The recurrent nova (RN) V3890 Sgr was observed during the seventh day after the onset of its most recent outburst, with the Chandra ACIS-S camera and High Energy Transmission Gratings. A rich emission line spectrum was detected, due to transitions of Fe-L and K-shell ions ranging from neon to iron. The measured absorbed flux is ≈10 −10 erg cm −2 s −1 in the 1.4-15 Årange (0.77-8.86 keV). The line profiles are asymmetric, blueshifted, and skewed toward the blue side, as if the ejecta moving

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... rd us are less absorbed than the receding ejecta. The full width at half-maximum of most emission lines is 1000-1200 km s −1 , with some extended blue wings. The spectrum is thermal and consistent with a plasma in collisional ionization equilibrium with column density 1.3×10 22 cm −2 and at least two components at temperatures of about 1 and 4 keV, possibly a forward and a reverse shock, or regions with differently mixed ejecta and a red giant wind. The spectrum is remarkably similar to the symbiotic RNe V745 Sco and RS Oph, but we cannot distinguish whether the shocks occurred at a distance of a few au from the red giant, or near the giant's photosphere, in a high-density medium containing only a low mass. The ratios of the flux in lines of aluminum, magnesium, and neon relative to the flux in lines of silicon and iron probably indicate a carbon-oxygen white dwarf. Unified Astronomy Thesaurus concepts: Novae (1127); Recurrent novae (1366); Cataclysmic variable stars (203); X-ray astronomy (1810); Atomic spectroscopy (2099); High resolution spectroscopy (2096)