arXiv subjects

Neale P. Gibson

Publications and source records attributed to Neale P. Gibson.

At least 37 records · Page 2Linked to original sources

arXiv2022

Early Release Science of the exoplanet WASP-39b with JWST NIRISS

Transmission spectroscopy provides insight into the atmospheric properties and consequently the formation history, physics, and chemistry of transiting exoplanets. However, obtaining precise inferences of atmospheric properties from transmission spectra requires simultaneously measuring the strength and shape of multiple spectral absorption features from a wide range of chemical species. This has been challenging given the precision and wavelength coverage of previous observatories. Here, we present the transmission spectrum of the Saturn-mass exoplanet WASP-39b obtained using the SOSS mode of the NIRISS instrument on the JWST. This spectrum spans $0.6 - 2.8 μ$m in wavelength and reveals multiple water absorption bands, the potassium resonance doublet, as well as 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, favoring a heavy element enhancement ("metallicity") of $\sim 10 - 30 \times$ 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 best explained by wavelength-dependent, non-gray clouds with inhomogeneous coverage of the planet's terminator.

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arXiv2022

High-resolution atmospheric retrievals of WASP-121b transmission spectroscopy with ESPRESSO: Consistent relative abundance constraints across multiple epochs and instruments

Recent progress in high-resolution transmission spectroscopy has offered new avenues in which to characterise the atmospheres of transiting exoplanets. High-resolution cross-correlation spectroscopy allows for the unambiguous detection of molecules/atoms. It has also been used to map both atmospheric dynamics and longitudinal variations in the abundance of species across the morning and evening limbs. We present multiple VLT/ESPRESSO observations of the ultra-hot Jupiter WASP-121b, from which we constrain relative abundances of various neutral metals consistently across all observations, whilst accounting for the distortion of the exoplanet's signal caused by traditional data processing techniques. We also constrain planetary orbital velocities and $T$-$P$ profiles. We compare our abundance constraints with previous constraints using VLT/UVES transmission spectroscopy of WASP-121b, and find our results to be consistent between observations, and also in agreement with stellar values for species previously detected in the atmosphere of WASP-121b. Our retrieval framework can also be used to identify potential exospheric species, resulting in extended absorption features beyond the transit equivalent Roche limit of WASP-121b ($R_{\rm eqRL}$ $\sim$ 1.3 $R_{\rm p}$). H$α$, Fe II, and Ca II were found to extend to high altitudes ($1.54\pm0.04$ $R_{\rm p}$, $1.17\pm0.01$ $R_{\rm p}$, and $2.52\pm0.34$ $R_{\rm p}$, respectively), which are broadly consistent with literature values. The consistency of our constraints across multiple high-resolution observations is a strong validation of our model filtering and retrieval framework, as well as the stability of the atmosphere over the timescales of months/years, and could allow for planet formation processes to be inferred from future ground-based observations of exoplanetary atmospheres.

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arXiv2022

Identification of carbon dioxide in an exoplanet atmosphere

Carbon dioxide (CO2) is a key chemical species that is found in a wide range of planetary atmospheres. In the context of exoplanets, CO2 is an indicator of the metal enrichment (i.e., elements heavier than helium, also called "metallicity"), and thus formation processes of the primary atmospheres of hot gas giants. It is also one of the most promising species to detect in the secondary atmospheres of terrestrial exoplanets. Previous photometric measurements of transiting planets with the Spitzer Space Telescope have given hints of the presence of CO2 but have not yielded definitive detections due to the lack of unambiguous spectroscopic identification. Here we present the detection of CO2 in the atmosphere of the gas giant exoplanet WASP-39b from transmission spectroscopy observations obtained with JWST as part of the Early Release Science Program (ERS). The data used in this study span 3.0 to 5.5 μm in wavelength and show a prominent CO2 absorption feature at 4.3 μm (26σ significance). The overall spectrum is well matched by one-dimensional, 10x solar metallicity models that assume radiative-convective-thermochemical equilibrium and have moderate cloud opacity. These models predict that the atmosphere should have water, carbon monoxide, and hydrogen sulfide in addition to CO2, but little methane. Furthermore, we also tentatively detect a small absorption feature near 4.0 μm that is not reproduced by these models.

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arXiv2022

Solar-to-supersolar sodium and oxygen absolute abundances for a "hot Saturn" orbiting a metal-rich star

We present new analysis of infrared transmission spectroscopy of the cloud-free hot-Saturn WASP-96b performed with the Hubble and Spitzer Space Telescopes (HST and Spitzer). The WASP-96b spectrum exhibits the absorption feature from water in excellent agreement with synthetic spectra computed assuming a cloud-free atmosphere. The HST-Spitzer spectrum is coupled with Very Large Telescope (VLT) optical transmission spectroscopy which reveals the full pressure-broadened profile of the sodium absorption feature and enables the derivation of absolute abundances. We confirm and correct for a spectral offset of $ΔR_{\rm p}/R_{\ast}=(-4.29^{+0.31}_{-0.37})\,\times10^{-3}$ of the VLT data relative to the HST-Spitzer spectrum. This offset can be explained by the assumed radius for the common-mode correction of the VLT spectra, which is a well-known feature of ground-based transmission spectroscopy. We find evidence for a lack of chromospheric and photometric activity of the host star which, therefore, make a negligible contribution to the offset. We measure abundances for Na and O that are consistent with solar to supersolar, with abundances relative to solar values of $21^{+27}_{-14}$ and $7^{+11}_{-4}$, respectively. We complement the transmission spectrum with new thermal emission constraints from Spitzer observations at 3.6 and $4.5μ$m, which are best explained by the spectrum of an atmosphere with a temperature decreasing with altitude. A fit to the spectrum assuming an isothermal blackbody atmosphere constrains the dayside temperature to be $T_{\rm{p}}$=$1545$$\pm$$90$K.

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arXiv2022

Constraints on TESS albedos for five hot Jupiters

Photometric observations of occultations of transiting exoplanets can place important constraints on the thermal emission and albedos of their atmospheres. We analyse photometric measurements and derive geometric albedo ($A_\mathrm{g}$) constraints for five hot Jupiters observed with TESS in the optical: WASP-18 b, WASP-36 b, WASP-43 b, WASP-50 b and WASP-51 b. For WASP-43 b, our results are complemented by a VLT/HAWK-I observation in the near-infrared at $2.09~μ$m. We derive the first geometric albedo constraints for WASP-50 b and WASP-51 b: $A_\mathrm{g}<0.445$ and $A_\mathrm{g}<0.368$, respectively. We find that WASP-43 b and WASP-18 b are both consistent with low geometric albedos ($A_\mathrm{g}<0.16$) even though they lie at opposite ends of the hot Jupiter temperature range with equilibrium temperatures of $\sim1400$ K and $\sim2500$ K, respectively. We report self-consistent atmospheric models which explain broadband observations for both planets from TESS, \HST, \Spitzer and VLT/HAWK-I. We find that the data of both hot Jupiters can be explained by thermal emission alone and inefficient day-night energy redistribution. The data do not require optical scattering from clouds/hazes, consistent with the low geometric albedos observed.

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arXiv2022

Day-side Fe I Emission, Day-Night Brightness Contrast and Phase Offset of the Exoplanet WASP-33b

We report on Fe I in the day-side atmosphere of the ultra-hot Jupiter WASP-33b, providing evidence for a thermal inversion in the presence of an atomic species. We also introduce a new way to constrain the planet's brightness variation throughout its orbit, including its day-night contrast and peak phase offset, using high-resolution Doppler spectroscopy alone. We do so by analyzing high-resolution optical spectra of six arcs of the planet's phase curve, using ESPaDOnS on the Canada-France-Hawaii telescope and HDS on the Subaru telescope. By employing a likelihood mapping technique, we explore the marginalized distributions of parameterized atmospheric models, and detect Fe I emission at high significance ($>10.4σ$) in our combined data sets, located at $K_{\rm p}=222.1\pm0.4$ km/s and $v_{\rm sys}=-6.5\pm0.3$ km/s. Our values agree with previous reports. By accounting for WASP-33b's brightness variation, we find evidence that its night-side flux is $<10\%$ of the day-side flux and the emission peak is shifted westward of the substellar point, assuming the spectrum is dominated by Fe I. Our ESPaDOnS data, which cover phases before and after the secondary eclipse more evenly, weakly constrain the phase offset to $+22\pm12$ degrees. We caution that the derived volume-mixing-ratio depends on our choice of temperature-pressure profile, but note it does not significantly influence our constraints on day-night contrast or phase offset. Finally, we use simulations to illustrate how observations with increased phase coverage and higher signal-to-noise ratios can improve these constraints, showcasing the expanding capabilities of high-resolution Doppler spectroscopy.

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arXiv2022

Relative abundance constraints from high-resolution optical transmission spectroscopy of WASP-121b, and a fast model-filtering technique for accelerating retrievals

High-resolution Doppler-resolved spectroscopy has presented new opportunities for studying the atmospheres of exoplanets. While the 'classical' cross-correlation approach has proven to be efficient at finding atmospheric species, it is unable to perform direct atmospheric retrievals. Recent work has shown that retrievals are possible using a direct likelihood evaluation or likelihood 'mappings'. The unique aspect of high-resolution retrievals is that the data-processing methods required to remove the stellar and telluric lines also distort the underlying exoplanet's signal and therefore the forward model must be pre-processed to match this filtering. This was the key remaining limitation in our previously published framework. This paper directly addresses this by introducing a simple and fast model-filtering technique that can replicate the processing performed by algorithms such as SysRem and PCA. This enables retrievals to be performed without having to perform expensive injection and pre-processing steps for every model. We show that we can reliably constrain quantitative measures of the atmosphere from transmission spectra including the temperature-pressure profile, relative abundances, planetary velocities and rotational broadening parameters. Finally, we demonstrate our framework using UVES transmission spectroscopy of WASP-121b. We constrain the temperature-pressure profile and relative abundances of Fe, Cr, and V to be $\log_{10}(χ_{\rm Fe}/χ_{\rm Cr})$=1.66$\pm$0.28, $\log_{10}(χ_{\rm Fe}/χ_{\rm V})$=3.78$\pm$0.29 and $\log_{10}(χ_{\rm Fe}/χ_{\rm Mg})$=-1.26$\pm$0.60. The relative abundances are consistent with solar values, with the exception of Fe/Mg, where the large Mg abundance is probably explained by the escaping atmosphere of WASP-121b that is not accounted for in our atmospheric model.

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arXiv2021

An inventory of atomic species in the atmosphere of WASP-121b using UVES high-resolution spectroscopy

Ultra-hot Jupiters (UHJs) present excellent targets for atmospheric characterisation. Their hot dayside temperatures (T $\gtrsim$ 2200 K) strongly suppress the formation of condensates, leading to clear and highly-inflated atmospheres extremely conducive to transmission spectroscopy. Recent studies using optical high-resolution spectra have discovered a plethora of neutral and ionised atomic species in UHJs, placing constraints on their atmospheric structure and composition. Our recent work has presented a search for molecular features and detection of Fe I in the UHJ WASP-121b using VLT/UVES transmission spectroscopy. Here, we present a systematic search for atomic species in its atmosphere using cross-correlation methods. In a single transit, we uncover potential signals of 17 atomic species which we investigate further, categorising 5 as strong detections, 3 as tentative detections, and 9 as weak signals worthy of further exploration. We confirm previous detections of Cr I, V I, Ca I, K I and exospheric H I and Ca II made with HARPS and ESPRESSO, and independently re-recover our previous detection of Fe I at 8.8 $σ$ using both the blue and red arms of the UVES data. We also add a novel detection of Sc II at 4.2 $σ$. Our results further demonstrate the richness of UHJs for optical high-resolution spectroscopy.

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arXiv2021

Transmission spectroscopy with VLT FORS2: a featureless spectrum for the low-density transiting exoplanet WASP-88b

We present ground-based optical transmission spectroscopy of the low-density hot Jupiter WASP-88b covering the wavelength range 4413-8333 Å with the FORS2 spectrograph on the Very Large Telescope. The FORS2 white light curves exhibit a significant time-correlated noise which we model using a Gaussian Process and remove as a wavelength-independent component from the spectroscopic light curves. We analyse complementary photometric observations from the Transiting Exoplanet Survey Satellite and refine the system properties and ephemeris. We find a featureless transmission spectrum with increased absorption towards shorter wavelengths. We perform an atmospheric retrieval analysis with the AURA code, finding tentative evidence for haze in the upper atmospheric layers and a lower likelihood for a dense cloud deck. Whilst our retrieval analysis results point toward clouds and hazes, further evidence is needed to definitively reject a clear-sky scenario.

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arXiv2021

Ground-Based Transmission Spectroscopy with VLT FORS2: Evidence for faculae and clouds in the optical spectrum of the warm Saturn WASP-110b

We present a ground-based optical transmission spectrum for the warm Saturn-mass exoplanet WASP-110b from two transit observations made with the FOcal Reducer and Spectrograph (FORS2) on the Very Large Telescope (VLT). The spectrum covers the wavelength range from 4000 to 8333Å, which is binned in 46 transit depths measured to an averaged precision of 220 parts per million (ppm) over an averaged 80Å~bin for a Vmag=12.8 star. The measured transit depths are unaffected by a dilution from a close A-type field dwarf, which was fully resolved. The overall main characteristic of the transmission spectrum is an increasing radius with wavelength and a lack of the theoretically predicted pressure-broadened sodium and potassium absorption features for a cloud-free atmosphere. We analyze archival high-resolution optical spectroscopy and find evidence for low to moderate activity of the host star, which we take into account in the atmospheric retrieval analysis. Using the AURA retrieval code, we find that the observed transmission spectrum can be best explained by a combination of unocculted stellar faculae and a cloud deck. Transmission spectra of cloud-free and hazy atmospheres are rejected at a high confidence. With a possible cloud deck at its terminator, WASP-110b joins the increasing population of irradiated hot-Jupiter exoplanets with cloudy atmospheres observed in transmission.

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arXiv2021

ACCESS & LRG-BEASTS: a precise new optical transmission spectrum of the ultrahot Jupiter WASP-103b

We present a new ground-based optical transmission spectrum of the ultrahot Jupiter WASP-103b ($T_{eq} = 2484$K). Our transmission spectrum is the result of combining five new transits from the ACCESS survey and two new transits from the LRG-BEASTS survey with a reanalysis of three archival Gemini/GMOS transits and one VLT/FORS2 transit. Our combined 11-transit transmission spectrum covers a wavelength range of 3900--9450A with a median uncertainty in the transit depth of 148 parts-per-million, which is less than one atmospheric scale height of the planet. In our retrieval analysis of WASP-103b's combined optical and infrared transmission spectrum, we find strong evidence for unocculted bright regions ($4.3σ$) and weak evidence for H$_2$O ($1.9σ$), HCN ($1.7σ$), and TiO ($2.1σ$), which could be responsible for WASP-103b's observed temperature inversion. Our optical transmission spectrum shows significant structure that is in excellent agreement with the extensively studied ultrahot Jupiter WASP-121b, for which the presence of VO has been inferred. For WASP-103b, we find that VO can only provide a reasonable fit to the data if its abundance is implausibly high and we do not account for stellar activity. Our results highlight the precision that can be achieved by ground-based observations and the impacts that stellar activity from F-type stars can have on the interpretation of exoplanet transmission spectra.

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arXiv2021

A New Window into Planet Formation and Migration: Refractory-to-Volatile Elemental Ratios in Ultra-hot Jupiters

A primary goal of exoplanet characterization is to use a planet's current composition to understand how that planet formed. For example, the C/O ratio has long been recognized as carrying important information on the chemistry of volatile species. Refractory elements, like Fe, Mg, and Si, are usually not considered in this conversation because they condense into solids like Fe(s) or MgSiO$_3$ and would be removed from the observable, gaseous atmosphere in exoplanets cooler than about 2000~K. However, planets hotter than about 2000~K, called ultra-hot Jupiters (UHJs), are warm enough to largely avoid the condensation of refractory species. In this paper, we explore the insight that the measurement of refractory abundances can provide into a planet's origins. Through refractory-to-volatile elemental abundance ratios, we can estimate a planet's atmospheric rock-to-ice fraction and constrain planet formation and migration scenarios. We first relate a planet's present-day refractory-to-volatile ratio to its rock-to-ice ratio from formation using various compositional models for the rocky and icy components of the protoplanetary disk. We discuss potential confounding factors like the sequestration of heavy metals in the core and condensation. We then show such a measurement using atmospheric retrievals of the low-resolution UV-IR transmission spectrum of WASP-121b with PETRA, from which we estimate a refractory-to-volatile ratio of 5.0$^{+6.0}_{-2.7}\times$ solar and a rock-to-ice ratio greater than 2/3. This result is consistent with significant atmospheric enrichment by rocky planetismals. Lastly, we discuss the rich future potential for measuring refractory-to-volatile ratios in ultra-hot Jupiters with the arrival of JWST and by combining observations at low- and high-resolution.

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arXiv2021

Gemini/GMOS Optical Transmission Spectroscopy of WASP-121b: signs of variability in an ultra-hot Jupiter?

We present ground-based, spectroscopic observations of two transits of the ultra-hot Jupiter WASP-121b covering the wavelength range $\approx$500 - 950 nm using Gemini/GMOS. We use a Gaussian process framework to model instrumental systematics in the light curves, and also demonstrate the use of the more generalised Student's-T process to verify our results. We find that our measured transmission spectrum, whilst showing overall agreement, is slightly discrepant with results obtained using HST/STIS, particularly for wavelengths shortward of $\approx$650 nm. In contrast to the STIS results, we find evidence for an increasing blueward slope and little evidence for absorption from either TiO or VO in our retrieval, in agreement with a number of recent studies performed at high-resolution. We suggest that this might point to some other absorbers, particularly some combination of recently detected atomic metals, in addition to scattering by hazes, being responsible for the excess optical absorption and observed vertical thermal inversion. Our results are also broadly consistent with previous ground-based photometry and 3D GCM predictions, however, these assumed different chemistry to our retrievals. In addition, we show that the GMOS observations are repeatable over short periods (days), similarly to the HST/STIS observations. Their difference over longer periods (months) could well be the result of temporal variability in the atmospheric properties (i.e. weather) as predicted by theoretical models of ultra-hot Jupiters; however, more mundane explanations such as instrumental systematics and stellar activity cannot be fully ruled out, and we encourage future observations to explore this possibility.

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arXiv2021

First Detection of Hydroxyl Radical Emission from an Exoplanet Atmosphere: High-dispersion Characterization of WASP-33b using Subaru/IRD

We report the first detection of a hydroxyl radical (OH) emission signature in the planetary atmosphere outside the solar system, in this case, in the day-side of WASP-33b. We analyze high-resolution near-infrared emission spectra of WASP-33b taken using the InfraRed Doppler spectrograph on the 8.2-m Subaru telescope. The telluric and stellar lines are removed using a de-trending algorithm, SysRem. The residuals are then cross-correlated with OH and H$_{2}$O planetary spectrum templates produced using several different line-lists. We check and confirm the accuracy of OH line-lists by cross-correlating with the spectrum of GJ 436. As a result, we detect the emission signature of OH at $K_\mathrm{p}$ of 230.9$^{+6.9}_{-7.4}$ km s$^{-1}$ and $v_{\mathrm{sys}}$ of $-$0.3$^{+5.3}_{-5.6}$ km s$^{-1}$ with S/N of 5.4 and significance of 5.5$σ$. Additionally, we marginally detect H$_{2}$O emission in the H-band with S/N of 4.0 and significance of 5.2$σ$ using the POKAZATEL line-list. However, no significant signal is detected using the HITEMP 2010, which might be due to differences in line positions and strengths, as well as the incompleteness of the line-lists. Nonetheless, this marginal detection is consistent with the prediction that H$_{2}$O is mostly thermally dissociated in the upper atmosphere of the ultra-hot Jupiters. Therefore, along with CO, OH is expected to be one of the most abundant O-bearing molecules in the day-side atmosphere of ultra-hot Jupiters and should be considered when studying their atmosphere.

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arXiv2020

Is TiO emission present in the ultra-hot Jupiter WASP-33b? A reassessment using the improved ExoMol Toto line list

[abridged] Efficient absorption of stellar UV and visible radiation by TiO and VO is predicted to drive temperature inversions in the upper atmospheres of hot Jupiters. However, few inversions or detections of TiO or VO have been reported, and results are often contradictory. Using the improved ExoMol Toto line list, we searched for TiO emission in the dayside spectrum of WASP-33b using the same data in which the molecule was previously detected with an older line list at 4.8$σ$. We intended to confirm the molecular detection and quantify the signal improvement offered by the ExoMol Toto line list. Data from the High Dispersion Spectrograph on the Subaru Telescope was extracted and reduced in an identical manner to the previous study. Stellar and telluric contamination were then removed. High-resolution TiO emission models of WASP-33b were created using the radiative transfer code petitRADTRANS and cross-correlated with the data. We measure a 4.3$σ$ TiO emission signature using the ExoMol Toto models, corresponding to a WASP-33b orbital velocity semi-amplitude of $K_\mathrm{p}=252.9^{+5.0}_{-5.3}\ \mathrm{km\ s^{-1}}$ and a system velocity of $v_\mathrm{sys}=-23.0^{+4.7}_{-4.6}\ \mathrm{km\ s^{-1}}$. Injection-recovery tests using models based on the new and earlier line lists indicate that if the new models provide a perfect match to the planet spectrum, the significance of the TiO detection should have increased by a factor of $\sim$2. Although the TiO signal we find is statistically significant, comparison with previous works makes our result too ambiguous to claim a clear-cut detection. Unexpectedly, the new ExoMol Toto models provide a weaker signal than that found previously, which is offset in $K_\mathrm{p}$-$v_\mathrm{sys}$ space. This sheds some doubt on both detections, especially in light of a recently published TiO non-detection using a different dataset.

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arXiv2020

Detection of Fe\,{\sc i} Emission in the Day-side Spectrum of WASP-33b

We analyze the high-resolution emission spectrum of WASP-33b taken using the High Dispersion Spectrograph (R\,$\approx$\,165,000) on the 8.2-m Subaru telescope. The data cover $λ$\,$\approx$\,$6170$-$8817$\,Å, divided over 30 spectral orders. The telluric and stellar lines are removed using a de-trending algorithm, {\sc SysRem}, before cross-correlating with planetary spectral templates. We calculate the templates assuming a 1-D plane-parallel hydrostatic atmosphere including continuum opacity of bound-free H$^{-}$ and Rayleigh scattering by H$_{2}$ with a range of constant abundances of Fe\,{\sc i}. Using a likelihood-mapping analysis, we detect an Fe\,{\sc i} emission signature at 6.4-$σ$ located at $K_{\mathrm{p}}$ of 226.0\,$^{+2.1}_{-2.3}$\,km\,s$^{-1}$and $v_{\mathrm{sys}}$ of -3.2\,$^{+2.1}_{-1.8}$\,km\,s$^{-1}$ -- consistent with the planet's expected velocity in the literature. We also confirm the existence of a thermal inversion in the day-side of the planet which is very likely to be caused by the presence of Fe\,{\sc i} and previously-detected TiO in the atmosphere. This makes WASP-33b one of the prime targets to study the relative contributions of both species to the energy budget of an ultra-hot Jupiter.

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arXiv2020

Searching for Thermal Inversion Agents in the Transmission Spectrum of MASCARA-2b/KELT-20b: Detection of Neutral Iron and Ionised Calcium H$\&$K Lines

We analyse the transmission spectra of KELT-20b/MASCARA-2b to search for possible thermal inversion agents. The data consist of three transits obtained using HARPSN and one using CARMENES. We removed stellar and telluric lines before cross-correlating the residuals with spectroscopic templates produced using a 1D plane-parallel model assuming an isothermal atmosphere and chemical equilibrium at solar metallicity. Using a likelihood-mapping method, we detect Fe\,{\sc i} at $>$ 13-$σ$, Ca\,{\sc ii} H$\&$K at $>$ 6-$σ$ and confirm the previous detections of Fe\,{\sc ii}, Ca\,{\sc ii} IRT and Na\,{\sc i} D. The detected signal of Fe\,{\sc i} is shifted by -3.4$\pm$0.4 km s$^{-1}$ from the planetary rest frame, which indicates a strong day-night wind. Our likelihood-mapping technique also reveals that the absorption features of the detected species extend to different altitudes in the planet's atmosphere. Assuming that the line lists are accurate, we do not detect other potential thermal inversion agents (NaH, MgH, AlO, SH, CaO, VO, FeH and TiO) suggesting that non-chemical equilibrium mechanisms (e.g. a cold-trap) might have removed Ti- and V-bearing species from the upper atmosphere. Our results, therefore, shows that KELT-20b/MASCARA-2b cannot possess an inversion layer caused by a TiO/VO-related mechanism. The presence of an inversion layer would therefore likely be caused by metal atoms such as Fe\,{\sc i} and Fe\,{\sc ii}. Finally, we report a double-peak structure in the Fe\,{\sc i} signal in all of our data-sets that could be a signature of atmospheric dynamics. However, further investigation is needed to robustly determine the origin of the signal.

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arXiv2020

Detection of Na, K and H$_2$O in the hazy atmosphere of WASP-6b

We present new observations of the transmission spectrum of the hot Jupiter WASP-6b both from the ground with the Very Large Telescope (VLT) FOcal Reducer and Spectrograph (FORS2) from 0.45-0.83 $μ$m, and space with the Transiting Exoplanet Survey Satellite (TESS) from 0.6-1.0 $μ$m and the Hubble Space Telescope (HST) Wide Field Camera 3 from 1.12-1.65 $μ$m. Archival data from the HST Space Telescope Imaging Spectrograph (STIS) and Spitzer is also reanalysed on a common Gaussian process framework, of which the STIS data show a good overall agreement with the overlapping FORS2 data. We also explore the effects of stellar heterogeneity on our observations and its resulting implications towards determining the atmospheric characteristics of WASP-6b. Independent of our assumptions for the level of stellar heterogeneity we detect Na I, K I and H$_2$O absorption features and constrain the elemental oxygen abundance to a value of [O/H] $\simeq -0.9\pm0.3$ relative to solar. In contrast, we find that the stellar heterogeneity correction can have significant effects on the retrieved distributions of the [Na/H] and [K/H] abundances, primarily through its degeneracy with the sloping optical opacity of scattering haze species within the atmosphere. Our results also show that despite this presence of haze, WASP-6b remains a favourable object for future atmospheric characterisation with upcoming missions such as the James Webb Space Telescope.

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