Doppler tomography of the Little Homunculus: High-resolution spectra of [Fe II] λ16 435 around Eta Carinae

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Abstract

High-resolution spectra of [Fe II] λ16435 around η Carinae provide powerful diagnostics of the geometry and kinematics of the 'Little Homunculus' (LH) growing inside the larger Homunculus nebula. The LH expansion is not perfectly homologous: while low latitudes are consistent with linear expansion since 1910, the polar caps imply ejection dates around 1920-1930. However, the expansion speed of the LH is much slower than the post-eruption wind, so the star's powerful wind may accelerate the LH. With an initial ejection speed of 200 km s-1 in 1890, the LH would have been accelerated to its present speed if the mass is roughly 0.1 M. This agrees with an independent estimate of the LH mass based on its density and volume. In any case, an ejection after 1930 is ruled out. Using the LH as a probe of the 1890 event then, it is evident that its most basic physical parameters (total mass and kinetic energy, which are 0.1 M and 1046.9 erg, respectively) are orders of magnitude less than during the giant eruption in the 1840s. Thus, the ultimate energy sources were different for these two events - yet their ejecta have the same bipolar geometry. This clue may point toward a collimation mechanism separate from the underlying causes of the outbursts.

Original languageEnglish (US)
Pages (from-to)1330-1336
Number of pages7
JournalMonthly Notices of the Royal Astronomical Society
Volume357
Issue number4
DOIs
StatePublished - Mar 11 2005
Externally publishedYes

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Keywords

  • Circumstellar matter
  • ISM: jets and outflows
  • Stars: individual: η Carinae
  • Stars: mass-loss
  • Stars: winds, outflows

ASJC Scopus subject areas

  • Astronomy and Astrophysics
  • Space and Planetary Science

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