Day 4/5, Session 1: Composition


David Sing here ready for the Thursday morning session.  Looks like we’ll start out with theoretical talks on clouds and spectral retrieval before moving to some observations.

Mark Marley begins with a broad overview on clouds and their convincing first order importance, scattering optical light and changing the IR flux.  He lists three approaches to modelling clouds: the microphysics “Top-down” Christiane Helling model, the simple parametrized “Bottom-up” Ackerman & Marley model, and the not good enough “make it up” model (guess that puts me in the last group).  Most of the talk is spent on brown dwarf spectra and how their model with clouds changes and improves the model fits.  Moves to the directly imaged planets, encouraging the younger under 35 people to think seriously about these planets with all the data that’s coming (I’m too old damn!).  Their cloud model works for HR 8799 b, c, d too.  Ends showing our HD 189733 b transmission spectra (!!) interpreting the Rayleigh slope as due to soot, Kevin Zahnle’s work.  During questions, C. Helling picks up a difficult technical question on the soot paper, as they stop short of calculating actual soot (stoping at C2H6 or something where there’s data, how dare he).  Mark summarises Zahnle’s response, “do it yourself”, thus the paper remains on arXiv for the third year.

Caroline Morley is next, she describes the 5 new clouds she added to the Ackerman & Marley cloud model, which moves to lower temperatures (involves Cr, MnS, Na2S, ZnS, KCl condensation).  Bottom line, the clouds don’t help explain the GJ 1214 b flat spectra (as the water IR absorption bands are still there), but the photochemistry is still unmodeled.  Encouragingly, the model does seem to work for late T-dwarfs.

Jae-Min Lee kicks off the spectral retrieval talks with a very long list of the problems with transiting exoplanet work (I’m just glad both the theorists and observers are to blame, misery loves company).  He overviews his retrieval method and shows results on HD 189733 b, no evidence for CO and methane, but good constraints for water and CO2.
Bjorn Benneke follows with a similar talk aimed at super-Earths.  He finishes with a good breakdown of what information is in a transmission spectra, and the big need for optical Rayleigh scattering (head nodding up and down vigorously).

Joe Harrington is next after the break talking about the plethora of Spitzer secondary eclipse photometry.  Describes exoplanet community as “a curious social concept” (it’s sort of a pretty-planetary-scientist-uptown girl meets messy half-dressed-caffeine-tweeting-astro observer boy who always forgets his keys and never offers to pay the check type of relationship).  He gives us all a good stern lecture on how to work with the messy data, and calls out everyones weak peer-review (perhaps we can just put our papers on wikipedia and let their editors clean it all up).  Bottom line, he believes everyone’s eclipse depths but not their error bars.  He finishes by showing the brightness Temp vs equilibrium temperature plot, which shows hot-Js above ~1800 K trend ~700 K hotter.  He lists a myriad of possibilities to explain the trend, though the audience is mostly caught up on the albedo=0 assumption, which of course he did to simply make things easier to understand (please dumb it down more for the theorists).

Mark Swain finishes the session with a nice talk on the possible future Finesse mission.  Could exoplanet atmospheres finally get their own instrument?  I’d be nice not to have to use high-Z redshift filters to look for CO (see Ian Crossfield’s talk).


About Author

David Sing is a Lecturer of Physics (equivalent of assistant professor) at the University of Exeter. He studied at the University of Arizona, where he obtained his bachlor in Astronomy and Physics, before doing his PhD on observations of white dwarf stars and cataclysmic variables. He did a posdoc at the University of Arizona and one at the Institut d’Astrophysique de Paris. He now works on exo-planetary atmospheres and precision photometry.