Introduction

The availability of the ESO/SERC Sky Survey has made scanning of the southern skies for planetary nebulae, supernova remnants and diffuse nebulae possible. Several catalogues of sources on these plates have been published, sometimes accompanied by photographs of the more important objects.

With the advent of low cost PC computers, frame grabbers and video cameras it has become possible to digitise and enhance areas of interest on these survey plates. Applying digital techniques to the images from the IIIaJ, IIIaF and IVN surveys allows the separation of line and continuum sources in the galactic plane (Zealey et al., 1994).

In this paper we outline an application of digital methods to the study of outflows driven by mass loss from Young Stellar Objects (YSOs). Evidence that a YSO is undergoing mass loss is provided through the effect the stellar wind has on the surrounding medium. Phenomena such as bipolar molecular outflows, masers and the Herbig-Haro (HH) objects and jets are all indicators of a YSO undergoing mass loss.

Observations at optical and infrared wavelengths have shown that HH objects and jets are regions of shock-excited gas emitting in H and forbidden excitation lines of [O I]6300,6363 and [SII]6716,6731 in the visible and H (2.12 m) in the infrared. The different shock structures and excitation conditions of a HH complex can be distinguished by comparing images obtained in optical and infrared emission lines with differing excitation parameters i.e.: [S II] emission is indicative of 100 km s, while the presence of H emission indicates slower shocks ( 40 km s).

HH objects and jets are associated with both low-luminosity (L 1-100 L) T Tauri stars and high-luminosity YSOs (L 10 L) such as IRAS sources (Mundt 1988, Reipurth 1994). The visibility of the source depends on the amount of obscuration, the orientation of the flow and circumstellar disk. Due to heavy extinction from the surrounding star forming clouds, many YSOs are obscured at optical wavelengths. Near Infrared images often provide the first identification of the driving source of the outflow as the optical extinction becomes less important at longer wavelengths.

Morphological features present in most outflows include:

• An embedded YSO which drives the outflow;
• A collimated jet and counter jet;
• A section where the jet disappears, but isolated emission knots remain;
• A working surface (bow shock) with associated HH complex.

© Copyright Astronomical Society of Australia 1997