2023 Course Pages
Exoplanets & Habitability Seminars / Spring Semester 2023
Lionel Garcia: Exoplanets transiting small and cool stars
Abstract: Given current technologies, detecting life on exoplanets as small as Earth will only be possible for exoplanets transiting stars much smaller than the Sun: very late M-dwarfs. By using transmission spectroscopy – which consists in measuring the wavelength-dependent radius of a planet as it transits its star – one can access the composition of its atmosphere, and search for signatures indicative of life-like processes. But interpreting such measurements holds a major challenge: the effect of stellar contamination. Indeed, transmission spectra contain the signatures of stars non-uniform surface, such as starspots, able to mimic or hide planetary signals. From the observation of very-late M-dwarfs, detection of planets around them, to the characterisation of the surface of these cool stars, this talk gives an overview of the ongoing effort to unlock the study of rocky exoplanets atmospheres outside of our solar system.
Host: Peter Pedersen
Thursday, May 11th, 10:30 h
COPL Room HIT F 23.2
Kielan Hoch: Moderate Resolution Spectroscopy of Directly Imaged Exoplanets
Thursday, April 25, 16:00 h
Abstract: Direct imaging of exoplanets has revealed a population of Jupiter-like objects that orbit at large separations (~10-100 AU) from their host stars. These planets, with masses of ~2-14MJup and temperatures of ~500-2000 K, remain a mystery for the two main planet formation models—core accretion and gravitational instability. Observations that probe elemental abundances in the atmospheres of these young gas giants can shed light on their formation. I present results both from my survey of directly imaged planets with moderate resolution spectra (R~4000) using the OSIRIS IFU on the W.M. Keck I telescope, as well as my JWST Cycle 1 Program 2044 to directly image the multi-planet system TYC 8998-760-1 (YSES-1) using NIRSpec and MIRI. With OSIRIS, we observed nine companions in the K-band (2.2 um), including Kappa Andromeda b, VHS 1256 b, and HD 284149 b. The spectra reveal resolved molecular lines from water and CO, allowing for the derivation of temperature, surface gravity, metallicity, and C/O ratio. Comparing directly imaged planet C/O ratios to a uniform sample of transiting planets reveals that the C/O ratio may be correlated with mass, with two distinct groups split at 4MJup. With JWST, I am leading a program that is fundamental in pushing current direct imaging spectroscopy to longer wavelengths inaccessible from the ground. The YSES-1 spectra will be one of the most comprehensive datasets of a multi-planet system ever imaged. Pushing to longer wavelengths will better constrain C/O, non-equilibrium chemistry, and cloud composition increasing our understanding of substellar atmospheres and formation.
Thea Kozakis: Is ozone a reliable proxy for molecular oxygen?
Tuesday, March 14, 10:00 h
Abstract: As the primary technique in high contrast imaging, angular differential imaging (ADI) is limited by the self-subtraction effect, which lowers its sensitivity to exoplanets at short angular separations (e.g., <0.3“) and prevents a good recovery of disk emission in total intensity. To avoid the self-subtraction effect, we can use reference-star differential imaging (RDI) as an alternative technique. We present the performance of RDI on SPHERE. We made use of all the archival data obtained by SPHERE in the past 5 years to build the reference library. In the point-source detection, RDI can outperform ADI at small angular separations (<0.4”) with a peak gain of 0.85 mag over ADI at 0.15”. In disk imaging, RDI can reveal more disk features than ADI and provide a more robust recovery of disk morphology. In combination with advanced PSF reconstruction techniques (such as non-negative matrix factorization), our RDI technique obtains even better disk images than the usual RDI-PCA reductions by mitigating the over-fitting problem. The reference library we built can be easily implemented into legacy or future SPHERE surveys to perform RDI without additional observations of reference stars, achieving better performance than that of ADI.