The bipolar structure of the LBV nebula around HR Carinae

Abstract

HR Carinae is one of the few Luminous Blue Variables (LBVs) in the Galaxy. It has a nebula that appears bipolar. We have obtained imaging and high-dispersion, long-slit echelle data of the HR Car nebula, and confirmed that it is a bipolar nebula. Its polar axis lies along the position angle of 125 +- 5 degree; each lobe has, at a distance of 5 kpc a diameter of about 0.65 pc and a line-of-sight expansion velocity of 75-150 km/sec. Beside the expanding bipolar lobes, a number of [NII]-bright knots are detected. These knots have lower expansion velocities than the lobes and are detected only within the projected boundary of the lobes. These knots are most likely nitrogen-enriched material ejected by HR Car. On a larger scale, a funnel-shaped nebula is detected at 2.5" northwest of HR Car. The axis of the funnel is roughly aligned with the polar axis of the HR Car nebula, suggesting that HR Car may be responsible for the ionization and shaping of this nebula. Future observations of kinematics and abundances are needed to determine the nature of this nebula. We propose that the bipolar nebula of HR Car is a more evolved version of the Homunculus Nebula around eta Car. The recently developed theory of wind-compressed disks may explain the higher density of the equatorial plane and the formation of bipolar nebulae of LBVs.