text: 431,100,991723765720481792,70874545,Josh Lothringer,"As @V_Parmentier and @lkreidberg have been describing, ultra-hot Jupiters are weird and unique for several reasons, from dissociation of molecules to the presence of H- opacity. Here's just a couple of the things we found in my new paper: <LINK> Once the planet gets above a Teq of about 2500 K, TiO/VO become dissocated as well, so you might expect the atmosphere to becomes non-inverted. We find that that's not the case; something is doing the work of TiO/VO after those molecules have disappeared. <LINK> The short-wavelength radiation being pumped out by early-type host stars is absorbed by atomic metals, metal hydrides, SiO, and bound-free opacities. This, combined with a dearth of IR-active molecules to cool the atmosphere, causes the atmosphere heats up. This plot is showing where the stellar flux is being absorbed: look at all that short wavelength flux being absorbed right where the temperature inversion is beginning, around 10 mbar! <LINK> We also show the first self-consistent model of the hottest known jovian planet, KELT-9b (Tdayside = 4600 K). Nearly all molecules are dissocated, even CO, and most atoms are ionized. But the spectrum doesn't look like a blackbody... H- is the main opacity source whose bound-free opacity varies smoothly with wavelength such that the brightness temperature of KELT-9b varies by about 1000 K across the JWST spectral range! <LINK> There's much more in the paper, but, in short, ultra-hot/extremely irradiated hot Jupiters are fascinating and unique astrophysical objects, worthy of further characterization. This is good because their hot dayside atmosphere and their inflated radii make these great targets. See also: Mansfield+ <LINK> @V_Parmentier+ <LINK> @lkreidberg+ <LINK>",https://arxiv.org/abs/1805.00038,"Extremely irradiated hot Jupiters, exoplanets reaching dayside temperatures ${>}$2000 K, stretch our understanding of planetary atmospheres and the models we use to interpret observations. While these objects are planets in every other sense, their atmospheres reach temperatures at low pressures comparable only to stellar atmospheres. In order to understand our \textit{a priori} theoretical expectations for the nature of these objects, we self-consistently model a number of extreme hot Jupiter scenarios with the PHOENIX model atmosphere code. PHOENIX is well-tested on objects from cool brown dwarfs to expanding supernovae shells and its expansive opacity database from the UV to far-IR make PHOENIX well-suited for understanding extremely irradiated hot Jupiters. We find several fundamental differences between hot Jupiters at temperatures ${>}$2500 K and their cooler counterparts. First, absorption by atomic metals like Fe and Mg, molecules including SiO and metal hydrides, and continuous opacity sources like H$^-$ all combined with the short-wavelength output of early-type host stars result in strong thermal inversions, without the need for TiO or VO. Second, many molecular species, including H$_2$O, TiO, and VO are thermally dissociated at pressures probed by eclipse observations, biasing retrieval algorithms that assume uniform vertical abundances. We discuss other interesting properties of these objects, as well as future prospects and predictions for observing and characterizing this unique class of astrophysical object, including the first self-consistent model of the hottest known jovian planet, KELT-9b. ","Extremely Irradiated Hot Jupiters: Non-Oxide Inversions, H- Opacity, and