arXiv subjects

Alessio Turchi

Publications and source records attributed to Alessio Turchi.

18 recordsLinked to original sources

arXiv2026

Stellar rotation and binaries in open clusters with Gaia DR3

Stellar rotation is a fundamental ingredient in shaping the evolution of stars and it can also be used to trace past stellar interactions. Yet, systematic studies of stellar rotation in large samples of stars belonging to different populations have only recently been made possible, thanks to spectroscopic surveys. We profit from the catalogue of rotational broadening and rotation periods released with Gaia DR3. We focus on open clusters to study the rotational behaviour of several interesting populations including, among others, blue stragglers and extended main sequence turnoffs (eMSTO). We use literature lists of almost a million member stars in several thousand open clusters in the Milky Way. We collect properties of stars and clusters from large surveys, including Gaia, and from various literature sources. We include a comprehensive collection of known variables and binary stars from various databases. We manually select (exotic) stellar populations from the color-magnitude diagrams of individual clusters and study their rotational properties. Our catalogue contains more than 44 000 rotationally characterised stars, almost 57 000 variables (excluding binaries) and more than 22 000 binary stars. We find several interesting results, including a few hundred new blue stragglers, several fast rotating red giants, and we increase the number of clusters with an eMSTO to 96. We discover that most clusters more massive than $10^3$ $M_{\odot}$ display an eMSTO. We present a new parametrization of the number of blue stragglers as a function of cluster mass and age. We find that the percentage of binary stars in the equal-mass binary sequence and in the main sequence are similar. We present the first large-scale statistical exploration of stellar rotation in open clusters, which already yielded new interesting results and which can be used as the basis for several detailed follow-up studies.

astro-ph.SR↗

arXiv2025

Optical turbulence forecast for ground-based astronomy and free-space optical communication

Forecasting optical turbulence in the Earth's atmosphere has been an ambitious challenge for the astronomical scientific community for several decades. While earlier research primarily focused on whether it was possible to predict optical turbulence and its vertical distribution, current efforts are more concentrated on the accuracy achievable at different timescales, the efficiency of various forecasting methods and the contributions of new statistical approaches, such as auto-regression and machine learning to this field. In this contribution, I will present the state of the art of the research conducted by our group, positioned within the international research scenery. Most of our past activity has been primarily focused on ground-based astronomy but recent advancements in space research opened new opportunities for applications in the free-space optical communication.

astro-ph.IM↗

arXiv2024

FATE -- an operational automatic system for optical turbulence forecasting at the Very Large Telescope

In this contribution we report the on-going progresses of the project FATE, an operational automatic forecast system conceived to deliver forecasts of a set of astroclimatic and atmospheric parameters having the aim to support the science operations (i.e. the Service Mode) at the Very Large Telescope. The project has been selected at conclusion of an international open call for tender opened by ESO and it fits with precise technical specifications. In this contribution we will present the ultimate goals of this service once it will be integrated in the VLT operations, the forecasts performances at present time and the state of the art of the project. FATE is supposed to draw the roadmap towards the optical turbulence forecast for the ELT.

astro-ph.IM↗

arXiv2024

Optical turbulence forecast for the European Solar Telescope (EST): the challenge of the day-time regime

In this contribution we present preliminary results of a study applied to the Observatories of Roque de Los Muchachos (La Palma) and Teide (Tenerife) in Canary Islands aiming to investigate the possibility to implement an automatic system for the optical turbulence forecasting for the European Solar Telescope (EST) telescope. The study has been carried out in the context of the SOLARNET project and the two mentioned sites were the pre-selected sites for EST. This analysis aimed to investigate the possibility to extend the methodology of the forecast of the optical turbulence developed by our team and performed on top-class ground-based telescopes dedicated to night time observations such as ALTA (@ LBT) and FATE (@ VLT) to the day-time regime. As an ancillary output our very preliminary analysis concludes, that the two sites of Roque de Los Muchachos Observatory (ORM) and Teide Observatory (TO) show comparable characteristics during the day time. Considering that the site of EST has been already identified to be at ORM this can be considered a very useful information from a scientific point of view.

astro-ph.IM↗

arXiv2024

The MICADO first light imager for the ELT: off-axis performance of PSF reconstruction

The highest scientific return, for adaptive optics (AO) observations, is achieved with a reliable reconstruction of the PSF. This is especially true for MICADO@ELT. In this presentation, we will focus on extending the MICADO PSF reconstruction (PSF-R) method to the off-axis case. Specifically, a novel approach based on temporal-based tomography of AO telemetry data has been recently implemented. Results from the PSF-R of both simulated and real data show that, at half isoplanatic angle distances, a precision of about 10-15% is achievable in both Strehl ratio and full-width at half maximum, paving the way to extend the MICADO PSF-R tool also to the multi-conjugated AO case.

astro-ph.IM↗

arXiv2023

Towards operational optical turbulence forecast systems at different scales

The forecast on a time scale of 1 or 2 hours is crucial for all kind of new generation facilities (ELTs) instrumentation supported by the adaptive optics that will be mainly operated in Service Mode. In a recent study (Masciadri et al. 2020) we have showed that we can forecast the seeing and atmospheric parameters at such short time scales using an autoregressive method achieving unprecedented model accuracies with a substantial gain with respect to forecasts performed the day before (i.e. on longer time scales) obtained with an atmospheric mesoscale model. Equally we showed a gain with respect to the method by persistence using simply real-time measurements in situ on the same short time scale (1-2 hours). The auto-regressive method makes use of the forecasts done with mesoscale atmospheric models and real-time measurements and since 2019 has been implemented in the operational forecast system ALTA Center supporting LBT observations. In this contribution we apply the same approach to the VLT site extending the method to all the main astroclimatic parameters i.e. the seeing, the wavefront coherence time, the isoplanatic angle and the ground layer fraction. We prove that such a method offers unprecedented forecast accuracies for all the astroclimatic parameters with clear gains with respect to the prediction by persistence. Preliminary calculations indicate also better accuracies than those obtained with the machine learning based approach using in situ measurements. We will apply soon such a method in an operational forecast system that we conceived for the VLT.

astro-ph.IM↗

arXiv2021

Optical Turbulence forecast: new perspectives

In this contribution I present results achieved recently in the field of the OT forecast that push further the limit of the accuracy of the OT forecasts and open to new perspectives in this field.

astro-ph.IM↗

arXiv2020

New achievements in optical turbulence forecast systems in operational mode

In this contribution, we present the most recent progresses we obtained in the context of a long-term program we undertook since a few years towards the implementation of operational forecast systems (a) on top-class ground-based telescopes assisted by AO systems to support the flexible scheduling of observational scientific programs in night as well in day time and (b) on ground-stations to support free space optical communication. Two topics have been treated and presented in the Conference AO4ELT6: 1. ALTA is an operational forecast system for the OT and all the critical atmospheric parameters affecting the astronomical ground-based observations conceived for the LBT. It operates since 2016 and it is in continuous evolution to match with necessities/requirements of instruments assisted by AO of the LBT (SOUL, SHARK-NIR, SHARK-VIS, LINC-NIRVANA,...). In this contribution, we present a new implemented version of ALTA that, thanks to an auto-regression method making use of numerical forecasts and real-time OT measurements taken in situ, can obtain model performances (for forecasts of atmospherical and astroclimatic parameters) never achieved before on time scales of the order of a few hours. 2. We will go through the main differences between optical turbulence forecast performed with mesoscale and general circulation models (GCM) by clarifying some fundamental concepts and by correcting some erroneous information circulating recently in the literature.

astro-ph.IM↗

arXiv2019

Optical turbulence forecast in the Adaptive Optics realm

(35-words maximum) In this talk I present the scientific drivers related to the optical turbulence forecast applied to the ground-based astronomy supported by Adaptive Optics, the state of the art of the achieved results and the most relevant challenges for future progresses.

astro-ph.IM↗

arXiv2018

Forecasting water vapour above the sites of ESO's Very Large Telescope (VLT) and the Large Binocular Telescope (LBT)

Water vapour in the atmosphere is the main source of the atmospheric opacity in the infrared and sub-millimetric regimes and its value plays a critical role in observations done with instruments working at these wavelengths on ground-based telescopes. The scheduling of scientific observational programs with instruments such as the VLT Imager and Spectrometer for mid Infrared (VISIR) at Cerro Paranal and the Large Binocular Telescope Interferometer (LBTI) at Mount Graham would definitely benefit from the ability to forecast the atmospheric water vapour content. In this contribution we present a study aiming at validating the performance of the non-hydrostatic mesoscale Meso-NH model in reliably predicting precipitable water vapour (PWV) above the two sites. For the VLT case we use, as a reference, measurements done with a Low Humidity and Temperature PROfiling radiometer (LHATPRO) that, since a few years, is operating routinely at the VLT. LHATPRO has been extensively validated on previous studies. We obtain excellent performances on forecasts performed with this model, including for the extremely low values of the PWV (<= 1 mm). For the LBTI case we compare one solar year predictions obtained with the Meso-NH model with satellite estimates again obtaining an excellent agreement. This study represents a further step in validating outputs of atmospheric parameters forecasts from the ALTA Center, an operational and automatic forecast system conceived to support observations at LBT and LBTI.

astro-ph.IM↗

arXiv2017

Forecasting surface layer atmospheric parameters at the LBT site

In this paper we quantify the performances of an automated weather forecast system implemented on the Large Binocular Telescope (LBT) site at Mt. Graham (Arizona) in forecasting the main atmospheric parameters close to the ground. The system employs a mesoscale non-hydrostatic numerical model (Meso-Nh). To validate the model we compare the forecasts of wind speed, wind direction, temperature and relative humidity close to the ground with the respective values measured by instrumentation installed on the telescope dome. The study is performed over a large sample of nights uniformly distributed over two years. The quantitative analysis is done using classical statistical operators (bias, RMSE and $σ$) and contingency tables, which allows to extract complementary key information, such as the percentage of correct detection (PC) and the probability to obtain a correct detection within a defined interval of values (POD). Results of our study indicate that the model performances in forecasting the atmospheric parameters we have just cited are very good, in some cases excellent: RMSE for temperature is below 1° C, for relative humidity is 14%, for the wind speed is around 2.5m/s. The relative error of the RMSE for wind direction varies from 9% to 17% depending on the wind speed conditions. This work is performed in the context of ALTA (Advanced LBT Turbulence and Atmosphere) Center project, which final goal is to provide forecasts of all the atmospheric parameters and the optical turbulence to support LBT observations, adaptive optics facilities and interferometric facilities.

astro-ph.IM↗

arXiv2016

Optical turbulence forecast: ready for an operational application

One of the main goals of the feasibility study MOSE (MOdellig ESO Sites) is to evaluate the performances of a method conceived to forecast the optical turbulence above the ESO sites of the Very Large Telescope and the European-Extremely Large Telescope in Chile. The method implied the use of a dedicated code conceived for the optical turbulence (OT) called Astro-Meso-Nh. In this paper we present results we obtained at conclusion of this project concerning the performances of this method in forecasting the most relevant parameters related to the optical turbulence (CN2, seeing , isoplanatic angle theta_0 and wavefront coherence time tau_0). Numerical predictions related to a very rich statistical sample of nights uniformly distributed along a solar year and belonging to different years have been compared to observations and different statistical operators have been analyzed such as classical bias, RMSE and and more sophisticated statistical operators derived by the contingency tables that are able to quantify the score of success of a predictive method such as the percentage of correct detection (PC) and the probability to detect a parameter within a specific range of values (POD). The main conclusions of the study tell us that the Astro-Meso-Nh model provides performances that are already very good to definitely guarantee a not negligible positive impact on the Service Mode of top-class telescopes and ELTs. A demonstrator for an automatic and operational version of the Astro-Meso-Nh model will be soon implemented on the sites of VLT and E-ELT.

astro-ph.IM↗

arXiv2016

Forecasts of the atmospherical parameters close to the ground at the LBT site in the context of the ALTA project

In this paper we study the abilities of an atmospherical mesoscale model in forecasting the classical atmospherical parameters relevant for astronomical applications at the surface layer (wind speed, wind direction, temperature, relative humidity) on the Large Binocular Telescope (LBT) site - Mount Graham, Arizona. The study is carried out in the framework of the ALTA project aiming at implementing an automated system for the forecasts of atmospherical parameters (Meso-Nh code) and the optical turbulence (Astro-Meso-Nh code) for the service-mode operation of the LBT. The final goal of such an operational tool is to provide predictions with high time frequency of atmospheric and optical parameters for an optimized planning of the telescope operation (dome thermalization, wind-dependent dome orientation, observation planning based on predicted seeing, adaptive optics optimization, etc...). Numerical simulations are carried out with the Meso-Nh and Astro-Meso-Nh codes, which were proven to give excellent results in previous studies focused on the two ESO sites of Cerro Paranal and Cerro Armazones (MOSE Project). In this paper we will focus our attention on the comparison of atmospherical parameters forescasted by the model close to the ground with measurements taken by the observatory instrumentations and stored in the LBT telemetry in order to validate the numerical predictions. As previously done for Cerro Paranal (Lascaux et al., 2015), we will also present an analysis of the model performances based on the method of the contingency tables, that allows us to provide complementary key information with the respect to the bias and RMSE (systematic and statistical errors), such as the percentage of correct detection and the probability to obtain a correct detection inside a defined interval of values.

astro-ph.IM↗

arXiv2015

Emergence of a collective crystal in a classical system with long-range interactions

A one-dimensional long-range model of classical rotators with an extended degree of complexity, as compared to paradigmatic long-range systems, is introduced and studied. Working at constant density, in the thermodynamic limit one can prove the statistical equivalence with the Hamiltonian Mean Field model (HMF) and $α$-HMF: a second order phase transition is indeed observed at the critical energy threshold $\varepsilon_c=0.75$. Conversely, when the thermodynamic limit is performed at infinite density (while keeping the length of the hosting interval $L$ constant), the critical energy $\varepsilon_c$ is modulated as a function of $L$. At low energy, a self-organized collective crystal phase is reported to emerge, which converges to a perfect crystal in the limit $ε\rightarrow 0$. To analyze the phenomenon, the equilibrium one particle density function is analytically computed by maximizing the entropy. The transition and the associated critical energy between the gaseous and the crystal phase is computed. Molecular dynamics show that the crystal phase is apparently split into two distinct regimes, depending on the the energy per particle $\varepsilon$. For small $\varepsilon$, particles are exactly located on the lattice sites; above an energy threshold $\varepsilon{*}$, particles can travel from one site to another. However, $\varepsilon{*}$ does not signal a phase transition but reflects the finite time of observation: the perfect crystal observed for $\varepsilon >0$ corresponds to a long lasting dynamical transient, whose life time increases when the $\varepsilon >0$ approaches zero.

cond-mat.stat-mech↗

arXiv2014

Oseledets' Splitting in Large Hamiltonian Systems: the HMF Phase Transition

We consider the covariant Lyapunov vectors (CLV) of a high-dimensional Hamiltonian flow in the case of long range potential, namely the Hamiltonian Mean Field (HMF) problem, by studying the behavior of the Lyapunov spectra and the Oseledets' splitting principal angles (the mutual orientation between stable and unstable subspaces) when a phase transition takes place. Motivated by several results connecting the dynamical properties of systems to their Lyapunov exponents and vectors, we first find confirmation of an explicit sensitivity of such quantities to the transition: our main finding is that the mutual orientation between stable and unstable subspaces fluctuates in time around specific constant values. Moreover, the fluctuations statistics are different above and below the critical threshold, and thus intimately connected to the transition. Pictorially, the evolution of the stability subspaces along a reference orbits turns out to happen only through rigid global rotations plus weak internal deformations between the two subspaces; we are not aware of any theoretical explanation for such a non- trivial setting but, through analogies with integrable systems, we provide some little insight on 'how much' the system resembles an integrable one.

nlin.CD↗

arXiv2011

Statistical theory of quasi stationary states beyond the single water-bag case study

An analytical solution for the out-of-equilibrium quasi-stationary states of the paradigmatic Hamiltonian Mean Field (HMF) model can be obtained from a maximum entropy principle. The theory has been so far tested with reference to a specific class of initial condition, the so called (single-level) water-bag type. In this paper a step forward is taken by considering an arbitrary number of overlapping water bags. The theory is benchmarked to direct microcanonical simulations performed for the case of a two-levels water-bag. The comparison is shown to return an excellent agreement.

cond-mat.stat-mech↗

arXiv2011

Efficiency of cyclic devices working with non-Boltzmannian fluids: challenging the second principle of thermodynamics

According to classical Boltzmannian thermodynamics, the efficiency of a cyclic machine is strictly lower than one. Such a result is a straightforward consequence of the second principle of thermodynamics. Recent advances in the study of the thermodynamics of long-range interacting system report however on a rather intricate zoology of peculiar behaviors, which are occasionally in contrast with customarily accepted scenarios, dueling with intuition and common sense. In this paper, a thermodynamical cycle is assembled for an ideal device working with non-Boltzmaniann long-range fluid and operating in contact with two thermal reservoirs. The system is analytically shown to violate the second principle of thermodynamics, a phenomenon that ultimately relates to the existence of regions with negative kinetic specific heat, in the canonical ensemble for the system under scrutiny. We argue that the validity of the second principle of thermodynamics can be possibly restored, by revisiting the definition of canonical ensemble, as well as the Fourier law of heat transport, and consequently relaxing the constraint on the maximal efficiency as imposed by the Carnot theorem.

cond-mat.stat-mech↗

arXiv2010

Existence of Quasi-stationary states at the Long Range threshold

In this paper the lifetime of quasi-stationary states (QSS) in the $α-$HMF model are investigated at the long range threshold ($α=1$). It is found that QSS exist and have a diverging lifetime $τ(N)$ with system size which scales as $\mbox{\ensuremathτ(N)\ensuremath{\sim}}\log N$, which contrast to the exhibited power law for $α<1$ and the observed finite lifetime for $α>1$. Another feature of the long range nature of the system beyond the threshold ($α>1$) namely a phase transition is displayed for $α=1.5$. The definition of a long range system is as well discussed.

cond-mat.stat-mech↗