The nature of HH 223 from long-slit spectroscopy

HH 223 is a knotty, wiggling nebular emission of ~30" length found in the L723 star-forming region. It lies projected onto the largest blueshifted lobe of the cuadrupolar CO outflow powered by a low-mass YSO system embedded in the core of L723. We analysed the physical conditions and kinematics along HH 223 with the aim of disentangling whether the emission arises from shock-excited, supersonic gas characteristic of a stellar jet, or is only tracing the wall cavity excavated by the CO outflow. We performed long-slit optical spectroscopy along HH 223, crossing all the bright knots (A to E) and part of the low-brightness emission nebula (F filament). One spectrum of each knot, suitable to characterize the nature of its emission, was obtained. The physical conditions and the radial velocity of the HH 223 emission along the slits were also sampled at smaller scale (0.6") than the knot sizes. {The spectra of all the HH 223 knots appear as those of the intermediate/high excitation Herbig-Haro objects. The emission is supersonic, with blueshifted peak velocities ranging from -60 to -130 km/s. Reliable variations in the kinematics and physical conditions at smaller scale that the knot sizes are also found. The properties of the HH 223 emission derived from the spectroscopy confirm the HH nature of the object, the supersonic optical outflow most probably also being powered by the YSOs embedded in the L723 core.

💡 Research Summary

The paper investigates the nature of HH 223, a knotty, wiggling nebular emission about 30 arcseconds long located in the L723 star‑forming region. HH 223 lies projected onto the brightest blueshifted lobe of a quadrupolar CO outflow that is driven by a low‑mass young stellar object (YSO) system deeply embedded in the L723 core. The central question is whether the optical emission traces shock‑excited, supersonic gas typical of a stellar jet, or merely delineates the cavity walls excavated by the CO outflow.

To address this, the authors performed long‑slit optical spectroscopy along the entire extent of HH 223, positioning the slit so that it crossed all bright knots (designated A through E) and a portion of the faint surrounding nebula (the F filament). For each knot a high‑signal‑to‑noise spectrum was obtained, and the slit was sampled at a spatial resolution of 0.6 arcseconds—significantly finer than the typical knot size—allowing the authors to probe variations in physical conditions and kinematics on sub‑knot scales.

The spectra of all knots display the classic emission‑line suite of intermediate to high‑excitation Herbig‑Haro (HH) objects: strong Hα,