Non-LTE calculations of semiempirical chromospheric models are present
ed for 30 g Her (M6 III). This star is one of the coolest (T-eff = 325
0 K) SRb (semiregular) variable stars and has a mass perhaps as great
as 4 M(.). Chromospheric features we have observed in its spectrum inc
lude Mg II h and k; C II] UV0.01, which is sensitive to electron densi
ty; Mg I lambda 2852; Ca II H, K, and IRT; Ca I lambda 4227 and lambda
6573; Al II] UV1; and H alpha. We pay special attention to fitting th
e C II intersystem lines and the Mg II resonance lines but use all the
other features as constraints to some extent. The equations of radiat
ive transfer and statistical equilibrium are solved self-consistently
for H I, H-, H-2, He I, C I, C II, Na I, Mg I, Mg II, Al I, Al II, Ca
I, and Ca II with the equivalent two-level technique. To simplify thes
e calculations, a one-dimensional hydrostatic, plane-parallel atmosphe
re is assumed. We investigate 10 separate ''classical'' chromospheric
models, differing most importantly in total mass column density above
the temperature minimum. Synthetic spectra from these models fit some
but not all of the observations. These comparisons are discussed in de
tail. However, we find that no single-component classical model in hyd
rostatic equilibrium is able to reproduce both the Mg II line profiles
and the relative strengths of the C II] lines. In all these models, c
hromospheric emission features are formed relatively close to the star
(less than or similar to 0.05R double dagger). The circumstellar envi
ronment has a thick, cool component overlying the Mg II emission regio
n, which is relatively static and very turbulent. Finally, we find tha
t thermalization in the Mg II h and k lines in the coolest giant stars
is controlled by continuum absorption from Ca I 4 rho(3 rho 0) 3PO bo
und-free opacity and not collisional de-excitation as is the case for
warmer K giants.