Young stars show variability on different time-scales from hours to decades,
with a range of amplitudes. We studied two young stars, which triggered the
Gaia Science Alerts system due to brightenings on a time-scale of a year.
Gaia20bwa brightened by about half a magnitude, whereas Gaia20fgx brightened by
about two and half magnitudes. We analyzed the Gaia light curves, additional
photometry, and spectra taken with the Telescopio Nazionale Galileo and the
Gran Telescopio Canarias. Several emission lines were detected toward
Gaia20bwa, including hydrogen lines from Hα to Hδ, Paβ,
Brγ, and lines of Ca II, O I, and Na I. The Hα and Brγ
lines were detected toward Gaia20fgx in emission in its bright state, with
additional CO lines in absorption, and the Paβ line with an inverse P
Cygni profile during its fading. Based on the Brγ lines the accretion
rate was (2.4−3.1)×10−8M⊙ yr−1 for Gaia20bwa and
(4.5−6.6)×10−8M⊙ yr−1 for Gaia20fgx during their bright
state. The accretion rate of Gaia20fgx dropped by almost a factor of 10 on a
time-scale of half a year. The accretion parameters of both stars were found to
be similar to those of classical T Tauri stars, lower than those of young
eruptive stars. However, the amplitude and time-scale of these brightenings
place these stars to a region of the parameter space, which is rarely populated
by young stars. This suggests a new class of young stars, which produce
outbursts on a time-scale similar to young eruptive stars, but with smaller
amplitudes.Comment: Accepted to MNRA