  In this work we study the effect of disequilibrium processes on mixing ratio
profiles of neutral species and on the simulated spectra of a hot Jupiter
exoplanet that orbits stars of different spectral types. We also address the
impact of stellar activity that should be present to a different degree in all
stars with convective envelopes. We used the VULCAN chemical kinetic code to
compute number densities of species. The temperature-pressure profile of the
atmosphere was computed with the HELIOS code. We also utilized the $\tau$-ReX
forward model to predict the spectra of planets in primary and secondary
eclipses. In order to account for the stellar activity we made use of the
observed solar XUV spectrum taken from Virtual Planetary Laboratory (VPL) as a
proxy for an active sun-like star. We find large changes in mixing ratios of
most chemical species in planets orbiting A-type stars that radiate strong XUV
flux inducing a very effective photodissociation. For some species, these
changes can propagate very deep into the planetary atmosphere to pressures of
around 1 bar. To observe disequilibrium chemistry we favor hot Jupiters with
temperatures Teq=1000 K and ultra-hot Jupiters with Teq=3000$ K that also have
temperature inversion in their atmospheres. On the other hand, disequilibrium
calculations predict little changes in spectra of planets with intermediate
temperatures. We also show that stellar activity similar to the one of the
modern Sun drives important changes in mixing ratio profiles of atmospheric
species. However, these changes take place at very high atmospheric altitudes
and thus do not affect predicted spectra. We estimate that the effect of
disequilibrium chemistry in planets orbiting nearby bright stars could be
robustly detected and studied with future missions with spectroscopic
capabilities in infrared such as, e.g., JWST and ARIEL.
