Nataly A. Katysheva

X-RAY/OPTICAL STUDIES OF TWO OUTBURSTS OF THE INTERMEDIATE POLAR YY (DO) DRACONIS

YY Draconis (likely the same variable called DO Draconis) is one of a small number of intermediate polars (IPs) that show outburst behavior. We report results from Target of Opportunity observations with the Rossi X-Ray Timing Explorer, together with ground-based optical photometry during outbursts in 1999 September and 2000 November. Similar behavior was evident in both outbursts. At outburst, the X-ray flux increased by more than a factor of 12, and the spectrum became hotter and more absorbed compared to quiescence. While the spin pulse at 529 s is clearly present in the X-ray data at 2–4 days past outburst peak and during quiescence, it was not detected in the X-ray data closest to outburst (1.5 days). This is contrary to the large increase in spin pulse amplitude that has been seen during outbursts of the IPs GK Per, XY Ari, and EX Hya. The differences in YY Dra are likely due to its unique geometry, with two relatively equal poles located near the white dwarf equator. The equal enhancement of both poles near outburst could account for the low pulse amplitude, while unequal feeding of the poles as the magnetosphere recedes during decline could explain the changes in amplitude and pulse shape. The changing height of the shocks may also have an effect on the visibility of both poles.

Discovery of a WZ Sge-Type Dwarf Nova, SDSS J102146.44+234926.3: Unprecedented Infrared Activity during a Rebrightening Phase

Several SU UMa-type dwarf novae and WZ Sge-type stars tend to exhibit rebrightenings after superoutbursts. The rebrightening phenomenon is problematic for the disk instability theory of dwarf novae, since it requires a large amount of remnant matter in the disk, even after superoutbursts. Here, we report on our optical and infrared observations during the first-ever outburst of a new dwarf nova, SDSS J102146.44 + 234926.3. During the outburst, we detected superhumps with a period of 0.056281 ˙ 0.000015 d, which is typical for superhump periods in WZ Sge stars. In conjunction with the appearance of a long-lived rebrightening, we concluded that the object is a new member of WZ Sge stars. Our observations, furthermore, revealed infrared behaviors for the first time in the rebrightening phase of WZ Sge stars. We discovered prominent infrared superhumps. We calculated the color temperature of the infrared superhump source to be 4600–6400 K. These temperatures are too low to be explained by a fully ionized disk appearing during dwarf-nova outbursts. We also found a Ks-band excess over the hot disk component. These unprecedented infrared activities provide evidence for the presence of mass reservoir at the outermost part of the accretion disk. We propose that a moderately high mass-accretion rate at this infrared active region leads to the long-lived rebrightening observed in SDSS J102146.44 + 234926.3.

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.

The dwarf nova V1239 herculis in quiescence

The results of a study of the integrated brightness of the SU UMa eclipsing binary V1239 Her are presented. The systemwas monitored on nine nights in 2013–2014 when the binary was in quiescence. The orbital period is refined (Porb = 0.100082222(2)d) and the system’s light curves obtained. These curves provide evidence for active processes in the system between outbursts: the depths of both minima and the amplitude of the pre-eclipse hump vary, and one of the light curves exhibits no hump at all. The parameters of the accretion disk, hot spot, and gas stream in V1239 Her for several epochs are determined in a “combined” model taking into account the contributions to the total radiation flux from the opaque part of the gas stream and the hot spot on the lateral surface of the disk. Lower limits for the time scale for variations of the disk characteristics are estimated: the viscosity parameter (αg), temperature of the inner parts of the disk (Tin), and thickness of the outer edge of the disk (βd). These can vary appreciably over less than 10 orbital cycles. In the model used, the solution for the light curve that lacks a pre-eclipse hump (JD 2456746) implies the absence of a hot spot on the disk’s lateral surface: the radius of the spot is negligible, and temperatures of the spot and at the base of the gas stream are lower than those obtained for the other light curves. The disappearance of the hot spot is accompanied by an abrupt decrease in the disk radius and αg, as well as a decrease in the thickness of the disk’s outer edge. A comparison with the system’s parameters derived from the light curve for the previous observation date (JD 2456718) suggests that the disk mass decreased significantly between these two dates (∼280Porb); this decrease could be due to a reduced outflow rate from the secondary, as well as the possible infall of a considerable fraction of the matter from the disk onto the surface of the white dwarf.

Cataclysmic Variables in the “Period Gap”

This article reviews observational data on cataclysmic variables (CVs) whose orbital periods fall within the so-called “period gap” between 2 and 3 hours. The orbital period distribution of cataclysmic variables and the filling of the period gap by various types of CVs are demonstrated. Roughly half the stars in the period gap are magnetic, of which the majority are polars, while the other half (except a few stars) are SU UMa-type stars characterized by “superbursts” and “superhumps”. It is also interesting to note that those intermediate polars whose periods fall within the “gap” are among the stars with constant “superhumps”. The height above the galactic plane is estimated for the nonmagnetic stars and it is shown that, contrary to predictions, the stars in the period gap do not belong (except for one) to the spherical component of the galaxy. Light curves, some characteristic times, burst amplitudes, etc. are given for a number of Su UMa-type stars observed by the authors. The evolution of superbursts from the stars NY Ser, V725 Aql, and Var73 Dra is described. Observational data are presented on the classical nova V Per, a star whose period lies right in the middle of the period gap but whose status (magnetic or nonmagnetic) has still unclear.

Discovery of a bright microlensing event with planetary features towards the Taurus region: a super-Earth planet

The transient event labeled as TCP J05074264+2447555 recently discovered towards the Taurus region was quickly recognized to be an ongoing microlensing event on a source located at distance of only

Spectroscopic study of the polar BS Tri

700-800

Superoutburst of a New Sub-Period-Minimum Dwarf Nova CSS130418 in Hercules

pc from Earth. Here, we show that observations with high sampling rate close to the time of maximum magnification revealed features that imply the presence of a binary lens system with very low mass ratio components. We present a complete description of the binary lens system which hosts an Earth-like planet with most likely mass of

Outbursts of selected dwarf novas and postnovas

9.2\pm 6.6

Accretion disk of the cataclysmic variable IY UMa in quiescence and its active state

M