Sergei N. Fabrika

Photometric and spectroscopic study of nova Cassiopeiae 1995 (V723 Cas)

We report an 11-year long series of U BV RI observations and the results of our monitoring of the classical slow nova V723 Cas. We analyze the spectra of this star taken using the 6-m telescope of the Special Astrophysical Observatory of the Russian Academy of Sciences with a spectral resolution of 3.5–8.5 Å during the nebular stage and at the supersoft X-ray source phase (SSS). This systemhas a large orbital inclination and its orbital period is equal to 0.693265 days. The orbital period increases. We found low-amplitude light variations with the orbital period during the early stages of the outburst and even at the pre-maximum stage. The orbital light curve at the nebular stage is asymmetric and gradually increases its amplitude up to V=2m in 2006. The asymmetry of the light curve of V723 Cas can be explained by the reflection effect, eclipse of the extended accretion disk, and high rate of mass transfer in the system. The light curve of V723 Cas has developed a plateau due to the SSS phase. In the spectrum of V723 Cas the transition to the SSS phase shows up in an order-of-magnitude increase of the flux of the [Fe X] λ 6374 Å emission, which forms in the expanding envelope. In addition, narrow emission lines λ 6466.4 Å (O V) and λ 6500.5 Å (Fe XVII) also emerged in the spectrum.

Magnetic fields of white dwarfs

We present results of Zeeman CCD measurements of DA white dwarfs carried out with the 6-m telescope of the Special Astrophysical Observatory in 1995–2000. The accuracy of the measurements ranges from 0.5 to 15 kG. Magnetic fields were detected in three of the 26 observed white dwarfs. We have confirmed the existence of magnetic fields on WD 1953-011 (Be=28±6 kG) and 40 Eri B (Be(min)=−2.8 kG, Be(max)=1.8 kG). The data are discussed in the context of a statistical study of the occurrence of magnetic white dwarfs.

Microvariability of Line Profiles in the Spectrum of the Star ι Her

We present the results of a search for and analysis of line-profile variations in the spectrum of the star ι Her. The observations were acquired with the 1.8 m telescope of the Bohyunsan Optical Astronomy Observatory (Republic of Korea) in May–June 2004. We obtained 69 spectra of the star with signal-to-noise ratios ≈300 and a time resolution of 5–7 min. Profile variability was revealed for six lines of HI, HeI, and SiIII, in the central parts of the lines. The variability amplitude is ≈(1–2)% in units of the intensity of the adjacent continuum. Evidence was found for cyclic variations of the lines, with periods from ≈7h to ≈2.9d. We conclude that ι Her belongs to the group of slowly pulsating stars.

Integral Field Spectroscopy of a Peculiar Supernova Remnant MF16 in NGC6946

We present a study of a peculiar Supernova Remnant MF16, associated with the Ultraluminous X-ray Source (ULX) NGC6946 ULX-1. Observations were taken with the Multi-Pupil Fiber Spectrograph (MPFS) on 6-m telescope in January 2005. The nebula is found to be highly asymmetric, one of the parts being much denser and colder. Two-component structure of the emission lines and radial velocity gradient in some of them argue for a non-spherical shell, expanding with a velocity of about 100 km s-1. Neither shock models nor X-ray emission can adequately explain the actual emission line spectrum of MF16, so we suggest an additional ultraviolet source with a luminosity of about 1040 erg s -1. We confirm coincidence of the ULX with the central star and identify radio emission observed by VLA with the densest part of the nebula.

Integral Field Spectroscopy Survey of Classical LBV Stars in M33

Five well-known LBV stars in M33 were observed with the Multi-Pupil Fiber Spectrograph (MPFS) on the 6-m Russian telescope. We observed LBVs varA, var B, varC, var 2 and var 83. In three of them, var 2, var 83, varB, largescale nebulae were found with sizes from 15 pc and larger. The nebula shapes are complex, like one-side tails or conical nebulae. They all are related to their LBV stars. In var 2 and var 83 stars we found radial velocity gradients 15–30 km/s across their nebulae. The stars varA and varC do not show extended nebulae, but nebular lines are certainty present in their spectra.

Analysis of Balmer Lines Intensities and Radiation Non-Isotropy of SS 433 Jets

The relative intensities of Balmer emission lines forming in the relativistic jets of the SS 433 were selected for a long term data of observations. The Balmer decrements are different for the red and blue lets. Using emission line spectrum calculations by Drake and Ulrich (1980) we have found the jets gas clouds have a big enough electron density n e ≈ 1013 cm-3, a normal range of temperatures, T e = (1 − 2) · 104 K and the optical depth in Hα line of 40 – 60. The kinetic luminosity of the jets we obtain is about ≈ 1039 ergs-1. We could understand the observed BDs in terms of two-phase model of emission line cloud in the jet, the cloud consisting of two slabs, foreside hot one with the temperature ≈ 2 · 104 K and back slab with the temperature ≈ 1 · 104 K. The study of the Hα moving lines intensities with the precession phase independently confirms this two-phase model. The front side of the gas cloud is brighter in the Hα line than the back side. The cloud itself radiates in non-isotropic a way in two antiparallel directions, whose axis does not coincide with the jets axis. Such an asymmetry of the jet cloud radiation could be produced by both non-spherical shape of the cloud and shocks in the clouds, rising an escape probability for a line radiation in the direction of a shock.