The evolution of the jet from Herbig Ae star HD 163296 from 1999 to 2011

TL;DR

This study analyzes the jet from Herbig Ae star HD 163296 over 12 years, revealing changes in shock speed, knot properties, and emission features, enhancing understanding of jet evolution in young stars.

Contribution

It provides new multi-epoch observations of the jet HH 409, demonstrating temporal variations in shock speed, knot characteristics, and emission features, which were not previously documented.

Findings

The shock speed decreased from 50 km/s to 30 km/s between 1999 and 2011.

Knot B shows a proper motion of 0.37 arcsec/yr and requires continuous reheating.

Variations in ionization and mass loss rate indicate changing jet launching conditions.

Abstract

Young A and B stars, the so-called Herbig Ae/Be stars (HAeBe), are surrounded by an active accretion disk and drive outflows. We study the jet HH 409, which is launched from the HAeBe star HD 163296, using new and archival observations from Chandra and HST/STIS. In X-rays we can show that the central source is not significantly extended. The approaching jet, but not the counter-jet, is detected in Ly alpha. In addition, there is red-shifted Ly alpha emission extended in the same direction as the jet, that is also absent in the counter-jet. We can rule out an accretion or disk-wind origin for this feature. In the optical we find the knots B and B2 in the counter-jet. Knot B has been observed previously, so we can derive its proper motion of 0.37+-0.01 arcsec/yr. Its electron density is 3000/cm^3, thus the cooling time scale is a few months only, so the knot needs to be reheated continuously. The shock speed derived from models of H alpha and forbidden emission lines (FELs) decreased from 50 km/s in 1999 to 30 km/s in 2011 because the shock front loses energy as it travels along the jet. Knot B2 is observed at a similar position in 2011 as knot B was in 1999, but shows a lower ionization fraction and higher mass loss rate, proving variations in the jet launching conditions.