Mv Lyr: Transition from Low to High Brightness State

We present results of multicolour photometry of the nova-like binary MV Lyr in the years 2002–2003, corresponding to the transition of the star from its low (V = 17.8) to high (V = 12.3) brightness state. The transition lasted at most 200 days. During the first ∼50 days MV Lyr brightened at the rate 0.06 mag/day, and during the next ∼150 days at the rate 0.01 mag/day. The brightening was accompanied by a blue shift from 0.45 to 0.05 in V−R, interpreted as an increase of the accretion disk contribution to the total light. During the transition MV Lyr displayed well-known ‘quasi-orbital’ light variations and fast quasi-periodic oscillations with a typical time scale of tens of minutes.     

Spectral and photometric studies of polar CRTS CSS 130604 J 215427+155714

We present the results of spectroscopic and photometric studies of a new polar CRTS CSS130604 J 215427+155714, conducted at the telescopes of the SAO RAS. Analysis of the photometric series of observations allowed to clarify the orbital period of the system, P _o = 0_. ^d 0672879 (±0.0000003). We build radial velocity curves and trace the intensity variations in the Hβ and H_γ hydrogen lines and He II λ 4686 ?A ionized heliumline. Based on the Hβ and He II lines we build Doppler maps. It is shown that the line formation region is localized near the Lagrange point. The following parameter estimates of the system are obtained:M ₁ = 0.83 ± 0.10M _⊙, M ₂ = 0.15 ± 0.01M _⊙, q = M ₂/M ₁ = 0.18 ± 0.03, i = 53? ± 5?. Based on the results of spectral, photometric and previously published polarimetric observations the possible geometric model of the system is discussed.     

Outbursts of selected dwarf novas and postnovas

Observations are presented of selected cataclysmic variables (the dwarf novas V1504 Cyg and GO Com and the postnovas Q Cyg, V446 Her, and DI Lac) carried out at the Crimean Astrophysical Observatory and the Crimean Laboratory of the Sternberg Astronomical Institute in 1995–2007. The outburst parameters and the behavior of these objects on the “magnitude (V)-color (V-R)” diagram are described. The tracks of postnova outbursts on this diagram are similar to the dwarf-nova behavior. On average, all the studied systems show a break on the “brightness-color” dependence. The color V-R before the break increases more weakly than after it or does not increase at all.     

Observations of the Deeply Eclipsing Dwarf Nova Gy Cnc

We present photometric measurements of the eclipsing dwarf nova and X-ray source GY Cnc. The observations were collected during outbursts and in quiescence. The investigation of plates from the Sonneberg archive showed that the mean outburst interval is about 210–270 days, that the outburst is very fast, and lasts for about 5 days.     

CCD Photometry of the Cataclysmic Variable SW Ursae Majoris at a Late Stage of the 2000 Superoutburst

We carried out CCD photometry of the cataclysmic variable SW UMa during the decay of the recent (February-April 2000) superoutburst at the Crimean Astrophysical Observatory, Crimean Laboratory of the Shternberg State Astronomical Institute (SSAI), and at the student observatory in Moscow at Vorob'ev Hills (SSAI, Moscow State University). A detailed picture of the late evolution of superhumps was obtained, an analysis of which yielded a period of 0.1197 days for the late superhumps and enabled us to conclude that their period increases during a superoutburst. Such behavior of superhumps is reproduced from one superoutburst to another and occurs at the same rate. Our observations are also consistsent with the existence of 15.9-min oscillations, at least during several cycles.     

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 and spectral studies of the eclipsing polar CRTS CSS081231 J071126+440405

We present the results of the study of the eclipsing polar CRTS CSS081231 J071126+440405. Photometric observations allowed us to refine the orbital period of the system \(P_ \circ = 0_ \cdot ^d 0.08137673\). Considerable changes in the appearance of the object’s spectra have occurred over the period of September 20–21, 2001: the slope of the continuum changed from “red” to “blue”, and the variability of the line profiles over the duration of the orbital period has also changed. Doppler maps have shown a shift of the emission line-forming region along the accretion stream closer to the white dwarf. We measured the duration of the eclipse of the system and imposed constraints on the inclination angle \(78_ \cdot ^ \circ 7 < i < 79_ \cdot ^ \circ 3\). The derived radial velocity amplitude was used to obtain the basic parameters of the system: M₁ = 0.86 ± 0.08M_⊙, M₂ = 0.18 ± 0.02 M_⊙, q = 0.21 ± 0.01, R_L2 = 0.20 ± 0.03 R_⊙, A = 0.80 ± 0.03 R_⊙. The spectra of the object exhibit cyclotron harmonics. Their comparison with model spectra allowed us to determine the parameters of the accretion column: B = 31–34 MG, T_e = 10–12 keV, θ = 80–90°, and Λ = 10⁵.     

Astronomical aspects of building a system for detecting and monitoring hazardous space objects

In order to meet the practical priority of the mass detection of hazardous celestial bodies (HCBs) during the creation of a system to counteract space hazards (asteroids, comet hazards and space debris), we need clear technical requirements for the detection instruments designed (created). Specially targeted astronomical investigations into the basic properties of the HCB ensemble were conducted to specify such requirements (limitations). The paper presents these findings. As to asteroid and comet hazards, quantitative limitations on the HCB size (50 m) have been introduced and quantitative definitions of threatening and collisional HCB orbits have been proposed for the first time. It is shown that at a lead time of 30 days, it is necessary to detect HCBs at distances of about 1 AU, which corresponds to a telescope’s resolving power of V ～ 23 ^m . This entails the necessity to design wide-angle large-aperture telescopes. For detecting and monitoring space debris objects and meteoroids in the near-earth space at a time scale of about several days, faster instruments with smaller apertures but larger vision fields are efficient. An example is given of a basic design of a space-based system that takes into account the astronomical requirements discussed.     

Nova Cygni 1975 (V1500 Cyg) in 2000–2009 and the nature of its synodic period

Multicolor photometric data are presented for the asynchronous polar V1500 Cyg during 2000–2009, i.e., 23–35 years after its outburst. Some examples of individual light curves of the system are shown. An analysis of these reveals large variations in its brightness and color with the phase of the orbital period owing to a “reflection effect” caused by reradiation from the side of the red dwarf facing the hot white dwarf and heated by its hard ultraviolet radiation. The variations in the O-C residuals and in the maximum intensity with the phase of the synodic period are illustrated. It is found that the amplitude A of the orbital fluctuations increases in proportion to the intensity I at a rate dA/dI=0.64. This behavior of V1500 Cyg is most likely caused by periodic shading of the illuminated part of the red dwarf, where the degree of shading depends on the phase of the synodic cycle.