have also been summed for this plot with weighting corresponding to the different sensitivities at the locations of the Ca[ii]{} lines.

A Gaussian fit to each of the three absorption components yields heliocentric velocities $v_0 \simeq -44$, $-26$ and $-5$ km s$^{-1}$. These velocities are consistent with an absorption component clearly seen at $\sim -44$ km s$^{-1}$ and the hint of another component at $-26$ km s$^{-1}$ in NaI $\lambda\lambda 5889, 5895$. The presence of strong Na emission at the rest wavelength (sky emission) precludes the detection of the presumed third absorption component at $-5$ km s$^{-1}$ and the use of Na absorption for the determination of the H[i]{} absorption column, N$_{\rm H{\sc i}}$, to XTE J1118+480.

We proceed as follows to determine N$_{\rm H{\sc i}}$.[^3] We assume that the gas in each absorbing cloud has a Maxwellian velocity distribution centered on its heliocentric velocity $v_0$, so that the Ca[ii]{} optical depth of the cloud can be described by (Spitzer 1978): $$\tau [v-v_0] = {\rm N_{Ca{\sc ii}}} \frac{\sqrt{\pi} e^2 f \lambda_0}{m_e c b}
e^{-[(v-v_0)/b]^2},$$ where ${\rm N_{Ca{\sc ii}}}$ is the total cloud absorption column, $\lambda_0 = 3933.6~\AA$ is the rest wavelength of the Ca[ii]{} K line, $f=0.688$ is the oscillator 