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SUMMARY:An Ever-Evolving Story of the Chemical Composition and Accretion H
 istory of the HR 8799 Planets  - Ji Wang
DTSTART:20251106T160000Z
DTEND:20251106T170000Z
UID:TALK238246@talks.cam.ac.uk
CONTACT:Jan Scholtz
DESCRIPTION:As the poster child of directly-imaged exoplanets\, the HR 879
 9 system consists of four young gas giant planets that are likely to be in
  mean motion resonance. Their formation origin and evolutionary history re
 main uncertain but can be constrained by a rich set of archival and newly-
 obtained proprietary data. I will present the detection of key molecular s
 pecies such as H2O and CO in the planetary atmosphere using the combinatio
 n of high-contrast imaging and high-resolution spectroscopy. Despite solid
  detections\, interpreting the data through spectral retrieval analysis ha
 s been controversial\, largely due to systematics introduced by inhomogene
 ous data sets and differing underlying model assumptions. I will present a
  calibration procedure using benchmark brown dwarfs to understand the syst
 ematic errors. This leads to an accurate constraint of atmospheric composi
 tion\, which in turn allows us to robustly trace the formation history. Mo
 reover\, using a sample of directly-imaged exoplanets including the HR 879
 9 planets\, we convert their atmospheric metallicities to the accreted mas
 s of solid during formation through a Bayesian framework that marginalizes
  the probabilities of disk conditions\, formation locations\, planetary in
 terior structures\, and accretion physics. We show that more than 50 M⊕ 
 solid mass has been accreted\, pointing to an extremely early formation ti
 me scale (<1-2 Myrs) when the protoplanetary disk is massive enough to mai
 ntain a sufficient solid mass reservoir. While severely challenging existi
 ng models\, I will provide a new self-consistent model that traces dust fo
 rmation\, migration\, and accretion to demonstrate the feasibility of new 
 observational findings.  
LOCATION:Hoyle Lecture Theatre\, Institute of Astronomy
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