New variable stars on digitized Moscow collection plates. The field of 66 Ophiuchi

In the course of a program to digitize the astronomical plates of the Sternberg Astronomical Institute’s plate stacks, we are developing algorithms for searching for new variable stars and studying them using digitized photographic plates. We have discovered and studied 480 new variable stars in a 10° × 10° field of view centered on 66 Ophiuchi. The digitized plate negatives used are from the 40-cm astrograph, and are 30 × 30 cm in size. These stars include three new Cepheids of the Galaxy’s spherical component, 157 eclipsing binaries, 11 high-amplitude δ Scuti stars (HADSs), 144 RR Lyrae stars, 110 irregular variables (109 LB and one white star), and 55 semi-regular red variables. New important information has been obtained for 43 known variables, which we have classified and derived or improved their light elements; an erroneous identification of the Mira V404 Oph has been corrected. We have also identified more than 50 suspect brightness variables; a program of CCD observations of these suspected variables has been initiated. Our discoveries of new variable stars were performed in a star field with a large number of known variables, detected earlier photographically or using CCD techniques. The discovery of hundreds of new variables in a well-studied region of sky demonstrates that archive photographs possess a large information potential that has remained unrealized.     

A search for evolutionary period variations of Cepheids using the Harvard plates: V396 Cyg

We obtained 503 photographic brightness estimates for the long-period classical Cepheid V396 Cyg (P = 33.3 days) from the plates of the Harvard Observatory and the Sternberg Astronomical Institute (SAI). Combined with published photoelectric observations, these data were used to plot an O-C diagram covering a time interval of 108 years. The O-C diagram is parabolic in shape, enabling the first determination of quadratic light elements and calculation of the evolutionary rate of decrease of the period, dP/dt = 14.1(±0.8) s per year (log(?/P) = ?6.35), in agreement with theoretical computations for the second crossing of the instability strip. The available data, reduced using the method introduced by Eddington and Plakidis, demonstrate the presence of small random period fluctuations that do not distort the evolutionary changes of the O-C residuals.     

The LYRA-B space experiment: Goals and principles for its realization

We describe goals and principles for the realization the Lyra-B space experiment onboard the International Space Station, which is currently being prepared at the Sternberg Astronomical Institute. The main goal of the experiment is to carry out a high-accuracy, multicolor all-sky survey of stars down to 16 ^m –17 ^m . The detailed structure of the expected observational data, their possible scientific use, and a number of technical problems are discussed.     

Analysis of Photometric Observations of the New Cataclysmic Variable ASASSN-13cx

Photometric observations of the variable star ASASSN-13cx acquired in the course of a program of studies of cataclysmic variables and their parameters recently carried out at the Sternberg Astronomical Institute (SAI) are presented. The star was observed with the 50-cm and 60-cm telescopes of the SAI Crimean Astronomical Station and a CCD photometer (～1800 images in the V and Rc filters) during the variable’s outburst of August–September 2014 and in a period of quiescence in October–November 2016. The ASASSN-13cx system is confirmed to be a SU UMa variable. Parameters of the system are derived from eight light curves using a “composite” model that takes into account the presence of a hot spot on the lateral surface of the geometrically thick disk and of a region of enhanced energy release near the disk edge, at the base of the gas flow (the so-called “hot line”). Parameters of the system for three light curves during the outburst were obtained in the framework of a “spiral” model that additionally takes into account the presence of geometric perturbations on the accretion-disk surface. The parameters of ASASSN-13cx determined using these models provide good accuracy in reproducing the system’s light curves in both states. The basic parameters of the system have been determined for the first time: the component mass ratio q = M₁/M₂ = 7.0 ± 0.2, the orbital inclination i = 79.9°?80.1°, the distance between the components’ centers of mass a₀ = 0.821(1) R_?, and the sizes and temperatures of the stars: R₁ = 0.0124(5)a₀ = 0.0102(4) R_?, T₁ = 12 500 ± 280 K, 〈R₂〉 = 0.236(4)a₀ = 0.194(3) R_?, T₂ = 2550 ± 400 K, corresponding to M4–9V for the spectral type of the secondary. Parameters of the accretion disk have been derived for both activity states. The mass of matter in the accretion disk increased by almost a factor of two during ～400 orbital periods in quiescence.     

Shack-Hartmann wavefront sensor for testing the quality of the optics of the 2.5-m SAI telescope

A Shack-Hartmann wavefront sensor for testing the quality of telescope optics based on observations of stars has been developed and constructed. Results of laboratory tests of the sensor and test data obtained on the 70-cm telescope of the Sternberg Astronomical Institute are presented. Estimates of the quality of the optics and of the mirror support of the main mirror of the telescope have been obtained.     

Kinematics of OB Associations and the First Data from the Gaia Satellite

The first data release from the Gaia mission (Gaia DR1) is used to study kinematics of OB associations. The mean velocity dispersion in 18 OB associations containing at least 10 stars with proper motions from the TGAS catalog is 3.9 km/s. The contribution of binary systems to the velocity dispersions in OB associations is, on average, 1.2 km/s. Expansion of the OB associations Per OB1 and Car OB1 is observed. This paper is based on a presentation made at the conference “Modern Astrometry 2017,” dedicated to the memory of K.V. Kuimov (Sternberg Astronomical Institute, Moscow State University, October 23–25, 2017).

     

A photometric and spectroscopic study of the B[e]/X-ray transient CI Cam

We compare U BV R photometry of CI Cam obtained using facilities at the Sternberg Astronomical Institute in 1998–2001 and medium-resolution spectroscopy obtained at the Special Astrophysical Observatory in the same period. The photometric measurements and fluxes in the Balmer and some Fe II emission lines in the post-outburst quiescent spectrum of CI Cam display cyclic variations with a period of 1100±50^d. These variations could be due to orbital motion in a widely separated binary; one component, a giant, produces a reflection effect on the surface facing the other, compact component. Our V-band photometry confirms the \(11\mathop d\limits_. 7\) period found by Miroshnichenko before the outburst but shows a lower amplitude (3%). We investigate the possibility that this photometric period is the same as the rotational period of the radio jets measured using the VLA. Based on modeling of the radio map, we estimate the inclination of the jet rotation axis to the line of sight, i=35°–40°; the angle between the rotational axis and jet ejection direction, ?=7°–10°; and the jet spatial velocity, 0.23–0.26 c. The equivalent widths and fluxes of various spectral lines show different variation amplitudes during outburst and significantly different behavior during quiescence. We have detected five patterns of behavior, which provide evidence for stratification of the gas and dust envelope surrounding the system. The brightening of the [N II] forbidden line is delayed by 50–250^d relative to the X-ray outburst maximum.     

Variability of the planetary nebula NGC 6572 and its central star during the interval covered by optical observations

Estimates of relative line intensities available in the literature and integrated Hβ fluxes of the planetary nebula NGC 6572 during the time covered by optical observations (1938–2013) are compared to search for possible variations. Line intensities measured from observations obtained at the Crimean Station of the Sternberg Astronomical Institute in 2013 are presented, as well as previously unpublished photographic spectroscopic data obtained 1972–2005. Our analysis of all the available data shows that the line intensities do not vary within the observational uncertainties, with the possible exception of the [OIII] 4959 and 5007 Å lines, which show a tendency for their intensity increase with time. This can be interpreted as a manifestation of a temperature increase of the central star, or radial stratification of the [OIII] emission in the nebula, with the latter explanation being less probable. However, stratification is clearly visible in the [OII] and [NII] line intensities. The integrated Hβ flux is most probably constant at F(Hβ) = (1.50 ± 0.03) × 10^?10 erg cm^?2 s^?1. A refined estimate of the interstellar extinction toward NGC 6572 has been obtained from radio and optical data, c(Hβ) = 0.42 ± 0.03. The MAST spectroscopy data were used to derive the central star’s UBV magnitudes in 2004. Integrated photoelectric UBV observations of the nebula and central star for 1971–2005 are presented.     

Statistics of Stars with Relativistic Velocities

The scenario for the dynamical capture of a binary system in the neighborhood of a supermassive black hole used byHills in 1988 to predict the existence of hypervelocity stars (~1000 km/s) allows the existence of stars with relativistic velocities attaining (1/3?2/3)c, where c is the speed of light. The increase of the kinetic energy of these stars by more than a factor of 100 is due to the replacement of one component of the binary with a supermassive black hole. This scenario takes candidate of relativisti©velocity stars outside our Galaxy, into intergalactic space, where they could be ejected from merging galaxies populated by supermassive black holes. At present, this is a hypothetical class of stars with anomalous kinematics, but it is already posing a serious challenge for modern astrometry, which, like 300 years ago, is still concerned with the detection of proper motions. While this was related to stars in the solar neighborhood at the time of Halley, is now a problem for studies of the most remote and weakest stars in intergalactic space. Possibilities for detecting such stars must be based on estimates of their abundances, that is, on their statistics. This paper is based on a presentation made at the conference “Modern Astrometry 2017,” dedicated to the memory of K.V. Kuimov (Sternberg Astronomical Institute, Moscow State University, October 23–25, 2017).

     

Konstantin Vladislavovich Kuimov

The conference “Modern Astrometry 2017,” which took place on Octobr 23–25, 2017 at the Sternberg Astronomical Institute of Lomonosov Moscow State University, was dedicated to the memory of the eminent astrometrist, teacher, and outstanding scientist and Doctor of Physical–Mathematical Siences Konstantin Vladslavovich Kuimov, who worked at the Sternberg Astronomical Institute during 1962–2017. This article is based on a presentation made at this conference.     

Iosif Samuilovich Shklovskii

July 1, 2016 was the 100th anniversary of the birthday of the eminent Russian astrophysicist Iosif Samuilovich Shklovskii (1916–1985), who was a corresponding member of the USSR Academy of Sciences, a recipient of the Lenin Prize, and a member of the National Academy of Sciences of the USA, the Royal Astronomical Society, and many other academies. Iosif Samuilovich made important and fundamental contributions in many areas of modern astrophysics, and is the author of nine books and more than 300 scientific publications. The Russian Academy of Science, Astro Space Center of the Lebedev Physical Institute, Space Research Institute of the Russian Academy of Sciences, the Sternberg Astronomical Institute of Moscow State University, and the Astronomical Society held the international conference “All-Wave Astronomy. Shklovskii-100” to commemorate this anniversary. This issue of Astronomy Reports presents papers based on selected talks at this conference.     

BVI c Observations and Search for Evolutionary Variations in the Cepheid V811 Oph Period

For the first time, BVIc observations of the Cepheid V811 Oph were obtained by using a new 60‑cm telescope at the Caucasus Mountain Observatory, Sternberg Astronomical Institute, Moscow State University (SAI MSU). An $$O{-}C$$ diagram covering a time span of 124 years was plotted using photometry from old photographic and modern sky surveys. The diagram has a parabola shape, which made it possible to determine for the first time the quadratic elements of the brightness variations. Furthermore, it made it possible to calculate the rate of an evolutionary decrease in the period of V811 Oph $$dP{\text{/}}dt = - 0.00375( \pm 0.00177)$$ s/year, which is consistent with the theoretical calculation results for the second intersection of the instability strip if this Cepheid is a classical one. The pulsation stability test proposed by Lombard and Koen confirmed the actual decrease in the period.     

The eclipsing binary HS hercules: Photometric elements and the evolutionary stages of its components

We used a photoelectric photometer designed by V.M. Lyutyi and the Zeiss-600 telescope of the Sternberg Astronomical Institute’s Crimean Observatory to acquire precise UBV brightness measurements (σ _obs ^V ～ 0.007^m) for the eclipsing binary system HS Her in 1984–1991. These measurements continue the homogeneous series of observations of this star commenced in 1969 by D.Ya. Martynov using the same equipment. Our detailed analysis of this homogeneous 22-year series of photoelectric observations has yielded a self-consistent set of physical and geometric parameters of the binary, and enabled us to establish the evolutionary stages of its components. The systems’s primary, M ₁ = 5 M _⊙, is at the beginning of its main-sequence evolution, whereas its secondary, M ₂ = 1.6 M _⊙, has not yet reached the main sequence. The binary’s age is estimated to be t = (17 ± 3) × 10⁶ years.     

A Catalog of Variable Stars based on the new name list

We present a new electronic version of the General Catalog of Variable Stars (GCVS) based on the new IAU name list of confirmed variable stars. The catalog contains 1270 stars, most of them contained earlier in the New Catalog of Suspected Variable Stars or its supplement. A number of recent studies—including those by authors of the catalog, who investigated many stars using data from modern automatic surveys, determined light-curve elements for periodic stars, and plotted numerous light curves—have made it possible to move these stars to the GCVS. Among the catalog objects, 24 stars are novae or other unusual variable stars that acquired their GCVS names out of the usual order, upon communication from the Bureau of Astronomical Telegrams of the International Astronomical Union. We present the GCVS names, coordinates, classifications (in two forms: the GCVS system and a new, proposed system), brightness-variation limits, and light-curve elements for the catalog stars, as well as bibliographic references and remarks when necessary. We discuss several catalog stars that are of astrophysical interest or caused problems during the compilation of the catalog.     

Photometric elements and apsidal motion of the eclipsing binary ES Lac

We have obtained high-accuracy photoelectric measurements of ES Lac, an eclipsing binary with an elliptical orbit (B9III + B9III; P = 4.459^d, e = 0.198) in 1985–2004 at the Sternberg Astronomical Institute’s Tien Shan High-Altitude Observatory. Our detailed analysis of the 19-year uniform series of measurements has yielded the first photometric elements for this system, as well as a self-consistent set of physical and geometrical parameters for the binary. The virtually identical components (M ₁ = M ₂ = 3.0 M _⊙; R ₁ = R ₂ = 4.12 R _⊙) are appreciably separated from the main sequence, and are located on the giant branch: their age is t = (3.5 ± 0.2) × 10⁸ yrs. An analysis of our observations together with previously published times of minima has enabled a considerable refinement of the period of the apsidal motion, U = 355 ± 20 years, and a first determination of the apsidal parameter reflecting the radial density distributions for the components stars: k ₂ ^obs = 0.00213(18). This value is in a good agreement with the value expected theoretically for current evolutionary models of such stars: k ₂ ^th = 0.00257(15).     

Analysis of errors in the tracking mechanisms of the 1.25-m telescope of the Crimean Laboratory of the SAI and the 1.5-m telescope of the Maidanak Observatory

Low-frequency (0–0.5 Hz) errors in the positions of stars in the focal plane of the ZTE 1.25-m telescope of the Crimean Laboratory of the Sternberg Astronomical Institute and the AZT-22 1.5-m telescope of the Maidanak Observatory in Uzbekistan are analyzed using data obtained during the operation of two optical compensators designed to correct the tilt of incoming wave fronts. A spectral analysis is used to identify possible origins of these errors. The amplitudes of periodic errors in the main worm-and-worm gears of the tracking mechanisms have been measured to be 1.5″ (a period of 240 s) for the 1.25-m telescope and 0.15″ (167 s) for the 1.5-m telescope. The rates of constant drifts have also been determined.     

Apsidal motion and physical parameters of the eclipsing binary system AR Cas

Using the four-channel automatic photoelectric photometer of the Sternberg Astronomical Institute’s Tien Shan Mountain Observatory, we have acquired accurate (σ_obs≈0.004^m) W BV R brightness measurements for the eclipsing binary AR Cas during selected phases before eclipse ingress and after egress, as well as at the center of minima. A joint analysis of these measurements with other published data has enabled us to derive for the first time a self-consistent set of physical and geometrical parameters for the star and the evolutionary age of its components, t=(60±3)×10⁶ years. We have found the period of the apsidal motion (U_obs=1100±160 years, \(\dot \omega _{obs} = 0^\circ .327 \pm 0^\circ .049\) years^?1) and the apsidal parameter of the primary, logk _2,1 ^obs =?2.41±0.08, with the apsidal parameter being in good agreement with current models of stellar evolution. There is an ultraviolet excess in the primary’s radiation, Δ(U?B)=?0.12^m and Δ(B?V)=?0.06^m, possibly due to a metal deficiency in the star’s atmosphere.     

Visual extinction towards the Omega Nebula (M17) and the ionization of nitrogen in the nebula

We estimate the absolute intensity of the Hα emission line in M17 based on spectroscopic observations with the 70 cm telescope of the Fesenkov Astrophysical Institute and the 1.25 m telescope of the Sternberg Astronomical Institute’s Crimean Laboratory. The visual extinction, A _v , is derived for about 250 regions in the nebula via a comparison of the optical (Hα) and radio (21 cm continuum) emissions. The A _v values for the eastern, optically bright, part of the nebula are 2–6^m. For the western part, which is covered by a dark cloud, the extinction is A _v = 7?14.5^m. We derived I(Hα)/I([NII] λ6584) ratios and estimated the degree of ionization of nitrogen in the nebula; we find that most nitrogen is in the [NIII] state.     

Solar structures related to coronal holes

The nature of structures detected recently on the Sun in soft X rays by I.F. Nikulin (Sternberg Astronomical Institute) and called by him “partings” is discussed. It is shown that these structures are sign-reversal lines for the normal component of the curvature vector of the magnetic lines. Equations describing these lines are derived and models of the corresponding fields calculated.