Detection of Temperature-Dependent Spectral Variation on the Asteroid Eros and New Evidence for the Presence of an Olivine-Rich Silicate Assemblage

Data obtained by the near-infrared spectrometer carried by the NEAR-Shoemaker spacecraft show that the spectral properties of the asteroid Eros vary with temperature. The manner in which they vary demonstrates that the mineral olivine is a major constituent of the surface. The near-IR temperature-dependent spectral properties of Eros in the northern hemisphere, and for two individual regions on the surface, show clear evidence of the presence of the mineral olivine and are a close match to the temperature-spectral behavior of LL-type ordinary chondrite meteorites. While the presence of other olivine-rich meteorites cannot be excluded, H-type ordinary chondrites are clearly too pyroxene-rich to be permitted as a major surface component of Eros. The results of the thermal-spectral analysis are consistent with results from analysis of conventional reflectance spectra of the asteroid and contribute unambiguous detection of olivine to the understanding of the surface composition of Eros.     

Towards a 4D topographic view of the Norwegian sea margin

The present-day topography/bathymetry of the Norwegian mainland and passive margin is a product of complex interactions between large-scale tectonomagmatic and climatic processes that can be traced back in time to the Late Silurian Caledonian Orogeny. The isostatic balance of the crust and lithosphere was clearly influenced by orogenic thickening during the Caledonian Orogeny, but was soon affected by post-orogenic collapse including overprinting of the mountain root, and was subsequently affected by a number of discrete extensional events eventually leading to continental break-up in Early Eocene time. In the mid-Jurassic the land areas experienced deep erosion in the warm and humid climate, forming a regional paleic surface. Rift episodes in the Late Jurassic and Early Cretaceous, with differential uplift along major fault zones, led to more pronounced topographic contrasts during the Cretaceous, and thick sequences of clastic sediments accumulated in the subsiding basins on the shelf. Following renewed extension in the Late Cretaceous, a new paleic surface developed in the Paleocene. Following break-up the margin has largely subsided thermally, but several Cenozoic shortening events have generated positive contraction structures. On the western side of the on-shore drainage divide, deeper erosion took place along pre-existing weakness zones, creating the template of the present day valleys and fjords. In the Neogene the mainland and large portions of the Barents Sea were uplifted. It appears that this uplift permitted ice caps to nucleate and accumulate during the Late Pliocene northern hemisphere climatic deterioration. The Late Pliocene to Pleistocene glacial erosion caused huge sediment aprons to be shed on to the Norwegian Sea and Barents Sea margins. Upon removal of the ice load the landmass adjusted isostatically, and this still continues today.     

Active galactic nuclei dust tori at low and high luminosities

A cornerstone of active galactic nuclei (AGN) unification schemes is the presence of an optically and a geometrically thick dust torus. It provides the obscuration to explain the difference between type 1 and type 2 AGN. We investigate the influence of the dust distribution on the Eddington limit of the torus. For smooth dust distributions, the Eddingtion limit on the dust alone is five orders of magnitudes below the limit for electron scattering in a fully ionized plasma, while a clumpy dust torus has an Eddington limit slightly larger than the classical one. We study the behaviour of a clumpy torus at low and high AGN luminosities. For low luminosities of the order of  ∼10⁴² erg s⁻¹  , the torus changes its characteristics and obscuration becomes insufficient. In the high-luminosity regime, the clumpy torus can show a behaviour which is consistent with the 'receding torus' picture. The derived luminosity-dependent fraction of type 2 objects agrees with recent observational results. Moreover, the luminosity-dependent covering factor in a clumpy torus may explain the presence of broad-line AGN with high column densities in X-rays.     

The accelerated Kepler problem

The accelerated Kepler problem (AKP) is obtained by adding a constant acceleration to the classical two-body Kepler problem. This setting models the dynamics of a jet-sustaining accretion disk and its content of forming planets as the disk loses linear momentum through the asymmetric jet-counterjet system it powers. The dynamics of the accelerated Kepler problem is analyzed using physical as well as parabolic coordinates. The latter naturally separate the problem’s Hamiltonian into two unidimensional Hamiltonians. In particular, we identify the origin of the secular resonance in the AKP and determine analytically the radius of stability boundary of initially circular orbits that are of particular interest to the problem of radial migration in binary systems as well as to the truncation of accretion disks through stellar jet acceleration.     

Nature of the small main belt Asteroid 3169 Ostro

We present a set of rotational lightcurve measurements of the small main belt Asteroid 3169 Ostro. Our observations reveal an unambiguous, double-peaked rotational lightcurve with a peak-to-peak variation up to 1.2±0.05 mag and a synodic period of 6.509±0.001 h. From the large flux variation and the overall shape of the lightcurves, we suggest that 3169 Ostro could be a tightly bound binary or a contact binary, similar to the Trojan Asteroid 624 Hektor. A shape model of this system is proposed on the assumption that 3169 Ostro is a Roche binary described by a pair of homogeneous elongated bodies, with a size ratio of 0.87, in hydrostatic equilibrium and in circular synchronous motion around each other. The direction of the spin axis is determined modulo 180° by its J2000 ecliptic coordinates λ₀=50±10°, β₀=±54±5°. The binary interpretation and the pole solution adequately fit the earlier photometric observations made in 1986 and 1988. However, additional supporting lightcurves are highly desirable especially in the next mutual events occurrence of 2008 and 2009 in order to remove the pole ambiguity and to confirm unambiguously the binary nature of 3169 Ostro.     

Physical investigation of the potentially hazardous Asteroid (144898) 2004 VD17

In this paper we present the observational campaign carried out at ESO NTT and VLT in April and May 2006 to investigate the nature and the structure of the near-Earth object (144898) 2004 VD17. In spite of a great quantity of dynamical information, according to which it will have a close approach with the Earth in the next century, the physical properties of this asteroid are largely unknown. We performed visible and near-infrared photometry and spectroscopy, as well as polarimetric observations. Polarimetric and spectroscopic data allowed us to classify 2004 VD17 as an E-type asteroid. A good agreement was also found with the spectrum of the aubrite meteorite Mayo Belwa. On the basis of the polarimetric albedo (pv=0.45) and of photometric data, we estimated a diameter of about 320 m and a rotational period of about 2 h. The analysis of the results obtained by our complete survey have shown that (144898) 2004 VD17 is a peculiar NEO, since it is close to the breakup limits for fast rotator asteroids, as defined by Pravec and Harris [Pravec, P., Harris, A.W., 2000. Icarus 148, 12-20]. These results suggest that a more robust structure must be expected, as a fractured monolith or a rubble pile in a “strength regime” [Holsapple, K.A., 2002. Speed limits of rubble pile asteroids: Even fast rotators can be rubble piles. In: Workshop on Scientific Requirements for Mitigation of Hazardous Comets and Asteroids, Washington, September, 2002].     

Search for GRB related prompt optical emission and other fast varying objects with “Pi of the Sky” detector

Experiment “Pi of the Sky” is designed to search for prompt optical emission from GRB sources. 32 CCD cameras covering 2 steradians will monitor the sky continuously. The data will be analysed on-line in search for optical flashes. The prototype with 2 cameras operated at Las Campanas (Chile) since 2004 has recognised several outbursts of flaring stars and has given limits for a few GRB.     

Identification of high energy gamma-ray sources and source populations in the era of deep all-sky coverage

A large fraction of the anticipated source detections by the Gamma-ray Large Area Space Telescope (GLAST-LAT) will initially be unidentified. We argue that traditional approaches to identify individuals and/or populations of gamma ray sources will encounter procedural limitations. Those limitations are discussed on the background of source identifications from EGRET observations. Generally, our ability to classify (faint) source populations in the anticipated GLAST dataset with the required degree of statistical confidence will be hampered by sheer source wealth. A new paradigm for achieving the classification of gamma ray source populations is discussed.     

Rapid variability of the line He I λ 587.6 nm in the spectrum of the Herbig Ae/Be star WW Vul

We investigate the behavior of the relatively strong absorption line He I λ 587.6 nm in the spectrum of the rapid irregular variable star WW Vul (Sp A3) with the Algol-like brightness fadings. As many as 76 spectra of this star were acquired with the 2.6-m ZTSh telescope of the Crimean Astrophysical Observatory with the use of the medium-dispersion spectrograph SPEM. We show that the equivalent width of the He I line exhibits not only daily variations but also rapid oscillations with a typical period of several tens of minutes. Quasi-simultaneous observations of several standard stars with known energy distributions allowed us to calculate the monochromatic magnitudes of the variable at λ = 550 nm. There was no correlation between the equivalent widths of the line He I λ 587.6 nm and the monochromatic brightness of the star. At times we could identify the short-wave emission component of the He I line. We used the H_β profiles to confirm the spectral type A2–A3 of WW Vul.     

Structure of radio sources at wavelengths 10.5 and 12.0 cm from observations of the Solar eclipse on March 29, 2006

The eclipse observations were performed at the Laboratory of Radio Astronomy of the CrAO in Katsiveli with stationary instrumentation of the Solar Patrol at wavelengths of 10.5 and 12.0 cm. The data obtained were used to determine the brightness temperature of the undisturbed Sun at solar activity minimum between 11-year cycles 23 and 24: T _d10.5 = (43.7 ± 0.5) × 10³ K at 10.5 cm and T _d12.0 = (51.8 ± 0.5) × 10³ K at 12.0 cm. The radio brightness distribution above the limb group of sunspots NOAA 0866 was calculated. It shows that at both wavelengths the source consisted of a compact bright nucleus about 50 × 10³ km in size with temperatures T _b10.5 = 0.94 × 10⁶ K and T _b12.0 = 2.15 × 10⁶ K located, respectively, at heights h _10.5 = 33.5 × 10³ km and h _12.0 = 43.3 × 10³ km above the sunspot and an extended halo with a temperature T _b = (230–300) × 10³ K stretching to a height of 157 × 10³ km above the photosphere. The revealed spatial structure of the local source is consistent with the universally accepted assumption that the radiation from the bright part of the source is generated by electrons in the sunspot magnetic fields at the second-third cyclotron frequency harmonics and that the halo is the bremsstrahlung of thermal electrons in the coronal condensation forming an active region. According to the eclipse results, the electron density near the upper boundary of the condensation was N _e ≈ 2.3 × 10⁸ cm^?3, while the optical depth was τ ≈ 0.1 at an electron temperature T _e ≈ 10⁶ K. Thus, the observations of the March 29, 2006 eclipse have allowed the height of the coronal condensation at solar activity minimum to be experimentally determined and the physical parameters of the plasma near its upper boundary to be estimated.