Physical Structure and Dust Reprocessing in a sample of HH Jets

TL;DR

This study examines the physical conditions and dust reprocessing in shocks along Herbig-Haro jets, revealing how shock velocity influences dust destruction and gas-phase calcium abundance.

Contribution

It provides detailed measurements of physical parameters and dust depletion in HH jets, highlighting the impact of shock velocity on dust reprocessing and revealing discrepancies with existing models.

Findings

Electron density varies from 0.05 to 4×10^3 cm^-3.

Calcium depletion is up to 80%, higher in low-excitation jets.

Dust reprocessing efficiency depends on shock velocity.

Abstract

We investigate the physical structure and dust reprocessing in the shocks along the beam of a number of classical Herbig-Haro jets in the Orion and Lupus molecular cloud. Spectral diagnostic techniques are applied to obtain the jet physical conditions from the ratios between selected forbidden lines. The presence of dust grains is investigated by estimating the gas-phase abundance of calcium with respect to its Solar value. We find the electron density, ne, varies between 0.05-4 10^3 cm^-3, the ionisation fraction, xe, is 0.01-0.7, the temperature, te, ranges between 0.6-3 10^4 K, and the hydrogen density between 0.01-6 10^4 cm^-3. Interestingly, in the HH 111 jet, ne, xe, and te, peak in the High Velocity Interval (HVI) of the strongest working surfaces, confirming the prediction from shocks models. Calcium turns out to be depleted with respect to its Solar value, but its gas-phase abundance is higher than that estimated in the interstellar medium in Orion. The depletion is high (up to 80%) along the low-excited jets, while low or no depletion is measured in the jets which show higher excitation conditions. Moreover, in HH 111 the depletion is lower in the HVI of the faster shock. Our results confirm the shock structure predicted by models and indicate that the shocks occurring along the jets are partially destroying the dust grains and that the efficiency of dust reprocessing strongly depend on shock velocity. However, the high Ca gas-phase abundance estimated in some of the knots is not well justified by existing models of dust reprocessing in shocks, and indicates that the dust must have been partially reprocessed in the region where the flow originates.