83 research outputs found
Exoplanet Research with the Stratospheric Observatory for Infrared Astronomy (SOFIA)
When the Stratospheric Observatory for Infrared Astronomy (SOFIA) was
conceived and its first science cases defined, exoplanets had not been
detected. Later studies, however, showed that optical and near-infrared
photometric and spectrophotometric follow-up observations during planetary
transits and eclipses are feasible with SOFIA's instrumentation, in particular
with the HIPO-FLITECAM and FPI+ optical and near infrared (NIR) instruments.
Additionally, the airborne-based platform SOFIA has a number of unique
advantages when compared to other ground- and space-based observatories in this
field of research. Here we will outline these theoretical advantages, present
some sample science cases and the results of two observations from SOFIA's
first five observation cycles -- an observation of the Hot Jupiter HD 189733b
with HIPO and an observation of the Super-Earth GJ 1214b with FLIPO and FPI+.
Based on these early products available to this science case, we evaluate
SOFIA's potential and future perspectives in the field of optical and infrared
exoplanet spectrophotometry in the stratosphere.Comment: Invited review chapter, accepted for publication in "Handbook of
Exoplanets" edited by H.J. Deeg and J.A. Belmonte, Springer Reference Work
EXONEST: The Bayesian Exoplanetary Explorer
The fields of astronomy and astrophysics are currently engaged in an
unprecedented era of discovery as recent missions have revealed thousands of
exoplanets orbiting other stars. While the Kepler Space Telescope mission has
enabled most of these exoplanets to be detected by identifying transiting
events, exoplanets often exhibit additional photometric effects that can be
used to improve the characterization of exoplanets. The EXONEST Exoplanetary
Explorer is a Bayesian exoplanet inference engine based on nested sampling and
originally designed to analyze archived Kepler Space Telescope and CoRoT
(Convection Rotation et Transits plan\'etaires) exoplanet mission data. We
discuss the EXONEST software package and describe how it accommodates
plug-and-play models of exoplanet-associated photometric effects for the
purpose of exoplanet detection, characterization and scientific hypothesis
testing. The current suite of models allows for both circular and eccentric
orbits in conjunction with photometric effects, such as the primary transit and
secondary eclipse, reflected light, thermal emissions, ellipsoidal variations,
Doppler beaming and superrotation. We discuss our new efforts to expand the
capabilities of the software to include more subtle photometric effects
involving reflected and refracted light. We discuss the EXONEST inference
engine design and introduce our plans to port the current MATLAB-based EXONEST
software package over to the next generation Exoplanetary Explorer, which will
be a Python-based open source project with the capability to employ third-party
plug-and-play models of exoplanet-related photometric effects.Comment: 30 pages, 8 figures, 5 tables. Presented at the 37th International
Workshop on Bayesian Inference and Maximum Entropy Methods in Science and
Engineering (MaxEnt 2017) in Jarinu/SP Brasi
An Ensemble of Bayesian Neural Networks for Exoplanetary Atmospheric Retrieval
Machine learning is now used in many areas of astrophysics, from detecting
exoplanets in Kepler transit signals to removing telescope systematics. Recent
work demonstrated the potential of using machine learning algorithms for
atmospheric retrieval by implementing a random forest to perform retrievals in
seconds that are consistent with the traditional, computationally-expensive
nested-sampling retrieval method. We expand upon their approach by presenting a
new machine learning model, \texttt{plan-net}, based on an ensemble of Bayesian
neural networks that yields more accurate inferences than the random forest for
the same data set of synthetic transmission spectra. We demonstrate that an
ensemble provides greater accuracy and more robust uncertainties than a single
model. In addition to being the first to use Bayesian neural networks for
atmospheric retrieval, we also introduce a new loss function for Bayesian
neural networks that learns correlations between the model outputs.
Importantly, we show that designing machine learning models to explicitly
incorporate domain-specific knowledge both improves performance and provides
additional insight by inferring the covariance of the retrieved atmospheric
parameters. We apply \texttt{plan-net} to the Hubble Space Telescope Wide Field
Camera 3 transmission spectrum for WASP-12b and retrieve an isothermal
temperature and water abundance consistent with the literature. We highlight
that our method is flexible and can be expanded to higher-resolution spectra
and a larger number of atmospheric parameters
An astrobiological experiment to explore the habitability of tidally locked M-dwarf planets
We present a summary of a three-year academic research proposal drafted during the Sao Paulo Advanced School of Astrobiology (SPASA) to prepare for upcoming observations of tidally locked planets orbiting M-dwarf stars. The primary experimental goal of the suggested research is to expose extremophiles from analogue environments to a modified space simulation chamber reproducing the environmental parameters of a tidally locked planet in the habitable zone of a late-type star. Here we focus on a description of the astronomical analysis used to define the parameters for this climate simulation
Parameterizing pressure-temperature profiles of exoplanet atmospheres with neural networks
Atmospheric retrievals (AR) of exoplanets typically rely on a combination of
a Bayesian inference technique and a forward simulator to estimate atmospheric
properties from an observed spectrum. A key component in simulating spectra is
the pressure-temperature (PT) profile, which describes the thermal structure of
the atmosphere. Current AR pipelines commonly use ad hoc fitting functions here
that limit the retrieved PT profiles to simple approximations, but still use a
relatively large number of parameters. In this work, we introduce a
conceptually new, data-driven parameterization scheme for physically consistent
PT profiles that does not require explicit assumptions about the functional
form of the PT profiles and uses fewer parameters than existing methods. Our
approach consists of a latent variable model (based on a neural network) that
learns a distribution over functions (PT profiles). Each profile is represented
by a low-dimensional vector that can be used to condition a decoder network
that maps to . When training and evaluating our method on two publicly
available datasets of self-consistent PT profiles, we find that our method
achieves, on average, better fit quality than existing baseline methods,
despite using fewer parameters. In an AR based on existing literature, our
model (using two parameters) produces a tighter, more accurate posterior for
the PT profile than the five-parameter polynomial baseline, while also speeding
up the retrieval by more than a factor of three. By providing parametric access
to physically consistent PT profiles, and by reducing the number of parameters
required to describe a PT profile (thereby reducing computational cost or
freeing resources for additional parameters of interest), our method can help
improve AR and thus our understanding of exoplanet atmospheres and their
habitability.Comment: Accepted for publication in Astronomy & Astrophysic
Large Interferometer For Exoplanets (LIFE): VIII. Where is the phosphine? Observing exoplanetary PH3 with a space based MIR nulling interferometer
Phosphine could be a key molecule in the understanding of exotic chemistry
happening in (exo)planetary atmospheres. While it has been detected in the
Solar System's giant planets, it has not been observed in exoplanets yet. In
the exoplanetary context however it has been theorized as a potential
biosignature molecule. The goal of our study is to identify which illustrative
science cases for PH3 chemistry are observable with a space-based mid-infrared
nulling interferometric observatory like the LIFE (Large Interferometer For
Exoplanets) concept. We identified a representative set of scenarios for PH3
detections in exoplanetary atmospheres varying over the whole dynamic range of
the LIFE mission. We used chemical kinetics and radiative transfer calculations
to produce forward models of these informative, prototypical observational
cases for LIFEsim, our observation simulator software for LIFE. In a detailed,
yet first order approximation it takes a mission like LIFE: (i) about 1h to
find phosphine in a warm giant around a G star at 10 pc, (ii) about 10 h in H2
or CO2 dominated temperate super-Earths around M star hosts at 5 pc, (iii) and
even in 100h it seems very unlikely that phosphine would be detectable in a
Venus-Twin with extreme PH3 concentrations at 5 pc. Phosphine in concentrations
previously discussed in the literature is detectable in 2 out of the 3 cases
and about an order of magnitude faster than comparable cases with JWST. We show
that there is a significant number of objects accessible for these classes of
observations. These results will be used to prioritize the parameter range for
the next steps with more detailed retrieval simulations. They will also inform
timely questions in the early design phase of a mission like LIFE and guide the
community by providing easy-to-scale first estimates for a large part of
detection space of such a mission.Comment: In press. Accepted for publication in Astrobiology on 02 November
2022. 26 pages, 5 figures and 8 table
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