SIMBAD references

2013MNRAS.429.3379O - Mon. Not. R. Astron. Soc., 429, 3379-3389 (2013/March-2)

Thin-shell mixing in radiative wind-shocks and the lx ∼ lbol scaling of o-star x-rays.


Abstract (from CDS):

X-ray satellites since Einstein have empirically established that the X-ray luminosity from single O-stars scales linearly with bolometric luminosity, Lx ∼ 10–7Lbol. But straightforward forms of the most favoured model, in which X-rays arise from instability-generated shocks embedded in the stellar wind, predict a steeper scaling, either with mass-loss rate L_x ∼{dot}M∼L_bol^1.7 if the shocks are radiative or with L_x ∼{dot}M^2 ∼L_bol^3.4 if they are adiabatic. This paper presents a generalized formalism that bridges these radiative versus adiabatic limits in terms of the ratio of the shock cooling length to the local radius. Noting that the thin-shell instability of radiative shocks should lead to extensive mixing of hot and cool material, we propose that the associated softening and weakening of the X-ray emission can be parametrized as scaling with the cooling length ratio raised to a power m, the `mixing exponent'. For physically reasonable values m ~ 0.4, this leads to an X-ray luminosity L_x ∼{dot}M^0.6 ∼L_bol that matches the empirical scaling. To fit observed X-ray line profiles, we find that such radiative-shock-mixing models require the number of shocks to drop sharply above the initial shock onset radius. This in turn implies that the X-ray luminosity should saturate and even decrease for optically thick winds with very high mass-loss rates. In the opposite limit of adiabatic shocks in low-density winds (e.g. from B-stars), the X-ray luminosity should drop steeply with {dot}M^2. Future numerical simulation studies will be needed to test the general thin-shell mixing ansatz for X-ray emission.

Abstract Copyright: © 2013 The Authors Published by Oxford University Press on behalf of the Royal Astronomical Society (2013)

Journal keyword(s): shock waves - stars: early-type - stars: mass-loss - stars: winds, outflows - X-rays: stars

Status at CDS:  

Simbad objects: 5

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