Characterizing cool giants in symbiotic binaries using the Gaia EDR3 data Jaroslav Merc1,2; Rudolf Gális2; Marek Wolf1 1Astronomical Institute of Charles University, 2 Institute of Physics, P. J. Šafárik University Jaroslav Merc Astronomical Institute of Charles University V Holešovičkách 2, 180 00 Prague, Czech Republic Email: jaroslav.merc@gmail.com Website: https://sirrah.troja.mff.cuni.cz/~merc/ http://astronomy.science.upjs.sk/symbiotics Contact 1. Gaia Collaboration et al. (2020). arXiv:2012.01533 2. Lindegren, L., Bastian, U., Biermann, M., Bombrun A., de Torres, A. et al. (2020). arXiv:2012.01742 3. Merc, J., Gális, R., & Wolf, M. (2019), Research Notes of the American Astronomical Society, 3, 28. 4. Merc, J., Gális, R., & Wolf, M. (2020a), Contributions of the Astronomical Observatory Skalnate Pleso, 50, 426. 5. Merc, J., Mikołajewska, J., Gromadzki, M., Gałan, C., Iłkiewicz, K., et al. (2020b). Astronomy & Astrophysics, 644, A49. 6. Mikołajewska, J. (2012), Baltic Astronomy, 21, 5. 7. Sion, E. M., Godon, P., Mikolajewska, J., & Katynski, M. (2019), The Astrophysical Journal, 874, 178. 8. Teyssier, F. (2019), Contributions of the Astronomical Observatory Skalnate Pleso, 49, 217. References Symbiotic stars are strongly interacting binaries, which consist of a cool giant of spectral type M (or less commonly K) and a hot compact star, mostly a white dwarf (see e. g. the review by Mikołajewska, 2012). Both stellar components radiate at distinct wavelength intervals (see Fig. 1). Their orbital periods range from hundreds to thousands of days. Symbiotic binaries are unique astrophysical laboratories in the study of the stellar evolution, mass transfer and accretion processes, stellar winds, jets, dust formation, or thermonuclear outbursts. Gaia observations made public in the Gaia EDR3 (Gaia Collaboration et al., 2020), as demonstrated in this contribution, could be very suitable for characterizing the Galactic symbiotic population. Introduction A factor that significantly limits analysis of the parameters of the components of symbiotic binaries is their unknown distance. Astrometric observations of the Gaia satellite can significantly help in this task. However, in the case of symbiotic binaries, many parallaxes are only poorly measured: some of them are even negative or are measured with large relative errors (Fig. 3). Moreover, the zero-point offset of parallaxes is present in the data (Lindegren et al., 2020). Another issue may be related to the binarity of symbiotics and their orbital motion, as the astrometric parameters from Gaia are obtained considering only the one-star model. In nearby long-period binaries, the shift caused by their orbital motion can be comparable to the effect caused by their parallax (e. g. as noted for AG Peg by Sion et al., 2019). Therefore, all the Gaia distance measurements for symbiotics must be interpreted with regards to these issues. In Fig. 4, we show the distribution of vertical distances of symbiotics from Galactic plane. Positions Thanks to several programs focused on discovering symbiotic binaries, the number of known symbiotic stars is growing rapidly in the recent decades. Based on the recent progress in the study of symbiotic stars, we have decided to prepare a new database of these interacting binaries (New Online Database of Symbiotic Variables; Merc et al., 2019). The purpose of the database is not only to serve as a catalogue of data for all known symbiotics with consistent references, but we have also prepared a web-portal for easy access to this information. For the catalogued symbiotic stars, we have prepared specific object pages covering all available information included in the database. Making the database online allows us to add new objects as soon as they are discovered and update data when new information becomes available. Database of symbiotics In addition to precise astrometric measurements, photometric data from the Gaia satellite could be used to monitor varia