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19 April 2024 |
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Numerical simulations of high-energy flows in accreting magnetic white dwarfs | | Lucile Van Box Som
; Emeric Falize
; Jean-Marc Bonnet-Bidaud
; Martine Mouchet
; Clotilde Busschaert
; Andrea Ciardi
; | | Date: |
27 Sep 2017 | | Abstract: | Some polars show quasi-periodic oscillations (QPO) in their optical light
curves which have been interpreted as the result of shock oscillations driven
by the cooling instability. Although numerical simulations can recover this
physics, they wrongly predict QPOs in the X-ray luminosity and have also failed
to reproduce the observed frequencies, at least for the limited range of
parameters explored so far. Given the uncertainties on the observed polar
parameters, it is still unclear whether simulations can reproduce the
observations. The aim of this work is to study QPOs covering all relevant
polars showing QPOs. We perform numerical simulations including gravity,
cyclotron and bremsstrahlung radiative losses, for a wide range of polar
parameters, and compare our results with the astronomical data using synthetic
X-ray and optical luminosities.We show that shock oscillations are the result
of complex shock dynamics triggered by the interplay of two radiative
instabilities. The secondary shock forms at the acoustic horizon in the
post-shock region in agreement with our estimates from steady-state solutions.
We also demonstrate that the secondary shock is essential to sustain the
accretion shock oscillations at the average height predicted by our
steady-state accretion model. Finally, in spite of the large explored parameter
space, matching the observed QPO parameters requires a combination of
parameters inconsistent with the observed ones. This difficulty highlights the
limits of one-dimensional simulations, suggesting that multi-dimensional
effects are needed to understand the non-linear dynamics of accretion columns
in polars and the origins of QPOs. | | Source: | arXiv, 1709.9554 | | Services: | Forum | Review | PDF | Favorites | |
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