Bhavesh Rajpoot (India)
rajpoot @ mpia.de
Exploring the physical diversity of young exoplanets and brown dwarfs through high-resolution spectroscopy at VLT and ELT
Since the first resolved image of a planetary-mass companion, 2M1207 b, high-contrast imaging (HCI) has revealed a population of young, self-luminous giant planets and brown dwarfs on wide orbits, with archetypes such as the HR 8799 system, β Pic b, and the cooler 51 Eri b. This yield reflects the method's selection function: HCI is most sensitive to intrinsically hot (high-entropy), low-gravity companions at ∼10–100 au, typically around nearby, early-type or otherwise young, rapidly rotating, and often active hosts. These
stellar properties (high rotation rates, pulsations, spot modulation) make classical m/s-precision Doppler work using high-resolution spectroscopy (HRS) difficult. Therefore, many imaged companions lack robust radial velocity constraints and dynamical masses. On the other hand, HCI specialises in providing the planet's own light, photometry, and spectra disentangled from the host, enabling atmospheric composition, thermal structure, rotation, and cloud properties to be measured directly. Although classical HCI techniques limit the characterization of companions to low resolution, making it difficult to access the planetary information, until high-resolution spectroscopy (HRS) is employed, presenting its own challenges. This PhD work tackles this limitation by not only providing the community with a detailed characterisation of directly imaged exoplanets using high-dispersion coronagraphy (HDC), but also by preparing the upcoming ground-based facilities, such as ELT, for this high-resolution characterisation work. This PhD is split between two projects under their respective collaborations.
The first project, shared between MPIA and Laboratoire d'Astrophysique de Marseille (LAM), is focused on exploring the physical (atmospheric and orbital) properties of imaged companions at a very high spectral resolution (R=140,000) in H-band using the HiRISE instrument at the VLT-UT3. I'll lead the observations and analysis of the HiRISE survey targets to pin the atmospheric properties such as composition, signs of accretion, atmospheric structure, and global circulation of the young gas giants, as well as measuring their radial and rotational velocities to pin planet obliquity, orbital and rotational period, dynamical masses, and hence their formation history and dynamical evolution.
The second project, shared between MPIA and Laboratoire Lagrange/Observatoire de la Côte d'Azur (OCA), focuses on the exploration of the detection and characterization performance of SCAO-IFU, the future spectro-imager mode of the ANDES instrument at the ELT. The goal will be to determine the yield of exoplanets that ANDES will detect in emitted and potentially reflected light, and to study its characterization performance in terms of detecting atomic and molecular signatures connected to the exoplanet atmosphere characteristics. This aims to bring us closer to the ultimate goal of characterizing the atmosphere of temperate exoplanets in habitable zones and to detect the first biosignatures.
Supervisor: Gael Chauvin (MPIA)