M-dwarf spectral types; reionization

Jessica Birky (UCSD) and I met with Derek Homeier (Heidelberg) and Matthias Samland (MPIA) to update them on the status of the various things Birky has been doing, and discuss next steps. One consequence of this meeting is that we were able to figure out a few well-defined goals for Birky's project by the end of the summer:

Because of a combination of too-small training set and optimization issues in The Cannon, we don't have a great model for M-dwarf stars (yet) as a function of temperature, gravity, and metallicity. That's too bad! But on the other hand, we do seem to have a good (one-dimensional) model of M-dwarf stellar spectra as a function of spectral type. So my proposal is the following: We use the type model to paint types onto all M-dwarf stars in the APOGEE data set, which will probably correlate very well with temperature in a range of metallicities, and then use those results to create recommendations about what spectral modeling would lead to a good model in the more physical parameters.

Late in the day, José Oñorbe (MPIA) gave a great talk about the empirical study of reionization. He began with a long and much needed review of all the ways you can measure reionization, using radio imaging, lyman-alpha forest, damping wings, cosmic microwave background polarization, and so on. This brought together a lot of threads I have been hearing about over the last few years. He then showed his own work on the lyman-alpha forest, where they exploit the thermodynamic memory the low-density gas has about its thermal history. They get good results even with fairly toy models, which is very promising. All indicators, by the way, suggest a very late reionization (redshifts 7 to 9 for the mid-point of the process). That's good for observability.

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