Detail of the X-Shooter spectrum of ISO Cha I-217 (black solid line) in the wavelength range around the Na iλλ 8183.3, 8194.8 Å absorption doublet. The spectrum of ISO-ChaI 217 has been corrected for extinction and for telluric absorption lines. The green and the red dotted lines represent synthetic spectra with log g values of 3.5 and 4.0, respectively, for T_eff = 2950 K and rotationally broadened to v sin i = 20 km s^-1.