CRA Cosmic Coffee: Ziqian Hong

Could there be an undetected inner planet near the stability limit in Kepler-1647?

Abstract:

Kepler-1647b  is  the  most  recently  discovered  planet  that  transits  two  stars,  e.g.,  a  circumbinary planet (CBP). Due to its large orbital separation, Kepler-1647b stands out from the rest of the Kepler CBPs, which mostly reside on much tighter orbits near the stability limit.  The large separation of  Kepler-1647b  challenges  inward  disk  migration  as a dominant  formation  pathway,  suggested  by the other Kepler CBPs.  In this paper, we consider the possibility of an undetected planet near the stability  limit  by  examining  observational  consequences  of  such  a  planet.   We  calculate  the  transit probability of the putative planet, transit timing variations (TTVs) of the known planet, and eclipsing timing variations (ETVs) of the host binary caused by the putative planet.  We find that a low mutual inclination (0.5-1.5 deg.) allows for the inner planet to hide from transit observations, even if it is close to the stability limit; and the presence of a massive (~Saturn mass) inner planet can be ruled out by TTVs.  In addition, we provide future TTV and ETV observation windows,which will further constrain possible undetected planets with lower masses near the stability limit.