  The smallest extreme-ultraviolet (EUV) brightening events that were detected
so far, called campfires, have recently been uncovered by the High Resolution
EUV telescope (HRIEUV), which is part of the Extreme Ultraviolet Imager (EUI)
on board Solar Orbiter. HRIEUV has a broad bandpass centered at 17.4 nm that is
dominated by Fe ix and Fe x emission at about 1 MK. We study the thermal
properties of EUI brightening events by simultaneously observing their
responses at different wavelengths using spectral data from the Spectral
Imaging of the Coronal Environment (SPICE) also on board Solar Orbiter and
imaging data from EUI. We studied three EUI brightenings that were identified
in HRIEUV data that lie within the small areas covered by the slit of the SPICE
EUV spectrometer. We obtained the line intensities of the spectral profiles by
Gaussian fitting. These diagnostics were used to study the evolution of the EUI
brightenings over time at the different line-formation temperatures. We find
that (i) the detection of these EUI brightenings is at the limit of the SPICE
capabilities. They could not have been independently identified in the data
without the aid of HRIEUV observations. (ii) Two of these EUI brightenings with
longer lifetimes are observed up to Ne viii temperatures (0.6 MK). (iii) All of
the events are detectable in O vi (0.3 MK), and the two longer-lived events are
also detected in other transition region (TR) lines. (iv) In one case, we
observe two peaks in the intensity light curve of the TR lines that are
separated by 2.7 min for C iii and 1.2 min for O vi. The Ne viii intensity
shows a single peak between the two peak times of the TR line intensity.
Spectral data from SPICE allow us to follow the thermal properties of EUI
brightenings. Our results indicate that at least some EUI brightenings barely
reach coronal temperatures.
