M-dwarf spectral models; time-variable spectra

I spoke to Jessica Birky (UCSD) today about her #AAS231 poster on using The Cannon to label M-dwarf spectra in the APOGEE spectra. She has beautiful results, using spectral types from the Burgasser group, and using physical labels (temperatures and compositions) from Andrew Mann (Columbia). We discussed things to emphasize on the poster and things to emphasize in discussions with people who come by. For my loyal reader: It will be up at #AAS231 poster session 349 on Thursday January 11.

I also spent some time working on a set of issues around measuring precise radial velocities for stars in the presence of time-variable spectral features in both the star and the tellurics. I worked out derivatives for the spectral model when the telluric absorption is permitted to come from a low-dimensional subspace of spectrum space. I then turned my attention to the ill-posed problem of determining precise radial velocities when the star changes its spectral shape (or line strengths or line positions, etc). In the case that the stellar spectrum changes completely randomly, and independently or separably from the stellar velocity, I believe (oddly) that the problem is going to be easy. The problem is that it won't change completely separably: There will be stellar surface variations that co-vary with spectral changes. This is the reality, and the hardest case, I think.

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