Atmospheric Monitoring and Precise Spectroscopy of the HR 8799 Planets with SCExAO/CHARIS

Abstract

The atmospheres of gas giant planets are thought to be inhomogeneous due to weather and patchy clouds. We present two full nights of coronagraphic observations of the HR 8799 planets using the CHARIS integral field spectrograph behind the SCExAO adaptive optics system on the Subaru Telescope to search for spectrophomometric variability. We did not detect significant variability signals, but placed the lowest variability upper limits for HR 8799 c and d. Based on injection-recovery tests, we expected to have a 50% chance to detect signals down to 10% H-band photometric variability for HR 8799 c and down to 30% H-band variability for HR 8799 d. We also investigated spectral variability and expected a 50% chance to recovery 20% variability in the H/K flux ratio for HR 8799 c. We combined all the data from the two nights to obtain some of the most precise spectra obtained for HR 8799 c, d, and e. Using a grid of cloudy radiative-convective-thermochemical equilibrium models, we found all three planets prefer supersolar metallicity with effective temperatures of ~1100 K. However, our high signal-to-noise spectra show that HR 8799 d has a distinct spectrum from HR 8799 c, possibly preferring more vertically extended and uniform clouds and indicating that the planets are not identical.

arXiv comment21 pages, 12 figures, Accepted to AJ, time series photometry and stacked spectra available as text files

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• Detecting exomoons from radial velocity measurements of self-luminous planets: application to observations of HR 7672 B and future prospects
• Four-of-a-kind? Comprehensive atmospheric characterisation of the HR 8799 planets with VLTI/GRAVITY
• Roaring Storms in the Planetary-Mass Companion VHS 1256-1257 b: Hubble Space Telescope Multi-epoch Monitoring Reveals Vigorous Evolution in an Ultra-cool Atmosphere
• Retrieving C and O Abundance of HR 8799 c by Combining High- and Low-Resolution Data
• Imaging detection of the inner dust belt and the four exoplanets in the HR8799 system with JWST's MIRI coronagraph
• End-to-end numerical modeling of the Roman Space Telescope coronagraph
• JWST-TST High Contrast: Living on the Wedge, or, NIRCam Bar Coronagraphy Reveals CO${}_2$ in the HR 8799 and 51 Eri Exoplanets' Atmospheres
• Direct-imaging Discovery of a Substellar Companion Orbiting the Accelerating Variable Star, HIP 39017
• Measuring the variability of directly imaged exoplanets using vector Apodizing Phase Plates combined with ground-based differential spectrophotometry
• Global weather map reveals persistent top-of-atmosphere features on the nearest brown dwarfs
• The compositions of the HR 8799 planets reflect accretion of both solids and metal-enriched gas
• Exploring the directly imaged HD 1160 system through spectroscopic characterization and high-cadence variability monitoring
• Mapping the Skies of Ultracool Worlds: Detecting Storms and Spots with Extremely Large Telescopes
• The ExoGRAVITY survey: A K-band spectral library of giant exoplanet and brown dwarf companions
• Post-processing CHARIS integral field spectrograph data with PyKLIP
• Chasing the storm: Investigating the application of high-contrast imaging techniques in producing precise exoplanet light curves