The two spectrometers on board the Infrared Space Observatory were used to observe the Herbig-Haro objects HH 80, 81, and 80N, as well as their candidate exciting source IRAS 18162-2048. The fine structure lines of [O I] 63 ìm, [O I] 145 ìm, and [C II] 158 ìm are detected everywhere, while [N II] 122 ìm and [O III] 88.3 ìm are only detected toward the HH objects; line ratios confirm for the first time the collisionally excited HH nature of HH 80N. No molecular line is detected in any of the observed positions. We use a full shock code to diagnose shock velocities vs~100 km s-1 toward the HH objects, as expected from the optical spectroscopy. Since proper motions suggest velocities in excess of 600 km s-1, the HH objects probably represent the interface between two flow components with velocity differing by ~vs. Aside from the flow exciting source, the [C II] 158 ìm line is everywhere brighter than the [O I] 63 ìm line, indicating the presence of a photodissociation region (PDR) all along the flow. Continuum emission from the HH objects and from other positions along the flow is only detected longward of ~50 ìm, and its proportionality to the [C II] 158 ìm line flux suggests it is PDR in origin. We propose that the far-ultraviolet continuum irradiated by the HH objects and the jet is responsible for the generation of a PDR at the walls of the flow cavity. We develop a very simple model which strengthens the plausibility of this hypothesis. Based on observations with ISO, an ESA project with instruments funded by ESA Member States (especially the PI countries: France, Germany, the Netherlands, and the United Kingdom) with the participation of ISAS and NASA.
A Shock-induced Photodissociation Region in the HH 80/81 Flow: Far-Infrared Spectroscopy
2001
Abstract
The two spectrometers on board the Infrared Space Observatory were used to observe the Herbig-Haro objects HH 80, 81, and 80N, as well as their candidate exciting source IRAS 18162-2048. The fine structure lines of [O I] 63 ìm, [O I] 145 ìm, and [C II] 158 ìm are detected everywhere, while [N II] 122 ìm and [O III] 88.3 ìm are only detected toward the HH objects; line ratios confirm for the first time the collisionally excited HH nature of HH 80N. No molecular line is detected in any of the observed positions. We use a full shock code to diagnose shock velocities vs~100 km s-1 toward the HH objects, as expected from the optical spectroscopy. Since proper motions suggest velocities in excess of 600 km s-1, the HH objects probably represent the interface between two flow components with velocity differing by ~vs. Aside from the flow exciting source, the [C II] 158 ìm line is everywhere brighter than the [O I] 63 ìm line, indicating the presence of a photodissociation region (PDR) all along the flow. Continuum emission from the HH objects and from other positions along the flow is only detected longward of ~50 ìm, and its proportionality to the [C II] 158 ìm line flux suggests it is PDR in origin. We propose that the far-ultraviolet continuum irradiated by the HH objects and the jet is responsible for the generation of a PDR at the walls of the flow cavity. We develop a very simple model which strengthens the plausibility of this hypothesis. Based on observations with ISO, an ESA project with instruments funded by ESA Member States (especially the PI countries: France, Germany, the Netherlands, and the United Kingdom) with the participation of ISAS and NASA.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
