The arc-shaped radio source at the center of NGC 6334A: Is it a colliding wind region of two young massive stars or the bow shock of a runaway star?

TL;DR

This study uses multi-epoch, multi-frequency VLA observations to analyze an arc-shaped radio source in NGC 6334A, exploring whether it is a colliding wind region or a bow shock from a runaway star.

Contribution

It provides new high-resolution, multi-frequency radio observations and proper motion measurements, offering insights into the nature of the arc-shaped source in NGC 6334A.

Findings

The source shows a non-thermal spectral index of -0.68.

The arc-shaped structure suggests a bow shock or colliding wind region.

Proper motion indicates a velocity of approximately 120 km/s.

Abstract

New multi-wavelength Karl G. Jansky VLA observations of CKR02A, the compact radio source in the center of the compact HII region NGC 6334A, are presented. The observations were carried out in five epochs and included the frequency ranges 8.0 - 12.0 GHz (X-band), 18.0 - 26.0 GHz (K-band), and 29.0 - 37.0 GHz (Ka-band). The source is detected and resolved in all the observed epochs and in all bands. The source shows a clear arc-shaped structure consistent with a bow shock. The analysis of the spectral index maps indicates that its spectral index is $\alpha=-0.68\pm0.17$, suggesting that the emission is non-thermal. Two astronomical objects can explain the emission nature and morphology of the source: a colliding wind region of two massive stars or the bow shock of a massive runaway star. However, no massive stars are reported so far in the center of NGC 6334A, though its presence is also suggested by the free-free radio emission of the C-HII region itself. Using ancillary VLA data, we measured a preliminary proper motion of $19\pm6$ mas yr$^{-1}$, equivalent to a velocity of $120\pm40$ km s$^{-1}$. A detailed discussion of the implications of both scenarios is provided. Finally, a list of compact radio sources in the vicinity of NGC 6334A is given and briefly discussed.