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Published October 2022 | public
Journal Article

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 8799c 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 8799c and down to 30% H-band variability for HR 8799d. We also investigated spectral variability and expected a 50% chance to recover 20% variability in the H/K flux ratio for HR 8799c. We combined all the data from the two nights to obtain some of the most precise spectra obtained for HR 8799c, 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 8799d has a distinct spectrum from HR 8799c, possibly preferring more vertically extended and uniform clouds and indicating that the planets are not identical.

Additional Information

We thank the anonymous referee for helpful suggestions that improved the manuscript. J.J.W. thanks Jean-Pierre Véran for helpful discussions on atmospheric turbulence. J.J.W. and P.G. were supported by the Heising-Simons Foundation 51 Pegasi b postdoctoral fellowship during the bulk of this research project. CHARIS was built at Princeton University under a Grant-in-Aid for Scientific Research on Innovative Areas from MEXT of the Japanese government (# 23103002) The development of SCExAO was supported by the Japan Society for the Promotion of Science (Grant-in-Aid for Research #23340051, #26220704, #23103002, #19H00703, and #19H00695), the Astrobiology Center of the National Institutes of Natural Sciences, Japan, the Mt. Cuba Astronomical Foundation and the director's contingency fund at Subaru Telescope. The authors wish to recognize and acknowledge the very significant cultural role and reverence that the summit of Maunakea has always had within the indigenous Hawaiian community, and are most fortunate to have the opportunity to conduct observations from this mountain.

Additional details

Created:
August 22, 2023
Modified:
October 24, 2023