Galaxy B2 in the field of GRB 050820A. Top: spectrum acquired with VLT/FORS2. The identified Ca ii H&K absorption lines and the Balmer break are marked. The inset zooms-in on the position of the both absorption lines. Based on the identification of the three absorption features the redshift of the galaxy is z = 0.693. The error spectrum is overplotted. Regions of strong telluric features (atmosphere transparency <20%) are not used in the spectral analysis and are marked by small boxes at the top. Bottom: SED from g′-band to 5.8   μm. The observed data points (corrected Galactic extinction) are shown as circles with error bars. The solid line displays the best-fit model of the SED (χ² = 16.3; number of filters =9). The model-predicted magnitudes are superposed (squares). The grey area highlights the interval that is covered by the spectrum above.