Abstract
The near-infrared transmission spectrum of the warm sub-Neptune exoplanet GJ 1214 b has been observed to be flat and featureless, implying a high metallicity atmosphere with abundant ...aerosols. Recent JWST MIRI Low Resolution Spectrometer observations of a phase curve of GJ 1214 b showed that its transmission spectrum is flat out into the mid-infrared. In this paper, we use the combined near- and mid-infrared transmission spectrum of GJ 1214 b to constrain its atmospheric composition and aerosol properties. We generate a grid of photochemical haze models using an aerosol microphysics code for a number of background atmospheres spanning metallicities from 100 to 1000× solar, as well as a steam atmosphere scenario. The flatness of the combined data set largely rules out atmospheric metallicities ≤300× solar due to their large corresponding molecular feature amplitudes, preferring values ≥1000× solar and column haze production rates ≥10
−10
g cm
−2
s
−1
. The steam atmosphere scenario with similarly high haze production rates also exhibits sufficiently small molecular features to be consistent with the transmission spectrum. These compositions imply that atmospheric mean molecular weights ≥15 g mol
−1
are needed to fit the data. Our results suggest that haze production is highly efficient on GJ 1214 b and could involve non-hydrocarbon, non-nitrogen haze precursors. Further characterization of GJ 1214 b’s atmosphere would likely require multiple transits and eclipses using JWST across the near- and mid-infrared, potentially complemented by ground-based high-resolution transmission spectroscopy.
Abstract
High-resolution spectroscopy has allowed for unprecedented levels of atmospheric characterization, especially for the hottest gas-giant exoplanets known as ultrahot Jupiters (UHJs). ...High-resolution spectra are sensitive to 3D effects, making complex 3D atmospheric models important for interpreting data. Moreover, these planets are expected to host magnetic fields that will shape their resulting atmospheric circulation patterns, but little modeling work has been done to investigate these effects. In this paper, we generate high-resolution transmission spectra from General Circulation Models for the canonical UHJ WASP-76b with three different magnetic treatments in order to understand the influence of magnetic forces on the circulation. In general, spectra from all models have increasingly blueshifted net Doppler shifts as transit progresses, but we find that the differing temperature and wind fields in the upper atmospheres of these models result in measurable differences. We find that magnetic effects may be contributing to the unusual trends previously seen in transmission for this planet. Our
B
= 3 Gauss active drag model in particular shows unique trends not found in the models with simpler or no magnetic effects. The net Doppler shifts are additionally influenced by the dominant opacity sources in each wavelength range considered, as each species probes different regions of the atmosphere and are sensitive to spatial differences in the circulation. This work highlights the ongoing need for models of planets in this temperature regime to consider both 3D and magnetic effects when interpreting high-resolution transmission spectra.
ABSTRACT
Exoplanet atmospheres are inherently three-dimensional systems in which thermal/chemical variation and winds can strongly influence spectra. Recently, the ultra-hot Jupiter WASP-76 b has ...shown evidence for condensation and asymmetric Fe absorption with time. However, it is currently unclear whether these asymmetries are driven by chemical or thermal differences between the two limbs, as precise constraints on variation in these have remained elusive due to the challenges of modelling these dynamics in a Bayesian framework. To address this, we develop a new model, HyDRA-2D, capable of simultaneously retrieving morning and evening terminators with day-night winds. We explore variations in Fe, temperature profile, winds, and opacity deck with limb and orbital phase using VLT/ESPRESSO observations of WASP-76 b. We find Fe is more prominent on the evening for the last quarter of the transit, with $\log (X_\mathrm{Fe}) = {-4.03}^{+0.28}_{-0.31}$, but the morning shows a lower abundance with a wider uncertainty, $\log (X_\mathrm{Fe}) = {-4.59}^{+0.85}_{-1.0}$, driven by degeneracy with the opacity deck and the stronger evening signal. We constrain 0.1-mbar temperatures ranging from $2950^{+111}_{-156}$ to $2615^{+266}_{-275}$ K, with a trend of higher temperatures for the more irradiated atmospheric regions. We also constrain a day-night wind speed of $9.8^{+1.2}_{-1.1}$ km s−1 for the last quarter, higher than $5.9^{+1.5}_{-1.1}$ km s−1 for the first, in line with general circulation models. We find our new spatially and phase-resolved treatment is statistically favoured by 4.9σ over traditional 1D-retrievals, and thus demonstrate the power of such modelling for robust constraints with current and future facilities.
Abstract
The large radii of many hot Jupiters can only be matched by models that have hot interior adiabats, and recent theoretical work has shown that the interior evolution of hot Jupiters has a ...significant impact on their atmospheric structure. Due to its inflated radius, low gravity, and ultrahot equilibrium temperature, WASP-76b is an ideal case study for the impact of internal evolution on observable properties. Hot interiors should most strongly affect the nonirradiated side of the planet, and thus full phase-curve observations are critical to ascertain the effect of the interior on the atmospheres of hot Jupiters. In this work, we present the first Spitzer phase-curve observations of WASP-76b. We find that WASP-76b has an ultrahot dayside and relatively cold nightside with brightness temperatures of 2471 ± 27 K/1518 ± 61 K at 3.6
μ
m and 2699 ± 32 K/1259 ± 44 K at 4.5
μ
m, respectively. These results provide evidence for a dayside thermal inversion. Both channels exhibit small phase offsets of 0.68 ± 0.°48 at 3.6
μ
m and 0.67 ± 0.°2 at 4.5
μ
m. We compare our observations to a suite of general circulation models (GCMs) that consider two endmembers of interior temperature along with a broad range of frictional drag strengths. Strong frictional drag is necessary to match the small phase offsets and cold nightside temperatures observed. From our suite of cloud-free GCMs, we find that only cases with a cold interior can reproduce the cold nightsides and large phase-curve amplitude at 4.5
μ
m, hinting that the hot interior adiabat of WASP-76b does not significantly impact its atmospheric dynamics or that clouds blanket its nightside.
Abstract
Due to their likely tidally synchronized nature, (ultra)hot Jupiter atmospheres should experience strongly spatially heterogeneous instellation. The large irradiation contrast and resulting ...atmospheric circulation induce temperature and chemical gradients that can produce asymmetries across the eastern and western limbs of these atmospheres during transit. By observing an (ultra)hot Jupiter’s transmission spectrum at high spectral resolution, these asymmetries can be recovered—namely through net Doppler shifts originating from the exoplanet’s atmosphere yielded by cross-correlation analysis. Given the range of mechanisms at play, identifying the underlying cause of observed asymmetry is nontrivial. In this work, we explore sources and diagnostics of asymmetries in high-resolution cross-correlation spectroscopy of hot and ultrahot Jupiters using both parameterized and self-consistent atmospheric models. If an asymmetry is observed, we find that it can be difficult to attribute it to equilibrium chemistry gradients because many other processes can produce asymmetries. Identifying a molecule that is chemically stable over the temperature range of a planetary atmosphere can help establish a
baseline
to disentangle the various potential causes of limb asymmetries observed in other species. We identify CO as an ideal molecule, given its stability over nearly the entirety of the ultrahot Jupiter temperature range. Furthermore, we find that if limb asymmetry is due to morning terminator clouds, blueshifts for a number of species should decrease during transit. Finally, by comparing our forward models to those of Kesseli et al., we demonstrate that binning high-resolution spectra into two phase bins provides a desirable trade-off between maintaining signal to noise and resolving asymmetries.
Abstract The atmospheric dynamics of tidally locked hot Jupiters is characterized by strong equatorial winds. Understanding the interaction between global circulation and chemistry is crucial in ...atmospheric studies and interpreting observations. Two-dimensional (2D) photochemical transport models shed light on how the atmospheric composition depends on circulation. In this paper, we introduce the 2D photochemical (horizontal and vertical) transport model, VULCAN 2D, which improves on the pseudo-2D approaches by allowing for nonuniform zonal winds. We extensively validate our VULCAN 2D with analytical solutions and benchmark comparisons. Applications to HD 189733 b and HD 209458 b reveal a transition in mixing regimes: horizontal transport predominates below ∼0.1 mbar, while vertical mixing is more important at higher altitudes above 0.1 mbar. Motivated by the previously inferred carbon-rich atmosphere, we find that HD 209458 b with supersolar carbon-to-oxygen ratio (C/O) exhibits pronounced C 2 H 4 absorption on the morning limb but not on the evening limb, due to horizontal transport from the nightside. We discuss when a pseudo-2D approach is a valid assumption and its inherent limitations. Finally, we demonstrate the effect of horizontal transport in transmission observations and its impact on the morning−evening limb asymmetry with synthetic spectra, highlighting the need to consider global transport when interpreting exoplanet atmospheres.
Abstract
High-resolution spectra are unique indicators of three-dimensional (3D) processes in exoplanetary atmospheres. For instance, in 2020, Ehrenreich et al. reported transmission spectra from the ...ESPRESSO spectrograph yielding an anomalously large Doppler blueshift from the ultrahot Jupiter WASP-76b. Interpretations of these observations invoke toy model depictions of gas-phase iron condensation in lower-temperature regions of the planet’s atmosphere. In this work, we forward model the atmosphere of WASP-76b with double-gray general circulation models (GCMs) and ray-striking radiative transfer to diagnose the planet’s high-resolution transmission spectrum. We confirm that a physical mechanism driving strong east–west asymmetries across the terminator must exist to reproduce large Doppler blueshifts in WASP-76b’s transmission spectrum. We identify low atmospheric drag and a deep radiative-convective boundary as necessary components of our GCM to produce this asymmetry (the latter is consistent with existing Spitzer phase curves). However, we cannot reproduce either the magnitude or the time-dependence of the WASP-76b Doppler signature with gas-phase iron condensation alone. Instead, we find that high-altitude, optically thick clouds composed of Al
2
O
3
, Fe, or Mg
2
SiO
4
provide reasonable fits to the Ehrenreich et al. observations—with marginal contributions from condensation. This fit is further improved by allowing a small orbital eccentricity (
e
≈ 0.017), consistent with prior WASP-76b orbital constraints. We additionally validate our forward-modeled spectra by reproducing lines of nearly all species detected in WASP-76b by Tabernero et al. Our procedure’s success in diagnosing phase-resolved Doppler shifts demonstrates the benefits of physical, self-consistent, 3D simulations in modeling high-resolution spectra of exoplanet atmospheres.
Abstract Magnetic fields connect an array of planetary processes, from atmospheric escape to interior convection. Despite their importance, exoplanet magnetic fields are largely unconstrained by both ...theory and observation. In this Letter, we propose a novel method for constraining the B field strength of hot gas giants: comparing the velocities of heavy ions and neutral gas with high-resolution spectroscopy. The core concept of this method is that ions are directly deflected by magnetic fields. While neutrals are also affected by B fields via friction with field-accelerated ions, ionic gas should be more strongly coupled to the underlying magnetic field than bulk neutral flow. Hence, measuring the difference between the two velocities yields rough constraints on the B field, provided an estimate of the stellar UV flux is known. We demonstrate that heavy ions are particularly well suited for this technique because they are less likely to be entrained in complex hydrodynamic outflows than their lighter counterparts. We perform a proof-of-concept calculation with Ba ii , an ion whose velocity has been repeatedly measured at high confidence with high-resolution spectroscopy. Our work shows that a 10 G magnetic field would produce ∼1 km s −1 ion–neutral velocity differences at a microbar, whereas a 50 G magnetic field would produce ∼20 km s −1 velocity difference. With new leverage on magnetic fields, we will be able to investigate magnetic field generation in the extreme edge cases of hot gas giants, with wide-ranging consequences for planetary interior structure, dynamo theory, and habitability.
Abstract
We present the first public version of
SImMER
, an open-source
Python
reduction pipeline for astronomical images of point sources. Current capabilities include dark-subtraction, ...flat-fielding, sky-subtraction, image registration, FWHM measurement, contrast curve calculation, and table and plot generation.
SImMER
supports observations taken with the ShARCS camera on the Shane 3 m telescope and the PHARO camera on the Hale 5.1 m telescope. The modular nature of
SImMER
allows users to extend the pipeline to accommodate additional instruments with relative ease. One of the core functions of the pipeline is its image registration module, which is flexible enough to reduce saturated images and images of similar-brightness, resolved stellar binaries. Furthermore,
SImMER
can compute contrast curves for reduced images and produce publication-ready plots. The code is developed online at
https://github.com/arjunsavel/SImMER
and is both pip- and conda-installable. We develop tutorials and documentation alongside the code and host them online. With
SImMER
, we aim to provide a community resource for accurate and reliable data reduction and analysis.
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