New broad-band N and narrow-band [Ne II ] 12.8 m imaging of the HR Car show that its surrounding nebula has a clumpy non point-symmetric structure on the scale of a few arcseconds, more so in the ionized gas than in the dust, which is seen at a projected distance of less than 0.04 pc from the central star. We also observe a faint, probably clumpy nebula about across, which does not appear to be bipolar and which is therefore thought to represent an earlier period of increased mass-loss.
The size of the compact IR nebula can well be explained by a dust shell which is composed mainly of silicates and is in thermal equilibrium with the central star. The dust and the gas emission appear to originate from different areas, which suggests the shielding of stellar radiation by the circumstellar dust. A simple dust shell model, which gives a reasonable fit to the ISO-SWS spectrum, shows that based on the dust optical depth of the nebula at 10 µm, this is well possible.
The morphology of the dust and gas close to the star is not in agreement with that of optical images of the star, which suggest a filamentary and highly symmetric nebula. This indicates that the geometry of the mass ejections in HR Car is time-dependent. Together with the two-component nebula we observe, now at least three different episodes of shell ejection can be distinguished for HR Car.
© European Southern Observatory (ESO) 1997
Online publication: June 30, 1998