Spectroscopic studies of three novae

We present our spectroscopic observations of the novae V1425, V1493, and V1494 Aql carried out with the 125-cm telescope at the Crimean Station of the Sternberg Astronomical Institute in the wavelength range 4000–11000 Å. We measured the emission-line intensities, determined the nova shell expansion velocities from the line profile FWHMs and components, and estimated the interstellar reddening from the first members of the Balmer series. The chemical composition of the nova shells is analyzed. Nitrogen and oxygen were found to be overabundant in V1425 and V1494 Aql; the helium abundance turned out to be normal in the two stars.     

Optical Monitoring of SS 433 in 2017–2021

Astronomy Reports - The observed characteristics of the spectral and photometric variability of SS 433 are discussed based on the data for 2018–2021 and compared with earlier results. The...     

Variability of hot supergiant IRAS 19336-0400 in the early phase of planetary nebula ionization

We present photoelectric and spectral observations of a hot candidate proto-planetary nebula—early B-type supergiant with emission lines in spectrum—IRAS 19336-0400. The light and color curves display fast irregular brightness variations with maximum amplitudes \(\Delta V = 0_ \cdot ^m 30\), \(\Delta B = 0_ \cdot ^m 35\), \(\Delta U = 0_ \cdot ^m 40\) and color-brightness correlations. By the variability characteristics IRAS 19336-0400 appears similar to other hot proto-planetary nebulae. Based on low-resolution spectra in the range λ4000–7500 Å we have derived absolute intensities of the emission lines Hα, Hβ, Hγ, [S II], [N II], physical conditions in gaseous nebula: n _e = 10⁴ cm^?3, T _e = 7000 ± 1000 K. The emission line Hα, Hβ equivalent widths are found to be considerably variable and related to light changes. By UBV-photometry and spectroscopy the color excess has been estimated: E _B-V = 0.50–0.54. Joint photometric and spectral data analysis allows us to assume that the star variability is caused by stellar wind variations.     

Determining the interstellar extinction and distances for Galactic novae

Using photometric data for Galactic novae, we compared the Sharov (1963) and Schlegel et al. (1998) interstellar extinction maps. We found the distances and extinctions for 64 novae.     

Optical Spectroscopy of SRG/eROSITA Objects with 2.5-m Telescope at the Caucasus Mountain Observatory of the SAI MSU

Astronomy Letters - Based on observations with the new transient double-beam spectrograph (TDS) at the 2.5-m telescope of the Caucasus Mountain Observatory of SAI MSU, we have determined the types...     

Spectroscopic studies of four planetary nebulae with emission-line nuclei

Spectroscopic observations of four planetary nebulae (PNe) with emission-line central stars of different spectral types are presented: Cn 1-5, Pe 1-1, NGC 5873, and M1-19. The interstellar extinction, physical conditions (n _e , T _e ), and abundances of several elements (He, N, O, Ne, S, Ar, Cl) have been determined for all nebulae. The nebula Cn 1–5 with fairly high abundances of helium and nitrogen is shown to belong to type I PNe. Possible variability of the intensities of low-excitation emission lines in NGC 5873 has been found; it can be related to variations of the stellar wind from the central star. The measured α-element abundance ratios (S/O, Ne/O, Ar/O, Cl/O) are in good agreement with those typical of HII regions.     

A study of the shell of Nova V705 Cas

Spectroscopic observations of the DQ Her-type Nova V705 Cas in the wavelength range Hγ-7400 Å at the nebular stage are presented. The Balmer decrement yields E _B–V =0.98. Based on statistical relationships, we estimated E _B–V to be 0.7 and the distance to the Nova to be 1.17 kpc. The discrepancy between the estimates of E _B–V may result from circumstellar reddening after the formation of a dust shell. The helium, oxygen, nitrogen, argon, iron, and calcium abundances in the Nova shell are determined. The shell of V705 Cas is similar in chemical composition to those of other DQ Her-type novae.     

Comparison and Interpretation of Spectral Characteristics of the Leading and Trailing Hemispheres of Europa and Callisto

Europa and Callisto are two “extreme members” in a sequence of the Galilean ice satellites formed at different distances from Jupiter. The difference in their mean density probably reflects the material density gradient that appeared even in the subplanetary disk of Jupiter. At the same time, general peculiarities in the composition of the surfaces of Europa and Callisto apparently characterize the accumulated effect of all subsequent evolutionary processes, including current volcanic activity on the satellite Io and its ionized material transfer in Jovian magnetosphere, as well as chemical reactions taking place under low-temperature (within ~90–130 K) and irradiation conditions. In 2016–2017, we observed the leading and trailing hemispheres of Europa and Callisto in the spectral range of 1.0–2.5 μm at 2-m telescope of Caucasian Mountain Observatory (CMO) of Sternberg Astronomical Institute (SAI) of Moscow State University (MSU). We found that, on a global scale, Europa and Callisto exhibit similar spectral characteristics and, particularly, the maxima in the distributions of sulfuric acid hydrate in the trailing hemispheres of the both moons, which agrees with the data of previous measurements. This can be considered as evidence for general ion implantation on these and other moons in the radiation belts of Jupiter. Moreover, our spectral data suggest that water ice and hydrates (clathrates) of other compounds are dominant or abundant in the leading hemispheres of Europa and Callisto. Specifically, we detected a weak absorption band of CH₄ clathrate centered at ~1.67 μm in the reflectance spectra of the leading (the band is more intense) and trailing (the band is less intense) hemispheres of Europa. Weak signs of the same absorption band are also in the reflectance spectra of Callisto measured at its different orientations.     

The Long-Period Dwarf Nova V2466 Cyg: The 2003 and 2019 Superoutbursts

Astronomy Letters - Results of the first multicolor photometric observations of the unusual dwarf nova V2466 Cygni during its 2003 and 2019 superoutbursts are presented. The total amplitude of the...     

A search for photometric and spectroscopic evolutionary changes in the young planetary nebula Vy 2-2

The results of long-term photometric and spectroscopic observations of the young compact planetary nebula Vy 2-2 (PNG 045.4-02.7) are presented. The UBV photometry in 1990–2016 has revealed a slight brightness trend in the yearly averaged data, most pronounced in the V band. We have measured the relative fluxes of optical emission lines on the spectrograms taken with the 1.25-m telescope at the Southern Station of the SAI MSU in 1999–2016, estimated the absolute flux in the Hβ line to be F(Hβ) = (2.1 ± 0.4) × 10^?12 erg cm^?2 s^?1, and determined the interstellar extinction constant c(Hβ) = 1.8. The electron temperature and density in the nebula have been estimated from diagnostic line ratios: T_e = (10?12) × 10³ K and Ne ≥ 10⁵ cm^?3. To detect any possible evolutionary changes, we have compared the new observations with the archival data obtained over the entire history of spectroscopic observations of Vy 2-2. No significant changes in the relative intensities of the strongest emission lines and the integrated flux in the Hβ line exceeding the observational errors have been found. We have revealed a tendency for the intensity ratio F(λ4363)/F(λ4959) to decrease with time, which may be related to a decrease in the electron density in the nebula. Based on our photometric and spectroscopic data, we have estimated the luminosity of the central star of Vy 2-2, which corresponds to the evolutionary tracks for the most massive post-AGB stars of the O-rich sequence.