J/A+A/621/A6 Spectro-interferometric observation of SW Vir (Ohnaka+, 2019)
Spatially resolving the atmosphere of the non-Mira-type AGB star SW Vir in
near-infrared molecular and atomic lines with VLTI/AMBER.
Ohnaka K., Hadjara M., Maluenda Berna M.Y.L.
<Astron. Astrophys. 621, A6 (2019)>
=2019A&A...621A...6O 2019A&A...621A...6O (SIMBAD/NED BibCode)
ADC_Keywords: Interferometry; Stars, giant; Stars, M-type; Stars, variable
Keywords: infrared: stars - techniques: interferometric - stars: atmospheres -
stars: AGB and post-AGB - stars: mass-loss - stars: individual: SW Vir
Abstract:
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. While the
uniform-disk diameter of the star is 16.23±0.20mas in the continuum,
it increases up to 22-24mas in the CO lines. 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
1019-1020cm-2 in the outer atmosphere extending out to ∼2R*.
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.
Description:
VLTI/AMBER data of SW Vir obtained from 2.279 to 2.308 micron,
including the spectrocopically calibrated spectrum, visibilities and
differential phases measured at three baselines, and closure phase.
Objects:
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RA (2000) DE Designation(s)
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13 14 04.39 -02 48 25.2 SW Vir = HD 114961
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File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
visswvir.dat 245 318 Spectrocopically calibrated spectrum, visibilities
and differential phases measured at three
baselines, and closure phase
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Byte-by-byte Description of file: visswvir.dat
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Bytes Format Units Label Explanations
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2- 4 I3 --- Index [1/318] Index
8- 14 F7.5 um WL Spectral channel index
17- 25 E9.3 --- Flux Normalized flux
28- 36 E9.3 --- Vis1 Visibility measured at baseline 1
39- 47 E9.3 --- e_Vis1 Error in visibility at baseline 1
49- 58 E10.3 deg DP1 Differential phase measured at baseline 1
61- 69 E9.3 deg e_DP1 Error in differential phase at baseline 1
72- 80 E9.3 --- Vis2 Visibility measured at baseline 2
83- 91 E9.3 --- e_Vis2 Error in visibility at baseline 2
93-102 E10.3 deg DP2 Differential phase measured at baseline 2
105-113 E9.3 deg e_DP2 Error in differential phase at baseline 2
116-124 E9.3 --- Vis3 Visibility measured at baseline 3
127-135 E9.3 --- e_Vis3 Error in visibility at baseline 3
137-146 E10.3 deg DP3 Differential phase measured at baseline 3
149-157 E9.3 deg e_DP3 Error in differential phase at baseline 3
159-168 E10.3 deg CP Closure phase
171-179 E9.3 deg e_CP Error in closure phase
182-190 E9.3 m BP1 Projected baseline 1
193-201 E9.3 deg PA1 Position angle of baseline 1
204-212 E9.3 m BP2 Projected baseline 2
215-223 E9.3 deg PA2 Position angle of baseline 2
226-234 E9.3 m BP3 Projected baseline 3
237-245 E9.3 deg PA3 Position angle of baseline 3
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Acknowledgements:
Keiichi Ohnaka, k1.ohnaka(at)gmail.com
(End) Patricia Vannier [CDS] 13-Nov-2018