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| Paper: |
The Physical Basis of the LX = Lbol Empirical Law for O-Star X-Rays |
| Volume: |
465, Four Decades of Massive Star Research - A Scientific Meeting in Honor of Anthony J. Moffat |
| Page: |
153 |
| Authors: |
Owocki, S. P.; Sundqvist, J. O.; Cohen, D. H.; Gayley, K. G. |
| Abstract: |
X-ray satellites since Einstein have empirically established that the
X-ray luminosity from single O-stars scales linearly with bolometric
luminosity, LX = 10–7 Lbol.
But straightforward forms of the most
favored model, in which X-rays arise from instability-generated shocks
embedded in the stellar wind, predict a steeper scaling, either with
mass-loss rate LX = M = Lbol1.7
if the shocks are radiative, or
with LX = M2 = Lbol3.4 if they are adiabatic.
We present here a
generalized formalism that bridges these radiative vs. 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 then propose that the
associated softening and weakening of the X-ray emission can be parameterized
by 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 LX = M0.6 = Lbol
that matches the empirical scaling.
We conclude by noting that
such thin-shell mixing may also be important
for X-rays from colliding wind binaries,
and that
future
numerical simulation studies will be needed to test this thin-shell mixing
ansatz for X-ray emission. |
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