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[Ti II] and [Ni II] emission from the strontium filament of eta Carinae

Bautista, M A ; Hartman, Henrik LU ; Gull, T. R. ; Smith, N. and Lodders, K. (2006) In Monthly Notices of the Royal Astronomical Society 370(4). p.1991-2003
Abstract
We study the nature of the [Ti II] and [Ni II] emission from the so-called strontium filament found in the ejecta of eta Carinae. To this purpose, we employ multilevel models of the Ti II and Ni II systems, which are used to investigate the physical condition of the filament and the excitation mechanisms of the observed lines. For the Ti II ion, for which no atomic data were previously available, we carry out ab initio calculations of radiative transition rates and electron impact excitation rate coefficients. It is found that the observed spectrum is consistent with the lines being excited in a mostly neutral region with an electron density of the order of 10(7) cm(-3) and a temperature around 6000 K. In analysing three observations with... (More)
We study the nature of the [Ti II] and [Ni II] emission from the so-called strontium filament found in the ejecta of eta Carinae. To this purpose, we employ multilevel models of the Ti II and Ni II systems, which are used to investigate the physical condition of the filament and the excitation mechanisms of the observed lines. For the Ti II ion, for which no atomic data were previously available, we carry out ab initio calculations of radiative transition rates and electron impact excitation rate coefficients. It is found that the observed spectrum is consistent with the lines being excited in a mostly neutral region with an electron density of the order of 10(7) cm(-3) and a temperature around 6000 K. In analysing three observations with different slit orientations recorded between 2000 March and 2001 November, we find line ratios that change among various observations, in a way consistent with changes of up to an order of magnitude in the strength of the continuum radiation field. These changes result from different samplings of the extended filament due to the different slit orientations used for each observation, and yield clues on the spatial extent and optical depth of the filament. The observed emission indicates a large Ti/Ni abundance ratio relative to solar abundances. It is suggested that the observed high Ti/Ni ratio in gas is caused by dust-gas fractionation processes and does not reflect the absolute Ti/Ni ratio in the ejecta of eta Carinae. We study the condensation chemistry of Ti, Ni and Fe within the filament and suggest that the observed gas phase overabundance of Ti is likely the result of selective photoevaporation of Ti-bearing grains. Some mechanisms for such a scenario are proposed. (Less)
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author
; ; ; and
organization
publishing date
type
Contribution to journal
publication status
published
subject
keywords
stars : abundances, line : formation, atomic data, atomic processes
in
Monthly Notices of the Royal Astronomical Society
volume
370
issue
4
pages
1991 - 2003
publisher
Oxford University Press
external identifiers
  • wos:000239517300038
  • scopus:33746887840
ISSN
1365-2966
DOI
10.1111/j.1365-2966.2006.10624.x
language
English
LU publication?
yes
id
3a81f8f5-0e7e-47d1-907c-0940d67830f7 (old id 399047)
date added to LUP
2016-04-01 12:21:07
date last changed
2020-01-12 09:40:45
@article{3a81f8f5-0e7e-47d1-907c-0940d67830f7,
  abstract     = {We study the nature of the [Ti II] and [Ni II] emission from the so-called strontium filament found in the ejecta of eta Carinae. To this purpose, we employ multilevel models of the Ti II and Ni II systems, which are used to investigate the physical condition of the filament and the excitation mechanisms of the observed lines. For the Ti II ion, for which no atomic data were previously available, we carry out ab initio calculations of radiative transition rates and electron impact excitation rate coefficients. It is found that the observed spectrum is consistent with the lines being excited in a mostly neutral region with an electron density of the order of 10(7) cm(-3) and a temperature around 6000 K. In analysing three observations with different slit orientations recorded between 2000 March and 2001 November, we find line ratios that change among various observations, in a way consistent with changes of up to an order of magnitude in the strength of the continuum radiation field. These changes result from different samplings of the extended filament due to the different slit orientations used for each observation, and yield clues on the spatial extent and optical depth of the filament. The observed emission indicates a large Ti/Ni abundance ratio relative to solar abundances. It is suggested that the observed high Ti/Ni ratio in gas is caused by dust-gas fractionation processes and does not reflect the absolute Ti/Ni ratio in the ejecta of eta Carinae. We study the condensation chemistry of Ti, Ni and Fe within the filament and suggest that the observed gas phase overabundance of Ti is likely the result of selective photoevaporation of Ti-bearing grains. Some mechanisms for such a scenario are proposed.},
  author       = {Bautista, M A and Hartman, Henrik and Gull, T. R. and Smith, N. and Lodders, K.},
  issn         = {1365-2966},
  language     = {eng},
  number       = {4},
  pages        = {1991--2003},
  publisher    = {Oxford University Press},
  series       = {Monthly Notices of the Royal Astronomical Society},
  title        = {[Ti II] and [Ni II] emission from the strontium filament of eta Carinae},
  url          = {http://dx.doi.org/10.1111/j.1365-2966.2006.10624.x},
  doi          = {10.1111/j.1365-2966.2006.10624.x},
  volume       = {370},
  year         = {2006},
}