Spatially resolving the atmosphere of the non-Mira-type AGB star SW Vir in near-infrared molecular and atomic lines with VLTI/AMBER. (arXiv:1811.05989v1 [astro-ph.SR])
<a href="http://arxiv.org/find/astro-ph/1/au:+Ohnaka_K/0/1/0/all/0/1">K. Ohnaka</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Hadjara_M/0/1/0/all/0/1">M. Hadjara</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Berna_M/0/1/0/all/0/1">M. Y. L. Maluenda Berna</a>
We present a near-infrared spectro-interferometric observation of the
non-Mira-type, semiregular asymptotic giant branch star SW Vir. Our aim is to
probe the physical properties of the outer atmosphere with spatially resolved
data in individual molecular and atomic lines. We observed SW Vir in the
spectral window between 2.28 and 2.31 micron with the near-infrared
interferometric instrument AMBER at ESO’s Very Large Telescope Interferometer
(VLTI). Thanks to AMBER’s high spatial resolution and high spectral resolution
of 12000, the atmosphere of SW Vir has been spatially resolved not only in
strong CO first overtone lines but also in weak molecular and atomic lines of
H2O, CN, HF, Ti, Fe, Mg, and Ca. Comparison with the MARCS photospheric models
reveals that the star appears larger than predicted by the hydrostatic models
not only in the CO lines but also even in the weak molecular and atomic lines.
We found that this is primarily due to the H2O lines (but also possibly due to
the HF and Ti lines) originating in the extended outer atmosphere. Although the
H2O lines manifest themselves very little in the spatially unresolved spectrum,
the individual rovibrational H2O lines from the outer atmosphere can be
identified in the spectro-interferometric data. Our modeling suggests an H2O
column density of 10^{19}–10^{20} cm^{-2} in the outer atmosphere extending
out to ~2 Rstar. Our study has revealed that the effects of the nonphotospheric
outer atmosphere are present in the spectro-interferometric data not only in
the strong CO first overtone lines but also in the weak molecular and atomic
lines. Therefore, analyses of spatially unresolved spectra, such as for example
analyses of the chemical composition, should be carried out with care even if
the lines appear to be weak.
We present a near-infrared spectro-interferometric observation of the
non-Mira-type, semiregular asymptotic giant branch star SW Vir. Our aim is to
probe the physical properties of the outer atmosphere with spatially resolved
data in individual molecular and atomic lines. We observed SW Vir in the
spectral window between 2.28 and 2.31 micron with the near-infrared
interferometric instrument AMBER at ESO’s Very Large Telescope Interferometer
(VLTI). Thanks to AMBER’s high spatial resolution and high spectral resolution
of 12000, the atmosphere of SW Vir has been spatially resolved not only in
strong CO first overtone lines but also in weak molecular and atomic lines of
H2O, CN, HF, Ti, Fe, Mg, and Ca. Comparison with the MARCS photospheric models
reveals that the star appears larger than predicted by the hydrostatic models
not only in the CO lines but also even in the weak molecular and atomic lines.
We found that this is primarily due to the H2O lines (but also possibly due to
the HF and Ti lines) originating in the extended outer atmosphere. Although the
H2O lines manifest themselves very little in the spatially unresolved spectrum,
the individual rovibrational H2O lines from the outer atmosphere can be
identified in the spectro-interferometric data. Our modeling suggests an H2O
column density of 10^{19}–10^{20} cm^{-2} in the outer atmosphere extending
out to ~2 Rstar. Our study has revealed that the effects of the nonphotospheric
outer atmosphere are present in the spectro-interferometric data not only in
the strong CO first overtone lines but also in the weak molecular and atomic
lines. Therefore, analyses of spatially unresolved spectra, such as for example
analyses of the chemical composition, should be carried out with care even if
the lines appear to be weak.
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