The HH 24 Complex: Jets, Multiple Star Formation, and Orphaned Protostars

TL;DR

This study provides a detailed multi-wavelength analysis of the HH 24 complex, revealing a dynamic, multi-star system with jets, ejected protostars, and complex gas interactions, highlighting the role of chaotic dynamics in star formation.

Contribution

It offers the first comprehensive multi-wavelength characterization of the HH 24 complex, revealing the dynamics of a non-hierarchical multiple system and its role in star formation and ejection processes.

Findings

The system contains at least 7 sources with diverse masses.

A borderline brown dwarf was ejected at 25 km/s about 5,800 years ago.

The jets extend at least 3 parsecs, tracing large-scale shock chains.

Abstract

The HH 24 complex harbors five collimated jets emanating from a small protostellar multiple system. We have carried out a multi-wavelength study of the jets, their driving sources, and the cloud core hosting the embedded stellar system, based on data from the HST, Gemini, Subaru, APO 3.5m, VLA, and ALMA telescopes. The data show that the multiple system, SSV 63, contains at least 7 sources, ranging in mass from the hydrogen-burning limit to proto-Herbig Ae stars. The stars are in an unstable non-hierarchical configuration, and one member, a borderline brown dwarf, is moving away from the protostellar system with 25 km/s, after being ejected about 5,800 yr ago as an orphaned protostar. Five of the embedded sources are surrounded by small, possibly truncated, disks resolved at 1.3 mm with ALMA. Proper motions and radial velocities imply jet speeds of 200-300 km/s. The two main HH 24 jets, E and C, form a bipolar jet system which traces the innermost portions of parsec-scale chains of Herbig-Haro and H2 shocks with a total extent of at least 3 parsec. H2CO and C18O observations show that the core has been churned and continuously fed by an infalling streamer. 13CO and 12CO trace compact, low-velocity, cavity walls carved by the jets and an ultra-compact molecular outflow from the most embedded object. Chaotic N-body dynamics likely will eject several more of these objects. The ejection of stars from their feeding zones sets their masses. Dynamical decay of non-hierarchical systems can thus be a major contributor to establishing the initial mass function.