Posterior distributions after using MCMC to fit the stellar PSF at the position of the companion HD 19467 B to the reduced I_Q- and I_U -images of the 2018-08-07 data set of HD 19467. The fitted parameters are the companion position in x and y, the companion-to-star contrast in I_Q and I_U , the background’s z-intercept and slopes inthe x- and y-direction in I_Q and I_U , and the standard deviation σ that accounts for the noise in the images. The diagonal panels show the marginalized 1D distributions of the fitted parameters and the off-diagonal panels show the 2D projections of the posterior, revealing the covariance of the parameter pairs. The median and uncertainties (computed as the 18th and84th percentiles) of the distributions are shown above the histograms and are indicated with the dashed vertical lines. The contours superimposed on the off-diagonal panels indicate the 1σ, 2σ and 3σ confidence levels assuming Gaussian statistics. The figure is created using the Python package corner (Foreman-Mackey 2016).