Exomoons in Systems with a Strong Perturber: Applications to α Cen AB
Abstract
The presence of a stellar companion can place constraints on occurrence and orbital evolution of satellites orbiting exoplanets, i.e., exomoons. In this work we revise earlier orbital stability limits for retrograde orbits in the case of a threebody system consisting of a star, planet, and satellite. The revised limit reads ${a}_{\mathrm{sat}}^{\mathrm{crit}}\approx 0.668(11.236{e}_{{\rm{p}}})$ for e_{p} ≤ 0.8 in units of the Hill Radius and represents the lower critical orbit as a function of the planetary eccentricity e_{p}. A similar formula is determined for exomoons hosted by planets in binary star systems, where e_{p} is replaced with the components of free and forced eccentricity from secular orbit evolution theory. By exploring the dynamics of putative exomoons in α Centauri AB we find that the outer stability limit can be much less than half the Hill Radius due to oscillations in the planetary orbital eccentricity caused by the gravitational interaction with the binary star. We show, furthermore, how the resulting truncation of the outer stability limit can affect the outward tidal migration and potential observability of exomoons through transittiming variations (TTVs). Typical TTV (rms) amplitudes induced by exomoons in binary systems are ≲10 minutes and appear more likely for planets orbiting the less massive stellar component.
 Publication:

The Astronomical Journal
 Pub Date:
 August 2021
 DOI:
 10.3847/15383881/ac042a
 arXiv:
 arXiv:2105.00034
 Bibcode:
 2021AJ....162...58Q
 Keywords:

 Natural satellites (Extrasolar);
 Binary stars;
 Exoplanet tides;
 Orbits;
 Exoplanet dynamics;
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 154;
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 Astrophysics  Earth and Planetary Astrophysics
 EPrint:
 16 pages, 11 figures, 3 tables