2016-05-06

radial velocity pipeline hacking

I spent small bits of time between things writing in my short paper about inferring the variance of a distribution, given only samples from that distribution. I am trying to have a companion paper for the ABC paper being written by Hahn and Vakili about large-scale structure. Foreman-Mackey gave me some advice this week about how to pitch the paper, and I am trying to obey it.

In the afternoon I had a long phone call with Megan Bedell (Chicago) about how high-precision radial velocity spectrograph data are turned into radial-velocity measurements. She wants to reconsider parts of the pipeline, without rebuilding the whole pipeline from scratch (which is something I would like to do some day). She is currently analyzing her data with a closed-source pipeline, which is, apparently, the standard practice in this field. That has all sorts of bad properties, including that no-one can assert with confidence what the code is doing, nor check it! Bedell and I discussed the stage at which the code goes from a cross-correlation function (as a function of velocity) at every Echelle order to a single velocity. Apparently we can get the data-reduction black box to return enough information that we can reprocess this step.

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