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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] 5007, [Ne III] 3869, and He II 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 () obtained with the new CMO spectrograph showed the double-peaked shape of the H line and the presence of an absorption component in it. The October 14, 2023 photometric monitoring revealed a flickering in the band with an amplitude of on a timescale of 10–15 minutes. The luminosity, effective temperature, and radius of the V520 And cool component were determined: , K, and , respectively. Evidence for the presence in the system of an accretion disk with the luminosity was also found.

We present time-series CCD photometry in the BVRI passbands of the recently identified symbiotic nova V1835 Aquilae (NSV 11749) over an interval of 5.1 yr with 7–14 day cadence, observed during its quiescence. We find slow light variations with a range of ∼0.9 mag in V and ∼0.3 mag in I . Analysis of these data show strong periodicity at 419 ± 10 days, which we interpret to be the system’s orbital period. A dip in the otherwise-sinusoidal phased light curve suggests a weak ellipsoidal effect due to tidal distortion of the giant star, which in turn opens the possibility that V1835 Aql transfers some of its mass to the hot component via Roche lobe overflow rather than via a stellar wind. We also find evidence that V1835 Aql is an S-type symbiotic star, relatively free of circumstellar dust, and include it among the nuclear burning group of symbiotics. Finally, we provide photometry, periods, and light curve classifications for 22 variable stars in the field around V1835 Aql, about half of which are newly identified.

Symbiotic stars are interacting binary systems composed of an evolved star (generally a late-type red giant) and a degenerate or dwarf companion in orbit close enough for mass transfer to occur. Understanding the status of the late-type star is important for developing binary models for the symbiotic systems as it affects the transfer of matter needed to activate the hot component. Infrared observations have been very useful in probing the nature of late-type stars in symbiotic systems. This work presents a set of symbiotic stars observed with SOAR/OSIRIS (R∼3000) in the H-band. We aimed to search for possible molecular circumstellar emission, to characterize the cool companion in these systems, and to confront the new findings with those obtained from the previous K-band classifications. We detected molecular emission from just one object, BI Cru, which displays the second-overtone CO-bands. To fit the observed photospheric CO absorption bands, we used the MARCS atmosphere models. We present our results as a mini atlas of symbiotic stars in the near-infrared region to facilitate the comparison among different observed symbiotic systems.

The origin of chemically peculiar stars and nonzero eccentricity in evolved close binaries have been long-standing problems in binary stellar evolution. Answers to these questions may trace back to an intense mass transfer during the asymptotic-giant-branch (AGB) binary phase. We use AstroBEAR to solve the 3D radiation hydrodynamic equations and calculate the mass transfer rate in AGB binaries that undergo the wind-Roche-lobe overflow or Bondi-Hoyle-Lyttleton (BHL) accretion. One of the goals of this work is to illustrate the transition from the wind- Roche-lobe overflow to BHL accretion. Both circumbinary disks and spiral structure outflows can appear in the simulations. As a result of enhanced mass transfer and angular momentum transfer, some AGB binaries may undergo orbit shrinkage, and some will expand. The high mass transfer efficiency is closely related to the presence of the circumbinary disks.

The results of the analysis of photometric and spectral monitorings of the recurrent symbiotic nova T CrB, carried out using the low-resolution spectrograph TDS of the 2.5-m telescope and the CCD photometer of the 0.6-m telescope of the CMO SAI, are presented. It is shown that the fluxes in the emission lines H , H , He I 5876 change by 6–16 , and in the emission line He II 4686 by about 60 on timescales of 20–60 minutes. The line flux curves on August 25, 2020 are similar to the light curve of T CrB, but with a time delay of up to 600 s for different lines. The observed spectrum is approximated by the radiation of the system components with the following parameters: a red giant of spectral type M4 III, a nebula with K and emission measure of cm , and the accretion disk with , (at inclination ).

Masses have been computed for the white dwarfs (WDs) in eclipsing, mass exchange (symbiotic), WD–red giant (RG) binaries by using single-lined spectroscopic orbits, orbital inclinations, and the RG masses. Inclinations have been measured for 13 eclipsing symbiotic binaries. Using Gaia data the mass of the RG can be found from evolutionary tracks. Since the WD evolved from the more massive star in the binary, the WD should be more massive than predicted from the mass of the current RG. Typically the WD has a lower mass than expected implying a previous mass exchange stage for these systems.

We report on high-resolution spectra of the two recurring novae, T CrB and RS Oph, obtained in 2004 when no outbursts were in progress. Selected regions of the spectra between 6500 and 8800 Å were measured for equivalent widths and analyzed for metallicity. Lines of Fe I, Ni I, Si I, and Ti Iwere used to establish the effective temperature. The metallicity as derived using models is near solar with an uncertainty estimated to be near a factor of 2 for both stars. Both stars show a strong lithium line at 6707.8 Å. Approximate Li abundances were derived using model atmospheres for a direct comparison with the nearby Fe Iline at 6710.31 Å and the Ca Iground level line at 6572.78 Å. The Li abundances are nearlog N(Li) = 1.2 log N ( Li ) = 1.2 for RS Oph and 0.8 for T CrB on the scale oflog N(H) = 12.0 log N ( H ) = 12.0 . Such Li abundances are high for single K and M giants. A survey of symbiotic stars with cool components of types K and M showed no recognizable Li line in 28 stars with high quality spectra. This makes the two repeating novae different from the other symbiotics that consist of a red giant and a white dwarf.

The progress in planetary nebulae (PN) research reported in this symposium is reviewed in the context of our current understanding of the PN phenomenon.

We present the first results from the systematic observational campaign aimed at studying rapid photometric variability (i.e., flickering) in southern symbiotic stars. In particular, we report on the discovery of strong flickering from V648Car (also known as SS73-17), a poorly studied system belonging to the small class of hard X-ray emitting symbiotic stars. To our knowledge, with a U-band flickering amplitude >0.6mag over time scales of minutes, it is one of the most significant flickering ever reported from a symbiotic star.