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L. Moore

Publications and source records attributed to L. Moore.

5 recordsLinked to original sources
arXiv2020

ExoMol line lists -- XL. Ro-vibrational molecular line list for the hydronium ion (H$_3$O$^+$)

A new line list for hydronium (H$_3$$^{16}$O$^+$) is computed. The line list is based on a new ab initio dipole moment surface (CCSD(T)/aug-cc-pVQZ) and a new empirical potential energy surface (PES). The empirical PES of H$_3$O$^+$ was obtained by refining an ab initio surface through a global fit to the experimentally determined ro-vibrational energies collected from the literature covering the ground, $\nu_1^{\pm}$, $\nu_2^{\pm}$, $2\nu_2^{\pm}$, $\nu_3^{\pm}$ and $\nu_4^{\pm}$ vibrational states. The line list covers the wavenumber range up to 10 000 cm$^{-1}$ (wavelengths $>1 \mu$m) and should be complete for temperatures up to $T=1500$ K. This is the first comprehensive line list for H$_3$O$^+$ with extensive wavenumber coverage and accurate transitional probabilities. Prospects of detection of hydronium in spectra of solar system giant planets as well as exoplanets are discussed. The eXeL line list is publicly available from the ExoMol and CDS databases.

astro-ph.EP↗
arXiv2019

Modelling H$_{3}^{+}$ in planetary atmospheres: effects of vertical gradients on observed quantities

Since its discovery in the aurorae of Jupiter ~30 years ago, the H$_{3}^{+}$ ion has served as an invaluable probe of giant planet upper atmospheres. However, the vast majority of monitoring of planetary H$_{3}^{+}$ radiation has followed from observations that rely on deriving parameters from column-integrated paths through the emitting layer. Here, we investigate the effects of density and temperature gradients along such paths on the measured H$_{3}^{+}$ spectrum and its resulting interpretation. In a non-isothermal atmosphere, H$_{3}^{+}$ column densities retrieved from such observations are found to represent a lower limit, reduced by 20% or more from the true atmospheric value. Global simulations of Uranus' ionosphere reveal that measured H$_{3}^{+}$ temperature variations are often attributable to well-understood solar zenith angle effects rather than indications of real atmospheric variability. Finally, based on these insights, a preliminary method of deriving vertical temperature structure is demonstrated at Jupiter using model reproductions of electron density and H$_{3}^{+}$ measurements. The sheer diversity and uncertainty of conditions in planetary atmospheres prohibits this work from providing blanket quantitative correction factors; nonetheless, we illustrate a few simple ways in which the already formidable utility of H$_{3}^{+}$ observations in understanding planetary atmospheres can be enhanced.

astro-ph.EP↗
arXiv2019

The Machine Learning Landscape of Top Taggers

Based on the established task of identifying boosted, hadronically decaying top quarks, we compare a wide range of modern machine learning approaches. Unlike most established methods they rely on low-level input, for instance calorimeter output. While their network architectures are vastly different, their performance is comparatively similar. In general, we find that these new approaches are extremely powerful and great fun.

hep-ph↗
arXiv2017

The quest for H$_3^+$ at Neptune: deep burn observations with NASA IRTF iSHELL

Emission from the molecular ion H$_3^+$ is a powerful diagnostic of the upper atmosphere of Jupiter, Saturn, and Uranus, but it remains undetected at Neptune. In search of this emission, we present near-infrared spectral observations of Neptune between 3.93 and 4.00 $\mu$m taken with the newly commissioned iSHELL instrument on the NASA Infrared Telescope Facility in Hawaii, obtained 17-20 August 2017. We spent 15.4 h integrating across the disk of the planet, yet were unable to unambiguously identify any H$_3^+$ line emissions. Assuming a temperature of 550 K, we derive an upper limit on the column integrated density of $1.0^{+1.2}_{-0.8}\times10^{13}$ m$^{-2}$, which is an improvement of 30\% on the best previous observational constraint. This result means that models are over-estimating the density by at least a factor of 5, highlighting the need for renewed modelling efforts. A potential solution is strong vertical mixing of polyatomic neutral species from Neptune's upper stratosphere to the thermosphere, reacting with H$_3^+$, thus greatly reducing the column integrated H$_3^+$ densities. This upper limit also provide constraints on future attempts at detecting H$_3^+$ using the James Webb Space Telescope.

astro-ph.EP↗