Astron. Astrophys. 321, 189-201 (1997)

5. Conclusions

From our observations of 28 HAEBESs with detected [OI] 6300 emission, a number of conclusions can be drawn:

• Herbig Ae/Be star forbidden [OI] 6300 emission falls into one of four categories: I - strongly blueshifted emission, accompanied by a second emission component at a considerably lower, but still blueshifted, velocity, II - low velocity blueshifted emission similar to the low velocity component in category I, III - low velocity redshifted emission and IV - symmetric and unshifted emission.
• More than half the sample possess clearly blueshifted emission lines with radial velocities, 10 kms . There is no corresponding group of stars with even moderately redshifted forbidden emission and most of the remaining stars have unshifted lines within observational errors. Thus there is a close analogy with cTTSs where a similar asymmetry is taken as evidence for the presence of opaque circumstellar disks.
• The HVC forbidden line emission from HAEBESs is best interpreted in terms of a high velocity outflow, in keeping with the model of Kwan & Tademaru (1988, 1995). This is exemplified by the fact that all stars we observe with HVC emission are known jet sources. The LVC emission can be interpreted in terms of a disk wind, with a low velocity and rotationally broadened. Both the velocity and the width of the LVC appear to be larger than the corresponding component in cTTSs.
• The relatively small number (4/28) of HAEBESs with high velocity blueshifted forbidden line emission (category I) indicates a small number of HH jets in this class of young star, if the model of Kwan & Tademaru (1988) is correct and the HVC is evidence of a stellar jet. Direct imaging of HAEBESs (Corcoran & Ray 1997b) confirms this conclusion.
• It is possible to construct an evolutionary sequence based on the degree of outflow and forbidden emission line activity. Our category I stars, which are also Hillenbrand Group II stars (Hillenbrand et al. 1992), are all jet sources and are highly embedded. Such stars appear less evolved that our category II stars, which show lower blueshifted velocities and a reduced frequency of outflow activity, judged by the lower number of jets associated with the category. The lower velocities of the [OI] 6300 emission in the category II stars may be due to the evolution of the outflow mechanism. The category III stars show low velocity redshifted emission and no association with jet or molecular outflow activity. The category IV stars show symmetric and unshifted (relative to the systemic velocity) [OI] 6300 emission and are not generally believed to power outflow phenomena. Two category IV stars, LkH 234 and BD+46 3471, have been associated with an optical jet (LkH 234, Ray et al. 1990) and a HH object (BD 3471, Goodrich 1992) but there is some doubt, at least in the case of LkH 234 (Weintraub et al. 1994), as to the true source of the outflow. Category IV stars may be regarded as more evolved than the category I and II stars.
• The presence of [SII] emission is predominantly detected in those stars with jets.

© European Southern Observatory (ESO) 1997

Online publication: June 30, 1998
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