  We report on a 39 ks observation of the 7.7-s low-mass X-ray binary pulsar
4U1626-67 with the High Energy Transmission Grating Spectrometer (HETGS) on the
Chandra X-Ray Observatory. This ultracompact system consists of a
disk-accreting magnetic neutron star and a very low mass, hydrogen-depleted
companion in a 42-min binary. We have resolved the previously reported Ne/O
emission line complex near 1 keV into Doppler pairs of broadened (2500 km/s
FWHM) lines from highly ionized Ne and O. In most cases, the blue and red line
components are of comparable strength, with blueshifts of 1550-2610 km/s and
redshifts of 770-1900 km/s. The lines appear to originate in hot (10^6 K),
dense material just below the X-ray-heated skin of the outer Keplerian
accretion disk, or else possibly in a disk wind driven from the pulsar's
magnetopause. The observed photoelectric absorption edges of Ne and O appear
nearly an order of magnitude stronger than expected from interstellar material
and are likely formed in cool, metal-rich material local to the source. Based
on the inferred local abundance ratios, we argue that the mass donor in this
binary is probably the 0.02 M_sun chemically fractionated core of a C-O-Ne or
O-Ne-Mg white dwarf which has previously crystallized.
