On the planar motion in the full two-body problem with inertial symmetry

Relative motion of binary asteroids, modeled as the full two-body planar problem, is studied, taking into account the shape and mass distribution of the bodies. Using the Lagrangian approach, the equations governing the motion are derived. The resulting system of four equations is nonlinear and coupled. These equations are solved numerically. In the particular case where the bodies have inertial symmetry, these equations can be reduced to a single equation, with small nonlinearity. The method of multiple scales is used to obtain a first-order solution for the reduced nonlinear equation. The solution is shown to be sufficient when compared with the numerical solution. Numerical results are provided for different example cases, including truncated-cone-shaped and peanut-shaped bodies.     

Thermodynamics of accelerating and rotating black holes

Thermodynamics of a large family of black holes from electrovacuum solutions of Einstein’s equations is studied. This family includes rotating and non-accelerating black holes with NUT charge, and rotating and accelerating black holes. The surface gravity, Hawking temperature and the area laws for these black holes are presented. The first law of thermodynamics is also given. An interesting outcome of our analysis is the restriction obtained on the magnitude of acceleration for these black holes.     

Solar Flare Prediction Using Advanced Feature Extraction, Machine Learning, and Feature Selection

Novel machine-learning and feature-selection algorithms have been developed to study: i) the flare-prediction-capability of magnetic feature (MF) properties generated by the recently developed Solar Monitor Active Region Tracker (SMART); ii) SMART’s MF properties that are most significantly related to flare occurrence. Spatiotemporal association algorithms are developed to associate MFs with flares from April 1996 to December 2010 in order to differentiate flaring and non-flaring MFs and enable the application of machine-learning and feature-selection algorithms. A machine-learning algorithm is applied to the associated datasets to determine the flare-prediction-capability of all 21 SMART MF properties. The prediction performance is assessed using standard forecast-verification measures and compared with the prediction measures of one of the standard technologies for flare-prediction that is also based on machine-learning: Automated Solar Activity Prediction (ASAP). The comparison shows that the combination of SMART MFs with machine-learning has the potential to achieve more accurate flare-prediction than ASAP. Feature-selection algorithms are then applied to determine the MF properties that are most related to flare occurrence. It is found that a reduced set of six MF properties can achieve a similar degree of prediction accuracy as the full set of 21 SMART MF properties.     

Zw 1718.10108: a highly disturbed galaxy cluster at low Galactic latitude

We report the discovery of highly distorted X-ray emission associated with the nearby cluster Zw 1718.10108, one of the dominant members of which is the powerful radio galaxy 3C353. This cluster has been missed by previous X-ray cluster surveys because of its low Galactic latitude ( b =19.5°), despite its brightness in the hard X-ray band (210 keV flux of 1.210¹¹ erg cm² s¹). Our optical charge-coupled device image of the central part of the cluster reveals many member galaxies which are dimmed substantially by heavy Galactic extinction. We have measured redshifts of three bright galaxies near the X-ray emission peak and they are all found to be around z =0.028. The ASCA gas imaging spectrometer and ROSAT high-resolution imager images show three aligned X-ray clumps embedded in low surface-brightness X-ray emission extended by 30 arcmin. The averaged temperature measured with ASCA is kT =4.3±0.2 keV, which appears to be hot for the bolometric luminosity when compared with the temperatureluminosity correlation of galaxy clusters. The irregular X-ray morphology and evidence for a non-uniform temperature distribution suggest that the system is undergoing a merger of substructures. Since the sizes and luminosities of the individual clumps are consistent with those of galaxy groups, Zw 1718.10108 is interpreted as an on-going merger of galaxy groups in a dark matter halo forming a cluster of galaxies and thus is in a transition phase of cluster formation.     

Modelling the bar in the centre of the starburst galaxy M82

We present VLA A-array 21-cm atomic hydrogen (H  i ) absorption observed against the central region of the starburst galaxy M82 with an angular resolution of ∼1.3 arcsec (≃20 pc). These observations, together with MERLIN H  i absorption measurements, are compared with the molecular (CO) and ionized ([Ne  ii ]) gas distributions and are used to constrain the dynamics and structure of the ionized, neutral and molecular gas in this starburst.
A position–velocity diagram of the H  i distribution reveals an unusual 'hole' feature which, when previously observed in CO, has been interpreted as an expanding superbubble contained within a ring of gas in solid body rotation. However, we interpret this feature as a signature of a nearly edge-on barred galaxy. In addition, we note that the CO, H  i and [Ne  ii ] position–velocity diagrams reveal two main velocity gradients, and we interpret these as gas moving on x₁- and x₂-orbits within a bar potential. We find the best fit to the data to be produced using a bar potential with a flat rotation curve velocity v _b=140 km s⁻¹ and a total length of 1 kpc, a non-axisymmetry parameter q =0.9, an angular velocity of the bar Ω_b=217 km s⁻¹ arcsec⁻¹, a core radius R _c=25 pc, an inclination angle i =80° and a projected angle between the bar and the major axis of the galaxy φ '=4°. We also discuss the orientation of the disc and bar in M82.     

Testing the Gaussianity of the COBE DMR data with spherical wavelets

We investigate the Gaussianity of the 4-yr COBE DMR data (in HEALPix pixelization) using an analysis based on spherical Haar wavelets. We use all the pixels lying outside the Galactic cut and compute the skewness, kurtosis and scale–scale correlation spectra for the wavelet coefficients at each scale. We also take into account the sensitivity of the method to the orientation of the input signal. We find a detection of non-Gaussianity at >99 per cent level in just one of our statistics. Taking into account the total number of statistics computed, we estimate that the probability of obtaining such a detection by chance for an underlying Gaussian field is 0.69. Therefore, we conclude that the spherical wavelet technique shows no strong evidence of non-Gaussianity in the COBE DMR data.     

Submillimetre imaging of NGC 3079

Submillimetre mapping observations of the active edge-on spiral galaxy NGC 3079 are presented. These maps at 850 and 450 μm were made with the Submillimetre Common User Bolometer Array (SCUBA) at the James Clerk Maxwell Telescope (JCMT).
The source structure at these wavelengths consists of a central unresolved source embedded in diffuse disc emission, similar to that displayed at 1.2 mm. The disc emission is fitted with two optically thin, isothermal dust models which give temperatures of 12 and 31 K, similar to those derived previously by Braine et al. The core component is well described by a single-temperature fit (∼32 K). The combined dust mass from these observations, using the same mass absorption coefficient as Devereux & Young (1990) is 3.5×10⁸ M_⊙, of which ∼90 per cent resides in the cold component of the galactic disc. The effect of the cold dust component detected by SCUBA is thus to reduce the global gas-to-dust mass ratio from ∼1400 found in the above study to 85, very similar to the Galactic level. Calculations using the models of Draine & Lee and/or alternative molecular gas mass estimates yield gas-to-dust mass ratios in the range 60–190.
The data presented here, together with previously published 1.2-mm mapping observations and IRAS data, are inconsistent with detections made with the Infrared Space Observatory ( ISO ). In particular, the latter give an excess of flux at 200 and 180 μm relative to that predicted by our simple model fits (approximately a factor of 2–3).     

The Non-Linear Stability of L4 in the Restricted Three-Body Problem when the Bigger Primary is a Triaxial Rigid Body

The non-linear stability of L ₄ in the restricted three-body problem has been studied when the bigger primary is a triaxial rigid body with its equatorial plane coincident with the plane of motion. It is found that L ₄ is stable in the range of linear stability except for three mass ratios:

Ca X line ratios in solar flares

Theoretical Ca X electron temperature sensitive emission line ratios, derived using electron excitation rates interpolated from accurateR-matrix calculations, are presented forR ₁ =I(419.74 )/I(574.02 ,),R ₂ =I(411.65 )/I(574.02 ),R ₃ =I(419.74 )/I(557.75 ), andR ₄ =I(411.65 )/I(557.75 ). A comparison of these with observational data for three solar flares, obtained by the Naval Research Laboratory's S082A slitless spectrograph on boardSkylab, reveals good agreement between theory and observation forR ₁ andR ₃ in one event, which provides limited support for the accuracy of the atomic data adopted in the analysis. However, in the other flares the observed values ofR ₁ –R ₄ are much larger than the theoretical high-temperature limits, which is probably due to blending of the 419.74 line with Civ 419.71 , and 411.65 with possibly Ciii 411.70 .     

Mid-infrared imaging of ultracompact H II regions

We discuss preliminary results of an 11.7 m imaging survey of ultracompact H II regions from the Wood and Churchwell radio survey. We find that that the morphologies of ionized gas and warm dust are often significantly different, indicating that an H II region classification scheme should be based on more than radio data.