Low Excitation HH Objects

Hartigan, P. (Rice)

A number of Herbig-Haro objects show anomalously strong lines of neutral oxygen and singly ionized sulphur. In this paper I review current ideas about the formation of these `low-excitation' HH objects. Molecules in the preshock gas of HH 7 help to produce the low-excitation spectrum in this bow shock. In contrast, the low-excitation spectrum in the stellar jet HH 47 can be modeled successfully by weak atomic shocks in the flow. New shock models indicate that the ionization fraction in HH 47 is only a few percent, considerably smaller than previous estimates. A wide field H_2 image of the HH 7 region reveals a new emission line object located to the southeast of HH 7, suggesting that HH 7 does not represent the first major ejection from the infrared source.

1994, PASP Conference Series 57, 94.