We present one of the most precise emission spectra of an exoplanet observed so far. We combine five secondary eclipses of the hot Jupiter WASP-18b (Tday ∼ 2900 K) that we secured between 1.1 and 1.7 ...m with the Wide Field Camera 3 instrument on board the Hubble Space Telescope. Our extracted spectrum (S/N = 50, R ∼ 40) does not exhibit clearly identifiable molecular features but is poorly matched by a blackbody spectrum. We complement this data with previously published Spitzer/Infrared Array Camera observations of this target and interpret the combined spectrum by computing a grid of self-consistent, 1D forward models, varying the composition and energy budget. At these high temperatures, we find there are important contributions to the overall opacity from H− ions, as well as the removal of major molecules by thermal dissociation (including water), and thermal ionization of metals. These effects were omitted in previous spectral retrievals for very hot gas giants, and we argue that they must be included to properly interpret the spectra of these objects. We infer a new metallicity and C/O ratio for WASP-18b, and find them well constrained to be solar (M/H = −0.01 0.35, C/O < 0.85 at 3 confidence level), unlike previous work but in line with expectations for giant planets. The best-fitting self-consistent temperature-pressure profiles are inverted, resulting in an emission feature at 4.5 m seen in the Spitzer photometry. These results further strengthen the evidence that the family of very hot gas giant exoplanets commonly exhibit thermal inversions.
We present thermal phase curve measurements for the hot Jupiter WASP-103b observed with Hubble/WFC3 and Spitzer/IRAC. The phase curves have large amplitudes and negligible hotspot offsets, indicative ...of poor heat redistribution to the nightside. We fit the phase variation with a range of climate maps and find that a spherical harmonics model generally provides the best fit. The phase-resolved spectra are consistent with blackbodies in the WFC3 bandpass, with brightness temperatures ranging from 1880 40 K on the nightside to 2930 40 K on the dayside. The dayside spectrum has a significantly higher brightness temperature in the Spitzer bands, likely due to CO emission and a thermal inversion. The inversion is not present on the nightside. We retrieved the atmospheric composition and found that it is moderately metal-enriched ( ) and the carbon-to-oxygen ratio is below 0.9 at 3 confidence. In contrast to cooler hot Jupiters, we do not detect spectral features from water, which we attribute to partial H2O dissociation. We compare the phase curves to 3D general circulation models and find that magnetic drag effects are needed to match the data. We also compare the WASP-103b spectra to brown dwarfs and young, directly imaged companions. We find that these objects have significantly larger water features, indicating that surface gravity and irradiation environment play an important role in shaping the spectra of hot Jupiters. These results highlight the 3D structure of exoplanet atmospheres and illustrate the importance of phase curve observations for understanding their complex chemistry and physics.
Secondary eclipse observations of several of the hottest hot Jupiters show featureless, blackbody-like spectra or molecular emission features, which are consistent with thermal inversions being ...present in those atmospheres. Theory predicts a transition between warmer atmospheres with thermal inversions and cooler atmospheres without inversions, but the exact transition point is unknown. In order to further investigate this issue, we observed two secondary eclipses of the hot Jupiter HAT-P-7b with the Hubble Space Telescope (HST) WFC3 instrument and combined these data with previous Spitzer and Kepler secondary eclipse observations. The HST and Spitzer data can be well fit by a blackbody with T = 2692 14 K, and the Kepler data point constrains the geometric albedo to Ag = 0.077 0.006. We modeled these data with a three-dimensional (3D) GCM and one-dimensional (1D) self-consistent forward models. The 1D models indicate that the atmosphere has a thermal inversion, weak heat redistribution, and water dissociation that limits the range of pressures probed. This result suggests that WFC3 observations of HAT-P-7b and possibly some other ultra-hot Jupiters appear blackbody-like because they probe a region near the tropopause where the atmospheric temperature changes slowly with pressure. Additionally, the 1D models constrain the atmospheric metallicity ( ) and the carbon-to-oxygen ratio (C/O < 1 at 99% confidence). The solar composition 3D GCM matches the Spitzer data but generally underpredicts the flux in the WFC3 bandpass and cannot reproduce its featureless shape. This discrepancy could be explained by high atmospheric drag or nightside clouds and may be better understood through further observation with the James Webb Space Telescope.
Abstract
The presence of aerosols is intimately linked to the global energy budget and the composition of a planet’s atmosphere. Their ability to reflect incoming light prevents energy from being ...deposited into the atmosphere, and they shape the spectra of exoplanets. We observed five near-infrared secondary eclipses of WASP-80b with the Wide Field Camera 3 (WFC3) aboard the Hubble Space Telescope to provide constraints on the presence and properties of atmospheric aerosols. We detect a broadband eclipse depth of 34 ± 10 ppm for WASP-80b. We detect a higher planetary flux than expected from thermal emission alone at 1.6
σ
, which hints toward the presence of reflecting aerosols on this planet’s dayside, indicating a geometric albedo of
A
g
< 0.33 at 3
σ
. We paired the WFC3 data with Spitzer data and explored multiple atmospheric models with and without aerosols to interpret this spectrum. Albeit consistent with a clear dayside atmosphere, we found a slight preference for near-solar metallicities and for dayside clouds over hazes. We exclude soot haze formation rates higher than 10
−10.7
g cm
−2
s
−1
and tholin formation rates higher than 10
−12.0
g cm
−2
s
−1
at 3
σ
. We applied the same atmospheric models to a previously published WFC3/Spitzer transmission spectrum for this planet and found weak haze formation. A single soot haze formation rate best fits both the dayside and the transmission spectra simultaneously. However, we emphasize that no models provide satisfactory fits in terms of the chi-square of both spectra simultaneously, indicating longitudinal dissimilarity in the atmosphere’s aerosol composition.
Climate of an ultra hot Jupiter Arcangeli, Jacob; Désert, Jean-Michel; Parmentier, Vivien ...
Astronomy & astrophysics,
05/2019, Letnik:
625
Journal Article
Recenzirano
Odprti dostop
We present the analysis of a full-orbit, spectroscopic phase curve of the ultra hot Jupiter (UHJ) WASP-18b, obtained with the Wide Field Camera 3 aboard the Hubble Space Telescope. We measured the ...normalised day-night contrast of the planet as >0.96 in luminosity: the disc-integrated dayside emission from the planet is at 964 ± 25 ppm, corresponding to 2894 ± 30 K, and we place an upper limit on the nightside emission of <32 ppm or 1430 K at the 3σ level. We also find that the peak of the phase curve exhibits a small, but significant offset in brightness of 4.5 ± 0.5° eastward. We compare the extracted phase curve and phase-resolved spectra to 3D global circulation models and find that broadly the data can be well reproduced by some of these models. We find from this comparison several constraints on the atmospheric properties of the planet. Firstly we find that we need efficient drag to explain the very inefficient day-night recirculation observed. We demonstrate that this drag could be due to Lorentz-force drag by a magnetic field as weak as 10 gauss. Secondly, we show that a high metallicity is not required to match the large day-night temperature contrast. In fact, the effect of metallicity on the phase curve is different from cooler gas-giant counterparts because of the high-temperature chemistry in the atmosphere of WASP-18b. Additionally, we compared the current UHJ spectroscopic phase curves, WASP-18b and WASP-103b, and show that these two planets provide a consistent picture with remarkable similarities in their measured and inferred properties. However, key differences in these properties, such as their brightness offsets and radius anomalies, suggest that UHJ could be used to separate between competing theories for the inflation of gas-giant planets.
Climate of an ultra hot Jupiter Arcangeli, Jacob; Désert, Jean-Michel; Parmentier, Vivien ...
Astronomy and astrophysics (Berlin),
05/2019, Letnik:
625
Journal Article
Recenzirano
We present the analysis of a full-orbit, spectroscopic phase curve of the ultra hot Jupiter (UHJ) WASP-18b, obtained with the Wide Field Camera 3 aboard the
Hubble
Space Telescope. We measured the ...normalised day-night contrast of the planet as >0.96 in luminosity: the disc-integrated dayside emission from the planet is at 964 ± 25 ppm, corresponding to 2894 ± 30 K, and we place an upper limit on the nightside emission of <32 ppm or 1430 K at the 3
σ
level. We also find that the peak of the phase curve exhibits a small, but significant offset in brightness of 4.5 ± 0.5° eastward. We compare the extracted phase curve and phase-resolved spectra to 3D global circulation models and find that broadly the data can be well reproduced by some of these models. We find from this comparison several constraints on the atmospheric properties of the planet. Firstly we find that we need efficient drag to explain the very inefficient day-night recirculation observed. We demonstrate that this drag could be due to Lorentz-force drag by a magnetic field as weak as 10 gauss. Secondly, we show that a high metallicity is not required to match the large day-night temperature contrast. In fact, the effect of metallicity on the phase curve is different from cooler gas-giant counterparts because of the high-temperature chemistry in the atmosphere of WASP-18b. Additionally, we compared the current UHJ spectroscopic phase curves, WASP-18b and WASP-103b, and show that these two planets provide a consistent picture with remarkable similarities in their measured and inferred properties. However, key differences in these properties, such as their brightness offsets and radius anomalies, suggest that UHJ could be used to separate between competing theories for the inflation of gas-giant planets.
A key hypothesis in the field of exoplanet atmospheres is the trend of atmospheric thermal structure with planetary equilibrium temperature. We explore this trend and report here the first ...statistical detection of a transition in the near-infrared atmospheric emission between hot and ultra-hot Jupiters. We measure this transition using secondary eclipse observations and interpret this phenomenon as changes in atmospheric properties, and more specifically in terms of transition from non-inverted to inverted thermal profiles. We examine a sample of 78 hot Jupiters with secondary eclipse measurements at 3.6 and 4.5 μ m measured with Spitzer Infrared Array Camera. We calculate the planetary brightness temperatures using PHOENIX models to correct for the stellar flux. We measure the deviation of the data from the blackbody, which we define as the difference between the observed 4.5 μ m eclipse depth and that expected at this wavelength based on the brightness temperature measured at 3.6 μ m. We study how the deviation between 3.6 and 4.5 μ m changes with theoretical predictions with equilibrium temperature and incoming stellar irradiation. We reveal a clear transition in the observed emission spectra of the hot Jupiter population at 1660 ± 100 K in the zero albedo, full redistribution equilibrium temperature. We find the hotter exoplanets have even hotter daysides at 4.5 μ m compared to 3.6 μ m, which manifests as an exponential increase in the emitted power of the planets with stellar insolation. We propose that the measured transition is a result of seeing carbon monoxide in emission due to the formation of temperature inversions in the atmospheres of the hottest planets. These thermal inversions could be caused by the presence of atomic and molecular species with high opacities in the optical and/or the lack of cooling species. Our findings are in remarkable agreement with a new grid of 1D radiative and convective models varying metallicity, carbon to oxygen ratio (C/O), surface gravity, and stellar effective temperature. We find that the population of hot Jupiters statistically disfavors high C/O planets (C/O ≥ 0.85).
Abstract
Secondary eclipse observations of hot Jupiters can reveal both their compositions and thermal structures. Previous observations have shown a diversity of hot Jupiter eclipse spectra, ...including absorption features, emission features, and featureless blackbody-like spectra. We present a secondary eclipse spectrum of the hot Jupiter WASP-77Ab observed between 1 and 5
μ
m with the Hubble Space Telescope (HST) and the Spitzer Space Telescope. The HST observations show signs of water absorption indicative of a noninverted thermal structure. We fit the data with both a one-dimensional free retrieval and a grid of one-dimensional self-consistent forward models to confirm this noninverted structure. The free retrieval places a 3
σ
lower limit on the atmospheric water abundance of
log
(
n
H
2
O
)
>
−
4.78
and cannot constrain the CO abundance. The grid fit produces a slightly superstellar metallicity and constrains the carbon-to-oxygen ratio to less than or equal to the solar value. We also compare our data to recent high-resolution observations of WASP-77Ab taken with the IGRINS/IGRINS spectrograph. We find that the best-fit model to the IGRINS data gives a reduced chi squared of χ
2
ν
= 1.32 when compared to the WFC3 data. However, the metallicity derived from the IGRINS data is significantly lower than that derived from our self-consistent model fit. We find that this difference may be due to disequilibrium chemistry, and the varying results between the models applied here demonstrate the model dependence of derived metallicities when comparing to low-resolution, low-wavelength coverage data alone. Future work to combine observations from IGRINS, HST, and the James Webb Space Telescope will improve our estimate of the atmospheric composition of WASP-77Ab.
ABSTRACT
Planetary atmospheres are inherently 3D objects that can have strong gradients in latitude, longitude, and altitude. Secondary eclipse mapping is a powerful way to map the 3D distribution of ...the atmosphere, but the data can have large correlations and errors in the presence of photon and instrument noise. We develop a technique to mitigate the large uncertainties of eclipse maps by identifying a small number of dominant spectra to make them more tractable for individual analysis via atmospheric retrieval. We use the eigencurves method to infer a multiwavelength map of a planet from spectroscopic secondary eclipse light curves. We then apply a clustering algorithm to the planet map to identify several regions with similar emergent spectra. We combine the similar spectra together to construct an ‘eigenspectrum’ for each distinct region on the planetary map. We demonstrate how this approach could be used to isolate hot from cold regions and/or regions with different chemical compositions in observations of hot Jupiters with the James Webb Space Telescope (JWST). We find that our method struggles to identify sharp edges in maps with sudden discontinuities, but generally can be used as a first step before a more physically motivated modelling approach to determine the primary features observed on the planet.
The presence of aerosols is intimately linked to the global energy budget and the composition of a planet's atmospheres. Their ability to reflect incoming light prevents energy from being deposited ...into the atmosphere, and they shape spectra of exoplanets. We observed five near-infrared secondary eclipses of WASP-80b with the Wide Field Camera 3 (WFC3) aboard the \textit{Hubble Space Telescope} to provide constraints on the presence and properties of atmospheric aerosols. We detect a broadband eclipse depth of \(34\pm10\)\,ppm for WASP-80b. We detect a higher planetary flux than expected from thermal emission alone at \(1.6\sigma\), which hints toward the presence of reflecting aerosols on this planet's dayside, indicating a geometric albedo of \(A_g<0.33\) at 3\(\sigma\). We paired the WFC3 data with Spitzer data and explored multiple atmospheric models with and without aerosols to interpret this spectrum. Albeit consistent with a clear dayside atmosphere, we found a slight preference for near-solar metallicities and for dayside clouds over hazes. We exclude soot haze formation rates higher than \(10^{-10.7}\) g cm\(^{-2}\)s\(^{-1}\) and tholin formation rates higher than \(10^{-12.0}\) g cm\(^{-2}\)s\(^{-1}\) at \(3\sigma\). We applied the same atmospheric models to a previously published WFC3/Spitzer transmission spectrum for this planet and found weak haze formation. A single soot haze formation rate best fits both the dayside and the transmission spectra simultaneously. However, we emphasize that no models provide satisfactory fits in terms of the chi-square of both spectra simultaneously, indicating longitudinal dissimilarity in the atmosphere's aerosol composition.
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