CE31 - Physique Subatomique, Sciences de l'Univers, Structure et Histoire de la Terre

The SPIRou Planet Search for Habitable worlds – SPlaSH

SPlaSH : The SPIRou Planet Search for Habitable worlds

Exploitation and coordination of the SPIRou Legacy Survey, a radial velocity survey dedicated to the search (for) and characterization of low mass exoplanets around M dwarfs.

Search and characterization of very low mass planets around M dwarf

The objective of the SPlaSH project is to exploit the part of the SPIRor Legacy Survey dedicated to the search and characterization of extrasolar planets around M dwarfs. SPIRou, the new near-infrared spectropolarimeter and velocimeter installed at the CFH Telescope, is designed to be a world leader in this scientific field. Our team is co-leading (with Canadian collaborators) the operation of the SPIRou Legacy Survey. <br /><br />The objectives are organised around 4 work packages: (WP1) to carry out a radial velocity survey of the 100-120 M dwarf stars closest to the Sun in order to complete the population of planets in the near solar neighbourhood and explore planetary diversity; (WP2) to measure the masses of planets located in transiting systems (notably discovered by the TESS satellite) in order to estimate their bulk density and therefore their composition; (WP3) optimising data processing of SPIRou data and obtaining the most accurate stellar radial velocity measurements and (WP4) efficiently filtering the effect of stellar activity on radial velocity measurements using spectropolarimetry.

There is presently a considerable interest to search for exoplanets around very-low-mass stars (M dwarfs), particularly to study planets in their habitable zones (HZ) and to characterize both their core density and their atmosphere. M dwarfs have the great advantage that their HZ planets are much easier to detect than those of other types of stars. But what makes M dwarfs truly unique targets is that the detected planets will be amenable to characterization of their atmosphere in the coming decade

The disadvantage of M-dwarfs to search for planets is that they are intrinsically faint in the optical and velocimeters such as HARPS only achieve a 1 m/s precision on the few brightest M dwarfs (Bonfils et al 2013). To break this barrier it is essential to develop a survey with a velocimeter working in the near-infrared (nIR) and with very good throughput. Given their low temperatures, M-dwarfs have a photon flux 1 to 3 orders of magnitude higher than in the nIR than in the optical.

Among the first generation nIR velocimeters (CARMENES, IRD, HPF), SPIRou is the only one that combines the K band (totaling ~40% of the near-infrared RV Contents for a mid-M dwarfs), polarimetry (crucial to filter activity effect on RV measurements) and a large throughput. The validated performance of SPIRou makes it the ideal instrument for carrying-out extensive monitoring programs of M dwarfs requiring large amounts of observing time.

The observations of our survey started in February 2019 and will be spread over 4 or 5 years. By October 2020 we have achieved a completion rate of approximately 54%. The SPIRou data show important differences compared to the data provided by previous instruments. This is one of the strengths of the instrument, but it is also a difficulty because we have to re-invent many steps in the data analysis. A lot of work has therefore been done and we have improved the data analysis pipeline to extract the most accurate radial velocities.

Among the first results obtained, we highlight our measurements of unequalled quality on the AU Mic system, a very important system for understanding the evolution of young planets as it is the only one known with a planet of Neptune's mass at an age of only a few million years. There we demonstrate our ability to filter the effect of stellar activity on Radial Velocities and thus obtain the best determination of the orbital alignment of the planet with the star's rotation plane (Martioli et al. 2020) and the first determination of the mass, and thus density, of the planet (Klein et al. 2021).

We demonstrate the capabilities of SPIRou in the analysis of atmospheric chemical components, in the case of the warm Jupiter Tau Bootis b (Pelletier et al. 2021, in prep).

Our monitoring of ToI-1278, a transiting system detected with TESS, allows us to highlight a rare case of a brown dwarf in close orbit around a red dwarf (Artigau et al. 2021, in prep).

The progress of the project, with the first publications submitted 1,5 years after the start of the survey, and less than a year after the recruitment of the first CDDs of the project, is as expected. Such surveys will give the maximum of these results several years after the beginning of the acquisition, since a long follow-up of the target (over several months or years) is essential for this science.

We thus expect the great majority of our results in the second part of this project, and in particular a statistical vision of the SPIRou discoveries.

1. Donati, Kouach, Moutou, Doyon, Delfosse, et al. 2020 « SPIRou : nIR velocimetry & spectropolarimetry at CFHT » MNRAS, 498, 5684

2. Moutou, Dala, Donati, Martioli, et al. 2020, « Early science with SPIRou: near-infrared radial velocity and spectro-polarimetry of the planet-host star HD 189733 », Astronomy & Astrophysics, 642, 72

3. Martioli, Hébrard, Moutou, Donati, Artigau, Cale et al. 2020, « Spin-Orbit alignement and magnetic activity in the young planetary systemAU Mic », Astronomy & Astrophysics, 641, 1

4. Hobson, Bouchy, Cook, Artigau, Moutou, Boisse, Lovis, Carmona, Delfosse, Donati, and the SPIRou Team, 2021 « The SPIRou wavelength calibration for precise radial velocities inthe near infrared » accepté par Astronomy & Astrophysics

5. Klein, Donati, Moutou, Delfosse, Bonfils, Martioli et al., 2021 « Investigating the young AU Mic system with SPIRou: large-scalestellar magnetic field and close-in planet mass », accepté par MNRAS

6. Pelletier, Benneke, Darveau-Bernier et al. 2021, « Where is the Water? Jupiter-like C/H ratio but strong H2O depletion found on Tau Bootis b using
SPIRou. » soumis à Astrophysical Journal

7. Artigau, Cook, Doyon et al. 2021. « ToI-1278b : a rare case of Brown Dwarf Companion in Close-In orbit around an M dwarf », soumis à Astronomical Journal

Since the pioneering discovery of a giant planet orbiting 51 Peg (Mayor & Queloz 1995), about 3500 extra-solar planets have now been detected, revealing the diversity of planetary systems and revolutionizing our ideas on planet formation and evolution. Identifying habitable Earth-like planets and searching for biomarkers in their atmospheres is one of the main challenges of 21st century Astronomy (e.g.,`A Science vision for European Astronomy'). This endeavor aims at understanding how unique our own Earth is, and eventually at assessing whether life could exist elsewhere in the universe. Meeting this challenge motivates ambitious space missions -- such as JWST, TESS, PLATO -- and is one of the primary objectives of the 40m-class ELTs for the next decades.
In this context there is presently a considerable interest to search for exoplanets around very-low-mass stars (M dwarfs), particularly to study planets in their habitable zones (HZ) and to characterize both their core density and their atmosphere. M dwarfs have the great advantage that their HZ planets are much easier to detect than those of other types of stars. But what makes M dwarfs truly unique targets is that the detected planets will be amenable to characterization of their atmosphere in the coming decade through transit spectroscopy either with JWST (Doyon et al. 2014; Beichman et al. 2014), or by combining high-dispersion spectroscopy with high contrast imaging with ELT (Snellen et al. 2015) or even with VLT for the most favorable cases (Lovis et al. 2017). Similar planets around solar type stars will only be accessible for characterization with highly ambitious space missions such as LUVOIR, which will not be in operation before the middle of the century.
SPIRou, the new near-infrared spectropolarimeter and velocimeter for CFHT, is designed to be a world-leader in this scientific field. Our team will co-lead (with canadian collaborators) its exploitation in coordinating a Radial Velocity survey (starting in Sept-Oct 2018) dedicated to the search (for) and characterization of low mass exoplanets. Our project shall be highly competitive to search for low-mass planets orbiting M-dwarfs, and ideally phased with both space missions TESS and JWST. With the present ANR proposal we aim to strengthen and coordinate our team in order to reach our 4 main scientific goals : (Sc1) detect the best systems for future atmospheric characterization by a new generation facilities including JWST and ELT; (Sc2) determine how diverse planetary systems of nearby M-dwarfs are, in particular for the lowest mass down to the brown dwarfs domain – a mostly unexplored mass range so far; (Sc3) understand how the structure and bulk composition of low-mass transiting planets change with planet mass and equilibrium temperature, in particular for temperate planets for which very few data exist, and (Sc4) model the surface distribution of large-scale magnetic fields, spots and plages causing the RV jitter and study the star-planets magnetic interactions and their influence on habitability.
To achieve these ambitious goals, our efforts will be organized around 4 work packages. WP1 will focus on the monitoring of the 100-120 closest M dwarfs to meet (Sc 1) and (Sc 2). WP2 will be devoted to a follow up of 70-80 transiting planets candidates (mainly from TESS catalog) to measure the accurate masses and to meet (Sc 3). WP3 will optimize the RV data processing taking advantage of the experience of the participants on the RV analysis of HARPS, SOPHIE and ESPaDOnS. WP4 aims to filter the RV-activity jitter by using simultaneous spectropolarimetry and to characterize the space weather environment of exoplanets (Sc 4).
The SPIRou exoplanet survey has received continued support in terms of instrument design and building, and telescope time. Our ANR project aims at coordinating the science activities of the French exoplanet community to maximize its scientific outcomes.

Project coordinator

Monsieur Xavier Delfosse (Institut de Planétologie et d'Astrophysique de Grenoble)

The author of this summary is the project coordinator, who is responsible for the content of this summary. The ANR declines any responsibility as for its contents.

Partner

LAM Laboratoire d'astrophysique de Marseille
IRAP Institut de recherche en astrophysique et planétologie
IAP Institut d'astrophysique de Paris
IPAG - UGA Institut de Planétologie et d'Astrophysique de Grenoble

Help of the ANR 692,240 euros
Beginning and duration of the scientific project: December 2018 - 48 Months

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