The Mysterious Sickle Object in the Carina Nebula: A stellar wind induced bow shock grazing a clump?

TL;DR

This study investigates a peculiar arc in the Carina Nebula, revealing it as a bow shock caused by a high-velocity B-type star interacting with a dense clump, combining multi-wavelength observations and simulations.

Contribution

It provides evidence that the Sickle is a stellar wind-induced bow shock from a fast-moving star grazing a dense interstellar clump, supported by multi-wavelength data and numerical modeling.

Findings

The Sickle is a bow shock caused by stellar wind.

The star MJ 218 moves at ~100 km/s, grazing the clump surface.

Multi-wavelength data supports the bow shock interpretation.

Abstract

Optical and near-infrared images of the Carina Nebula show a peculiar arc-shaped feature, which we call the "Sickle", next to the B-type star Trumpler 14 MJ 218. We use multi-wavelength observations to explore and constrain the nature and origin of the nebulosity. Using sub-mm data from APEX/LABOCA as well as Herschel far-infrared maps, we discovered a dense, compact clump with a mass of ~ 40 Msun located close to the apex of the Sickle. We investigate how the B-star MJ 218, the Sickle, and the clump are related. Our numerical simulations show that, in principle, a B-type star located near the edge of a clump can produce a crescent-shaped wind shock front, similar to the observed morphology. However, the observed proper motion of MJ 218 suggest that the star moves with high velocity (~ 100 km/s) through the ambient interstellar gas. We argue that the star is just about to graze along the surface of the clump, and the Sickle is a bow shock induced by the stellar wind, as the object moves supersonically through the density gradient in the envelope of the clump.