Thermal emission from bow shocks I: 2D Hydrodynamic Models of the Bubble Nebula

Abstract

The Bubble Nebula (or NGC 7635) is a parsec-scale seemingly spherical wind-blown bubble around the relatively unevolved O star BD+60${}^{\circ }$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 $n=50-200{\mathrm{cm}}^{-3}$ and stellar velocities of $v_{\star }=20-40$ km s${}^{-1}$. Synthetic H$\alpha$ and 24 $\mu$m 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 $v_{\star }\approx 20$ km s${}^{-1}$ into an ISM with $n\sim 100{\mathrm{cm}}^{-3}$, at an angle of 60${}^{\circ }$ 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 $\sim 10^{32}-10^{33}$ erg s${}^{-1}$. The hard X-rays are fainter, luminosity $\sim 10^{30}-10^{31}$ erg s${}^{-1}$, 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${}^{\circ }$2522 and its strong wind suggest that it could be a good candidate for detecting non-thermal emission.

Accepted for publication in Astronomy & Astrophysics

References in corpus (10)

• The effect of photo-ionization on the cooling rates of enriched, astrophysical plasmas
• Gone With the Wind: Where is the Missing Stellar Wind Energy from Massive Star Clusters?
• Models of the circumstellar medium of evolving, massive runaway stars moving through the Galactic plane
• Wind bubbles within H II regions around slowly moving stars
• Radiation-hydrodynamical simulations of massive star formation using Monte Carlo radiative transfer: I. Algorithms and numerical methods
• Vortices in the wakes of AGB stars
• Bow shock nebulae of hot massive stars in a magnetized medium
• Formation and X-ray Emission from Hot Bubbles in Planetary Nebulae. II. Hot bubble X-ray emission
• Modelling interstellar structures around Vela X-1
• Hot gas in the Wolf-Rayet nebula NGC3199

Cited by in corpus (21)

• MHD-shock structures of astrospheres: $\lambda$ Cephei-like astrospheres
• Wind nebulae and supernova remnants of very massive stars
• Inside the core of a young massive star cluster: 3D MHD simulations
• 3D MHD astrospheres: applications to IRC-10414 and Betelgeuse
• The IACOB project VIII. Searching for empirical signatures of binarity in fast-rotating O-type stars
• On the ring nebulae around runaway Wolf-Rayet stars
• PION: Simulating bow shocks and circumstellar nebulae
• A wind-blown bubble in the Central Molecular Zone cloud G0.253+0.016
• Mixing of materials in magnetised core-collapse supernova remnants
• Thermal emission from bow shocks II: 3D magnetohydrodynamic models of Zeta Ophiuchi
• And then they were two: detection of non-thermal radio emission from the bow shocks of two runaway stars
• Core-collapse supernova inside the core of a young massive star cluster: 3D MHD simulations
• Inverse Compton cooling of thermal plasma in colliding-wind binaries
• Simulations of Magnetised Stellar-Wind Bubbles
• Investigating dusty Red Supergiant outflows in Westerlund 1 with 3D Hydrodynamic simulations
• Thermal emission from bow shocks. III. Variable diffuse X-ray emission from stellar-wind bow shocks driven by dynamical instabilities
• Molecular gas properties in young stellar clusters with a suppressed star cluster wind
• Diffuse Hot Plasma in the Interstellar Medium and Galactic Outflows
• EWOCS-V: Is Wd1-72 a recent post-interaction WR+O binary?
• Shells and bubbles around compact clusters of massive stars: 3D MHD simulations
• Radio polarization from runaway star bowshocks-I. The general case