Synthetic photometry for carbon-rich giants

IV. An extensive grid of dynamic atmosphere and wind models^⋆,⋆⋆

¹ Department of Physics and Astronomy, Division of Astronomy and Space Physics, Uppsala University, Box 516, 75120 Uppsala, Sweden
e-mail: kjell.eriksson@physics.uu.se
² University of Vienna, Department of Astrophysics, Türkenschanzstraße 17, 1180 Wien, Austria
³ Departamento de Astronomia de la Universidad de Guanajuato, Apartado Postal 144, C.P. 36000 Guanajuato, GTO, Mexico

Received: 12 December 2013
Accepted: 1 April 2014

Abstract

Context. The evolution and spectral properties of stars on the asymptotic giant branch (AGB) are significantly affected by mass loss through dusty stellar winds. Dynamic atmosphere and wind models are an essential tool for studying these evolved stars, both individually and as members of stellar populations, to understand their contribution to the integrated light and chemical evolution of galaxies.

Aims. This paper is part of a series with the purpose of testing state-of-the-art atmosphere and wind models of C-type AGB stars against observations, and making them available to the community for use in various theoretical and observational studies.

Methods. We have computed low-resolution spectra and photometry (in the wavelength range 0.35–25 μm) for a grid of 540 dynamic models with stellar parameters typical of solar-metallicity C-rich AGB stars and with a range of pulsation amplitudes. The models cover the dynamic atmosphere and dusty outflow (if present), assuming spherical symmetry, and taking opacities of gas-phase species and dust grains consistently into account. To characterize the time-dependent dynamic and photometric behaviour of the models in a concise way we defined a number of classes for models with and without winds.

Results. Comparisons with observed data in general show a quite satisfactory agreement for example regarding mass-loss rates vs. (J − K) colours or K magnitudes vs. (J − K) colours. Some exceptions from the good overall agreement, however, are found and attributed to the range of input parameters (e.g. relatively high carbon excesses) or intrinsic model assumptions (e.g. small particle limit for grain opacities).

Conclusions. While current results indicate that some changes in model assumptions and parameter ranges should be made in the future to bring certain synthetic observables into better agreement with observations, it seems unlikely that these pending improvements will significantly affect the mass-loss rates of the models.