摘要：The transit technique is responsible for the majority of exoplanet discoveries to date. Characterizing these planetsinvolves careful modeling of their transit profiles. A common technique involves expressing the transit durationusing a density-like parameter, r˜, often called the “circular density.” Most notably, the Kepler project—the largestanalysis of transit light curves to date—adopted a linear prior on r˜. Here, we show that such a prior biasesmeasurements of impact parameter, b, due to the nonlinear relationship between r˜ and transit duration. This biasslightly favors low values (b 0.3) and strongly disfavors high values (b 0.7) unless the transit signal-to-noiseratio is sufficient to provide an independent constraint on b, a criterion that is not satisfied for the majority ofKepler planets. Planet-to-star radius ratio, r, is also biased due to r − b covariance. Consequently, the medianKepler DR25 target suffers a 1.6% systematic underestimate of r. We present a techniques for correcting thesebiases and for avoiding them in the first place.
