Comparative analysis of photometric variability of TT ARI in the years 1994–1995 and 2001, 2004

We present the results of photometric observations of a bright cataclysmic variable TT Ari with an orbital period of 0.13755 days. CCD observations were carried out with the Russian-Turkish RTT 150 telescope in 2001 and 2004 (13 nights). Multi-color photoelectric observations of the system were obtained with the Zeiss 600 telescope of SAO RAS in 1994–1995 (6 nights). In 1994–1995, the photometric period of the system was smaller than the orbital one (0 _. ^d 132 and 0 _. ^d 134), whereas it exceeded the latter (0 _. ^d 150 and 0 _. ^d 148) in 2001, 2004. An additional period exceeding the orbital one (0 _. ^d 144) is detected in 1995 modulations. We interpret it as indicating the elliptic disc precession in the direction of the orbital motion. In 1994, the variability in colors shows periods close to the orbital one (0 _. ^d 136, b-v), as well as to the period indicating the elliptic disk precession (0 _. ^d 146, w-b). We confirm that during the epochs characterized by photometric periods shorter than the orbital one, the quasi-periodic variability of TT Ari at time scales about 20 min is stronger than during epochs with long photometric periods. In general, the variability of the system can be described as a “red” noise with increased amplitudes of modulations at characteristic time scales of 10–40 min.     

Earth’s precession–nutation motion: the error analysis of the theories IAU 2000 and IAU 2006 applying the VLBI data of the years 1984–2006

The long-term systematic errors of the analytical theories IAU 2000 and IAU 2006 of the Earth’s precession–nutational motion are studied making use of the VLBI data of 1984–2007. Several independent methods give indubitable evidence of the significant quadratic error in the IAU 2000 residuals of the precessional angle while the adopted value of the secular decrease /cy of the Earth’s ellipticity e (derived from Satellite Laser Ranging data) should manifest itself in the residuals of as the negative quadratic trend . The problem with the precession of the IAU 2006 theory adopted as a new international standard and based on the precession model P03 (Capitaine et al., Astron Astrophys 432:355–367, 2005) appears to be even more serious because the above mentioned quadratic term has already been incorporated into the P03 precession. Our analysis of the VLBI data demonstrates that the quadratic trend of the IAU 2006 residuals does amount to the expected value (30.0 ± 3) mas/cy². It means, first, that the theoretical precession rate of IAU 2006 should be augmented by the large secular correction and, second, that the available VLBI data have potentiality of estimating the rate . And indeed, processing these data by the numerical theory ERA of the Earth’s rotation (Krasinsky, Celest Mech Dyn Astron 96:169–217, 2006, Krasinsky and Vasilyev, Celest Mech Dyn Astron 96:219–237, 2006) yields the estimate /cy statistically in accordance with the satellite-based . On the other hand, applying IAU 2000/2006 models, the positive value /cy is found which is incompatible with the SLR estimate and, evidently, has no physical meaning. The large and steadily increasing error of the precession motion of the IAU 2006 theory makes the task of replacing IAU 2006 by a more accurate model be most pressing.     

Appulses and occultations of SAO stars by mercury: 1987–1995

Predictions are presented for 78 close approaches by Mercury to stars in the SAO catalog between 1 January 1987 and 31 December 1995. No easily observable occultations were found, but 7 occultations of stars with visual magnitudes of 7 or fainter were found. These events are presented for the use of observers searching for material in the vicinity of Mercury and for those who need close bright stars for the improvement of ground-based images of Mercury.     

Physical properties of the particles composing the Martian dust storm of 1971–1972

Infrared spectra obtained from the Mariner 9 spacecraft during the 1971–1972 dust storm are used to derive information on the composition and particle size distribution of the dust and to study the time evolution of the storm. The dust is not composed of pure granite, basalt, basaltic glass, obsidian, quartz, andesite, or montmorillonite. The infrared spectra suggest that the dust is a mixture of materials, dominated by igneous silicates with >62;60% SiO₂, or weathering products such as clay minerals, but the dust could possibly have a significant component of lower SiO₂ materials such as basalt. Substantial quantities of carbonates, nitrates, or carbon suboxide are excluded from the mixture. All infrared, visible, and ultraviolet data on the Martian surface composition seem consistent with a mixture of basalt and clay minerals or high SiO₂ igneous rocks, with a surface patina of oxides of iron. For all candidate compositions, the data are best matched with a size distribution that approximates a differential power law function of slope ?4. This size distribution is quite similar to terrestial size distributions in regions remote from sources of dust. The relative abundance of particles between 1- and 10-μm radius did not change during the Mariner 9 mission; thus suspended particles did not experience Stokes-Cunningham fallout but instead were supported by turbulence with an eddy diffusion coefficient, $\text{K}{}_{\mathrm{<mtext>e</mtext>}}\text{? 7 × 10}{}^6\text{cm}{}^2\text{sec}{}^{\mathrm{?1}}$. The aerosol optical depth, standardized to 0.3-μm wavelength, varied from about 1.5 early in the mission to about 0.2 at Orbit 200.     

Observations of Three Stellar Occultations by Comet Hale–Bopp

On June 12 1996 UT, three 11–12 R magnitude stars were occulted by comet Hale–Bopp. The passage of these stars through the cometary atmosphere was monitored at the Observatorio do Pico dos Dias (Brazil) using a 0.6 m telescope. We detected an absorption of starlight by the comet dust implying in a drop of \((6\pm 1) \times 10^{-2}\) magnitude of occulted star XPM 152-0898466 at a minimum distance of (\(4.3 \pm 0.2)\times 10^{4}\) km from the central condensation. This result, combined with magnitude variations of other stars, suggests the detection of a jet in the coma. From our measurement of extinction, we infer that the opacity of the nucleus surface was \(\tau \sim 3\). The mean geometric albedo p of dust grains is \((4.5 \pm 0.7) \times 10^{-3}\). This low albedo may suggest a difference in the grain population associated to coma and jets.     

Structural Invariance of Sunspot Umbrae over the Solar Cycle: 1993 – 2004

Measurements of maximum magnetic flux, minimum intensity, and size are presented for 12 967 sunspot umbrae detected on the National Aeronautics and Space Administration/National Solar Observatory (NASA/NSO) spectromagnetograms between 1993 and 2004 to study umbral structure and strength during the solar cycle. The umbrae are selected using an automated thresholding technique. Measured umbral intensities are first corrected for center-to-limb intensity dependence. Log-normal fits to the observed size distribution confirm that the size-spectrum shape does not vary with time. The intensity – magnetic-flux relationship is found to be steady over the solar cycle. The dependence of umbral size on the magnetic flux and minimum intensity are also independent of the cycle phase and give linear and quadratic relations, respectively. While the large sample size does show a low-amplitude oscillation in the mean minimum intensity and maximum magnetic flux correlated with the solar cycle, this can be explained in terms of variations in the mean umbral size. These size variations, however, are small and do not substantiate a meaningful change in the size spectrum of the umbrae generated by the Sun. Thus, in contrast to previous reports, the observations suggest the equilibrium structure, as manifested by the invariant size-magnetic field relationship, as well as the mean size (i.e., strength) of sunspot umbrae do not significantly depend on the solar-cycle phase.     

Power law distribution of pressure drops in dust devils: Observation techniques and Earth–Mars comparison

Data from the Pathfinder and Phoenix landers on Mars show transient pressure drops (～1–4 per day) attributed to nearby encounters with dust devils or dust-free vortices. The distribution of pressure drop amplitudes is consistent with a truncated power law distribution with a slope of ?2, similar to that suggested previously for the optical diameters of dust devils. Comparable data from terrestrial field observations are very sparse: the only published dataset is half a century old and lists only 19 pressure drops. That dataset is too small to permit a robust comparison with Mars and likely suffers from a low detection efficiency at small dust devil sizes. Observed pressure drops in these fixed-station Mars datasets (30–300 μbar) are 10× lower than those typically observed on Earth (0.3–3 mbar): some higher drops have been reported for large terrestrial devils sampled by pursuing vehicles. The needed terrestrial data for comparison with Mars in-situ data (soon to be augmented, we hope, by the Mars Science Laboratory mission) is noted. Prospects for obtaining such data via field campaigns using new data acquisition technology, and with microbarographs for nuclear test monitoring, are discussed.     

Ubvri photometry of nova 1934 dq her during 1982–1995: Brightness variability

The principal results of a photometric investigation of Nova 1934 DQ Her during 1982–1995 are presented. Simultaneous high-speed UBVRI photometry was used to investigate for the first time the behavior of its brightness on time scales from several days to several years. Relationships are found between the changes in brightness of DQ Her in various regions of the spectrum and the corresponding changes in the energy distribution of its radiation. The observed variations in brightness of the system are caused by the variability in the radiation from the accretion disk with the white dwarf at the center. The brightness variations on the time scale of several days to several dozen days, may be caused by changes in the rate of accretion from the disk onto the white dwarf due to inherent disk instability or by irregular delivery of material in the jet from the red dwarf. Cyclic variations in brightness of DQ Her with an amplitude of several tenths of a magnitude and a characteristic time of about 5 yr, as well as the cyclic variations of the parameter "O-C" with the same characteristic time and amplitude of about 2–4 min may be the response of the accretion disk to activity of the red dwarf itself.Translated fromAstrofizika, Vol. 39, No. 1, pp. 41–55, January–March, 1996.     

Surface age of the ice–dust mantle deposit in Malea Planum,Mars

The mid- and high-latitudes of Mars are covered by a smooth young mantle that is interpreted as an atmospherically derived air-fall deposit of ice and dust related to recent climate changes. In order to determine relative and absolute ages of this surface unit within the southern hemisphere, a systematic survey of all available HiRISE and CTX images in the Malea Planum region from 55–60°S latitude and 50–70°E longitude was performed and the distribution and the morphology of small impact craters on the mantle deposit were investigated. Using crater size-frequency measurements, we derived absolute model ages of ～3–5 Ma for the surface of the mantle, immediately south of the Hellas basin rim. Morphologic observations of the mantle, its fresh appearance, very low number of craters, and superposition on older units support this very young Amazonian age. Nearly all observed craters on the smooth mantle in Malea Planum are small and show signs of erosion, evidence for the ongoing modification of the ice–dust mantle. However, this modification has not been strong enough to reset the surface age. Compared to the ice–dust mantle at higher latitudes in the northern and southern hemisphere, the surface of the mantle in Malea Planum is older and thus has been relatively stable during obliquity changes in the last ～3–5 Ma. This is consistent with the hypothesis that the ice–dust mantle is a complex surface deposit of different layers, that shows a strong latitude dependence in morphology and has been deposited and degraded at different times in martian history.     

Precise positions of selected minor planets from the observations of 1991–1993

We present two catalogues of positions of selected asteroids in the system of the Tycho Reference Catalogue from the photographic observations carried out on Mt. Maidanak with the AFR-1 wide-field astrograph (D = 230 mm, F = 2300 mm) and in Zvenigorod with the Zeiss wide-field astrograph (D = 400 mm, F = 2000 mm) in 1991–1993. The catalogue obtained on Maidanak contains 109 positions of selected asteroids; the one obtained in Zvenigorod contains 177 asteroid positions. The two catalogues are compared to show that they are uniform. The one-position mean square errors in the Maidanak and Zvenigorod catalogues are calculated: 0.306″, 0.153″ and 0.370″, 0.219″.     

Sixty-five years of solar radioastronomy: flares, coronal mass ejections and Sun–Earth connection

This paper will review the input of 65 years of radio observations to our understanding of solar and solar–terrestrial physics. It is focussed on the radio observations of phenomena linked to solar activity in the period going from the first discovery of the radio emissions to present days. We shall present first an overview of solar radio physics focussed on the active Sun and on the premices of solar–terrestrial relationships from the discovery to the 1980s. We shall then discuss the input of radioastronomy both at metric/decimetric wavelengths and at centimetric/millimetric and submillimetric wavelengths to our understanding of flares. We shall also review some of the radio, X-ray and white-light signatures bringing new evidence for reconnection and current sheets in eruptive events. The input of radio images (obtained with a high temporal cadence) to the understanding of the initiation and fast development in the low corona of coronal mass ejections (CMEs) as well as the radio observations of shocks in the corona and in the interplanetary medium will be reviewed. The input of radio observations to our knowledge of the interplanetary magnetic structures (ICMEs) will be summarized; we shall show how radio observations linked to the propagation of electron beams allow to identify small scale structures in the heliosphere and to trace the connection between the Sun and interplanetary structures as far as 4AU. We shall also describe how the radio observations bring useful information on the relationship and connections between the energetic electrons in the corona and the electrons measured in-situ. The input of radio observations on the forecasting of the arrival time of shocks at the Earth as well as on Space Weather studies will be described. In the last section, we shall summarize the key results that have contributed to transform our knowledge of solar activity and its link with the interplanetary medium. In conclusion, we shall indicate the instrumental radio developments at Earth and in space, which are from our point of view, necessary for the future of solar and interplanetary physics.     

Some Features of Comet Hale–Bopp (According to the Observations of 1995–1998)

Solar System Research - “The Great Comet of 1997” was a significant event in cometary physics. Numerous interesting scientific studies are devoted to this comet. Unfortunately, in the...     

GPS data analysis center of the main astronomical observatory: Results of observation processing for GPS weeks 1236–1399

Observations of GPS satellites at permanent stations located in Ukraine and in Eastern Europe have been processed at the GPS Data Analysis Centre of the Main Astronomical Observatory. The processing was carried out with the Bernese GPS Software Version 4.2. The processing procedure is described. The obtained coordinates of the GPS stations for GPS week 1399 are presented. Variations in the coordinates and zenith troposphere refractions for POLV and TRAB stations are shown.     

Activity of the Leonid meteor shower in the years 1944–1953

The activity of the Leonid shower in the years 1944–1953 was derived from visual records obtained at the Skalnaté Pleso Observatory, using the zenithal exponent = 1.47 in the reduction factor cos z _R.