  With the discovery of ever smaller and colder exoplanets, terrestrial worlds
with hazy atmospheres must be increasingly considered. Our Solar System's Titan
is a prototypical hazy planet, whose atmosphere may be representative of a
large number of planets in our Galaxy. As a step towards characterizing such
worlds, we present simulations of exoplanets that resemble Titan, but orbit
three different stellar hosts: G-, K-, and M-dwarf stars. We use general
circulation and photochemistry models to explore the circulation and chemistry
of these Titan-like planets under varying stellar spectra, in all cases
assuming a Titan-like insolation. Due to the strong absorption of visible light
by atmospheric haze, the redder radiation accompanying later stellar types
produces more isothermal stratospheres, stronger meridional temperature
gradients at mbar pressures, and deeper and stronger zonal winds. In all cases,
the planets' atmospheres are strongly superrotating, but meridional circulation
cells are weaker aloft under redder starlight. The photochemistry of
hydrocarbon and nitrile species varies with stellar spectra, with variations in
the FUV/NUV flux ratio playing an important role. Our results tentatively
suggest that column haze production rates could be similar under all three
hosts, implying that planets around many different stars could have similar
characteristics to Titan's atmosphere. Lastly, we present theoretical emission
spectra. Overall, our study indicates that, despite important and subtle
differences, the circulation and chemistry of Titan-like exoplanets are
relatively insensitive to differences in host star. These findings may be
further probed with future space-based facilities, like WFIRST, LUVOIR, HabEx,
and OST.
