Ten New and Updated Multiplanet Systems and a Survey of Exoplanetary Systems

Abstract

We present the latest velocities for ten multiplanet systems, including a re-analysis of archival Keck and Lick data, resulting in improved velocities that supersede our previously published measurements. We derive updated orbital fits for 10 Lick and Keck systems, including two systems (HD 11964, HD 183263) for which we provide confirmation of second planets only tentatively identified elsewhere, and two others (HD 187123 and HD 217107) for which we provide a major revision of the outer planet's orbit. We compile orbital elements from the literature to generate a catalog of the 28 published multiple-planet systems around stars within 200 pc. From this catalog we find several intriguing patterns emerging: (1) including those systems with long-term radial velocity trends, at least 28% of known planetary systems appear to contain multiple planets; (2) planets in multipleplanet systems have somewhat smaller eccentricities than single planets; and (3) the distribution of orbital distances of planets in multiplanet systems and single planets are inconsistent: single-planet systems show a pileup at P ∼ 3 days and a jump near 1 AU, while multiplanet systems show a more uniform distribution in log-period. In addition, among all planetary systems we find the following. (1) There may be an emerging, positive correlation between stellar mass and giant-planet semimajor axis. (2) Exoplanets with M sin i > 1 M Jup more massive than Jupiter have eccentricities broadly distributed across 0 < e < 0.5, while lower mass exoplanets exhibit a distribution peaked near e = 0.

On the potentially dramatic history of the super-Earth ρ 55 Cancri e

“…The results above suggest that the 55 Cancri system may exhibit a substantial inclination dispersion, but this is also a relatively unusual planetary system, as most short period Jupiters do not reside in systems of non-hierachical high multiplicity (Wright et al 2009;Steffen et al 2012). Thus, it is of interest to enquire as to the frequency of such secular resonances in compact planetary systems.…”

“…It is known that the long term stability of the terrestrial planets of our solar system is imperilled by the influence of secular gravitational interactions between Mercury, Venus and Jupiter (Laskar 1994;Batygin & Laughlin 2008;Laskar & Gastineau 2009). With the discovery of a host of extrasolar planet systems over the past twenty years, including many multiple systems (Wright et al 2009;Lissauer et al 2011a;Fabrycky et al 2014), the role of secular interactions in determining the stability and architecture of planetary systems is becoming of ever greater importance.…”

Planets, evolved stars, and how they might influence each other.

“…Johnson et al 2007;Lovis & Major 2007;Wright et al 2009). One can learn a lot from these searches regarding the planet formation mechanism around more massive stars, as they allow to extend the mass range of applicability of the Doppler techniques.…”

Exoplanet Observations

“…Currently, there are 33 well-characterized multiplanet systems and ∼30% of systems with only a single identified planet show significant evidence for multiplicity [43]. This percentage must be considered a lower limit to the frequency of multiplanet systems because of the incompleteness of surveys for lower mass and longer period planets.…”

“…One system is known with five planets (55 Cnc [44]), one is known to harbor four (µ Arae [35]), and the others harbor two or three. The orbital eccentricities in systems known to have three or more planets (median e = 0.13) are typically lower than those of planets in other systems (median e = 0.25) [43,45]. This suggests that dynamical instabilities (see Chapter 11) could play an important role in the evolution of planetary systems because the higher order multiples that survive are intrinsically more stable.…”