Publications
Section: PZ: main journal
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On 2012 April 25, we acquired spectra and images of NGC 5775 OT PSN J14535395+0334049, classified as a calcium transient similar to NGC 300 OT and SN 2008S in NGC 6496. The Russian 6-m telescope and the SCORPIO focal reducer were used. The spectral range was 4070 - 5830 A and the spectral resolution, 5.4 A. The spectrum is noisy and shows a continuum with an H_{beta} emission line. The line has a two-component profile containing a narrow component, with FWHM ~ 300 km/s, and a broad one, with FWHM ~ 4000 km/s. The object is located at the front of the edge-on galaxy disk, it is weakly reddened. We estimate its M_V as -13.7m on the date of observation, typical of a calcium-type supernova impostor.
Photometric CCD observations of the pre-main-sequence Herbig Ae star WW Vul on separate nights during 2007-2011 are presented. The star exhibited long-term non-periodic variability in the range of 0.8 mag; rapid variations with a small amplitude were superimposed. The results of a search for periodicity in the light variations are reported.
We have recovered the "lost" variable star NSV 08092 = HV 8988. Form archive data, its brightness variations are rather unusual. In some aspects, it resembles R CrB stars, but it can be an analog of the famous unusual post-AGB star FG Sge.
After 33 years of extensive studies of SS 433, we have learnt much about this unique system with moving emission lines in the spectrum. The orbital inclination is known from spectroscopic observations of moving lines; the distance is derived from radio interferometry of relativistic jets; the mass ratio of its components is determined from X-ray observations of jets' eclipses. In 2005, the accretion donor was detected as an A4-A8 giant, and its contribution to eclipse light was measured spectroscopically. In the present paper, the A-type star was detected via multicolor photometry on the basis of its Balmer jump. A method is proposed to estimate the interstellar reddening, able to measure the individual law of interstellar absorption for SS 433 from spectrophotometry. The method is based on extracting the energy distribution of the spectral component of a very hot source covered in eclipse and on the comparison of its energy distribution to the Planck energy distribution of a black body with the temperature exceeding one million K. The determination of general parameters of SS 433 leads to fairly accurate estimates of luminosity, radius, and mass of the A star in the system, and consequently leads to an accurate estimate of the mass of the compact component, the source of jets. The latter mass is between 1.25 and 1.87 solar masses. The reasons for overestimating this mass when using the dynamical method are discussed. In our opinion, the presence of a black hole in this system is excluded.
Working on identifications of objects from the NSV catalog, we found that NSV 07212 and NSV 07329 were two probable variables of the rare RCB type. Both stars enter the ASAS-3 variable-star catalog as "MISC" variables (i.e. those lacking a reliable variable-star classification), with spurious periods. We present the results we obtained for the two variables, mainly from our analysis of the ASAS-3 photometry. NSV 07212, a known carbon star, is a variable with an amplitude as large as 7m. Though, in this case, the RCB classification is rather certain, spectroscopy of both stars is needed.
I report on the discovery of two cataclysmic variables in the same field in Lyra, originally identified on the base of their magnitudes in the USNO-B1.0 catalog and on Palomar images. The historical light curves were analyzed from 300+ photographic plates of the Moscow collection, covering 35 years of observations. One of the two stars, USNO-B1.0 1320-0390658, is showing rather frequent outbursts from B~20 to B=15.2 and is likely a dwarf nova of the UGSS subtype. The other variable, USNO-B1.0 1321-0397655, with only one observed outburst in 1993, from R~19 to I=11.8, is either an UGWZ dwarf nova or a recurrent nova. In both cases, its next outburst can occur in the nearest future.
New GCVS names are announced for several young variable stars of special astrophysical interest. These stars will enter the 80th Name List of Variable Stars but are given GCVS names now in order to make it possible for investigators to use permanent names in their publications.
An initial investigation of two poorly studied eclipsing binaries separated by about 3' in the sky is presented. The first star (GSC 2576-01248) was discovered by the TrES exoplanet search project. The second one (GSC 2576-02071) was identified by the authors during CCD observations of GSC 2576-01248. We combine our dedicated CCD photometry with the archival TrES observations and data from the digitized photographic plates of the Moscow collection to determine periods of the two variable stars with high precision. For GSC 2576-01248, addition of historical photographic data provides a major improvement in accuracy of period determination. No evidence for period change in these binary systems was found. The lightcurve of GSC 2576-01248 is characterized by a prominent variable O'Connell effect suggesting the presence of a dark starspot and asynchronous rotation of a binary component. GSC 2576-02071 shows a shift of the secondary minimum from the phase 0.5 indicating a significant orbit eccentricity.
V445 Pup was a peculiar nova with no hydrogen spectral lines during the outburst. The spectrum contained strong emission lines of carbon, oxygen, calcium, sodium, and iron. We have performed digital processing of photographic images of the V445 Pup progenitor using astronomical plate archives. The brightness of the progenitor in the B band was 14.3m. It was a periodic variable star, its most probable period being 0.650654+/-0.000011 days. The light curve shape suggests that the progenitor was a common-envelope binary with a spot on the surface and variable surface brightness. The spectral energy distribution of the progenitor between 0.44 and 2.2 microns was similar to that of an A0V type star. After the explosion in 2001, the dust was formed in the ejecta, and the star became a strong infrared source. This resulted in the star's fading below 20m in the V band. Our CCD BVR observations acquired between 2003 and 2009 suggest that the dust absorption minimum finished in 2004, and the remnant reappeared at the level of 18.5m V. The dust dispersed but a star-like object was absent in frames taken in the K band with the VLT adaptive optics. Only expanding ejecta of the explosion were seen in these frames till March 2007. No reddened A0V type star reappeared in the spectral energy distribution. The explosion of V445 Pup in 2000 was a helium flash on the surface of a CO-type white dwarf. Taking into account the results of modern dynamic calculations, we discuss the possibility of a white-dwarf core detonation triggered by the helium flash and the observational evidence for it. Additionally, the common envelope of the system was lost in the explosion. Destruction in the system and mass loss from its components exclude the future SN Ia scenario for V445 Pup.
CCD BVRI photometry is presented for the type Ia supernova 2008gy. The light curves match the template curves for a fast-declining SN Ia, but the colors appear redder than average, and the SN may also be slightly subluminous. SN 2008gy is found to be located far outside the boundaries of the three nearest galaxies, each of them has a nearly equal probability to be the host galaxy. |
