We present moderate and high-dispersion 1–2.5 \micron spectra of the \sim 10″-radius nebula around P Cygni , dominated by bright emission lines of [ Fe ii ] .
Observed [ Fe ii ] line ratios disagree with theoretical transition rates in the literature , so we use the spectrum of P Cygni ’ s nebula to constrain the atomic data for low-lying levels of [ Fe ii ] .
Of particular interest is the ratio [ Fe ii ] \lambda 12567/ \lambda 16435 , often used as a reddening indicator , for which we empirically derive an intrinsic value of 1.49 , which is 10–40 % higher than previous estimates .
High-dispersion spectra of [ Fe ii ] \lambda 16435 constrain the geometry , detailed structure , and kinematics of P Cygni ’ s nebula , which is the major product of P Cygni ’ s outburst in 1600 A.D. We use the [ N ii ] / [ N i ] line ratio to conclude that the nebula is mostly ionized with a total mass of \sim 0.1 M _ { \odot } ; more than the mass lost by the stellar wind since the eruption .
For this mass , we would expect a larger infrared excess than observed .
We propose that the dust which obscured the star after the outburst has since been largely destroyed , releasing Fe into the gas phase to produce the bright [ Fe ii ] emission .
The kinetic energy of this shell is \sim 10 ^ { 46.3 } ergs , far less than the kinetic energy released during the giant eruption of \eta Car in the 1840s , but close to the value for \eta Car ’ s smaller 1890 outburst .
In this respect , it is interesting that the infrared spectrum of P Cygni ’ s nebula resembles that of the “ Little Homunculus ” around \eta Car , ejected in that star ’ s 1890 eruption .
The mass and kinetic energy in the nebulae of \eta Car and P Cygni give insight to the range of parameters expected for extragalactic \eta Car-like eruptions .