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

David H. Cohen, Jiaming Wang, Lamiaa Dakir, Maurice Leutenegger, Veronique Petit, Alexandre David-Uraz

Published 2020-06-16Version 1

New long Chandra grating observations of the O supergiant $\zeta$ Pup show not only a brightening in the x-ray emission line flux of a little more than 25 per cent in the 18 years since Chandra's first observing cycle, but also clear evidence of increased wind absorption signatures in its Doppler-broadened x-ray emission line profiles. Model fitting of ten lines in three day-long HETGS datasets taken during August 2018 (Chandra cycle 19) finds a mass-loss rate of $2.68 \pm 0.12 \times 10^{-6}$ Msun/yr which is a 50 per cent increase over the value obtained from fitting 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.