Spectroscopic binaries near the North Galactic Pole paper 18: HD 118670

Photoelectric radial-velocity measurements show that HD 118670 is a double-lined spectroscopic binary in an orbit which is not quite circular and whose period is about 48 days. Spectral types of K0 V and K7 V would satisfy the photometry and the mass ratio; the mass function would then suggest the possibility of eclipses. However, actual spectral classification indicates a luminosity somewhat above the main sequence     

Magnetic Field Strengths and Structures from Radio Observations of Solar Active Regions

Radio observations of some active regions (ARs) obtained with the Nobeyama radioheliograph at λ=1.76cm are used for estimating the magnetic field strength in the upper chromosphere, based on thermal bremsstrahlung. The results are compared with the magnetic field strength in the photosphere from observations with the Solar Magnetic Field Telescope (SMFT) at Huairou Solar Observing Station of Beijing Astronomical Observatory. The difference in the magnetic field strength between the two layers seems reasonable. The solar radio maps of active regions obtained with the Nobeyama radioheliograph, both in total intensity (I-map) and in circular polarizations (V-map), are compared with the optical magnetograms obtained with the SMFT. The comparison between the radio map in circular polarization and the longitudinal photospheric magnetogram of a plage region suggest that the radio map in circular polarization is a kind of magnetogram of the upper chromosphere. The comparison of the radio map in total intensity with the photospheric vector magnetogram of an AR shows that the radio map in total intensity gives indications of magnetic loops in the corona, thus we have a method of defining the coronal magnetic structure from the radio I-maps at λ=1.76 cm. Analysing the I-maps, we identified three components: (a) a compact bright source; (b) a narrow elongated structure connecting two main magnetic islands of opposite polarities (observed in both the optical and radio magnetograms); (c) a wide, diffuse, weak component that corresponds to a wide structure in the solar active region which shows in most cases an S or a reversed S contour, which is probably due to the differential rotation of the Sun. The last two components suggest coronal loops on different spatial scales above the neutral line of the longitudinal photospheric magnetic field.     

Sonar acoustic facies and sediment distribution on an area of the deep ocean floor

Long-range sidescan sonar can be used to map sediment distributions over wide expanses of deep ocean floor. Seven acoustic facies that arise from differing sediment or rock types have been mapped over the low-relief Saharan continental rise and Madeira abyssal plain. These have been calibrated with sampling, profiling and camera studies and the facies can be traced confidently on a regional scale using the sidescan data. The mapping of the sediment distribution shows that a complex interplay of turbidity current and debris flow processes can occur at a continental rise/abysaal plain transition over 1000 km from the nearest continental slope.     

Upscaling of elastic properties for large scale geomechanical simulations

Large scale geomechanical simulations are being increasingly used to model the compaction of stress dependent reservoirs, predict the long term integrity of under‐ground radioactive waste disposals, and analyse the viability of hot‐dry rock geothermal sites. These large scale simulations require the definition of homogenous mechanical properties for each geomechanical cell whereas the rock properties are expected to vary at a smaller scale. Therefore, this paper proposes a new methodology that makes possible to define the equivalent mechanical properties of the geomechanical cells using the fine scale information given in the geological model. This methodology is implemented on a synthetic reservoir case and two upscaling procedures providing the effective elastic properties of the Hooke's law are tested. The first upscaling procedure is an analytical method for perfectly stratified rock mass, whereas the second procedure computes lower and upper bounds of the equivalent properties with no assumption on the small scale heterogeneity distribution. Both procedures are applied to one geomechanical cell extracted from the reservoir structure. The results show that the analytical and numerical upscaling procedures provide accurate estimations of the effective parameters. Furthermore, a large scale simulation using the homogenized properties of each geomechanical cell calculated with the analytical method demonstrates that the overall behaviour of the reservoir structure is well reproduced for two different loading cases. Copyright © 2004 John Wiley & Sons, Ltd.     

Geometry and kinematics of recent deformation in the Mondy–Tunka area (south-westernmost Baikal rift zone, Mongolia–Siberia)

We used satellite imagery and field data to investigate the south‐westernmost Baikal rift zone. We focus our study in the Mondy and Ikhe Ukhgun valleys, site of an Mw = 6.9 seismic event in 1950. Surface deformations are observed along the E–W‐trending Mondy strike‐slip fault and along the Ikhe Ukhgun thrust. The Mondy fault system is 80 km long and is composed of four segments 10–15 km long. These segments are characterized by subvertical planes with left‐lateral movements. The Ikhe Ukhgun thrust is 20 km long, dips 40° to the south and shows reverse movement with a left‐lateral component. These observations are consistent with the present‐day regional NNE–SSW compression and with the focal mechanism of the 1950 Mondy earthquake that was recently re‐evaluated. These features, like those observed in the Tunka basin, demonstrate a recent change of regional strain regime from transtension to transpression that we place before the Late Pleistocene.     

Photometry of EX Hya

Photometric observations of EX Hya inB andVfilters are reported. The 67 min modulation of the light curve also is found to be in good agreement with the results of earlier studies. The (B-V) colour variation with respect to the 67 min variation is found to be opposite to those of typical colour variation during hump/superhump activity in other dwarf novae. The model of an intermediate polar is discussed.     

Preliminary organic petrography of Palaeozoic rocks from the Grand Banks,Newfoundland

Samples of lower Palaeozoic bedrock from the Grand Banks of Newfoundland were examined using reflected light microscopy and Rock-Eval pyrolysis. These samples contained organic material which included bitumen (structureless organic material), acritarchs, chitinozoa, scolecodonts and graptolites. The reflectance of the organic material increased from acritarchs towards graptolites with bitumen showing a wide range of reflectance. Multiple phases of oil migration through one sample were inferred by examination of the bitumens: the lowest reflecting being more recent than the highest reflecting bitumen. Combined reflectance and Rock-Eval analysis indicate that these samples are mature to overmature. The two oldest samples (Arenig-Llanvirn, Ordovician) are assessed as mature and as having potential for generation of liquid hydrocarbons, but must be considered as mainly gas prone.     

Readout Techniques for Drift and Low Frequency Noise Rejection in Infrared Arrays

Three different methods are presented to subtract thermal drifts and low-frequency noise from the signal of infrared array. The first is dead pixels with open Indium bumps, the second is reference output as implemented on the Hawaii2 multiplexer, and the third is dark pixels to emulate reference cells having a capacity connected to the gate of the unit cell field-effect transistor (FET). The third method is the most effective and yields a reduction in readout noise from15.4–9.4 erms. A novel method will be described to extend this readout technique to the Aladdin 1 K × 1 K InSb array. This revised version was published online in July 2006 with corrections to the Cover Date.     

The height,spectrum and mechanism of type-B red aurora and its bearing on the excitation of O(1S) in aurora

The height of the lower red border of type-B aurora has been determined by triangulation using TV cameras at two ground stations. A mean height of 91.4 ± 1.1 km was determined from a set of 12 measurements made under ideal conditions. A TV spectrograph was used simultaneously to seek possible spectral changes between 6400 and 6900 Å which would be indicative of changes in the vibrational distribution in the N₂ First Positive bands. No significant difference was found in this distribution between the spectra from 93 and 122 km. The height distribution of contributions to the OI 5577 Å emission relative to the N⁺₂ First Negative emission was modelled from 80 to 160 km. Contributions from electron impact on atomic O, O⁺₂ dissociative recombination and N₂(A)O energy transfer were included. Account was taken of recent laboratory data on O(¹S) quenching. It was concluded that these processes could explain the excitation of O(¹S) in normal aurora and the height distribution of OI 5577 Å in type-B red aurora. It was confirmed that the lifetime ofO(¹S) in type-B red auroral rapid time variations is about 0.5 s and it was found from the model that the observed time variation can be reproduced by the mechanisms considered, provided the concentration of NO in the auroral atmosphere is about 1 × 10⁹ at 95 km. Before reasonable certainty can be attained in the correctness of the interpretation it will however be necessary to have reliable simultaneous observations of neutral atmospheric composition particularly for O and NO as well as unchallengeable measurements of the yields of O(¹S) for the processes considered and for several other processes which have been suggested recently.