  Ground-based, high-resolution spectrographs are providing us with an
unprecedented view of the dynamics and chemistry of the atmospheres of planets
outside the Solar System. While there is a large number of stable and precise
high-resolution spectrographs on modest-size telescopes, it is the
spectrographs at observatories with apertures larger than 3.5 metres that
dominate the atmospheric follow-up of exoplanets. In this work, we explore the
potential of characterising exoplanetary atmospheres with FIES, a
high-resolution spectrograph at the 2.56 metre Nordic Optical Telescope. We
observed two transits of MASCARA-2 b (also known as KELT-20 b) and one transit
of KELT-9 b to search for atomic iron, a species that has been recently
discovered in both neutral and ionised forms in the atmospheres of these
ultra-hot Jupiters using large telescopes. Using a cross-correlation method, we
detect a signal of Fe II at the $4.5\sigma$ and $4.0\sigma$ level in the
transits of MASCARA-2 b. We also detect Fe II in the transit of KELT-9 b at the
$8.5\sigma$ level. Although we do not find any significant Doppler shift in the
signal of MASCARA-2 b, we do measure a moderate blueshift (3-6 km/s) of the
feature in KELT-9 b, which might be a manifestation of high-velocity winds
transporting Fe II from the planetary dayside to the nightside. Our work
demonstrates the feasibility of investigating exoplanet atmospheres with FIES,
potentially unlocking a wealth of additional atmosphere detections with this
and other high-resolution spectrographs mounted on similar-size telescopes.
