Maximum Angular Separation Epochs for Exoplanet Imaging Observations

TL;DR

This paper develops methods to determine optimal observation times for exoplanet imaging by calculating maximum angular separation epochs, improving planning for direct imaging missions.

Contribution

It introduces analytical expressions for star-planet angular separation and strategies to refine ephemerides for better observation scheduling.

Findings

Derived formulas for maximum angular separation as a function of true anomaly.

Calculated uncertainties in maximum separation timing for known exoplanets.

Proposed methods to improve ephemerides for upcoming imaging missions.

Abstract

Direct imaging of exoplanets presents both significant challenges and significant gains. The advantages primarily lie in receiving emitted and, with future instruments, reflected photons at phase angles not accessible by other techniques, enabling the potential for atmospheric studies and the detection of rotation and surface features. The challenges are numerous and include coronagraph development and achieving the necessary contrast ratio. Here, we address the specific challenge of determining epochs of maximum angular separation for the star and planet. We compute orbital ephemerides for known transiting and radial velocity planets, taking Keplerian orbital elements into account. We provide analytical expressions for angular star--planet separation as a function of the true anomaly, including the locations of minimum and maximum. These expressions are used to calculate uncertainties for maximum angular separation as a function of time for the known exoplanets, and we provide strategies for improving ephemerides with application to proposed and planned imaging missions.