Evidence for Stability of 𝜁 Puppis’s Mass-loss Rate

We fit the high-resolution X-ray spectra of the O supergiant zeta Puppis using a new model for X-ray line generation in hot stars. Instead of assuming a turn-on radius for the hot gas (as appropriate for the line-deshadowing instability internal to the wind), we parametrize the hot gas in terms of a mean-free path for accelerated low-density gas to encounter slower, dense material. As such, this new model is formulated to track the heating of the gas instead of assuming that it is proportional to the cool gas emission measure, as the former is more appropriate for efficiently generated X-rays from radiatively cooled gas. We used our model to test the robustness of a previous calculation that found a significant 40 percent increase in zeta Puppis’s mass-loss rate in the 20-year time span between the two epochs, 2000 March and 2018 July — 2019 August, of observation with the Chandra X-ray Observatory. The results of our fits are consistent with a constant mass-loss rate, which is more in line with common expectations. We close with a discussion of the differing conclusions of the contrasting heating models, and the circumstances favoring one or the other.