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Register a new userHighly supersonic motions within the outer features of the Eta Carinae nebulosity
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Spatially resolved H$alpha$ and [N{sc ii}] line profiles have been obtained over striking features in the outer regions of the Eta Carinae nebula. The highly irregular outer `shell of low ionization, [N{sc ii}] bright, knots has been shown to exhibit radial velocities between -1200 and +300 km/s with respect to the systemic radial velocity, over its perimeter. Furthermore, several knots have been found which appear to emit only in the H$alpha$ line with radial velocities up to -1450 km/s. However, the most intriguing features are a narrow `spike that projects through this outer shell and a faint `arc of emission that extends well beyond it. The `spike, which exhibits a change of radial velocity along its length, could be a narrow collimated jet with an outflow velocity of > 1000 km/s. In one interpretation the `arc is modelled by a conical outflow and mechanisms for generating [N{sc ii}] emission from highly supersonic gas are also discussed.
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Previous submillimetre (submm) observations detected 0.7 solar masses of cool dust emission around the Luminous Blue Variable (LBV) star Eta Carinae. These observations were hindered by the low declination of Eta Carinae and contamination from free-free emission orginating from the stellar wind. Here, we present deep submm observations with LABOCA at 870um, taken shortly after a maximum in the 5.5-yr radio cycle. We find a significant difference in the submm flux measured here compared with the previous measurement: the first indication of variability at submm wavelengths. A comparison of the submm structures with ionised emission features suggests the 870um is dominated by emission from the ionised wind and not thermal emission from dust. We estimate 0.4 +/- 0.1 solar masses of dust surrounding Eta Carinae. The spatial distribution of the submm emission limits the mass loss to within the last thousand years, and is associated with mass ejected during the great eruptions and the pre-outburst LBV wind phase; we estimate that Eta Carinae has ejected > 40 solar masses of gas within this timescale.
The nebula around eta Carinae consists of two distinct parts: the Homunculus and the outer ejecta. The outer ejecta are mainly a collection of numerous filaments, shaped irregularly and distributed over an area of 1arcminx1arcmin. While the Homunculus is mainly a reflection nebula, the outer ejecta are an emission nebula. Kinematic analysis of the outer ejecta (as the Homunculus) show their bi-directional expansion. Radial velocities in the outer ejecta reach up to >2000km/s and the gas gives rise to X-ray emission. The temperature of the X-ray gas is of the order of 0.65 keV. These shock temperatures indicate velocities of the shocking gas of 750km/s, about what was found for the average expansion velocity of the outer ejecta. HST/STIS data from the strings, long, highly collimated structures in the outer ejecta, show that the electron density of the strings is of the order of 10^4cm^-3 Other structures in the outer ejecta show similar values. String 1 has a mass of about 3 10^-4M_sun, a density gradient along the strings or a denser leading head was not found.
The narrow optical filaments (`strings or `spikes) emerging from the Homunculus of Eta Carinae are modelled as resulting from the passage of ballistic `bullets of material through the dense circumstellar environment. In this explanation, the string is the decelerating flow of ablated gas from the bullet. An archive HST image and new forbidden line profiles of the most distinct of the strings are presented and discussed in terms of this simple model.
The outer ejecta is part of the nebula around Eta Carinae. They are filamentary, shaped irregularly and larger than the Homunculus, the central bipolar nebula. While the Homuculus is mainly a reflection nebula, the outer ejecta is an emission structure. However, we showed with kinematic analysis that the outer ejecta (as the Homunculus) expands bi-directional despite of its complex morphology. Radial velocities in the outer ejecta reach up to 2000km/s and give rise to X-ray emission. An analysis showing the distribution of the soft X-ray emission and its comparison to the optical emitting gas is presented here. X-ray maxima are found in areas in which the expansion velocities are highest. The temperature of 0.65 keV determined with the CHANDRA/ACIS data and thermal equilibrium models indicates post-shock velocities of 750km/s, about what was found in the spectra. In addition analysis of the new HST-STIS data from the Strings--long, highly collimated structures in the outer ejecta--are presented. The data show that the electron density of the Strings is of the order of 10^4 cm^-3. The same value was detected for other structures in the outer ejecta. With this density String 1 has a mass of about 3 10^-4 M_sun and the total ejecta could be as massive as 0.5 M_sun.
During the years 1838-1858, the very massive star {eta} Carinae became the prototype supernova impostor: it released nearly as much light as a supernova explosion and shed an impressive amount of mass, but survived as a star.1 Based on a light-echo spectrum of that event, Rest et al.2 conclude that a new physical mechanism is required to explain it, because the gas outflow appears cooler than theoretical expectations. Here we note that (1) theory predicted a substantially lower temperature than they quoted, and (2) their inferred observational value is quite uncertain. Therefore, analyses so far do not reveal any significant contradiction between the observed spectrum and most previous discussions of the Great Eruption and its physics.
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