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
Though the global atmospheres of hot Jupiters have been extensively studied using phase curve observations, the level of time variability in these data is not well constrained. To ...investigate possible time variability in a planetary phase curve, we observed two full-orbit phase curves of the hot Jupiter WASP-43b at 4.5
μ
m using the Spitzer Space Telescope, and reanalyzed a previous 4.5
μ
m phase curve from Stevenson et al. We find no significant time variability between these three phase curves, which span timescales of weeks to years. The three observations are best fit by a single phase curve with an eclipse depth of 3907 ± 85 ppm, a dayside-integrated brightness temperature of 1479 ± 13 K, a nightside integrated brightness temperature of 755 ± 46 K, and an eastward-shifted peak of 10.°4 ± 1.°8. To model our observations, we performed 3D general circulation model simulations of WASP-43b with simple cloud models of various vertical extents. In comparing these simulations to our observations, we find that WASP-43b likely has a cloudy nightside that transitions to a relatively cloud-free dayside. We estimate that any change in WASP-43b’s vertical cloud thickness of more than three pressure scale heights is inconsistent with our observed upper limit on variation. These observations, therefore, indicate that WASP-43b’s clouds are stable in their vertical and spatial extent over timescales up to several years. These results strongly suggest that atmospheric properties derived from previous, single Spitzer phase curve observations of hot Jupiters likely show us the equilibrium properties of these atmospheres.
Abstract
Inhomogeneous cloud formation and wavelength-dependent phenomena are expected to shape hot Jupiter atmospheres. We present a general circulation model with multiwavelength “picket fence” ...radiative transfer and radiatively active, temperature-dependent clouds, and compare the results to those of a double gray routine. The double gray method inherently fails to model polychromatic effects in hot Jupiter atmospheres, while picket fence captures these non-gray aspects and performs well compared to fully wavelength-dependent methods. We compare both methods with radiatively active clouds and cloud-free models, assessing the limitations of the double gray method. Although there are broad similarities, the picket fence models have larger dayside–nightside temperature differences, nonisothermal upper atmospheres, and multiwavelength effects in the presence of radiatively active clouds. We model the well-known hot Jupiters HD 189733 b and HD 209458 b. For the hotter HD 209458 b, the picket fence method prevents clouds from thermostating dayside temperatures, resulting in hotter upper atmospheres and the dissipation of dayside clouds. Differences in the temperature structures are then associated with nuanced differences in the circulation patterns and clouds. Models of the cooler HD 189733 b have global cloud coverage, regardless of the radiative transfer scheme, whereas there are larger differences in the models of HD 209458 b, particularly in the extent of the partial cloud coverage on its dayside. This results in minor changes to the thermal and reflected light phase curves of HD 189733 b, but more significant differences for the picket fence and double gray versions of HD 209458 b.
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 Measurements of the carbon-to-oxygen (C/O) ratios of exoplanet atmospheres can reveal details about their formation and evolution. Recently, high-resolution cross-correlation analysis has ...emerged as a method of precisely constraining the C/O ratios of hot Jupiter atmospheres. We present two transits of the ultrahot Jupiter WASP-76b observed between 1.4 and 2.4 μ m with the high-resolution Immersion GRating INfrared Spectrometer on the Gemini-S telescope. We detected the presence of H 2 O, CO, and OH at signal-to-noise ratios of 6.93, 6.47, and 3.90, respectively. We performed two retrievals on this data set. A free retrieval for abundances of these three species retrieved a volatile metallicity of C + O H = − 0.70 − 0.93 + 1.27 , consistent with the stellar value, and a supersolar carbon-to-oxygen ratio of C/O = 0.80 − 0.11 + 0.07 . We also ran a chemically self-consistent grid retrieval, which agreed with the free retrieval within 1 σ but favored a slightly more substellar metallicity and solar C/O ratio ( C + O H = − 0.74 − 0.17 + 0.23 and C/O = 0.59 − 0.14 + 0.13 ). A variety of formation pathways may explain the composition of WASP-76b. Additionally, we found systemic ( V sys ) and Keplerian ( K p ) velocity offsets which were broadly consistent with expectations from 3D general circulation models of WASP-76b, with the exception of a redshifted V sys for H 2 O. Future observations to measure the phase-dependent velocity offsets and limb differences at high resolution on WASP-76b will be necessary to understand the H 2 O velocity shift. Finally, we find that the population of exoplanets with precisely constrained C/O ratios generally trends toward super-solar C/O ratios. More results from high-resolution observations or JWST will serve to further elucidate any population-level trends.
Ultrahot Jupiters represent an exciting avenue for testing extreme physics and observing atmospheric circulation regimes not found in our solar system. Their high temperatures result in thermally ...ionized particles embedded in atmospheric winds interacting with the planet’s interior magnetic field by generating current and experiencing bulk Lorentz force drag. Previous treatments of magnetic drag in 3D general circulation models (GCMs) of ultrahot Jupiters have mostly been uniform drag timescales applied evenly throughout the planet, which neglects the strong spatial dependence of these magnetic effects. In this work, we apply our locally calculated active magnetic drag treatment in a GCM of the planet WASP-76b. We find the effects of this treatment to be most pronounced in the planet’s upper atmosphere, where strong differences between the day and night side circulation are present. These circulation effects alter the resulting phase curves by reducing the hot spot offset and increasing the day–night flux contrast. We compare our models to Spitzer phase curves, which imply a magnetic field of at least 3 G for the planet. We additionally contrast our results to uniform drag timescale models. This work highlights the need for more careful treatment of magnetic effects in atmospheric models of hot gas giants.
Abstract
High-resolution spectroscopy has opened the way for new, detailed study of exoplanet atmospheres. There is evidence that this technique can be sensitive to the complex, three-dimensional ...(3D) atmospheric structure of these planets. In this work, we perform cross-correlation analysis of high-resolution (
R
∼ 100,000) CRIRES/VLT emission spectra of the hot Jupiter HD 209458b. We generate template emission spectra from a 3D atmospheric circulation model of the planet, accounting for temperature structure and atmospheric motions—winds and planetary rotation—missed by spectra calculated from one-dimensional models. In this first-of-its-kind analysis, we find that using template spectra generated from a 3D model produces a more significant detection (6.9
σ
) of the planet’s signal than any of the hundreds of one-dimensional models we tested (maximum of 5.1
σ
). We recover the planet’s thermal emission, its orbital motion, and the presence of CO in its atmosphere at high significance. Additionally, we analyzed the relative influences of 3D temperature and chemical structures in this improved detection, including the contributions from CO and H
2
O, as well as the role of atmospheric Doppler signatures from winds and rotation. This work shows that the hot Jupiter’s 3D atmospheric structure has a first-order influence on its emission spectra at high resolution and motivates the use of multidimensional atmospheric models in high-resolution spectral analysis.
Abstract
Ultrahot Jupiters represent an exciting avenue for testing extreme physics and observing atmospheric circulation regimes not found in our solar system. Their high temperatures result in ...thermally ionized particles embedded in atmospheric winds interacting with the planet’s interior magnetic field by generating current and experiencing bulk Lorentz force drag. Previous treatments of magnetic drag in 3D general circulation models (GCMs) of ultrahot Jupiters have mostly been uniform drag timescales applied evenly throughout the planet, which neglects the strong spatial dependence of these magnetic effects. In this work, we apply our locally calculated active magnetic drag treatment in a GCM of the planet WASP-76b. We find the effects of this treatment to be most pronounced in the planet’s upper atmosphere, where strong differences between the day and night side circulation are present. These circulation effects alter the resulting phase curves by reducing the hot spot offset and increasing the day–night flux contrast. We compare our models to Spitzer phase curves, which imply a magnetic field of at least 3 G for the planet. We additionally contrast our results to uniform drag timescale models. This work highlights the need for more careful treatment of magnetic effects in atmospheric models of hot gas giants.
Abstract
Ultrahot Jupiters are ideal candidates to explore with high-resolution emission spectra. Detailed theoretical studies are necessary to investigate the range of spectra that we can expect to ...see from these objects throughout their orbit, because of the extreme temperature and chemical longitudinal gradients that exist across their dayside and nightside regions. Using previously published 3D general circulation models of WASP-76b with different treatments of magnetic drag, we postprocess the 3D atmospheres to generate high-resolution emission spectra for two wavelength ranges, throughout the planet’s orbit. We find that the high-resolution emission spectra vary strongly as a function of phase, at times showing emission features, absorption features, or both, which are a direct result of the 3D structure of the planet. At phases exhibiting both emission and absorption features, the Doppler shift differs in direction between the two spectral features, making them differentiable, instead of canceling each other out. Through the use of cross correlation, we find different patterns in net Doppler shift for models with different treatments of drag: the nightside spectra show opposite signs in their Doppler shift, while the dayside phases display a reversal in the trend of net shift with phase. Finally, we caution researchers against using a single spectral template throughout the planet’s orbit; this can bias the corresponding net Doppler shift returned, as it can pick up on a bright region on the edge of the planet disk that is highly redshifted or blueshifted.
With orbital periods of only a few days, hot Jupiters and the even hotter ultrahot Jupiters are classes of planets that exist in an irradiation regime unlike anything in our solar system. These ...atmospheres are drastically influenced by the extreme levels of irradiation from their host star. Due to their proximity, these planets are expected to become tidally locked into synchronous orbits, meaning that their rotation period and orbital period are equal. This results in a permanent dayside and nightside on the planets, causing the large scale atmospheric dynamics of these objects to be governed by heat redistribution. In addition, these extreme temperatures cause atmospheric species to ionize on planet daysides, which can contribute to the lack of uniformity in the spatial distribution of species in these planets’ atmospheres. The movement of these ions also opens the door to interactions with the planet’s magnetic field. Very little is known about how magnetic effects can shape the atmospheres of these planets. In order to understand these planets more thoroughly, I use two main tools: 3D numerical modeling and high resolution spectroscopy. In this thesis, I explore multiple numerical treatments of magnetic effects, highlighting the strengths and weaknesses of each. Using our model’s state-of-the-art kinematic magneto-hydrodynamic (MHD) approach, I characterize a magnetic circulation regime that manifests in the upper atmosphere of ultrahot Jupiters as a result of our magnetic drag treatment. I also dive into the observational signatures of this regime, reviewing the effects on phase curves, emission, and transmission spectroscopy. Too often are magnetic effects ignored in analyses and models, and this thesis works to emphasize the importance of these effects.
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