The Anglo-Australian Planet Search XXIV: The Frequency of Jupiter Analogs

Robert A. Wittenmyer, et al, 'The Anglo-Australian planet search XXIV: The frequency of Jupiter analogs', The Astrophysical Journal, Vol. 819 (1), first published online 24 February 2016. The version of record is available online at doi: https://doi.org/10.3847/0004-637X/819/1/28 © 2016. The American Astronomical Society. All rights reserved.We present updated simulations of the detectability of Jupiter analogs by the 17-year Anglo-Australian Planet Search. The occurrence rate of Jupiter-like planets that have remained near their formation locations beyond the ice line is a critical datum necessary to constrain the details of planet formation. It is also vital in our quest to fully understand how common (or rare) planetary systems like our own are in the Galaxy. From a sample of 202 solar-type stars, and correcting for imperfect detectability on a star-by-star basis, we derive a frequency of ${6.2}_{-1.6}^{+2.8}$% for giant planets in orbits from 3 to 7 au. When a consistent definition of "Jupiter analog" is used, our results are in agreement with those from other legacy radial-velocity surveys.Peer reviewedFinal Published versio

Infrared Observations During the Secondary Eclipse of HD 209458 b II. Strong Limits on the Infrared Spectrum Near 2.2 Microns

We report observations of the transiting extrasolar planet, HD 209458 b, designed to detect the secondary eclipse. We employ the method of `occultation spectroscopy', which searches in combined light (star and planet) for the disappearance and reappearance of weak infrared spectral features due to the planet as it passes behind the star and reappears. Our observations cover two predicted secondary eclipse events, and we obtained 1036 individual spectra of the HD 209458 system using the SpeX instrument at the NASA IRTF in September 2001. Our spectra extend from 1.9 to 4.2 microns with a spectral resolution of 1500. We have searched for a continuum peak near 2.2 microns (caused by CO and water absorption bands), as predicted by some models of the planetary atmosphere to be approximately 6E-4 of the stellar flux, but no such peak is detected at a level of about 3E-4 of the stellar flux. Our results represent the strongest limits on the infrared spectrum of the planet to date and carry significant implications for understanding the planetary atmosphere. In particular, some models that assume the stellar irradiation is re-radiated entirely on the sub-stellar hemisphere predict a flux peak inconsistent with our observations. Several physical mechanisms can improve agreement with our observations, including the re-distribution of heat by global circulation, a nearly isothermal atmosphere, and/or the presence of a high cloud.Comment: Accepted to the Astrophysical Journal 17 pages, 6 figure

A Dynamical Analysis of the Proposed Circumbinary HW Virginis Planetary System

In 2009, the discovery of two planets orbiting the evolved binary star system HW Virginis was announced, based on systematic variations in the timing of eclipses between the two stars. The planets invoked in that work were significantly more massive than Jupiter, and moved on orbits that were mutually crossing - an architecture which suggests that mutual encounters and strong gravitational interactions are almost guaranteed. In this work, we perform a highly detailed analysis of the proposed HW Vir planetary system. First, we consider the dynamical stability of the system as proposed in the discovery work. Through a mapping process involving 91,125 individual simulations, we find that the system is so unstable that the planets proposed simply cannot exist, due to mean lifetimes of less than a thousand years across the whole parameter space. We then present a detailed re-analysis of the observational data on HW Vir, deriving a new orbital solution that provides a very good fit to the observational data. Our new analysis yields a system with planets more widely spaced, and of lower mass, than that proposed in the discovery work, and yields a significantly greater (and more realistic) estimate of the uncertainty in the orbit of the outermost body. Despite this, a detailed dynamical analysis of this new solution similarly reveals that it also requires the planets to move on orbits that are simply not dynamically feasible. Our results imply that some mechanism other than the influence of planetary companions must be the principal cause of the observed eclipse timing variations for HW Vir. If the sys- tem does host exoplanets, they must move on orbits differing greatly from those previously proposed. Our results illustrate the critical importance of performing dynamical analyses as a part of the discovery process for multiple-planet exoplanetary systems.Comment: Accepted for publication in Monthly Notices of the Royal Astronomical Societ

A Detailed Investigation of the Proposed NN Serpentis Planetary System

The post-main sequence eclipsing binary NN Serpentis was recently announced as the potential host of at least two massive planetary companions. In that work, the authors put forward two potential architectures that fit the observations of the eclipsing binary with almost identical precision. In this work, we present the results of a dynamical investigation of the orbital stability of both proposed system architectures, finding that they are only stable for scenarios in which the planets are locked in mutual mean motion resonance. In the discovery work, the authors artificially fixed the orbital eccentricity of the more massive planet, NN Ser(AB) c, at 0. Here, we reanalyse the observational data on NN Serpentis without this artificial constraint, and derive a new orbital solution for the two proposed planets. We detail the results of further dynamical simulations investigating the stability of our new orbital solution, and find that allowing a small non-zero eccentricity for the outer planet renders the system unstable. We conclude that, although the original orbits proposed for the NN Serpentis planetary system prove dynamically feasible, further observations of the system are vital in order to better constrain the system's true architecture.Comment: Accepted for publication in Monthly Notices of the Royal Astronomical Society; 5 figures, 2 table

The Anglo-Australian Planet Search XXV : A Candidate Massive Saturn Analog Orbiting HD 30177

This is an author-created, un-copyedited version of an article published in The Astronomical Journal. IOP Publishing Ltd is not responsible for any errors or omissions in this version of the manuscript or any version derived from it. The Version of Record is available online at DOI: https://doi.org/10.3847/1538-3881/aa5f17.We report the discovery of a second long-period giant planet orbiting HD 30177, a star previously known to host a massive Jupiter analog (HD 30177b: a=3.8$\pm$0.1 au, m sin $i=9.7\pm$0.5 Mjup). HD 30177c can be regarded as a massive Saturn analog in this system, with a=9.9$\pm$1.0 au and m sin $i=7.6\pm$3.1 Mjup. The formal best fit solution slightly favours a closer-in planet at $a\sim$7 au, but detailed n-body dynamical simulations show that configuration to be unstable. A shallow local minimum of longer-period, lower-eccentricity solutions was found to be dynamically stable, and hence we adopt the longer period in this work. The proposed $\sim$32 year orbit remains incomplete; further monitoring of this and other stars is necessary to reveal the population of distant gas giant planets with orbital separations $a\sim$10 au, analogous to that of Saturn.Peer reviewedFinal Accepted Versio

A detailed analysis of the HD 73526 2:1 resonant planetary system

We present six years of new radial velocity data from the Anglo-Australian and Magellan Telescopes on the HD 73526 2:1 resonant planetary system. We investigate both Keplerian and dynamical ( interacting) fits to these data, yielding four possible configurations for the system. The new data now show that both resonance angles are librating, with amplitudes of 40 degrees and 60 degrees, respectively. We then perform long-term dynamical stability tests to differentiate these solutions, which only differ significantly in the masses of the planets. We show that while there is no clearly preferred system inclination, the dynamical fit with i = 90 degrees provides the best combination of goodness-of-fit and long-term dynamical stability.Peer reviewe