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megbedell / wobble

precise data-driven RV fitting, now with tellurics!
https://wobble.readthedocs.io
MIT License
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Question on the resulting RVs and barycentric correction #49

Open JonasKemmer opened 5 years ago

JonasKemmer commented 5 years ago

Hello, as far as I can understand, the resulting values for the RVs do not include the barycentric correction. Does this mean, they are just converted by: v_meas = c * z_meas? My Question is: How is the barycentric correction considered in wobble? In Bedell+(2019) you write:

The apparent stellar RV, [...], is a sum of the star's actual velocity about its center of mass [..] and the projected motion of the Earth about the Solar System barycenter..

However, according to Wright and Eastman (2014) this is not valid:

Note that the correction to z_meas is multiplicative, not additive. One should not, therefore, formulate the "barycentric correction" as the velocity that should be added or subtracted from z_meas to find z_true, [...]. That is, the difference between z_meas and z_true includes a cross term of magnitude 3 m/s.

But as far as I understand from the example scripts, that is exactly what you do, isn't it?

Best regards, Jonas Kemmer

megbedell commented 5 years ago

Yes, you're right! I don't expect that change to matter much for the sort of RV amplitudes we're looking at, but it's a good point and I will implement a results.apply_bervs() function to do the correction in a relativity-safe way.

JonasKemmer commented 5 years ago

Thank's for your response. So for now I can easily apply barycorrpy myself - however an implementation in the code itself is certainly an useful enhancement.