phoebe-project
sigmas_lnf for radial velocities with system velocity, and request for a simpler "jitter" term
Hello!
This is a question about the fractional increase of uncertainties through the "sigmas_lnf" parameter.
For radial velocity data, it seems to me that it scales based on the full radial velocity model; meaning that if the system radial velocity is not 0 km/s, the uncertainty will be applied asymmetrically to the RV curve.
Is that correct? I've looked at the code on https://github.com/phoebe-project/phoebe2/blob/7bc4489a5b2bd3f349291deec850589537109c0b/phoebe/parameters/parameters.py#LL3858C18-L3858C18 I cannot find any clear indication that the system RV is "ignored" when performing this rescaling.
Separately, I have a feature request. Some exoplanet people forego the use of a fractional RV uncertainty in favor of a less conservative additive component, simply a jitter term that can be sampled over as a constant quadrature addition to all RV uncertainties:
sigma**2 = formal**2 + jitter**2
Would you be interested in implementing that feature into PHOEBE? This would only work in cases where the additional "uncertainty" can be assumed to be independent from the model.
The first part of this should be covered by #901 and I think the additional request for a jitter term might be possible through the possible upcoming support for custom dataset features in #902 or using the existing functionality for custom cost function if you want to give either of those a shot and see if they are flexible enough for what you need.
