arXiv subjects

Massinissa Hadjara

Publications and source records attributed to Massinissa Hadjara.

5 recordsLinked to original sources

arXiv2026

Laboratory characterization of Hierarchical Fringe Tracking

One of the main limitations in long-baseline interferometry lies in its fringe tracking sensitivity. The challenge is therefore to maximize this sensitivity while minimizing the spreading of the signal on the detector. This is the goal at the core of the hierarchical fringe tracking (HFT) concept. We present the laboratory characterization of the $2^{nd}$ generation HFT chips operating in the near infrared (H band) for up to 4 telescopes with more linear phase and group delay estimators, allowing a strong simplification of the tracking algorithm. We show a comparison between theoretical intensity outputs for an optimized phase delay chip, and the laboratory measurements of two chips with different designs. The results do not reach the expectations but get close to them with the 10-outputs chip. Ultimately, this new chip is intended for implementation on the VLTI, CHARA or on the future Xuyi 100m-baseline Stellar Interferometer using three telescopes.

astro-ph.IM↗

arXiv2025

The Astronomical Plate Digitization at SHAO

The digitization of historical astronomical plates is essential for preserving century-long observational data. This work presents the development and application of the specialized digitizers at the Shanghai Astronomical Observatory (SHAO), including technical details, international collaborations, and scientific applications on the plates.

astro-ph.IM↗

arXiv2023

Current status of the Extension of the FRIPON network in Chile

FRIPON is an efficient ground-based network for the detection and characterization of fireballs, which was initiated in France in 2016 with over one hundred cameras and which has been very successfully extended to Europe and Canada with one hundred more stations. After seven successful years of operation in the northern hemisphere, it seems necessary to extend this network towards the southern hemisphere - where the lack of detection is evident - to obtain an exhaustive view of fireball activity. The task of extending the network to any region outside the northern hemisphere presents the challenge of a new installation process, where the recommended and tested version of the several sub-systems that compose a station had to be replaced due to regional availability and compatibility considerations, as well as due to constant software and hardware obsolescence and updates. In Chile, we have a unique geography, with a vast extension in latitude, as well as desert regions, which have generated the need to evaluate the scientific and technical performance of the network under special conditions, prioritizing the optimization of a set of factors related to the deployment process, as well as the feasible and achievable versions of the required components, the geographical location of the stations, and their respective operational, maintenance, safety, and communication conditions. In this talk, we will present the current status of this effort, including a brief report on the obstacles and difficulties encountered and how we have solved them, the current operational status of the network in Northern Chile, as well as the challenges and prospects for the densification of the network over South America.

astro-ph.IM↗

arXiv2021

Potential and sky coverage for off-axis fringe tracking in optical long baseline interferometry

The spectacular results provided by the second-generation VLTI instruments GRAVITY and MATISSE on active galactic nuclei (AGN) trigger and justify a strong increase in the sensitivity limit of optical interferometers. A key component of such an upgrade is off-axis fringe tracking. To evaluate its potential and limitations, we describe and analyse its error budget including fringe sensing precision and temporal, angular and chromatic perturbations of the piston. The global tracking error is computed using standard seeing parameters for different sites, seeing conditions and telescope sizes for the current GRAVITY Fringe Tracker (GFT) and a new concept of Hierarchical Fringe Tracker. Then, it is combined with a large catalogue of guide star candidates from Gaia to produce sky coverage maps that give the probability to find a usable off-axis guide star in any part of the observable sky. These maps can be used to set the specifications of the system, check its sensitivity to seeing conditions, and evaluate the feasibility of science programs. We check the availability of guide stars and the tracking accuracy for a large set of 15 799 Quasars to confirm the feasibility of a large program on Broad Line Regions in the K band with the GFT and show how it can be extended to the L, M, and N bands. Another set of 331 well-characterized nearby AGNs shows the high potential of MATISSE for imaging and characterization of the dust torus in the N band under off-axis tracking on both Unit Telescopes and Auxiliary Telescopes.

astro-ph.IM↗

arXiv2017

Etude et mise en oeuvre des techniques Temps-Distance en Heliosismologie

In the same way that seismologists study the interior of the earth from the waves generated by earthquakes, heliosismology is the science that is interested in the study of oscillatory waves inside the Sun. Temperature, chemical composition, rotational velocities at different depths are all factors that influence the oscillation frequencies of the waves trapped inside the Sun. The observation and measurement of the frequencies (or velocities) of oscillations of the principal modes on the surface of the Sun allow us to study the internal properties of the star. In our study, we use a local helioseismic method, called "Time-Distance"; the latter, after appropriate treatment (remapping, tracking, and filtering) of the data, which carried out from the GONG (Global Oscillation Network Group) observation network, allows us to deduce, by correlation of the observed signals, the relationship between the time of the wave path and its crossed distance (hence the name of the method) between different points on the surface as a function of the different solar sub-surface parameters, via the dispersion relation. Once the travel times have been established by approximation of the correlation function by a Gaussian wave packet and based on the Fermat principle dealing with acoustic waves, we find the relationship between these times and the internal parameters of the crossed medium. Two models are considered in this study. The first does not include the effects of the magnetic field and takes into account the flow velocity and the sound speed. The second, on the other hand, includes the magnetic effects, by means of the Alfven velocity (magnetic field perturbation velocity), in addition to the parameters mentioned above. The last part of this paper was devoted to the inversion of the obtained times, which allows us to go back to the solar internal parameters.

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