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Near-infrared spectro-interferometry of Mira variables and comparisons to 1D dynamic model atmospheres and 3D convection simulations
ESO, Karl Schwarzschild Str 2, D-85748 Garching, Germany..
Univ Nice Sophia Antipolis, CNRS, Observ Cote Azur, Lab Lagrange,UMR 7293, BP 4229, F-06304 Nice 4, France..
Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Theoretical Astrophysics.
Univ Heidelberg ZAH, Zentrum Astron, Inst Theoret Astrophys, Albert Ueberle Str 2, D-69120 Heidelberg, Germany.;Univ Sydney, Sch Phys, Sydney Inst Astron, Sydney, NSW 2006, Australia..
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2016 (English)In: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 587, A12Article in journal (Refereed) PublishedText
Abstract [en]

Aims:

We aim at comparing spectro-interferometric observations of Mira variable asymptotic giant branch (AGB) stars with the latest 1D dynamic model atmospheres based on self-excited pulsation models (CODEX models) and with 3D dynamic model atmospheres including pulsation and convection (CO5BOLD models) to better understand the processes that extend the molecular atmosphere to radii where dust can form.

Methods: We obtained a total of 20 near-infrared K-band spectro-interferometric snapshot observations of the Mira variables o Cet, R Leo, R Aqr, X Hya, W Vel, and R Cnc with a spectral resolution of about 1500. We compared observed flux and visibility spectra with predictions by CODEX 1D dynamic model atmospheres and with azimuthally averaged intensities based on CO5BOLD 3D dynamic model atmospheres.

Results: Our visibility data confirm the presence of spatially extended molecular atmospheres located above the continuum radii with large-scale inhomogeneities or clumps that contribute a few percent of the total flux. The detailed structure of the inhomogeneities or clumps show a variability on time scales of 3 months and above. Both modeling attempts provided satisfactory fits to our data. In particular, they are both consistent with the observed decrease in the visibility function at molecular bands of water vapor and CO, indicating a spatially extended molecular atmosphere. Observational variability phases are mostly consistent with those of the best-fit CODEX models, except for near-maximum phases, where data are better described by near-minimum models. Rosseland angular diameters derived from the model fits are broadly consistent between those based on the 1D and the 3D models and with earlier observations. We derived fundamental parameters including absolute radii, effective temperatures, and luminosities for our sources.

Conclusions: Our results provide a first observational support for theoretical results that shocks induced by convection and pulsation in the 3D CO5BOLD models of AGB stars are roughly spherically expanding and of similar nature to those of self-excited pulsations in 1D CODEX models. Unlike for red supergiants, the pulsation- and shock-induced dynamics can levitate the molecular atmospheres of Mira variables to extensions that are consistent with observations.

Place, publisher, year, edition, pages
2016. Vol. 587, A12
Keyword [en]
techniques: interferometric, stars: AGB and post-AGB, stars: atmospheres, stars: fundamental parameters, stars: mass-loss
National Category
Astronomy, Astrophysics and Cosmology
Identifiers
URN: urn:nbn:se:uu:diva-295587DOI: 10.1051/0004-6361/201527614ISI: 000371589800023OAI: oai:DiVA.org:uu-295587DiVA: diva2:934170
Funder
Swedish Research CouncilSwedish National Infrastructure for Computing (SNIC), p2003019, p2013234
Available from: 2016-06-08 Created: 2016-06-08 Last updated: 2016-06-08Bibliographically approved

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Freytag, Bernd
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