Astronomy and Astrophysics, volume 600A, 92-92 (2017/4-1)
The adventure of carbon stars. Observations and modeling of a set of C-rich AGB stars.
RAU G., HRON J., PALADINI C., ARINGER B., ERIKSSON K., MARIGO P., NOWOTNY W. and GRELLMANN R.
Abstract (from CDS):
Context. Modeling stellar atmospheres is a complex and intriguing task in modern astronomy. A systematic comparison of models with multi-technique observations is the only efficient way to constrain the models.
Aims. We intend to perform self-consistent modeling of the atmospheres of six carbon-rich AGB stars (R Lep, R Vol, Y Pav, AQ Sgr, U Hya, and X TrA) with the aim of enlarging the knowledge of the dynamic processes occurring in their atmospheres.
Methods. We used VLTI/MIDI interferometric observations, in combination with spectro-photometric data, and compared them with self-consistent, dynamic model atmospheres.
Results. We found that the models can reproduce spectral energy distribution (SED) data well at wavelengths longer than 1µm, and the interferometric observations between 8µm and 10µm. Discrepancies observed at wavelengths shorter than 1µm in the SED, and longer than 10µm in the visibilities, could be due to a combination of data- and model-related effects. The models best fitting the Miras are significantly extended, and have a prominent shell-like structure. On the contrary, the models best fitting the non-Miras are more compact, showing lower average mass loss. The mass loss is of episodic or multi-periodic nature but causes the visual amplitudes to be notably larger than the observed ones. A number of stellar parameters were derived from the model fitting: TRoss, LRoss, M, C/O, and M. Our findings agree well with literature values within the uncertainties. TRoss, and LRoss are also in good agreement with the temperature derived from the angular diameter T(θ(V–K)) and the bolometric luminosity from the SED fitting Lbol, except for AQ Sgr. The possible reasons are discussed in the text. Finally, θRoss and θ(V–K) agree with one another better for the Miras than for the non-Miras targets, which is probably connected to the episodic nature of the latter models. We also located the stars in the H-R diagram, comparing them with evolutionary tracks. We found that the main derived properties (L, Teff, C/O ratios and stellar masses) from the model fitting are in good agreement with TP-AGB evolutionary calculations for carbon stars carried out with the COLIBRI code.
© ESO, 2017
stars: AGB and post-AGB - stars: atmospheres - stars: mass-loss - stars: carbon - techniques: interferometric - techniques: high angular resolution - techniques: high angular resolution
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