18 research outputs found
The impact of signal-to-noise, redshift, and angular range on the bias of weak lensing 2-point functions
Weak lensing data follow a naturally skewed distribution, implying the data
vector most likely yielded from a survey will systematically fall below its
mean. Although this effect is qualitatively known from CMB-analyses, correctly
accounting for it in weak lensing is challenging, as a direct transfer of the
CMB results is quantitatively incorrect. While a previous study (Sellentin et
al. 2018) focused on the magnitude of this bias, we here focus on the frequency
of this bias, its scaling with redshift, and its impact on the signal-to-noise
of a survey. Filtering weak lensing data with COSEBIs, we show that weak
lensing likelihoods are skewed up until , whereas
CMB-likelihoods Gaussianize already at . While
COSEBI-compressed data on KiDS- and DES-like redshift- and angular ranges
follow Gaussian distributions, we detect skewness at 6 significance for
half of a Euclid- or LSST-like data set, caused by the wider coverage and
deeper reach of these surveys. Computing the signal-to-noise ratio per data
point, we show that precisely the data points of highest signal-to-noise are
the most biased. Over all redshifts, this bias affects at least 10% of a
survey's total signal-to-noise, at high redshifts up to 25%. The bias is
accordingly expected to impact parameter inference. The bias can be handled by
developing non-Gaussian likelihoods. Otherwise, it could be reduced by removing
the data points of highest signal-to-noise.Comment: Accepted by the Open Journal of Astrophysic
Using a neural network approach to accelerate disequilibrium chemistry calculations in exoplanet atmospheres
In this era of exoplanet characterisation with JWST, the need for a fast
implementation of classical forward models to understand the chemical and
physical processes in exoplanet atmospheres is more important than ever.
Notably, the time-dependent ordinary differential equations to be solved by
chemical kinetics codes are very time-consuming to compute. In this study, we
focus on the implementation of neural networks to replace mathematical
frameworks in one-dimensional chemical kinetics codes. Using the gravity
profile, temperature-pressure profiles, initial mixing ratios, and stellar flux
of a sample of hot-Jupiters atmospheres as free parameters, the neural network
is built to predict the mixing ratio outputs in steady state. The architecture
of the network is composed of individual autoencoders for each input variable
to reduce the input dimensionality, which is then used as the input training
data for an LSTM-like neural network. Results show that the autoencoders for
the mixing ratios, stellar spectra, and pressure profiles are exceedingly
successful in encoding and decoding the data. Our results show that in 90% of
the cases, the fully trained model is able to predict the evolved mixing ratios
of the species in the hot-Jupiter atmosphere simulations. The fully trained
model is ~1000 times faster than the simulations done with the forward,
chemical kinetics model while making accurate predictions.Comment: 13 pages, 9 figures, accepted for publication at MNRA
Retrieval survey of metals in six ultra-hot Jupiters: Trends in chemistry, rain-out, ionisation and atmospheric dynamics
Ground-based high-resolution spectroscopy (HRS) has detected numerous
chemical species and atmospheric dynamics in exoplanets, most notably ultra-hot
Jupiters (UHJs). However, quantitative estimates on abundances have been
challenging but are essential for accurate comparative characterisation and to
determine formation scenarios. In this work we retrieve the atmospheres of six
UHJs (WASP-76~b, MASCARA-4~b, MASCARA-2~b, WASP-121~b, HAT-P-70~b and
WASP-189~b) with ESPRESSO and HARPS-N/HARPS observations, exploring trends in
eleven neutral species and dynamics. While Fe abundances agree well with
stellar values, Mg, Ni, Cr, Mn and V show more variation, highlighting the
difficulty in using a single species as a proxy for metallicity. We find that
Ca, Na, Ti and TiO are under-abundant, potentially due to ionisation and/or
night-side rain-out. Our retrievals also show that relative abundances between
species are more robust, consistent with previous works. We perform spatially-
and phase-resolved retrievals for WASP-76~b and WASP-121~b given their high
signal-to-noise observations, and find the chemical abundances in each of the
terminator regions are broadly consistent. We additionally constrain dynamics
for our sample through Doppler shifts and broadening of the planetary signals
during the primary eclipse, with median blue shifts between 0.9-9.0~km/s
due to day-night winds. Furthermore, we constrain spectroscopic masses for
MASCARA-2~b and HAT-P-70~b consistent with their known upper limits, but we
note that these may be biased due to degeneracies. This work highlights the
importance of future HRS studies to further probe differences and trends
between exoplanets.Comment: 26 pages, 11 figures, 5 tables, published in A
Photochemically produced SO2 in the atmosphere of WASP-39b
Photochemistry is a fundamental process of planetary atmospheres that regulates the atmospheric composition and stability1. However, no unambiguous photochemical products have been detected in exoplanet atmospheres so far. Recent observations from the JWST Transiting Exoplanet Community Early Release Science Program2,3 found a spectral absorption feature at 4.05 μm arising from sulfur dioxide (SO2) in the atmosphere of WASP-39b. WASP-39b is a 1.27-Jupiter-radii, Saturn-mass (0.28 MJ) gas giant exoplanet orbiting a Sun-like star with an equilibrium temperature of around 1,100 K (ref. 4). The most plausible way of generating SO2 in such an atmosphere is through photochemical processes5,6. Here we show that the SO2 distribution computed by a suite of photochemical models robustly explains the 4.05-μm spectral feature identified by JWST transmission observations7 with NIRSpec PRISM (2.7σ)8 and G395H (4.5σ)9. SO2 is produced by successive oxidation of sulfur radicals freed when hydrogen sulfide (H2S) is destroyed. The sensitivity of the SO2 feature to the enrichment of the atmosphere by heavy elements (metallicity) suggests that it can be used as a tracer of atmospheric properties, with WASP-39b exhibiting an inferred metallicity of about 10× solar. We further point out that SO2 also shows observable features at ultraviolet and thermal infrared wavelengths not available from the existing observations
Photochemically-produced SO in the atmosphere of WASP-39b
Photochemistry is a fundamental process of planetary atmospheres that
regulates the atmospheric composition and stability. However, no unambiguous
photochemical products have been detected in exoplanet atmospheres to date.
Recent observations from the JWST Transiting Exoplanet Early Release Science
Program found a spectral absorption feature at 4.05 m arising from SO
in the atmosphere of WASP-39b. WASP-39b is a 1.27-Jupiter-radii, Saturn-mass
(0.28 M) gas giant exoplanet orbiting a Sun-like star with an equilibrium
temperature of 1100 K. The most plausible way of generating SO in
such an atmosphere is through photochemical processes. Here we show that the
SO distribution computed by a suite of photochemical models robustly
explains the 4.05 m spectral feature identified by JWST transmission
observations with NIRSpec PRISM (2.7) and G395H (4.5). SO
is produced by successive oxidation of sulphur radicals freed when hydrogen
sulphide (HS) is destroyed. The sensitivity of the SO feature to the
enrichment of the atmosphere by heavy elements (metallicity) suggests that it
can be used as a tracer of atmospheric properties, with WASP-39b exhibiting an
inferred metallicity of 10 solar. We further point out that
SO also shows observable features at ultraviolet and thermal infrared
wavelengths not available from the existing observations.Comment: 39 pages, 14 figures, accepted to be published in Natur
Metallicity and Spectral Evolution of WASP 39b: The Limited Role of Hydrodynamic Escape
The recent observations on WASP-39 b by JWST have revealed hints of high metallicity within the atmosphere compared to its host star. There are various theories on how these high metallic atmospheres emerge. In this study, we closely investigate the impact of extreme escape in the form of hydrodynamic escape to see its impact on atmospheric metallicity and spectral features such as CH _4 , CO _2 and SO _2 . We perform a grid simulation, with an adapted version of MESA that includes hydrodynamic escape to fully evolve planets with similar masses and radii to the currently observed WASP-39 b estimates. By making use of (photo)chemical kinetics and radiative transfer codes, we evaluate the transmission spectra at various time intervals throughout the simulation. Our results indicate that the massive size of WASP-39 b limits the metal enhancement to a maximum of ∼1.23× the initial metallicity. When incorporating metal drag, this enhancement factor is repressed to an even greater degree, resulting in an enrichment of at most ∼0.4%. As a consequence, when assuming an initial solar metallicity, metal-enriched spectral features like SO _2 are still missing after ∼9 Gyr into the simulation. This paper, thus, demonstrates that hydrodynamic escape cannot be the primary process behind the high metallicity observed in the atmosphere of WASP-39 b, suggesting instead that a metal-enhanced atmosphere was established during its formation
The deep atmospheric composition of Jupiter from thermochemical calculations based on Galileo and Juno data
The deep atmosphere of Jupiter is obscured beneath thick clouds. This causes direct observations to be difficult, and thermochemical equilibrium models fill in the observational gaps. This research uses Galileo and Juno data together with the Gibbs free energy minimization code GGCHEM to update the gas phase and condensation equilibrium chemistry of the deep atmosphere of Jupiter down to 1000 bars. Specifically, the Galileo data provides helium abundances and, with the incorporated Juno data, we use new enrichment values for oxygen, nitrogen, carbon and sulphur. The temperature profile in Jupiter’s deep atmosphere is obtained following recent interior model calculations that fit the gravitational harmonics measured by Juno. Following this approach, we produced pressure–mixing ratio plots for H, He, C, N, O, Na, Mg, Si, P, S and K that give a complete chemical model of all species occurring to abundances down to a 10−20 mixing ratio. The influence of the increased elemental abundances can be directly seen in the concentration of the dominant carriers for each element: the mixing ratio of NH3 increased by a factor of 1.55 as compared with the previous literature, N2 by 5.89, H2O by 1.78, CH4 by 2.82 and H2S by 2.69. We investigate the influence of water enrichment values observed by Juno on these models and find that no liquid water clouds form at the oxygen enrichment measured by Galileo, EH2O = 0.47, while they do form at higher water abundance as measured by Juno. We update the mixing ratios of important gas phase species, such as NH3, H2O, CO, CH4 and H2S, and find that new gas phase species, such as CN−, (NaCN)2, S2O and K+, and new condensates, namely H3PO4 (s), LiCl (s), KCl (s), NaCl (s), NaF (s), MgO (s), Fe (s) and MnS (s), form in the atmosphere.Publisher PDFPeer reviewe
The interaction of energetic particles with the winds of cool stars
Energetic particles, such as stellar energetic particles and Galactic cosmic rays, are an important part of space weather for exoplanets orbiting cool stars and the young Earth. Energetic particles bombard exoplanetary atmospheres, leading to unique chemical effects that may be detectable with JWST. The flux of energetic particles reaching an exoplanet depends on the stellar wind properties which vary with stellar age, as the star spins down. This means it is important to constrain the stellar wind properties of other stars.
I will present our results which modelled the energetic particle flux reaching Earth at different ages, such as when life is thought to have begun (approximately 3.8Gyr ago). I will discuss how, at this time, our model shows that stellar energetic particles dominated over Galactic cosmic rays up to GeV energies. At these energies, energetic particles can cause particle showers in the planet atmosphere that can reach the surface of the planet. At the same time, to connect with upcoming observations we need to consider exoplanets orbiting stars with well-constrained stellar winds. For instance, the stellar mass-loss rate is important in determining the size of the astrosphere. Thus, I will also discuss our recent results for the Galactic cosmic ray fluxes reaching the habitable zone and exoplanets of a number of nearby stars. Finally, I will discuss our ongoing efforts to connect these energetic particle fluxes closely to upcoming JWST observations