Europlanet Science Congress 2021
Virtual meeting
13 – 24 September 2021
Europlanet Science Congress 2021
Virtual meeting
13 September – 24 September 2021


Synergies between techniques for characterising exoplanets from space and ground-based facilities

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.

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

Session assets

Discussion on Slack

Oral and Poster presentations and abstracts

Chairperson: Giuseppe Morello
Giuseppe Morello

We try to reconcile contrasting results about the composition of exoplanet atmospheres investigated with high-resolution and low-resolution spectroscopy.

How to cite: Morello, G.: The HR-LR duality of exoplanet atmospheres, Europlanet Science Congress 2021, online, 13–24 Sep 2021, EPSC2021-788,, 2021.

Emma Esparza-Borges, Mahmoud Oshagh, Nuria Casasayas-Barris, and Enric Pallé

Multi-band photometric transit observations or low resolution spectroscopy (spectro-photometry) are normally used to retrieve the broadband transmission spectra of transiting exoplanets in order to assess the chemical composition of their atmospheres. In this work, we present an alternative approach for recovering the broadband transmission spectra using chromatic Doppler Tomography. To validate the method and examine its performance, we used new observational data obtained with the ESPRESSO instruments to retrieve the  transmission spectra of the archetypal hot Jupiter HD209458b. Our findings indicate that the recovered transmission spectrum is in good agreement with the results presented in previous studies, which used different methodologies to extract the spectrum.

How to cite: Esparza-Borges, E., Oshagh, M., Casasayas-Barris, N., and Pallé, E.: Retrieving the transmission spectrum of HD 209458b usingCHOCOLATE: a new Chromatic Doppler Tomography technique, Europlanet Science Congress 2021, online, 13–24 Sep 2021, EPSC2021-856,, 2021.

Vatsal Panwar, Jean-Michel Desert, Kamen Todorov, Jacob Bean, Catherine Huitson, Kevin Stevenson, Jonathan Fortney, and Marcel Bergmann

Ground-based spectrophotometric observations of transiting exoplanet atmospheres conventionally rely on correcting for instrumental and telluric systematics in the light curves by using reference stars that are simultaneously observed. However, this approach often leads to sub-optimal corrections due to multiple accounts on which the target and reference star spectra can be affected by systematics differently through the night, ultimately limiting the achievable precision and accuracy on the measurement of planetary atmospheric signatures. We introduce a new method based on Gaussian Processes regression to address this challenge by extracting the transmission or emission spectrum without relying explicitly on the reference stars. Our new method overcomes the necessity of using reference stars and opens up the doors to ground-based atmospheric observations of exoplanets orbiting bright host stars (e.g. those discovered by TESS) that intrinsically lack proper reference stars. We present results from the application of our method to a broad sample of exoplanets observed in the optical and near-infrared using Gemini/GMOS and Keck/MOSFIRE. We also discuss the challenges and possible solutions arising from stellar variability towards combining high precision ground-based low-resolution spectroscopy observations in complementarity with future infrared observations from HST and JWST.

How to cite: Panwar, V., Desert, J.-M., Todorov, K., Bean, J., Huitson, C., Stevenson, K., Fortney, J., and Bergmann, M.: Novel methods to probe exoplanet atmospheres using ground-based spectrophotometry, Europlanet Science Congress 2021, online, 13–24 Sep 2021, EPSC2021-700,, 2021.

 The instruments at Telescopio Nazionale Galileo as resources for a broad community
Ennio Poretti
Observability of Exo-Atmospheres in emission using Ariel
Andrea Bocchieri, Enzo Pascale, Lorenzo Mugnai, Quentin Changeat, and Giovanna Tinetti
Detection and physical parameters
Laetitia Delrez and the CHEOPS Consortium

***Results under embargo. Paper accepted for publication at Nature Astronomy, to be published in June.***

Multi-transiting planetary systems around bright stars offer unique windows to comparative exoplanetology. Nu2 Lupi (HD 136352) is a naked-eye (V=5.8) Sun-like star that was discovered to host three low-mass planets with orbital periods of 11.6, 27.6, and 107.6 days via radial velocity monitoring with the HARPS spectrograph. The two inner planets (b and c) were recently found to transit by the TESS mission, prompting us to follow up the system with ESA's brand-new CHaracterizing ExOPlanets Satellite (CHEOPS). This led to the exciting discovery that the outer planet d is also transiting. With its bright Sun-like star, long period, and mild irradiation (∼5.7 times the irradiation of Earth), Nu2 Lupi d unlocks a completely new region in the parameter space of exoplanets amenable to detailed characterization. By combining all available space and ground-based data, we measured its radius and mass to be 2.56±0.09 REarth and 8.82±0.94 MEarth, respectively, and refined the properties of all three planets: planet b likely has a rocky mostly dry composition, while planets c and d seem to have retained small hydrogen-helium envelopes and a possibly large water fraction. This diversity of planetary compositions makes the Nu2 Lupi system an excellent laboratory for testing formation and evolution models of low-mass planets.

How to cite: Delrez, L. and the CHEOPS Consortium: Exploring the Nu2 Lupi system with CHEOPS, Europlanet Science Congress 2021, online, 13–24 Sep 2021, EPSC2021-810,, 2021.

Adrien Leleu

Determining the architecture of multi-planetary systems is one of the cornerstones of understanding planet formation and evolution. Resonant systems are especially important as the fragility of their orbital configuration ensures that no significant scattering or collisional event has taken place since the earliest formation phase when the parent protoplanetary disc was still present. As unveiled by TESS, CHEOPS, ESPRESSO, NGTS and SPECULOOS, TOI-178 harbours at least six planets in the super-Earth to mini-Neptune regimes, all planets but the innermost one form a 2:4:6:9:12 chain of Laplace resonances, and the planetary densities show important variations from planet to planet. TOI-178 have hence several characteristics that were not previously observed in a single system, making it a key system for the study of processes of formation and evolution of planetary systems. We will review what we know of TOI-178, and what we expect from futur observations.

How to cite: Leleu, A.: Six transiting planets and a chain of Laplace resonances in TOI-178, Europlanet Science Congress 2021, online, 13–24 Sep 2021, EPSC2021-811,, 2021.

Vladislava Ananyeva, Alexander Tavrov, Oleg Korablev, and Jean-Loup Bertaux

More than 95% of the known exoplanets were discovered by the transit- and radial velocity techniques. However, the observed distributions of planets by their masses and by their orbital periods are significantly distorted by numerous observational selections, different for these techniques and different surveys.

We found and studied the de-biased statistical distributions of exoplanets by masses and by orbital periods for three groups of exoplanets: I. transiting planets discovered by Kepler ST, whose masses were measured by the follow-up radial velocity technique, II. transiting planets discovered by ground-based surveys (SuperWASP, HATNet, NGTS, XO, KELT, etc.), III. planets discovered by the radial velocity technique. The synthetic projective-mass distribution of RV planets obeys the piecewise power law with the breakpoints at ~0.14MJ and ~1.7MJ. The distribution of RV-planets with m = (0.011-0.087)MJ (or (3.5-28)ME) accurately obeys the power law with an exponent of -2, dN/dm ∝ m^-2. The distribution of RV planets with m = (0.21-1.7)MJ follows the power law with an exponent ranging from -0.7 to -0.8, dN/dm ∝ m^(-0.7…-0.8). The distribution of RV planets with m = (1.7-13)MJ is fitted by a power law with an exponent ranging from -1.7 to -2.0, dN/dm ∝ m^(-1.7…-2.0). In general, the synthetic projective-mass distribution of RV planets well agrees with the predictions of the population synthesis theory (Mordasini, 2018) and includes more detailed features to be discussed.

The exoplanets distribution by periods generally follows a power law with an exponent of -0.75 and indicates a predominant (averaged) structuring of the planetary systems.

De-biased mass distribution of RV-planets with orbital periods of 2-58 days is well consistent with a similar distribution of the Kepler planets. The mass distribution of the transit exoplanets detected by ground-based surveys is consistent with the similar distribution of RV planets with periods of 1-20 days.

How to cite: Ananyeva, V., Tavrov, A., Korablev, O., and Bertaux, J.-L.: Distribution of RV- and transiting exoplanets by masses and orbital periods taking into account observational selection, Europlanet Science Congress 2021, online, 13–24 Sep 2021, EPSC2021-802,, 2021.

Emily Rickman

Very little is known about giant planets and brown dwarfs at an orbital separation great than 5 AU. And yet, these are important puzzle pieces needed for constraining the uncertainties that exist in giant planet formation and evolutionary models that are plagued by a lack of observational constraints. In order to observationally probe this mass-separation parameter space, direct imaging is necessary but faces the difficulty of low detection efficiency.

To utilise the power of direct imaging, pre-selecting companion candidates with long-period radial velocities, coupled with proper anomalies from Hipparcos and Gaia, provide a powerful tool to hunt for the most promising candidates for direct imaging. Not only does this increase the detection efficiency, but this wealth of information removes the degeneracy of unknown orbital parameters, like the inclination, leading to derived dynamical masses which can serve as benchmark objects to test models of formation and evolution.

With upcoming missions like JWST and Roman, as well as ground-based facilities like the ELT, observing time is valuable and the strategy of direct imaging needs to be re-defined to pre-select targets. Looking further ahead, perfecting these strategies will be necessary as we look toward HabEx and LUVOIR to pinpoint the location of terrestrial planets amenable to direct imaging.

I present the ongoing work towards creating a tool to use this information to select candidates for direct imaging with upcoming and future instruments. Ultimately this will lead us to a catalogue of benchmark objects that can be used to test models of planet formation and evolution.

How to cite: Rickman, E.: Preparing for the future of direct imaging exoplanets through combining other exoplanet detection techniques, Europlanet Science Congress 2021, online, 13–24 Sep 2021, EPSC2021-417,, 2021.

Marion Cointepas, Xavier Bonfils, and Jose Almenara

ExTrA (Exoplanets in Transits and their Atmospheres - Bonfils et al. 2015) is a new instrument composed of an array of three 60-cm telescopes capable of infrared photometry and located in La Silla, Chile. This instrument relies on a new approach that involves combining optical photometry with spectroscopic information in order to mitigate the disruptive effect of Earth’s atmosphere, as well as effects introduced by instruments and detectors.  ExTrA is currently being used to confirm TESS planet detections around M-dwarfs, refine transit parameters, and search for additional exoplanets in the same systems. ExTrA obtains a better precision for the planetary radius and for the transit timings for late M-type stars with one or a few TESS transits. This work already led to the confirmation of a mini-Neptune around the M-dwarf TOI-269 (Cointepas et al. 2021). ExTrA will also work in tandem with NIRPS, a near-infrared spectrograph that will join HARPS (High Accuracy Radial velocity Planet Searcher) on the 3.6m ESO telescope to conduct a comprehensive radial-velocity survey on M dwarfs. 

How to cite: Cointepas, M., Bonfils, X., and Almenara, J.: Searching for exoplanets around M-dwarfs with ExTrA, Europlanet Science Congress 2021, online, 13–24 Sep 2021, EPSC2021-632,, 2021.

José Rodrigues, Susana Barros, and Nuno Santos

TESS is now routinely discovering new exoplanets and candidates (2647 TOIs in April 2021). Detailed analysis of the TESS lightcurves is necessary to select the best candidates for Radial Velocities (RV) follow-up as we cannot realistically observe all TOIs using ground facilities due to the instrument time required.
We developed a modular tool called "Follow-Up Lightcurves Multitool Assisting Radial velocities (FULMAR)" to select suitable follow-up targets more effectively, as the ones with lower stellar activity would require fewer observations to be confirmed. Our code compiles available TESS lightcurves for any selected target. It can filter the activity using different methods, compute the rotation period of the star using Gaussian Processes, search for transits in the detrended lightcurve using BLS or TLS and probe signals that were detected with RV. FULMAR could also reduce the necessary observation time per target, for example by killing aliases, allowing for the characterization of more systems with a given instrument. 

How to cite: Rodrigues, J., Barros, S., and Santos, N.: Follow-Up Lightcurves Multitool Assisting Radial velocities (FULMAR), Europlanet Science Congress 2021, online, 13–24 Sep 2021, EPSC2021-776,, 2021.