Left panel: observed (thin gray line) and modelled (red line) profile of the He i 5875 Å line for all the stars analysed. The vertical line shows the rest position of the line displaced to the v_hel velocity of the gas in Sh2-284, which coincides within observational errors with the measured velocity of S1, S17, and S33, and HD 292764. Right panel: shape of the interstellar Na i D1 line for each star. The different components of the line are probing the velocity of the intervening medium.