i have read that Riess and his team are able to measure $H_0$ from supernovae calibrated using Cepheid in a model independent way.
from what i have gathered they find the absolute luminosity of Cepheid $M_c$ with the parallax method and a bunch of other geometric methods then, once they have $ M_c$, they use the luminosity redshift relation of SN Ia to find $M_{sn}$.
my question is:
once they have the parallax distance of Cepheid, how do they find their distance moduli without imposing a model? in other words, how do they convert the parallax distance in the luminosity distance without assuming a model? otherwise i don't understand how can they find their absolute luminosity or the distance moduli needed to find $M_c$
