Molecular line-transition lists are an essential ingredient for radiative-transfer calculations. With recent databases now surpassing the billion-line mark, handling them has become computationally ...prohibitive, due to both the required processing power and memory. Here I present a temperature-dependent algorithm to separate strong from weak line transitions, reformatting the large majority of the weaker lines into a cross-section data file, and retaining the detailed line-by-line information of the fewer strong lines. For any given molecule over the 0.3-30 m range, this algorithm reduces the number of lines to a few million, enabling faster radiative-transfer computations without a significant loss of information. The final compression rate depends on how densely populated the spectrum is. I validate this algorithm by comparing Exomol's HCN extinction-coefficient spectra between the complete (65 million line transitions) and compressed (7.7 million) line lists. Over the 0.6-33 m range, the average difference between extinction-coefficient values is less than 1%. A Python/C implementation of this algorithm is open-source and available at https://github.com/pcubillos/repack. So far, this code handles the Exomol and HITRAN line-transition format.
ABSTRACT
We present the open-source python Radiative-transfer in a Bayesian framework (pyrat bay) framework for exoplanet atmospheric modelling, spectral synthesis, and Bayesian retrieval. The ...modular design of the code allows the users to generate atmospheric 1D parametric models of the temperature, abundances (in thermochemical equilibrium or constant-with-altitude), and altitude profiles (in hydrostatic equilibrium); sample ExoMol and HITRAN line-by-line cross-sections with custom resolving power and line-wing cutoff values; compute emission or transmission spectra considering cross-sections from molecular line transitions, collision-induced absorption, Rayleigh scattering, grey clouds, and alkali resonance lines; and perform Markov chain Monte Carlo atmospheric retrievals for a given transit or eclipse data set. We benchmarked the pyrat bay framework by reproducing line-by-line sampling of ExoMol cross-sections, producing transmission and emission spectra consistent with petitradtrans models, accurately retrieving the atmospheric properties of simulated transmission and emission observations generated with taurex models, and closely reproducing aura retrieval analyses of the space-based transmission spectrum of HD 209458 b. Finally, we present a retrieval analysis of a population of transiting exoplanets, focusing on those observed in transmission with the HST WFC3/G141 grism. We found that this instrument alone can confidently identify when a data set shows H2O-absorption features; however, it cannot distinguish whether a muted H2O feature is caused by clouds, high atmospheric metallicity, or low H2O abundance. Our results are consistent with previous retrieval analyses. The pyrat bay code is available at PyPI (pip install pyratbay) and conda. The code is heavily documented (https://pyratbay.readthedocs.io) and tested to provide maximum accessibility to the community and long-term development stability.
The James Webb Space Telescope (JWST) is expected to revolutionize the field of exoplanets. The broad wavelength coverage and the high sensitivity of its instruments will allow characterization of ...exoplanetary atmospheres with unprecedented precision. Following the Call for the Cycle 1 Early Release Science Program, the Transiting Exoplanet Community was awarded time to observe several targets, including WASP-43b. The atmosphere of this hot Jupiter has been intensively observed but still harbors some mysteries, especially concerning the day-night temperature gradient, the efficiency of the atmospheric circulation, and the presence of nightside clouds. We will constrain these properties by observing a full orbit of the planet and extracting its spectroscopic phase curve in the 5-12 m range with JWST/MIRI. To prepare for these observations, we performed extensive modeling work with various codes: radiative transfer, chemical kinetics, cloud microphysics, global circulation models, JWST simulators, and spectral retrieval. Our JWST simulations show that we should achieve a precision of 210 ppm per 0.1 m spectral bin on average, which will allow us to measure the variations of the spectrum in longitude and measure the nightside emission spectrum for the first time. If the atmosphere of WASP-43b is clear, our observations will permit us to determine if its atmosphere has an equilibrium or disequilibrium chemical composition, eventually providing the first conclusive evidence of chemical quenching in a hot Jupiter atmosphere. If the atmosphere is cloudy, a careful retrieval analysis will allow us to identify the cloud composition.
ABSTRACT
High-resolution Doppler-resolved spectroscopy has opened up a new window into the atmospheres of both transiting and non-transiting exoplanets. Here, we present VLT/UVES observations of a ...transit of WASP-121b, an ‘ultra-hot’ Jupiter previously found to exhibit a temperature inversion and detections of multiple species at optical wavelengths. We present initial results using the blue arm of UVES (≈3700–5000 Å), recovering a clear signal of neutral Fe in the planet’s atmosphere at >8$\, \sigma$, which could contribute to (or even fully explain) the temperature inversion in the stratosphere. However, using standard cross-correlation methods, it is difficult to extract physical parameters such as temperature and abundances. Recent pioneering efforts have sought to develop likelihood ‘mappings’ that can be used to directly fit models to high-resolution data sets. We introduce a new framework that directly computes the likelihood of the model fit to the data, and can be used to explore the posterior distribution of parametrised model atmospheres via MCMC techniques. Our method also recovers the physical extent of the atmosphere, as well as account for time- and wavelength-dependent uncertainties. We measure a temperature of $3710^{+490}_{-510}$ K, indicating a higher temperature in the upper atmosphere when compared to low-resolution observations. We also show that the Fe i signal is physically separated from the exospheric Fe ii. However, the temperature measurements are highly degenerate with aerosol properties; detection of additional species, using more sophisticated atmospheric models, or combining these methods with low-resolution spectra should help break these degeneracies.
The atmospheres of gaseous giant exoplanets orbiting close to their parent stars (hot Jupiters) have been probed for nearly two decades
. They allow us to investigate the chemical and physical ...properties of planetary atmospheres under extreme irradiation conditions
. Previous observations of hot Jupiters as they transit in front of their host stars have revealed the frequent presence of water vapour
and carbon monoxide
in their atmospheres; this has been studied in terms of scaled solar composition
under the usual assumption of chemical equilibrium. Both molecules as well as hydrogen cyanide were found in the atmosphere of HD 209458b
, a well studied hot Jupiter (with equilibrium temperature around 1,500 kelvin), whereas ammonia was tentatively detected there
and subsequently refuted
. Here we report observations of HD 209458b that indicate the presence of water (H
O), carbon monoxide (CO), hydrogen cyanide (HCN), methane (CH
), ammonia (NH
) and acetylene (C
H
), with statistical significance of 5.3 to 9.9 standard deviations per molecule. Atmospheric models in radiative and chemical equilibrium that account for the detected species indicate a carbon-rich chemistry with a carbon-to-oxygen ratio close to or greater than 1, higher than the solar value (0.55). According to existing models relating the atmospheric chemistry to planet formation and migration scenarios
, this would suggest that HD 209458b formed far from its present location and subsequently migrated inwards
. Other hot Jupiters may also show a richer chemistry than has been previously found, which would bring into question the frequently made assumption that they have solar-like and oxygen-rich compositions.
Abstract
Ultraviolet observations of ultrahot Jupiters, exoplanets with temperatures over 2000 K, provide us with an opportunity to investigate if and how atmospheric escape shapes their upper ...atmosphere. Near-ultraviolet transit spectroscopy offers a unique tool to study this process owing to the presence of strong metal lines and a bright photospheric continuum as the light source against which the absorbing gas is observed. WASP-189b is one of the hottest planets discovered to date, with a dayside temperature of about 3400 K orbiting a bright A-type star. We present the first near-ultraviolet observations of WASP-189b, acquired with the Colorado Ultraviolet Transit Experiment (CUTE). CUTE is a 6U NASA-funded ultraviolet spectroscopy mission, dedicated to monitoring short-period transiting planets. WASP-189b was one of the CUTE early science targets and was observed during three consecutive transits in 2022 March. We present an analysis of the CUTE observations and results demonstrating near-ultraviolet (2500–3300 Å) broadband transit depth (
1.08
−
0.08
+
0.08
%
) of about twice the visual transit depth indicating that the planet has an extended, hot upper atmosphere with a temperature of about 15,000 K and a moderate mass-loss rate of about 4 × 10
8
kg s
−1
. We observe absorption by Mg
ii
lines (
R
p
/
R
s
of
0.212
−
0.061
+
0.038
) beyond the Roche lobe at >4
σ
significance in the transmission spectrum at a resolution of 10 Å, while at lower resolution (100 Å), we observe a quasi-continuous absorption signal consistent with a “forest” of low-ionization metal absorption dominated by Fe
ii
. The results suggest an upper atmospheric temperature (∼15,000 K), higher than that predicted by current state-of-the-art hydrodynamic models.
The Saturn-mass exoplanet WASP-39b has been the subject of extensive efforts to determine its atmospheric properties using transmission spectroscopy
. However, these efforts have been hampered by ...modelling degeneracies between composition and cloud properties that are caused by limited data quality
. Here we present the transmission spectrum of WASP-39b obtained using the Single-Object Slitless Spectroscopy (SOSS) mode of the Near Infrared Imager and Slitless Spectrograph (NIRISS) instrument on the JWST. This spectrum spans 0.6-2.8 μm in wavelength and shows several water-absorption bands, the potassium resonance doublet and signatures of clouds. The precision and broad wavelength coverage of NIRISS/SOSS allows us to break model degeneracies between cloud properties and the atmospheric composition of WASP-39b, favouring a heavy-element enhancement ('metallicity') of about 10-30 times the solar value, a sub-solar carbon-to-oxygen (C/O) ratio and a solar-to-super-solar potassium-to-oxygen (K/O) ratio. The observations are also best explained by wavelength-dependent, non-grey clouds with inhomogeneous coverageof the planet's terminator.
Abstract
Photochemistry is a fundamental process of planetary atmospheres that regulates the atmospheric composition and stability
1
. However, no unambiguous photochemical products have been ...detected in exoplanet atmospheres so far. Recent observations from the JWST Transiting Exoplanet Community Early Release Science Program
2,3
found a spectral absorption feature at 4.05 μm arising from sulfur dioxide (SO
2
) in the atmosphere of WASP-39b. WASP-39b is a 1.27-Jupiter-radii, Saturn-mass (0.28
M
J
) 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 SO
2
in such an atmosphere is through photochemical processes
5,6
. Here we show that the SO
2
distribution computed by a suite of photochemical models robustly explains the 4.05-μm spectral feature identified by JWST transmission observations
7
with NIRSpec PRISM (2.7
σ
)
8
and G395H (4.5
σ
)
9
. SO
2
is produced by successive oxidation of sulfur radicals freed when hydrogen sulfide (H
2
S) is destroyed. The sensitivity of the SO
2
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 SO
2
also shows observable features at ultraviolet and thermal infrared wavelengths not available from the existing observations.
Measuring the abundances of carbon and oxygen in exoplanet atmospheres is considered a crucial avenue for unlocking the formation and evolution of exoplanetary systems
. Access to the chemical ...inventory of an exoplanet requires high-precision observations, often inferred from individual molecular detections with low-resolution space-based
and high-resolution ground-based
facilities. Here we report the medium-resolution (R ≈ 600) transmission spectrum of an exoplanet atmosphere between 3 and 5 μm covering several absorption features for the Saturn-mass exoplanet WASP-39b (ref.
), obtained with the Near Infrared Spectrograph (NIRSpec) G395H grating of JWST. Our observations achieve 1.46 times photon precision, providing an average transit depth uncertainty of 221 ppm per spectroscopic bin, and present minimal impacts from systematic effects. We detect significant absorption from CO
(28.5σ) and H
O (21.5σ), and identify SO
as the source of absorption at 4.1 μm (4.8σ). Best-fit atmospheric models range between 3 and 10 times solar metallicity, with sub-solar to solar C/O ratios. These results, including the detection of SO
, underscore the importance of characterizing the chemistry in exoplanet atmospheres and showcase NIRSpec G395H as an excellent mode for time-series observations over this critical wavelength range
.
ABSTRACT
The exoplanet WASP-12b is the prototype for the emerging class of ultrahot, Jupiter-mass exoplanets. Past models have predicted – and near-ultraviolet observations have shown – that this ...planet is losing mass. We present an analysis of two sets of 3.6 and 4.5 $\mu \rm{m}$Spitzer phase curve observations of the system which show clear evidence of infrared radiation from gas stripped from the planet, and the gas appears to be flowing directly toward or away from the host star. This accretion signature is only seen at 4.5 $\mu \rm{m}$, not at 3.6 $\mu \rm{m}$, which is indicative either of CO emission at the longer wavelength or blackbody emission from cool, ≲600 K gas. It is unclear why WASP-12b is the only ultrahot Jupiter to exhibit this mass-loss signature, but perhaps WASP-12b’s orbit is decaying as some have claimed, while the orbits of other exoplanets may be more stable; alternatively, the high-energy irradiation from WASP-12A may be stronger than the other host stars. We also find evidence for phase offset variability at the level of 6.4σ (46.2°) at 3.6 $\mu \rm{m}$.
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