Europlanet Science Congress 2020
Virtual meeting
21 September – 9 October 2020
Europlanet Science Congress 2020
Virtual meeting
21 September – 9 October 2020

Oral presentations and abstracts


The characterisation of exoplanets is among the most active and rapidly advancing fields in modern astrophysics. An increasing number of observing techniques have enabled the characterisation of exoplanet system properties and provided access to the planetary atmospheres (chemical composition, thermal state and dynamics). Recently, combined analyses using different types of observations have outperformed the standard approaches, e.g. enabling precise constraints on the chemical abundances and elemental ratios in their atmospheres, or measurements of both the star and planet spin-orbit angles.

The goal of this session is to inspire the cooperation between specialised teams to overcome the limits of the fragmented data analyses and to break degeneracies in their interpretation. Contributions are invited to present new methods and/or analyses that combine different kind of observations for comprehensive exoplanet characterisation.

Convener: Giuseppe Morello | Co-conveners: Camilla Danielski, Pierre-Olivier Lagage, Lisa Nortmann, Enric Palle, Fei Yan

Session assets

Session summary

Chairperson: Giuseppe Morello, Camilla Danielski, Lisa Nortmann, Fei Yan, Pierre-Olivier Lagage, Enric Pallé
Kai Hou Yip, Quentin Changeat, Billy Edwards, Mario Morvan, Katy Chubb, Angelos Tsiaras, Ingo Waldmann, and Giovanna Tinetti

The study of exoplanetary atmosphere relies on detecting minute changes in the transit depth at different wavelengths. To date, a number of ground and space based instruments have been used to obtain transmission spectra of exoplanets in different waveband. One common practice is to combine observations from different instruments in order to achieve a broader wavelength coverage. We present here two inconsistent observations on WASP-96 b, one by Hubble Space Telescope (HST) and the other by Very Large Telescope (VLT). We present two key findings in our investigation: 1.) a strong water signature is detected via the HST WFC3 observations. 2.) A notable offset in transit depth (>1100 ppm) can be seen when the ground-based and space-based observations are combined together. The discrepancy raises the question of whether observations from different instruments could indeed be combined together. We attempt to align the observations by including an additional parameter in our retrieval studies but are unable to definitively ascertain that the aligned observations are indeed compatible. The case of WASP-96 b signals that compatibility of instruments should not be assumed. While wavelength overlaps between instruments can help, it should be noted that combining datasets remains a risky business. The difficulty in combining observations also strengthens the need for next generation instruments which will possess broader spectral coverage.

How to cite: Yip, K. H., Changeat, Q., Edwards, B., Morvan, M., Chubb, K., Tsiaras, A., Waldmann, I., and Tinetti, G.: On The Compatibility of Ground-based and Space-based Data: WASP-96 b, An Example, Europlanet Science Congress 2020, online, 21 Sep–9 Oct 2020, EPSC2020-67,, 2020.

Aurélien Wyttenbach

Spin-orbit angle measurments (e.g., with the Rossiter-McLaughlin effect) are often degenerates. This is due to fundamental symetries in the problem, to complex correlations between parameters, and to the difficulty to measure some parameters (e.g., the stellar inclination). Recently, independent teams reported spin-orbit angle measurments of the same systems (e.g., KELT-9) using different instruments and methods. In particular, exoplanetary systems around rapidly rotating and pulsating early-type stars present different possibilities to measure their spin-orbit angles. For these systems, one can access the stellar inclination thanks to the independent detections and studies of stellar differential rotations, of stellar gravity darkening, and of stellar pulsations. In this presentation, we will show that these measurments don't necessary have the same symetries. Thus, it may be possible to break degenaracies in the spin-orbit angle measurment by combining precise photometric transit (that allow us to measure, e.g., gravity darkening) and precise spectroscopic transit measurments (that allow us to measure, e.g., differential rotation and pulsations). A tentative coherent explanation of recent data on the KELT-9 system will be presented as an example and as a motivation to develop new synergies in this domain.

How to cite: Wyttenbach, A.: Breaking spin-orbit measurement degeneracies with precise photometric and spectroscopic transit observations, Europlanet Science Congress 2020, online, 21 Sep–9 Oct 2020, EPSC2020-124,, 2020.

Widest broadband transmission spectra (0.38-1.71 micrometer) obtained through ground based chromatic Rossiter-McLaughlin observations
Mahmoudreza Oshagh
Rafael Luque and the MuSCAT2 collaboration

In this work, we present new transit observations of the hot Jupiter WASP-74 b using the high-resolution spectrograph HARPS-N and the multi-color simultaneous imager MuSCAT2. The new data allow us to refine the orbital properties of the planet, the physical parameters of the host star, and reveal some properties about the planet's atmosphere using different techniques. We measure, for the first time, the sky-projected angle between the stellar spin-axis and the planet’s orbital axis, which is compatible with an orbit well-aligned with the equator of the host star. We build up an observational low-resolution transmission spectrum from the optical to the near-infrared of the planet using all the available transit photometry for this planet. Our joint reanalysis shows a slope in the transmission spectrum steeper than expected from Rayleigh scattering alone and no signs of strong optical absorbers such as TiO and/or VO, in disagreement with previous claims of the presence of these gases in the atmosphere of WASP-74 b.

How to cite: Luque, R. and the MuSCAT2 collaboration: A comprehensive study of the WASP-74 planetary system, Europlanet Science Congress 2020, online, 21 Sep–9 Oct 2020, EPSC2020-399,, 2020.

Characterizing HDS209458b and HD189733b with combined High and Low Resolution Spectroscopy
Joe Zalesky, Michael Line, and Matteo Brogi
Núria Casasayas-Barris, Enric Palle, Monika Stangret, Guo Chen, and Fei Yan and the ESPRESSO consortium

HD 209458b was the first transiting planet discovered, and the first for which its atmosphere, in particular Na I, was detected. With time, it has become one of the most studied planets, with a large diversity of atmospheric studies using low- and high-resolution spectroscopy. Here, we present the analysis of high-resolution transmission spectroscopy of HD 209458b using a total of five transit observations with HARPS-N and CARMENES spectrographs. In contrast to previous studies where atmospheric Na I absorption is detected, we find that, for all of the nights, either individually or combined, the transmission spectra can be explained by the combination of the centre-to-limb variation and the Rossiter-McLaughlin effect. Thus, the transmission spectrum reveals no detectable Na I absorption in HD 209458b. This is also observed in the time-evolution maps and transmission light curves, but at lower signal-to-noise ratio. Other strong lines such as Hα, Ca II IRT, the Mg I triplet region, and K I D1 are analysed, and are also consistent with the modelled effects, without considering any contribution from the exoplanet atmosphere. New ESPRESSO observations, with state-of-the-art stability and considerably larger signal-to-noise, confirm the results of our study and will also be shown.

How to cite: Casasayas-Barris, N., Palle, E., Stangret, M., Chen, G., and Yan, F. and the ESPRESSO consortium: Revisiting the atmosphere of HD 209458b with HARPS-N, CARMENES and ESPRESSO, Europlanet Science Congress 2020, online, 21 Sep–9 Oct 2020, EPSC2020-811,, 2020.

Anna Brucalassi




Ariel has been selected as the next ESA M4 science mission and it will observe the atmospheres of a large and diversified population of transiting exoplanets. Key factor for the achievement of the scientific goal of ARIEL is the selection strategy for the definition of the input target list. A meaningful choice of the targets requires an accurate knowledge of the planet hosting star properties and this is necessary to be obtained well before the launch.
We present the results of a bench-marking analysis between three different spectroscopic techniques used to determine stellar parameters for a selected number of targets belonging to the Ariel reference sample.
Our goal is to consolidate a method that will be used to homogeneously determine the stellar parameters of the complete Ariel reference sample.

How to cite: Brucalassi, A.: A comparison analysis for the determination of stellar parameters of Ariel targets, Europlanet Science Congress 2020, online, 21 Sep–9 Oct 2020, EPSC2020-898,, 2020.

Flavien Kiefer, Guillaume Hébrard, Alain Lecavelier, Eder Martoli, Shweta Dalal, and Alfred Vidal-Madjar

Mass is one of the most important parameters for determining the true nature of an astronomical object. Yet, many published exoplanets in on-line database, such as or the NASA exoplanet archive, still lacks a measurement of their true mass, in particular those detected thanks to radial velocity (RV) variations of their host star. For those, only the minimum mass, or m sin(i), is known, owing to the insensitivity of RVs to the inclination of the detected orbit compared to the plane-of-the-sky. The mass that is given in database is generally that of an assumed edge-on system (90 degrees), but many other inclinations are likely, even extreme values closer to 0 degree (face-on configuration). In such case, the mass of the published object could be strongly underestimated, even by 1 or 2 orders of magnitude. We used a recently developed tool, called GASTON (Kiefer et al. 2019b & 2019c), to take advantage of the voluminous Gaia astrometric database, in order to constrain the inclination and true mass of several hundreds of published exoplanet candidates (Kiefer et al. 2020, submitted). In this presentation, we will present the method and report on several exoplanet candidates reclassified in the stellar domain, among which unknown brown/M-dwarf. We also confirm the planetary nature of a few tens of candidates.

How to cite: Kiefer, F., Hébrard, G., Lecavelier, A., Martoli, E., Dalal, S., and Vidal-Madjar, A.: Determining the mass of RV exoplanet candidates using Gaia, Europlanet Science Congress 2020, online, 21 Sep–9 Oct 2020, EPSC2020-926,, 2020.

Baptiste Klein, Jean-François Donati, Claire Moutou, Xavier Delfosse, Xavier Bonfils, Eder Martioli, Pascal Fouque, Ryan Cloutier, Etienne Artigau, René Doyon, Guillaume Hebrard, Julien Morin, Julien Rameau, Peter Plavchan, and Eric Gaidos

Measuring the mean densities of close-in planets orbiting pre-main-sequence (PMS) stars is crucially needed by planet formation and evolution models. This requires to measure both planet radii, from the depth of their transit light curves, and masses, from the radial velocity (RV) wobbles induced by the planet on its host star. However, PMS stars exhibit intense magnetic activity responsible for fluctuations in both photometric and RV curves that are much stronger than planet signatures. As a result, no close-in planet younger than 25 Myr has a well-constrained bulk density.

AU Microscopii (AU Mic) is a nearby active 22-Myr old M1 star around which a close-in transiting planet was recently detected from TESS and Spitzer light-curves (Plavchan et al., 2020). Despite velocimetric follow-ups in the optical domain, the authors reported no more than an upper limit for the planet mass due to the large dispersion induced by stellar activity in their RV time-series. The high stellar brightness, and the expected decrease in the amplitude of stellar activity RV signals from the optical to the near-infrared domains, makes the nIR (YJHK bands) spectropolarimeter SPIRou (Canada-France-Hawaii Telescope, atop Mauna Kea) the ideal instrument to measure the mass of AU Mic b.

In this study, we present a spectropolarimetric and velocimetric analysis of 27 observations of AU Mic collected with SPIRou from September to November 2019. The dispersion of our RV time-series is about 45 m/s, ~2.5 times lower than that obtained in the optical domain. We jointly model the planet and stellar activity components of the RV data set, resulting in a 3.5σ detection a close-in transiting planet AU Mic b, with an estimated mass of 16.7 +/- 4.9 Earth mass, implying a Neptune-like bulk density of 1.3 +/- 0.4 g/cm³. A consistent detection of the planet is independently obtained by simultaneously reconstructing the surface brightness of the star and estimating the planet parameters using Zeeman-Doppler imaging (ZDI). Using ZDI, we invert our intensity and circularly-polarized spectra into surface brightness and large-scale magnetic field, resulting in a mainly poloidal and axisymmetric field of 475 G, dominated by a 450 G dipole tilted at 19° to the rotation axis towards phase 0.2. Moreover, we find that the large-scale magnetic field is sheared by solar-like differential rotation of 0.167 rad/d, twice as large as that shearing the spot/plage distribution. Finally, we compute various indicators of the stellar activity and study their rotational modulation and correlation with RVs. We find that the bisector inverse slope and small-scale magnetic field correlate best with the stellar activity RV signal. Surprisingly, chromospheric indices based on Helium I (HeI, 1083 nm) and Paschen Beta (PaB, 1282 nm) probe different regions of the stellar disc, HeI being mostly emitted around the magnetic equator while PaB emission is linked to the magnetic pole.

AU Mic b already appears as a prime target for constraining planet formation and evolution models. Moreover, the interactions between the planet and the debris disk surrounding the system could give rise to promising synergies between photometric, spectroscopic and imaging techniques. Finally, AU Mic b is a primary candidate for an atmosphere characterization and, potentially, the detection of an extended H/He exosphere around AU Mic b with upcoming space- and ground-based missions.

How to cite: Klein, B., Donati, J.-F., Moutou, C., Delfosse, X., Bonfils, X., Martioli, E., Fouque, P., Cloutier, R., Artigau, E., Doyon, R., Hebrard, G., Morin, J., Rameau, J., Plavchan, P., and Gaidos, E.: Investigating the young AU Mic system with SPIRou: large-scale stellar magnetic field and close-in planet mass, Europlanet Science Congress 2020, online, 21 Sep–9 Oct 2020, EPSC2020-944,, 2020.

Thomas Vandal, Julien Rameau, and René Doyon

Nearly 15 years of radial velocity (RV) monitoring and direct imaging (DI) enabled the detection oftwo giant planets orbiting the young, nearby star β Pictoris. The δ Scuti pulsations of the star, overwhelming planetary signals, need however to be carefully suppress. In this talk, we propose a new and independent analysis of the system, making use of all available data, including photometric light curve from the ground and space, long term RV and DI monitoring. We demonstrate how all data can be consistently modelled in a Bayesian framework. We show how modern and physically motivated kernels for Gaussian Process can effectively model complex stellar activity. Using further carefull statistical treatment of the data to extend the monitoring, we detect both planets from RV data only for the first time. To characterize the system more accurately, we also perform a joint fit of 
all available relative astrometry and RV data. We provide precise orbital parameters and discuss the whole system architecture. The inferred dynamical mass measurements for both planets are also compared to mass-luminosity evolutionary tracks. This work opens the path towards a precise characterization of young planetary systems combing photometry, spectroscopy, and astrometry.

How to cite: Vandal, T., Rameau, J., and Doyon, R.: New Dynamical Mass Estimates of the beta Pictoris Planetary System Through Gaussian Process Stellar Activity Modelling, Europlanet Science Congress 2020, online, 21 Sep–9 Oct 2020, EPSC2020-954,, 2020.

Victoria Foing, Ana Heras, and Bernard Foing

This work compares the information obtained from TESS and Kepler lightcurves, and integrates information obtained from ground based observatories. We apply Machine learning methods for modelling stellar and instrumental systematics in lightcurves because they can quickly identify patterns in data without prior knowledge of the functional form. We use a Gaussian Process to model the stellar activity, background granulation, and transit signals simultaneously because we expect that using a multi-component model can improve planetary characterisation.  This work seeks to address the following questions:

RQ1: How accurately can we model the stellar activity and transit signals in TESS and Kepler lightcurves with machine learning?

RQ2: To what extent can we use these models to interpret the rotation periods and activity cycles of the stars?

RQ3: To what extent can we use these models to detrend the lightcurves and improve transit exoplanet characterization?

The model is initialized using information from Box Least Squares, LombScargle analysis, and Autocorrelation functions, and then Markov Chain Monte Carlo algorithms are run to fit rotational modulation parameters and planet parameters.  We compare the results of this method across different missions (TESS and Kepler) and compare the results of this method with results obtained from ground based surveys. We illustrate the comparison and the astrophysical results in the case of WASP62 and Kepler 78 targets.


How to cite: Foing, V., Heras, A., and Foing, B.: Combining Kepler, TESS and ground based data for characterising exoplanets and stellar activity, Europlanet Science Congress 2020, online, 21 Sep–9 Oct 2020, EPSC2020-1097,, 2020.