Phase closure nulling of HD 59717 with AMBER/VLTI . Detection of the close faint companion

Aims: The detection of close and faint companions is an essential step in many astrophysical fields, including the search for planetary companions. A new method called "phase closure nulling" has been proposed for the detection of such faint and close companions based on interferometric observations when the system visibility amplitude is close to zero due to the large diameter of the primary star. We aim at demonstrating this method by analyzing observations obtained on the spectroscopic binary HD 59717. Methods: Using the AMBER/VLTI instrument in the K-band with ~1500 spectral resolution, we record the spectrally dispersed closures phases of the SB1 binary HD 59717 with a three-baseline combination adequate for applying phase closure methods. After a careful data reduction, we fit the primary diameter, the binary flux ratio, and the separation using the phase closure data. Results: We detect the 5-mag fainter companion of HD 59717 at a distance of 4 stellar radii from the primary. We determine the diameter of the primary, infer the secondary's spectral type and determine the masses and sizes of the stars in the binary system. This is one of the highest contrasts detected by interferometry between a companion and its parent star. Based on observations collected at the European Southern Observatory, Paranal, Chile, within the commissioning programme 60.A-9054(A)

Extrasolar planets and brown dwarfs around A-F type stars. II. A planet found with ELODIE around the F6V star HD 33564

We present here the detection of a planet orbiting around the F6V star HD 33564. The radial velocity measurements, obtained with the ELODIE echelle spectrograph at the Haute-Provence Observatory, show a variation with a period of 388 days. Assuming a primary mass of 1.25 Mo, the best Keplerian fit to the data leads to a minimum mass of 9.1 MJup for the companion.Comment: 5 pages. Final version, accepted for publication (A&A). Some Spitzer results on HD33564 (taken this year; not yet published), finally show that the detection of IR excess around this star (by IRAS) is spuriou

Estimating the phase in ground-based interferometry: performance comparison between single-mode and multimode schemes

In this paper we compare the performance of multi and single-mode interferometry for the estimation of the phase of the complex visibility. We provide a theoretical description of the interferometric signal which enables to derive the phase error in presence of detector, photon and atmospheric noises, for both multi and single-mode cases. We show that, despite the loss of flux occurring when injecting the light in the single-mode component (i.e. single-mode fibers, integrated optics), the spatial filtering properties of such single-mode devices often enable higher performance than multimode concepts. In the high flux regime speckle noise dominated, single-mode interferometry is always more efficient, and its performance is significantly better when the correction provided by adaptive optics becomes poor, by a factor of 2 and more when the Strehl ratio is lower than 10%. In low light level cases (detector noise regime), multimode interferometry reaches better performance, yet the gain never exceeds 20%, which corresponds to the percentage of photon loss due to the injection in the guides. Besides, we demonstrate that single-mode interferometry is also more robust to the turbulence in both cases of fringe tracking and phase referencing, at the exception of narrow field of views (<1 arcsec).Comment: 9 pages (+ 11 online material appendices) -- 8 Figures. Accepted in A&

Dynamics and conceptual model of the Rossena castle landslide (Northern Apennines, Italy)

In the Northern Apennines there are many historical villages and castles, which are of great value and represent a cultural heritage of great importance. Their presence within a territory greatly affected by landslide hazards creates, in many circumstances, the need to solve problems of land management and to act for the preservation of historical monuments. </p><p style='line-height: 20px;'> This paper describe an interesting landslide, failed during the night of 28 February 2004, that involved the village of Rossena: the failure damaged the village (Fig.&nbsp;1), the road and the fields down to the stream but, fortunately, the castle just upslope the village was not involved at all. </p><p style='line-height: 20px;'> The 10th century massive castle of Rossena stands on the top of a cliff at about 500 m a.s.l., on the border between the provinces of Parma and Reggio Emilia, and it is surrounded by a small ancient village. The castle of Rossena is the best preserved stronghold of the Longobard times, enlarged and reinforced in the tenth century and partially rebuilt by Bonifacio, the father of Matilda of Canossa (the Vice-Queen of Italy and probably the most important woman in the Middle Ages) as a defensive structure guarding the Enza Valley. In addition, at Conossa, very close to Rossena, there was the meeting between Pope Gregory VII and the Emperor of Germany Henry IV, during the historical event known as 'fight for the investitures'. For these reasons, the area of Rossena is one of the most relevant from a historical point of view in the entire western part of the Emilia Romagna Region and it also has a high value as a geosite (Coratza et al., 2004). </p><p style='line-height: 20px;'>&nbsp;</p

An effective control algorithm for dynamic voltage restorer under symmetrical and asymmetrical grid voltage conditions

Introduction. Voltage sag, which is associated to a transitory drop in the root mean square voltage characterizing an electrical source network. During these perturbations, the corresponding electronic customers and devices will suffer from serious operating troubles causing dangerous damages. Purpose. In order to attenuate this disturbance effects, the Controlled Dynamic Voltage Restorer constitutes a very interesting solution among many others that have been proposed. The novelty of the proposed work consists in presenting an enhanced algorithm to control efficiently the dynamic voltage restorer when voltage sag is suddenly occurred. Methods. The proposed algorithm is based on an instantaneous phase locked loop using a multi variable filter to synthesize unitary signals involved in compensation voltages computation relative to the sag apparition. Practical value. A detailed study concerning typical voltage sag, which is consolidated by simulation and experimental results, is conducted to show the used algorithm’s effectiveness to cancel the corresponding voltage sag.Вступ. Провал напруги, який пов’язаний із тимчасовим падінням середньоквадратичної напруги, характеризує мережу джерел електричної енергії. Під час цих збурень відповідні споживачі (електронні прилади та інші пристрої) будуть страждати від серйозних проблем у їхній експлуатації, що спричиняють небезпечні пошкодження. Призначення. Для того, щоб послабити вплив цих збурень, контрольований динамічний відновник напруги видається дуже цікавим рішенням серед багатьох інших, які були запропоновані. Новизна запропонованої роботи полягає у представленні вдосконаленого алгоритму ефективного управління динамічним відновником напруги, коли раптово відбувається провал напруги. Методи. Запропонований алгоритм базується на миттєвому фазовому замкненому контурі з використанням багатоваріантного фільтра для синтезу унітарних сигналів, що беруть участь у обчисленні напруги компенсації стосовно прояву провалу. Практичне значення. Детальне дослідження стосовно типового провалу напруги, яке узагальнено за допомогою моделювання та експериментальних результатів, проведено, щоб показати ефективність використовуваного алгоритму для ліквідації відповідного провалу напруги

Fiber optic interferometry: Statistics of visibility and closure phase

Interferometric observations with three telescopes or more provide two observables: closure phase information together with visibilities measurements. When using single-mode interferometers, both observables have to be redefined in the light of the coupling phenomenon betwe en the incoming wavefront and the fiber. We introduce in this paper the estimator of both so-called modal visibility and modal closure phase. Then, we compute the statistics of the two observables in presence of partial correction by Adaptive Optics. From this theoretical analysis, data reduction process using classical least square minimization is investigated. In the framework of the AMBER instrument, the three beams recombiner of the VLTI, we simulate the observation of a single Gaussian source and we study the performances of the interferometer in terms of diameter measurements. We show that the observation is optimized, i.e. that the Signal to Noise Ratio (SNR) of the diameter is maximal, when the full width half maximum (FWHM) of the source is roughly 1/2 of the mean resolution of the interferometer. We finally point out that in the case of an observation with 3 telescopes, neglecting the correlation between the measurements leads to overestimate the SNR by a factor of $\sqrt{2}$. We infer that in any cases, this value is an upper limit.Comment: 7 (+4 appendix) pages, 6 (+1) figures, accepte

Single-Mode versus multimode interferometry: a performance study

We compare performances of ground-based single-mode and multimode (speckle) interferometers in the presence of partial Adaptive Optics correction of atmospheric turbulence. It is first shown that for compact sources (i.e. sources smaller than the Airy disk of a single telescope) not entirely resolved by the interferometer, the remarkable property of spatial filtering of single-mode waveguides coupled with AO correction significantly reduces the speckle noise which arises from residual wavefront corrugations. Focusing on those sources, and in the light of the AMBER experiment (the near infrared instrument of the VLTI), we show that single-mode interferometry produces a better Signal-to-Noise Ratio on the visibility than speckle interferometry. This is true for bright sources (K < 5), and in any case as soon as Strehl ratio of 0.2 is achieved. Finally, the fiber estimator is much more robust -- by two orders of magnitude -- than the speckle estimator with respect to Strehl ratio variations during the calibration procedure. The present analysis theoretically explains why interferometry with fibers can produce visibility measurements with a very high precision, 1% or lessComment: 13 pages (5 pages of appendices), 6 figures to be published in A&