Study of Nine Symbiotic Star Candidates. Discovery of the Symbiotic Nature of V520 And

We present the results of spectroscopic observations of nine symbiotic star candidates in the 360–735 nm wavelength range carried out with the TDS spectrograph of the 2.5-m SAI MSU CMO telescope. Eight selected sample stars were classified as red giants of the M3–M6 spectral types. Light curve analysis revealed that all nine stars can be attributed to SRA- and SRB-type variables (based on the classification of the General Catalog of Variable Stars–GCVS). It is shown that one of the stars, V520 And, can be classified as a symbiotic star. Its spectrum reveals H I, He I, Fe II emission lines, weak lines of [O III] $$\lambda$$ 5007, [Ne III] $$\lambda$$ 3869, and He II $$\lambda$$ 4686, and a Balmer jump in emission. The emission spectrum is found to be variable on both the long and very short timescales. A high-resolution spectrum ( $$R=25000$$ ) obtained with the new CMO spectrograph showed the double-peaked shape of the H $$\alpha$$ line and the presence of an absorption component in it. The October 14, 2023 photometric monitoring revealed a flickering in the $$B$$ band with an amplitude of $$0\overset{\textrm{m}}{.}8$$ on a timescale of 10–15 minutes. The luminosity, effective temperature, and radius of the V520 And cool component were determined: $$L=1400{-}2200\;L_{\odot}$$ , $$T_{\textrm{eff}}=3200$$ K, and $$R=120{-}155\;R_{\odot}$$ , respectively. Evidence for the presence in the system of an accretion disk with the luminosity $$L<10\;L_{\odot}$$ was also found.