On the binarity of Eta Carinae

Summary

Multiple observations reinforce the binarity of Eta Carinae including the 5.54-year periodicity in x-rays, spectroscopic excitation of the Weigelt blobs and the behavior of the stellar line profiles. The Hubble Space Telescope (HST) STIS observations from 1998.0 to 2004.3 provide considerable new evidence of the binary system. We focus on the lines of He I, HI, FeII and [N II] and provide initial visualizations of the binary system. Recent observations with VLTI/AMBER are consistent with a binary model.

Introduction

Eta Carinae (η Car) has intrigued astronomers for well over a century, beginning with its brightening to —1 magnitude in the late 1830s, rivaling Sirius as the brightest star in the sky for nearly two decades, then fading below naked-eye sensitivity. Observers in the Southern Hemisphere have pointed their telescopes in its direction since the 1820s; some navigational records exist even back to the late sixteenth century with visual magnitudes noted between 2nd and 4th magnitude (Frew 2004). Characterization of this peculiar star has been a challenge; D. Frew (private communication, 2003) noted that η Car was monitored by observers at Sydney Observatory in the nineteenth century in the suspicion that it was a binary system. Yet still today not all are convinced as direct evidence of the secondary star is not in hand.

η Car is of great interest, as at least one of the companions is at the end of its hydrogenburning phase.