The general applicability of self-similar solutions for thermal disc winds. (arXiv:2106.05362v1 [astro-ph.EP])
<a href="http://arxiv.org/find/astro-ph/1/au:+Sellek_A/0/1/0/all/0/1">Andrew D. Sellek</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Clarke_C/0/1/0/all/0/1">Cathie J. Clarke</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Booth_R/0/1/0/all/0/1">Richard A. Booth</a>
Thermal disc winds occur in many contexts and may be particularly important
to the secular evolution and dispersal of protoplanetary discs heated by high
energy radiation from their central star. In this paper we generalise previous
models of self-similar thermal winds – which have self-consistent morphology
and variation of flow variables – to the case of launch from an elevated base
and to non-isothermal conditions. These solutions are well-reproduced by
hydrodynamic simulations, in which, as in the case of isothermal winds launched
from the mid-plane, we find winds launch at the maximum Mach number for which
the streamline solutions extend to infinity without encountering a singularity.
We explain this behaviour based on the fact that lower Mach number solutions do
not fill the spatial domain. We also show that hydrodynamic simulations reflect
the corresponding self-similar models across a range of conditions appropriate
to photoevaporating protoplanetary discs, even when gravity, centrifugal
forces, or changes in the density gradient mean the problem is not inherently
scale free. Of all the parameters varied, the elevation of the wind base
affected the launch velocity and flow morphology most strongly, with
temperature gradients causing only minor differences. We explore how launching
from an elevated base affects Ne II line profiles from winds, finding it
increases (reduces) the full width at half maximum (FWHM) of the line at low
(high) inclination to the line of sight compared with models launched from the
disc mid-plane and thus weakens the dependence of the FWHM on inclination.
Thermal disc winds occur in many contexts and may be particularly important
to the secular evolution and dispersal of protoplanetary discs heated by high
energy radiation from their central star. In this paper we generalise previous
models of self-similar thermal winds – which have self-consistent morphology
and variation of flow variables – to the case of launch from an elevated base
and to non-isothermal conditions. These solutions are well-reproduced by
hydrodynamic simulations, in which, as in the case of isothermal winds launched
from the mid-plane, we find winds launch at the maximum Mach number for which
the streamline solutions extend to infinity without encountering a singularity.
We explain this behaviour based on the fact that lower Mach number solutions do
not fill the spatial domain. We also show that hydrodynamic simulations reflect
the corresponding self-similar models across a range of conditions appropriate
to photoevaporating protoplanetary discs, even when gravity, centrifugal
forces, or changes in the density gradient mean the problem is not inherently
scale free. Of all the parameters varied, the elevation of the wind base
affected the launch velocity and flow morphology most strongly, with
temperature gradients causing only minor differences. We explore how launching
from an elevated base affects Ne II line profiles from winds, finding it
increases (reduces) the full width at half maximum (FWHM) of the line at low
(high) inclination to the line of sight compared with models launched from the
disc mid-plane and thus weakens the dependence of the FWHM on inclination.
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