Non-monotonic spatial distribution of the interstellar dust in astrospheres: finite gyroradius effect

Katushkina, Olga; Alexashov, D. B.; Izmodenov, Vladislav; Gvaramadze, V. V.

doi:10.1093/mnras/stw2833

Cited by 16 publications

(13 citation statements)

References 32 publications

(47 reference statements)

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“…For a more detailed discussion see also Scherer et al (2016b). Although this being the termination shock distance, other authors (del Valle & Pohl 2018;Katushkina et al 2017, among others) call the above distance the standoff distance or the bow shock distance (Meyer et al 2016). The reason why only the TS distance can be determined is the fact that in ideal HD between the TS and the BS Bernoulli's law holds, while in the downstream region of TS and BS the ram (ρv 2 /2) and thermal pressure (P) can be calculated via the Rankine-Hugoniot equations.…”

Section: The Shock and Astropause Distancesmentioning

confidence: 99%

MHD-shock structures of astrospheres: λ Cephei -like astrospheres

Scherer

Baalmann

Fichtner

et al. 2020

Monthly Notices of the Royal Astronomical Society

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The interpretation of recent observations of bow shocks around O-stars and the creation of corresponding models require a detailed understanding of the associated (magneto-)hydrodynamic structures. We base our study on three-dimensional numerical (magneto-)hydrodynamical models, which are analyzed using the dynamically relevant parameters, in particular, the (magneto)sonic Mach numbers. The analytic Rankine-Hugoniot relation for HD and MHD are compared with those obtained by the numerical model. In that context we also show that the only distance which can be approximately determined is that of the termination shock, if it is a hydrodynamical shock. For MHD shocks the stagnation point does not, in general, lie on the inflow line, which is the line parallel to the inflow vector and passing through the star. Thus an estimate via the Bernoulli equation as in the HD case is, in general, not possible. We also show that in O-star astrospheres, distinct regions exist in which the fast, slow, Alfvénic, and sonic Mach numbers become lower than one, implying sub-slow magnetosonic as well as sub-fast and sub-sonic flows. Nevertheless, the analytic MHD Rankine Hugoniot relations can be used for further studies of turbulence and cosmic ray modulation.

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Section: The Shock and Astropause Distancesmentioning

confidence: 99%

MHD-shock structures of astrospheres: λ Cephei -like astrospheres

Scherer

Baalmann

Fichtner

et al. 2020

Monthly Notices of the Royal Astronomical Society

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“…Recently, Katushkina et al (2017; hereafter Paper I) presented a physical mechanism possibly responsible for the origin of the cirrus-like structure of astrospheres around runaway stars. It was shown that, under proper conditions, alternating minima and maxima of the dust density (seen like filaments) might appear between the astrospheric bow shock (BS) and the astropause (AP) because of periodical gyromotion of the dust grains around the interstellar magnetic field lines.…”

Section: Introductionmentioning

confidence: 99%

An astrosphere around the blue supergiant κ Cas: possible explanation of its filamentary structure

Katushkina

Alexashov

Gvaramadze

et al. 2017

Monthly Notices of the Royal Astronomical Society

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High-resolution mid-infrared observations carried out by the Spitzer Space Telescope allowed one to resolve the fine structure of many astrospheres. In particular, they showed that the astrosphere around the B0.7 Ia star κ Cas (HD 2905) has a clear-cut arc structure with numerous cirrus-like filaments beyond it. Previously, we suggested a physical mechanism for the formation of such filamentary structures. Namely, we showed theoretically that they might represent the non-monotonic spatial distribution of the interstellar dust in astrospheres (viewed as filaments) caused by interaction of the dust grains with the interstellar magnetic field disturbed in the astrosphere due to colliding of the stellar and interstellar winds. In this paper, we invoke this mechanism to explain the structure of the astrosphere around κ Cas. We performed 3D magnetohydrodynamic modelling of the astrosphere for realistic parameters of the stellar wind and space velocity. The dust dynamics and the density distribution in the astrosphere were calculated in the framework of a kinetic model. It is found that the model results with the classical MRN size distribution of dust in the interstellar medium do not match the observations, and that the observed filamentary structure of the astrosphere can be reproduced only if the dust is composed mainly of big (µm-sized) grains. Comparison of the model results with observations allowed us to estimate parameters (number density and magnetic field strength) of the surrounding interstellar medium.

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“…Interestingly, the perpendicular orientation of the ISM magnetic field can result in series of multiple arcs normal to the direction of motion of the star (Fig. 11f) as modelled in the context of hot OB stars in Katushkina et al (2017Katushkina et al ( , 2018, see also Baalmann et al (2021). Furthermore, the opening of the bow shock can significantly differ from a projection model to another, with rounder termination shocks (Fig.…”

Section: Emission Mapsmentioning

confidence: 86%

3D MHD astrospheres: applications to IRC-10414 and Betelgeuse

Meyer,

Mignone,

Petrov

et al. 2021

Preprint

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A significative fraction of all massive stars in the Milky Way move supersonically through their local interstellar medium (ISM), producing bow shock nebulae by wind-ISM interaction. The stability of these observed astrospheres around cool massive stars challenges precedent two-dimensional (magneto-)hydrodynamical simulations of their surroundings. We present three-dimensional magneto-hydrodynamical (3D MHD) simulations of the circumstellar medium of runaway M-type red supergiant stars moving with velocity v = 50 km s −1 . We treat the stellar wind with a Parker spiral and assume a 7 µG magnetisation of the ISM. Our free parameter is the angle θ mag between ISM flow and magnetisation, taken to 0 • , 45 • and 90 • . It is found that simulation dimension, coordinate systems and grid effects can greatly affect the development of the modelled astrospheres. Nevertheless, as soon as the ISM flow and magnetisation directions differs by more than a few degrees (θ mag 5 • ), the bow shock is stabilised, most clumpiness and ragged structures vanishing. The complex shape of the bow shocks induce important projection effects, e.g. at optical Hα line, producing complex of astrospheric morphologies. We speculate that those effects are also at work around earlier-type massive stars, which would explain their diversity of their observed arc-like nebula around runaway OB stars. Our 3D MHD models are fitting well observations of the astrospheres of several runaway red supergiant stars. The results interpret the smoothed astrosphere of IRC-10414 and Betelgeuse (αOri) are stabilised by an organised, non-parallel ambient magnetic field. Our findings suggest that IRC-10414 is currently in a steady state of its evolution, and that Betelgeuse's bar is of interstellar origin.

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Non-monotonic spatial distribution of the interstellar dust in astrospheres: finite gyroradius effect

Cited by 16 publications

References 32 publications

MHD-shock structures of astrospheres: λ Cephei -like astrospheres

MHD-shock structures of astrospheres: λ Cephei -like astrospheres

An astrosphere around the blue supergiant κ Cas: possible explanation of its filamentary structure

3D MHD astrospheres: applications to IRC-10414 and Betelgeuse

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