101 research outputs found
ExoGAN: Retrieving Exoplanetary Atmospheres Using Deep Convolutional Generative Adversarial Networks
Atmospheric retrievals on exoplanets usually involve computationally
intensive Bayesian sampling methods. Large parameter spaces and increasingly
complex atmospheric models create a computational bottleneck forcing a
trade-off between statistical sampling accuracy and model complexity. It is
especially true for upcoming JWST and ARIEL observations. We introduce ExoGAN,
the Exoplanet Generative Adversarial Network, a new deep learning algorithm
able to recognise molecular features, atmospheric trace-gas abundances and
planetary parameters using unsupervised learning. Once trained, ExoGAN is
widely applicable to a large number of instruments and planetary types. The
ExoGAN retrievals constitute a significant speed improvement over traditional
retrievals and can be used either as a final atmospheric analysis or provide
prior constraints to subsequent retrieval.Comment: 19 pages, 17 figures, 7 table
A new look at Spitzer primary transit observations of the exoplanet HD189733b
Blind source separation techniques are used to reanalyse two exoplanetary
transit lightcurves of the exoplanet HD189733b recorded with the IR camera IRAC
on board the Spitzer Space Telescope at 3.6m during the "cold" era. These
observations, together with observations at other IR wavelengths, are crucial
to characterise the atmosphere of the planet HD189733b. Previous analyses of
the same datasets reported discrepant results, hence the necessity of the
reanalyses. The method we used here is based on the Independent Component
Analysis (ICA) statistical technique, which ensures a high degree of
objectivity. The use of ICA to detrend single photometric observations in a
self-consistent way is novel in the literature. The advantage of our reanalyses
over previous work is that we do not have to make any assumptions on the
structure of the unknown instrumental systematics. Such "admission of
ignorance" may result in larger error bars than reported in the literature, up
to a factor . This is a worthwhile trade-off for much higher objectivity,
necessary for trustworthy claims. Our main results are (1) improved and robust
values of orbital and stellar parameters, (2) new measurements of the transit
depths at 3.6m, (3) consistency between the parameters estimated from the
two observations, (4) repeatability of the measurement within the photometric
level of in the IR, (5) no evidence of stellar
variability at the same photometric level within 1 year.Comment: 43 pages, 18 figure
Non-Local thermal equilibrium spectra of atmospheric molecules for exoplanets
Here we present a study of non-LTE effects on the exoplanetary spectra of a
collection of molecules which are key in the investigation of exoplanet
atmospheres: water, methane, carbon monoxide and titanium oxide. These
molecules are chosen as examples of different spectral ranges (IR and UV),
molecular types (diatomics and polyatomics) and spectral types (electronic and
ro-vibrational); the importance of different vibrational bands in forming
distinct non-LTE spectral features are investigated. Most notably, such key
spectral signatures for distinguishing between the LTE and non-LTE cases
include: for CH4 the 3.15 m band region; for H2O the 2.0 m and 2.7
m band regions; for TiO, a strong variation in intensity in the bands
between 0.5 and 0.75 m; and a sole CO signature between 5 and 6 m.
The analysis is based on the ExoMol cross sections and takes advantage of the
extensive vibrational assignment of these molecular line lists in the ExoMol
database. We examine LTE and non-LTE cross sections under conditions consistent
with those on WASP-12b and WASP-76b using the empirically motivated
bi-temperature Treanor model. In addition, we make a simplistic forward model
simulation of transmission spectra for H2O in the atmosphere of WASP-12b using
the TauREx 3 atmospheric modelling code
Blind extraction of an exoplanetary spectrum through Independent Component Analysis
Blind-source separation techniques are used to extract the transmission
spectrum of the hot-Jupiter HD189733b recorded by the Hubble/NICMOS instrument.
Such a 'blind' analysis of the data is based on the concept of independent
component analysis. The de-trending of Hubble/NICMOS data using the sole
assumption that nongaussian systematic noise is statistically independent from
the desired light-curve signals is presented. By not assuming any prior, nor
auxiliary information but the data themselves, it is shown that spectroscopic
errors only about 10 - 30% larger than parametric methods can be obtained for
11 spectral bins with bin sizes of ~0.09 microns. This represents a reasonable
trade-off between a higher degree of objectivity for the non-parametric methods
and smaller standard errors for the parametric de-trending. Results are
discussed in the light of previous analyses published in the literature. The
fact that three very different analysis techniques yield comparable spectra is
a strong indication of the stability of these results.Comment: ApJ accepte
Non-Local thermal equilibrium spectra of atmospheric molecules for exoplanets
Here we present a study of non-LTE effects on the exoplanetary spectra of a
collection of molecules which are key in the investigation of exoplanet
atmospheres: water, methane, carbon monoxide and titanium oxide. These
molecules are chosen as examples of different spectral ranges (IR and UV),
molecular types (diatomics and polyatomics) and spectral types (electronic and
ro-vibrational); the importance of different vibrational bands in forming
distinct non-LTE spectral features are investigated. Most notably, such key
spectral signatures for distinguishing between the LTE and non-LTE cases
include: for CH4 the 3.15 m band region; for H2O the 2.0 m and 2.7
m band regions; for TiO, a strong variation in intensity in the bands
between 0.5 and 0.75 m; and a sole CO signature between 5 and 6 m.
The analysis is based on the ExoMol cross sections and takes advantage of the
extensive vibrational assignment of these molecular line lists in the ExoMol
database. We examine LTE and non-LTE cross sections under conditions consistent
with those on WASP-12b and WASP-76b using the empirically motivated
bi-temperature Treanor model. In addition, we make a simplistic forward model
simulation of transmission spectra for H2O in the atmosphere of WASP-12b using
the TauREx 3 atmospheric modelling code.Comment: Accepted for publication in MNRA
PyLightcurve-torch: a transit modelling package for deep learning applications in PyTorch
We present a new open source python package, based on PyLightcurve and
PyTorch, tailored for efficient computation and automatic differentiation of
exoplanetary transits. The classes and functions implemented are fully
vectorised, natively GPU-compatible and differentiable with respect to the
stellar and planetary parameters. This makes PyLightcurve-torch suitable for
traditional forward computation of transits, but also extends the range of
possible applications with inference and optimisation algorithms requiring
access to the gradients of the physical model. This endeavour is aimed at
fostering the use of deep learning in exoplanets research, motivated by an ever
increasing amount of stellar light curves data and various incentives for the
improvement of detection and characterisation techniques.Comment: 7 pages, 3 figures; submission status updated, fig 2 caption adde
Impact of planetary mass uncertainties on exoplanet atmospheric retrievals
In current models used to interpret exoplanet atmospheric observations, the
planet mass is treated as a prior and is estimated independently with external
methods, such as RV or TTV techniques. This approach is necessary as available
spectroscopic data do not have sufficient wavelength coverage and/or SNR to
infer the planetary mass. We examine here the impact of mass uncertainties on
spectral retrieval analyses for a host of atmospheric scenarios. Our approach
is both analytical and numerical: we first use simple approximations to extract
analytically the influence of each parameter to the wavelength-dependent
transit depth. We then adopt a fully Bayesian retrieval model to quantify the
propagation of the mass uncertainty onto other atmospheric parameters. We found
that for clear-sky, gaseous atmospheres the posterior distributions are the
same when the mass is known or retrieved. The retrieved mass is very accurate,
with a precision of more than 10%, provided the wavelength coverage and S/N are
adequate. When opaque clouds are included in the simulations, the uncertainties
in the retrieved mass increase, especially for high altitude clouds. However
atmospheric parameters such as the temperature and trace-gas abundances are
unaffected by the knowledge of the mass. Secondary atmospheres are more
challenging due to the higher degree of freedom for the atmospheric main
component, which is unknown. For broad wavelength range and adequate SNR, the
mass can still be retrieved accurately and precisely if clouds are not present,
and so are all the other atmospheric/planetary parameters. When clouds are
added, we find that the mass uncertainties may impact substantially the
retrieval of the mean molecular weight: an independent characterisation of the
mass would therefore be helpful to capture/confirm the main atmospheric
constituent.Comment: 19 pages, 12 figures, Accepted in Ap
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