Helios-r2: A New Bayesian, Open-source Retrieval Model for Brown Dwarfs and Exoplanet Atmospheres

Kitzmann, Daniel; Heng, Kevin; Oreshenko, Maria; Grimm, Simon L.; Apai, Dániel; Bowler, Brendan P.; Burgasser, Adam J.; Marley, Mark S.

doi:10.3847/1538-4357/ab6d71

Cited by 97 publications

(148 citation statements)

References 88 publications

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“…This behavior could be due to the random noise instantiation used in the retrieval, and the fact that especially the scaling may introduce biases in the retrieved atmospheric parameters in cases where differences are introduced between model and observation. This has also been described in Kitzmann et al (2020). In their case the differences arose from using two different models for generating the mock observation and the retrieval, here the differences arise from the random noise properties.…”

Section: Testing the Retrieval Modelmentioning

confidence: 93%

“…One way of reducing such oscillations is by smoothing the resulting P-T profile (as done in Irwin et al 2008;Lee et al 2012). Another way to circumvent this problem is to retrieve temperatures at a limited number of altitudes in the atmosphere, which are then connected via (spline) interpolation to yield a temperature at all layers, thereby reducing the number of free parameters (Line et al 2015;Kitzmann et al 2020). In addition, Line et al (2015) included a penalty term on the spatial sum of second derivatives of the temperature profile which further discouraged oscillatory solutions.…”

Section: Temperature Modelmentioning

confidence: 99%

“…Moreover, to prevent the formation of temperature inversions, which are not expected in self-luminous objects, we required that the three free temperature points in the high altitude region of the atmosphere are colder than the highest point of the "photosphere" (middle altitude region), and that they decrease in temperature monotonically with increasing altitude. This prior is enforced by setting the upper boundary of the allowed temperature range of such a free temperature point equal to the temperature of the underlying temperature point, identical to the treatment in Kitzmann et al (2020). In Gravity Collaboration (2020) we had found that we had to impose further priors on the temperature parameterization based on the structure of the atmospheric opacity of a given forward modeling realization.…”

Section: Priorsmentioning

confidence: 99%

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Retrieving scattering clouds and disequilibrium chemistry in the atmosphere of HR 8799e

Mollière

Stolker

Lacour

et al. 2020

A&A

179

218

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Context. Clouds are ubiquitous in exoplanet atmospheres and they represent a challenge for the model interpretation of their spectra. When generating a large number of model spectra, complex cloud models often prove too costly numerically, whereas more efficient models may be overly simplified. Aims. We aim to constrain the atmospheric properties of the directly imaged planet HR 8799e with a free retrieval approach. Methods. We used our radiative transfer code petitRADTRANS for generating the spectra, which we coupled to the PyMultiNest tool. We added the effect of multiple scattering which is important for treating clouds. Two cloud model parameterizations are tested: the first incorporates the mixing and settling of condensates, the second simply parameterizes the functional form of the opacity. Results. In mock retrievals, using an inadequate cloud model may result in atmospheres that are more isothermal and less cloudy than the input. Applying our framework on observations of HR 8799e made with the GPI, SPHERE, and GRAVITY, we find a cloudy atmosphere governed by disequilibrium chemistry, confirming previous analyses. We retrieve that C/O = 0.60−0.08+0.07. Other models have not yet produced a well constrained C/O value for this planet. The retrieved C/O values of both cloud models are consistent, while leading to different atmospheric structures: either cloudy or more isothermal and less cloudy. Fitting the observations with the self-consistent Exo-REM model leads to comparable results, without constraining C/O. Conclusions. With data from the most sensitive instruments, retrieval analyses of directly imaged planets are possible. The inferred C/O ratio of HR 8799e is independent of the cloud model and thus appears to be a robust. This C/O is consistent with stellar, which could indicate that the HR 8799e formed outside the CO2 or CO iceline. As it is the innermost planet of the system, this constraint could apply to all HR 8799 planets.

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Section: Testing the Retrieval Modelmentioning

confidence: 93%

Section: Temperature Modelmentioning

confidence: 99%

Section: Priorsmentioning

confidence: 99%

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Retrieving scattering clouds and disequilibrium chemistry in the atmosphere of HR 8799e

Mollière

Stolker

Lacour

et al. 2020

A&A

179

218

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“…For the rest of this derivation, we consider standard assumptions in current retrieval models published in the literature (Irwin et al 2008;Madhusudhan & Seager 2009;Line et al 2013;Benneke 2015;Waldmann et al 2015aWaldmann et al , 2015bHarrington 2016;Lavie et al 2017;MacDonald & Madhusudhan 2017;Cubillos 2018;Gandhi & Madhusudhan 2018;Al-Refaie et al 2019;Mollière et al 2019;Ormel & Min 2019;Zhang et al 2019;Kitzmann et al 2020). We assume the atmosphere is isothermal and in hydrostatic equilibrium.…”

Section: Discussionmentioning

confidence: 99%

TOI-132 b: A short-period planet in the Neptune desert transiting a V = 11.3 G-type star★

Díaz

Jenkins

Gandolfi

et al. 2020

Monthly Notices of the Royal Astronomical Society

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The Neptune desert is a feature seen in the radius-period plane, whereby a notable dearth of short period, Neptune-like planets is found. Here, we report the Transiting Exoplanet Survey Satellite (TESS) discovery of a new short-period planet in the Neptune desert, orbiting the G-type dwarf TYC 8003-1117-1 (TOI-132). TESS photometry shows transit-like dips at the level of ∼1400 ppm occurring every ∼2.11 d. High-precision radial velocity follow-up with High Accuracy Radial Velocity Planet Searcher confirmed the planetary nature of the transit signal and provided a semi-amplitude radial velocity variation of 11.38 $^{+0.84}_{-0.85}$ m s−1, which, when combined with the stellar mass of 0.97 ± 0.06 M⊙, provides a planetary mass of 22.40$^{+1.90}_{-1.92}$ M⊕. Modelling the TESS light curve returns a planet radius of 3.42$^{+0.13}_{-0.14}$ R⊕, and therefore the planet bulk density is found to be 3.08$^{+0.44}_{-0.46}$ g cm−3. Planet structure models suggest that the bulk of the planet mass is in the form of a rocky core, with an atmospheric mass fraction of 4.3$^{+1.2}_{-2.3}$ per cent. TOI-132 b is a TESS Level 1 Science Requirement candidate, and therefore priority follow-up will allow the search for additional planets in the system, whilst helping to constrain low-mass planet formation and evolution models, particularly valuable for better understanding of the Neptune desert.

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“…The field of exoplanetary atmospheres has seen a rapid development of novel methods and techniques. Some of the more recent breakthroughs include spatial scanning methods using the Wide Field Camera 3 (WFC3; McCullough & MacKenty 2012), automated data reduction pipelines (Tsiaras et al 2016), and retrievals using Bayesian sampling methods (Irwin et al 2008;Line et al 2013;Benneke 2015;Waldmann et al 2015bWaldmann et al , 2015aHarrington 2016;MacDonald & Madhusudhan 2017;Cubillos 2018;Gandhi & Madhusudhan 2018;Mollière et al 2019;Ormel & Min 2019;Zhang et al 2019;Kitzmann et al 2020). Most current retrieval analyses rely on specific geometric configurations such as transits, when the planet passes in front of its host star (Sing et al 2016;Tsiaras et al 2018), or eclipses, when the planet passes behind the star (Haynes et al 2015;Evans et al 2017).…”

Section: Introductionmentioning

confidence: 99%

TauREx3 PhaseCurve: A 1.5D Model for Phase-curve Description

Changeat

Al-Refaie

2020

ApJ

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In recent years, retrieval analysis of exoplanet atmospheres have been very successful, providing deep insights on the composition and the temperature structure of these worlds via transit and eclipse methods. Analysis of spectral phase-curve observations, which in theory provide even more information, are still limited to a few planets. In the next decade, new facilities such as NASA-James Webb Space Telescope and ESA-Ariel will revolutionize the field of exoplanet atmospheres and we expect that a significant time will be spent on spectral phase-curve observations. Most current models are still limited in their analysis of phase-curve data as they do not consider the planet atmosphere as a whole or they require large computational resources. In this paper we present a semi-analytical model that will allow computing exoplanet emission spectra at different phase angles. Our model provides a way to simulate a large number of observations while being only about four times slower than the traditional forward model for plane-parallel primary eclipse. This model, which is based on the newly developed TauREx 3 framework, will be further developed to allow for phase-curve atmospheric retrievals.

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Helios-r2: A New Bayesian, Open-source Retrieval Model for Brown Dwarfs and Exoplanet Atmospheres

Cited by 97 publications

References 88 publications

Retrieving scattering clouds and disequilibrium chemistry in the atmosphere of HR 8799e

Retrieving scattering clouds and disequilibrium chemistry in the atmosphere of HR 8799e

TOI-132 b: A short-period planet in the Neptune desert transiting a V = 11.3 G-type star★

TauREx3 PhaseCurve: A 1.5D Model for Phase-curve Description

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