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Stefan Kraus

Exoplanet Spectroscopy and Planetary System Architectures with Asgard/BIFROST at VLTI

We present the exoplanet science case for a proposed new beam combination instrument for ESO's VLT Interferometer, named BIFROST. This instrument recently received funding from the European Research Council and aims for first light on Paranal in late 2024 as part of the Asgard Suite of VLTI visitor instruments. BIFROST will be the first VLTI instrument optimised for short wavelengths (1-1.6 micrometer) and high spectral resolution (up to R=25,000). This will allow us to measure the alignment between the stellar spin axis and the planetary orbital axis - even for wide-separation systems where this information is inaccessible with other techniques, such as the Rossiter McLaughin effect. We will use these unique constraints to study the dynamical processes that shape system architectures, over the whole mass range from stellar-mass companions down to planets. Furthermore, BIFROST will enable the atmospheric characterisation of cold giant planets that are due to be discovered with the RV method or GAIA astrometry. GRAVITY has demonstrated that the star-light suppression from adaptive optics can be combined with star-light suppression from interferometry by placing the instrument fiber off-axis and adjusting the optical path delay to record at the predicted delay position of the planet. BIFROST will be able to employ this method in J and H-band, providing access to additional molecular tracers, such as the O2 absorption bands. These tracers are highly complementary to the K-band probed by GRAVITY and provide further constraints for atmospheric retrieval. Due to the small inner working angle of about 0.025", BIFROST also offers the best chance in near future for performing spectroscopy on rocky planets in the terrestrial zone.