No Giant Planet Pileup Near 1 AU [EPA]

A pileup near 1~AU in the semimajor axis distribution of giant exoplanets has been visually identified using log-spaced distribution plots. Here we propose that looking for features in a log-spaced semimajor axis distribution of giant planets is problematic. We use the Bayesian Blocks algorithm to analyze the linear-spaced semimajor axis distribution, and find that the apparent pileup is not significant.

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A. Wise and S. Dodson-Robinson
Mon, 19 Feb 18

Comments: 3 pages, 1 figure, accepted to RNAAS Feb 8, 2018

AD Leonis: Radial velocity signal of stellar rotation or spin-orbit resonance? [EPA]

AD Leonis is a nearby magnetically active M dwarf. We find Doppler variability with a period of 2.23 days as well as photometric signals: (1) a short period signal which is similar to the radial velocity signal albeit with considerable variability; and (2) a long term activity cycle of 4070$\pm$120 days. We examine the short-term photometric signal in the available ASAS and MOST photometry and find that the signal is not consistently present and varies considerably as a function of time. This signal undergoes a phase change of roughly 0.8 rad when considering the first and second halves of the MOST data set which are separated in median time by 3.38 days. In contrast, the Doppler signal is stable in the combined HARPS and HIRES radial velocities for over 4700 days and does not appear to vary in time in amplitude, phase, period or as a function of extracted wavelength. We consider a variety of star-spot scenarios and find it challenging to simultaneously explain the rapidly varying photometric signal and the stable radial velocity signal as being caused by starspots co-rotating on the stellar surface. This suggests that the origin of the Doppler periodicity might be the gravitational tug of a planet orbiting the star in spin-orbit resonance. For such a scenario and no spin-orbit misalignment, the measured $v \sin i$ indicates an inclination angle of 15.5$\pm$2.5 deg and a planetary companion mass of 0.237$\pm$0.047 M$_{\rm Jup}$.

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M. Tuomi, H. Jones, G. Anglada-Escude, et. al.
Mon, 19 Feb 18

Comments: 19 pages (incl. example data tables), accepted for publication in AJ

A dual origin for water in carbonaceous asteroids revealed by CM chondrites [EPA]

Carbonaceous asteroids represent the principal source of water in the inner Solar System and might correspond to the main contributors for the delivery of water to Earth. Hydrogen isotopes in water-bearing primitive meteorites, e.g. carbonaceous chondrites, constitute a unique tool for deciphering the sources of water reservoirs at the time of asteroid formation. However, fine-scale isotopic measurements are required to unravel the effects of parent body processes on the pre-accretion isotopic distributions. Here we report in situ micrometer-scale analyses of hydrogen isotopes in six CM-type carbonaceous chondrites revealing a dominant deuterium-poor water component ({\delta}D = -350 +/- 40 permil) mixed with deuterium-rich organic matter. We suggest that this D-poor water corresponds to a ubiquitous water reservoir in the inner protoplanetary disk. A deuterium-rich water signature has been preserved in the least altered part of the Paris chondrite ({\delta}DParis > -69 +/- 163 permil) in hydrated phases possibly present in the CM rock before alteration. The presence of the D-enriched water signature in Paris might indicate that transfers of ice from the outer to the inner Solar System have been significant within the first million years of the Solar System history.

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L. Piani, H. Yurimoto and L. Remusat
Mon, 19 Feb 18

Comments: 20 pages, 3 figures, 2 tables

Secular dynamics of hierarchical multiple systems composed of nested binaries, with an arbitrary number of bodies and arbitrary hierarchical structure. II. External perturbations: flybys and supernovae [SSA]

We extend the formalism of a previous paper to include the effects of flybys and instantaneous perturbations such as supernovae on the long-term secular evolution of hierarchical multiple systems with an arbitrary number of bodies and hierarchy, provided that the system is composed of nested binary orbits. To model secular encounters, we expand the Hamiltonian in terms of the ratio of the separation of the perturber with respect to the barycentre of the multiple system, to the separation of the widest orbit. Subsequently, we integrate over the perturber orbit numerically or analytically. We verify our method for secular encounters, and illustrate it with an example. Furthermore, we describe a method to compute instantaneous orbital changes to multiple systems, such as asymmetric supernovae and impulsive encounters. The secular code, with implementation of the extensions described in this paper, is publicly available within AMUSE, and we provide a number of simple example scripts to illustrate its usage for secular and impulsive encounters, and asymmetric supernovae. The extensions presented in this paper are a next step toward efficiently modeling the evolution of complex multiple systems embedded in star clusters.

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A. Hamers
Mon, 19 Feb 18

Comments: Accepted for publication in MNRAS. 24 pages, 7 figures

OSSOS IX: two objects in Neptune's 9:1 resonance — implications for resonance sticking in the scattering population [EPA]

We discuss the detection in the Outer Solar System Origins Survey (OSSOS) of two objects in Neptune’s distant 9:1 mean motion resonance at semimajor axis $a\approx 130$~au. Both objects are securely resonant on 10 Myr timescales, with one securely in the 9:1 resonance’s leading asymmetric libration island and the other in either the symmetric or trailing asymmetric island. These two objects are the largest semimajor axis objects known with secure resonant classifications, and their detection in a carefully characterized survey allows for the first robust population estimate for a resonance beyond 100~au. The detection of these two objects implies a population in the 9:1 resonance of $1.1\times10^4$ objects with $H_r<8.66$ ($D \gtrsim 100$~km) on similar orbits, with 95\% confidence range of $\sim0.4-3\times10^4$. Integrations over 4 Gyr of an ensemble of clones chosen from within the orbit fit uncertainties for these objects reveal that they both have median resonance occupation timescales of $\sim1$~Gyr. These timescales are consistent with the hypothesis that these two objects originate in the scattering population but became transiently stuck to Neptune’s 9:1 resonance within the last $\sim1$~Gyr of solar system evolution. Based on simulations of a model of the current scattering population, we estimate the expected resonance sticking population in the 9:1 resonance to be 1000–5000 objects with $H_r<8.66$; this is marginally consistent with the OSSOS 9:1 population estimate. We conclude that resonance sticking is a plausible explanation for the observed 9:1 population, but we also discuss the possibility of a primordial 9:1 population, which would have interesting implications for the Kuiper belt’s dynamical history.

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K. Volk, R. Murray-Clay, B. Gladman, et. al.
Mon, 19 Feb 18

Comments: submitted to AAS journals

Single Transits and Eclipses Observed by K2 [EPA]

Photometric survey data from the Kepler mission have been used to discover and characterize thousands of transiting exoplanet and eclipsing binary (EB) systems. These discoveries have enabled empirical studies of occurrence rates which reveal that exoplanets are ubiquitous and found in a wide variety of system architectures and physical compositions. Because the detection strategy of these missions is most sensitive to short orbital periods, the vast majority of these objects reside within 1 AU of their host star. Although other detection techniques have successfully identified exoplanets at wider orbits beyond the snow lines of their respective host stars (e.g., radial velocity, microlensing, direct imaging), occurrence rates within this population remain poorly constrained. As such, identifying long period objects (LPOs) from archival Kepler and K2 data is valuable from both a statistical and theoretical standpoint, particularly for massive gas giants which are thought to heavily influence the formation and evolution dynamics of their respective systems. Here we present a catalog of 164 single transit and eclipse candidates detected during a comprehensive survey of all currently available K2 data.

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D. LaCourse and T. Jacobs
Mon, 19 Feb 18

Comments: 3 pages, 1 Table; accepted to RNAAS

Impact of Gas Giant Instabilities on Habitable Planets [EPA]

The detection of many extrasolar gas giants with high eccentricities indicates that dynamical instabilities in planetary systems are common. These instabilities can alter the orbits of gas giants as well as the orbits of terrestrial planets and therefore eject or move a habitable planet out of the habitable zone. In this work 423 simulations with 153 different hypothetical planetary systems with gas giants and terrestrial planets have been modelled to explore the orbital stability of habitable planets. The initial parameter variations include the number, distances and masses of the giant planets and the star type. Linear correlations between the initial number and the initial distances of gas giants and the survival rate of habitable planets were found. Planetary systems consisting of two giant planets are fairly benign to terrestrial planets, whereas six giant planets very often lead to a complete clearing of the habitable zone. Systems with initial distances of five Hill Radii between the giant planets have a high chance to harbour a habitable planet, although more compact systems are very destructive. The giant planet masses have a smaller impact on the stability of habitable worlds. Additionally, a link between the present-day orbit of an observed giant exoplanet and the survival rate of habitable planets was established. As a rule of thumb, observed gas giants with eccentricities higher than 0.4 and inclinations higher than 20 degrees have experienced strong planet-planet scatterings and are unlikely to have a habitable planet in its system. Furthermore, it was found that habitable planets surrounding a K or M-star have a higher survival rate than those surrounding a G-star.

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S. Seppeur
Mon, 19 Feb 18

Comments: 12 pages, 15 figures