  Magnetic features on the surface of stars, such as spots and faculae, cause
stellar spectral variability on time-scales of days and longer. For stars other
than the Sun, the spectral signatures of faculae are poorly understood,
limiting our ability to account for stellar pollution in exoplanet transit
observations. Here we present the first facular contrasts derived from
magnetoconvection simulations for K0, M0 and M2 main-sequence stars and compare
them to previous calculations for G2 main-sequence stars. We simulate
photospheres and immediate subsurface layers of main-sequence spectral types
between K0 and M2, with different injected vertical magnetic fields (0 G, 100
G, 300 G and 500 G) using MURaM, a 3D radiation-magnetohydrodynamics code. We
show synthetic spectra and contrasts from the UV (300 nm) to the IR (10000 nm)
calculated using the ATLAS9 radiative transfer code. The calculations are
performed for nine viewing angles to characterise the facular radiation across
the disc. The brightness contrasts of magnetic regions are found to change
significantly across spectral type, wavelength and magnetic field strength,
leading to the conclusion that accurate contrasts cannot be found by scaling
solar values. This is due to features of different size, apparent structure and
spectral brightness emerging in the presence of a given magnetic field for
different spectral types.
