Extrasolar Binary Planets. Ii. Detectability by Transit Observations

Abstract

We discuss the detectability of gravitationally bounded pairs of gas-giant planets (which we call "binary planets") in extrasolar planetary systems that are formed through orbital instability followed by planet-planet dynamical tides during their close encounters, based on the results of N-body simulations by Ochiai, Nagasawa and Ida (Paper I). Paper I showed that the formation probability of a binary is as much as ∼ 10% for three giant planet systems that undergo orbital instability, and after post-capture long-term tidal evolution, the typical binary separation is 3-5 times the sum of physical radii of the planets. The binary planets are stable during main sequence lifetime of solar-type stars, if the stellarcentric semimajor axis of the binary is larger than 0.3 AU. We show that detecting modulations of transit light curves is the most promising observational method to detect binary planets. Since the likely binary separations are comparable to the stellar diameter, the shape of the transit light curve is different from transit to transit, depending on the phase of the binary's orbit. The transit durations and depth for binary planet transits are generally longer and deeper than those for the single planet case. We point out that binary planets could exist among the known inflated gas giant planets or objects classified as false positive detections at orbital radii 0.3 AU, propose a binary planet explanation for the CoRoT candidate SRc01 E2 1066, and show that binary planets are likely to be present in, and could be detected using Kepler-quality data.

Liberating exomoons in white dwarf planetary systems

“…In the Solar system, centaurs, Main Belt asteroids, Jupiter trojans, and trans-Neptunian objects have all been observed to contain moons. Also, although not yet observed, double planets may form through close encounters (Ochiai, Nagasawa & Ida 2014;Lewis et al 2015). Further, moons of moons of planets may be formed through a similar mechanism.…”

The initial mass function in the extended ultraviolet disc of M83

“…Usually studies of resolved stellar populations assume a universal IMF (e.g. that of Kroupa 2001, also known as the Kroupa IMF) and solve for the SFH (relatively recent examples include Gogarten et al 2009;Weisz et al 2011Weisz et al , 2013Annibali et al 2013;Lianou & Cole 2013;Meschin et al 2014;Lewis et al 2015). Instead, we adopt a plausible recent SFH of constant rate star formation and solve for the IMF.…”

Detecting and Characterizing Exomoons and Exorings

“…One particularly interesting candidate object is CoRoT SRc01 E2 1066, which shows a peculiar bump near the center of the transit light curve that might be induced by the mutual eclipse of a transiting binary planet system (Lewis et al 2015), i.e., a giant planet with a very large and massive satellite. However, only one single transit of this object (or these two objects) has been observed, and so it is currently impossible to discriminate between a binary planet and a star-spot crossing interpretation of the data.…”

“…This is a particularly interesting method, since the mutual eclipses of two transiting planets have already been observed (de Wit et al 2016). Yet, in the latter case, the two planets were known to exist prior to the observation of their common transit, whereas for a detection of an exomoon through mutual eclipses it would be necessary to test the data against a possible origin from star-spot crossings of the planet (Lewis et al 2015) and to use an independent method for validation.…”