Possible detection of an old bipolar shell associated with η Carinae

Continuum-subtracted dereddened images in the light of several atomic lines show the presence of an extended bipolar nebula surrounding eta Carinae with size similar to 100 x 45 arcsec(2) (1.3 x 0.5 pc(2)). This feature is best delineated in [O III] 5007. The geometrical disposition and mass of the shell suggest that it was formed by mass ejections from eta Carinae, The dynamic age of the nebula is similar to 13 000/V-7 yr, where V-7 is the mean expansion velocity in 100 km s(-1), and its mass is between 5 and 10 M.. The nebula is photoionized and composed of unprocessed material. The major axes of the nebula and of the Homunculus are nearly perpendicular. We also report the discovery of elongated emission knots prominent in [N II] located 64 to 100 arcsec away from eta Carinae, which implies that they were ejected either centuries ago or at a more recent date bht with extremely large velocities.