Properties of bow-shock sources at the Galactic center

TL;DR

This study investigates the nature and kinematics of bow-shock sources near the Galactic Center, revealing they are likely not part of the known stellar disk and providing insights into their emission mechanisms and motions.

Contribution

Introduces a new self-calibration method for sparse aperture masking and models bow-shock sources to determine their nature and orbital dynamics.

Findings

IRS21, IRS1W, and IRS5 are confirmed bow-shocks caused by stellar interactions with the ISM.

IRS10W's nature remains uncertain.

Sources are not part of the clockwise disk, indicating random orbital orientations.

Abstract

There are an enigmatic population of massive stars around the Galactic Center (GC) that were formed some Ma ago. A fraction of these stars has been found to orbit the supermassive black hole, SgrA*, in a projected clockwise disk, which suggests that they were formed in a formerly existing dense disk around SgrA*. We focus on the extended, near-infrared (NIR) sources IRS1W, IRS5, IRS10W, and IRS21 that have been suggested to be young, massive stars that form bow-shocks through their interaction with the ISM. Their nature has impeded accurate determination of their orbital parameters. We aim at establishing their nature and kinematics to test whether they form part of the clockwise disk. We performed NIR multi-wavelength imaging using adaptive optics (AO) and sparse aperture masking (SAM). We introduce a new method for self-calibration of the SAM PSF in dense stellar fields. The emission mechanism, morphology and kinematics of the targets were examined via 3D bow-shock models. We confirm previous findings that IRS21, IRS1W, and IRS5 are bow-shocks created by the interaction between mass-losing stars and the interstellar gas. The nature of IRS10W remains unclear. Our modeling shows that the bow-shock-emission is caused by thermal emission while the scattering of stellar light does not play any significant role. IRS 1W appears to be a bow-shock produced by an anisotropic stellar wind or by locally inhomogeneous ISM density. Our best-fit models provide an estimate of the local proper motion of the ISM in the NA in agreement with the published models. Assuming that all of the sources are tied to SgrA*, their orbital planes were obtained via a Monte-Carlo simulation. Our orbital analysis suggests that they are not part of any of the clockwise disk. We thus add more evidence to recent findings that a large part of the massive stars show apparently random orbital orientations.