How black holes accrete surrounding matter is a fundamental yet unsolved question in astrophysics. It is generally believed that matter is absorbed into black holes via accretion disks, the state of which depends primarily on the mass-accretion rate. When this rate approaches the critical rate (the Eddington limit), thermal instability is supposed to occur in the inner disk, causing repetitive patterns of large-amplitude X-ray variability (oscillations) on timescales of minutes to hours. In fact, such oscillations have been observed only in sources with a high mass-accretion rate, such as GRS 1915+105 (refs 2, 3). These large-amplitude, relatively slow timescale, phenomena are thought to have physical origins distinct from those of X-ray or optical variations with small amplitudes and fast timescales (less than about 10 seconds) often observed in other black-hole binaries-for example, XTE J1118+480 (ref. 4) and GX 339-4 (ref. 5). Here we report an extensive multi-colour optical photometric data set of V404 Cygni, an X-ray transient source containing a black hole of nine solar masses (and a companion star) at a distance of 2.4 kiloparsecs (ref. 8). Our data show that optical oscillations on timescales of 100 seconds to 2.5 hours can occur at mass-accretion rates more than ten times lower than previously thought. This suggests that the accretion rate is not the critical parameter for inducing inner-disk instabilities. Instead, we propose that a long orbital period is a key condition for these large-amplitude oscillations, because the outer part of the large disk in binaries with long orbital periods will have surface densities too low to maintain sustained mass accretion to the inner part of the disk. The lack of sustained accretion--not the actual rate--would then be the critical factor causing large-amplitude oscillations in long-period systems.

Кафедра астрономии и Астрономическая обсерватория Одесского национального университета Описан алгоритм средневзвешенной звезды сравнения при фотометрии с использованием ПЗС-камер. Приведены формулы самосогласованного определения весов и среднеквадратичного разброса звезд сравнения и средневзвешенной звезды. Данный алгоритм использования искуственной звезды сравнения, вместо одной контрольной звезды позволяет улучшить точность определения звезды сравнения до десятков процентов и иногда раз. Описана компьютерная программа Multi-Column View (MCV), которая дополнительно позволяет проводить визуализацию, удаление или интерполяцию данных перед использованием алгоритма средневзвешенной звезды сравнения. АЛГОРИТМ ШТУЧНОЇ ЗОРI ПОРIВНЯННЯ ДЛЯ ПЗС ФОТОМЕТРIЇ, Андронов I.Л., Бакланов О.В. Описано алгоритм середньозваженої зорi порiвняння при фотометрии з використанням ПЗС-камер. Приведенi формули самоузгодженого визначення ваги та середньоквадратичного розсiяння зорь порiвняння i середньозваженої зорi. Цей алгоритм використання штучної зорi порiвняння замiсть однiєї контрольної зорi дозволяє покращити точнiсть визначення зорi порiвняння до десяткiв вiдсоткiв и iнодi разiв. Описана комп'ютерна программа Multi-Column View (MCV), що додатково дозволяє проводити вiзуалiзацiю, вилучення або iнтерполяцiю даних перед використанням алгоритму середньозваженої зорi порiвняння.

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Results of a CCD study of the variability of the unique magnetic cataclysmic variable V1432 Aql from the Astronomical Observatory of Mallorca are presented. The "multi-comparison star" method had been applied for better accuracy estimates. The linear ephemeris based on 76 timings of orbital eclipses for 1993-2004 is HJD min = 2 451 492.09876(14) + 0.140235812(12) · E. For the wide minima due to the spin variability, the quadratic ephemeris HJD spin = 2 449 638.327427(74) + 0.14062831(23) · E − 7.81(11) × 10 −10 E 2 was determined. The rate of the spin-up of the white dwarf corresponds to the synchronization time-scale determined to be (96.7 ± 1.5) years, in an agreement with theoretical model of the accretion torque. A third type of minima was detected that occur with the spin period. It was interpreted as indicating presence of the second accretion column. For adopted values of mass M 1 = 0.9 M and M 2 = 0.3 M , the estimated accretion rate is ∼7 × 10 −10 M /yr. Further multi-colour monitoring is needed to study of late stages of the "spin-orbital" synchronization and periodic changes of the accretion geometry caused by "idling" of the white dwarf.

Continuing the project described by Kato et al. (2009), we collected times of superhump maxima for 128 SU UMa-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, the relation between period variations and the rebrightening type in WZ Sge-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, 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, SDSS J074859.55+312512.6 and CRTS J200331.3−284941 are newly identified eclipsing SU UMa-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 the future observations will be more astrophysically beneficial and rewarding to observers, we propose guidelines how to organize observations of various superoutbursts.