Abstract
We derive a new model of the lower chromosphere of the dwarf K2 star ε Eridani by matching flux profiles of the Ca IR triplet lines λλ8498 and 8542, Hα and Hβ lines and the Na D lines (all observed simultaneously at the AAT), and the Ca IIK line (observed by Zarro & Rogers). The coupled non-LTE equations of statistical equilibrium and radiative transfer are solved under the constraint of hydrostatic equilibrium using the Carlsson (1986) code. The extra constraints imposed by data from a large number of lines originating from different but overlapping atmospheric depths imply that previous models need to be changed in the photosphere, in the temperature minimum by raising it and placing it further out in the atmosphere, and by placing the base of the transition zone at log m = − 4.54. Within the framework of the model we find that the Na D lines are an important photospheric diagnostic and that the Ca IR triplet lines can be used to locate the temperature minimum. The computed Hα and Hβ depths are highly sensitive constraints on the transition zone gradients and base pressures allowing us to derive a pressure at the base of the transition zone of 0.9 dyn cm−2.
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