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Kudrin A.V.,Nizhny Novgorod State Technical University | Shkokova N.M.,Nizhny Novgorod State Technical University | Ferencz O.E.,Research Center for Astronomy and Earth science | Zaboronkova T.M.,Nizhny Novgorod State Technical University
Physics of Plasmas | Year: 2014

Pulsed radiation from a loop antenna located in a cylindrical duct with enhanced plasma density is studied. The radiated energy and its distribution over the spatial and frequency spectra of the excited waves are derived and analyzed as functions of the antenna and duct parameters. Numerical results referring to the case where the frequency spectrum of the antenna current is concentrated in the whistler range are reported. It is shown that under ionospheric conditions, the presence of an artificial duct with enhanced density can lead to a significant increase in the energy radiated from a pulsed loop antenna compared with the case where the same source is immersed in the surrounding uniform magnetoplasma. The results obtained can be useful in planning active ionospheric experiments with pulsed electromagnetic sources operated in the presence of artificial field-aligned plasma density irregularities that are capable of guiding whistler waves. © 2014 AIP Publishing LLC. Source


Kereszturi A.,Research Center for Astronomy and Earth science | Noack L.,Royal Observatory of Belgium
Origins of Life and Evolution of Biospheres | Year: 2016

In this work various factors on the habitability were considered, focusing on conditions irrespective of the central star’s radiation, to see the role of specific planetary body related effects. These so called planetary factors were evaluated to identify those trans-domain issues where important information is missing but good chance exit to be filled by new knowledge that might be gained in the next decade(s). Among these strategic knowledge gaps, specific issues are listed, like occurrence of radioactive nucleides in star forming regions, models to estimate the existence of subsurface liquid water from bulk parameters plus evolutionary context of the given system, estimation on the existence of redox gradient depending on the environment type etc. These issues require substantial improvement of modelling and statistical handling of various cases, as “planetary environment types”. Based on our current knowledge it is probable that subsurface habitability is at least as frequent, or more frequent than surface habitability. Unfortunately it is more difficult from observations to infer conditions for subsurface habitability, but specific argumentation might help with indirect ways, which might result in new methods to approach habitability in general. © 2016 Springer Science+Business Media Dordrecht Source


Ness M.,Australian National University | Freeman K.,Australian National University | Athanassoula E.,French National Center for Scientific Research | Wylie-De-Boer E.,Australian National University | And 8 more authors.
Astrophysical Journal | Year: 2012

Near the minor axis of the Galactic bulge, at latitudes b < -5°, the red giant clump stars are split into two components along the line of sight. We investigate this split using the three fields from the ARGOS survey that lie on the minor axis at (l, b) = (0°, -5°), (0°, -75), (0°, -10°). The separation is evident for stars with [Fe/H] > - 0.5 in the two higher-latitude fields, but not in the field at b = -5°. Stars with [Fe/H] < - 0.5 do not show the split. We compare the spatial distribution and kinematics of the clump stars with predictions from an evolutionary N-body model of a bulge that grew from a disk via bar-related instabilities. The density distribution of the peanut-shaped model is depressed near its minor axis. This produces a bimodal distribution of stars along the line of sight through the bulge near its minor axis, very much as seen in our observations. The observed and modeled kinematics of the two groups of stars are also similar. We conclude that the split red clump of the bulge is probably a generic feature of boxy/peanut bulges that grew from disks, and that the disk from which the bulge grew had relatively few stars with [Fe/H] < - 0.5. © © 2012. The American Astronomical Society. All rights reserved.. Source


Ness M.,Australian National University | Freeman K.,Australian National University | Athanassoula E.,Aix - Marseille University | Wylie-de-Boer E.,Australian National University | And 8 more authors.
Monthly Notices of the Royal Astronomical Society | Year: 2013

We present the metallicity results from the ARGOS spectroscopic survey of the Galactic bulge. Our aim is to understand the formation of the Galactic bulge: did it form via mergers, as expected from Λ cold dark matter theory, or from disc instabilities, as suggested by its boxy/peanut shape, or both? Our stars are mostly red clump giants, which have a well-defined absolute magnitude from which distances can be determined. We have obtained spectra for 28 000 stars at a spectral resolution of R = 11 000. From these spectra, we have determined stellar parameters and distances to an accuracy of <1.5 kpc. The stars in the inner Galaxy span a large range in [Fe/H], -2.8 ≤ [Fe/H] ≤ +0.6. From the spatial distribution of the red clump stars as a function of [Fe/H], we propose that the stars with [Fe/H] > -0.5 are part of the boxy/peanut bar/bulge. We associate the lower metallicity stars ([Fe/H] < -0.5) with the thick disc, which may be puffed up in the inner region, and with the inner regions of the metal-weak thick disc and inner halo. For the bulge stars with [Fe/H] > -0.5, we find two discrete populations: (i) stars with [Fe/H] ≈ -0.25 which provide a roughly constant fraction of the stars in the latitude interval b = -5° to -10°, and (ii) a kinematically colder, more metal-rich population with mean [Fe/H] ≈ +0.15 which is more prominent closer to the plane. The changing ratio of these components with latitude appears as a vertical abundance gradient of the bulge. We attribute both of these bulge components to instability-driven bar/bulge formation from the thin disc. We associate the thicker component with the stars of the early less metal-rich thin disc, and associate the more metal-rich population concentrated to the plane with the colder more metal-rich stars of the early thin disc, similar to the colder and younger more metal-rich stars seen in the thin disc in the solar neighbourhood today. We do not exclude a weak underlying classical merger-generated bulge component, but see no obvious kinematic association of any of our bulge stars with such a classical bulge component. The clear spatial and kinematic separation of the two bulge populations (i) and (ii) makes it unlikely that any significant merger event could have affected the inner regions of the Galaxy since the time when the bulge-forming instabilities occurred. © 2013 The Authors Published by Oxford University Press on behalf of the Royal Astronomical Society. Source


Frey S.,FOMI Satellite Geodetic Observatory | Paragi Z.,Joint Institute for VLBI in Europe | An T.,Chinese Academy of Sciences | An T.,Netherlands Institute for Radio Astronomy | And 2 more authors.
Monthly Notices of the Royal Astronomical Society | Year: 2012

The radio-emitting quasar SDSS J1425+3231 (z = 0.478) was recently found to have double-peaked narrow [Oiii] optical emission lines. Based on the analysis of the optical spectrum, Peng et al. suggested that this object harbours a dual active galactic nucleus (AGN) system, with two supermassive black holes (SMBHs) separated on a kpc scale. SMBH pairs should be ubiquitous according to hierarchical galaxy formation scenarios in which the host galaxies and their central black holes grow together via interactions and eventual mergers. Yet the number of presently confirmed dual SMBHs on kpc or smaller scales remains small. A possible way to obtain direct observational evidence for duality is to conduct high-resolution radio interferometric measurements, provided that both AGN are in an evolutionary phase when some activity is going on in the radio. We used the technique of very long baseline interferometry (VLBI) to image SDSS J1425+3231. Observations made with the European VLBI Network at 1.7- and 5-GHz frequencies in 2011 revealed compact radio emission at sub-mJy flux density levels from two components with a projected linear separation of ∼2.6kpc. These two components support the possibility of a dual AGN system. The weaker component remained undetected at 5 GHz due to its steep radio spectrum. Further study will be necessary to securely rule out a jet-shock interpretation of the less dominant compact radio source. Assuming the dual AGN interpretation, we discuss black hole masses, luminosities and accretion rates of the two components using available X-ray, optical and radio data. While high-resolution radio interferometric imaging is not an efficient technique to search blindly for dual AGN, it is an invaluable tool to confirm the existence of selected candidates. © 2012 The Authors Monthly Notices of the Royal Astronomical Society © 2012 RAS. Source

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