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26 April 2024 |
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The wind of the M-type AGB star RT Virginis probed by VLTI/MIDI | | Stéphane Sacuto
; Sofia Ramstedt
; Susanne Höfner
; Hans Olofsson
; Sara Bladh
; Kjell Eriksson
; Bernhard Aringer
; Daniela Klotz
; Matthias Maercker
; | | Date: |
24 Jan 2013 | | Abstract: | We study the circumstellar environment of the M-type AGB star RT Vir using
mid-infrared high spatial resolution observations from the ESO-VLTI focal
instrument MIDI. The aim of this study is to provide observational constraints
on theoretical prediction that the winds of M-type AGB objects can be driven by
photon scattering on iron-free silicate grains located in the close environment
(about 2 to 3 stellar radii) of the star. We interpreted
spectro-interferometric data, first using wavelength-dependent geometric
models. We then used a self-consistent dynamic model atmosphere containing a
time-dependent description of grain growth for pure forsterite dust particles
to reproduce the photometric, spectrometric, and interferometric measurements
of RT Vir. Since the hydrodynamic computation needs stellar parameters as
input, a considerable effort was first made to determine these parameters. MIDI
differential phases reveal the presence of an asymmetry in the stellar
vicinity. Results from the geometrical modeling give us clues to the presence
of aluminum and silicate dust in the close circumstellar environment (< ~5
stellar radii). Comparison between spectro-interferometric data and a
self-consistent dust-driven wind model reveals that silicate dust has to be
present in the region between 2 to 3 stellar radii to reproduce the 59 and 63 m
baseline visibility measurements around 9.8 micron. This gives additional
observational evidence in favor of winds driven by photon scattering on
iron-free silicate grains located in the close vicinity of an M-type star.
However, other sources of opacity are clearly missing to reproduce the 10-13
micron visibility measurements for all baselines. This study is a first attempt
to understand the wind mechanism of M-type AGB stars by comparing photometric,
spectrometric, and interferometric measurements with state-of-the-art,
self-consistent dust-driven wind models. The agreement of the dynamic model
atmosphere with interferometric measurements in the 8-10 micron spectral region
gives additional observational evidence that the winds of M-type stars can be
driven by photon scattering on iron-free silicate grains. Finally, a larger
statistical study and progress in advanced self-consistent 3D modeling are
still required to solve the remaining problems. | | Source: | arXiv, 1301.5872 | | Services: | Forum | Review | PDF | Favorites | |
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