Importance of Eccentricities in Parameter Estimation of Compact Binary Inspirals with Decihertz Gravitational-Wave Detectors

Accurate and precise parameter estimation for compact binaries is essential for gravitational wave (GW) science. Future decihertz GW detectors, like B-DECIGO and MAGIS, are anticipated to realize exquisite precision in the parameter estimation of stellar-mass compact binaries. Most of the compact binaries are expected to have very small orbital eccentricities, but the small eccentricities can have non-negligible effects on the parameter estimation due to the high precision measurement in the detectors. Here we discuss the accuracy requirements of GW waveform models for the parameter estimation of stellar-mass eccentric binaries with B-DECIGO and MAGIS. We find that if the quasi-circular GW waveform model is used, even very small eccentricity ($\sim 10^{-4}$) existing at GW frequency $0.1\, \text{Hz}$ induces systematic errors that exceed statistical errors. We also show that eccentricity measurement in the decihertz detectors is precise enough to detect the small eccentricity ($\sim 10^{-4}$). Ignoring the high-order Post-Newtonian (PN) corrections of eccentricity effects does not make significant systematic errors. As a result, including the 2 PN corrections of the effects will be enough for the accurate eccentricity measurement.