Spectroscopic and photometric variability of HD 51585 as a manifestation of stellar wind

We present the results of our photoelectric observations of HD 51585 (OY Gem), a B[e] star with an infrared excess and a candidate for protoplanetary nebulae, obtained with a 60-cm telescope at the Crimean Station of the Sternberg Astronomical Institute in 1992–2005. The star exhibited rapid irregular brightness variations with amplitudes from We present the results of our photoelectric observations of HD 51585 (OY Gem), a B[e] star with an infrared excess and a candidate for protoplanetary nebulae, obtained with a 60-cm telescope at the Crimean Station of the Sternberg Astronomical Institute in 1992–2005. The star exhibited rapid irregular brightness variations with amplitudes from in the V band to in U band within the observing season as well as slow systematic variations with amplitudes from in the V band to in the U band and with a quasi-period of ∼2800 days. The B-V color index varied within and did not follow the slow systematic brightness variations, while U-B correlated with the U brightness and varied between at maximum light and at minimum light. Our low-resolution spectroscopy performed in 1994–2005 has revealed significant variability of the Balmer and Paschen hydrogen emission lines as well as the He I and O I lines. Equivalent widths are given for the H I, He I, O I, and Fe II lines; a correlation has been found between the star’s photometric variability and the hydrogen line intensities. Our joint analysis of the photometric and spectroscopic data suggests that variations in a strong stellar wind are responsible for the variability of the star. Original Russian Text ? V.P. Arkhipova, N.P. Ikonnikova, G. V. Komissarova, V. F. Esipo, 2006, published in Pis’ma v Astronomicheskiĭ Zhurnal, 2006, Vol. 32, No. 9, pp. 662–671.     

Light variations in the candidate for protoplanetary objects HD 179821=V1427 Aql in 1899–1999

We present photoelectric and photographic observations of the supergiant HD 179821 with a large infrared excess, a candidate for protoplanetary objects. Over, ten years of our UBV observations, the star exhibited semiregular light variations with amplitudes $\Delta V = 0\mathop .\limits^m 10$ , $\Delta B = 0\mathop .\limits^m 15$ , and $\Delta U = 0\mathop .\limits^m 25$ , as well as systematic color and light variations. From 1990 until 1996, the yearly mean U-B and B-V color indices decreased by 0.25 and 0.15, respectively. After 1996, the motion of the star in the two-color (B-V)-(U-B) diagram upward and to the left slowed down. The color excess that we derived from our observations, by assuming that the star’s spectral type was F3 I in the 1990s, is E(B-V)=1.0. The photographic observations of HD 179821 from 1899 until 1989 show that its brightness m _pg generally increased while significantly fluctuating. An analysis of the observational data suggests that HD 179821 is most likely a post-AGB star of intermediate or low mass.     

Photometric variability of the protoplanetary nebula LSIV-12°111

We present our photometric observations of an early B supergiant with an infrared excess, the protoplanetary object LSIV-12°111, and the previously suspected variable star NSV 24971. We confirm its photometric variability. During two observing seasons (2000–2001), the star exhibited rapid irregular light variations with amplitudes $\Delta V \sim 0\mathop .\limits^m 3$ , $\Delta B \sim 0\mathop .\limits^m 3$ , and $\Delta U \sim 0\mathop .\limits^m 4$ and a time scale of ～1^d. There is no correlation between the colors and magnitudes of the star. The variability patterns of LSIV-12°111 and two other hot post-AGB stars, V886 Her and V1853 Cyg, are shown to be similar.     

Photometric and spectroscopic study of the supergiant with an infrared excess V1027 Cygni

We present the results of our UBV and JHKLM photometry for the semiregular pulsating variable V1027 Cyg, a supergiant with an infrared excess, over the period from 1997 to 2015 (UBV) and in 2009–2015 (JHKLM). Together with the new data, we analyze the photometric observations of V1027 Cyg that we have obtained and published previously. Our search for a periodicity in the UBV brightness variations has led to several periods from P = 212^d to 320^d in different time intervals. We have found the period P = 237^d based on our infrared photometry. The variability amplitude, the lightcurve shape, and themagnitude of V1027 Cyg atmaximum light change noticeably from cycle to cycle. The deepest minimum was observed in 2011, when the amplitudes of brightness variations in the star reached the following values: ΔU = 1 _. ^m 28, ΔB = 1 _. ^m 10, ΔV = 1 _. ^m 05, ΔJ = 0 _. ^m 30, ΔH = 0 _. ^m 35, ΔK = 0 _. ^m 32, ΔL = 0 _. ^m 26, and ΔM = 0 _. ^m 10. An ambiguous correlation of the B ? V and U ? B colors with the brightness has been revealed. For example, a noticeable bluing of the star was observed during the deep 1992, 2008, and 2011 minima, while the variations with smaller amplitudes show an increase in B ? V at the photometric minima. The spectral energy distribution for V1027 Cyg from our photometry in the range 0.36 (U)–5.0 (M) μm corresponds to spectral types from G8I to K3I at different phases of the pulsation cycle. Low-resolution spectra of V1027 Cyg in the range λ4400–9200 ?A were taken during 16 nights over the period 1995–2015. At the 1995 and 2011 photometric minima the star’s spectrum exhibited molecular TiO bands whose intensity corresponded to spectral types M0–M1, while the photometric data point to a considerably earlier spectral type. We hypothesize that the TiO bands are formed in the upper layers of the extended stellar atmosphere. We have measured the equivalent widths of the strongest absorption lines, in particular, the infrared Ca II triplet in the spectrum of V1027 Cyg. The calcium triplet (Ca T) with W _λ(Ca T) = 20.3 ± 1.8 ?A as a luminosity indicator for supergiants places V1027 Cyg in the region of the brightest G–K supergiants. V1027 Cyg has been identified with the infrared source IRAS 20004+2955 and is currently believed to be a candidate for post-AGB stars. The evolutionary status of the star and its difference from other post-AGB objects are discussed.     

Galaxies with rows

The results of a search for galaxies with straight structural elements, usually spiral-arm rows (“rows” in the terminology of Vorontsov-Vel'yaminov), are reported. The list of galaxies that possess (or probably possess) such rows includes about 200 objects, of which about 70% are brighter than 14^m. On the whole, galaxies with rows make up 6–8% of all spiral galaxies with well-developed spiral patterns. Most galaxies with rows are gas-rich Sbc-Scd spirals. The fraction of interacting galaxies among them is appreciably higher than among galaxies without rows. Earlier conclusions that, as a rule, the lengths of rows are similar to their galactocentric distances and that the angles between adjacent rows are concentrated near 120° are confirmed. It is concluded that the rows must be transient hydrodynamic structures that develop in normal galaxies.     

Second Outburst of the Yellow Symbiotic Star LT Delphini

Astronomy Letters - We present the results of our photoelectric UBV observations of the yellow symbiotic star LT Del over 2010–2018. The binary system LT Del, which consists of a bright K...     

Spectroscopic Variability of the Compact Planetary Nebula Hb 12

Astronomy Letters - We present the results of our new low-resolution spectroscopic observations of the young compact planetary nebula Hb 12 performed in 2011–2020 with SAI MSU telescopes. We...     

Symbiotic halo star LT Del: Phase variations of the emission spectrum and parameters of the cool component

Long-term photometric and spectroscopic observations of the yellow symbiotic star LT Del are analyzed. UBV light curves are presented. Based on the observations of 20 cycles, we have refined the orbital period of the star, P = 476 _· ^d 0 ± 1 _· ^d 0. The brightness has been found to be unstable at some orbital phases with an amplitude up to 0 _· ^m 3. We have measured the fluxes in hydrogen and helium emission lines and in continuum and investigated their relationship to the orbital period. The fluxes in hydrogen and HeI lines follow the UBV light curves in phase; the He II 4686 Å flux does not depend on the phase and is constant within the accuracy of our measurements. The intensity ratio of the 4686 Å andHβ lines changes from 0.2 to 0.9 over the period. We interpret the spectroscopic observations based on the hypothesis of heating and ionization of the stellar wind from a cool component by high-frequency radiation from a hot star with a temperature of 105 K. We have estimated the spectral type of the cool star from our photometry and its continuum energy distribution as a bright K2–4 red giant branch halo star. The bolometric luminosity and mass loss rate have been estimated for the K component to be L _bol ～ 700L _⊙ and \(\dot{M}\) ～ 10^?8 M _⊙ yr^?1, respectively.     

Photometric and spectroscopic evolution of the symbiotic nova V1016 Cygni after its outburst

We have constructed the light curves of the symbiotic nova V1016 Cyg for the period 1971–2007 in a homogeneous photometric system close to UBV using our observations with the Zeiss-600 SAI telescope. Based on the observational data obtained with the 125-cm SAI telescope in 2000–2007, we have performed absolute spectrophotometry of the star in the range λ3700–9300 Å. The derived line intensities are compared with the data of other authors in the preceding years (1965–1988). The behavior of nebular lines showed the variations in electron density and, probably, electron temperature in the [OIII] emission region caused by a variable stellar wind from the hot component. All the available observations of the star confirm the theoretical conclusion that the nova-like outburst of V1016 Cyg was produced by a thermonuclear flash in the accreted envelope of a white dwarf.