Since 2017, the Institute of Astronomy of the Russian Academy of Sciences (Russia) and the Institute of Geophysics and Astronomy (Cuba) have been implementing a joint international project with the aim of building a distributed global optical telescope network. The first 20 cm robotic telescope of this network has been operated since 2021 in Havana. The construction of the second 50 cm telescope has been underway since 2023 and it is expected to be finished and installed in 2025 near Kislovodsk (Russia). According to the current plan, a third 1 m telescope will be installed in 2030 at Valle de Picadura (Cuba). In the present contribution, the main parameters and scientific equipment of the 50 cm telescope are described and its role in the Russian-Cuban distributed global telescope network is discussed.

Beginning of operation of the first Russian–Cuban Observatory telescope, a wide-field 20-cm robotic telescope installed at the observational site optical station in Havana, Republic of Cuba, is reported. The general view of the telescope is shown and attached equipment is described. The “first light” obtained using a 20-cm telescope is demonstrated and briefly discussed. Multi-task observational projects supposed to be conducted using mentioned RCO telescope are described. Russian–Cuban complexication scheme is described and some of its features are briefly discussed.

The prolongation of a project to create an optical observation station in the frame of the Russian-Cuban Observatory (RCO) is described. The paper reports some important elements regarding the creation of the RCO optical station layout in Havana. The equipment and some scientific observation projects planned to be done using the layout are discussed. The main instrument of the optical station layout is a wide-field 20 cm robotic telescope. The observational project program includes both fundamental and applied tasks. It is argued that the layout itself could be used as an independent observatory because of its ability to solve universal observational tasks and to serve as a real segment of a global optical telescope network.

We describe here the formulation of our search for additional bodies in fifteen short period eclipsing binary stars and some results obtained by now. We intended to use two methods: transits across the surface of one or both stars (in order to detect planets) in the binary and a timing of eclipses of central binary stars (that can indicate the presence of a stellar mass body in the system). Observations were carried out using ground based photometry with 50-60 cm telescopes in 2013-2017. Until now no transits had been detected in our data. But at the same time we found several candidates for additional bodies in four systems. Further data processing will be performed.

We homogeneously analyse similar to 3.2 x 10(5) photometric measurements for similar to 1100 transit light curves belonging to 17 exoplanet hosts. The photometric data cover 16 years (2004-2019) and include amateur and professional observations. Old archival light curves were reprocessed using up-to-date exoplanetary parameters and empirically debiased limb-darkening models. We also derive self-consistent transit and radial-velocity fits for 13 targets. We confirm the non-linear transit timing variation (TTV) trend in the WASP-12 data at a high significance, and with a consistent magnitude. However, Doppler data reveal hints of a radial acceleration of about -7.5 +/- 2.2 ms(-1) yr(-1), indicating the presence of unseen distant companions, and suggesting that roughly 10 per cent of the observed TTV was induced via the light-travel (or Roemer) effect. For WASP-4, a similar TTV trend suspected after the recent TESS observations appears controversial and model dependent. It is not supported by our homogeneous TTV sample, including 10 ground-based EXPANSION light curves obtained in 2018 simultaneously with TESS. Even if the TTV trend itself does exist in WASP-4, its magnitude and tidal nature are uncertain. Doppler data cannot entirely rule out the Roemer effect induced by possible distant companions.

This study aims timing the eclipses of the short period low mass binary star AB And. The times of minima are taken from the literature and from our observations in October 2013 (22 times of minima) and in August 2014 (23 times of minima). We find and discuss an inaccuracy in the determination of the types of minima in the previous investigation by Li et al. (2014). We study the secular evolution of the central binary’s orbital period and the possibility of the existence of third and fourth companions in the system.

This study aims timing the eclipses of the short period low mass binary star AB And. The times of minima are taken from the literature and from our observations in October 2013 (22 times of minima) and in August 2014 (23 times of minima). We find and discuss an inaccuracy in the determination of the types of minima in the previous investigation by Li et al. (2014). We study the secular evolution of the central binary's orbital period and the possibility of the existence of third and fourth companions in the system. (C) 2017 Elsevier B.V. All rights reserved.

AR CrB is a short-period low-mass eclipsing binary.We conducted photometric observations of the system in 2013, 2014, 2016, 2017, and obtained times of its light curves minima.The timing of eclipses (our times of minima combined with data from the literature) shows that the orbital period of AR CrB could possess periodical variations that can be explained by the gravitational influence of a third companion in a highly eccentric orbit around the central binary.

A short period eclipsing binary star CV Boo is tested for the possible existence of additional bodies in the system with a help of the light equation method. We use data on the moments of minima from the literature as well as from our observations during 2014 May–July. A variation of the CV Boo’s orbital period is found with a period of \({\approx}75~\mbox{d}\). This variation can be explained by the influence of a third star with a mass of \({\approx}0.4~\mbox{M}_{\odot}\) in an eccentric orbit with \(e\approx0.9\). A possibility that the orbital period changes on long time scales is discussed. The suggested tertiary companion is near the chaotic zone around the central binary, so CV Boo represents an interesting example to test its dynamical evolution. A list of 14 minima moments of the binary obtained from our observations is presented.

We analyze a set of moments of minima of eclipsing variable V0873 Per. V0873 Per is a short-period low-mass binary star. Data about moments of minima of V0873 Per were taken from the literature and our observations during 2013–2014. Our aim is to test the system on existence of new bodies using timing of minima of eclipses. We found a periodic variation of orbital period of V0873 Per. This variation can be explained by the gravitational influence of a third companion on the central binary star. The mass of the third body candidate is \(\approx 0.2~M_{\odot}\), and its orbital period is \(\approx300~\mbox{days}\). The paper also includes a table with moments of minima calculated from our observations, which can be used in future investigations of V0873 Per.

CCD-photometry of three Jupiter Trojan asteroids were carried out to study their opposition effect. We obtained well-sampled magnitude-phase curves for (588) Achilles, (884) Priamus, and (1143) Odysseus in the maximal attainable phase angle range down to 0.1-0.2 degrees. The magnitude-phase relations have a linear behavior in all observed range of phase angles and do not show any non-linear opposition brightening. We have not found any confident differences between phase slopes measured in B, V and R bands. The values of the measured phase slopes of Trojans are different from available data for Centaurs. They are within the range of phase slopes measured for some low-albedo main belt asteroids, also exhibit a linear behavior down to small phase angles. An absence of non-linear opposition brightening puts constraints on the surface properties of the studied objects, assuming very dark surfaces where single scattering plays dominating role.We also determined the rotation periods, amplitudes, the values of color indexes B-V and V-R, and the absolute magnitudes of these asteroids. (C) 2011 Elsevier Inc. All rights reserved.

We have determined the realistic seeing of the 1.5-m AZT-22 telescope of the Mt. Maidanak Observatory (Astronomical Institute, Uzbek Academy of Sciences) using more than 20 000 CCD frames with stellar images in the UBV RI bands acquired in 1996–2005: ε = 1.065″ in the V band. The characteristic seeing reduced to unit air mass, ε med V (M(z) = 1), is 0.945″. We derived color equations for the CCD detectors used with the telescope. Atmospheric-extinction coefficients in different photometric bands were also determined. The mean V -band atmospheric extinction is 0.20 m ± 0.04 m . The time needed for the conditions to settle, in the free atmosphere as well as inside the telescope dome, is 2–2.5 hours after the end of astronomical twilight. For nights with ε med V > 0.9″, we find a persistent difference between the seeing found at this telescope and measured simultaneously with a differential image motion monitor, amounting to ∼0.1 m .

Since 1997, BL Lacertae has undergone a phase of high optical activity, with the occurrence of several prominent outbursts. Starting from 1999, the Whole Earth Blazar Telescope (WEBT) consortium has organized various multifrequency campaigns on this blazar, collecting tens of thousands of data points. One of the main issues in the study of this huge dataset has been the search for correlations between the optical and radio flux variations, and for possible periodicities in the light curves. The analysis of the data assembled during the first four campaigns (comprising also archival data to cover the period 1968-2003) revealed a fair optical-radio correlation in 1994-2003, with a delay of the hard radio events of ~100 days. Moreover, various statistical methods suggested the existence of a radio periodicity of ~8 years. In 2004 the WEBT started a new campaign to extend the dataset to the most recent observing seasons, in order to possibly confirm and better understand the previous results. In this campaign we have collected and assembled about 11000 new optical observations from twenty telescopes, plus near-IR and radio data at various frequencies. Here, we perform a correlation analysis on the long-term R-band and radio light curves. In general, we confirm the ~100-day delay of the hard radio events with respect to the optical ones, even if longer (~200-300 days) time lags are also found in particular periods. The radio quasi-periodicity is confirmed too, but the "period" seems to progressively lengthen from 7.4 to 9.3 years in the last three cycles. The optical and radio behaviour in the last forty years suggests a scenario where geometric effects play a major role. In particular, the alternation of enhanced and suppressed optical activity (accompanied by hard and soft radio events, respectively) can

PHOTOMETRY OF ASTEROIDS: DETECTION OF THE YORP EFFECT. Yu. N. Krugly, N. M. Gaftonyuk, J. Durech, D. Vokrouhlicky, M. Kaasalainen, V. G. Shevchenko, M. A. Ibrahimov, A. L. Marshalkina, V.V. Rumyantsev, I. E. Molotov. Institute of Astronomy of Kharkiv National University, Kharkiv 61022, Sumska str. 35, Ukraine, krugly@astron.kharkov.ua. SRI "Crimean Astrophysical Observatory", Crimea, Ukraine. Astronomical Institute, Charles University, Prague, Czech Republic. Department of Mathematic and Statistic, Rolf Nevanlinna Institute, University of Helsinki, Finland. 5 Ulugh Beg Astronomical Institute, Uzbek Academy of Sciences, Tashkent, Uzbekistan. Keldysh Institute of Applied Mathematics, Moscow, Russia

Aims. Asteroid (1862) Apollo is one of two asteroids in which the YORP effect was detected. We carried out new photometric observations of Apollo in April 2007 to enlarge the time line and to derive a more precise shape and spin state model. We also observed another YORP-candidate, asteroid (25143) Itokawa, in December 2006 and January 2007 to obtain a longer time line. An estimation of the YORP strength on Itokawa based on its precise shape model from the Hayabusa mission predicted the deceleration to be already observable during the 2007 apparition.Methods. We used the lightcurve inversion method to model the shape and spin state of Apollo. For Itokawa, the shape and pole direction are known to a high degree of accuracy from the Hayabusa mission, so we used a modified version of lightcurve inversion with only two free parameters -the rotation period and its linear change in time.Results. The new model of Apollo confirms earlier results. The observed acceleration of Apollo's rotation rate is (5.5 +/- 1.2) x 10(-8) rad d(-2), which is in agreement with the theoretically predicted value. For Itokawa, the theoretical YORP value is sensitive to the resolution of the shape model and lies in the range from -2 to -3 x 10(-7) rad d(-2). This is inconsistent with results of lightcurve inversion that place an upper limit to the change of Itokawa's rotation rate similar to 1.5 x 10(-7) rad d(-2).

Context. The quasar 3C 279 is among the most extreme blazars in terms of luminosity and variability of flux at all wavebands. Its variations in flux and polarization are quite complex and therefore require intensive monitoring observations at multiple wavebands to characterise and interpret the observed changes.Aims. In this paper, we present radio-to-optical data taken by the WEBT, supplemented by our VLBA and RXTE observations, of 3C 279. Our goal is to use this extensive database to draw inferences regarding the physics of the relativistic jet.Methods. We assemble multifrequency light curves with data from 30 ground-based observatories and the space-based instruments SWIFT (UVOT) and RXTE, along with linear polarization vs. time in the optical R band. In addition, we present a sequence of 22 images (with polarization vectors) at 43 GHz at resolution 0.15 milliarcsec, obtained with the VLBA. We analyse the light curves and polarization, as well as the spectral energy distributions at different epochs, corresponding to different brightness states.Results. We find that the IR-optical-UV continuum spectrum of the variable component corresponds to a power law with a constant slope of -1.6, while in the 2.4-10 keV X-ray band it varies in slope from -1.1 to -1.6. The steepest X- ray spectrum occurs at a flux minimum. During a decline in flux from maximum in late 2006, the optical and 43 GHz core polarization vectors rotate by similar to 300 degrees.Conclusions. The continuum spectrum agrees with steady injection of relativistic electrons with a power-law energy distribution of slope -3.2 that is steepened to -4.2 at high energies by radiative losses. The X- ray emission at flux minimum comes most likely from a new component that starts in an upstream section of the jet where inverse Compton scattering of seed photons from outside the jet is important. The rotation of the polarization vector implies that the jet contains a helical magnetic field that extends similar to 20 pc past the 43 GHz core.

We present UBVRI light curves of BL Lacertae from May 2000 to January 2001, obtained by 24 telescopes in 11 countries. More than 15 000 observations were performed in that period, which was the extension of the Whole Earth Blazar Telescope (WEBT) campaign originally planned for July–August 2000. The exceptional sampling reached allows one to follow the flux behaviour in fine detail. Two different phases can be distinguished in the light curves: a first, relatively low-brightness phase is followed by an outburst phase, after a more than 1 mag brightening in a few weeks. Both the time duration (about 100 d) and the variation amplitude (roughly 0.9 mag) are similar in the two phases. Rapid flux oscillations are present all the time, involving variations up to a few tenths of mag on hour time scales, and witnessing an intense intraday activity of this source. In particular, a half-mag brightness decrease in about 7 h was detected on August 8–9, 2000, immediately followed by a ∼0.4 mag brightening in 1.7 h. Colour indexes have been derived by coupling the highest precision B and R data taken by the same instrument within 20 min and after subtracting the host galaxy contribution from the fluxes. The 620 indexes obtained show that the optical spectrum is weakly sensitive to the long-term trend, while it strictly follows the short-term flux behaviour, becoming bluer when the brightness increases. Thus, spectral changes are not related to the host galaxy contribution, but they are an intrinsic feature of fast flares. We suggest that the achromatic mechanism causing the long-term flux base-level modulation can be envisaged in a variation of the relativistic Doppler beaming factor, and that this variation is likely due to a change of the viewing angle. Discrete correlation function (DCF) analysis reveals the existence of a characteristic time scale of variability of ∼7 h in the light curve of the core WEBT campaign, while no measurable time delay between variations in the B and R bands is found.

The Angstrom Project is undertaking an optical survey of stellar microlensing events across the bulge region of the Andromeda galaxy (M31) using a distributed network of 2 m class telescopes. The Angstrom Project Alert System (APAS) has been developed to identify candidate microlensing and transient events in real time, using data from the Liverpool and Faulkes North robotic telescopes. This is the first time that real-time microlensing discovery has been attempted outside of the Milky Way and its satellite galaxies. The APAS is designed to enable follow-up studies of M31 microlensing systems, including searches for gas giant planets in M31. Here we describe the APAS, and we present a few example light curves obtained during its commissioning phase that clearly demonstrate its real-time capability to identify microlensing candidates as well as other transient sources.

Context. Being dominated by non-thermal emission from aligned relativistic jets, blazars allow us to elucidate the physics of extragalactic jets, and, ultimately, how the energy is extracted from the central black hole in radio-loud active galactic nuclei. Aims. Crucial information is provided by broad-band spectral energy distributions (SEDs), their trends with luminosity and correlated multi-frequency variability. With this study we plan to obtain a database of contemporaneous radio-to-optical spectra of a sample of blazars, which are and will be observed by current and future high-energy satellites. Methods. Since December 2004 we are performing a monthly multi-frequency radio monitoring of a sample of 35 blazars at the antennas in Medicina and Noto. Contemporaneous near-IR and optical observations for all our observing epochs are organised. Results. Until June 2006 about 4000 radio measurements and 5500 near-IR and optical measurements were obtained. Most of the sources show significant variability in all observing bands. Here we present the multi-frequency data acquired during the first eighteen months of the project, and construct the SEDs for the best-sampled sources.