Bow shocks, bow waves, and dust waves – III. Diagnostics

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

doi:10.1093/mnras/stz2283

Cited by 19 publications

(15 citation statements)

References 154 publications

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“…Recently, a very promising technique based on bow shocks to infer 𝑀 has been explored in the literature (e.g. Gvaramadze et al 2012;Henney & Arthur 2019;Kobulnicky et al 2019). The winds of massive stars can produce shocks when encountering the ISM medium, producing arc-shaped emission that can be successfully detected and imaged at infrared wavelengths (e.g., at 24𝜇m).…”

Section: Bow-shock Measurementsmentioning

confidence: 99%

Wind properties of Milky Way and SMC massive stars: empirical Z dependence from CMFGEN models

Marcolino,

Bouret,

Rocha-Pinto

et al. 2022

Preprint

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Detailed knowledge about stellar winds and evolution at different metallicities is crucial for understanding stellar populations and feedback in the Local Group of galaxies and beyond. Despite efforts in the literature, we still lack a comprehensive, empirical view of the dependence of wind properties on metallicity (𝑍). Here, we investigate the winds of O and B stars in the Milky Way (MW) and Small Magellanic Cloud (SMC). We gathered a sample of 96 stars analyzed by means of the NLTE code CMFGEN. We explored their wind strengths and terminal velocities to address the 𝑍 dependence, over a large luminosity range. The empirical wind-luminosity relation (WLR) obtained updates and extends previous results in the literature. It reveals a luminosity and 𝑍 dependence, in agreement with the radiatively driven wind theory. For bright objects (log 𝐿/𝐿 5.4), we infer that 𝑀 ∼ 𝑍 0.5−0.8 . However, this dependence seems to get weaker or vanish at lower luminosities. The analysis of the terminal velocities suggests a shallow 𝑍 𝑛 dependence, with 𝑛 ∼ 0.1 − 0.2, but it should be confirmed with a larger sample and more accurate 𝑉 ∞ determinations. Recent results on SMC stars based on the PoWR code support our inferred WLR. On the other hand, recent bow-shocks measurements stand mostly above our derived WLR. Theoretical calculations of the WLR are not precise, specially at low 𝐿, where the results scatter. Deviations between our results and recent predictions are identified to be due to the weak wind problem and the extreme terminal velocities predicted by the models. The Z dependence suggested by our analysis deserves further investigations, given its astrophysical implications.

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Section: Bow-shock Measurementsmentioning

confidence: 99%

Wind properties of Milky Way and SMC massive stars: empirical Z dependence from CMFGEN models

Marcolino,

Bouret,

Rocha-Pinto

et al. 2022

Preprint

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“…Bow shocks emit predominantly at mid-infrared wavelengths through thermal emission (TE) from dust that is radiatively heated by the wind-driving star (van Buren & McCray 1988;Meyer et al 2014;Henney & Arthur 2019b). Infrared observations can, however, be difficult to interpret because they trace the dust and not the gas directly, and so the uncertainties in obtaining the gas density distribution are not small.…”

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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“…These may be combined with the rates determined from Hα line and from radio emission, which are also severely affected by clumping (Puls et al 2006). In such a situation, alternative mass-loss rate determinations based on the interaction of the wind with the circumstellar environment (Henney & Arthur 2019;Kobulnicky et al 2019) may provide estimates that are free of the influence of inhomogeneities.…”

Section: Introductionmentioning

confidence: 99%

New mass-loss rates of B supergiants from global wind models

Krtička

Kubát

Krtičková

2021

A&A

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Massive stars lose a significant fraction of mass during their evolution. However, the corresponding mass-loss rates are rather uncertain, especially for evolved stars. To improve this, we calculated global line-driven wind models for Galactic B supergiants. Our models predict radial wind structure and particularly the mass-loss rates and terminal velocities directly from basic stellar parameters. The hydrodynamic structure of the flow is consistently determined from the photosphere in nearly hydrostatic equilibrium to supersonically expanding wind. The radiative force is derived from the solution of the radiative transfer equation in the comoving frame. We provide a simple formula that predicts theoretical mass-loss rates as a function of stellar luminosity and effective temperature. The mass-loss rate of B supergiants slightly decreases with temperature down to about 22.5 kK, where the region of recombination of Fe IV to Fe III starts to appear. In this region, which is about 5 kK wide, the mass-loss rate gradually increases by a factor of about 6. The increase of the mass-loss rate is associated with a gradual decrease of terminal velocities by a factor of about 2. We compared the predicted wind parameters with observations. While the observed wind terminal velocities are reasonably reproduced by the models, the situation with mass-loss rates is less clear. The mass-loss rates derived from observations that are uncorrected for clumping are by a factor of 3 to 9 higher than our predictions on cool and hot sides of the studied sample, respectively. These observations can be reconciled with theory assuming a temperature-dependent clumping factor that is decreasing toward lower effective temperatures. On the other hand, the mass-loss rate estimates that are not sensitive to clumping agree with our predictions much better. Our predictions are by a factor of about 10 lower than the values currently used in evolutionary models appealing for reconsideration of the role of winds in the stellar evolution.

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Bow shocks, bow waves, and dust waves – III. Diagnostics

Cited by 19 publications

References 154 publications

Wind properties of Milky Way and SMC massive stars: empirical Z dependence from CMFGEN models

Wind properties of Milky Way and SMC massive stars: empirical Z dependence from CMFGEN models

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

New mass-loss rates of B supergiants from global wind models

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