Three-dimensional hydrodynamical CO5BOLD model atmospheres of red giant stars VI. First chromosphere model of a late-type giant

Abstract

Although observational data unequivocally point out to the presence of chromospheres in red giant stars, no attempts have been made so far to model them using 3D hydrodynamical model atmospheres. We therefore compute an exploratory 3D hydrodynamical model atmosphere for a cool red giant in order to study the dynamical and thermodynamic properties of its chromosphere, as well as the influence of the chromosphere on its observable properties. 3D radiation hydrodynamics simulations are carried out with the CO5BOLD model atmosphere code for a star with the atmospheric parameters (Teff=4010 K, log g=1.5, [M/H]=0.0), which are similar to those of the K-type giant star Aldebaran (alpha Tau). ... we compute the emergent continuum intensity maps at different wavelengths, spectral line profiles of Ca II K, the Ca II infrared triplet line at 854.2nm, and H alpha, as well as the spectral energy distribution (SED) of the emergent radiative flux. The initial model quickly develops a dynamical chromosphere characterised by propagating and interacting shock waves. The peak temperatures in the chromospheric shock fronts reach values on the order of up to 5000 K although the shock fronts remain quite narrow. Like for the Sun, the gas temperature distribution in the upper layers is composed of a cool component due to adiabatic cooling in the expanding post-shock regions and a hot component due to shock waves. For this red giant model, the hot component is a rather flat high-temperature tail, which nevertheless affects the resulting average temperatures significantly. The simulations show that the atmospheres of red giant stars are dynamic and intermittent. Consequently, many observable properties cannot be reproduced with one-dimensional static models but demand for advanced 3D HD modelling. Furthermore, including a chromosphere in the models might produce significant contributions to the emergent UV flux.

arXiv comment14 pages, 8 figures, A&A (2017, accepted)

References in corpus (23)

• A grid of MARCS model atmospheres for late-type stars I. Methods and general properties
• Solar Chemical Abundances Determined with a CO5BOLD 3D Model Atmosphere
• The stellar atmosphere simulation code Bifrost
• Simulations of stellar convection with CO5BOLD
• Does a Non-Magnetic Solar Chromosphere Exist?
• Numerical simulation of the three-dimensional structure and dynamics of the non-magnetic solar chromosphere
• High Resolution Observations and Modeling of Dynamic Fibrils
• Resolving the stellar activity of the Mira AB binary with ALMA
• Solar science with the Atacama Large Millimeter/submillimeter Array - A new view of our Sun
• The Gaia FGK Benchmark Stars - High resolution spectral library
• Coupling from the photosphere to the chromosphere and the corona
• The Magnetic Fields at the Surface of Active Single G-K Giants
• The photospheric solar oxygen project: IV. 3D-NLTE investigation of the 777 nm triplet lines
• The solar chromosphere at high resolution with IBIS. II. Acoustic shocks in the quiet internetwork and the role of magnetic fields
• A Far-Ultraviolet Spectroscopic Survey of Luminous Cool Stars
• Mass Outflow and Chromospheric Activity of Red Giant Stars in Globular Clusters I: M15
• Structure of the outer layers of cool standard stars
• Three-dimensional magnetohydrodynamic simulations of M-dwarf chromospheres
• Chromospheric Thermal Continuum Millimetre Emission from non-dusty K and M Red Giants
• The Gaia-ESO survey: Hydrogen lines in red giants directly trace stellar mass
• Modelling chromospheric line profiles as diagnostics of velocity fields in ω Centauri red giant stars
• Chromospheric Models and the Oxygen Abundance in Giant Stars
• Evidence of asymmetries in the Aldebaran photosphere from multi-wavelength lunar occultations

Cited by in corpus (9)

• An extended and refined grid of 3D STAGGER model atmospheres. Processed snapshots for stellar spectroscopy
• Using the CIFIST grid of CO5BOLD 3D model atmospheres to study the effects of stellar granulation on photometric colours. II. The role of convection accross the H-R diagram
• Spatially resolving the thermally inhomogeneous outer atmosphere of the red giant Arcturus in the 2.3 micron CO lines
• Constraining stellar parameters and atmospheric dynamics of the carbon AGB star V Oph
• Internal Gravity Waves in the Magnetized Solar Atmosphere. II. Energy Transport
• Multiple populations within globular clusters in Early-type galaxies Exploring their effect on stellar initial mass function estimates
• Performance of high-order Godunov-type methods in simulations of astrophysical low Mach number flows
• 3D non-LTE Ca II line formation in metal-poor FGK stars. I. Abundance corrections, radial velocity corrections, and synthetic spectra
• Observational constraints on the origin of the elements. X. Combining NLTE and machine learning for chemical diagnostics of 4 million stars in the 4MIDABLE-HR survey