The atmospheric composition,extinction and luminosity of the LBV R71

ESO 3.6m Caspec spectra of the LMC luminous blue variable (LBV) taken at minimum have been analysed using NLTE model atmospheres and line formation calculations to derive atmospheric parameters and chemical composition. Using the silicon ionization balance and the hydrogen Balmer lines we deriveT _eff =17250, log g=1.80 and a microturbulent velocity of 15–20 km/s. The analysis yields abundance ratios by number of approximately 0.43 for He/H, 0.03 for C/N and 0.14 for O/N, implying that enrichment of the atmosphere by processed material has taken place. We have re-evaluated the reddening of R71 using IUE low resolution data and published UBVRIJHKL photometry and derive a value for A _V of 0.63. We also construct an extinction curve using archive IUE data for mid-B LMC supergiants and show that the extinction is anomalous; the 2175A bump being almost absent and the far UV rise very pronounced. A comparison of our model flux in theV-band with the observed (dereddened)V magnitude and the D.M. of the LMC (18.45), implies that the bolometric magnitude or R71 is –9.9. This is significantly higher than the value of –9.0 usually adopted for R71 and suggests that this object may not in fact be a subluminous LBV.     

Frequency-hopping signal detection using partial band coverage

The performance of a channelized radiometer in detecting a frequency-hopping signal is analyzed for a variable number of parallel radiometers not necessarily covering the entire hopping band. The full band may not be covered because of an attempt to avoid interfering signals, limited radiometer resources, lack of knowledge of the band frequency location, or combinations of these factors. The analysis provides for calculation of the value of the signal-to-noise ratio (SNR) required to achieve a given probability of detection for a specified false-alarm rate, assuming an observation interval equivalent to N hops using either a fixed or a moving observation window. The dependence of the probability of detection on a misalignment of the detector observation intervals with the hop transitions is also analyzed. Numerical results are presented and discussed. Applied to a typical slow-hopping VHF radio, the results imply that a 150-hop transmission can be detected by a channelized radiometer covering half the hopping band when the SNR is about 2 dB     

Doppler tomography of O-type binaries: The physical properties of seven systems

We have analyzed UV photospheric lines of seven O-type binaries, by means of crosscorrelation and Doppler tomographic methods, with the goal of estimating the physical properties of the individual stars. These systems are HD 1337 (AO Cas), HD 47129 (Plaskett's star), HD 57060 (29 UW CMa), HD 37043 (Iota Ori), HD 215835 (DH Cep), HD 152218, and HD 152248. Mass ratios have been obtained primarily from a cross-correlation technique, but also by several other techniques. The tomographic techniques allow us to separate the spectra of the components. We then can estimate the individual spectral types and luminosity classes of the stars (and henceT _eff and logg, respectively), the luminosity ratio, and projected rotational velocities. We discuss the physical properties of these O-type binaries. These are some of the early results of a large scale project involving 36 O-type double-lined binary systems (from the catalog of Battenet al. 1989) which we will study using IUE and complementary ground-based data.     

A Self-Consistent Determination of the Temperature Profile and The Magnetic Field Geometry in Winds of Late-Type Stars

Cool giant and supergiant stars generally present low velocity winds with high mass-loss rates. Several models have been proposed to explain the acceleration process of these winds. Although dust is known to be present in these objects, the radiation pressure on these particles is uneffective in reproducing the observed physical parameters of the wind. The most promising acceleration mechanism cited in the literature is the transference of momentum and energy from Alfvén waves to the gas. Usually, these models consider the wind to be isothermal. We present a stellar wind model in which the Alfvén waves are used as the main acceleration mechanism, and determine the temperature profile by solving the energy equation taking into account both the radiative losses and the wave heating. We also determine, self-consistently, the magnetic field geometry as the result of the competition between the magnetic field and the thermal pressure gradient. As the main result, we show that the magnetic geometry presents a super-radial index in the region where the gas pressure is increasing. However, this super-radial index is greater than that observed for the solar corona.     

Solar Influences on Dynamical Coupling Between the Stratosphere and Troposphere

We use a simplified atmospheric general circulation model (AGCM) to investigate the response of the lower atmosphere to thermal perturbations in the lower stratosphere. The results show that generic heating of the lower stratosphere tends to weaken the sub-tropical jets and the tropospheric mean meridional circulations. The positions of the jets, and the extent of the Hadley cells, respond to the distribution of the stratospheric heating, with low latitude heating displacing them poleward, and uniform heating displacing them equatorward. The patterns of response to the low latitude heating are similar to those found to be associated with solar variability in previous observational data analysis, and to the effects of varying solar UV radiation in sophisticated AGCMs. In order to investigate the chain of causality involved in converting the stratospheric thermal forcing to a tropospheric climate signal we conduct an experiment which uses an ensemble of model spin-ups to analyse the time development of the response to an applied stratospheric perturbation. We find that the initial effect of the change in static stability at the tropopause is to reduce the eddy momentum flux convergence in this region. This is followed by a vertical transfer of the momentum forcing anomaly by an anomalous mean circulation to the surface, where it is partly balanced by surface stress anomalies. The unbalanced part drives the evolution of the vertically integrated zonal flow. We conclude that solar heating of the stratosphere may produce changes in the circulation of the troposphere even without any direct forcing below the tropopause. We suggest that the impact of the stratospheric changes on wave propagation is key to the mechanisms involved.     

Performance comparison of PRF schedules for medium PRF radar

Previous work has shown how evolutionary algorithms (EAs) are an effective tool in optimising the selection of pulse repetition frequency (PRF) values of medium PRF schedules in an airborne fire control radar (FCR) application requiring target data in three PRFs. The optimisation is driven by the requirement to minimise range/Doppler blindness whilst maintaining full decodability. In this paper we detail work in which the optimisation process is applied to design novel short medium PRF schedules requiring target data in just two PRFs. The paper reports on the testing of a variety of near-optimum schedules to compare their blindness, decoding, and ghosting performances. The results show that in many situations, the 2 of N schedules are a practical alternative to conventional 3 of N processing.     

A detailed FLUKA-2005 Monte-Carlo simulation for the ATIC detector

We have performed a detailed Monte-Carlo (MC) simulation for the Advanced Thin Ionization Calorimeter (ATIC) detector using the MC code FLUKA-2005 which is capable of simulating particles up to 10 PeV. The ATIC detector has completed two successful balloon flights from McMurdo, Antarctica lasting a total of more than 35 days. ATIC is designed as a multiple, long duration balloon flight, investigation of the cosmic ray spectra from below 50 GeV to near 100 TeV total energy; using a fully active Bismuth Germanate (BGO) calorimeter. It is equipped with a large mosaic of silicon detector pixels capable of charge identification, and, for particle tracking, three projective layers of x–y scintillator hodoscopes, located above, in the middle and below a 0.75 nuclear interaction length graphite target. Our simulations are part of an analysis package of both nuclear (A) and energy dependences for different nuclei interacting in the ATIC detector. The MC simulates the response of different components of the detector such as the Si-matrix, the scintillator hodoscopes and the BGO calorimeter to various nuclei. We present comparisons of the FLUKA-2005 MC calculations with GEANT calculations and with the ATIC CERN data.     

Leaf proteomic analysis of three rice heritable mutants after seed space flight

To explore the proteomic changes of heritable variant rice plants induced by space environment, three mutants were selected after seed space flight by comparing the phenotypes with their on-ground controls. R955 grew more tillers and became dwarf, 971-5 acquired higher grain yield and better stress resistance, 974-5 matured earlier. Leaf proteins were extracted during the tiller development and analyzed by two-dimensional polyacrylamide gel electrophoresis (2-D PAGE). More than 300 proteins were detected as reproducible Coomassie Brilliant Blue stained spots with pI values from around 4.0 to 7.0. Five proteins that changed significantly over the controls were identified by matrix-assisted laser desorption/ionization-time of flight mass spectrometry (MALDI-TOF MS). The main functions of these proteins were photosynthesis, stress defense and metabolism including RuBisCO activase, glycine rich RNA binding protein, peroxidase, triosephosphate isomerase and phosphoenolpyruvate carboxylase, which might be probably associated with the altered phenotypes. Quantitative analyses were also applied: less total protein spots and more down-regulated protein spots were detected in the mutants, indicating there might be a major loss of protein in heritable variant rice plants after seed space flight. These results may provide new insights to understand the biological effects of space environment to rice.     

Magnetospheric electric field variations caused by storm-time shock fronts

On January 20, 2005 there was an X 7.1 solar flare at 0636 UT with an accompanied halo coronal mass ejection (CME). The resultant interplanetary shock impacted earth ∼36 h later. Near earth, the Advanced Composition Explorer (ACE) spacecraft observed two impulses with a staircase structure in density and pressure. The estimated earth-arrival times of these impulses were 1713 UT and 1845 UT on January 21, 2005. Three MINIature Spectrometer (MINIS) balloons were aloft on January 21st; one in the northern polar stratosphere and two in the southern polar stratosphere. MeV relativistic electron precipitation (REP) observed by all three balloons is coincident (<3 min) with the impulse arrivals and magnetospheric compression observed by both GOES 10 and 12. Balloon electric field data from the southern hemisphere show no signs of the impulse electric field directly reaching the ionosphere. Enhancement of the balloon-observed convection electric field by as much as 40 mV/m in less than 20 min during this time period is consistent with typical substorm growth. Precipitation-induced ionospheric conductivity enhancements are suggested to be (a) the result of both shock arrival and substorm activity and (b) the cause of rapid (<6 min) decreases in the observed electric field (by as much as 40 mV/m). There is poor agreement between peak cross polar cap potential in the northern hemisphere calculated from Super Dual Auroral Radar Network (SuperDARN) echoes and horizontal electric field at the MINIS balloon locations in the southern hemisphere. Possible reasons for this poor agreement include (a) a true lack of north–south conjugacy between measurement sites, (b) an invalid comparison between global (SuperDARN radar) and local (MINIS balloon) measurements and/or (c) radar absorption resulting from precipitation-induced D-region ionosphere density enhancements.