High-Velocity Interstellar Bullets in IRAS05506+2414: A Very Young Protostar

TL;DR

This paper reports the discovery of a very young, high-velocity outflow from IRAS 05506+2414, likely a massive protostar, characterized by optical jets, high-velocity knots, and dense star-forming core indicators, indicating an early stage of stellar evolution.

Contribution

The study provides the first detailed multi-wavelength characterization of IRAS 05506+2414 as a young protostar with high-velocity outflows, challenging previous classifications as a pre-planetary nebula.

Findings

High-velocity outflows with radial velocities up to 350 km/s.

Presence of dense, dusty star-forming core indicators.

IRAS 05506 is likely a very young intermediate-mass or massive protostar.

Abstract

We have made a serendipitous discovery of an enigmatic outflow source, IRAS 05506+2414 (hereafter IRAS 05506), as part of a multi-wavelength survey of pre-planetary nebulae (PPNs). The HST optical and near-infrared images show a bright compact central source with a jet-like extension, and a fan-like spray of high-velocity (with radial velocities upto 350 kms/s) elongated knots which appear to emanate from it. These structures are possibly analogous to the near-IR "bullets" seen in the Orion nebula. Interferometric observations at 2.6 mm show the presence of a high-velocity CO outflow and a continuum source also with a faint extension, both of which are aligned with the optical jet structure. IRAS 05506 is most likely not a PPN. We find extended NH3 (1,1) emission towards IRAS 05506; these data together with the combined presence of far-IR emission, H2O and OH masers, and CO and CS J=2-1 emission, strongly argue for a dense, dusty star-forming core associated with IRAS 05506. IRAS 05506 is probably an intermediate-mass or massive protostar, and the very short time-scale (200 yr) of its outflows indicates that it is very young. If IRAS 05506 is a massive star, then the lack of radio continuum and the late G -- early K spectral type we find from our optical spectra implies that in this object we are witnessing the earliest stages of its life, while its temperature is still too low to provide sufficient UV flux for ionisation.