Atronomical CCD observations of the main Saturn’s satellites at Pulkovo Observatory in 2004–2007

The results of astrometric observations of Saturn’s satellites (S1–S8) obtained using a 26-inch refractor and a normal astrograph at Pulkovo Observatory in 2004–2007 are given. High-accuracy equatorial coordinates of Saturn’s satellites in the system of the UCAC2 reference catalog and the relative “satellite-satellite” positions suitable for specifying their motion theories are obtained. The observations are compared with the DE405 + TASS1.7 and INPOP06 + TASS1.7 theories of motion. The root-mean-square errors of the obtained satellite positions lie within the range of 10–50 mas, as far as the intrinsic convergence is concerned, and 20–70 mas, as far as the extrinsic one is concerned. The observation results are included into the astrometrical database of the Pulkovo Observatory (www.puldb.ru).     

Astrometric Observations of the Galilean Moons of Jupiter at the Pulkovo Normal Astrograph in 2016−2017

We present the results of observations of the Galilean moons of Jupiter carried out at the Normal Astrograph of the Pulkovo Observatory in 2016?2017. We obtained 761 positions of the Galilean moons of Jupiter in the system of the Gaia DR1 catalog (ICRF, J2000.0) and 854 differential coordinates of the satellites relative to each other. The mean errors in the satellites’ normal places and the corresponding root-mean-square deviations are ε_α = 0.0020′′, ε_δ = 0.0027′′, σ_α = 0.0546′′, and σ_δ = 0.0757′′. The equatorial coordinates of the moons are compared to the motion theories of planets and satellites. On average, the (O–C) residuals in the both coordinates relative to the motion theories are less than 0.031′′. The best agreement with observations is achieved by a combination of the EPM2015 and V. Lainey-V.2.0|V1.1 motion theories, which yields the average (O–C) residuals of approximately 0.02″. Peculiarities in the behavior of the (O–C) residuals and error values in Ganymede have been noticed.     

Measurements of visual double stars with PISCO2 at the Nice 76-cm refractor in 2013–2014 (new data) and in 2015

We present relative astrometric and photometric measurements of visual double stars made in 2013–2015, with PISCO2 installed at the 76-cm refractor of Côte d'Azur Observatory in Nice (France). Our observing list contains orbital couples as well as double stars whose motion is still uncertain. Most of the observations were done in 2015, but some other observations of wide couples were done in 2013–2014 (0.3% of the total of the observations). Three different techniques were used for obtaining measurements: lucky imaging, speckle interferometry and the direct vector autocorrelation method. From our observations of 2837 multiple stars, we obtained 5182 new measurements with angular separations in the range of 0 ${}^{″}$.1–32 ${}^{″}$ and an average accuracy of $0^{″}.018$. The mean error on the position angles is 0°.8. Most of the position angles were determined without the usual 180° ambiguity with the application of the direct vector autocorrelation technique and/or by inspection of the Lucky images or the long integration files. We managed to routinely monitor faint systems ( $m_V\approx 9-11$) with large magnitude difference (up to $\mathrm{\Delta }{m}_V\approx 4.5$). We have thus been able to measure 21 systems containing red dwarf stars that had been poorly monitored since their discovery, from which we estimated the stellar masses thanks to Gaia measurements. We also measured the magnitude difference of the two components of 1079 double stars with an estimated error of 0.2 mag. Except for a few objects that are discussed, our measurements are in good agreement with the ephemerides computed with published orbital elements, even for the double stars whose separation is smaller than the diffraction limit. Thanks to good seeing images and with the use of high-contrast numerical filters, we have also been able to obtain 196 measurements with an angular separation smaller than the diffraction limit of our instrumentation, and consistent with those obtained with larger telescopes. We also report measurements of the 164 new double stars that we found in the files obtained during the observations. Finally, from a study of the DR3 Gaia release, it is shown that all the objects of the Tycho Double Star Catalog that we did not resolve in 2015 are probably false detections by Tycho.     

Observations of the Galilean moons of Jupiter in 2013–2015 at Pulkovo

Observational results are presented for Jupiter and its Galilean moons from the Normal Astrograph at Pulkovo Observatory in 2013–2015. The following data are obtained: 154 positions of the Galilean satellites and 47 calculated positions of Jupiter in the system of the UCAC4 (ICRS, J2000.0) catalogue; the differential coordinates of the satellites relative to one another are determined. The mean errors of the satellites’ normal places in right ascension and declination over the entire observational period are, respectively: ε_α = 0.0065″ and ε_δ = 0.0068″, and their standard deviations are σ_α = 0.0804″ and σ_δ = 0.0845″. The equatorial coordinates are compared with planetary and satellite motion theories. The average (O–C) residuals in the two coordinates relative to the motion theories are 0.05″ or less. The best agreement with the observations is achieved by a combination of the EPM2011m and V. Lainey-V.2.0|V1.1 motion theories; the average (O–C) residuals are 0.03″ or less. The (O–C) residuals for the features of the positions of Io and Ganymede are comparable with measurement errors. Jupiter’s positions calculated from the observations of the satellites and their theoretical jovicentric coordinates are in good agreement with the motion theories. The (О–С) residuals for Jupiter’s coordinates are, on average, 0.027″ and–0.025″ in the two coordinates.     

Results of astrometric observations of Jupiter’s Galilean satellites at the Pulkovo Observatory from 1986 to 2005

The results of photographic observations of Jupiter’s Galilean satellites made with the 26-inch refractor at the Pulkovo Observatory from 1986 to 2005 are given. Satellite coordinates with respect to Jupiter and the mutual distances between the satellites have been determined. A scale-trale technique that does not require reference stars for the astrometric reduction of measurements has been used. The effect of the Jupiter phase has been taken into account in the jovicentric coordinates. The observation results have been compared with a modern theory of the Galilean satellites’ motions. Systematic observation errors depending on the observation technique have been studied. The intrinsic observation accuracy in the random quotient is characterized by the values 0.041″ over X and Y. The external accuracy of the relative Galilean satellite coordinates determined by comparing the observations with modern ephemerides turned out to be equal to 0.165″, 0.213″ for the Jovicentric coordinates and 0.134″, 0.170″ for the “satellite-satellite” coordinates. The highest accuracy of the relative satellite coordinates is reached at small distances between the satellites which are less than 100″: the corresponding mean-square errors of one observation are equal in to the external convergence to 0.050″, 0.070″. The results of photographic observations have been compared with the first CCD observations of the Jupiter satellites made in 2004 with the 26-inch refractor.     

Astrometric results of observations at Russian observatories of mutual occultations and eclipses of Jupiter’s Galilean satellites in 2009

In 2009, in five Russian observatories photometric observations of Jupiter’s Galilean satellites during their mutual occultations and eclipses were carried out. Based on these observations, an original method was used to ascertain astrometric results such as the difference between the coordinates of pairs of satellites. Fifty-three phenomena were successfully observed. A total of 94 light curves of satellites were measured. The error in the coordinates of satellites due to random errors in photometry, calculated on all data obtained, was 0.041″ in right ascension and 0.046″ in declination. The discrepancies between the theory and observations in these coordinates was found to be 0.060″ and 0.057″, respectively. The results were uploaded to the common database for all observations of natural satellites of planets at the Natural Satellites Data Center (NSDC), which is available online at http://www.sai.msu.ru/neb/nss/index.htm. For the first time in the practice of photometric observations of satellites in epochs of mutual occultations and eclipses a new method of observation was tested, which eliminates from astrometric results the major systematic errors caused by an inaccurate account of the background level. The tests were conducted in the Terskol Observatory and the observatory of the Crimean laboratory of the Sternberg State Astronomical Institute of the Moscow State University. The application of the new method showed that the elimination of the background level at these observatories was carried out correctly.     

IUE observations of CH Cygni continuum during 1979–1986

Variations of the UV continuum have been analyzed. The observed UV continuum may be reproduced by a superposition of a Kurucz model atmosphere (log g=2), T_eff8500–15000 K) and optically thin hydrogen bound-free and free-free emission (T_e 1000 K). The temperature of the Kurucz atmosphere is the lowest at the maximum of brightness. The flat minimum in the UV integrated flux was observed in May–October 1985.Paper presented at the IAU Colloquium No. 93 on Cataclysmic Variables. Recent Multi-Frequency Observations and Theoretical Developments, held at Dr. Remeis-Sternwarte Bamberg, F.R.G.,16–19 June, 1986.     

Photographic observations of comet Hale–Bopp at the Zvenigorod Observatory

We describe the archive of scans of the astronomical plates obtained in the observations of comet Hale–Bopp. The observations were carried out from August 17, 1996, to April 29, 1997, at the Zeiss-400/2000 astrograph of the Zvenigorod Observatory of the Institute of Astronomy of the Russian Academy of Sciences (INASAN). The archive contains the images that can be used in astrometric, photometric, and astrophysical studies. In some of the plates, the size of the comet reaches 6.3° (23 cm). In many scans, the details of the cometary tail, including individual jets, vortexes, etc., are clearly distinguishable. The archive of the images is available free.     

Oscillations of the Sun: Results of observations in 1974–2007

Doppler measurements of the photosphere of the entire Sun carried out at the Crimean Astrophysical Observatory (CrAO) in 1974–2007 by the differential technique showed the presence of an enigmatic periodicity of P ₁ = 159.967(4) min. The phase of this oscillation was constant over the entire 34-year of surveys and interval. The true nature of this phenomenon is unknown. Pulsation with the former period P ₀ = 160.0101(15) min has been reliably detected only in the first nine years, from 1974 to 1982. It is noted that (a) the average amplitude of the P ₁ oscillation in the first half of the data was nearly 34% higher than in the second half and (b) the beat period of 400(14) d of these two pulsations is equal within error to the Jovian synodic period (399 d). A hypothesis is discussed relating the P ₁ oscillation to the superfast rotation of the inner solar core.     

Full-disk synoptic observations of the chromosphere using Hα telescope at the Kodaikanal Observatory

This paper reports on the installation and observations of a new solar telescope installed on 2014 October 7 at the Kodaikanal Observatory. The telescope is a refractive type equipped with a tunable Lyot Hα filter. A CCD camera with size 2k×2k acquires images of the Sun and has a pixel size of 1.21′′pixel-1and a full field-of-view of 41′. The telescope is equipped with a guiding system which keeps the image of the Sun within a few pixels throughout the observations. The FWHM of the Lyot filter is 0.4 A? and the filter is motorized, capable of scanning the Hα line profile at a smaller step size of 0.01 A?. Partial-disk imaging covering about 10′is also possible with the help of a relay lens kept in front of the CCD camera. In this paper, we report the detailed specifications of the telescope, filter unit, the installation, observations and the procedures we have followed to calibrate and align the data. We also present preliminary results with this new full-disk telescope.     

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 symbiotic 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, 6828  Raman scattering line. We determine the temperature of the hot component by means of the Zanstra method applied to the He II, 4686  line. Our estimate is about 150 000 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.     

High-dispersion spectroscopic observations of Venus during 1968 and 1969 II. The carbon-dioxide band at 8689 Å

Thirty well-exposed photographic plates showing the spectrum of the carbon-dioxide band at 8689 Å in the atmosphere of Venus were obtained during 1968 and 1969. All spectra were obtained at a dispersion of 2 Å/mm for Venus phase angles varying from 10° to 126°. We find rotational temperatures ranging from 236 to 274 K. The average value of the rotational temperature is 246 ± 1 K (one standard deviation); for our 1967 observations, the rotational temperatures ranged from 222 to 248 K, with an average value of 238 ± 4 K. The variation of the equivalent width of the 8689 Å band, with Venus phase angle, was very similar for the two sets of observations (53 plates). The temporal variations, of approximately 30% were comparable with the phase variations over this limited range of phase angle.     

Photographic observations of Saturn’s moons at the MAO NAS of Ukraine in 1961–1990

A catalog of 1385 astrometric positions of Saturn’s moons S2–S9 has been compiled with Tycho-2 as a reference frame from photographic observations obtained at the Main Astronomical Observatory, National Academy of Sciences of Ukraine, in 1961–1990. Astronegatives have been digitized with an Epson Expression 10000XL commercial scanner in 16-bit grayscale with a resolution of 1200 dpi. Reduction has been performed in the LINUX-MIDAS-ROMAFOT software supplemented with additional modules. The internal positional accuracy of the reduction is 0.09…0.23′′ for both coordinates and 0.27…0.37^m for the photographic magnitudes of the Tycho-2 catalog. The calculated topocentric positions of the moons are compared online with the IMCCE ephemeris data (DE405 + TASS1,7). Moon-minus-moon differential coordinates are found for most of the moons and compared with theoretical data (http://lnfm1.sai.msu.ru/neb/nss/nssephmr.htm).     

Study of X-ray and γ-ray flare from Mkn-421 during February 2010 using Swift and Fermi observations

In this work, we report on the intense flaring activity from Mkn-421 in X-ray and γ-ray regimes simultaneously observed by Swift-XRT/BAT and Fermi-LAT satellite telescopes in February 2010. With the aim of understanding the underlying physics of the flaring state in Mkn-421, we have performed a detailed spectral analysis of Swift/XRT and Fermi/LAT observations of Mkn-421 during February 12–25, 2010 (MJD 55239–55252). Over this period, we study the daily light curves and spectral variability of the source in 1–10 keV, 0.1–1 GeV and 1–100 GeV energy bands. We have performed the spectral analysis of Swift-XRT and Fermi/LAT observations to study the spectral evolution in the X-ray and gamma-ray energy domains respectively. We also compute the fractional variability amplitude in both the energy bands during the above period. We study trends between spectral parameters and physical insights provided by the parameter responsible for X-ray and γ-ray emission from the source. We search for energetic features phenomenologically linked to the single zone SSC model for blazar emission. We also produce the broad band SED with a leptonic single zone SSC model for the source.     

High dispersion observations of Venus during 1972: The CO2 band at 7820Å

Forty-seven well exposed photographic plates of Venus which show the spectrum of the carbon dioxide band at 7820Å were obtained at Table Mountain Observatory in September and October 1972. These spectra showed a semiregular four-day variation in the CO₂ abundance over the disk of the planet (Young et al., 1974). We also find evidence for temporal variations in the rotational temperature of this band and temperature variations over the disk. The two quantities, CO₂ abundance and temperature, do not show any obvious relationship; however, an increase in the temperature usually is accompanied by a decrease in the abundance of CO₂. The average temperature, found from a curve-of-growth analysis assuming a constant CO₂ line width, is 249±1.4K (one standard deviation). This temperature is noticeably higher than the rotational temperature of 242±2K found for this same band in 1967 (Schorn et al., 1969) and of 242±1.2K in 1968–1969 (Young et al., 1971).     

Study of the nuclear activity of the Seyfert galaxy NGC 7469 over the period of observations 2008–2014

We present the results of our multicolor UBV RI observations of NGC 7469, a type 1 Seyfert galaxy (SyG 1), in 2008–2014 at the Maidanak Observatory. Analysis of the long-term variability of NGC 7469 for two observing periods, 1990–2007 and 2008–2014, has shown the existence of yet another activity cycle of the slow component in 2009–2014 with an activity maximum in 2011–2012. We have studied the slow variability component in 2009–2014 and constructed the color–color (U ? B), (B ? V) diagrams for the variability maxima and minima of NGC 7469 in various apertures and for the blackbody gas radiation modeling the accretion disk radiation. It can be seen from the color–color diagram that the color of the nuclear part of NGC 7469 becomes bluer at maximum brightness, suggesting a higher temperature of the accretion disk. We have analyzed the X-ray variability of NGC 7469 in 2008 and 2009 in comparison with the activity minimum in 2003. The optical–X ray correlation coefficient in 2008 is close to 0.5. The weak correlation is explained by the influence of an SN 1a explosion in the circumnuclear part of NGC 7469, which manifests itself in the optical band but does not change the pattern of X-ray variability. Comparison of the variability data for 2009 shows an optical–X ray (U band–7–10 keV) correlation with a correlation coefficient of about 0.93. The correlation coefficient and the lag depend on the wavelength in the optical and X-ray bands. The lag between the X-ray and optical fluxes in 2009 is observed to a lesser extent in 2003.     

Astrometric Results for Observations of Jupiter’s Galilean Satellites During Mutual Occultations and Eclipses in 2009 and 2014–2015

Solar System Research - Photometric observations of satellites during their mutual occultations and eclipses are a valuable source of astrometric data for studying the motion of natural planetary...