ExoGemS The Effect of Offsets from True Orbital Parameters on Exoplanet High-Resolution Transmission Spectra

High-resolution spectroscopy (HRS) plays a crucial role in characterizing exoplanet atmospheres, revealing detailed information about their chemical composition, temperatures, and dynamics. However, inaccuracies in orbital parameters can affect the result of HRS analyses. In this paper, we simulated HRS observations of an exoplanet's transit to model the effects of an offset in transit midpoint or eccentricity on the resulting spectra. We derived analytical equations to relate an offset in transit midpoint or eccentricity to shifted velocities, and compared it with velocities measured from simulated HRS observations. Additionally, we compared velocity shifts in the spectrum of the ultra-hot Jupiter WASP-76b using previously reported and newly measured transit times. We found that transit midpoint offsets on the order of minutes, combined with eccentricity offsets of approximately $0.1$, lead to significant shifts in velocities, yielding measurements on the order of several kilometers per second. Thus, such uncertainties could conflate derived wind measurements.