The adventure of carbon stars : Observations and modeling of a set of C-rich AGB stars

• 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 1 mu m, and the interferometric observations between 8 mu m and 10 mu m. Discrepancies observed at wavelengths shorter than 1 mu m in the SED, and longer than 10 mu m 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: T-Ross, L-Ross, 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(theta((V-K))) and the bolometric luminosity from the SED fitting L-bol, except for AQ Sgr. The possible reasons are discussed in the text. Finally, theta(Ross) and theta((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, T-eff, 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.

Ämnesord

NATURVETENSKAP  -- Fysik -- Astronomi, astrofysik och kosmologi (hsv//swe)

NATURAL SCIENCES  -- Physical Sciences -- Astronomy, Astrophysics and Cosmology (hsv//eng)

Nyckelord

stars: AGB and post-AGB

stars: atmospheres

stars: mass-loss

stars: carbon

techniques: interferometric

techniques: high angular resolution

Publikations- och innehållstyp

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