  Utilizing QCD sum rules, we extract the temperature dependences of the
spectral properties of the pseudo-scalar and scalar D mesons regarded as chiral
partners. Besides the masses also decay constants are analyzed as the D meson
yields in heavy-ion collisions may be sensitive to their altered decay
properties in an ambient strongly interacting medium. Our findings are ($i$) a
decreasing scalar D meson mass for growing temperatures while its pseudo-scalar
partner meson seems hardly affected, which is in qualitative agreement with
hadronic model calculations; ($ii$) inferring an equally weak temperature
dependence of the pseudo-scalar D meson decay properties the decreasing residua
and decay constants of the scalar particle point towards partial chiral
restoration. As a bonus of our analysis in the pseudo-scalar sector we
determine the pseudo-scalar decay constant at vanishing temperature. Due to the
connection to particular leptonic branching fractions this decay constant is of
great interest allowing for the determination of the off-diagonal CKM matrix
element $|V_{cd}|$ at zero temperature.
