Chandra spectral measurements of the O supergiant $\zeta$ Puppis indicate a surprising increase in the wind mass-loss rate over 18 years

TL;DR

Recent Chandra observations of the O supergiant ζ Puppis reveal an 18-year increase in x-ray emission and wind absorption, indicating a significant rise in its wind mass-loss rate, challenging previous assumptions.

Contribution

This study provides the first long-term X-ray spectral analysis showing a substantial increase in the wind mass-loss rate of ζ Puppis over 18 years.

Findings

X-ray emission line flux increased by 13% over 18 years

Wind absorption signatures in line profiles have strengthened significantly

Derived mass-loss rate increased by 40% from previous measurements

Abstract

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.