Maximum Angular Separation Epochs for Exoplanet Imaging Observations

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.

Transits of Known Planets Orbiting a Naked-eye Star

“…The ancillary science includes investigations of the radius gap, evaporation scenarios, and the structure of planets that span the planetary radius gap (Mousis et al 2020). Furthermore, the relative proximity of the RV systems makes them attractive targets for direct imaging surveys that aim to directly detect the known planets (Kane 2013;Kane et al 2018;Kopparapu et al 2018). Thus, when planets in RV systems are also found to transit their host star, they become truly exceptional in the scope of possible science, particularly when multiple planets are found to transit in the same system.…”

Science Extraction from TESS Observations of Known Exoplanet Hosts

“…At the current time, it remains unknown if many of the radial velocity (RV) detected exoplanets transit their host stars. Since these host stars are relatively bright, they provide numerous opportunities for detailed characterization of the systems, such as transmission spectroscopy, orbital dynamics, and potential targets for future imaging missions (Winn & Fabrycky 2015;Kane et al 2018;Batalha et al 2019). The detection of transits for known planets has been discussed in detail (Kane 2007;Hill et al 2020), including the transit probabilities of such planets (Kane & von Braun 2008;Stevens & Gaudi 2013).…”

TESS Asteroseismology of the Known Red-giant Host Stars HD 212771 and HD 203949

“…Furthermore, the evolution of orbits as stars move off the main sequence depends on the stellar mass and radius, as these relate to the mass loss relative to the progenitor (Damiani & Mathis 2018). Additionally, the angular size of the host star will be invaluable information when considering known systems as potential direct imaging targets (Kane et al 2018). Finally, accurate stellar radii for evolved stars will greatly improve transit probability estimates.…”