Wednesday, December 01, 2021, 12:00pm - 01:00pm
This repeat is an exception to the normal repeat pattern
Melanie Rowland, The University of Texas at Austin
Towards Robust Atmospheric Retrievals for Cloudy L dwarfs: Tests on Sonora Spectra
Abstract
Retrieving atmospheric properties from spectra is the only method through which properties of brown dwarf atmospheres can be determined since in situ measurements are impossible at astronomical distances. However, our ability to characterize these atmospheres is complicated by the degeneracies produced between the thermal structure, chemical abundances, and the presences of clouds in cooling brown dwarf atmospheres. Incorporating the complex physics that govern cloudy brown dwarf and planetary atmospheres into retrieval frameworks necessitates making assumptions, many of which are not yet robustly verified for accuracy. We test two key assumptions regarding the thermal profile and abundances using state-of-the-art cloud-free models (the Sonora model grid) to create mock data sets. We use the CHIMERA retrieval framework to test these assumptions on a wide temperature range of cloud-free Sonora spectra for which ground truth values are known. These tests reveal under what conditions these assumptions break down, and which assumptions are valid in the warm brown dwarf temperature regime.
Kedron Silsbee, Max Planck Institute for Extraterrestrial Physics
Core Accretion in Tight Binary Systems: viable despite destructive planetesimal collisions?
Abstract
The observed presence of planets in tight binary systems places significant constraints on the planet formation process. A close-by companion star is expected to stir up planetesimals in the protoplanetary disk, leading to high-speed destructive collisions. Simple estimates based on the parameters of known planet-hosting binary systems suggest that kilometer per second collision velocities are not unreasonable. These are sufficient to destroy planetesimals 100’s of km in size. This raises questions about the viability of the standard core accretion model of planet formation, in which planetesimals stick together in mutual collisions to form rocky planets or the cores of giant planets. I will give an overview of the special challenges that tight binaries pose for planet formation theories. I will then discuss the dynamical evolution of planetesimals in binary systems. I describe work in which we accurately calculated planetesimal collision speeds and rates, and then used these to run a coagulation-fragmentation simulation to model their growth or destruction. We find that for reasonable disk parameters, planetesimal coagulation is possible starting from bodies of a few to a few tens of km. This necessary starting planetesimal size is smaller than that found in previous work, suggesting that core accretion is a viable scenario even in these challenging environments.
Location: PMA 15.216B and online
