Setting the scene for Gaia and LAMOST Proceedings IAU Symposium No. 298, 2013 S. Feltzing, G. Zhao, N. A. Walton & P. A. Whitelock, eds. c  International Astronomical Union 2014 doi:10.1017/S1743921313006844 Symbiotic stars as tracers of Galactic structures L. Leedj¨ arv Tartu Observatory, 61602 T˜ oravere, Estonia email: leed@aai.ee Abstract. 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. Keywords. stars: binaries: symbiotic, Galaxy: bulge, Galaxy: disk, Galaxy: halo Symbiotic stars are binary stars consisting of a red giant and a hot white dwarf. The hot component ionizes part of the cool giant’s wind, generating a characteristic symbiotic spectrum – a blue continuum and high excitation emission lines superimposed on the red giant’s spectrum. About 200+ known symbiotic stars (Belczynski et al. 2000) form a heterogeneous class of objects. Here we adopt the classification proposed by Munari (1994), based on the nature of the cool component of the symbiotic star (SyS): (1) classical SyS, cool component M or late K giant, ∼70% of known SyS; (2) Mira SyS, late M Mira, ∼20% of known SyS; (3) carbon SyS, carbon star (giant), ∼5%; (4) yellow SyS, F–G or early K giant or supergiant, ∼5%. Yellow SyS can be divided into yellow S and yellow D’ type. When plotting positions of SyS in Galactic coordinates, a strong concentration towards the Galactic plane can be noticed. Referring to the papers by Munari (1994) and Leedj¨ arv (2006), we suggest the following general trends: • Classical SyS belong to the bulge / thick disk population. • Mira SyS belong to the younger (thin disk?) population than classical SyS, concen- trating closer to the Galactic plane. • Yellow SyS are divided between two distinct populations: yellow S-type stars belong to the Galactic halo, and dusty yellow D’ type stars to the young Galactic disk. We have two expectations related to the Gaia mission: (1) Gaia would provide total number of SyS and their membership in stellar popula- tions. The current discrepancy in the estimates spanning from 3000 to 400 000 (Magrini et al. 2003) should be solved. Knowing the number of SyS in the Galaxy would clarify their evolutionary status and role as possible progenitors of type Ia supernovae. (2) SyS could be used as test objects for analysis of the Gaia data. Many of SyS have narrow strong emission lines in their spectra. This allows to use them as reference stars in the algorithms for recognizing emission-line-stars in the Gaia data. References Belczynski, K., Mikolajewska, J., Munari, U., et al. 2000, A&AS, 146, 407 Leedj¨arv, L. 2006, Ap&SS, 304, 103 Magrini, L., Corradi, R. L.M., Munari, U. 2003, In: Symbiotic Stars Probing Stellar Evolution, eds. R. L.M. Corradi, J. Miko lajewska, T. J. Mahoney, ASPC, 303, 539 Munari, U. 1994, Mem. Soc. Astron. It., 65, 157 417 https://www.cambridge.org/core/terms. https://doi.org/10.1017/S1743921313006844 Downloaded from https://www.cambridge.org/core. IP address: 18.206.13.133, on 16 Jun 2020 at 23:17:23, subject to the Cambridge Core terms of use, available at