Thermal emission from bow shocks I: 2D hydrodynamic models of the Bubble Nebulaстатья Исследовательская статья

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1. Полный текст pdf BubbleNebula.pdf 15,3 МБ 30 апреля 2019 [Gvaramadze]

[1] Thermal emission from bow shocks i: 2d hydrodynamic models of the bubble nebula / S. Green, J. Mackey, T. J. Haworth et al. // Astronomy and Astrophysics. — 2019. — Vol. 625. — P. A4. The Bubble Nebula (or NGC 7635) is a parsec-scale seemingly spherical wind-blown bubble around the relatively unevolved O star BD+60 2522. The small dynamical age of the nebula and significant space velocity of the star suggest that the Bubble Nebula might be a bow shock. We have run 2D hydrodynamic simulations to model the interaction of the central star's wind with the interstellar medium (ISM). The models cover a range of possible ISM number densities of n=50-200 cm^{-3} and stellar velocities of v_*=20-40 km/s. Synthetic Halpha and 24 micron emission maps predict the same apparent spherical bubble shape with quantitative properties similar to observations. The synthetic maps also predict a maximum brightness similar to that from the observations and agree that the maximum brightness is at the apex of the bow shock. The best-matching simulation had v_*≈ 20 km/s into an ISM with n∼100 cm^{-3}, at an angle of 60 with respect to the line of sight. Synthetic maps of soft (0.3-2 keV) and hard (2-10 keV) X-ray emission show that the brightest region is in the wake behind the star and not at the bow shock itself. The unabsorbed soft X-rays have luminosity ∼10^{32}-10^{33} erg/s. The hard X-rays are fainter, luminosity ∼10^{30}-10^{31} erg/s, and may be too faint for current X-ray instruments to successfully observe. Our results imply that the O star creates a bow shock as it moves through the ISM and in turn creates an asymmetric bubble visible at optical and infrared wavelengths, and predicted to be visible in X-rays. The Bubble Nebula does not appear to be unique, it could be just a favourably oriented very dense bow shock. The dense ISM surrounding BD+60 2522 and its strong wind suggest that it could be a good candidate for detecting non-thermal emission. [ DOI ]

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