Double-peaked X-Ray Lines from the Oxygen/Neon-rich Accretion Disk in 4U 1626–67

摘要: We report on a 39 ks observation of the 7.7 s low-mass X-ray binary pulsar 4U 1626-67 with High Energy Transmission Grating Spectrometer (HETGS) Chandra X-Ray Observatory. This ultracompact system consists disk-accreting magnetic neutron star and very low mass, hydrogen-depleted companion in 42 minute binary. have resolved previously reported Ne/O emission line complex near 1 keV into Doppler pairs broadened (≈2500 km s-1 FWHM) lines from highly ionized Ne O. In most cases, blue red components are comparable strength, blueshifts 1550-2610 redshifts 770-1900 s-1. The appear to originate hot (≈106 K), dense material just below X-ray-heated skin outer Keplerian accretion disk, or else possibly disk wind driven pulsar's magnetopause. observed photoelectric absorption edges O nearly an order magnitude stronger than expected interstellar likely formed cool, metal-rich local source. Based inferred abundance ratios, we argue that mass donor this is probably 0.02 M☉ chemically fractionated core C-O-Ne O-Ne-Mg white dwarf which has crystallized.