A Multi-Epoch HST Study of the Herbig-Haro Flow from XZ Tauri

TL;DR

This study uses nine epochs of HST imaging over a decade to analyze the morphology, kinematics, and emission properties of the bipolar outflow from the pre-main sequence binary XZ Tauri, revealing bubble dynamics and jet activity.

Contribution

First multi-epoch HST imaging of XZ Tauri's outflow, providing detailed insights into bubble evolution, jet velocities, and emission characteristics over ten years.

Findings

Northern bubble expanded ballistically until 1999, then deformed and decelerated.

Southern counterbubble detected at 6" from the binary in 2004.

Jets from each binary component show distinct velocities and proper motions.

Abstract

We present nine epochs of Hubble Space Telescope optical imaging of the bipolar outflow from the pre-main sequence binary XZ Tauri. Our data monitors the system from 1995-2005 and includes emission line images of the flow. The northern lobe appears to be a succession of bubbles, the outermost of which expanded ballistically from 1995-1999 but in 2000 began to deform and decelerate along its forward edge. It reached an extent of 6" from the binary in 2005. A larger and fainter southern counterbubble was detected for the first time in deep ACS images from 2004. Traces of shocked emission are seen as far as 20" south of the binary. The bubble emission nebulosity has a low excitation overall, as traced by the [S II]/H-alpha line ratio, requiring a nearly comoving surrounding medium that has been accelerated by previous ejections or stellar winds. Within the broad bubbles there are compact emission knots whose alignments and proper motions indicate that collimated jets are ejected from each binary component. The jet from the southern component, XZ Tau A, is aligned with the outflow axis of the bubbles and has tangential knot velocities of 70-200 km/s. Knots in the northern flow are seen to slow and brighten as they approach the forward edge of the outermost bubble. The knots in the jet from the other star, XZ Tau B, have lower velocities of ~100 km/s.