Anomalous Fe II spectral effects and high H I Lyα temperature in gas blobs near η Carinae

We consider the origin of the anomalously high intensity of the ultraviolet Fe II λλ2507/2509 Å lines observed with high spatial and spectral resolutions from gas blobs (GBs) near η Carinae. This rare effect in stellar spectra is attributable to a combination of several factors: (1) the high hydrogen density(>10⁸ cm^?3) that ensures the blockingof the Lyman continuum by GBs and, accordingly, the formation of a cold H I region with completely ionized Fe atoms; (2) the small distance between the GBs and the central star that ensures a high (>8000–10000 K) Lyα H spectral temperature, which photoexcites Fe II selectively; and (3) the population of Fe II levels and, accordingly, the opening of a stimulated emission channel, which together with spontaneous transitions creates a radiative cycle where a single Fe II ion can multiply absorb Lyα emission.