2024ApJ...976L..25L

We report the detection of broad, flat-topped emission in the fine-structure lines of [Ne V], [Ne VI], and [O IV] in mid-infrared spectra of the O9 V star 10 Lacertae obtained with James Webb Space Telescope/Mid-Infrared Instrument. Optically thin emission in these high ions traces a hot, low-density component of the wind. The observed line fluxes imply a mass-loss rate of >3 × 10^–8M_⊙ yr^–1, which is 1 order of magnitude larger than previous estimates based on UV and optical diagnostics. The presence of this hot component reconciles measured values of the mass-loss rate with theoretical predictions and appears to solve the “weak wind” problem for the particular case of 10 Lac.