Examples of Digital Images

At present, there are over 250 HH objects listed in Reipurth's Catalogue of Herbig Haro objects. The digital images obtained from the ESO/SERC IIIaJ, IIIaF and IVN survey material can be used to discriminate between emission and reflection nebulosity and to identify heavily reddened continuum sources.

The IIIaJ and IIIaF images provide a road map of shock-excited gas. The IIIaJ + GG395 plate/filter combination (3950A 5400A) is responsive to high excitation emission lines which include the [O III] 4959,5007 line.

The IIIaF + RG630 plate/filter combination (6300A 6900A) is dominated by the low excitation H, [NII]6548,6583 and [S II]6717,6731 emission lines.

The IVN plates (6950A 9000A) do not contain any major emission lines that are known to be prominent in shock-excited regions of HH objects. The IVN band images therefore act as a probe for scattered continuum light from the embedded YSO.

The IIIaJ and IIIaF images can used together with published H infrared images to clearly identify shock-excited emission regions over a range of excitation conditions (Zealey et al., 1992). In many cases, emission features in the IIIaJ, IIIaF and H images do not coincide, which is indicative that either obscuration or excitation conditions vary across the objects.

The IVN images can be combined with published near infrared and continuum images to identify the driving sources of the outflows.

Examples of the digitised images are presented in Figures 1 and 2 for the HH 34 and HH 46/47 systems respectively. Both areas have also been studied in detail using CCD and IR cameras allowing a clear comparison to be made on the usefulness of the IIIaJ, IIIaF and IVN band digital imaging.

HH 34

HH 34 is an archetypal outflow which has been well studied at visible, infrared and millimetre wavelengths.

Inspection of the digitised IIIaJ and IIIaF images (Figure 1) show similar features to those visible in the deep [S II] image of Mundt (1988). Visible are the bow-shaped emission nebulosity, HH 34S, and the continuum reflection nebula, Re 24 (Reipurth 1985).

The IVN image (Figure 1) shows many of the strong infrared sources including HH 34 IRS, IRS5 and Re 22 (Reipurth 1985).

 
Figure 1: ESO/SERC IIIaJ (J), IIIaF (R) and IVN (I) images of the HH 34 system. The reflection nebulosity Re 23 may be tracing a cavity created by the HH 34 jet. The location of the energy source (HH 34 IRS) is clearly seen in the IVN band. North is up and East is left in all images.

The reflection nebulosity, Re 23 (Reipurth 1985), may represent the brightest part the western wall of a cavity that contains the HH 34 jet. Re 23 shows a different morphology in the IIIaJ and IIIaF images and has been associated with a linear H emission structure which is possibly a separate outflow (Zealey et al. 1993). HH 34N is just visible in the IIIaF band, no visible counterparts to an arc of infrared emission north of HH 34 IRS are seen.

HH 46/47

HH 46/47 is also a well studied flow at visible, infrared and millimetre wavelengths. Many of the optical features discovered using CCD techniques are clearly visible on the ESO/SERC survey films, without enhancement.

The IIIaJ and IIIaF images (Figure 2) of HH 46/47 show the faint emission features associated with the blue shifted, bow shaped nebulosity HH 47D and red shifted bow shock working surface HH 47C as observed in the [S II] CCD images of Eislffel and Mundt (1994).

The strong reflection nebulosity around the source and in the region of HH 46 dominates the IIIaJ image. Both the IVN (Figure 2) image and the infrared image (Figure 3; Zealey et al., 1993) fail to show a central point source, due to the presence of a dense obscuring disk surrounding the source.

 
Figure 2: ESO/SERC IIIaJ (J), IIIaF (R) and IVN (I) images of the HH 46/47 system. The position of HH 46/47 IRS is indicated by the cross.

The IVN band image displays emission, which may be due to reflection nebulosity associated with HH 46, HH 46SW and the region of the counterjet.

None of the IVN, IIIaF or IIIaJ images shows emission from the red shifted flow which is clearly seen in the 2.12 m image (Zealey et al., 1993). This again indicates the high obscuration in this direction due to the dark cloud in which HH 46/47 is embedded.

 
Figure 3: H image of the HH 46/47 system from Zealey et al. (1993). The blue shifted flow terminates in HH 47D. The red shifted lobe occupying the lower right of the image can be traced back to HH 46/47 IRS, at field centre.

© Copyright Astronomical Society of Australia 1997