P(γ|data) (in green) Approximate posterior PDF for the γ parameter resulting from case A, given the adopted prior (see text). The vertical red dotted line indicates the mode of the distribution γ = 0.13 with an uncertainty in the range indicated by the two black vertical lines corresponding to the quantiles 0.16 and 0.84, respectively (). We obtain these results when using as observational data the stars in Tycho-2 catalogue with visual apparent magnitude V_T < 11. In blue we show the adopted prior PDF.