Kavli Affiliate: Bruce Macintosh
| First 5 Authors: Jason J. Wang, Peter Gao, Jeffrey Chilcote, Julien Lozi, Olivier Guyon
| Summary:
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.
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