Chandra observations of the dwarf nova WX hydri in quiescence

We report Chandra observations of the dwarf nova WX Hyi in quiescence. The X-ray spectrum displays strong and narrow emission lines of N, O, Mg, Ne, Si, S, and Fe. The various ionization states implied by the lines suggest that the emission is produced within a flow spanning a wide temperature range, from T ∼ 10⁶ K to T ≳ 10⁸ K. Line diagnostics indicate that most of the radiation originates from a very dense region, with n ∼ 10¹³-10¹⁴ cm^-3. The Chandra data allow the first tests of specific models proposed in the literature for the X-ray emission in quiescent dwarf novae. We have computed the spectra for a set of models ranging from hot boundary layers, to hot settling flow solutions, to X-ray-emitting coronae. WX Hyi differs from other dwarf novae observed at minimum in having much stronger low-temperature lines, which prove difficult to fit with existing models, and possibly a very strong, broad O vu line, perhaps produced in a wind moving at a few times 10³ km s^-1. The accretion rate inferred from the X-rays is lower than the value inferred from the UV. The presence of high-velocity mass ejection could account for this discrepancy while at the same time explaining the presence of the broad O VII line. If this interpretation is correct, it would provide the first detection of a wind from a dwarf nova in quiescence.