Corner plot for the parameters fit to the photometry of HD1 using Bagpipes, assuming a constant SFH. From left to right (and top to bottom) posterior probability distributions are shown for the minimum and maximum age (i.e. the time since star formation switched off and on), the stellar mass (M/M_⊙), metallicity (Z/Z_⊙), optical extinction (A_V), 2175 Å bump strength (B) and redshift (z). With so few photometric detections, the 2175 Å bump strength and metallicity are unconstrained. As shown in the bottom right corner, the z ∼ 0.2 − 0.3 solution dominates, with the z ∼ 14 solution the next most probable. The low-z solution, which corresponds to a dwarf galaxy (M_⋆ ∼ 10^8.3 M_⊙) with a very high optical extinction (A_V ∼ 7.5) also dominates for other assumed SFHs (not shown here). However, the relative probabilities of these solutions are highly dependent on on the priors, as described in Sect. 4.3.