Cross-method Analysis of Corotation Radii Data Set for Spiral Galaxies

A corotation radius is a key characteristic of disk galaxies that is essential to determine the angular speed of the spiral structureΩ_p,and therefore understand its nature.In the literature,there are plenty of methods to estimate this value,but do these measurements have any consistency?In this work,we collected a data set of corotation radius measurements for 547 galaxies,300 of which had at least two values.An initial analysis reveals that most objects have rather inconsistent corotation radius positions.Moreover,a significant fraction of galactic disks is distinguished by a large error coverage and almost uniform distribution of measurements.These findings do not have any relation to spiral type,Hubble classification,or presence of a bar.Among other reasons,obtained results could be explained by the transient nature of spirals in a considerable part of galaxies.We have made our collected data sample publicly available,and have demonstrated on one example how it could be useful for future research by investigating a winding time value for a sample of galaxies with possible multiple spiral arm patterns.

Searching For Wide Binary Stars with Non-coeval Components in the Southern Sky

We have completed our observational program to search for wide binary systems with non-coeval components in the southern sky and report our results here.The final set of four systems was spectroscopically investigated in this paper.No binary systems with components of different ages were found among them.Taking into account our previous studies,we estimate the fraction of such binaries(i.e.,binaries formed,presumably,by capture)to be not higher than 0.06%.The study will be continued on the northern sky.

Earth crust vertical movements according to ITRF2000, ITRF2005,ITRF2008 and ITRF2014 coordinate systems and their comparing analysis

The analysis of Earth’s crust movement vertical velocities was made both for separate regions, and averaged on regions. As input data coordinates and velocities of earth crust points, obtained in International Coordinate Systems ITRF2000, ITRF2005,ITRF2008 on the base of processing radio interferometric(VLBI), laser(SLR), Doppler(DORIS) and GPS observations was used. For the purpose of global analysis all input velocity values were averaged in the x trapezoids. For filling trapezoids the spherical function expansion to N=36 was made. Expansion harmonic coefficients allowed determine the global characteristics of earth crust movements both for all Earth, and for separate hemispheres, polar and equatorial regions, continents and oceans. It appears, that polar regions were risen, and equatorial ones were lowered, that can indicate the modern Earth oblateness reduction. The constructed maps of vertical velocities were compared with obtained by us map of earth crust strain distribution. It is appeared, that regions of modern earth surface rising(Fennoscandia, Canada, Antarctica) coincide with regions of vertical extension strain, and the lowering regions-with compression regions. Simultaneously with the determination of harmonious coefficients the mean-square error of approximation for expansion of power n=1 N and power dispersion were determined. Whereas the results converge badly and dispersion increased with the n grows, hence we can concludes, that vertical movements do not characterized global earth crust movement and denotes the unrelated character of these movement. Seemingly, the main cause of such movement origin is the local seismic events(earthquake, volcanic eruption and so on). It confirms by our conclusions about correspondence of vertical strain maximal gradient(and therefore vertical velocities) map of the earthquake distribution. In work the detailed analysis of obtained results for separate Earth’s regions was made.

A possible interrelation between Earth rotation and climatic variability at decadal time-scale

Using multichannel singular spectrum analysis （MSSA） we decomposed climatic time se- ries into principal components, and compared them with Earth rotation parameters. The global warming trends were initially subtracted. Similar quasi 60 and 20 year periodic os- cillations have been found in the global mean Earth temperature anomaly （HadCRUT4） and global mean sea level （GMSL）. Similar cycles were also found in Earth rotation variation. Over the last 160 years multi-decadal change of Earth＇s rotation velocity is correlated with the 60-year temperature anomaly, and Chandler wobble envelope reproduces the form of the 60-year oscillation noticed in GMSL. The quasi 20-year oscillation observed in GMSL is correlated with the Chandler wobble excitation. So, we assume that Earth＇s rotation and climate indexes are connected. Despite of all the clues hinting this connection, no sound conclusion can be done as far as ocean circulation modelling is not able to correctly catch angular momentum of the oscillatory modes.

Measurement of Density Inhomogeneity for Glass Pendulum

The density inhomogeneity of a glass pendulum is determined by an optical interference method. The relative variations of the densities over a volume with sizes of 5 × 5×5 mm^3 are （0.64 ± 0.97） × 10^-5 and （0.99 ± 0.92） × 10^-5 for the K9 glass and silica glass pendulum, respectively. These variations of densities contributing to the relative uncertainties of the Newtonian gravitational constant G are 0.20 ppm and 0.21 ppm in our experiment on measurement of G.

Evidences of the expanding Earth from space-geodetic data over solid land and sea level rise in recent two decades

According to the space-geodetic data recorded at globally distributed stations over solid land spanning a period of more than 20-years under the International Terrestrial Reference Frame 2008,our previous estimate of the average-weighted vertical variation of the Earth＇s solid surface suggests that the Earth＇s solid part is expanding at a rate of 0.24 ± 0.05 mm/a in recent two decades.In another aspect,the satellite altimetry observations spanning recent two decades demonstrate the sea level rise（SLR） rate 3.2 ± 0.4 mm/a,of which1.8 ± 0.5 mm/a is contributed by the ice melting over land.This study shows that the oceanic thermal expansion is 1.0 ± 0.1 mm/a due to the temperature increase in recent half century,which coincides with the estimate provided by previous authors.The SLR observation by altimetry is not balanced by the ice melting and thermal expansion,which is an open problem before this study.However,in this study we infer that the oceanic part of the Earth is expanding at a rate about 0.4 mm/a.Combining the expansion rates of land part and oceanic part,we conclude that the Earth is expanding at a rate of 0.35 ± 0.47 mm/a in recent two decades.If the Earth expands at this rate,then the altimetry-observed SLR can be well explained.

Long-term trends in solar activity. Variations of solar indices in the last 40 years

We analyze long-term variations of several solar activity indices(AIs) that have been measured over the last 40 years.With this goal,we study the AIs that characterize the fluxes from different areas in the solar atmosphere.Our consideration of mutual correlations between the solar indices is based on the study of relationships between them in the period from 1950 to 1990.This period of time,covering activity cycles 19–22,is characterized by relatively stable relations between the indices.We investigate the normalized variations of these indices in recent time in relation to their values which were calculated by considering radiation from the Sun in the radio range at a wavelength of 10.7 cm(F10.7) in 1950–1990.The analysis of time series,representing variations of the normalized AI(AIFF) in solar cycles 23–24,shows different trends exist for different indices in terms of their long-term behavior.We assume that variations of normalized International Sunspot Number(SSN),F530.3 and Flare Index,which have shown sharp decreases in the last 40 years,are possibly associated with a decrease in the intensity of large-scale magnetic fields in the photosphere(SSN) and in the corona(the coronal index and the Flare Index).

The Fifth Edition of the General Catalogue of Variable Stars:experiences in the constellation Centaurus

We have recently announced that the General Catalogue of Variable Stars enters the stage of its fifth, purely electronic edition （GCVS 5.1）. We have included 1408 variable stars in the constellation Centaurus in this new version, GCVS 5.1. Working on this revision, we applied current possibilities from data mining, suggested new variability types for many variable stars and found new light elements for a large number of periodic variables. This paper describes the work completed during the preparation of GCVS 5.1 for Centaurus and discusses in detail a number of the most astrophysically significant cases.

Contribution of the Earth's gravitational potential to variations in orbital motion of short-period comets

We present simulation results on evolution development of orbital motion of short-period comets with the revolution period not exceeding 6-7 years, namely comets 21P/Giacobini-Zinner, 26P/Grigg- Skjellerup and 7P/Pons-Winnecke. The calculations cover the range from the date of the object＇s discovery to 2100. Variations in the objects＇ orbital elements under the action of gravity disturbances, taking Earth＇s gravitational potential into account when the small body approaches, are analyzed. Corrected dates of peri- helion passages can be used for scheduling observations.

Revolving scheme for solving a cascade of Abel equations in dynamics of planar satellite rotation

The main objective for this research was the analytical exploration of the dynamics of planar satellite rotation during the motion of an elliptical orbit around a planet. First, we revisit the results of J. Wisdom et al. （1984）, in which, by the elegant change of variables （considering the true anomaly f as the independent variable）, the governing equation of satellite rotation takes the form of an Abel ordinary differential equation （ODE） of the second kind, a sort of generalization of the Riccati ODE. We note that due to the special character of solutions of a Riccati-type ODE, there exists the possibility of sudden jumping in the magnitude of the solution at some moment of time. In the physical sense, this jumping of the Riccati-type solutions of the governing ODE could be associated with the effect of sudden acceleration[deceleration in the satellite rotation around the chosen principle axis at a definite moment of parametric time. This means that there exists not only a chaotic satellite rotation regime （as per the results of J. Wisdom et al. （1984））, but a kind of gradient catastrophe （Arnold, 1992） could occur during the satellite rotation process. We especially note that if a gradient catastrophe could occur, this does not mean that it must occur： such a possibility depends on the initial conditions. In addition, we obtained asymptotical solutions that manifest a quasi-periodic character even with the strong simplifying assumptions e → 0, p -- 1, which reduce the governing equation of J. Wisdom et al. （1984） to a kind of Beletskii＇s equation.

Magnetic cycles of Sun-like stars with different levels of coronal and chromospheric activity——comparison with the Sun

The atmospheric activity of the Sun and Sun-like stars is analyzed involving observations from the HK-project at the Mount Wilson Observatory, the California and Carnegie Planet Search Program at the Keck and Lick Observatories and the Magellan Planet Search Program at the Las Campanas Observatory. We show that for stars of E G and K spectral classes, the cyclic activity, similar to the 11-yr solar cycle, is different： it becomes more prominent in K-stars. Comparative study of Sun-like stars with different levels of chromospheric and coronal activity confirms that the Sun belongs to stars with a low level of chromospheric activity and stands apart among these stars by its minimum level of coronal radiation and minimum level of variations in photospheric flux.

Forecast of the key parameters of the 24-th solar cycle

To predict the key parameters of the solar cycle, a new method is proposed based on the empirical law describing the correlation between the maximum height of the preceding solar cycle and the entropy of the forthcoming one. The entropy of the forthcoming cycle may be estimated using this empirical law, if the maximum height of the current cycle is known. The cycle entropy is shown to correlate well with the cycle＇s maximum height and, as a consequence, the height of the forthcoming maximum can be estimated. In turn, the correlation found between the height of the maximum and the duration of the ascending branch （the Waldmeier rule） allows the epoch of the maximum, Tmax, to be estimated, if the date of the minimum is known. Moreover, using the law discovered, one can find out the analogous cycles which are similar to the cycle being forecasted, and hence, obtain the synoptic forecast of all main features of the forthcoming cycle. The estimates have shown the accuracy level of this technique to be 86%. The new regularities discovered are also interesting because they are fundamental in the theory of solar cycles and may provide new empirical data. The main parameters of the future solar cycle 24 are as follows： the height of the maximum is Wmax = 95±20, the duration of the ascending branch is Ta = 4.5±0.5 yr, the total cycle duration according to the synoptic forecast is 11.3 yr.

Photometric and Spectroscopic Analysis of LBV Candidate J004341.84+411112.0 in M31

We study Luminous Blue Variable(LBV)candidate J004341.84+411112.0 in the Andromeda galaxy.We present optical spectra of the object obtained with the 6 m telescope of BTA SAO RAS.The candidate shows typical LBV features in its spectra:broad and strong hydrogen lines and the He I lines with P Cygni profiles.Its remarkable spectral resemblance to the well known LBV P Cygni suggests a common nature of the objects and supports LBV classification of J004341.84+411112.0.We estimate the temperature,reddening,radius and luminosity of the star using its spectral energy distribution.Obtained bolometric luminosity of the candidate(M_(bol)=-10.41±0.12 mag)is quite similar to those of known LBV stars in the Andromeda galaxy.We analyzed a ten year light curve of the object in R filter.The candidate demonstrates photometric variations of the order of 0.4 mag,with an overall brightness increasing trendΔR>0.1 mag.Therewith,the corresponding color variations of the object are fully consistent with LBV behavior when a star become cooler and brighter in the optical spectral range with a nearly constant bolometric luminosity.LBV-type variability of the object,similarity of its spectrum and estimated luminosity to those of known LBVs allow us to classify J004341.84+411112.0 as an LBV.

Study of variable stars associated with maser sources: G025.65+1.05

We report variation of K-band infrared(IR) emission in the vicinity of the G025.65+1.05 water and methanol maser source. New observational data were obtained with the 2.5 m telescope at the Caucasian Mountain Observatory(CMO) of Moscow State University on 2017–09–21 during a strong water maser flare. We found that the IR source situated close to the maser position had decreased brightness in comparison to archive data. This source is associated with a massive young stellar object(MYSO) corresponding to the compact IR source IRAS 18316–0602(RAFGL 7009 S). A similar decrease in K-brightness of the IR source close to the maser position was observed in March 2011 when the water maser experienced a period of increased activity. The dips in MYSO brightness can be related to the maser flare phases. Maser flares that are concurrent with dips in the IR emission can be explained if the lower IR radiation field enables a more efficient sink for the pumping cycle by allowing IR photons to escape the maser region.

Multiple cycles of magnetic activity in the Sun and Sun-like stars and their evolution

The wavelet transform method for high-quality time-frequency analysis is applied to sets of observations of relative sunspot numbers and stellar chromosphere fluxes of 10 Sun-like stars. Wavelet analysis of solar data shows that in a certain interval of time there are several cycles of activity with pe- riods of duration which vary considerably from each other： from quasi-biennial cycles to lO0-yr cycles. Cyclic activity was detected in almost all Sun-like stars that we examined, even those that previously were not considered as stars with cyclic activity according to analysis using a Scargle periodogram. The durations of solar and stellar cycles significantly change during the observation period.

Long-term photometric behavior of the eclipsing Z Cam-type dwarf nova AY Psc

New eclipse timings of the Z Cam-type dwarf nova AY Psc were measured and the orbital ephemeris was revised. In addition, based on long-term AAVSO data, the outburst behaviors were also explored. Our analysis suggests that normal outbursts are quasi-periodic, with an amplitude of 2.5（4-0.1） mag and a period of - 18.3（4-0.7） d. The amplitude vs. recurrence-time relation ofAY Psc is discussed, and we conclude that this relation may represent general properties of dwarf nova outbursts. The observed standstill ends with an outburst, which is inconsistent with the general picture of Z Cam- type stars. This unusual behavior was considered to be related to mass-transfer outbursts. Moreover, the average luminosity Is brighter during standstills than during outburst cycles. The changes in brightness mark variations in M2 due to the fact that the disk of AY Psc is nearly steady state.M2 value was limited to the range from 6.35 × 10-9 to 1.18 × 10-8 M yr-1. More detailed examination shows that there are a few small outbursts present during standstills. These events with amplitudes of - 0.5 - 0.9 mag are very similar to the stunted outbursts reported in some nova-like cataclysmic variables. We discussed several possible mechanisms and suggested that the most reasonable mechanism for these stunted outbursts is a changing mass-transfer rate.

Spectroscopic and photometric observations of symbiotic nova PU Vul during 2009–2016

A new set of low-resolution spectral and UBVJHKL-photometric observations of the symbi- otic nova PU Vul is presented. The binary has been evolving after its symbiotic nova outburst in 1977 and now it is in the nebular stage. It is found that the third orbital cycle （after 1977） was characterized by great changes in associated light curves. Now, PU Vul exhibits a sine-wave shape in all the light curves （with an amplitude in the U band of about 0.7 mag）, which is typical for symbiotic stars in the quiescent state. Brightness variability due to pulsations of the cool component is now clearly visible in the VRI light curves. The amplitude of the pulsations increases from 0.5 mag in the V band to 0.8 mag in the I band. These two types of variability, as well as a very slow change in the physical parameters of the hot component due to evolution after the outburst of 1977, influence the spectral energy distribution （SED） of the system. The variability of emission lines is highly complex. Only hydrogen line fluxes vary with orbital phase. An important feature of the third orbital cycle is the first emergence of the OVI, 6828A Raman scattering line. We determine the temperature of the hot component by means of the Zanstra method applied to the He II, 4686A line. Our estimate is about 150000 K for the spectrum obtained near orbital maximum in 2014. The VO spectral index derived near pulsation minimum corresponds to M6 spectral class for the cool component of PU Vul.

Cooling and energy loss of partially ionized hydrogen gas behind a shock wave

We studied the difference in behavior of total energy and its thermal component during the radiative cooling of partially ionized hydrogen gas. Our calculations were fulfilled for the conditions in the atmosphere of a cool star. It is shown that the attenuation of total energy loss does not interfere with the cooling rate.

Geomorphological Features of Ancient Volcanic Terrain of Mars

The article considers geological and morphological features of a volcanic relief of a surface of a planet Mars. Effusive magmatism processes at early stages of planet crust forming come out in structure of solidified relief forms of Mars. Volcanic relief of a planet represents relic ancient line oriented forms, areal and central lava flooding. Linear forms generate shield volcanoes, chains of volcanic mountains and radial-concentric faults. This article deals with geological and morphological characteristics of the volcanic terrain of Mars. Hypsometric altitude profiles of volcanoes have been built based on the MOLA （Mars orbiter laser altimeter） of the spacecraft MGS （Mars global surveyor）. The gradient of volcano flanks has been calculated. The relative age of the volcanic terrain was estimated by the classical method of counting of the density of impact craters. Names of the volcanic landforms of Mars are given in the article in accordance with the name nomenclature system approved by the International Astronomical Union. Research results make it possible to compare the scientific and technical information about the planet and analyze the materials of satellite imagery of Mars.

Long-period eclipsing binaries:towards the true mass-luminosity relation.I.the test sample,observations and data analysis

The mass-luminosity relation is a fundamental law of astrophysics.We have suggested that the currently used mass-luminosity relation is not correct for the M/M⊙>2.7 range of mass since it was created utilizing double-lined eclipsing binaries,where the components are synchronized and consequently change each other's evolutionary path.To exclude this effect,we have started a project to study longperiod massive eclipsing binaries in order to construct radial velocity curves and determine masses for the components.We outline our project and present the selected test sample together with the first HRS/SALT spectral observations and the software package,FITTING BINARY STARS(FBS),that we developed for the analysis of our spectral data.As the first result,we present the radial velocity curves and best-fit orbital elements for the two components of the FP Car binary system from our test sample.