A Deep Exposure in High Resolution X-Rays Reveals the Hottest Plasma in the $ζ,$Puppis Wind

Kavli Affiliate: David P. Huenemoerder

| First 5 Authors: David P. Huenemoerder, Richard Ignace, Nathan A. Miller, Kenneth G. Gayley, Wolf-Rainer Hamann

| Summary:

We have obtained a very deep exposure (813 ks) of $zeta,$Puppis (O4
supergiant) with the Chandra/HETG Spectrometer. Here we report on analysis of
the 1-9 r{A} region, especially well suited for Chandra, which has a
significant contribution from continuum emission between well separated
emission lines from high-ionization species. These data allow us to study the
hottest plasma present through the continuum shape and emission line strengths.
Assuming a powerlaw emission measure distribution which has a high-temperature
cut-off, we find that the emission is consistent with a thermal spectrum having
a maximum temperature of 12 MK. This implies an effective wind shock velocity
of $900,mathrm{km,s^{-1}}$, well below the wind terminal speed of
$2250,mathrm{km,s^{-1}}$. For X-ray emission which forms close to the star,
the speed and X-ray flux are larger than can be easily reconciled with strictly
self-excited line-deshadowing-instability models, suggesting a need for a
fraction of the wind to be accelerated extremely rapidly right from the base.
This is not so much a dynamical instability as a nonlinear response to changing
boundary conditions.

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