Chandra spectral measurements of the O supergiant $\zeta$ Puppis
  indicate a surprising increase in the wind mass-loss rate over 18 years
  New long Chandra grating observations of the O supergiant $\zeta$ Pup show
not only a brightening of the x-ray emission line flux of 13 per cent in the 18
years since Chandra's first observing cycle, but also clear evidence - at more
than four sigma significance - of increased wind absorption signatures in its
Doppler-broadened x-ray emission line profiles. We demonstrate this with
non-parametric analysis of the profiles as well as Gaussian fitting and then
use the line-profile model fitting to derive a mass-loss rate of $2.47 \pm 0.09
\times 10^{-6}$ Msun/yr, which is a 40 per cent increase over the value
obtained from the cycle 1 data. The increase in the individual emission line
fluxes is greater for short-wavelength lines than long-wavelength lines, as
would be expected if a uniform increase in line emission is accompanied by an
increase in the wavelength-dependent absorption by the cold wind in which the
shock-heated plasma is embedded.
