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Exoplanet atmospheres photoevaporate because of XUV stellar irradiation.
Evaporation signs are mainly detected through the h Lyman-alpha line, or
more recently in the He I 10830 triplet. Despite of early efforts back
in 2000, it was not until 2018 that the line was detected in exoplanet
atmospheres. The He I line is not affected by interstellar medium
absorption, and that is pushing a number of observations to search for
its presence in exoplanet atmospheres. The stellar high energy
irradiation also plays a role in this line formation. But all the
attempts to relate the stellar XUV irradiation and the presence of the
line in exoplanets have ended in just a suggestive trend. Studies
related to photoevaporation, and also on the He I 10830 line, show the
importance of having good models of the XUV stellar emission. Along this
talk I will describe the update done to our early X-exoplanet models,
and how this accurate work has allowed us to define a clear correlation
between XUV stellar irradiation and the detection of He I 10830 triplet
in exoplanet atmospheres. Some hints on the future development of XUV
modelling will be discussed.