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Abstract: We investigate the estimation of orbital parameters by least-$\chi^2$Keplerian fits to radial velocity RV data using synthetic data sets. We findthat while the fitted period is fairly accurate, the best-fit eccentricity and$M p\sin i$ are systematically biased upward from the true values for lowsignal-to-noise ratio $K-\sigma\lesssim 3$ and moderate number of observations$N { m obs}\lesssim 60$, leading to a suppression of the number of nearlycircular orbits. Assuming intrinsic distributions of orbital parameters, wegenerate a large number of mock RV data sets and study the selection effect onthe eccentricity distribution. We find the overall detection efficiency onlymildly decreases with eccentricity. This is because although high eccentricityorbits are more difficult to sample, they also have larger RV amplitudes forfixed planet mass and orbital semi-major axis. Thus the primary source ofuncertainties in the eccentricity distribution comes from biases in Keplerianfits to detections with low-amplitude and-or small $N { m obs}$, rather thanfrom selection effects. Our results suggest that the abundance oflow-eccentricity exoplanets may be underestimated in the current sample and weurge caution in interpreting the eccentricity distributions of low-amplitudedetections in future RV samples.

Author: Yue Shen 1, Edwin L. Turner 1,2 1 Princeton 2 IPMU

Source: https://arxiv.org/

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