High-temperature geothermal reservoir possibilities in Hungary

Theoretical studies have shown the possibility of high-temperature ('high enthalpy') geothermal reservoirs in the pre-Tertiary rocks at 4–5 km depth range within the Pannonian Basin. This expectation was proven by the hotwater/steam blowout of Fábiánsebestyén-4 borehole (16.12.85–31.1.86). Exploration efforts carried out during 1987–88 in the broad vicinity of the borehole proved that reservoirs of this type can be found with the combination of seismic reflection, silica-thermometry and magnetotelluric sounding methods. Deliberate prospection should be continued in all suitable areas within the basin, since high enthalpy reservoirs promise profitable operation of geothermal power stations.     

Analysis of mapping coverage obtained from spacecraft

An exact analysis of the coverage obtained by spacecraft using cross-track scanning and nadir-centered conical imaging, under imposed viewing obliqueness and resolution requirements, is presented. In addition to exact expressions for the area acquired and the area acquisition rate, envelope theory is introduced to obtain the boundary of the imaged area. These expressions are relatively compact, allowing rapid machine computation. The effects of the sun phase angle, and of imaging system limitations are also examined. The Galileo mission encounter with Callisto is used as a numerical example, from which certain general conclusions are drawn regarding optimal imaging trajectories.     

Remarks on dynamical ellipticity at the Earth's

In this paper, two factors — the redistribution of the density and the variation in the angular velocity of the Earth rotation, that affect the adopted value of the flattening for equidensity surface within the Earth, are discussed. The computational results show that the contribution of the redistribution of the density in the Earth interior (especially in the core) on the change of the flattening at the core-mantle boundary (CMB) is marginal, and that the calculated value of the flattening at the CMB can be in good agreement with the VLBI observed value so long as the fact that the angular velocity of the Earth rotation has undergone the tidal evolution is taken into account. As a result, this paper presents a set of recommended values of the dynamical parameters of the Earth (see Table III) for computing Earth's forced nutation series.     

SARG: The High Resolution Spectrograph of TNG

SARG is a cross dispersed echelle spectrograph in operation since late spring 2000 at the Italian Telescopio Nazionale Galileo (TNG) 3.5 m telescope, La Palma. SARG offers both single object and long slit (up to 26 arcsec) observing modes covering a spectral range from λ = 0.37 up to1 μm, with resolution ranging from R = 29,000 up to R = 164,000. Cross dispersion is provided by means of a selection of four grisms; interference filters may be used for the long slit mode (up to 26 arcsec). A dioptric camera images the cross dispersed spectra onto a mosaic of two 2048 × 4096 EEV CCDs (pixel size: 13.5 μm) allowing complete spectral coverage at all resolving power for λ < 0.8 μm. In order to reach a high wavelength calibration precision an iodine-absorbing cell is provided. A Distributed Active Temperature Control System (DATCS) maintains constant the temperature of all spectrograph components at a preset value. Early results show that SARG works according to original specifications in terms of wavelength coverage, efficiency (measured peak efficiency is about 13%),resolution (maximum resolution R = 164,000 using a 0.3 arcsec slit, R ∼144,000 using an image slicer), and stability (preliminary estimates of radial velocity accuracy is ∼3 m/s using the iodine cell and ±150 m/s without the iodine cell). This revised version was published online in July 2006 with corrections to the Cover Date.     

Multiple stellar populations in the Sextans dwarf spheroidal galaxy?

We present wide-field     multiband ( BVI ) CCD photometry (down to     of the very low surface brightness dwarf spheroidal galaxy Sextans. In the derived colour–magnitude diagrams we find evidence suggesting the presence of multiple stellar populations in this dwarf spheroidal. In particular, we discover (i) a blue horizontal branch tail that appears to lie on a brighter sequence with respect to the prominent red horizontal branch and the RR Lyrae stars, very similar to what was found by Majewski et al. for the Sculptor dwarf spheroidal, (ii) hints of a bimodal distribution in colour of the red giant branch stars, (iii) a double red giant branch bump. All of these features suggest that (at least) two components are present in the old stellar population of this galaxy: the main one with     and a minor component around     . The similarity to the Sculptor case may indicate that multiple star formation episodes are also common in the most nearby dwarf spheroidals that ceased their star formation activity at very early epochs.     

Shape Analysis of Isoseismals Based on Empirical and Synthetic Data

—?We present an attempt to compare modeled ground-motion acceleration fields with macroseismic observations. Two techniques for the representation of the observed intensities by isoseismals, a smoothing technique and one which visualizes the local uncertainty of an isoseismal, are tested with synthetic and observed data. We show how noise in the data and irregularities in the distribution of observation sites affect the resolution of the isoseismal's shape. In addition to “standard” elongated shapes, we identify cross-like patterns in the macroseismic observations for two Italian earthquakes of strike-slip type; similar patterns are displayed by the theoretical peak acceleration fields calculated assuming the point source models given in the literature.     

Some New Observed Properties of Elliptical Galaxies

We suggest that elliptical galaxies, as stellar systems in a stage of quasi-equilibrium, may have a specific entropy. We use the Sérsic law to describe the light profile. The specific entropy (the Boltzmann–Gibbs definition) is then calculated assuming that the galaxy behaves as a spherical, isotropic, one-component system. We predict a relation between the three parameters of the Sérsic law linked to the specific entropy, defining a surface in the parameter space, an ‘entropic plane’. We have analysed a sample of simulated merging elliptical galaxies (virtual) and a sample of galaxies belonging to the Coma Cluster (real). Both virtual and realgalaxies are: 1) located in their own ‘entropic plane‘ and 2) in this plane, they are located on a straight line, indicating constant entropy: another physical property A careful examination of the value of the specific entropy indicates a very small increase in the specific entropy with the generation after merging (virtual sample). Although one cannot distinguish between various generations for real galaxies, the distribution of specific entropy in this sample is very similar to that in the virtual sample. This revised version was published online in July 2006 with corrections to the Cover Date.     

A detailed abundance analysis of the hot post-AGB star ZNG-1 in M10

We present a model-atmosphere analysis for the bright ( V ∼13) star ZNG-1, in the globular cluster M10. From high-resolution ( R ∼40 000) optical spectra we confirm ZNG-1 to be a post-asymptotic giant branch (post-AGB) star. The derived atmospheric parameters are T _eff=26 500±1000 K and log  g =3.6±0.2 dex . A differential abundance analysis reveals a chemical composition typical of hot post-AGB objects, with ZNG-1 being generally metal poor, although helium is approximately solar. The most interesting feature is the large carbon underabundance of more than 1.3 dex. This carbon deficiency, along with an observed nitrogen enhancement relative to other elements, may suggest that ZNG-1 evolved off the AGB before the third dredge-up occurred. Also, iron depletions observed in other similar stars suggest that gas–dust fractionation in the AGB progenitor could be responsible for the observed composition of these objects. However, we need not invoke either scenario since the chemical composition of ZNG-1 is in good agreement with abundances found for a Population II star of the same metallicity.     

Cosmic‐ray exposure history of two Frontier Mountain H‐chondrite showers from spallation and neutron‐capture products

Abstract— We measured the concentrations of ¹⁰Be, ²⁶Al, ³⁶Cl, ⁴¹Ca and ¹⁴C in the metal and/or stone fractions of 27 Antarctic chondrites from Frontier Mountain (FRO), including two large H‐chondrite showers. To estimate the pre‐atmospheric size of the two showers, we determined the contribution of neutron‐capture produced ³⁶Cl (half‐life = 3.01 times 10⁵ years) and ⁴¹Ca (1.04 times 10⁵ years) in the stone fraction. The measured activities of neutron‐capture ³⁶Cl and ⁴¹Ca, as well as spallation produced ¹⁰Be and ²⁶Al, were compared with Monte Carlo‐based model calculations. The largest shower, FRO 90174, includes eight fragments with an average terrestrial age of (100 ± 30) × 10³ years; the neutron‐capture saturation activities extend to 27 dpm/kg stone for ³⁶Cl and 19 dpm/kg stone for ⁴¹Ca. The concentrations of spallation produced ¹⁰Be, ²⁶Al and ³⁶Cl constrain the radius (R) to 80–100 cm, while the neutron‐capture ⁴¹Ca activities indicate that the samples originated from the outer 25 cm. With a pre‐atmospheric radius of 80–100 cm, FRO 90174 is among the largest of the Antarctic stony meteorites. The large pre‐atmospheric size supports our hypothesis that at least 50 of the ～150 classified H5/H6‐chondrites from the Frontier Mountain stranding area belong to this single fall; this hypothesis does not entirely account for the high H/L ratio at Frontier Mountain. The smaller shower, FRO 90001, includes four fragments with an average terrestrial age of (40 ± 10) × 10³ years; they contain small contributions of neutron‐capture ³⁶Cl, but no excess of ⁴¹Ca. FRO 90001 experienced a complex exposure history with high shielding conditions in the first stage (150 < R < 300 cm) and much lower shielding in the second stage (R < 30 cm), the latter starting ～1.0 million years (Ma) ago. Based on the measured ¹⁰Be/²¹Ne and ²⁶Al/²¹Ne ratios, the cosmic‐ray exposure ages of the two showers are 7.2 ± 0.5 Ma for FRO 90174 and 8 ± 1 Ma for FRO 90001. These ages coincide with the well‐established H‐chondrite peak and corroborate the observation that the exposure age distribution of FRO H‐chondrites is similar to that of non‐Antarctic falls. In addition, we found that corrections for neutron‐capture ³⁶Ar (from decay of ³⁶Cl) result in concordant ²¹Ne and ³⁸Ar exposure ages.