Recollimation boundary layers as X-ray sources in young stellar jets

This is a pre-print. The article was published in Astrophysical Journal, Volume 795, Issue 1, article id. 51, 11 pp. (2014). If you wish, you can cite this pre-print version using its URL.

Abstract

Young stars accrete mass from circumstellar disks and in many cases, the accretion coincides with a phase of massive outflows, which can be highly collimated. Those jets emit predominantly in the optical and IR wavelength range. However, in several cases X-ray and UV observations reveal a weak but highly energetic component in those jets. X-rays are observed both from stationary regions close to the star and from knots in the jet several hundred AU from the star. In this article we show semi-analytically that a fast stellar wind which is recollimated by the pressure from a slower, more massive disk wind can have the right properties to power stationary X-ray emission. The size of the shocked regions is compatible with observational constraints. Our calculations support a wind-wind interaction scenario for the high energy emission near the base of YSO jets. For the specific case of DG Tau, a stellar wind with a mass loss rate of \(5\cdot10^{-10}\;M_{\odot}\;\mathrm{ yr}^{-1}\) and a wind speed of 800 km s\(^{-1}\) reproduces the observed X-ray spectrum. We conclude that a stellar wind recollimation shock is a viable scenario to power stationary X-ray emission close to the jet launching point.