2023ApJ...951...35S

Bow shocks are produced in the local interstellar medium by the passage of fast stars from the Galactic thin-disk and thick-disk populations with velocities V_* = 40-80 km s^–1. Stellar transits of local H I clouds occur every 3500-7000 yr on average and last between 10⁴ and 10⁵ yr. There could be 10-20 active bow shocks around low-mass stars inside clouds within 15 pc of the Sun. At local cloud distances of 3-10 pc, their turbulent wakes have transverse radial extents R_wake ≈ 100-300 au, angular sizes 10″-100″, and Lyα surface brightnesses of 2-8 R in gas with total hydrogen density n_H ≈ 0.1 cm^–3 and V_* = 40-80 km s^–1. These transit wakes may cover an area fraction f_A ≈ (R_wake/R_cl) ≈ 10^–3 of local H I clouds and be detectable in IR (dust), UV (Lyα, two-photon), or nonthermal radio emission. Turbulent heating in these wakes could produce the observed elevated rotational populations of H₂ (J ≥ 2) and influence the endothermic formation of CH⁺ in diffuse interstellar gas at T > 10³ K.