catalogues.From this documentation it is possible to generate f77 program to load files into arrays or line by line

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