Chasing the Storm: Mapping Exoplanet Atmospheres with Direct Ground-based Observations
Year: 2026
Type: article
Abstract: Planetary rotation and atmospheric features, such as giant storms and hurricanes, give rise to variability in exoplanet atmospheres as they rotate in and out of view. By monitoring this brightness variability for directly imaged exoplanets and brown dwarfs, we can construct maps that detail their physical appearance and unlock information about their atmospheric structure and dynamics. Ground-based observatories have the resolution and photon collecting power to reach the high contrasts and small inner working angles needed to monitor these faint companions over their rotation timescales. However, bright host stars and a lack of reference stars accessible to the typically narrow fields-of-view of ground-based coronagraphic imagers makes this difficult. Here, I present a new approach for obtaining variability measurements from the ground, with results from our differential spectrophotometric monitoring campaigns of young, widely-separated substellar companions using vector Apodising Phase Plate (vAPP) coronagraphs. These include observations of a bright brown dwarf companion with LBT/ALES, an integral field spectrograph (R=40) operating in combination with a vAPP coronagraph. Unlike focal-plane coronagraphs, the vAPP is insensitive to telescope vibrations and reaches deep speckle suppression while simultaneously providing an unsaturated PSF of the star for use as a reference to remove variations due to Earth’s atmosphere. By adopting techniques traditionally used for exoplanet transmission spectroscopy, we can create light curves of companions directly to search for inhomogeneities in their atmospheres. I will show the ~4-5% differential precision we achieve with just one night of monitoring of a brown dwarf companion and an analysis of the astrophysical features we find in the light curve. Through this method, we can achieve high-precision differential spectrophotometry for directly imaged exoplanets inaccessible to space-based telescopes. This work is a path-finder for further studies with VLT/ERIS and exoplanet mapping with ELT/METIS.
Authors: Sutlieff, Ben, Birkby, Jayne, Doelman, David, Stone, Jordan, Kenworthy, Matthew, Biller, Beth, Ertel, Steve, Liu, Pengyu, Chen, Xueqing, Snik, Frans, Woodward, Chick, Skemer, Andrew, Leisenring, Jarron, Panwar, Vatsal, Bohn, Alexander, Parker, Luke Titus, Derkink, Annelotte, Backs, Frank, Strassmeier, Klaus, Ilyin, Ilya, Wang, Ji, Charbonneau, David
Institutions: University of Edinburgh, University of Oxford, Space Research Organisation Netherlands, University of Wyoming, Leiden University, University of Arizona, University of Minnesota, University of California, Santa Cruz, University of Warwick, AWK (Switzerland), University of Amsterdam, KU Leuven, Leibniz Institute for Astrophysics Potsdam, The Ohio State University, Harvard University
Subfield: Astronomy and Astrophysics
Field: Physics and Astronomy
Domain: Physical Sciences
Open Access status: green
Funder: UK Research and Innovation
Awards: G6895475279, G8428221222
OpenAlex ID: W7203613507
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