Poster presentations and abstracts

Planetary rings are exciting features yet to be detected around exoplanets despite their prevalence around the giant planets and other rocky bodies of the solar system. A number of studies have proposed methods to identify and characterise the signatures of rings mostly from transit light curves. Probing for the presence of rings in transit light curves is very useful as the rings can cause a number of effects both on the light curve shape and the inferred parameters of the planet.

The presence of rings around a transiting planet can cause it to appear larger and lead to an underestimation of its density if the mass is known. Therefore, a class of planets with extremely low densities, called Super puffs, can be planets with yet undetected rings. A Bayesian framework is employed here to show that the anomalously low density (~0.09 g/cm³) of the transiting long-period planet HIP 41378f might be due to the presence of opaque circum-planetary rings. Analysing the light curve data from the K2 mission, we construct physically motivated model priors and found that the statistical evidence for the ringed planet scenario is  comparable to that of the planet-only scenario. The ringed planet solution suggests a larger planetary density of ~1.23 g/cm³ similar to Uranus. The associated ring extends from 1.05 to 2.59 times the planetary radius and is inclined away from the sky-plane by ~25 degrees. However, the computed ring material density is lower than is expected for a planet with an equilibrium temperature of 294K so future high-precision transit observations of HIP 41378f would be necessary to confirm/dismiss the presence of planetary rings.

How to cite: Akinsanmi, B., Santos, N., Faria, J., Oshagh, M., Barros, S., Santerne, A., and Charnoz, S.: Possible case of exoplanetary rings around HIP 41378 f, Europlanet Science Congress 2020, online, 21 Sep–9 Oct 2020, EPSC2020-41, https://doi.org/10.5194/epsc2020-41, 2020.

Great advances have been made over the last few decades in probing the atmospheres of extra-solar planets, enabling us to further constrain the conditions that exist on these worlds. When modelling these atmospheres however, the work done to date has assumed that the species present are in local thermodynamic equilibrium (LTE). However it is known, for instance on Earth, that non-LTE effects are present in planetary atmospheres and give rise to spectra that vary from the LTE case.

Fast, high altitude jet streams in the atmospheres of hot Jupiters will produce shock regions where molecules may be found in non-LTE. Such effects are also likely in the upper atmospheres of planets barraged by solar flares, where the heavy stellar radiation drives the molecules to a state of non-LTE.  This poster presents a preliminary exploration into non-LTE effects in exoplanet atmospheres, showing the differences that arise in some notable molecular spectra due to these effects. This is achieved with the atmospheric retrieval framework TauRex 3, using custom cross sections generated with the ExoCross software’s capability to approximate non-LTE spectra via splitting the rotational and vibrational temperatures. 

An initial evaluation of the detectability of these differences by current and next generation space telescopes is presented through simulation with the PandExo package, showing forward atmospheric models with non-LTE variations clearly visible in spectra. It can be seen that the differences in spectra are resolvable, notably the absence of ‘shoulders’ in the case of the non-LTE water transmission models.

How to cite: Wright, S.: Exploring Non-LTE Effects in Exoplanet Atmospheres, Europlanet Science Congress 2020, online, 21 Sep–9 Oct 2020, EPSC2020-315, https://doi.org/10.5194/epsc2020-315, 2020.

The precise derivation of transit depths from stellar light curves is a key component in the construction of exoplanet transit spectra, and thereby for the characterization of exoplanet atmospheres. However, it is still deeply affected by various kinds of complex systematic errors and noises taking their source from host stars’ or instruments’ variability. On the other hand, as the volume of exoplanetary data is quickly increasing, a new way is being opened up for using machine learning as part of the data processing pipeline. By training a recurrent neural network to model the temporal dependencies in stellar light curves, our results on both real on simulated light curves highlight that it is possible to:

• Model accurately the compound of trends and periodic effects with few or no assumptions about the instrument, star, or planetary signals
• Improve the understanding of each instrument’s systematic behaviour
• Optimise a deep detrending model jointly with a transit fit
• Leverage the cross-light curves and cross-instruments information

Such an approach therefore paves the way for a global, flexible and efficient noise-correction pipeline which will be of paramount importance to make the most of exoplanets observations and provide high precision spectra to subsequent atmospheric retrieval pipelines.

How to cite: Morvan, M., Nikolau, N., Tsiaras, A., and Waldmann, I.: A Deep Learning Pipeline for Unified Modelling of Time-Correlated Noise in Exoplanets Observations, Europlanet Science Congress 2020, online, 21 Sep–9 Oct 2020, EPSC2020-373, https://doi.org/10.5194/epsc2020-373, 2020.

Spectra of brown dwarfs are key to exploring the chemistry and physics that take place in their atmospheres. Late T dwarf (850 - 500 K) spectra are particularly diagnostic due to their relatively cloud free atmospheres and deep molecular bands. With the use of powerful atmospheric retrieval tools, these properties permit proper allocation of constraints on the molecular/atomic abundances and temperature profiles. These constraints can be used to derive the elemental abundances (metallicity, C/O), chemical disequilibrium, and non-radiative-convective equilibrium temperature perturbations. Building upon previous analyses on T and Y dwarfs (Line et al. 2017; Zalesky et al. 2019), we present a uniform retrieval analysis of 52 T dwarfs via their low-resolution near-infrared spectra. This analysis more than doubles the sample of T dwarfs with retrieved properties. We present updates on current compositional trends and thermal profile constraints amongst the T dwarf population.

How to cite: Saboi, K., Line, M. R., Zalesky, J., Schneider, A., Zhang, Z., Liu, M. C., Best, W. M. J., and Marley, M. S.: Uniform Retrieval Analysis of Brown Dwarfs, Europlanet Science Congress 2020, online, 21 Sep–9 Oct 2020, EPSC2020-573, https://doi.org/10.5194/epsc2020-573, 2020.

The atmospheres of close-in, low-mass exoplanets are extremely vulnerable to the effects of stellar UV to X-ray radiation. Photoevaporation can significantly ablate planetary atmospheres or even strip them entirely, potentially rendering a planet inhabitable. Existing hydrodynamical studies of this important atmospheric mass loss mechanism have mainly considered hydrogen/helium dominated atmospheres. Currently, the effect of more complex chemistry on photoevaporative mass loss has only been the subject of a limited number of studies (e.g. Bolmont et al. 2017). In the era of more advanced exoplanet atmospheric observations, it is more important than ever to determine what, if any atmosphere, these planets may have been able to retain. Here, I present preliminary results of hydrodynamic simulations, showing how the atmosphere of a low-mass planet undergoing photoevaporation is affected by the inclusion of water.

How to cite: Harbach, L., Owen, J., and Mohanty, S.: Photoevaporation of Water Dominated Exoplanet Atmospheres, Europlanet Science Congress 2020, online, 21 Sep–9 Oct 2020, EPSC2020-718, https://doi.org/10.5194/epsc2020-718, 2020.

Exoplanet characterization is one of the main foci of current exoplanetary science. For super-Earths and sub-Neptunes, we mostly rely on mass and radius measurements, which allow to derive the body’s mean density and give a rough estimate of the planet’s bulk composition. However, the determination of planetary interiors is a very challenging task. In addition to the uncertainty in the observed fundamental parameters, theoretical models are limited due to the degeneracy in determining the planetary composition. We aim to study several aspects that affect internal characterization of super-Earths and sub-Neptunes: observational uncertainties, location on the M-R diagram, impact of additional constraints as bulk abundances or irradiation, and model assumptions.

We use a full probabilistic Bayesian inference analysis that accounts for observational and model uncertainties. We employ a Nested Sampling scheme to efficiently produce the posterior probability distributions for all the planetary structural parameter of interest. We include a structural model based on self-consistent thermodynamics of core, mantle, high-pressure ice, liquid water, and H-He envelope.  

Regarding the effect of mass and radius uncertainties on the determination of the internal structure, we find three different regimes: below the Earth-like composition line and above the pure-water composition line smaller observational uncertainties lead to better determination of the core and atmosphere mass respectively, and between them internal structure characterization only weakly depends on the observational uncertainties. We also find that using the stellar Fe/Si and Mg/Si abundances as a proxy for the bulk planetary abundances does not always provide additional constraints on the internal structure. Finally we show that small variations in the temperature or entropy profiles lead to radius variations that are comparable to the observational uncertainty. This suggests that uncertainties linked to model assumptions can eventually become more relevant to determine the internal structure than observational uncertainties.

How to cite: Fernandez Otegi, J., Dorn, C., Helled, R., Bouchy, F., Haldemann, J., and Alibert, Y.: The impact of exoplanets' measured parameters on the inferred internal structure., Europlanet Science Congress 2020, online, 21 Sep–9 Oct 2020, EPSC2020-721, https://doi.org/10.5194/epsc2020-721, 2020.

The study of exoplanets atmospheres is one of the most intriguing challenges in exoplanet field nowadays and the High Resolution Spectroscopy (HRS) has recently emerged as one of the leading methods for detecting atomic and molecular species in their atmospheres. In terms of numbers, if we define the resolution power R,  where λ is the wavelength and Δλ is the spectral resolution:

     R= λ/Δλ

then, “High Resolution Spectroscopy” means R > 50 000.

Nevertheless extraordinary results have been achieved (Birkby, 2018), High Resolution Spectroscopy alone is not enough. 1D models of the host star have been coupled to HRS observations, but they do not reproduce the complexity of stellar convection mechanism (Chiavassa & Brogi, 2019). On the contrary,  3D Radiative Hydrodynamical simulations (3D RHS) take it into account intrinsically, allowing us to correctly reproduce asymmetric and blue-shifted spectral lines due to the granulation pattern of the stellar disk, which is a very important source of uncertainties at this resolution level (Chiavassa et al. 2017).

However, numerical simulations have been computed independently for star and planet so far, while the acquired spectra are an entanglement of both the signals. In particular, some molecular species (e.g, CO) form in the same region of the spectrum, thus planetary and stellar spectral lines are completely mixed and overlapped. 

Therefore, a next step forward is needed: computing stellar and planetary models together.

With our work, we aim at upgrading the already-in-place 3D radiative transfer code Optim3D (Chiavassa et al. 2009) —largely used for stellar purposes so far — to taking into account also the exoplanetary contribution. We propose to use simultaneously 3D RHS, performed for stars, and the innovative Global Climate Model (GCM), drawn up for exoplanets, in order to generate unprecedented precise synthetic spectra. As a springboard to test the code, we are carrying out the analysis of CO and H2O molecules on the well-know benchmark HD189733. Indeed, to disentangle those star’s and its companion’s signals due to the same molecules is one of the most challenging problems. In the end, we will be able to compute a complete dynamic characterisation: on one side, a precise knowledge of the stellar dynamic (i.e. convection-related surface structures) would allow to extract unequivocally the planetary signal; on the other one, a well-modelled dynamic of the planet (i.e. depth, shape, and position of spectral lines) would provide us with considerable information about the planetary atmospheric circulation.

How to cite: Maimone, M. C., Chiavassa, A., Leconte, J., and Brogi, M.: Star And Planet’s Characterisation Through High Spectral Resolution, Europlanet Science Congress 2020, online, 21 Sep–9 Oct 2020, EPSC2020-789, https://doi.org/10.5194/epsc2020-789, 2020.

Stellar variability is a dominant noise source in exoplanet surveys and results largely from the presence of photospheric faculae and spots. The implementation of faculae in lightcurve models is an open problem, with scaling based on spectra equivalent to hot stellar atmospheres or assuming a solar-derived facular contrast. We model the lightcurves of active late-type stars as they rotate, using emergent intensity spectra calculated from 3D magnetoconvection simulations of G, K and M-type stellar atmosphere regions at different viewing angles to reproduce centre-to-limb brightness variations. We present mean expected variability levels for several cases and compare with solar and stellar observations. We also investigate the wavelength dependence of variability.

Fig. 1: Example of our geometrically accurate lightcurve modelling approach. Top: normalised intensity maps of a limb darkened, solar-type star viewed in the \textit{Kepler} band at rotational phase 0.5 with stellar inclinations 90 deg (left) and 30 deg (right). At 90 deg, the star is viewed equator-on. Middle: Corresponding lightcurves calculated at inclinations 90 deg (black line) and 30 deg (red line). Bottom: HealPix map representing the active stellar surface, cosine-scaled in latitude and flattened in longitude to resemble a solar synoptic map. The quiet photosphere is displayed in orange, facular regions are bright yellow and spot regions are dark blue. The crosses represent the centres of the stellar discs in the top panel.

Fig. 2: Example showing simulated lightcurves calculated at different wavelengths. Rotational lightcurves are on the left, transit lightcurves on the right. In the centre, one hemisphere of the simulated stellar surface is shown, with a quarter of the disc shown in each wavelength band. 'Giant' spots and facular regions are used in this example. The transit path is highlighted in grey.

How to cite: Johnson, L., Unruh, Y., Norris, C., Solanki, S., Krivova, N., Witzke, V., and Shapiro, A.: Simulating Variability due to Faculae and Spots on GKM Stars, Europlanet Science Congress 2020, online, 21 Sep–9 Oct 2020, EPSC2020-844, https://doi.org/10.5194/epsc2020-844, 2020.

As the upper atmospheres of the ‘habitable’ exoplanets orbiting M-Dwarfs are affected by more extreme environments than what Solar System bodies experience, the observations of such exoplanets raise questions to the mass-loss mechanisms and the sustainability of their atmospheres. For the first time, we examine the loss of neutral atmosphere from Proxima Centauri b (PCb) via photochemical mechanisms and formation processes of resulting exoplanetary hot atomic coronae or exospheres.

The study is conducted by utilizing our integrated model framework, which couples our 3D Adaptive Mesh Particle Simulator (AMPS) for planetary exospheres and a 3D multi-species magnetohydrodynamic (MHD) model originally developed for Venus and Mars. The coupling of the two models is achieved in one-way, such that the AMPS code incorporates pre-simulated results by the MHD model as inputs for exosphere simulation. The MHD model describes the ionosphere of the planet self-consistently based on the neutral atmosphere adopted for PCb. All simulations in this study assume a Venus-like condition for the ionosphere and thermosphere of PCb, which is also based on an assumption of the absence of an intrinsic dipole magnetic field. As most of the relevant planetary parameters of PCb are unknown, this study provides one possible interpretation of the atmospheric loss process of PCb as well as other exoplanets similar to PCb, which reside in the Habitable Zones (HZs) of M-Dwarfs, to help our understanding of their habitability.

How to cite: Lee, Y. and Dong, C.: First Study of Photochemical Escape from Proxima Centauri b, Europlanet Science Congress 2020, online, 21 Sep–9 Oct 2020, EPSC2020-888, https://doi.org/10.5194/epsc2020-888, 2020.

Abstract.

The upper atmosphere of HD 209458 b undergoes hydrodynamic escape that is the most atmospheric efficient mass-loss process. Previous works on its characterisation were mainly based on the available Ly-α observations, which provide limited information due to the interstellar medium absorption and the geocoronal emission contamination, and then a high degeneracy in the retrieved atmospheric parameters. Nevertheless, helium triplet lines, hereafter He(2³S), are not significantly affected by these processes so that the recent He(2³S) absorption spectra measurements by [1] are suitable for retrieving information of the HD 209458 b planetary upper atmosphere. In this work, we significantly improve the characterisation of the upper atmosphere of HD 209458 b by analysing the mid-transit He(2³S) spectral absorption measurements. Our study shows that hydrodynamic atmospheric escape expands the thermosphere from the thermobase (that we assume at 1.04 planet's radius, Rp) to the Roche lobe (at 4.22 Rp) by means of a strong and light wind (H/He composition of about 98/2) almost fully ionised beyond 2.9 Rp, in which the He(2³S) accumulates at low altitude. Details of this study can be found in [2]. 

1. Modelling

We applied a 1D hydrodynamic model with spherical symmetry for the structure of the thermosphere coupled with a non-local thermodynamic model for calculating the species density profiles (H, H⁺, He, He⁺ and  He(2³S)). In addition, for retrieving the atmospheric parameters, we calculated the synthetic spectra with a high-resolution radiative transfer model and compared to the He(2³S) measured absorption spectrum.    

Hydrodynamic continuity equations were solved by assuming a constant speed of sound. This approximation provided us with the same analytical solution than the isothermal Parker wind [3], although we note that constant speed of sound is not necessarily an isothermal approximation. All the production and loss processes (similar to those of [4] but extended), constants and XUV  (X-ray and extreme ultraviolet EUV) stellar fluxes used in the study can be found in [2]. The inputs of the model were the maximum temperature, the mass-loss rate (MLR) and the H/He composition of the thermosphere. He(2³S) absorption in HD 209458 b was observed with the high-resolution spectrograph CARMENES ([5], [6]) at the 3.5 m Calar Alto Telescope as reported by [1].  

The constant speed of sound approximation induces a degeneracy on temperature and MLR, that is added to the degeneracy on the H/He composition. In order to perform a suitable parameter study, we run a grid of simulations for a temperature range from 4000 K to 11500 K and an MLR range from 10⁸ to 10¹² g/s for three different H/He compositions, 90/10, 95/5 and 98/2.      

2. Results and discussion

Figure 1 shows the spectral transmission of the He(2³S) at mid-transit (black line with data points and error bars adapted from [1]) and the synthetic spectrum of one of our simulations that fit this signal (T= 6000 K, MLR of 1.9 x10⁹ g/s and H/He of 90/10, dashed cyan curve). The magenta curve represents an additional absorption necessary to reproduce the signal and the orange curve the total absoprtion. We did not include it in our fit as this gas is probably beyond the Roche lobe.          

Fig. 1. Spectral transmission of the He triplet at mid transit (adapted from [2]).

Figure 2 shows the degeneracy in MLR, maximum temperature and H/He composition of the thermosphere, and the strong constraints of the He(2³S) spectral absorption measurements on these parameters. We reduced the degeneracy comparing our results with other studies based on the Ly-α measurements of this exoplanet. Comparisons of H density profiles with those of [7], [8] and  [9],  suggest that H/He is lower than the canonical 90/10, and concluded that the most probable composition among our simulations is 98/2. Comparison of heating efficiencies allowed us to constrain the mass-loss rate, as we adopted the range of 0.1-0.2 according to [10].     

Fig. 2 Temperature-MLR curves that fit the He triplet absorption (adapted from [2]).

In summary, the constraints we found in our analysis are i) the MLR is in the range of (0.42-1.00) 10¹¹g/s; ii) the maximum thermospheric temperatures are from 7125 to 8125 K; iii) the H/He composition is about 98/2; iv) the  H/H⁺ transition altitude is in the range of 1.2-1.9 Rp; v) the atmosphere is almost fully ionised beyond 2.9 Rp; vi) the effective radii at which XUV absorption takes place is about 1.16-1.3 Rp, and vii) the average of the mean molecular weight is in the range of 0.61-0.73 g mole^-1.

3. Future work

Although our study can constrain the main structure of the hydrodynamic atmospheric escape, more comprehensive 3D magnetohydrodynamic models could reveal more details on the upper atmosphere of  HD 209458 b, especially on the kinetic and dynamics of the winds as they could be affected by possible magnetic fields, radiation pressure or interactions with the stellar wind.  Currently, we are working in a similar study of the exoplanets HD 189733 b and GJ3470 b.

Acknowledgements. 

IAA authors acknowledge financial support from the Spanish MCIU through the “Center of Excellence Severo Ochoa" award (SEV-2017-0709). CARMENES is funded by the German Max-Planck-Gesellschaft (MPG), the Spanish Consejo Superior de Investigaciones Científicas (CSIC), the European Union through FEDER/ERF FICTS-2011-02 funds, the members of the CARMENES Consortium and contributions by the Spanish Ministry of Economy, the German Science Foundation through the Major Research Instrumentation Programme and DFG Research Unit FOR2544 “Blue Planets around Red Stars”, the Klaus Tschira Stiftung, the states of Baden-Württemberg and Niedersachsen, and by the Junta de Andalucía. We acknowledge financial support from Spanish MCIU funds through projects: ESP2016–76076–R, ESP2017-87143-R, BES–2015–074542, BES–2015–073500, PGC2018-098153-B-C31,AYA2016-79425-C3-1/2/3-P.

References

[1] Alonso-Floriano, F.J. et al. 2019,  A&A, 629, A110

[2] Lampón, M. et al. 2020, A&A, 636, A13

[3] Parker, E.N. 1958, ApJ, 128, 664

[4] Oklopcic՛, A. & Hirata, C.M. 2018, ApJ, 855, L11

[5]  Quirrembach et al. 2016

[6]  Quirrembach et al. 2018

[7] Salz, M. et al. 2016, A&A, 586, A75

[8] García-Muñoz, A. 2007, Planetary and Space Science, 55, 1426

[9] Koskinen, T. et al. 2013, Icarus, 226, 1678

[10] Shematovich, V.I. et al. 2014, A&A, 571, A94

How to cite: Lampón, M., López-Puertas, M., Lara, L. M., Sánchez-López, A., Salz, M., Czesla, S., Sanz-Forcada, J., Molaverdikhani, K., Nortmann, L., Caballero, J. A., Bauer, F. F., Pallé, E., Montes, D., Quirrenbach, A., Nagel, E., Ribas, I., Reiners, A., and Amado, P. J.: Characterisation of the upper atmosphere of HD 209458 b by means of helium triplet absorption spectra, Europlanet Science Congress 2020, online, 21 Sep–9 Oct 2020, EPSC2020-973, https://doi.org/10.5194/epsc2020-973, 2020.

How to cite: Cristo, E.: CaRM: Retrieving exoplanets transmission spectra with high resolution spectroscopy, Europlanet Science Congress 2020, online, 21 Sep–9 Oct 2020, EPSC2020-1085, https://doi.org/10.5194/epsc2020-1085, 2020.

Launched on 18 December 2019, CHEOPS (CHaracterising ExOPlanet Satellite) is the first exoplanet mission dedicated to the search for transits of exoplanets by means of ultrahigh precision photometry of bright stars already known to host planets. It is S-(small) class mission in ESA’s Cosmic Vision 2015-2025, and a partnership between Switzerland and ESA, with important contributions from 10 other member states.

CHEOPS will provide the unique capability of determining accurate radii for a subset of planets in the super-Earth to Neptune mass range, for which masses have already been estimated from ground- based spectroscopic surveys. It will also provide precision radii for new planets discovered by ground- and space-based transit surveys, including TESS. By combining known masses with CHEOPS sizes, it will be possible to determine accurate densities for these smaller planets, providing key insight into their composition and internal structure. By identifying transiting exoplanets with high potential for in-depth characterisation – e.g. those that are potentially rocky and have thin atmospheres - CHEOPS will also provide prime targets for future instruments suited to the spectroscopic characterisation of exoplanetary atmospheres.

In this first poster in a series of three, we present an overview of the mission, including its capabilities and scientific performances.

How to cite: Isaak, K.: What is CHEOPS?, Europlanet Science Congress 2020, online, 21 Sep–9 Oct 2020, EPSC2020-1111, https://doi.org/10.5194/epsc2020-1111, 2020.

How to cite: Isaak, K., Queloz, D., and Benz, W.: The CHEOPS Guaranteed Time Observing Programme, Europlanet Science Congress 2020, online, 21 Sep–9 Oct 2020, EPSC2020-1112, https://doi.org/10.5194/epsc2020-1112, 2020.

Launched on 18 December 2019, CHEOPS (CHaracterising ExOPlanet Satellite) is the first exoplanet mission dedicated to the search for transits of exoplanets by means of ultrahigh precision photometry of bright stars already known to host planets. It is the first S-(small) class mission in ESA’s Cosmic Vision 2015-2025, and a partnership between Switzerland and ESA, with important contributions from 10 other member states.

CHEOPS will provide the unique capability of determining accurate radii for a subset of planets in the super-Earth to Neptune mass range, for which masses have already been estimated from ground- based spectroscopic surveys. It will also provide precision radii for new planets discovered by ground- and space-based transit surveys, including TESS. By combining known masses with CHEOPS sizes, it will be possible to determine accurate densities for these smaller planets, providing key insight into their composition and internal structure. By identifying transiting exoplanets with high potential for in-depth characterisation – e.g. those that are potentially rocky and have thin atmospheres - CHEOPS will also provide prime targets for future instruments suited to the spectroscopic characterisation of exoplanetary atmospheres.

How to cite: Isaak, K.: Community Access to CHEOPS, Europlanet Science Congress 2020, online, 21 Sep–9 Oct 2020, EPSC2020-1113, https://doi.org/10.5194/epsc2020-1113, 2020.