Strange velocities in the equatorial ejecta of eta Carinae

Abstract

We report HST/HRS observations of gas that appears to have been ejected in the equatorial zone of eta Carinae. Some of the observed emission lines are produced by Fe II fluorescence processes, which, for unknown reasons, are uniquely intense near eta Carinae. Surprisingly low velocities are found, most likely representing ejection events hundreds of years before the well-known Great Eruption of the 1840's. Alternative interpretations are possible with different geometrical assumptions, but they seem less straightforward and imply a different set of novel problems. The observed velocities less than 100 km s(-1) must be hints concerning the physical nature of eta Carinae; we propose one speculative scenario, combining the effects of rotation and a modified Eddington limit. The strong fluorescent emission lines occur only in the slowest gas, a result that we cannot yet explain. Altogether, these data pose a number of serious theoretical questions and clues, involving remarkably slow ejection speeds, formation of distinct dense condensations in the ejecta, and peculiarly intense radiative excitation of certain emission lines. Based on observations with the NASA/ESA Hubble Space Telescope, and supported by grant numbers GO-6041 and GO-6501 from the Space Telescope Science Institute. The STScI is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS5-26555.