Solar type II radio bursts associated with CME expansions as shown by EUV waves

We investigate the physical conditions of the sources of two metric Type-II bursts associated with CME expansions with the aim of verifying the relationship between the shocks and the CMEs, comparing the heights of the radio sources and the heights of the EUV waves associated with the CMEs. The heights of the EUV waves associated with the events were determined in relation to the wave fronts. The heights of the shocks were estimated by applying two different density models to the frequencies of the Type-II emissions and compared with the heights of the EUV waves. For the 13 June 2010 event, with band-splitting, the shock speed was estimated from the frequency drifts of the upper and lower branches of the harmonic lane, taking into account the H/F frequency ratio fH/fF = 2. Exponential fits on the intensity maxima of the branches revealed to be more consistent with the morphology of the spectrum of this event. For the 6 June 2012 event, with no band-splitting and with a clear fundamental lane on the spectrum, the shock speed was estimated directly from the frequency drift of the fundamental emission, determined by linear fit on the intensity maxima of the lane. For each event, the most appropriate density model was adopted to estimate the physical parameters of the radio source. The 13 June 2010 event presented a shock speed of 664-719 km/s, consistent with the average speed of the EUV wave fronts of 609 km/s. The 6 June 2012 event was related to a shock of speed of 211-461 km/s, also consistent with the average speed of the EUV wave fronts of 418 km/s. For both events, the heights of the EUV wave revealed to be compatible with the heights of the radio source, assuming a radial propagation of the shock.Comment: Accepted for publication in Astronomy and Astrophysic

Si doped and undoped chromium nitride coatings: a comparative study of physical properties

Chromium nitride and silicon doped chromium nitride thin films have been deposited by r.f. reactive magnetron sputtering. This study corresponds to the investigation of the influence of processing parameters and of the addition of silicon on the chromium nitride matrix on the properties of the produced films. The characterization of the coatings was performed by X-ray diffraction (XRD), and nano-indentation experiments. Results concerning the crystalline phases, crystal orientation/texture, crystallite size, mechanical properties and their correlations, are presented. The increase of the nitrogen partial pressure in the working atmosphere produces changes from a body-centered cubic (bcc) Cr structure, to hexagonal Cr2N, to face-centered cubic (fcc) CrN structure. The CrN crystallites evidence a fcc (111) preferred orientation. The highest hardness is achieved in a coating with dominant CrN phase (45 GPa) with a crystallite size around 18 nm. The addition of Si, in the films with CrN dominant phase, maintains the CrN (111) preferred orientation and produces changes in films hardness, depending on deposition conditions

Impact of micro-telluric lines on precise radial velocities and its correction

Context: In the near future, new instruments such as ESPRESSO will arrive, allowing us to reach a precision in radial-velocity measurements on the order of 10 cm/s. At this level of precision, several noise sources that until now have been outweighed by photon noise will start to contribute significantly to the error budget. The telluric lines that are not neglected by the masks for the radial velocity computation, here called micro-telluric lines, are one such noise source. Aims: In this work we investigate the impact of micro-telluric lines in the radial velocities calculations. We also investigate how to correct the effect of these atmospheric lines on radial velocities. Methods: The work presented here follows two parallel lines. First, we calculated the impact of the micro-telluric lines by multiplying a synthetic solar-like stellar spectrum by synthetic atmospheric spectra and evaluated the effect created by the presence of the telluric lines. Then, we divided HARPS spectra by synthetic atmospheric spectra to correct for its presence on real data and calculated the radial velocity on the corrected spectra. When doing so, one considers two atmospheric models for the synthetic atmospheric spectra: the LBLRTM and TAPAS. Results: We find that the micro-telluric lines can induce an impact on the radial velocities calculation that can already be close to the current precision achieved with HARPS, and so its effect should not be neglected, especially for future instruments such as ESPRESSO. Moreover, we find that the micro-telluric lines' impact depends on factors, such as the radial velocity of the star, airmass, relative humidity, and the barycentric Earth radial velocity projected along the line of sight at the time of the observation.Comment: Accepted in A&

Central Algarve tufa platforms, Southern Portugal. Geomorphological characterization and genesis.

Modern and fossil carbonate tufa outcrops exist in the Algarve (S Portugal), where climate is Mediterranean and all modern incrusting springs are intermittent and fed by Jurassic aquifers. The major Pleistocene tufa on the Algibre flexure southern slopes are in the Cadouço, São Lourenço and Rio Seco streams basins. There were identified fluvial barrier tufas and low energy fluvial tufas. The Algarve has three main geomorphological domains: the Paleozoic flysch mountains, the Meso-cenozoic karst hills and the littoral Plio-Pleistocene detrital platform.Located in the Eurasian-Nubian plates boundary, the whole system have been deformed by distensive and compressive tectonics, which give rise to a complex groundwater system. Neotectonical activity has been reported in many works. Feio (1952) identified Pliocene and Quaternary marine platforms up to 160 m a.s.l., but also mature levels at 200 m along with other plain surfaces. The largest tufa platforms lie in unconformity with the currentdrainage system, where outcrops are dominated by low gradient facies, v. g. detrital bedded lime muds. Machados platform is dominated by bryophytes and other rapid flow facies, and cemented riverbed upstream. These outcrops lie down on larger areas in Loulé and Lagos e Relva, at altitudes between 160-200 and 120-150 respectively. Environmentally conformal tufas occupy some sectors of the modern Cadouço, Rio Seco and São Lourenço streams. Modern tufa range from spring dominated mounds in Lagos eRelva and barrier and low gradient fluvial dominated tufas (v. g. São Lourenço and Loulé). The ocean proximity enables the formation of eustatic platforms, which provided substratum for tufa accumulations. Vertical movements, including salt tectonics, and lowstands promoted fluvial incision and later tufa developments in modern streams. Acknowledgments: Financed by the Fundação para a Ciência e Tecnologia PhD grant SFRH/BD/62323/2009

Cancellation of atmospheric turbulence effects in entangled two-photon beams

Turbulent airflow in the atmosphere and the resulting random fluctuations in its refractive index have long been known as a major cause of image deterioration in astronomical imaging and figures among the obstacles for reliable optical communication when information is encoded in the spatial profile of a laser beam. Here we show that using correlation imaging and a suitably prepared source of photon pairs, the most severe of the disturbances inflicted on the beam by turbulence can be cancelled out. Other than a two-photon light source, only linear passive optical elements are needed and, as opposed to adaptive optics techniques, our scheme does not rely on active wavefront correction.Comment: 5 pages, 3 figure