An In Situ Study of Turbulence near Stellar Bow Shocks

Stellar bow shocks are observed in a variety of interstellar environments and shaped by the conditions of gas in the interstellar medium (ISM). In situ measurements of turbulent density fluctuations near stellar bow shocks are only achievable with a few observational probes, including H alpha-emitting bow shocks and the Voyager Interstellar Mission (VIM). In this paper, we examine density variations around the Guitar Nebula, an H alpha bow shock associated with PSR B2224+65, in tandem with density variations probed by VIM near the boundary of the solar wind and ISM. High-resolution Hubble Space Telescope observations of the Guitar Nebula taken between 1994 and 2006 trace density variations over scales from hundreds to thousands of au, while VIM density measurements made with the Voyager 1 Plasma Wave System constrain variations from thousands of meters to tens of au. The power spectrum of density fluctuations constrains the amplitude of the turbulence wavenumber spectrum near the Guitar Nebula to log(10)C(n)(2) = -0.8 +/- 0.22 m(-20/3) and for the very local ISM probed by Voyager to log(10)C(n)(2) = -1.57 +/- 0.022 m(-20/3). Spectral amplitudes obtained from multiepoch observations of four other H alpha bow shocks also show significant enhancements from values that are considered typical for the diffuse, warm ionized medium, suggesting that density fluctuations near these bow shocks may be amplified by shock interactions with the surrounding medium or selection effects that favor H alpha emission from bow shocks embedded in denser media.

Automated summary

This paper examines density variations around the Guitar Nebula and compares them with density variations probed by VIM near the boundary of the solar wind and ISM. High-resolution observations from the Hubble Space Telescope and VIM measurements reveal the power spectrum of density fluctuations, indicating different amplitudes of turbulence wavenumber spectrum near the Guitar Nebula and in the very local ISM probed by Voyager.