Jonathan Horner

Jonathan Horner
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Jonathan Horner

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Earth and Planetary Astrophysics (35)
Solar and Stellar Astrophysics (11)
Cosmology and Nongalactic Astrophysics (6)
General Relativity and Quantum Cosmology (3)
High Energy Physics - Phenomenology (2)
Astrophysics (2)
Instrumentation and Methods for Astrophysics (2)
High Energy Physics - Theory (2)
Physics - Physics and Society (1)
Astrophysics of Galaxies (1)

Publications Authored By Jonathan Horner

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. Read More

Affiliations: 1UNSW, 2USyd, 3MPIA, 4RSAA/ANU, 5RSAA, 6AAO, 7MPIA/Uppsala, 8MPIA, 9UNSW, 10RSAA, 11USyd, 12IoA, 13AAO, 14RSAA, 15USyd, 16RSAA, 17Macquarie, 18Ljubljana, 19Macquarie, 20Macquarie, 21Notre Dame, 22RSAA, 23RSAA, 24USQ, 25USyd, 26U Western Sydney/AAO, 27UWA, 28USyd, 29RSAA, 30USyd, 31UNSW, 32AAO, 33UNSW

The Galactic Archaeology with HERMES (GALAH) Survey is a massive observational project to trace the Milky Way's history of star formation, chemical enrichment, stellar migration and minor mergers. Using high-resolution (R$\simeq$28,000) spectra taken with the High Efficiency and Resolution Multi-Element Spectrograph (HERMES) instrument at the Anglo-Australian Telescope (AAT), GALAH will determine stellar parameters and abundances of up to 29 elements for up to one million stars. Selecting targets from a colour-unbiased catalogue built from 2MASS, APASS and UCAC4 data, we expect to observe dwarfs at 0. Read More

In recent years, the striking gender imbalance in the physical sciences has been a topic for much debate. National bodies and professional societies in the astronomical and space sciences are now taking active steps to understand and address this imbalance. In order to begin this process in the Australian Space Research community, we must first understand the current state of play. Read More

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. Read More

The Neptune Trojans are the most recent addition to the panoply of Solar system small body populations. The orbit of the first discovered member, 2001 QR$_{322}$, was investigated shortly after its discovery, based on early observations of the object, and it was found to be dynamically stable on timescales comparable to the age of the Solar system. As further observations were obtained of the object over the following years, the best-fit solution for its orbit changed. Read More

We report the discovery of two giant planets orbiting the K giant HD 33844 based on radial velocity data from three independent campaigns. The planets move on nearly circular orbits with semimajor axes $a_b=1.60\pm$0. Read More

The bispectrum of single-field inflationary trajectories in which the speed of sound of the inflationary trajectories $c_s$ is constant but not equal to the speed of light $c=1$ is explored. The trajectories are generated as random realisations of the Hubble Slow-Roll (HSR) hierarchy and the bispectra are calculated using numerical techniques that extends previous work. This method allows for out-of-slow-roll models with non-trivial time dependence and arbitrarily low $c_s$. Read More

In this work we present the results of a suite of dynamical simulations following the orbital evolution of 8,022 hypothetical Centaur objects. These Centaurs begin our integrations on orbits in the vicinity of the 2:1 mean motion resonance with Neptune, and we follow their dynamical evolution for a period of 3 Myr under the gravitational influence of a motionless Sun and the four Jovian planets. The great majority of the test particles studied rapidly escaped from the vicinity of the 2:1 mean motion resonance of Neptune and diffused throughout the Solar System. Read More

Precise radial velocities from the Anglo-Australian Telescope confirm the presence of a rare short-period planet around the K0 giant HD 121056. An independent two-planet solution using the AAT data shows that the inner planet has P=89.1+/-0. Read More

We have investigated the dynamical stability of the proposed companions orbiting the Algol type short-period eclipsing binary SW Lyncis (Kim et al. 2010). The two candidate companions are of stellar to sub-stellar nature, and were inferred from timing measurements of the system's primary and secondary eclipses. Read More

The simplest interpretation of the Bicep2 result is that the scalar primordial power spectrum is slightly suppressed at large scales. These models result in a large tensor-to-scalar ratio $r$. In this work we show that the type of inflationary trajectory favoured by Bicep2 also leads to a larger non-Gaussian signal at large scales, roughly an order of magnitude larger than a standard slow-roll trajectory. Read More

We report the detection of GJ 832c, a super-Earth orbiting near the inner edge of the habitable zone of GJ 832, an M dwarf previously known to host a Jupiter analog in a nearly-circular 9.4-year orbit. The combination of precise radial-velocity measurements from three telescopes reveals the presence of a planet with a period of 35. Read More

In this work we revisit the proposed multi-circumbinary system RZ Dra. We find the proposed system to be highly unstable. We attempt to find a best-fit light-travel time model rendering the orbits to follow stable orbits. Read More

In coming years, the first truly Earth-like planets will be discovered orbiting other stars, and the search for signs of life on these worlds will begin. However, such observations will be hugely time-consuming and costly, and so it will be important to determine which of those planets represent the best prospects for life elsewhere. One of the key factors in such a decision will be the climate variability of the planet in question - too chaotic a climate might render a planet less promising as a target for our initial search for life elsewhere. Read More

In the last few years, a number of planets have been proposed to orbit several post main-sequence binary star systems on the basis of observed variations in the timing of eclipses between the binary components. A common feature of these planet candidates is that the best-fit orbits are often highly eccentric, such that the multiple planet systems proposed regularly feature mutually crossing orbits - a scenario that almost always leads to unstable planetary systems. In this work, we present the results of dynamical studies of all multiple-planet systems proposed to orbit these highly evolved binary stars, finding that most do not stand up to dynamical scrutiny. Read More

We report the discovery of two long-period giant planets from the Anglo-Australian Planet Search. HD 154857c is in a multiple-planet system, while HD 114613b appears to be solitary. HD 114613b has an orbital period P=10. Read More

We present a detailed dynamical analysis of the orbital stability of the BD +20 2457 system, which features planets or brown dwarfs moving on relatively eccentric orbits. We find that the system exhibits strong dynamical instability on astronomically short timescales across a wide range of plausible orbital eccentricities, semi-major axes, and inclinations. If the system truly hosts massive planets or brown dwarfs, our results suggest that they must move on orbits significantly different to those proposed in the discovery work. Read More

We use the Hamilton--Jacobi formalism to constrain the space of possible single field, inflationary Hubble flow trajectories when compared to the WMAP and Planck satellites Cosmic Microwave Background (CMB) results. This method yields posteriors on the space of Hubble Slow Roll (HSR) parameters that uniquely determine the history of the Hubble parameter during the inflating epoch. The trajectories are used to numerically determine the observable primordial power spectrum and bispectra that can then be compared to observations. Read More

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. Read More

In this work we carry out an analysis of the observed times of primary and secondary eclipses of the post-common envelope binary NSVS14256825. Recently, \cite{Almeida2013} proposed that two circumbinary companions orbit this short-period eclipsing binary, in order to explain observed variations in the timing of mutual eclipses between the two binary components. Using a standard weighted least-squares minimisation technique, we have extensively explored the topology of $\chi^2$ parameter space of a single planet model. Read More

We carry out a numerical calculation of the bispectrum in generalised trajectories of canonical, single--field inflation. The trajectories are generated in the Hamilton-Jacobi (HJ) formalism based on Hubble Slow Roll (HSR) parameters. The calculation allows generally shape and scale dependent bispectra, or dimensionless $f_{NL}$, in the out-of-slow-roll regime. Read More

Recent observations of the NN Serpentis post-common envelope binary system have revealed eclipse timing variations that have been attributed to the presence of two Jovian-mass exoplanets. Under the assumption that these planets are real and survived from the binary's Main Sequence state, we reconstruct initial binaries that give rise to the present NN Ser configuration and test the dynamical stability of the original system. Under standard assumptions about binary evolution, we find that survival of the planets through the entire Main Sequence life-time is very unlikely. Read More

In recent years, a number of planetary systems have been proposed to orbit evolved binary star systems. The presence of planets is invoked to explain observed variations in the timing of mutual eclipses between the primary and secondary components of the binary star system. The planets recently proposed orbiting the cataclysmic variable system QS Virginis are the latest in this on-going series of "extreme planets". Read More

Determining the orbital eccentricity of an extrasolar planet is critically important for understanding the system's dynamical environment and history. However, eccentricity is often poorly determined or entirely mischaracterized due to poor observational sampling, low signal-to-noise, and/or degeneracies with other planetary signals. Some systems previously thought to contain a single, moderate-eccentricity planet have been shown, after further monitoring, to host two planets on nearly-circular orbits. Read More

The Hamilton-Jacobi (HJ) approach for exploring inflationary trajectories is employed in the generation of generalised inflationary non-Gaussian signals arising from single field inflation. Scale dependent solutions for $f_{NL}$ are determined via the numerical integration of the three--point function in the curvature perturbation. This allows the full exploration of single field inflationary dynamics in the out-of-slow-roll regime and opens up the possibility of using future observations of non-Gaussianity to constraint the inflationary potential using model-independent methods. Read More

As a direct result of ongoing efforts to detect more exoplanetary systems, an ever-increasing number of multiple-planet systems are being announced. But how many of these systems are truly what they seem? In many cases, such systems are announced solely on the basis of orbital fits to observational data, and no attempt is made to see whether the proposed orbits are actually dynamically feasible. As a result, it is certain that planetary systems are being announced that involve planets moving on orbits that would be dynamically unstable on timescales of just a few hundred years. Read More

The details of the Solar system's formation are still heavily debated. Questions remain about the formation locations of the giant planets, and the degree to which volatile material was mixed throughout the proto-planetary system. One diagnostic which offers great promise in helping to unravel the history of planet formation is the study of the level of deuteration in various Solar system bodies. Read More

We present a detailed dynamical analysis of the orbital stability of the two circumbinary planets recently proposed to orbit the evolved eclipsing binary star system NSVS 14256825. As is the case for other recently proposed circumbinary planetary systems detected through the timing of mutual eclipses between the central binary stars, the proposed planets do not stand up to dynamical scrutiny. The proposed orbits for the two planets are extremely unstable on timescales of less than a thousand years, regardless of the mutual inclination between the planetary orbits. Read More

It is now accepted that the Solar system's youth was a dynamic and chaotic time. The giant planets migrated significant distances to reach their current locations, and evidence of that migration's influence on the Solar system abounds. That migration's pace, and the distance over which it occurred, is still heavily debated. Read More

The abilities of radial velocity exoplanet surveys to detect the lowest-mass extra-solar planets are currently limited by a combination of instrument precision, lack of data, and "jitter". Jitter is a general term for any unknown features in the noise, and reflects a lack of detailed knowledge of stellar physics (asteroseismology, starspots, magnetic cycles, granulation, and other stellar surface phenomena), as well as the possible underestimation of instrument noise. We study an extensive set of radial velocities for the star HD 10700 ($\tau$ Ceti) to determine the properties of the jitter arising from stellar surface inhomogeneities, activity, and telescope-instrument systems, and perform a comprehensive search for planetary signals in the radial velocities. Read More

We perform several suites of highly detailed dynamical simulations to investigate the architectures of the 24 Sextantis and HD 200964 planetary systems. The best fit orbital solution for the two planets in the 24 Sex system places them on orbits with periods that lie very close to 2:1 commensurability, while that for the HD 200964 system places the two planets therein in orbits whose periods lie close to a 4:3 commensurability. In both cases, the proposed best-fit orbits are mutually crossing - a scenario that is only dynamically feasible if the planets are protected from close encounters by the effects of mutual mean motion resonance. Read More

The observed properties of transiting exoplanets are an exceptionally rich source of information that allows us to understand and characterize their physical properties. Unfortunately, only a relatively small fraction of the known exoplanets discovered using the radial velocity technique are known to transit their host, due to the stringent orbital geometry requirements. For each target, the transit probability and predicted transit time can be calculated to great accuracy with refinement of the orbital parameters. Read More

We have performed a detailed dynamical study of the recently identified Neptunian Trojan 2004 KV18, only the second object to be discovered librating around Neptune's trailing Lagrange point, L5. We find that 2004 KV18 is moving on a highly unstable orbit, and was most likely captured from the Centaur population at some point in the last ~1 Myr, having originated in the Scattered Disk, beyond the orbit of Neptune. The instability of 2004 KV18 is so great that many of the test particles studied leave the Neptunian Trojan cloud within just ~0. Read More

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. Read More

The Neptune Trojans are the most recently discovered population of small bodies in the Solar System. To date, only eight have been discovered, though it is thought likely that the total population at least rivals that of the asteroid belt. Their origin is still the subject of some debate. Read More

In early 2011, the discovery of two planets moving on surprisingly extreme orbits around the eclipsing polar cataclysmic variable system HU Aquraii was announced based on variations in the timing of mutual eclipses between the two central stars. We perform a detailed dynamical analysis of the stability of the exoplanet system as proposed in that work, revealing that it is simply dynamically unfeasible. We then apply the latest rigorous methods used by the Anglo-Australian Planet Search to analyse radial velocity data to re-examine the data used to make the initial claim. Read More

Recently, the first collisional family was identified in the trans-Neptunian belt. The family consists of Haumea and at least ten other ~100km-sized trans-Neptunian objects (TNOs) located in the region a = 42 - 44.5 AU. Read More

We present results examining the fate of the Trojan clouds produced in our previous work. We find that the stability of Neptunian Trojans seems to be strongly correlated to their initial post-migration orbital elements, with those objects that survive as Trojans for billions of years displaying negligible orbital evolution. The great majority of these survivors began the integrations with small eccentricities (e < 0. Read More

Authors: Asantha Cooray, Steve Eales, Scott Chapman, David L. Clements, Olivier Dore, Duncan Farrah, Matt J. Jarvis, Manoj Kaplinghat, Mattia Negrello, Alessandro Melchiorri, Hiranya Peiris, Alexandra Pope, Mario G. Santos, Stephen Serjeant, Mark Thompson, Glenn White, Alexandre Amblard, Manda Banerji, Pier-Stefano Corasaniti, Sudeep Das, Francesco de_Bernardis, Gianfranco de_Zotti, Tommaso Giannantonio, Joaquin Gonzalez-Nuevo Gonzalez, Ali Ahmad Khostovan, Ketron Mitchell-Wynne, Paolo Serra, Yong-Seon Song, Joaquin Vieira, Lingyu Wang, Michael Zemcov, Filipe Abdalla, Jose Afonso, Nabila Aghanim, Paola Andreani, Itziar Aretxaga, Robbie Auld, Maarten Baes, Andrew Baker, Denis Barkats, R. Belen Barreiro, Nicola Bartolo, Elizabeth Barton, Sudhanshu Barway, Elia Stefano Battistelli, Carlton Baugh, Alexander Beelen, Karim Benabed, Andrew Blain, Joss Bland-Hawthorn, James~J. Bock, J. Richard Bond, Julian Borrill, Colin Borys, Alessandro Boselli, Francois R. Bouchet, Carrie Bridge, Fabrizio Brighenti, Veronique Buat, David Buote, Denis Burgarella, Robert Bussmann, Erminia Calabrese, Christopher Cantalupo, Raymond Carlberg, Carla Sofia Carvalho, Caitlin Casey, Antonio Cava, Jordi Cepa, Edward Chapin, Ranga Ram Chary, Xuelei Chen, Sergio Colafrancesco, Shaun Cole, Peter Coles, Alexander Conley, Luca Conversi, Jeff Cooke, Steven Crawford, Catherine Cress, Elisabete da Cunha, Gavin Dalton, Luigi Danese, Helmut Dannerbauer, Jonathan Davies, Paolo de Bernardis, Roland de Putter, Mark Devlin, Jose M. Diego, Herve Dole, Marian Douspis, Joanna Dunkley, James Dunlop, Loretta Dunne, Rolando Dunner, Simon Dye, George Efstathiou, Eiichi Egami, Taotao Fang, Patrizia Ferrero, Alberto Franceschini, Christopher C. Frazer, David Frayer, Carlos Frenk, Ken Ganga, Raphael Gavazzi, Jason Glenn, Yan Gong, Eduardo Gonzalez-Solares, Matt Griffin, Qi Guo, Mark Gurwell, Amir Hajian, Mark Halpern, Duncan Hanson, Martin Hardcastle, Evanthia Hatziminaoglou, Alan Heavens, Sebastien Heinis, Diego Herranz, Matt Hilton, Shirley Ho, Benne W. Holwerda, Rosalind Hopwood, Jonathan Horner, Kevin Huffenberger, David H. Hughes, John P. Hughes, Edo Ibar, Rob Ivison, Neal Jackson, Andrew Jaffe, Timothy Jenness, Gilles Joncas, Shahab Joudaki, Sugata Kaviraj, Sam Kim, Lindsay King, Theodore Kisner, Johan Knapen, Alexei Kniazev, Eiichiro Komatsu, Leon Koopmans, Chao-Lin Kuo, Cedric Lacey, Ofer Lahav, Anthony N. Lasenby, Andy Lawrence, Myung Gyoon Lee, Lerothodi L. Leeuw, Louis R. Levenson, Geraint Lewis, Nicola Loaring, Marcos Lopez-Caniego, Steve Maddox, Tobias Marriage, Gaelen Marsden, Enrique Martinez-Gonzalez, Silvia Masi, Sabino Matarrese, William G. Mathews, Shuji Matsuura, Richard McMahon, Yannick Mellier, Felipe Menanteau, Michal~J. Michalowski, Marius Millea, Bahram Mobasher, Subhanjoy Mohanty, Ludovic Montier, Kavilan Moodley, Gerald H. Moriarty-Schieven, Angela Mortier, Dipak Munshi, Eric Murphy, Kirpal Nandra, Paolo Natoli, Hien Nguyen, Seb Oliver, Alain Omont, Lyman Page, Mathew Page, Roberta Paladini, Stefania Pandolfi, Enzo Pascale, Guillaume Patanchon, John Peacock, Chris Pearson, Ismael Perez-Fournon, Pablo G. Perez-Gonz, Francesco Piacentini, Elena Pierpaoli, Michael Pohlen, Etienne Pointecouteau, Gianluca Polenta, Jason Rawlings, Erik~D. Reese, Emma Rigby, Giulia Rodighiero, Encarni Romero-Colmenero, Isaac Roseboom, Michael Rowan-Robinson, Miguel Sanchez-Portal, Fabian Schmidt, Michael Schneider, Bernhard Schulz, Douglas Scott, Chris Sedgwick, Neelima Sehgal, Nick Seymour, Blake~D. Sherwin, Jo Short, David Shupe, Jonathan Sievers, Ramin Skibba, Joseph Smidt, Anthony Smith, Daniel J. B. Smith, Matthew W. L. Smith, David Spergel, Suzanne Staggs, Jason Stevens, Eric Switzer, Toshinobu Takagi, Tsutomu Takeuchi, Pasquale Temi, Markos Trichas, Corrado Trigilio, Katherine Tugwell, Grazia Umana, William Vacca, Mattia Vaccari, Petri Vaisanen, Ivan Valtchanov, Kurt van der Heyden, Paul P. van der Werf, Eelco van_Kampen, Ludovic van_Waerbeke, Simona Vegetti, Marcella Veneziani, Licia Verde, Aprajita Verma, Patricio Vielva, Marco P. Viero, Baltasar Vila Vilaro, Julie Wardlow, Grant Wilson, Edward L. Wright, C. Kevin Xu, Min S. Yun

A large sub-mm survey with Herschel will enable many exciting science opportunities, especially in an era of wide-field optical and radio surveys and high resolution cosmic microwave background experiments. The Herschel-SPIRE Legacy Survey (HSLS), will lead to imaging data over 4000 sq. degrees at 250, 350, and 500 micron. Read More

We present a short review of the impact regime experienced by the terrestrial planets within our own Solar system, describing the three populations of potentially hazardous objects which move on orbits that take them through the inner Solar system. Of these populations, the origins of two (the Near-Earth Asteroids and the Long-Period Comets) are well understood, with members originating in the Asteroid belt and Oort cloud, respectively. By contrast, the source of the third population, the Short-Period Comets, is still under debate. Read More

The difference between the measured atmospheric abundances of neon, argon, krypton and xenon for Venus, the Earth and Mars is striking. Because these abundances drop by at least two orders of magnitude as one moves outward from Venus to Mars, the study of the origin of this discrepancy is a key issue that must be explained if we are to fully understand the different delivery mechanisms of the volatiles accreted by the terrestrial planets. In this work, we aim to investigate whether it is possible to quantitatively explain the variation of the heavy noble gas abundances measured on Venus, the Earth and Mars, assuming that cometary bombardment was the main delivery mechanism of these noble gases to the terrestrial planets. Read More

We consider the role of deuterium as a potential marker of location and ambient conditions during the formation of small bodies in our Solar system. We concentrate in particular on the formation of the regular icy satellites of Jupiter and the other giant planets, but include a discussion of the implications for the Trojan asteroids and the irregular satellites. We examine in detail the formation of regular planetary satellites within the paradigm of a circum-Jovian subnebula. Read More

We propose a scenario for the formation of the Main Belt in which asteroids incorporated icy particles formed in the outer Solar Nebula. We calculate the composition of icy planetesimals formed beyond a heliocentric distance of 5 AU in the nebula by assuming that the abundances of all elements, in particular that of oxygen, are solar. As a result, we show that ices formed in the outer Solar Nebula are composed of a mix of clathrate hydrates, hydrates formed above 50 K and pure condensates produced at lower temperatures. Read More