Symbiotic stars are strongly interacting binaries with long orbital periods, containing an evolved red giant and a white dwarf or a neutron star embedded in a circumbinary nebula. They constitute unique astrophysical laboratories important for understanding the binary evolution and diverse processes occurring also in many other types of astrophysical objects. In this contribution, we present the results of the analysis of the TESS light curves of a sample of symbiotic stars. In particular, we focus on the short-term photometric variability of these binaries on a timescale from minutes to days.

Although this variability reminds the solar-like oscillations of luminous red giants at first sight, we demonstrate that this variability originates from a different process, most likely from the accretion disks around the hot companions, and therefore is connected with the mass transfer. Up to now, such variability, known as flickering in the symbiotic stars community, has been observed only in a small fraction of these interacting systems, either from quasi-visual inspection of the light curves or from the comparison of the variability with nearby stars. We present an effective, quantitative method to reliably distinguish between flickering sources and oscillating red giants.

We detected flickering-like variability in 20 symbiotic stars utilizing TESS data, of which 13 had not previously been identified 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 is now likely to be detected in a total of 35 known symbiotic stars. While this represents only a small subset of all symbiotic binaries, 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 result suggests that accretion disks may indeed be prevalent in these binaries.