Low frequency radio search and study of exoplanet magnetospheres and star-planet plasma interactions

Informazioni relative al progetto

EXORADIO

ID dell’accordo di sovvenzione: 101020459

DOI

10.3030/101020459

Data della firma CE 26 Agosto 2021

Data di avvio 1 Settembre 2021

Data di completamento 31 Marzo 2027

Finanziato da

• EXCELLENT SCIENCE - European Research Council (ERC)

Costo totale

€ 2 212 500,00

Contributo UE

€ 2 212 500,00

Coordinato da

CENTRE NATIONAL DE LA RECHERCHE SCIENTIFIQUE CNRS
France

Periodic Reporting for period 2 - EXORADIO (Low frequency radio search and study of exoplanet magnetospheres and star-planet plasma interactions)

Periodo di rendicontazione: 2023-03-01 al 2024-08-31

Sintesi del contesto e degli obiettivi generali del progetto

The project aims at detecting with certainty for the first time radio emissions from the magnetospheres of exoplanets and from plasma interactions (magnetic, electric) between these planets and their stars. These detections will open the new fields of comparative magnetospheric physics and space weather applied to exoplanets (thus exo-mag. physics and exo-space weather), considerably expanding this field presently only applicable to the solar system.

Theory suggests that the low frequency radio range (≤100-200 MHz) is most adapted to detect exoplanetary emissions whereas star-planet emissions may occur at higher frequencies (~GHz). A direct by-product of these observations is the possible detection of low-frequency stellar radio emissions, signatures of space weather around other stars.

In order to achieve these detections we use the largest low-frequency radiotelescopes in the world, either in beamformed (or single-dish) mode, or in imaging mode:
• NenuFAR in France (10-85 MHz, beamformed and imaging), that we also finish building while continuously improving its hardware and software (detection pipelines) ;
• LOFAR in The Netherlands (30-200 MHz, beamformed and imaging), of which we create and improve original detection pipelines ;
• FAST, the giant Chinese "Arecibo" (in the range 1000-1500 MHz, single-dish), that has a huge sensitivity and in which our main participation is the interpretation of the detected emissions.

This research has deep implications in planetology. The 6 known magnetospheres in the Solar system (Mercury, Earth and the 4 giants) are very different albeit based on the same plasma physics. Expanding radio and plasma planet-star studies beyond the solar system will allow us to distinguish between the fundamental/universal mechanisms (of radio emission fuelling, beaming, variability, periodicity...) and the ones more specific to each system. The existence of a magnetic field also has potential implications on planetary habitability (particle bombardment, atmospheric escape). We aim at eventually mutualizing our observations with SETI (search for extra-terrestrial artificial signals) ones.

The development of expertise in low-frequency radio instruments, in processing pipelines, in interpretation tools also prepares the scientific community for the exploitation of SKA, the giant radiotelescope of the 21st century. It fosters collaboration between the major institutes involved (Paris & Nançay observatories, ASTRON, Chinese institutes...).

Lavoro eseguito dall’inizio del progetto fino alla fine del periodo coperto dalla relazione e principali risultati finora ottenuti

With NenuFAR, we have scheduled and performed since the start of the project 8000 h of beamformed observations of ~50 exoplanetary systems and ~30 stars in the range 15-80 MHz. 11 of these targets have also been observed for 700 h in imaging mode. We have written semi- or full-automatic pipelines that process these data:
• for beamformed data: reduction, identification of contaminations by strong radiosources, elimination of radio frequency interference - RFI -, calculation of Stokes parameters IQUV and of the rotation measure spectrum, integration, search for drifting time-frequency features and for periodic emissions (the pipeline, that uses high-volume data processing techniques, is 80% finalized and automatized).
• for imaging data: reduction, calibration, imaging, dynamic spectra from residual visibilities, detection of constant and variable sources (polarisation calibration is still under development, but the pipelines works in Stokes I).
Diagnostic plots are produced at all steps. We are analysing all the recorded data.

With LOFAR, we have obtained and analysed about 100 h of beamformed observations on the system of Tau Boötis in the range 15-80 MHz, for which tentative radio detections have been obtained in the past. In parallel, we have collaborated with C. Tasse to develop an original pipeline that uses the residual visibilities of LoTSS (the LOFAR two-meter sky survey, 120-168 MHz), i.e. 15000 h of calibrated data with all detected sources subtracted, to synthesize dynamic spectra (t-f images) in the direction of all known exoplanets and stars in the observed fields (~200000 targets). We have processed them in search for polarized radio bursts from stellar and exoplanetary systems.

With FAST, we have analysed observations of the active star AD Leonis (1000-1500 GHz), detected very fast bursts drifting in the time-frequency plane, and interpreted the observations based on the codes that we have developed for the study of Jupiter's radio emissions.

In order to optimize these activities, we have developed codes for target selection of exoplanets and star-planet systems in radio, and for orbital or rotational phase coverage, for producing contamination index maps for any target observed by NenuFAR, and for detecting automatically t-f drifting features in dynamic spectra.
In parallel, we have contributed to MHD simulations intended to characterize targets, predict signals to be observed, and interpret them, and near-completed the development of NenuFAR.

Progressi oltre lo stato dell’arte e potenziale impatto previsto (incluso l’impatto socioeconomico e le implicazioni sociali più ampie del progetto fino ad ora)

With NenuFAR in beamformed mode, we are completing the largest analysis of stellar and exoplanetary targets (8000 h on ~80 targets), that will provide detections of upper limites on each system.
In parallel, we have produced an extensive statistical map of the RFI impacting NenuFAR, as a function limits function of frequency, pointing direction in the sky (azimuth, declination), time of observation, and time of year. The better understanding of the NenuFAR RFI environment allows for a more efficient processing of all its observations (not only star/exoplanets) as well as an optimized scheduling of the observation parameters (e.g. avoiding polluted bands).
With NenuFAR in imaging mode, we have detected in the first 100-hour observation repeating bursts in a given direction. Physical analysis is ongoing.

With LOFAR in beamformed mode, we have not re-detected any emission from the Tau Boötes system, casting doubt on the previous tentative detection. But this has also motivated theoretical analyses to better understand the variability of a star-planet radio signature.
With LOFAR in imaging mode (LoTSS dynamic spectra), we are on the process of achieving detections, but it is too early to detail these results publicly.

With FAST, we are detecting the finest and most complex stellar bursts ever recorded, and we have performed the first study that takes advantage of radio and magnetic field observations to deduce strong constraints on the star's plasma environment (location of the radio sources, energy of the electrons involved). The methods developed will likely be applicable to all observed targets.

The exoplanet/star-planet radio target selection code is operational, and we are now building for it a database of all published values of stellar magnetic fields. This code enables target selection for any radio telescope, and provides help to interpret the detected signals.
The various pipelines developed for analysing the data have broad applications (possibly with adaptations) to low-frequency radiotelescopes.
The NenuFAR array is near completion, reaching maximum sensitivity and optimal performance. This will serve the exoplanet/star program as well as all other programs conducted on NenuFAR. The art project associated to the instrument ("Le Dôme") is in preparation.