Abstract
Context. The interstellar bubble RCW 120 seen around a type O runaway star is driven by the stellar wind and the ionising radiation emitted by the star. The boundary between the stellar wind and interstellar medium (ISM) is associated with the arc-shaped mid-infrared dust emission around the star within the HII region. Aims. We aim to investigate the arc-shaped bow shock in RCW 120 by means of numerical simulations, including the radiation, dust, HII region, and wind bubble. Methods. We performed 3D radiation-hydrodynamic simulations including dust using the GUACHO code. Our model includes a detailed treatment of dust grains in the ISM and takes into account the drag forces between dust and gas and the effect of radiation pressure on the gas and dust. The dust is treated as a pressureless gas component. The simulation uses typical properties of RCW 120. We analyse five simulations to deduce the effect of the ionising radiation and dust on both the emission intensity and the shape of the shock. Results. The interaction of the wind and the ionising radiation from a runaway star with the ISM forms an arc-shaped bow shock where the dust from the ISM accumulates in front of the moving star. Moreover, the dust forms a second small arc-shaped structure within the rarefied region at the back of the star inside the bubble. In order to obtain the decoupling between the gas and the dust, it is necessary to include the radiation-hydrodynamic equations together with the dust and the stellar motion. In this work all these elements are considered together, and we show that the decoupling between gas and dust obtained in the simulation is in agreement with the morphology of the infrared observations of RCW 120.
Highlights
The Infrared Astronomical Satellite (IRAS, Neugebauer et al 1984) all-sky survey detected many extended arc-like structures associated with OB-runaway stars and paved the way for further studies to reveal the bow shocks that are present around these powerful stellar winds
While this mechanism can explain the presence of dust inside HII bubbles, it is not capable of producing the morphology of the MIR radiation: an arc-shaped and a peaking close to the ionising source. (Ochsendorf et al 2014, see van Buren & McCray 1988) proposed that dust grains are expelled from ionised stars by radiation pressure and Pavlyuchenkov et al (2013) performed
Our models consider the photoionisation effect, the wind injected by the central star, and the effect of dust on the dynamical evolution of this object and the stellar motion
Summary
The Infrared Astronomical Satellite (IRAS, Neugebauer et al 1984) all-sky survey detected many extended arc-like structures associated with OB-runaway stars and paved the way for further studies to reveal the bow shocks that are present around these powerful stellar winds (van Buren et al 1995; Peri et al 2012). The mid-infrared (MIR) observations from SpitzerMIPSGAL (Carey et al 2009) of interstellar bubbles along the Galactic plane show that the interiors of HII regions contain dust, and some of them present 24 μm dust emission near to the central ionising source (Deharveng et al 2010; Kendrew et al 2012; Simpson et al 2012). Everett & Churchwell (2010) explored the possibility that the evaporation of small dense cloudlets could resupply the hot gas with a new generation of dust grains. While this mechanism can explain the presence of dust inside HII bubbles, it is not capable of producing the morphology of the MIR radiation: an arc-shaped and a peaking close to the ionising source. While this mechanism can explain the presence of dust inside HII bubbles, it is not capable of producing the morphology of the MIR radiation: an arc-shaped and a peaking close to the ionising source. (Ochsendorf et al 2014, see van Buren & McCray 1988) proposed that dust grains are expelled from ionised stars by radiation pressure and Pavlyuchenkov et al (2013) performed
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