HST FUV C IV observations of the hot DG Tauri jet

TL;DR

This study uses HST FUV spectra to spatially resolve C IV emission in the DG Tauri jet, revealing its temperature, velocity, and spatial distribution, and compares it with optical and X-ray data to understand jet heating mechanisms.

Contribution

First spatially resolved FUV C IV observations of the DG Tauri jet, providing insights into jet temperature, velocity, and heating processes, and comparing hot and locally heated jet scenarios.

Findings

C IV emission peaks 42 AU from the star

Jet velocity decreases with distance from the source

Mass loss rate is approximately 1e-9 solar masses per year

Abstract

Protostellar jets are tightly connected to the accretion process and regulate the angular momentum balance of accreting star-disk systems. The DG Tau jet is one of the best-studied protostellar jets and contains plasma with temperatures ranging over three orders of magnitude within the innermost 50 AU of the jet. We present new Hubble Space Telescope (HST) far ultraviolet (FUV) long-slit spectra spatially resolving the C IV emission (T~1e5 K) from the jet for the first time, and quasi-simultaneous HST observations of optical forbidden emission lines ([O I], [N II], [S II] and [O III]) and fluorescent H2 lines. The C IV emission peaks at 42 AU from the stellar position and has a FWHM of 52 AU along the jet. Its deprojected velocity of around 200 km/s decreases monotonically away from the driving source. In addition, we compare our HST data with the X-ray emission from the DG Tau jet. We investigate the requirements to explain the data by an initially hot jet compared to local heating. Both scenarios indicate a mass loss by the T~1e5 K jet of ~1e-9 Msun/year, i.e., between the values for the lower temperature jet (T~1e4 K) and the hotter X-ray emitting part (T>1e6 K). However, a simple initially hot wind requires a large launching region (~1 AU), and we therefore favor local heating.