A review of Bondi–Hoyle–Lyttleton accretion

If a point mass moves through a uniform gas cloud, at what rate does it accrete material? This is the question studied by Bondi, Hoyle and Lyttleton. This paper draws together the work performed in this area since the problem was first studied. Time has shown that, despite the simplifications made, Bondi, Hoyle and Lyttleton made quite accurate predictions for the accretion rate. Bondi–Hoyle–Lyttleton accretion has found application in many fields of astronomy, and these are also discussed.     

Re-Evaluation of the Flare–Type II–CME Association

We have re-evaluated the association of type II solar radio bursts with flares and/or coronal mass ejections (CMEs) using the year 2000 solar maximum data. For this, we consider 52 type II events whose associations with flares or CMEs were absent or not clearly identified and reported. These events are classified as follows; group I: 11 type IIs for which there are no reports of GOES X-ray flares and CMEs; group II: 12 type IIs for which there are no reports of GOES X-ray flares; and group III: 29 type IIs for which the flare locations are not reported. By carefully re-examining their association from GOES X-ray and H, Yohkoh SXT and EIT-EUV data, we attempt to answer the following questions: (i) if there really were no X-ray flares associated with the above 23 type IIs of groups I and II; (ii) whether they can be regarded as backside events whose X-ray emission might have been occulted. From this analysis, we have found that two factors, flare background intensity and flare location, play important roles in the complete reports about flare–type II–CME associations. In the above 23 cases, for more than 50% of the cases in total, the X-ray flares were not noticed and reported, because the background intensity of X-ray flux was high. In the remaining cases, the X-ray intensity might be greatly reduced due to occultation. From the H flare data, Yohkoh SXT data and EIT-EUV data, we found that ten cases out of 23 might be frontside events, and the remaining are backside events. While the flare–type II association is found to be nearly 90%, the type II–CME association is roughly around 75%. This analysis might be useful to reduce some ambiguities regarding the association among type IIs, flares and CMEs.     

Problems of asteroid–comet hazard

The most relevant tasks associated with the problem of asteroid–comet hazard are discussed. A review is given of the respective research at the Institute of Applied Astronomy. The institute is currently implementing a project to create an information center whose tasks include the collection and processing of optical and radar observations of small solar system bodies, determination of their orbits, and assessment of the impact hazard of the newly discovered small bodies with respect to the earth, moon, and the other major planets and their satellites.     

Theoretical investigation of interstellar C–C–O and C–O–C bonding backbone molecules

There are numerous complex organic molecules containing carbon and oxygen atoms which show either C–C–O or C–O–C bonding backbone. This paper examines altogether 51 C–C–O and C–O–C bonding backbone molecules from ten different isomeric groups (C₂H₂O, C₃H₂O, C₂H₄O, C₂H₄O₂, C₃H₄O, C₂H₆O, C₂H₆O₂, C₃H₆O, C₃H₆O₂, C₃H₈O) to summarize the present astronomical status of these molecules. Accurate calculations of enthalpy of formation of these molecules show that the isomers with C–C–O backbone are more stable than the C–O–C backbone. Interestingly, a detailed analysis of relevant astromolecules indicates that most of the observed astromolecules have the C–C–O backbone. As a matter of fact, of all the molecules examined in this study, 80% of the astronomically observed species have the C–C–O backbone while only 20% have the C–O–C backbone. In general, interstellar abundance of a molecule is controlled by some factors such as kinetics, formation and destruction pathways,thermodynamics etc. A proper consideration of these factors could explain the observed abundances of these molecules. All these possible key factors are discussed in this paper.     

Orbital Evolution of the Sun–Jupiter–Saturn–Uranus–Neptune Four-Planet System on Long-Time Scales

The four-planet problem is solved by constructing an averaged semi-analytical theory of secondorder motion by planetary masses. A discussion is given of the results obtained by numerical integration of the averaged equations of motion for the Sun–Jupiter–Saturn–Uranus–Neptune system over a time interval of 10 Gyr. The integration is based on high-order Runge–Kutta and Everhart methods. The motion of the planets is almost periodic in nature. The eccentricities and inclinations of the planetary orbits remain small. Short-period perturbations remain small over the entire interval of integration. Conclusions are drawn about the resonant properties of the motion. Estimates are given for the accuracy of the numerical integration.     

Cosmological Solutions of Tensor–Vector Theories of Gravity by Varying the Space-Time–Matter Coupling Constant

We consider tensor–vector theories by varying the space-time–matter coupling constant (varying Einstein velocity) in a spatially flat FRW universe. We examine the dynamics of this model by dynamical system method assuming a ΛCDM background and we find some exact solutions by considering the character of critical points of the theory and their stability conditions. Then we reconstruct the potential V(A ²) and the coupling Z(A ²) by demanding a background ΛCDM cosmology. Also we set restrictions on the varying Einstein velocity to solve the horizon problem. This gives a selection rule for choosing the appropriate stable solution. We will see that it is possible to produce the background expansion history H(z) indicated by observations. Finally we will discuss the behavior of the speed of light (c _E) for those solutions.     

Photon Spectra of Electron–Electron Bremsstrahlung

A formula is given for the cross section of electron–electron bremsstrahlung in the rest system of the target electron. It is in particular appropriate for the calculation of photon spectra in astrophysical applications, e.g., if the primary electrons have energy distributions in the form of a power law. For the long-wavelength limit of the spectrum the cross section is specified in closed form.     

Properties of Decameter IIIb–III Pairs

A large number of Type IIIb–III pairs, in which the first component is a Type IIIb burst and the second one is a Type III burst, are often recorded during decameter Type III burst storms. From the beginning of their observation, the question of whether the components of these pairs are the first and the second harmonics of radio emission or not has remained open. We discuss properties of decameter IIIb–III pairs in detail to answer this question. The components of these pairs, Type IIIb bursts and Type III bursts, have essentially different durations and polarizations. At the same time their frequency drift rates are rather close, provided that the drift rates of Type IIIb bursts are a little larger those of Type III bursts at the same frequency. Frequency ratios of the bursts at the same moment are close to two. This points at a harmonic connection of the components in IIIb–III pairs. At the same time there was a serious difficulty, namely why the first harmonic had fine frequency structure in the form of striae and the second harmonic did not have it. Recently Loi, Cairns, and Li (Astrophys. J.790, 67, 2014) succeeded in solving this problem. The physical aspects of observational properties of decameter IIIb–III pairs are discussed and pros and cons of harmonic character of Type IIIb bursts and Type III bursts in IIIb–III pairs are presented. We conclude that practically all properties of the IIIb–III pair components can be understood in the framework of the harmonic relation of the components of the IIIb–III pairs.     

Periodic orbits of the generalized Friedmann–Robertson–Walker Hamiltonian systems

The averaging theory of first order is applied to study a generalization of the Friedmann–Robertson–Walker Hamiltonian systems with three parameters. We provide sufficient conditions on the three parameters of the generalized system to guarantee the existence of continuous families of periodic orbits parameterized by the energy, and these families are given up to first order in a small parameter.     

Duality properties of Gorringe–Leach equations

In the category of motions preserving the angular momentum direction, Gorringe and Leach exhibited two classes of differential equations having elliptical orbits. After enlarging slightly these classes, we show that they are related by a duality correspondence of the Arnold–Vassiliev type. The specific associated conserved quantities (Laplace–Runge–Lenz vector and Fradkin–Jauch–Hill tensor) are then dual reflections of each other.     

The deviation of light path in Einstein–Brans–Dicke theory

Both Jordan–Brans–Dicke (shortened JBD) theory and Brans–Dicke theory in the Einstein’s frame (shortened EBD) are treated as Brans–Dicke theory. However, we learn that only Pauli metric represents the massless spin-two graviton and thus, should be identified as physical. If one just considers the weak field approximation and Newtonian limit, EBD theory gives the same results with Einstein’s general relativity. So, it is necessary to consider strong field effects and cosmological model. The purpose of this paper is to find the exact spherically symmetric metric in the strong field situation, and deduce the deviation of light path in EBD theory.     

Modulational instability of ion-acoustic waves in electron–positron–ion plasmas

The stability of modulation of ion-acoustic waves in a collisionless electron–positron–ion plasma with warm adiabatic ions is studied. Using the Krylov–Bogoliubov–Mitropolosky (KBM) perturbation technique a nonlinear Schrödinger equation governing the slow modulation of the wave amplitude is derived for the system. It is found that for given set of parameters having finite ion temperature ratio (T _i /T _e ) the waves are unstable for the values of k lying in the range k _min<k<k _max. On increasing the ion temperature ratio (T _i /T _e ), it is found that k _min and k _max, both decreases and product PQ increases. The range of unstable region shifts towards the small wave number k, as temperature ratio (T _i /T _e ) increases. The positron concentration and temperature ratio of positron to electron, change the unstable region slightly. As positron concentration increases both k _min and k _max for modulational instability increases and maximum value of the product PQ shifts towards the larger value of k.     

On the Synchronizability of Tayler–Spruit and Babcock–Leighton Type Dynamos

The solar cycle appears to be remarkably synchronized with the gravitational torques exerted by the tidally dominant planets Venus, Earth and Jupiter. Recently, a possible synchronization mechanism was proposed that relies on the intrinsic helicity oscillation of the current-driven Tayler instability which can be stoked by tidal-like perturbations with a period of 11.07 years. Inserted into a simple \(\alpha \)–\(\Omega \) dynamo model these resonantly excited helicity oscillations led to a 22.14 years dynamo cycle. Here, we assess various alternative mechanisms of synchronization. Specifically we study a simple time-delay model of Babcock–Leighton type dynamos and ask whether periodic changes of either the minimal amplitude for rising toroidal flux tubes or the \(\Omega \) effect could eventually lead to synchronization. In contrast to the easy and robust synchronizability of Tayler–Spruit dynamo models, our answer for those Babcock–Leighton type models is less propitious.     

The north–south asymmetry of filaments in solar cycles 16–21

In the present study, the north–south asymmetry of filaments in solar cycles 16–21 is investigated with the use of the solar filaments observed at the Observatoire de Paris, Section de Meudon from March 1919 to December 1989. Filament activity is found regularly dominated in each of cycles 16–21 in the same hemisphere as that inferred by sunspot activity, and it is found to run in a different asymmetrical behavior at different latitudinal bands, suggesting that the north–south asymmetry of filament activity should be a function of latitudes. The regularity on the north–south asymmetry of sunspot activity given by Li et al. (2002b) is demonstrated by filament activity. The periods in the north–south asymmetry of solar filament activity are 9.13, and 12.8 years without the solar cycle found.     

Timing irregularities of PSR J1705–1906

Timing analysis of PSR J1705–1906 using data from Nanshan 25-m and Parkes 64-m radio telescopes, which span over fourteen years, shows that the pulsar exhibits significant proper motion, and rotation instability. We updated the astrometry parameters and the spin parameters of the pulsar. In order to minimize the effect of timing irregularities on measuring its position, we employ the Cholesky method to analyse the timing noise. We obtain the proper motion of \(-77(3)\) mas?yr^?1 in right ascension and \(-38(29)\) mas?yr^?1 in declination. The power spectrum of timing noise is analyzed for the first time, which gives the spectral exponent \(\alpha =-5.2\) for the power-law model indicating that the fluctuations in spin frequency and spin-down rate dominate the red noise. We detect two small glitches from this pulsar with fractional jump in spin frequency of \(\Delta \nu /\nu \sim 2.9 \times 10^{-10}\) around MJD 55199 and \(\Delta \nu /\nu \sim 2.7\times 10^{-10}\) around MJD 55953. Investigations of pulse profile at different time segments suggest no significant changes in the pulse profiles around the two glitches.     

The Long-term Behavior of the North – South Asymmetry of Sunspot Activity

A new index, the cumulative difference of sunspot activity in the northern and southern hemispheres, respectively, is proposed to describe the long-term behavior of the North – South asymmetry of sunspot activity and to show the balance (or bias) of sunspot activity in the two solar hemispheres on a long-term scale. Sunspot groups and sunspot areas from June 1874 to January 2007 are used to show the advantage of the index. The index clearly shows a long-term characteristic time scale of about 12 cycles in the North – South asymmetry of sunspot activity. Sunspot activity is found to dominate in the southern hemisphere in cycle 23, and in cycle 24 it is predicted to dominate still in the southern hemisphere. A comparison of the new index with other similar indexes is also given.     

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.     

Identification of lines in the spectrum of the quasar 0237–233

The emission and absorption lines (3716–4290) in the spectrum of the quasar 0237–233 are identified within the framework of the PLS model. The available evidence indicates that it is a helium star. Similarities between the spectral properties of 0237–233 and the star Upsilon Sagittarii are pointed out. Predictions are made for the absorption-line spectrum which falls outside 3716–4290 and also for an expected discontinuity at 2600.