  We measured the galactic hydrogen column densities to the neutron-star
binaries GX 17+2, 4U 1705-44, and 4U 1728-34 by modeling the Mg and Si
absorption edges found in high-resolution X-ray spectra obtained by the Chandra
X-ray Observatory. We found for GX 17+2, N_H = (2.38 +/- 0.12) x 10^22 cm^-2,
for 4U 1705-44, N_H = (2.44 +/- 0.09) x 10^22 cm^-2, and for 4U 1728-34, N_H =
(2.49 +/- 0.14) x 10^22 cm^-2. These values are in reasonable agreement with
the hydrogen column densities inferred earlier from modeling of the continuum
spectra of the sources. Our results can be used to constrain the uncertainties
of model parameters of the X-ray spectra of these sources that are correlated
to the uncertainties of the hydrogen column density. In the case of continuum
spectra obtained during thermonuclear X-ray bursts, they will significantly
reduce the uncertainties in the spectroscopically measured masses and radii of
the neutron stars.
