Bow shocks, bow waves, and dust waves – II. Beyond the rip point

Henney, W. J.; Arthur, S. J.

doi:10.1093/mnras/stz1130

Cited by 18 publications

(9 citation statements)

References 78 publications

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“…Our results show good agreement with those obtained by Mackey et al (2016), and are in accordance with the general analysis of Henney & Arthur (2019b) for the case of a dust wave where the dust is decoupled from the gas. Indeed, the distribution of dust is mainly located in a region found immediately after the bow shock, as in the two works mentioned previously.…”

Section: Discussionsupporting

confidence: 91%

Numerical models for the dust in RCW 120

Rodríguez-González

Méliani

Sánchez-Cruces

et al. 2019

A&A

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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 midinfrared 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.

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Section: Discussionsupporting

confidence: 91%

Numerical models for the dust in RCW 120

Rodríguez-González

Méliani

Sánchez-Cruces

et al. 2019

A&A

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“…We note that magnetic fields can align dust grains in a way that produces polarization; they also play an important role in both the morphology and the emission properties of a stellar wind bow shock (e.g., Meyer et al 2017;Henney & Arthur 2019b). However, treating the complex effects of magnetic fields is beyond the scope of this paper.…”

Section: Introductionmentioning

confidence: 96%

Polarization simulations of stellar wind bow shock nebulae – II. The case of dust scattering

Shrestha

Neilson

Hoffman

et al. 2020

Monthly Notices of the Royal Astronomical Society

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We study the polarization produced by scattering from dust in a bow shock-shaped region of enhanced density surrounding a stellar source, using the Monte Carlo radiative transfer code SLIP. Bow shocks are structures formed by the interaction of the winds of fast-moving stars with the interstellar medium. Our previous study focused on the polarization produced in these structures by electron scattering; we showed that polarization is highly dependent on inclination angle and that multiple scattering changes the shape and degree of polarization. In contrast to electron scattering, dust scattering is wavelength-dependent, which changes the polarization behaviour. Here we explore different dust particle sizes and compositions and generate polarized spectral energy distributions for each case. We find that the polarization SED behaviour depends on the dust composition and grain size. Including dust emission leads to polarization changes with temperature at higher optical depth in ways that are sensitive to the orientation of the bow shock. In various scenarios and under certain assumptions, our simulations can constrain the optical depth and dust properties of resolved and unresolved bow shock-shaped scattering regions.Constraints on optical depth can provide estimates of local ISM density for observed bow shocks. We also study the impact of dust grains filling the region between the star and bow shock. We see that as the density of dust between the star and bow shock increases, the resulting polarization is suppressed for all the optical depth regimes.

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“…The mid-infrared brightness is very sensitive to the assumed grain size distribution and composition (Pavlyuchenkov et al 2013;Mackey et al 2016;Katushkina & Izmodenov 2019). The emission scales with the dust density, and there are regions of parameter space where it is expected that dust and gas are not strongly coupled and the dust is a poor tracer of gas (Akimkin et al 2015;Katushkina et al 2018;Henney & Arthur 2019a).…”

Section: Introductionmentioning

confidence: 99%

And then they were two: Detection of non-thermal radio emission from the bow shocks of two runaway stars

Moutzouri

Mackey

González

et al. 2022

A&A

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Context. In recent years, winds from massive stars have been considered promising sites for investigating relativistic particle acceleration. In particular, the resulting bow-shaped shocks from the interaction of the supersonic winds of runaway stars with interstellar matter have been intensively observed at many different wavelengths, from radio to γ-rays. Aims. In this study we investigate the O4If star, BD+43° 3654, the bow shock of which is, so far, the only one proven to radiate both thermal and non-thermal emission at radio frequencies. In addition, we consider NGC 7635, the Bubble Nebula, as a bow shock candidate and examine its apex for indications of thermal and non-thermal radio emission. Methods. We observed both bow shocks in radio frequencies with the Very Large Array (VLA) in the C and X bands (4–8 GHz and 8–12 GHz) and with the Effelsberg telescope at 4–8 GHz. We analysed single-dish and interferometric results individually, in addition to their combined emission, obtained spectral index maps for each source, and calculated their spectral energy distributions. Results. We find that both sources emit non-thermal emission in the radio regime, with the clearest evidence for NGC 7635, whose radio emission has a strongly negative spectral index along the northern rim of the bubble. We present the first high-resolution maps of radio emission from NGC 7635, finding that the morphology closely follows the optical nebular emission. Our results are less conclusive for the bow shock of BD+43° 3654, as its emission becomes weaker and faint at higher frequencies in VLA data. Effelsberg data show a much larger emitting region (albeit a region of thermal emission) than is detected with the VLA for this source. Conclusions. Our results extend the previous radio results from the BD+43° 3654 bow shock to higher frequencies, and with our NGC 7635 results we double the number of bow shocks around O stars with detected non-thermal emission, from one to two. Modelling of the multi-wavelength data for both sources shows that accelerated electrons at the wind termination shock are a plausible source for the non-thermal radio emission, but energetics arguments suggest that any non-thermal X-ray and γ-ray emission could be significantly below existing upper limits. Enhanced synchrotron emission from compressed galactic cosmic rays in the radiative bow shock could also explain the radio emission from the BD+43° 3654 bow shock, but not from NGC 7635. The non-detection of point-like radio emission from BD+43° 3654 puts an upper limit on the mass-loss rate of the star that is lower than values quoted in the literature.

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Bow shocks, bow waves, and dust waves – II. Beyond the rip point

Cited by 18 publications

References 78 publications

Numerical models for the dust in RCW 120

Numerical models for the dust in RCW 120

Polarization simulations of stellar wind bow shock nebulae – II. The case of dust scattering

And then they were two: Detection of non-thermal radio emission from the bow shocks of two runaway stars

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