Interstellar Bow Shocks around Fast Stars Passing through the Local Interstellar Medium

Abstract

Abstract 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.