I'm a high school student but have as much interests in Cepheid variable as the professionalists. I'm trying to derive independent distances to Cepheid with the Baade-Wesselink method.
I got the angular diameter variations data from the paper Cepheid distances from infrared long-baseline interferometry but I'm stuck from the afterward. I want to know how equation 9 in that paper is derived. Where did the number 9.305 suddenly came up?
The equation is the following:
θLimb-darkened model angular diameter = amplitude of limb-darkened observed angular diameter + 9.305 (∆D/d)
It seems like I need that equation to derive the distance from the angular diameter values with radial velocity values.