  Symbiotic binaries exhibit a wide range of photometric variability spanning
different timescales attributed to orbital motion, intrinsic variability of
individual components, or the interaction between the two stars. In the range
from minutes to hours, variability induced by accretion processes, likely
originating from the accretion disks, denoted as flickering, is detected. This
variability could mimic solar-like oscillations exhibited by luminous red
giants. We aim to investigate whether it is possible to utilize the precise
observations of the NASA TESS mission to detect flickering in symbiotic stars
despite such studies being usually performed at shorter wavelengths.
Additionally, our goal is to develop a quantitative method for the detection of
accretion-induced flickering that does not rely solely on subjective assessment
of the light curves. We obtain the light curves of known symbiotic stars and a
comprehensive control sample of assumed single red giants from the TESS FFIs.
From the processed light curves and their PSD, we measure the amplitudes of the
variability and other parameters. We introduce a method that enables the
differentiation between flickering sources and stars that do not exhibit this
variability. We detect flickering-like variability in 20 symbiotic stars
utilizing TESS data, with 13 of them being previously unidentified as
flickering sources. Moreover, the TESS observations facilitate the detection of
related variations occurring over timescales of a few days, as well as changes
in the flickering behavior across multiple sectors. The flickering has now been
likely detected in a total of 35 known symbiotic stars. When focusing solely on
accreting-only symbiotic stars where the detection of flickering is presumably
more straightforward, the fraction could reach as high as ~80%. This suggests
that accretion disks may be rather prevalent in these binaries.
