causal inference in EPRV

Lily Zhao (Yale), Megan Bedell (Flatiron), and I looked at Zhao's results trying to learn radial-velocity displacements from spectral shape changes for EPRV data. She finds that it works, which got me extremely excited! However, there is some suggestion in her results that the method might be making use of unmodeled (unmasked) telluric lines of very low amplitude. This is not permitted, because we want to just use changes in the star's intrinsic shape. We came to the realization in the call that this gets into questions of causal inference: When the signals are small or noisy, how do we know that we are learning from signals caused by the star itself, rather than the atmosphere or instrument? We decided to move to simulated spectra for a bit to look at these questions in a playground where we know the right answers.