VLBI observations of jupiter with the initial test station of LOFAR and the nancay decametric array

AIMS: To demonstrate and test the capability of the next generation of low-frequency radio telescopes to perform high resolution observations across intra-continental baselines. Jupiter's strong burst emission is used to perform broadband full signal cross-correlations on time intervals of up to hundreds of milliseconds. METHODS: Broadband VLBI observations at about 20 MHz on a baseline of ~50000 wavelengths were performed to achieve arcsecond angular resolution. LOFAR's Initial Test Station (LOFAR/ITS, The Netherlands) and the Nancay Decametric Array (NDA, France) digitize the measured electric field with 12 bit and 14 bit in a 40 MHz baseband. The fine structure in Jupiter's signal was used for data synchronization prior to correlation on the time-series data. RESULTS: Strong emission from Jupiter was detected during snapshots of a few seconds and detailed features down to microsecond time-scales were identified in dynamic spectra. Correlations of Jupiter's burst emission returned strong fringes on 1 ms time-scales over channels as narrow as a hundred kilohertz bandwidth. CONCLUSIONS: Long baseline interferometry is confirmed at low frequencies, in spite of phase shifts introduced by variations in ionospheric propagation characteristics. Phase coherence was preserved over tens to hundreds of milliseconds with a baseline of ~700 km. No significant variation with time was found in the correlations and an estimate for the fringe visibility of 1, suggested that the source was not resolved. The upper limit on the source region size of Jupiter Io-B S-bursts corresponds to an angular resolution of ~3 arcsec. Adding remote stations to the LOFAR network at baselines up to thousand kilometers will provide 10 times higher resolution down to an arcsecond.Comment: 6 pages, 4 figures. Nigl, A., Zarka, P., Kuijpers, J., Falcke, H., Baehren, L., VLBI observations of Jupiter with the Initial Test Station of LOFAR and the Nancay Decametric Array, A&A, 471, 1099-1104, accepted on 31/05/200

Predicting low-frequency radio fluxes of known extrasolar planets

Context. Close-in giant extrasolar planets (''Hot Jupiters'') are believed to be strong emitters in the decametric radio range. Aims. We present the expected characteristics of the low-frequency magnetospheric radio emission of all currently known extrasolar planets, including the maximum emission frequency and the expected radio flux. We also discuss the escape of exoplanetary radio emission from the vicinity of its source, which imposes additional constraints on detectability. Methods. We compare the different predictions obtained with all four existing analytical models for all currently known exoplanets. We also take care to use realistic values for all input parameters. Results. The four different models for planetary radio emission lead to very different results. The largest fluxes are found for the magnetic energy model, followed by the CME model and the kinetic energy model (for which our results are found to be much less optimistic than those of previous studies). The unipolar interaction model does not predict any observable emission for the present exoplanet census. We also give estimates for the planetary magnetic dipole moment of all currently known extrasolar planets, which will be useful for other studies. Conclusions. Our results show that observations of exoplanetary radio emission are feasible, but that the number of promising targets is not very high. The catalog of targets will be particularly useful for current and future radio observation campaigns (e.g. with the VLA, GMRT, UTR-2 and with LOFAR).Comment: 4 figures; Table 1 is available in electronic form at the CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or via http://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/475/35

Candidates for detecting exoplanetary radio emissions generated by magnetosphere-ionosphere coupling

In this paper we consider the magnetosphere-ionosphere (M-I) coupling at Jupiter-like exoplanets with internal plasma sources such as volcanic moons, and we have determined the best candidates for detection of these radio emissions by estimating the maximum spectral flux density expected from planets orbiting stars within 25 pc using data listed in the NASA/IPAC/NExScI Star and Exoplanet Database (NStED). In total we identify 91 potential targets, of which 40 already host planets and 51 have stellar X-ray luminosity 100 times the solar value. In general, we find that stronger planetary field strength, combined with faster rotation rate, higher stellar XUV luminosity, and lower stellar wind dynamic pressure results in higher radio power. The top two targets for each category are $\epsilon$ Eri and HIP 85523, and CPD-28 332 and FF And.Comment: Accepted for publication in Monthly Notices of the Royal Astronomical Society Letter

Images and perceptions of Hungary and Austria-Hungary in Ireland, 1815-1875

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X-Ray Topography

The purpose of this paper is to discuss some elements of dynamical theory and to introduce some basic ideas on defect image formation in X-ray topographs. After some explanations of the basic principles of dynamical theory of X-rays, examples of defect contrast are given. Two examples of studies of quartz single crystals by X-ray topography are developed. First, the analysis of the X-ray spherical wave topographs of various Y-cut plates of synthetic quartz crystals show that the coherence of the lattice between the seed and the grown crystal is directly related to the density of the dislocations present in the seed. For the samples, the local deformations are essentially related to the density of the dislocations. Plane-wave topography shows that the local deformations can be estimated with good precision and related to the growth defects. The second example concerns Stroboscopic X-ray topography. With the use of synchrotron radiation, we have examined three quartz resonators. Several types of vibration modes and the perturbations due to the defects are described. Defects such as growth bands and especially dislocations disturb acoustic wave propagation in the crystals and can induce losses by untrapping a part of the energy of the mode conversion

La tolerancia o cómo coexistir en un mundo desgarrado

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