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Results of the first multicolor photometric observations of the unusual dwarf nova V2466 Cygni during its 2003 and 2019 superoutbursts are presented. The total amplitude of the 2019 superoutburst in the $$R_{c}$$ band is 7.4 magnitudes. A single rebrightening was observed at the end of the 2019 superoutburst. While analyzing the $$O-C$$ diagram for the superhumps, we identified pronounced stages A, B, and C corresponding to the evolution of their period. The mean superhump period is $$P=0\overset{\textrm{d}}{.}08143(3)$$ for both superoutbursts; the superhump period derivative is $$P_{\textrm{dot}}=10.4(1.4)\times 10^{-5}$$ in stage B. We argue for the classification of V2466 Cyg as a member of a small group of objects combining the characteristics of SU UMa and WZ Sge dwarf novae and propose an explanation for the evolutionary status of these objects. As an additional result, we have discovered and studied 20 new variable stars in the neighborhoods of V2466 Cyg.

The new stage of work on digitizing the astronomical plates of the Sternberg Astronomical Institute’s collection and searching for new variable stars using the digitized photographic plates includes a considerable improvement of the automated search techniques for objects with variable brightnesses. In particular, the technique for taking into account the non-linear response of the photographic light detector has been improved. Applying the improved techniques to 182 digitized images of a 10° × 10° field centered at SA9, obtained from scanning photographic plates taken with the Sternberg Astronomical Institute 40-cm astrograph, has enabled the discover and study of 77 new variable stars (MDV 519–595). These include 3 Cepheids, 2 probable BY Draconis stars, 65 eclipsing binaries, 3RR Lyrae stars, 1 high-amplitude δ Scuti star (HADS), and 3 irregular variables. Special CCD observations have confirmed the presence of brightness variations in 7 of the 77 variables that were initially considered uncertain.

This is a study of the cataclysmic variable HS 0218 + 3229. An analysis of 2000 CCD and 200 photographic observations of this close binary system from 1963-2010 reveals two outbursts (in 1980 and 2007) with amplitudes of about 4m in the pg and V bands. This variable has been classified as a UGSS-type dwarf nova with rare, symmetric outbursts, which are typical of “inside-out” outbursts. The orbital period is found with greater accuracy to be 0d.2973559, during which a double wave is observed owing to the ellipsoidal shape of the secondary component— a class K5V star. The phase light curves and color index curves are introduced and explained, and an interpretation of the position of the object in two-color diagrams is provided. A difference in the orbital light curves before and after the outbursts is detected, and some physical characteristics of this close binary system are determined.

We have obtained data on various brightness states of the polar MT Dra over five years of observations, including the first multicolor photometry for this close binary. We confirm the known orbital period, which has remained constant over 17 years, which is unusual for cataclysmic binaries. Our observations in October 2006 demonstrated a transition of the polar to its low brightness state within one day.

Photometric measurements are prone to systematic errors presenting a challenge to low-amplitude variability detection. In search for a general-purpose variability detection technique able to recover a broad range of variability types including currently unknown ones, we test 18 statistical characteristics quantifying scatter and/or correlation between brightness measurements. We compare their performance in identifying variable objects in seven time series data sets obtained with telescopes ranging in size from a telephoto lens to 1m-class and probing variability on time-scales from minutes to decades. The test data sets together include lightcurves of 127539 objects, among them 1251 variable stars of various types and represent a range of observing conditions often found in ground-based variability surveys. The real data are complemented by simulations. We propose a combination of two indices that together recover a broad range of variability types from photometric data characterized by a wide variety of sampling patterns, photometric accuracies, and percentages of outlier measurements. The first index is the interquartile range (IQR) of magnitude measurements, sensitive to variability irrespective of a time-scale and resistant to outliers. It can be complemented by the ratio of the lightcurve variance to the mean square successive difference, 1/h, which is efficient in detecting variability on time-scales longer than the typical time interval between observations. Variable objects have larger 1/h and/or IQR values than non-variable objects of similar brightness. Another approach to variability detection is to combine many variability indices using principal component analysis. We present 124 previously unknown variable stars found in the test data., Comment: 29 pages, 8 figures, 7 tables; accepted to MNRAS; for additional plots, see http://scan.sai.msu.ru/~kirx/var_idx_paper/

Continuing the project described by Kato et al. (2009, PASJ, 61, S395), we collected times of superhump maxima for 128 SUUMa-type dwarf novae observed mainly during the 2015-2016 season and characterized these objects. The data have improved the distribution of orbital periods, the relation between the orbital period and the variation of superhumps, and the relation between period variations and the rebrightening type in WZSge-type objects. Coupled with new measurements of mass ratios using growing stages of superhumps, we now have a clearer and statistically greatly improved evolutionary path near the terminal stage of evolution of cataclysmic variables. Three objects (V452 Cas, KK Tel, and ASASSN-15cl) appear to have slowly growing superhumps, which is proposed to reflect the slow growth of the 3 : 1 resonance near the stability border. ASASSN-15sl, ASASSN-15ux, SDSSJ074859.55+312512.6, and CRTS J200331.3-284941 are newly identified eclipsing SUUMa-type (or WZ Sge-type) dwarf novae. ASASSN- 15cy has a short (0.050 d) superhump period and appears to belong to EI Psc-type objects with compact secondaries having an evolved core. ASASSN-15gn, ASASSN- 15hn, ASASSN-15kh, and ASASSN-16bu are candidate period bouncers with superhump periods longer than 0.06 d. We have newly obtained superhump periods for 79 objects and 13 orbital periods, including periods from early superhumps. In order that future observations will be more astrophysically beneficial and rewarding to observers, we propose guidelines on how to organize observations of various superoutbursts., This work was supported by the Grant-in-Aid “Initiative for High-Dimensional Data-Driven Science through Deepening of Sparse Modeling” (25120007) from the Ministry of Education, Culture, Sports, Science and Technology (MEXT) of Japan.

The photometric elements of the eclipsing binary NSV 18773 (HD 99898) have been determined for the first time by analyzing its V-and I-band light curves from the ASAS-2 and ASAS-3 catalogs. Based on these elements and using other published spectroscopic and photometric data, we constructed a consistent system of geometrical and physical parameters for the system that consists of two stars (M 1 = 20M ⊙, Sp1=B0V, R 1 = 5.0R ⊙ and M 2 = 14M ⊙, Sp2 = B1V, R 2 = 6.5R ⊙) in elliptical orbits (P = 5 . d 049, e = 0.365, a = 40.1R ⊙). The distance to the system is d = 3.3 kpc, the interstellar extinction is A V = 2 . 0, and the age is t = 2.8 × 106 yr. NSV 18773 is a visual binary with components V A = 9 . 9 and V B = 10 . 3 separated by 0 . " 8. The third light (L 3 = 0.61) that we found by analyzing the light curves shows that the eclipsing binary is the system’s fainter component B. We confirmed the rapid apsidal motion of the star detected by Otero and Wils (2006) and refined its observed period: U obs = 150 ± 6 yr. Our photometric elements and physical parameters allowed the apsidal parameter $$\bar k_2^{obs} = 0.0135(14)$$ , which reflects the density distribution along the radii of the component stars, to be determined. Within the error limits, the derived parameter agrees with its theoretically expected value, $$\bar k_2^{th} = 0.0119(8)$$ , from current evolutionary models of stars of the corresponding masses and ages.

A total of 1095 magnitude estimates for the long‐period classical Cepheid GY Sge (P = 51 days), derived from the photographic plate collections of Harvard College Observatory, Sonneberg Observatory, and Sternberg Astronomical Institute, were combined with 48 new radial velocity measures obtained using the correlation spectrometer on the 1 m reflector of the Crimean Astrophysical Observatory. The data, in combination with published photometry (including observations from the All Sky Automated Survey 3) and radial velocity measurements, cover a time baseline spanning 116 years. The resulting O - C data display evolutionary changes in the period of GY Sge amounting to + 203 ± 27 s yr−1, a value in good agreement with theoretical predictions for a star in the third crossing of the instability strip. Large cyclical drifts with durations of ~23,000 days superposed on the parabolic evolutionary trend in the O - C data exhibit the positive signature of random fluctuations in pulsation period, of magnitude similar to what is found in other pulsating stars of similar period.

We present the discovery and the first investigation of the new dwarf nova Var 73 Dra. We carried out monitoring and time-resolved CCD observations in 2001 August-October and detected several normal outbursts with a recurrence time of about 7-8 days and one slightly brighter superoutburst with a "plateau" phase that lasted 13 days. Our photometry during the superoutburst clearly shows the presence of superhumps with the period 0.0954 (0:0001) day (although the one-day alias period, 0.1053 d, could not be ruled out). So, the observed features allow us to classify Var 73 Dra as a new SU UMa-type dwarf nova within the well-known gap of orbital period distribution of cataclysmic variables.

Extensive discoveries of variable stars in ground-based photometric surveys and in observations from space missions that provide unprecedented accuracy demonstrate that, till the most recent time, we knew only a tiny fraction of all detectable variable stars of our Galaxy. As a result, our knowledge on stellar variability types, related physical processes, variable-star statistics turn out to be based on an unrepresentative sample and are expected to be radically revised in the near future. The flow of new discoveries results in quite difficult problems for catalogs of variable stars, making it impossible to proceed in their compilation in the traditional way. Regretfully, automatic solutions are still not completely satisfying. Though not able to suggest a perfect way out, we present our vision of the future of variable-star research.

We present the analysis of BV photometry of BY Cam based on observations carried out in Crimea. The long QPOs in brightness were detected in both high and low brightness states. Their typical periods, equal to 6, 12 and 24 m, are found. The amplitude of the QPOs depends on the phase of P beat.

V664 Cas is the central star of the planetary nebula HFG 1 discovered in 1982 (Heckathorn et al.). The star was observed using UBV photometer during J D=24,49245-24,49257. We found the brightness variations V=13. m 46-14. m 70, B=13. m 81-14. m 94, U=12. m 97-14. m 16. We also investigated this star on each of 265 plates obtained by using the 40-cm astrograph and equatorial camera of Sternberg Astronomical Institute in J D=24,14715-24,48627. V664 Cas showed the brightness variations 13. m 8-15. m l (see Fig.l). This data were combined with the photoelectric B-observations. They revealed a more precise value of the orbital period to be P orb = 0.d581647± 0.d000001. The period seems to be very stable.

The star was investigated on 224 plates taken from JD 2441893 to JD 2448092. The data reduction revealed the existence of regular light variations with a 148.d3 period. The light curve is presented in the Fig.l. It is clear that a sine-like modulation with superposed more rapid light variations with amplitude close to l. m are present.

A sequence similar to Hertzsprung progression was revealed for Cepheid radial-velocity curves. We separated two pulsation modes for six double-mode Cepheids and determined radii for five of them. Several new spectroscopic-binary Cepheids were discovered; we present new preliminary orbital periods for V496 Aql, VY Cyg, and V1334 Cyg, in a combined table of our results on Cepheid binarity.

We present the analysis of BV photometry of BY Cam based on observations carried out in Crimea. The long QPOs in brightness were detected in both high and low brightness states. Their typical periods, equal to 6, 12 and 24 m, are found. The amplitude of the QPOs depends on the phase of Pbeat.