HiRISE

HiRISE is funded by the European Research Council (ERC) under the European Union's Horizon 2020 research and innovation programme (grant agreement n°757561).

Positions currently opened for the project:

  • Postdoc: start expected as early as 1 December 2017
  • Internship: Master 2 level, academic year 2017-2018 (version française)
  • PhD: start expected in autumn 2018 (flexible, earlier date possible)

Other postdoc, PhD and engineer positions will be available soon. If you are interested by the project or one of the positions, please get in touch with me.

Context and goals

Atmospheric composition provides essential markers of the most fundamental properties of giant exoplanets, such as their formation mechanism or internal structure. New-generation exoplanet imagers, like VLT/SPHERE or Gemini/GPI, have been designed to achieve very high contrast (>10 mag) at small angular separations (<0.5") for the detection of young giant planets in the near-infrared, but they only provide very low spectral resolutions (R<100) for their characterization.

High-dispersion spectroscopy at resolutions up to 105 is one of the most promising pathways for the detailed characterization of exoplanets, but it is currently out of reach for most directly imaged exoplanets. The power of high-dispersion spectroscopy lies in the ability to disentangle the stellar and planetary signals using the distinct radial velocity component of the planet that originates from its orbital motion. However, this differential radial velocity can only be measured by overcoming the large contrast ratio between the star and the planet. Self-luminous, young giant planets potentially constitute ideal targets because of their intrinsic brightness in the near-infrared, but current high-dispersion spectrographs in the near-infrared lack coronagraphs to attenuate the stellar signal and the spatial resolution necessary to resolve the planet.

Providing very high spectral resolution to high-contrast imaging instruments is crucial if we want to achieve a major step forward in our understanding of the formation, evolution and composition of directly imaged exoplanets (Snellen et al. 2015; Wang et al. 2017; Mawet et al. 2017). Project HiRISE (High-Resolution Imaging and Spectroscopy of Exoplanets) ambitions to develop a novel demonstrator that will combine the capabilities of two flagship instruments installed on the ESO Very Large Telescope, the high-contrast exoplanet imager SPHERE and the high-resolution spectrograph CRIRES+, with the goal of answering fundamental questions on the formation, composition and evolution of young planets.

Implementation

HiRISE will implement a novel fiber coupling between SPHERE and CRIRES+ to leverage the performance capabilities of both instruments. A self-contained fiber injection module will be installed in SPHERE downstream of the coronagraph to pick-up the planetary signal and inject it to CRIRES+ through a fiber relay. Wavefront control using the ZELDA wavefront sensor installed in SPHERE will be used to optimize the injection at the entrance of the fiber and maximize the planetary signal transmission. In CRIRES+, an injection point is already available in the calibration unit of the instrument.

HiRISE will use theory, simulations and testbed validation on MITHIC (the LAM high-contrast imaging facility) to develop an optimal concept that can be implemented at the VLT. Signal processing and extraction will also be investigated to explore the feasibility of the science cases that can be addressed at high-spectral resolution. The project will follow a co-design strategy by studying the chain as a whole, from the instrumental design, up to the data analysis and finally the astrophysical interpretation.

Science case

The atmospheres of giant gaseous exoplanets bear important markers of their formation mechanism (Öberg et al. 2011), their internal structure (Madhusudhan et al. 2011) and the chemical and dynamical processes like winds or clouds (Knutson et al. 2007; Moses et al. 2011). Spectroscopic measurements of these atmospheres at high-spectral resolution provide a unique way to answer fundamental questions about exoplanets: where and how did they form in the protoplanetary disk? How does their luminosity evolve as a function of mass and time? What is the influence of dust clouds in their atmospheres? What are the chemical and dynamical processes at play in these atmospheres?

The main opportunity enabled by resolutions of several tens of thousands is the detection of the molecular lines of water (H2O), carbon monoxide (CO), methane (CH4), and potentially ammonia (NH3). Access to a direct measurement of spectral lines would enable species-by-species atmospheric characterization, which is of paramount importance to constraint abundances of individual elements.

Formation & migration
The core accretion (Pollack et al. 1996) and disk instability (Boss 1998) formation scenarios predict different abundances for C and O, which are related to the processes involved in the formation and to the location of the planet in the protoplanetary disk (Öberg et al. 2011; Piso et al. 2015). Being able to compare the C/O ratio of young giant planets to that of their host star would therefore provide a unique insight into their formation processes.
Atmospheric chemistry & dynamics
The detailed composition determined at very high-spectral resolution will provide an insight into the chemistry on-going in young exoplanets atmospheres. Time-resolved measurements of bright companions over several hours will be used to spatially map their photosphere with the Doppler imaging technique (Vogt et al. 1987). This will enable variability and cloud coverage studies on young companions for the first time.
Mass & internal structure
At resolutions of 105, the orbital velocity of the planets on their orbit will be determined directly and will enable constructing a full keplerian model of the planetary systems when combined with relative astrometry obtained from imaging. This will lead to the dynamical determination of the planets masses, which are crucially needed to calibrate the sub-stellar evolutionary models (Burrows et al. 1997; Baraffe et al. 2015).