2010ApJ...712.1003W

GU Boo is one of only a relatively small number of well-studied double-lined eclipsing binaries that contain low-mass stars. López-Morales & Ribas present a comprehensive analysis of multi-color light and radial velocity curves for this system. The GU Boo light curves presented by López-Morales & Ribas had substantial asymmetries, which were attributed to large spots. In spite of the asymmetry, López-Morales & Ribas derived masses and radii accurate to =~2%. We obtained additional photometry of GU Boo using both a CCD and a single-channel photometer and modeled the light curves with the ELC software to determine if the large spots in the light curves give rise to systematic errors at the few percent level. We also modeled the original light curves from the work of López-Morales & Ribas using models with and without spots. We derived a radius of the primary of 0.6329±0.0026 R_☉, 0.6413±0.0049 R_☉, and 0.6373±0.0029 R_☉ from the CCD, photoelectric, and López-Morales & Ribas data, respectively. Each of these measurements agrees with the value reported by López-Morales & Ribas (R₁= 0.623 ± 0.016 R_☉) at the level of ≈ 2%. In addition, the spread in these values is ≈ 1%-2% from the mean. For the secondary, we derive radii of 0.6074±0.0035 R_☉, 0.5944±0.0069 R_☉, and 0.5976 ±0.0059 R_☉ from the three respective data sets. The López-Morales & Ribas value is R₂= 0.620±0.020 R_☉, which is ≈ 2%-3% larger than each of the three values we found. The spread in these values is ≈ 2% from the mean. The systematic difference between our three determinations of the secondary radius and that of López-Morales & Ribas might be attributed to differences in the modeling process and codes used. Our own fits suggest that, for GU Boo at least, using accurate spot modeling of a single set of multi-color light curves results in radii determinations accurate at the ≈ 2% level.