3D simulations of clump formation in stellar wind collisions. (arXiv:1906.04181v1 [astro-ph.GA])

3D simulations of clump formation in stellar wind collisions. (arXiv:1906.04181v1 [astro-ph.GA])
<a href="http://arxiv.org/find/astro-ph/1/au:+Calderon_D/0/1/0/all/0/1">Diego Calder&#xf3;n</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Cuadra_J/0/1/0/all/0/1">Jorge Cuadra</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Schartmann_M/0/1/0/all/0/1">Marc Schartmann</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Burkert_A/0/1/0/all/0/1">Andreas Burkert</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Prieto_J/0/1/0/all/0/1">Joaqu&#xed;n Prieto</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Russell_C/0/1/0/all/0/1">Christopher M. P. Russell</a>

The inner parsec of our Galaxy contains tens of Wolf-Rayet stars whose
powerful outflows are constantly interacting while filling the region with hot,
diffuse plasma. Theoretical models have shown that, in some cases, the
collision of stellar winds can generate cold, dense material in the form of
clumps. However, their formation process and properties are not well-understood
yet. In this work we present, for the first time, a statistical study of the
clump formation process in unstable wind collisions. We study systems with
dense outflows $(dot{M}sim10^{-5}rm M_{odot} yr^{-1})$, wind speeds of
$sim500$-$1500rm km s^{-1}$, and stellar separations of $sim20$-$200rm
au$. We develop 3D high resolution hydrodynamical simulations of stellar wind
collisions, making use of the adaptive-mesh refinement grid-based code Ramses.
We aim to characterise the initial properties of clumps that form through
hydrodynamic instabilities, mostly via the non-linear thin shell instability.
Our results confirm that more massive clumps are formed in systems whose winds
are close to the transition between the radiative and adiabatic regimes, as
long as such collisions are capable of creating cold, thin shells. Also, we
find that increasing either the wind speed or the degree of asymmetry in the
wind interaction increases the dispersion of the clump masses and ejection
speed distribution. Nevertheless, our findings show that the most massive
clumps are very light $(sim10^{-3}$-$10^{-2}rm M_{oplus})$, approximately
three orders of magnitude less massive than theoretical upper limits. We apply
our results to the central parsec of our Galaxy finding that clumps formed are
not heavy enough neither to affect the thermodynamic state of the region nor to
survive for long enough in order to fall onto the central super-massive black
hole before being destroyed.

The inner parsec of our Galaxy contains tens of Wolf-Rayet stars whose
powerful outflows are constantly interacting while filling the region with hot,
diffuse plasma. Theoretical models have shown that, in some cases, the
collision of stellar winds can generate cold, dense material in the form of
clumps. However, their formation process and properties are not well-understood
yet. In this work we present, for the first time, a statistical study of the
clump formation process in unstable wind collisions. We study systems with
dense outflows $(dot{M}sim10^{-5}rm M_{odot} yr^{-1})$, wind speeds of
$sim500$-$1500rm km s^{-1}$, and stellar separations of $sim20$-$200rm
au$. We develop 3D high resolution hydrodynamical simulations of stellar wind
collisions, making use of the adaptive-mesh refinement grid-based code Ramses.
We aim to characterise the initial properties of clumps that form through
hydrodynamic instabilities, mostly via the non-linear thin shell instability.
Our results confirm that more massive clumps are formed in systems whose winds
are close to the transition between the radiative and adiabatic regimes, as
long as such collisions are capable of creating cold, thin shells. Also, we
find that increasing either the wind speed or the degree of asymmetry in the
wind interaction increases the dispersion of the clump masses and ejection
speed distribution. Nevertheless, our findings show that the most massive
clumps are very light $(sim10^{-3}$-$10^{-2}rm M_{oplus})$, approximately
three orders of magnitude less massive than theoretical upper limits. We apply
our results to the central parsec of our Galaxy finding that clumps formed are
not heavy enough neither to affect the thermodynamic state of the region nor to
survive for long enough in order to fall onto the central super-massive black
hole before being destroyed.

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