eta Carinae


Situated just East of the Keyhole Nebula in the Southern Sky, lies the super-luminous eruptive star eta Carinae. This strange star is is over one million times brighter than our sun and over one hundred times more massive, making it possibly the most massive star in the Galaxy. In the mid-1800s the star experienced an outburst named the "Great Eruption." During this time a large amount (1-2 solar masses) of material [Davidson, 1987] was ejected at high velocity. This material cooled and formed the expanding gas and dust cloud we see today.

From ground-based telescopes, the homunculus of eta Carinae appears as an ellipsoid roughly 18" x 10" with major along position angle 132 degrees. HST WFPC2 images resolve the ellipsoid into two roughly equal lobes (SE and NW) and an equatorial 'skirt.' Within the skirt, along the major axis is an oar-like shaped region called the `paddle.'

Astrometric Analysis

One can easily see the astrometric expansion (especially of the ``NN knot'') of eta Carinae by comparing images taken in 1949,1975 and 1993. It is very difficult to qualify these expansion from measurements taken from photographs. The non-linear properties of photographic film and image degradation due to the atmospheric seeing limit the accuracy with which these measurements can be made from the ground.

Our recent astrometric work (Currie et al, 1995a) using data from HST shows that the plane-of-the-sky motions in the homunculus are generally radial, linearly increase in magnitude with distance from the central star. Within the homunculus (and NN/NS knots) the measured expansion is 0.64%/year giving an average ejection date of 1839, in excellent agreement with the historical great eruption which peaked in 1843. The velocities of the outer condensations have be shown by Walborn(1978,1988) to be consistent with earlier eruptions, dating back as far as the 1300s.

Observations and Analysis have continued, using data from the WP/PC and WFPC2 of the Hubble Space Telescope as well as FORS1 and UVES of the European Southern Observatory's VLT at Paranal, Chile and ESO's ADONIS system on the 3.6 meter telescope at La Silla, Chile.

The astrometric work has continued, in particular, we have addressed the motion of the so-called "Weigelt Blobs", showing that Blob D was emitted about 1941, again, coincident with an increase in brightness by about a magnitude.

Combining the data from the HST and the VLT, we have address the photometry of the Spikes, long linear features that were emitted in 1839 but, moving at 2,000 km/sec, have proceeded far beyond the homunculus. They were studied in the theses of Liwing, Neasgaure and Svensson and reported in ESO's Messenger (Currie 2000) and workshops.

The high resolution of the UVES has allowed the spectroscopic and Doppler astrometric studies of the Weigelt Blobs. We have discovered a shell , presumably a shock wave from the 1841 Great Eruption, surrounding the homunculus. The Doppler astrometric studies also indicate an origin of about 1941 and indicate the filamentary nature of the objects, with a filament showing a constant velocity and another shown a continuous variation of the velocity, indicating deceleration.

Return to Astro-Metrology Homepage