The Gaia mission is expected to provide a total number of symbiotic stars in the Galaxy and their membership in stellar populations. Symbiotic stars with distinct emission lines in their spectra can be used as test objects in the analysis of Gaia data on peculiar stars.

During outbursts in symbiotic binaries a neutral medium in the form of a flared disk develops around their hot stars. The appearance of the disks is most probably connected with the enhanced wind from the hot star. The wind is compressed towards the equatorial plane of the hot star due to its rotation. To test this idea we calculated the ionization boundaries in the enhanced wind and thus confirmed the possibility of the formation of the neutral disk-like zones around the hot stars in symbiotic binaries during outbursts.

We investigated the ionization structure of symbiotic binaries during their active phases. We found that a neutral disk-like zone around the hot star can be created as a result of its enhanced wind and fast, 200 - 300 km s−1, rotation. Calculated column densities of the neutral hydrogen atoms throughout the neutral zone and emission measures of the ionized part of the wind from the hot star are in a good agreement with those derived from observations.

We present a circumstellar dust model around the symbiotic Mira RR Tel obtained by modeling the near-infrared JHKL magnitudes and ISO spectra. In order to follow the evolution of infrared colours in time, the published JHKL magnitudes were corrected by removing the Mira pulsations. The RR Tel light curves show three obscuration events in the near-IR. Using the simultaneously available JHKL magnitudes and ISO spectra in three different epochs, we obtained SEDs in the near- and mid-IR spectral region (1-20 μm) in epochs with and without obscuration.

The DUSTY numerical code was used to solve the radiative transfer and to determine the circumstellar dust properties of the inner dust regions around the Mira, assuming a spherical dust temperature distribution in its close neighbourhood. The physical properties of the dust, mass loss and optical depth during intervals with and without obscuration have been obtained. Both JHKL and ISO observations during the obscuration period can be reproduced with a spherical dust envelope, while ISO spectra outside obscuration show a different behaviour. The dynamical behaviour of the circumstellar dust was obtained by modeling the JHKL magnitudes observed during the span of more than 30 years.

The DUSTY code was also successfully applied in the modeling of circumstellar dust envelopes of young stellar objects, such as Herbig Ae/Be stars.

We present a study of the properties of circumstellar dust in symbiotic Miras during sufficiently long time intervals of minimal obscuration. The published JHKL magnitudes of o Ceti, RX Pup, KM Vel, V366 Car, V835 Cen, RR Tel and R Aqr have been collected. In order to investigate their long-term variations, we removed the Mira pulsations to correct their light curves. Assuming spherical temperature distribution of the dust in the close neighbourhood of the Mira, the DUSTY code was used to solve the radiative transfer in order to determine the dust temperature and its properties in each particular case.

The preliminary results of this systematic study of dust envelopes in symbiotic stars with Miras as cool components provide information on nature of dust in these objects.