Atmospheric characterization of planetary and substellar companions at 4-5 micron and in polarized light

Séminaire IPAG de Tomas Stolker (ETH Zurich), jeudi 14 novembre 2019 à 11h00, IPAG seminar room

We have entered an exciting era in which high-resolution instruments provide detailed insight into the formation, orbital architectures, and atmospheric characteristics of directly imaged planets and brown dwarfs. Along the spectral sequence towards later type objects, atmospheres emit the majority of their photons at mid-infrared wavelengths beyond 3 micron, a regime which is expected to provide complementary information about the atmosphere’s chemical abundances and cloud configuration. We have been conducting the MIRACLES survey with VLT/NACO to systematically complement the SEDs of about a dozen of objects with Brackett-alpha (4.05 micron) and M’ (4.8 micron) photometry in order to unravel their photometric characteristics in this wavelength regime and find trends related their spectral type and surface gravity.

In this talk, I will describe the challenges of observing at thermal wavelengths, how the data is processed and analyzed, and I will present a first comparison with the photometry and colors of isolated brown dwarfs and predictions by atmospheric models.

In the second part, I will provide a brief background on how atmospheric cloud variations and circumplanetary disks impact the near-infrared polarized appearance of self-luminous objects.

Finally, I will highlight some preliminary results from recent attempts with VLT/SPHERE to detect polarized light from directly imaged low-mass companions.