32 research outputs found
A parallel algorithm for Hamiltonian matrix construction in electron-molecule collision calculations: MPI-SCATCI
Construction and diagonalization of the Hamiltonian matrix is the
rate-limiting step in most low-energy electron -- molecule collision
calculations. Tennyson (J Phys B, 29 (1996) 1817) implemented a novel algorithm
for Hamiltonian construction which took advantage of the structure of the
wavefunction in such calculations. This algorithm is re-engineered to make use
of modern computer architectures and the use of appropriate diagonalizers is
considered. Test calculations demonstrate that significant speed-ups can be
gained using multiple CPUs. This opens the way to calculations which consider
higher collision energies, larger molecules and / or more target states. The
methodology, which is implemented as part of the UK molecular R-matrix codes
(UKRMol and UKRMol+) can also be used for studies of bound molecular Rydberg
states, photoionisation and positron-molecule collisions.Comment: Write up of a computer program MPI-SCATCI Computer Physics
Communications, in pres
ExoMol molecular line lists - XVII The rotation-vibration spectrum of hot SO
Sulphur trioxide (SO) is a trace species in the atmospheres of the Earth
and Venus, as well as well as being an industrial product and an environmental
pollutant. A variational line list for SO, named UYT2, is
presented containing 21 billion vibration-rotation transitions. UYT2 can be
used to model infrared spectra of SO at wavelengths longwards of 2 m
( cm) for temperatures up to 800 K. Infrared absorption
cross sections are also recorded at 300 and 500 C are used to validate the UYT2
line list. The intensities in UYT2 are scaled to match the measured cross
sections. The line list is made available in electronic form as supplementary
data to this article and at \url{www.exomol.com}.Comment: 15 pages, 10 figures, 9 tables MNRAS submitte
Disentangling Atmospheric Compositions of K2-18 b with Next Generation Facilities
Recent analysis of the planet K2-18b has shown the presence of water vapour
in its atmosphere. While the H2O detection is significant, the Hubble Space
Telescope (HST) WFC3 spectrum suggests three possible solutions of very
different nature which can equally match the data. These solutions include a
primary cloudy atmosphere with traces of water vapour and a secondary
atmosphere with a substantial amount of H2O and/or an undetectable gas such as
N2. Additionally, the atmospheric pressure and the possible presence of a
liquid/solid surface cannot be investigated with currently available
observations. In this paper we used the best fit parameters from Tsiaras et al.
(2019) to build JWST and Ariel simulations of the three scenarios. We have
investigated 18 retrieval cases, which encompass the three scenarios and
different observational strategies with the two observatories. Retrieval
results show that twenty combined transits should be enough for the Ariel
mission to disentangle the three scenarios, while JWST would require only two
transits if combining NIRISS and NIRSpec data. This makes K2-18b an ideal
target for atmospheric follow-ups by both facilities and highlights the
capabilities of the next generation of space-based infrared observatories to
provide a complete picture of low gravity planets.Comment: 12 pages, 12 figure
KELT-11 b: Abundances of water and constraints on carbon-bearing molecules from the Hubble transmission spectrum
In the past decade, the analysis of exoplanet atmospheric spectra has
revealed the presence of water vapour in almost all the planets observed, with
the exception of a fraction of overcast planets. Indeed, water vapour presents
a large absorption signature in the wavelength coverage of the Hubble Space
Telescope's (HST) Wide Field Camera 3 (WFC3), which is the main space-based
observatory for atmospheric studies of exoplanets, making its detection very
robust. However, while carbon-bearing species such as methane, carbon monoxide
and carbon dioxide are also predicted from current chemical models, their
direct detection and abundance characterisation has remained a challenge. Here
we analyse the transmission spectrum of the puffy, clear hot-Jupiter KELT-11 b
from the HST WFC3 camera. We find that the spectrum is consistent with the
presence of water vapor and an additional absorption at longer wavelengths than
1.5um, which could well be explained by a mix of carbon bearing molecules. CO2,
when included is systematically detected. One of the main difficulties to
constrain the abundance of those molecules is their weak signatures across the
HST WFC3 wavelength coverage, particularly when compared to those of water.
Through a comprehensive retrieval analysis, we attempt to explain the main
degeneracies present in this dataset and explore some of the recurrent
challenges that are occurring in retrieval studies (e.g: the impact of model
selection, the use of free vs self-consistent chemistry and the combination of
instrument observations). Our results make this planet an exceptional example
of chemical laboratory where to test current physical and chemical models of
hot-Jupiters' atmospheres.Comment: 24 pages, 14 figures, Accepted in A
Quantemol Electron Collisions (QEC): An Enhanced Expert System for Performing Electron Molecule Collision Calculations Using the R-Matrix Method
Collisions of low energy electrons with molecules are important for understanding many aspects of the environment and technologies. Understanding the processes that occur in these types of collisions can give insights into plasma etching processes, edge effects in fusion plasmas, radiation damage to biological tissues and more. A radical update of the previous expert system for computing observables relevant to these processes, Quantemol-N, is presented. The new Quantemol Electron Collision (QEC) expert system simplifyies the user experience, improving reliability and implements new features. The QEC graphical user interface (GUI) interfaces the Molpro quantum chemistry package for molecular target setups, and the sophisticated UKRmol+ codes to generate accurate and reliable cross-sections. These include elastic cross-sections, super elastic cross-sections between excited states, electron impact dissociation, scattering reaction rates, dissociative electron attachment, differential cross-sections, momentum transfer cross-sections, ionization cross sections, and high energy electron scattering cross-sections. With this new interface we will be implementing dissociative recombination estimations, vibrational excitations for neutrals and ions, and effective core potentials in the near future
Exploring the Ability of HST WFC3 G141 to Uncover Trends in Populations of Exoplanet Atmospheres Through a Homogeneous Transmission Survey of 70 Gaseous Planets
We present the analysis of the atmospheres of 70 gaseous extrasolar planets
via transit spectroscopy with Hubble's Wide Field Camera 3 (WFC3). For over
half of these, we statistically detect spectral modulation which our retrievals
attribute to molecular species. Among these, we use Bayesian Hierarchical
Modelling to search for chemical trends with bulk parameters. We use the
extracted water abundance to infer the atmospheric metallicity and compare it
to the planet's mass. We also run chemical equilibrium retrievals, fitting for
the atmospheric metallicity directly. However, although previous studies have
found evidence of a mass-metallicity trend, we find no such relation within our
data. For the hotter planets within our sample, we find evidence for thermal
dissociation of dihydrogen and water via the H opacity. We suggest that the
general lack of trends seen across this population study could be due to i) the
insufficient spectral coverage offered by HST WFC3 G141, ii) the lack of a
simple trend across the whole population, iii) the essentially random nature of
the target selection for this study or iv) a combination of all the above. We
set out how we can learn from this vast dataset going forward in an attempt to
ensure comparative planetology can be undertaken in the future with facilities
such as JWST, Twinkle and Ariel. We conclude that a wider simultaneous spectral
coverage is required as well as a more structured approach to target selection.Comment: Accepted for publication in ApJ
Exploring the Ability of Hubble Space Telescope WFC3 G141 to Uncover Trends in Populations of Exoplanet Atmospheres through a Homogeneous Transmission Survey of 70 Gaseous Planets
We present analysis of the atmospheres of 70 gaseous extrasolar planets via transit spectroscopy with Hubble’s Wide Field Camera 3 (WFC3). For over half of these, we statistically detect spectral modulation that our retrievals attribute to molecular species. Among these, we use Bayesian hierarchical modeling to search for chemical trends with bulk parameters. We use the extracted water abundance to infer the atmospheric metallicity and compare it to the planet’s mass. We also run chemical equilibrium retrievals, fitting for the atmospheric metallicity directly. However, although previous studies have found evidence of a mass–metallicity trend, we find no such relation within our data. For the hotter planets within our sample, we find evidence for thermal dissociation of dihydrogen and water via the H− opacity. We suggest that the general lack of trends seen across this population study could be due to (i) the insufficient spectral coverage offered by the Hubble Space Telescope’s WFC3 G141 band, (ii) the lack of a simple trend across the whole population, (iii) the essentially random nature of the target selection for this study, or (iv) a combination of all the above. We set out how we can learn from this vast data set going forward in an attempt to ensure comparative planetology can be undertaken in the future with facilities such as the JWST, Twinkle, and Ariel. We conclude that a wider simultaneous spectral coverage is required as well as a more structured approach to target selection