This article is focused on the analysis of observational data and improvement of orbital solutions of 8 objects. The listed objects are members of a sample of approximately 300 nearby (d < 100 pc) multiple systems compiled for long-term monitoring at the 6-meter telescope of the Special Astrophysical Observatory of the Russian Academy of Sciences. Speckle interferometric observations were carried out from 2007 to the present, which corresponds to 19 years of monitoring of the systems. Therefore, the new measurements are more numerous than or comparable to those in the literature, which makes it possible to make the observation series more complete. A long observation series made it possible to cover from 20

Based on the speckle observations of the wide double star ADS 15571 with the 6-m BTA telescope at the Special Astrophysical Observatory of the Russian Academy of Sciences in 2014, we have confirmed the existence of a close companion to component A that was previously detected from astrometric observations at the Pulkovo Observatory. An extension of the BTA observations from 2014 to 2022 has allowed 28 positions of the companion relative to the primary star to be obtained. From this series we have constructed the relative orbit of the companion and determined the sum of the masses of subsystem A ( 1.686± 0.014 M_⊙ ). A comparison of this orbit with the orbit of the photocenter of component A constructed from Pulkovo photographic observations has also allowed the mass ratio of the primary star and the companion and their individual masses to be estimated: M_Aa=(1.10± 0.07) M_⊙ and M_Ab=(0.59± 0.07) M_⊙ . Based on the estimates of the magnitude difference between the two stars of the system ADS 15571A, we have estimated the spectral types of the components: ADS 15571Aa—F8V; ADS 15571Ab—K5V–K5.5V. The speckle observations of component B have shown that it has no resolvable companions.

We present the results of a multiplicity study of T Tau-type stars in the Taurus-Auriga association. The observational data were obtained by speckle interferometry at the 6-meter telescope of the SAO RAS in 2020 and 2024. For the resolved stars, the positional parameters of the components, as well as the magnitude differences, were determined using the reference-independent power spectrum modeling method. Among the sample containing 58 bright stars ($m_{V} \leq 10$ mag), 12 binary, 5 triple and one quadruple speckle-interferometric systems were detected.

The results of seventeen years of speckle interferometric monitoring of seven objects (Chara 122Aa, GJ 3010, HIP 1987, GJ 3076, HIP 11253, HIP 11352, and HIP 14929) are presented. Observational data were obtained at the 6 m Big Telescope Alt-azimuthal Special Astrophysical Observatory of the Russian Academy of Science (BTA SAO RAS) from 2007 to the present. Analysis of previously published and new measurements made it possible to construct completely new orbits for Chara 122Aa, HIP 11253, and HIP 14929. The orbit of GJ 3076 cannot be constructed accurately due to the large influence of the weights assigned to the measurements. The resulting orbital solutions are classified based on a grading scheme suggested by W.I. Hartkopf, B.D. Mason and C.E. Worley; most orbits are "definitive" (Grade 1). The mass sums and masses of components calculated by two independent methods using Hipparcos and Gaia DR2 and DR3 parallaxes were compared for the objects under study.

We present a refined speckle-interferometric orbit of a binary system μ Cet, with the main component studied based on the analysis of photometric and spectroscopic data, obtained with the SAO RAS 6-m telescope. The object was initially classified as a giant with chemical composition anomalies. As a result of our analysis, we conclude that the star belongs to the Main Sequence, to the class of non-peculiar stars. Analysis of photometric data from the TESS mission indicates that the main component of the system belongs to the γ Dor pulsators.

We present a brief description of a joint Russian-Korean project abbreviated as EXPLANATION (EXoPLANet And Transient events InvestigatiON). The project is aimed at a massive photometric, speckle-interferometric, spectral, and radio bolometric search for non-stationary events in the Universe, as well as the study of exoplanets. The core of the project consists of several 0.07–2.5-m optical telescopes, 6-m telescope BTA and a six-hundred-meter radio telescope RATAN-600 of the Special Astrophysical Observatory of RAS (Russia), Moscow State University observatory (Russia), Kourovka Observatory (Russia), Crimean Astrophysical Observatory (Crimea), Korea Astronomy and Space Science Institute (Republic of Korea). We discuss the philosophy of the project and its instrumentation, as well as the first obtained results. In this paper we report the results related to the detection of several types of transient events and the study of exoplanets.

Over the past decades, the achievements in astronomical instrumentation have given rise to a number of novel advanced studies related to the analysis of large arrays of observational data. One of the most famous of these studies is a study of transient events in the near and far space and a search for exoplanets. The main requirements for such kinds of projects are a simultaneous coverage of the largest possible field of view with the highest possible detection limits and temporal resolution. In this study, we present a similar project aimed at creating an extensive, continuously updated survey of transient events and exoplanets. To date, the core of the project incorporates several 0.07–2.5 m optical telescopes and the 6-m BTA telescope of the Special Astrophysical Observatory of RAS (Russia), a number of other Russian observatories and the Bonhyunsan observatory of the Korea Astronomy and Space Science Institute (South Korea). Our attention is mainly focused on the description of two groups of small, wide-angle optical telescopes for primary detection. All the telescopes are originally designed for the goals of the project and may be of interest to the scientific community. A description is also given for a new, high-precision optical spectrograph for the Doppler studies of transient and exoplanet events detected within the project. We present here the philosophy, expectations and first results obtained during the first year of running the project.

The article presents new results on motion modeling and creation of ephemeris of satellites of asteroids based on observations. In previous work on the project, ephemeris of 62 satellites were built. Since then, new satellites of asteroids have been discovered and new observations have been published. The article gives the orbital parameters of four new satellites found from observations. Satellite ephemeris updates based on new observations are reported. An important and necessary characteristic of ephemeris is their accuracy. In this paper, we show how ephemeris accuracy estimates are made, and examples of estimates are given. An important circumstance has been revealed: for a large number of satellites, the accuracy of ephemeris has degraded by now to such an extent that the ephemeris have become practically unusable. There is an urgent need for new observations of satellites of asteroids.

Speckle observations of binary stars were performed in the 900–1600 nm infrared range at the 6‒m telescope using the commercially available CCD camera SWIR Snake-640 with InGaAs 640 × 512 pixels sensitive area. Peltier cooling of the sensor allows reaching –30°C temperature of the CCD. The thermal noise of the CCD remains significantly high under such temperature. That limits the speckle interferometric application of the camera to approximately 9th magnitude under moderate seeing conditions. To estimate other characteristics of the camera for interferometric application in the near-IR, we used it to measure separations, position angles and magnitude differences of some well-studied binary stars. Diffraction-limited angular resolution was achieved for each of the reconstructed images.

The results of a study on the binary HIP 18856 and construction of its orbit are presented. New observational data were obtained at the BTA of SAO RAS in 2007-2019. Earlier, Cvetkovic et al. constructed the orbit for this system. However, it is based on six measurements, which cover a small part of the orbit. The positional parameters of the ESA astrometric satellite Hipparcos published speckle interferometric data (Mason et al., Balega et al., Horch et al.) and new ones were used in this study. Based on the new orbital parameters, the mass sum was calculated and the physical parameters of the components were found. The obtained orbital and fundamental parameters were compared with the data from the study by Cvetkovic et al.. The comparison shows that the new orbital solution is better than the old one, since it fits new observational data accurately. Also based on a qualitative evaluation performed by Worley & Heintz, the new orbit was classified as "reliable", which means data cover more than half of the orbit with sufficient quantities of residuals of measurements.

We announce the discovery of GPX-1 b, a transiting brown dwarf with a mass of $19.7\pm 1.6$ $M_{\mathrm{Jup}}$ and a radius of $1.47\pm0.10$ $R_{\mathrm{Jup}}$, the first sub-stellar object discovered by the Galactic Plane eXoplanet (GPX) survey. The brown dwarf transits a moderately bright ($V$ = 12.3 mag) fast-rotating F-type star with a projected rotational velocity $v\sin{ i_*}=40\pm10$ km/s. We use the isochrone placement algorithm to characterize the host star, which has effective temperature $7000\pm200$ K, mass $1.68\pm0.10$ $M_{\mathrm{Sun}}$, radius $1.56\pm0.10$ $R_{\mathrm{Sun}}$ and approximate age $0.27_{-0.15}^{+0.09}$ Gyr. GPX-1 b has an orbital period of $\sim$1.75 d, and a transit depth of $0.90\pm0.03$ %. We describe the GPX transit detection observations, subsequent photometric and speckle-interferometric follow-up observations, and SOPHIE spectroscopic measurements, which allowed us to establish the presence of a sub-stellar object around the host star. GPX-1 was observed at 30-min integrations by TESS in Sector 18, but the data is affected by blending with a 3.4 mag brighter star 42 arcsec away. GPX-1 b is one of about two dozen transiting brown dwarfs known to date, with a mass close to the theoretical brown dwarf/gas giant planet mass transition boundary. Since GPX-1 is a moderately bright and fast-rotating star, it can be followed-up by the means of Doppler tomography.

Abstract—We present the study of the multiple system HD 52721 by means of speckle interferometry in 2019–2020 at the 6-m telescope of the SAO RAS. Formerly, HD 52721 was known as triple ( $$6.93$$ (B2V + B2V; $$P = {{1}^{{\text{d}}}}.6101570$$ ) + $$7.88$$ ; $$0_{.}^{'}65$$ ). In our work, the system is resolved as a speckle interferometric triple system, i.e., the total system multiplicity increased up to four components ( $$6.80$$ (B2Ve; $${{1}^{{\text{d}}}}.6101570$$ )+ $$8.95$$ (B9VХ, $$0_{.}^{{''}}03$$ ); $$0_{.}^{{''}}64$$ ). We have used the reference-dependent and reference-independent methods for measuring positional parameters and magnitude differences between the components. The obtained measurements of the brightness differences agree with the observed light curve of the eclipsing pair.

ABSTRACT We report on the occultation of the star TYC 1947-290-1 by the asteroid (87) Sylvia. While asteroidal occultations occurring at fixed professional-level locations are relatively rare and are only recently starting to be observed with sufficiently high time resolution and sensitivity, they have the capability to measure sub-milliarcsecond angular diameters. The event described here was especially outstanding because the star was revealed to be a small-separation binary (≈10 mas at discovery), while at the same time the asteroid is not only one of the largest in size but it also has two satellite moons. The observations were carried out at the Russian 6-m telescope in 2019 December, and initially consisted of both a fast photometric series of the occultation itself, as well as of extensive speckle interferometry of the star and asteroid in the time immediately before and after the occultation. Subsequently, we obtained speckle data of TYC 1947-290-1 over a period of 1 yr after the event. We are able to present a detailed study of the binary star including measurements of the angular diameter of the stellar components, their geometry, and relative fluxes over several bandpasses, and to provide an accurate determination of the size of (87) Sylvia. We emphasize that we have been able to obtain the smallest ever directly measured stellar diameter, below the 100 micro-arcsecond level. Our data are also suitable for imaging of the asteroid by speckle holography, a task which we intend to carry out in a separate work.

Long-term monitoring at the 6 m telescope of the Special Astrophysical Observatory of the Russian Academy of Sciences made it possible to improve the orbits of 15 objects (HIP 689, HIP 3951, HIP 10438, HIP 43948, HIP 69962, HIP 95995, HIP 102029, HIP 102357, HIP 104383, HIP 105947, HIP 106255, HIP 108917, HIP 111546, HIP 113726, HIP 114922) and construct an orbital solution for HIP 65327 for the first time. Observations have been carried out since 2007; that is, the accumulated data correspond to an interval of 13 yr. As a result, most of the orbits were classified as "accurate" using the qualitative criteria by Worley & Heintz. A comparison of the mass sums and masses of the components calculated by two independent methods was made for objects with orbital solutions. The Gaia EDR3 parallax was used to obtain the fundamental parameters, as well as the Hipparcos and Gaia DR2 parallaxes.

HIP 53731 is a binary consisting of stars of the spectral types K0 and K9. The orbit of this object was constructed previously by Cvetković et al. and improved by Tokovinin. It should be noted that there is a 180° ambiguity in the position angles of some published measurements. Speckle interferometric observations were obtained in 2007–2020 (21 measurements) at the 6-m telescope of the SAO RAS (BTA) by the authors of this article. The analysis of new data together with previously published ones made it possible to construct an accurate orbit of HIP 53731 and to halve the already known values of the orbital period of the system. As a result of the study, the mass sum, the masses of each component and their spectral types were determined by two independent methods. According to the qualitative classification of orbits, the orbital solution has grade 2 – “good” (observations cover more than half of the orbital period and correspond to different phases).

The orbits of eight systems with low-mass components (HIP 14524, HIP 16025, HIP 28671, HIP 46199, HIP 47791, HIP 60444, HIP 61100, and HIP 73085) are presented. Speckle interferometric data were obtained at the 6 m Big Telescope Alt-azimuth Special Astrophysical Observatory of the Russian Academy of Sciences (BTA SAO RAS) from 2007 to 2019. New data, together with measures already in the literature, made it possible to improve upon previous orbital solutions in six cases and to construct orbits for the first time in the two remaining cases (HIP 14524 and HIP 60444). Mass sums are obtained using both Hipparcos and Gaia parallaxes, and a comparison with previously published values is made. Using the Worley & Heintz criteria, the classification of the orbits constructed is carried out.