A HST study of the environment of the Herbig Ae/Be star LkHa 233 and its bipolar jet

TL;DR

This study uses HST observations to analyze the physical properties of the bipolar jet from the Herbig Ae/Be star LkHa 233, comparing it to jets from T Tauri stars, revealing scaled-up similarities.

Contribution

First detailed optical forbidden line analysis of LkHa 233's jet, providing physical parameters and comparing them to T Tauri star jets to understand stellar mass effects.

Findings

Electron density near or above critical for [SII] lines in the blueshifted lobe.

Ionisation fraction rises and shows re-ionisation events along the jet.

Jet temperatures vary between 10^4 K and 3x10^4 K, velocities increase with distance.

Abstract

We present the results of HST/STIS and WFPC2 observations of LkHa 233 and its environment. LkHa233 is a Herbig Ae/Be star with a collimated bipolar jet. We investigate optical forbidden lines along the LkHa 233 jet to determine physical parameters of this jet (electron density n_e, hydrogen ionisation fraction x_e, electron temperature T_e, and mass density n_H). The knowledge of these parameters allows us a direct comparison of a jet from a Herbig star with those from T Tauri stars. The WFPC2 images in broad-band filters clearly show a dark lane caused either by a circumstellar disk or a dust torus. In the blueshifted lobe, n_e is close to or above the critical density for [SII] lines (2.5x10^4 cm^-3) in the first arcsecond and decreases with distance from the source. The ionisation x_e~0.2-0.6 gently rises for the first 500 AU of the flow and shows two re-ionisation events further away from the origin. The T_e varies along the flow between 10^4 K and 3x10^4 K. The (radial) outflow velocities are ~ 80-160 km s^(-1), and they appear to increase with distance from the source. In the redshifted lobe, T_e, n_e, x_e, and n_H are all lower than in the blueshifted lobe, but have the same order of magnitude. All these derived parameters are just beyond or at the upper limits of those observed for classical T Tauri star jets. This may indicate that the flows from the higher mass Herbig stars are indeed scaled-up examples of the same phenomenon as in T Tauri stars.