Role of the impact parameter in exoplanet transmission spectroscopy

Alexoudi, X.; Mallonn, M.; Keles, Engin; Poppenhäger, Katja; Essen, C. von; Strassmeier, K. G.

doi:10.1051/0004-6361/202038080

Cited by 18 publications

(20 citation statements)

References 39 publications

(50 reference statements)

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“…It, hence, enters calculations of transmission depth being expressed in terms of pressure scale heights (H = k B T eq /(µg P ); e.g. Alexoudi et al 2020) or for deriving a cloud top pressure for defining an isothermal transit radius (Heng 2019). A constant value of µ is often assumed when running a 3D GCM (see introduction in Drummond et al 2018) as it is beneficial computationally.…”

Section: Mean Molecular Weightmentioning

confidence: 99%

Cloud property trends in hot and ultra-hot giant gas planets (WASP-43b, WASP-103b, WASP-121b, HAT-P-7b, and WASP-18b)

Helling

Lewis

Samra

et al. 2021

A&A

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Context. Ultra-hot Jupiters are the hottest exoplanets that have been discovered so far. Observations begin to provide insight into the composition of their extended atmospheres and their chemical day/night asymmetries. Both are strongly affected by cloud formation. Aims. We explore trends in cloud properties for a sample of five giant gas planets: the hot gas giant WASP-43b and the four ultra-hot Jupiters (UHJs) WASP-18b, HAT-P-7b, WASP-103b, and WASP-121b. This provides a reference frame for cloud properties for the JWST targets WASP-43b and WASP-121b. We further explore chemically inert tracers to observe geometrical asymmetries of UHJs and if the location of the inner boundary of a 3D global circulation model (3D GCM) matters for the clouds that form. Methods. A homogeneous set of 3D GCM results was used as input for a kinetic cloud formation code to evaluate the cloud opacity and gas parameters such as C/O, mean molecular weight, and degree of ionisation. We cast our results in terms of integrated quantities to enable a global comparison between the sample planets. Results. The large day/night temperature differences of UHJs cause the following chemical asymmetries: cloud-free days but cloudy nights, atomic versus molecular gases and their different mean molecular weights, deep thermal ionospheres versus low-ionised atmospheres, and undepleted versus enhanced C/O. WASP-18b, as the heaviest planet in the sample, has the lowest global C/O. Conclusions. The global climate may be considered as similar amongst UHJs, but different to that of hot gas giants. The local weather, however, is individual for each planet since the local thermodynamic conditions, and hence the local cloud and gas properties, differ. The morning and the evening terminator of UHJs will carry signatures of their strong chemical asymmetry such that ingress and egress asymmetries can be expected. An increased C/O ratio is a clear sign of cloud formation, making cloud modelling a necessity when utilising C/O (or other mineral ratios) as a tracer for planet formation. The changing geometrical extension of the atmosphere from the day to the nightside may be probed through chemically inert species such as helium. Ultra-hot Jupiters are likely to develop deep atmospheric ionospheres which may impact the atmosphere dynamics through magneto-hydrodynamic processes.

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Section: Mean Molecular Weightmentioning

confidence: 99%

Cloud property trends in hot and ultra-hot giant gas planets (WASP-43b, WASP-103b, WASP-121b, HAT-P-7b, and WASP-18b)

Helling

Lewis

Samra

et al. 2021

A&A

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“…Better constrained b values, derived from a well acquired information on ingress and egress, place the planet to a more precise orbital configuration around its host. This consequently can yield a more robust R p value, since the planetary radii are usually vulnerable towards the stellar limb darkening modeling process (Alexoudi et al 2020).…”

Section: Discussionmentioning

confidence: 99%

“…The derived value of the radius of an exoplanet is strongly affected by the orbital set-up of the system. If the planet is transiting its host star centrally ( b=0) or over the limbs ( b=1), this plays a major role in the correct estimation of the transit depth (Alexoudi et al 2020). As we saw previously, b depends on i and a/R s .…”

Section: The Relations Between the Planetary Radii And The Impact Par...mentioning

confidence: 99%

On the parameter refinement of inflated exoplanets with large radius uncertainty based on TESS observations

Alexoudi

2022

Preprint

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We revisited ten known exoplanetary systems using publicly available data provided by the Transiting Exoplanet Survey Satellite (TESS). The sample presented in this work consists of short period transiting exoplanets, with inflated radii and large reported uncertainty on their planetary radii. The precise determination of these values is crucial in order to develop accurate evolutionary models and understand the inflation mechanisms of these systems. Aiming to evaluate the planetary radius measurement, we made use of the planet-to-star radii ratio, a quantity that can be measured during a transit event. We fit the obtained transit light curves of each target with a detrending model and a transit model. Furthermore, we used emcee, which is based on a Markov chain Monte Carlo approach, to assess the best fit posterior distributions of each system parameter of interest. We refined the planetary radius of WASP-140 b by approximately 12%, and we derived a better precision on its reported asymmetric radius uncertainty by approximately 86% and 67%. We also refined the orbital parameters of WASP-120 b by 2σ. Moreover, using the high-cadence TESS datasets, we were able to solve a discrepancy in the literature, regarding the planetary radius of the exoplanet WASP-93 b. For all the other exoplanets in our sample, even though there is a tentative trend that planetary radii of (near-) grazing systems have been slightly overestimated in the literature, the planetary radius estimation and the orbital parameters were confirmed with independent observations from space, showing that TESS and ground-based observations are overall in good agreement.

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“…A.1), which should not be responsible for biases in a large wavelength range. Alexoudi et al (2018) and Alexoudi et al (2020) suggest that a fixed but inaccurate orbital inclination or impact parameter will cause a different slope and a systematic offset in the optical transmission spectrum. As illustrated in Fig.…”

Section: Rmse=381 Ppmmentioning

confidence: 99%

“…In contrast to the space-based observations, the ground-based observations reported by Mallonn et al (2015) and Yan et al (2020) presented relatively flat and featureless transmission spectra in the optical, favoring a cloudy atmosphere. Alexoudi et al (2018Alexoudi et al ( , 2020 proposed that such discrepancy in the offsets and slopes of transmission spectra can be attributed to the inaccuracy of orbital geometry parameters (semi-major axis, orbital inclination, or impact parameters) used in the spectroscopic light curve fitting. In addition, Deibert et al (2019) performed high-resolution transit spectroscopy on HAT-P-12b, and they revealed a 3.2σ detection of sodium absorption for the first time.…”

Section: Introductionmentioning

confidence: 99%

Evidence for stellar contamination in the transmission spectra of HAT-P-12b

Jiang,

Chen,

Palle

et al. 2021

Preprint

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Context. Transmission spectroscopy characterizes the wavelength dependence of transit depth, revealing atmospheric absorption features in planetary terminator regions. In this context, different optical transmission spectra of HAT-P-12b reported in previous studies exhibited discrepant atmospheric features (e.g., Rayleigh scattering, alkali absorption). Aims. We aim to understand the atmosphere of HAT-P-12b using two transit spectroscopic observations by the Gran Telescopio CANARIAS (GTC), and to search for evidence of stellar activity contaminating the transmission spectra, which might be the reason behind the discrepancies. Methods. We used Gaussian processes to account for systematic noise in the transit light curves and used nested sampling for Bayesian inferences. We performed joint atmospheric retrievals using the two transmission spectra obtained by GTC OSIRIS, as well as previously published results, coupled with stellar contamination corrections for different observations. Results. The retrieved atmospheric model exhibits no alkali absorption signatures, but shows tentative molecular absorption features including H 2 O, CH 4 and NH 3 . The joint retrieval of the combined additional public data analysis retrieves similar results, but with a higher metallicity. Conclusions. Based on Bayesian model comparison, the discrepancies of the transmission spectra of HAT-P-12b can be explained by the effect of different levels of unocculted stellar spots and faculae. In addition, we did not find strong evidence for a cloudy or hazy atmosphere from the joint analysis, which is inconsistent with prior studies based on the observations of Hubble Space Telescope.

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Role of the impact parameter in exoplanet transmission spectroscopy

Cited by 18 publications

References 39 publications

Cloud property trends in hot and ultra-hot giant gas planets (WASP-43b, WASP-103b, WASP-121b, HAT-P-7b, and WASP-18b)

Cloud property trends in hot and ultra-hot giant gas planets (WASP-43b, WASP-103b, WASP-121b, HAT-P-7b, and WASP-18b)

On the parameter refinement of inflated exoplanets with large radius uncertainty based on TESS observations

Evidence for stellar contamination in the transmission spectra of HAT-P-12b

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