Section: PZ: main journal
GSC 2576-02071 and GSC 2576-01248: two Algol-type eclipsing binaries studied using CCD observations and historical photographic data
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.
SN 2008fv: the Third Type Ia Supernova in NGC 3147
Multiple outbursts of type Ia SNe in one galaxy present a unique opportunity to study the homogeneity of these objects. NGC 3147 is only the second known galaxy with three SNe Ia, another one is NGC 1316. We present CCD UBVRI photometry for SN Ia 2008fv and compare the light and color curves of this object to those for SNe Ia discovered in NGC 3147 earlier: 1972H and 1997bq. The photometric properties of SNe 1997bq and 2008fv are nearly identical, while SN 1972H exhibits a faster-declining light curve.
We present our discovery of a new dwarf nova USNO-B1.0 1257-0089884. The object showed superhumps, which establish that it is an UGSU variable star. All observations were acquired at the Astrotel-Caucasus Observatory.
CCD UBVRI photometry covering about 320 days is presented for the type IIb SN 2008ax. Its photometric behavior is typical of core-collapse SNe with low amount of hydrogen. The main photometric parameters are derived and a comparison with SNe of similar types is reported. Preliminary modeling is carried out, and the results are compared to the observed light curves. The main parameters of the hydrodynamical models are close to those used for SN IIb 1993J.
UBV Photometry of the Post-AGB Star IRAS 22272+5435=V354 Lac in 1990 - 2008
New UBV photometry obtained in 2000 - 2008 is presented for the
post-AGB star IRAS 22272+5435 = V354 Lac. The star showed
semi-regular light variations with varying amplitudes. The maximal
amplitude did not exceed: Delta V = 0.5, Delta B = 0.7,
and Delta U = 1.0. For 2000 - 2008, we have found a
photometric period near 128 days. The analysis of long-term
observations in 1990 - 2008 reveals variations with two close
periods: 128 and 131 days, causing amplitude modulation. The
V -(B-V) diagram shows a clear correlation: the star is
generally bluer when brighter. From our UBV data, we derive
E(B-V)=0.5 and conclude that the spectral type of the star
varies between K1 and K7 during pulsations. The mean UBV data for
V354 Lac have not changed during the past 19 years:
Recent multicolor photometry of N. Kurochkin's nova or novalike variable star LW Cas has been obtained using the SAO 1-m Zeiss reflector. The amplitude of the outburst in 1952 was 5 mag in the B band. In 2008, LW Cas consists of a central stellar object of 20 mag B surrounded by a halo of the same brightness and a 7" comet-like tail directed to the east. The star is associated with a young star-forming region and seen through a dark cloudy nebulosity. There is evidence of bright light echo seen two years after the outburst.
The New Double-Mode RR Lyrae Variable USNO-A2.0 1650-01540181
We present our discovery of a new double-mode RR Lyrae variable, USNO-A2.0 1650-01540181. The study is based on our original CCD observations, carried out at the Astrotel-Caucasus Observatory.
RS CVn Stars Among Variables with Possible CW Classification in the ASAS-3 Survey
We present a list of 109 probable RS CVn variables among stars in the ASAS-3 catalog with Population II Cepheid classification as the main one or an alternative one. These stars are identified with X-ray sources and have light curves (from ASAS-3 data) in no contradiction with the suggested RS CVn classification.