The PHOENIX Exoplanet Retrieval Algorithm and Using H<sup>−</sup> Opacity as a Probe in Ultrahot Jupiters

Lothringer, Joshua D.; Barman, Travis

doi:10.3847/1538-3881/ab8d33

Cited by 27 publications

(34 citation statements)

References 77 publications

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“…They concluded that the upper atmospheric layers of these planets are characterised by a temperature inversion. According to the PHOENIX calculations, for KELT-9b this temperature inversion should lead to upper atmospheric temperatures of the order of about 6500 K (see also Lothringer & Barman 2020). Pino et al (2020) detected Fei emission from secondary eclipse groundbased high-resolution observations and arrived at the conclusion that the planetary atmosphere is indeed characterised by an inverted TP profile, confirming the modelling predictions.…”

Section: Introductionmentioning

confidence: 58%

Non-local thermodynamic equilibrium effects determine the upper atmospheric temperature structure of the ultra-hot Jupiter KELT-9b

Fossati

Young²,

Shulyak³

et al. 2021

A&A

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Context. Several observational and theoretical results indicate that the atmospheric temperature of the ultra-hot Jupiter KELT-9b in the main line formation region is a few thousand degrees higher than predicted by self-consistent models. Aims. Our aim was to test whether non-local thermodynamic equilibrium (NLTE) effects are responsible for the presumably higher temperature. Methods. We employed the Cloudy NLTE radiative transfer code to self-consistently compute the upper atmospheric temperature-pressure (TP) profile of KELT-9b, assuming solar metallicity and accounting for Roche potential. In the lower atmosphere, we used an updated version of the HELIOS radiative-convective equilibrium code to constrain the Cloudy model. Results. The Cloudy NLTE TP profile is ≈2000 K hotter than that obtained with previous models assuming LTE. In particular, in the 1–10−7 bar range the temperature increases from ≈4000 to ≈8500 K, remaining roughly constant at lower pressures. We find that the high temperature in the upper atmosphere of KELT-9b is driven principally by NLTE effects modifying the Fe and Mg level populations, which strongly influence the atmospheric thermal balance. We employed Cloudy to compute LTE and NLTE synthetic transmission spectra on the basis of the TP profiles computed in LTE and NLTE, respectively, finding that the NLTE model generally produces stronger absorption lines, particularly in the ultraviolet, than the LTE model (up to 30%). We compared the NLTE synthetic transmission spectrum with the observed Hα and Hβ line profiles obtaining an excellent match, thus supporting our results. Conclusions. The NLTE synthetic transmission spectrum can be used to guide future observations aiming at detecting features in the KELT-9b transmission spectrum. Metals, such as Mg and Fe, and NLTE effects shape the upper atmospheric temperature structure of KELT-9b, and thus affect the mass-loss rates derived from it. Finally, our results call for checking whether this is the case also for cooler planets.

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Section: Introductionmentioning

confidence: 58%

Non-local thermodynamic equilibrium effects determine the upper atmospheric temperature structure of the ultra-hot Jupiter KELT-9b

Fossati

Young²,

Shulyak³

et al. 2021

A&A

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“…However, the planetary temperature measured through phase curve observations can be at aid in further identifying the best fitting TP profile. As a matter of fact, at the photosphere (≈10 mbar level), the TP profiles number 047 and 125 are significantly hotter than the measured planetary dayside temperature, making TP model number 108 the most likely of the three (see also Lothringer & Barman 2020). Therefore, the TP profile number 108 is the one we employ to represent the family of TP profiles best fitting the observations and that we thoroughly discuss in the next section.…”

Section: Resultsmentioning

confidence: 99%

“…We analyse here in detail the results. We focus on the TP model profiles number 025, which is the closest to the one obtained with PHOENIX, and number 108, which, of the three models best fitting the planetary Hα and Hβ line profiles, is the one with the temperature of the lower atmosphere closer to what obtained from phase curve observations (Wong et al 2020;Mansfield et al 2020;Lothringer & Barman 2020).…”

Section: Discussionmentioning

confidence: 98%

A data-driven approach to constraining the atmospheric temperature structure of the ultra-hot Jupiter KELT-9b

Fossati

Shulyak

Sreejith

et al. 2020

A&A

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Context. Observationally constraining the atmospheric temperature-pressure (TP) profile of exoplanets is an important step forward for improving planetary atmosphere models, thus further enabling one to place the detection of spectral features and the measurement of atomic and molecular abundances through transmission and emission spectroscopy on solid ground. Aims. The aim is to constrain the TP profile of the ultra-hot Jupiter KELT-9b by fitting synthetic spectra to the observed Hα and Hβ lines and identify why self-consistent planetary TP models are unable to fit the observations. Methods. We constructed 126 one-dimensional TP profiles varying the lower and upper atmospheric temperatures, as well as the location and gradient of the temperature rise. For each TP profile, we computed the transmission spectra of the Hα and Hβ lines employing the Cloudy radiative transfer code, which self-consistently accounts for non-local thermodynamic equilibrium (NLTE) effects. Results. The TP profiles, leading to best fit the observations, are characterised by an upper atmospheric temperature of 10 000–11 000 K and by an inverted temperature profile at pressures higher than 10−4 bar. We find that the assumption of local thermodynamic equilibrium (LTE) leads one to overestimate the level population of excited hydrogen by several orders of magnitude and hence to significantly overestimate the strength of the Balmer lines. The chemical composition of the best fitting models indicate that the high upper atmospheric temperature is most likely driven by metal photoionisation and that FeII and FeIII have comparable abundances at pressures lower than 10−6 bar, possibly making the latter detectable. Conclusions. Modelling the atmospheres of ultra-hot Jupiters requires one to account for metal photoionisation. The high atmospheric mass-loss rate (>1011 g s−1), caused by the high temperature, may have consequences on the planetary atmospheric evolution. Other ultra-hot Jupiters orbiting early-type stars may be characterised by similarly high upper atmospheric temperatures and hence high mass-loss rates. This may have consequences on the basic properties of the observed planets orbiting hot stars.

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“…Multiple studies have recently considered the inclusion of H − opacity in atmospheric retrievals (e.g., Gandhi et al 2020;Lothringer & Barman 2020;Sotzen et al 2020). However, there remains no consensus on how to parameterize H − opacity in a retrieval context.…”

Section: Atmospheric Retrieval Approachmentioning

confidence: 99%

“…If confirmed, a high-significance H − detection and abundance constraint would result. Second, the longest wavelength observations (>4 μm) with NIRSpec G395H may detect free-free H − opacity, enabling one to measure the atmospheric electron mixing ratio (Lothringer & Barman 2020).…”

Section: Prospects For the Potential Jwst Ers Observationsmentioning

confidence: 99%

HST PanCET Program: A Complete Near-UV to Infrared Transmission Spectrum for the Hot Jupiter WASP-79b

Rathcke

Macdonald

Barstow

et al. 2021

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We present a new optical transmission spectrum of the hot Jupiter WASP-79b. We observed three transits with the STIS instrument mounted on the Hubble Space Telescope (HST), spanning 0.3-1.0 μm. Combining these transits with previous observations, we construct a complete 0.3-5.0 μm transmission spectrum of WASP-79b. Both HST and ground-based observations show decreasing transit depths toward blue wavelengths, contrary to expectations from Rayleigh scattering or hazes. We infer atmospheric and stellar properties from the full near-UV to infrared transmission spectrum of WASP-79b using three independent retrieval codes, all of which yield consistent results. Our retrievals confirm previous detections of H 2 O (at 4.0σ confidence) while providing moderate evidence of H − bound-free opacity (3.3σ) and strong evidence of stellar contamination from unocculted faculae (4.7σ). The retrieved H 2 O abundance (∼1%) suggests a superstellar atmospheric metallicity, though stellar or substellar abundances remain consistent with present observations (O/H = 0.3-34× stellar). All three retrieval codes obtain a precise H − abundance constraint: log( -X H ) ≈ −8.0 ± 0.7. The potential presence of H − suggests that James Webb Space Telescope observations may be sensitive to ionic chemistry in the atmosphere of WASP-79b. The inferred faculae are ∼500 K hotter than the stellar photosphere, covering ∼15% of the stellar surface. Our analysis underscores the importance of observing UV-optical transmission spectra in order to disentangle the influence of unocculted stellar heterogeneities from planetary transmission spectra.

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The PHOENIX Exoplanet Retrieval Algorithm and Using H⁻ Opacity as a Probe in Ultrahot Jupiters

Cited by 27 publications

References 77 publications

Non-local thermodynamic equilibrium effects determine the upper atmospheric temperature structure of the ultra-hot Jupiter KELT-9b

Non-local thermodynamic equilibrium effects determine the upper atmospheric temperature structure of the ultra-hot Jupiter KELT-9b

A data-driven approach to constraining the atmospheric temperature structure of the ultra-hot Jupiter KELT-9b

HST PanCET Program: A Complete Near-UV to Infrared Transmission Spectrum for the Hot Jupiter WASP-79b

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The PHOENIX Exoplanet Retrieval Algorithm and Using H− Opacity as a Probe in Ultrahot Jupiters

Cited by 27 publications

References 77 publications

Non-local thermodynamic equilibrium effects determine the upper atmospheric temperature structure of the ultra-hot Jupiter KELT-9b

Non-local thermodynamic equilibrium effects determine the upper atmospheric temperature structure of the ultra-hot Jupiter KELT-9b

A data-driven approach to constraining the atmospheric temperature structure of the ultra-hot Jupiter KELT-9b

HST PanCET Program: A Complete Near-UV to Infrared Transmission Spectrum for the Hot Jupiter WASP-79b

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The PHOENIX Exoplanet Retrieval Algorithm and Using H⁻ Opacity as a Probe in Ultrahot Jupiters