@article {2001ApJ...563..941S,
	title = {{Double-peaked X-Ray Lines from the Oxygen/Neon-rich Accretion Disk in 4U 1626-67}},
	journal = {\apj},
	volume = {563},
	year = {2001},
	note = {n/a},
	month = {dec},
	pages = {941-949},
	abstract = {{We report on a 39 ks observation of the 7.7 s low-mass X-ray binary pulsar 4U 1626-67 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 minute binary. We have resolved the previously reported Ne/O emission line complex near 1 keV into Doppler pairs of broadened (\~{}2500 km s$^{-1}$ 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$^{-1}$ and redshifts of 770-1900 km s$^{-1}$. 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{\textquoteright}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$_{solar}$ chemically fractionated core of a C-O-Ne or O-Ne-Mg white dwarf which has previously crystallized. }
},
	doi = {10.1086/323988},
	author = {{Schulz}, N.~S. and {Chakrabarty}, D. and {Marshall}, H.~L. and {Canizares}, C.~R. and {Lee}, J.~C. and {Houck}, J.}
}
