Acoustic Heating Models for the Basal Flux Star (tau)Ceti Including Time-dependent Ionization: Results for Ca II and Mg II Emission

We present new calculations of chromospheric heating for (tau)Ceti (G8 V), a star exhibiting an extremely low level of chromospheric activity, thus also referred to as a basal flux star or a flat activity star. Our simulations consider energy deposition by acoustic shocks and also take into account time-dependent (i.e., noninstantaneous) ionization processes of hydrogen, magnesium, and calcium, allowing us to attain a new generation of chromospheric heating models previously obtained for the Sun. We consider both monochromatic waves and acoustic frequency spectra. The latter are calculated using new models of acoustic energy generation based on an extended Kolmogorov spectrum with a modified Gaussian frequency factor. Our models show that the theoretically deduced emergent Ca II and Mg II emission very much agree with observations, adding to the argument that the chromospheres of basal flux stars are predominantly heated by acoustic shocks.