Apex I and Apex II software packages for the reduction of astronomical CCD observations

We describe in detail the Apex I and Apex II software packages created for astrometric and photometric reductions of astronomical observations with CCD cameras. The Apex I software package has been created for the semiautomatic reduction of astronomical observations and has a convenient user interface. The Apex II software package allows for the completely automatic reduction of astrometric and photometric observations to be performed.     

Radar and photometric observations and shape modeling of contact binary near-Earth Asteroid (8567) 1996 HW1

We observed near-Earth Asteroid (8567) 1996 HW1 at the Arecibo Observatory on six dates in September 2008, obtaining radar images and spectra. By combining these data with an extensive set of new lightcurves taken during 2008-2009 and with previously published lightcurves from 2005, we were able to reconstruct the object’s shape and spin state. 1996 HW1 is an elongated, bifurcated object with maximum diameters of 3.8 × 1.6 × 1.5 km and a contact-binary shape. It is the most bifurcated near-Earth asteroid yet studied and one of the most elongated as well. The sidereal rotation period is 8.76243 ± 0.00004 h and the pole direction is within 5° of ecliptic longitude and latitude (281°, −31°). Radar astrometry has reduced the orbital element uncertainties by 27% relative to the a priori orbit solution that was based on a half-century of optical data. Simple dynamical arguments are used to demonstrate that this asteroid could have originated as a binary system that tidally decayed and merged.     

Rotational dynamics of planetary satellites: A survey of regular and chaotic behavior

The problem of observability of chaotic regimes in the rotation of planetary satellites is studied. The analysis is based on the inertial and orbital data available for all satellites discovered up to now. The Lyapunov spectra of the spatial chaotic rotation and the full range of variation of the spin rate are computed numerically by integrating the equations of the rotational motion; the initial data are taken inside the main chaotic layer near the separatrices of synchronous resonance in phase space. The model of a triaxial satellite in a fixed elliptic orbit is adopted. A short Lyapunov time along with a large range of variation of the spin rate are used as criteria for observability of the chaotic motion. Independently, analysis of stability of the synchronous state with respect to tilting the axis of rotation provides a test for the physical opportunity for a satellite to rotate chaotically. Finally, a calculation of the times of despinning due to tidal evolution shows whether a satellite's spin could evolve close to the synchronous state. Apart from Hyperion, already known to rotate chaotically, only Prometheus and Pandora, the 16th and 17th satellites of Saturn, pass all these four tests.     

Chaotic Asteroidal Dynamics and Maximum Lyapunov Exponents

This paper describes the results of studies of dynamical chaos in the problem of the orbital dynamics of asteroids near the 3 : 1 mean-motion resonance with Jupiter. Maximum Lyapunov characteristic exponents (MLCEs) are used as an indicator and a measure of the chaoticity of motion. MLCE values are determined for trajectories calculated by the numerical integration of equations of motion in the planar elliptical restricted three-body problem. The dependence of the MLCE on the problem parameters and on the initial data is analyzed. The inference is made that the domain of chaos in the phase space of the problem considered consists of two components of different nature. The values of the MLCEs observed for one of the components (namely, for the component corresponding to low-eccentricity asteroidal orbits) are compared to the theoretical estimates obtained within the framework of model of the resonance as a perturbed nonlinear pendulum.     

The shapes and rotational dynamics of minor planetary satellites

Statistical analysis of the available data on the sizes and inertial parameters for all hitherto known satellites of the Solar system’s planets is performed. Analytical approximations are derived for the size distribution of satellites. Empirical relations are obtained to approximately estimate the inertial parameters of a satellite from its size. These relations can be used in statistical studies of the possibility of manifestations of various nonstandard rotational modes of planetary satellites. In particular, the probability of the “Amalthea effect” (the presence of two centers of synchronous resonance in the phase space of rotational motion) is shown to be much higher for minor (with diameters smaller than 100 km) satellites moving in close-to-circular orbits than for other satellites.     

Large-scale Structure of the Chromospheric Doppler Velocities on the Solar Disk from 2D-spectroscopy within the He I 10830 Å Line

A distribution map of the large-scale chromospheric Doppler velocities on the solar disk for 5 June 2002 is presented. The map was obtained using a 2D-spectroscopy technique within the He?i 10830 Å line. The spatial resolution of the map is about 30 arc sec. The map demonstrates a downflow in the chromosphere over active regions, especially significant around the spots and inside the plages. Positive Doppler velocities correspond to strong magnetic field areas, regardless of the field sign. Three major chromospheric outflow zones are observed: an equatorial and two polar ones. Each area of substantial negative Doppler velocities matches a zone of weak intensity of inner corona observed within the Fe?ix-x 171 Å line by the SOHO spacecraft. A Doppler velocity histogram and the dependence of the Doppler velocities on the cosine of the heliocentric angle for the solar disk are calculated. The total mass outflow from the upper chromosphere is estimated as 2×10¹³ g s^?1. Four percent of this amount is sufficient to produce the fast solar wind.