  Stellar dynamo processes can be explored by measuring the magnetic field.
This is usually obtained using the atomic and molecular Zeeman effect in
spectral lines. While the atomic Zeeman effect can only access warmer regions,
the use of molecular lines is of advantage for studying cool objects. The
molecules MgH, TiO, CaH, and FeH are suited to probe stellar magnetic fields,
each one for a different range of spectral types, by considering the signal
that is obtained from modeling various spectral types. We have analyzed the
usefulness of different molecules (MgH, TiO, CaH, and FeH) as diagnostic tools
for studying stellar magnetism on active G-K-M dwarfs. We investigate the
temperature range in which the selected molecules can serve as indicators for
magnetic fields on highly active cool stars and present synthetic Stokes
profiles for the modeled spectral type. We modeled a star with a spot size of
10% of the stellar disk and a spot comprising either only longitudinal or only
transverse magnetic fields and estimated the strengths of the polarization
Stokes V and Q signals for the molecules MgH, TiO, CaH, and FeH. We combined
various photosphere and spot models according to realistic scenarios. In G
dwarfs, the molecules MgH and FeH show overall the strongest Stokes V and Q
signals from the starspot, whereas FeH has a stronger Stokes V signal in all G
dwarfs, with a spot temperature of 3800K. In K dwarfs, CaH signals are
generally stronger, and the TiO signature is most prominent in M dwarfs.
Modeling synthetic polarization signals from starspots for a range of G-K-M
dwarfs leads to differences in the prominence of various molecular signatures
in different wavelength regions, which helps to efficiently select targets and
exposure times for observations.
