Normalised, averaged spectrum of J1727 in the observer rest frame (top, solid green line), as well as in the companion star rest frame (middle, solid blue line). A template K3/4V star (HD 219134) is shown in orange after applying the veiling factor derived in this work (X_veil = 0.74). They are offset vertically by 0.25 for visualisation purposes. Absorption features identified with known atomic transitions in this wavelength range are marked as dashed lines in blue for Ca I, and green for Fe I and Fe II. Disc emission lines are marked with dotted lines, black for H and red for He I. Telluric bands and interstellar absorption are marked with shaded grey and yellow regions, respectively. Note that absorption features associated with the companion star are revealed as narrow features only in the companion rest frame.