arXiv subjects

Rosanna Sordo

Publications and source records attributed to Rosanna Sordo.

9 recordsLinked to original sources

arXiv2026

Stellar masses and ages in Gaia Data Release 4 from the Final Luminosity Age Mass Estimator algorithm

The masses and ages of stars are key quantities for understanding exoplanetary, stellar, and galactic evolution. In the context of Gaia, these parameters provide insights into the stellar populations, helping to trace the formation and history of the Galaxy. As part of the Gaia Data Processing and Analysis Consortium (DPAC), the Final Luminosity Age Mass Estimator (FLAME) pipeline processes Gaia data to derive stellar parameters comprising luminosities, radii, masses and ages. This paper discusses the methods and data used in FLAME for Gaia Data releases and the expected performances of FLAME for the 4th Gaia Data Release. FLAME comprises two main components: the first one, which is analytical, is used to estimate luminosity, radius, and radial velocity correction due to gravitational redshift by exploiting the atmospheric, astrometric, and photometric parameters produced within Gaia. The second is a model inference based on two main approaches: a classical minimization approach, and a Bayesian framework. It aims to derive mass, age, and evolutionary stage. The two step implementation offers flexibility in handling photometric properties that are prone to systematic errors. Tests with simulated data, the Sun, and well characterised samples of stars show that the methods in FLAME perform as expected, producing results in statistical agreement with the literature. We provide new stellar fundamental parameters for some high velocity stars, stars with very low mass companions, and a selection of stars in the Plato Field of View. In Gaia Data Release 4 approximately 500 million sources will have results from the pipeline. [abridged]

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arXiv2023

MORFEO enters final design phase

MORFEO (Multi-conjugate adaptive Optics Relay For ELT Observations, formerly MAORY), the MCAO system for the ELT, will provide diffraction-limited optical quality to the large field camera MICADO. MORFEO has officially passed the Preliminary Design Review and it is entering the final design phase. We present the current status of the project, with a focus on the adaptive optics system aspects and expected milestones during the next project phase.

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arXiv2022

Estimating $\left[ α/ \text{Fe} \right]$ from Gaia low-resolution BP/RP spectra using the ExtraTrees algorithm

Gaia Data Release 3 will contain more than a billion sources with positions, parallaxes, and proper motions. In addition, for hundreds of millions of stars, it will include low-resolution blue photometer (BP) and red photometer (RP) spectra. Obtained by dispersing light with prisms, these spectra have resolutions that are too low to allow us to measure individual spectral lines and bands. However, the combined BP/RP spectra can be used to estimate some stellar properties such as $T_{\text{eff}}$, $\log{g}$, and $\left[ \text{M} / \text{H} \right]$. We investigate the feasibility of using the ExtraTrees algorithm to estimate the alpha element to iron abundance ratio $\left[ α/ \text{H} \right]$ from low-resolution BP/RP spectra. To infer $\left[ α/ \text{H} \right]$ from the spectra, we created regression models trained on two samples: a set of synthetic spectra and a set of observed spectra from stars that have known $\left[ α/ \text{H} \right]$ since they have been observed using HERMES. We applied each model to the other sample and to a larger observed sample to assess the performance of the models. In addition, we used our models to analyse stars from the Gaia-Enceladus structure. We find that models using the ExtraTrees algorithm can be used to estimate $\left[ α/ \text{H} \right]$ from low-resolution BP/RP spectra of cool stars. However, they do this by exploiting correlations between $\left[ α/ \text{H} \right]$ and other parameters, rather than the causal effect of $\left[ α/ \text{H} \right]$ on the spectrum. Hence, they are unlikely to be useful in studies that attempt to distinguish stars that only differ in $\left[ α/ \text{H} \right]$.

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arXiv2021

MAORY: A Multi-conjugate Adaptive Optics RelaY for ELT

MAORY is the adaptive optics module for ELT providing two gravity invariant ports with the same optical quality for two different client instruments. It enable high angular resolution observations in the near infrared over a large field of view (~1 arcmin2 ) by real time compensation of the wavefront distortions due to atmospheric turbulence. Wavefront sensing is performed by laser and natural guide stars while the wavefront sensor compensation is performed by an adaptive deformable mirror in MAORY which works together with the telescope's adaptive and tip tilt mirrors M4 and M5 respectively.

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arXiv2013

DOOp, an automated wrapper for DAOSPEC

Large spectroscopic surveys such as the Gaia-ESO Survey produce huge quantities of data. Automatic tools are necessary to efficiently handle this material. The measurement of equivalent widths in stellar spectra is traditionally done by hand or with semi-automatic procedures that are time-consuming and not very robust with respect to the repeatability of the results. The program DAOSPEC is a tool that provides consistent measurements of equivalent widths in stellar spectra while requiring a minimum of user intervention. However, it is not optimised to deal with large batches of spectra, as some parameters still need to be modified and checked by the user. Exploiting the versatility and portability of BASH, we have built a pipeline called DAOSPEC Option Optimiser (DOOp) automating the procedure of equivalent widths measurement with DAOSPEC. DOOp is organised in different modules that run one after the other to perform specific tasks, taking care of the optimisation of the parameters needed to provide the final equivalent widths, and providing log files to ensure better control over the procedure. In this paper, making use of synthetic and observed spectra, we compare the performance of DOOp with other methods, including DAOSPEC used manually. The measurements made by DOOp are identical to the ones produced by DAOSPEC when used manually, while requiring less user intervention, which is convenient when dealing with a large quantity of spectra. DOOp shows its best performance on high-resolution spectra (R>20 000) and high signal-to-noise ratio (S/N>30), with uncertainties ranging from 6 mÅ to 2 mÅ. The only subjective parameter that remains is the normalisation, as the user still has to make a choice on the order of the polynomial used for the continuum fitting. As a test, we use the equivalent widths measured by DOOp to re-derive the stellar parameters of four well-studied stars.

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arXiv2013

FAMA: An automatic code for stellar parameter and abundance determination

The large amount of spectra obtained during the epoch of extensive spectroscopic surveys of Galactic stars needs the development of automatic procedures to derive their atmospheric parameters and individual element abundances. Starting from the widely-used code MOOG by C. Sneden, we have developed a new procedure to determine atmospheric parameters and abundances in a fully automatic way. The code FAMA (Fast Automatic MOOG Analysis) is presented describing its approach to derive atmospheric stellar parameters and element abundances. The code, freely distributed, is written in Perl and can be used on different platforms. The aim of FAMA is to render the computation of the atmospheric parameters and abundances of a large number of stars using measurements of equivalent widths as automatic and as independent of any subjective approach as possible. It is based on the simultaneous search for three equilibria: excitation equilibrium, ionization balance, and the relationship between \fei\ and the reduced equivalent widths. FAMA also evaluates the statistical errors on individual element abundances and errors due to the uncertainties in the stellar parameters. The convergence criteria are not fixed 'a priori' but are based on the quality of the spectra. In this paper we present tests performed on the Solar spectrum EWs which tests the dependency on the initial parameters, and the analysis of a sample of stars observed in Galactic open and globular clusters.

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arXiv2009

Pre-main sequence stars in the stellar association N11 in the Large Magellanic Cloud

Magellanic Clouds are of extreme importance to the study of the star formation process in low metallicity environments. In this paper we report on the discovery of pre-main sequence candidates and young embedded stellar objects in N11 located in the Large Magellanic Cloud to cast light on the star formation scenario. We would like to remind that this comparison is complicated by the presence of a large age dispersion detected in the fields. Deep archive HST/ACS photometry is used to derive color-magnitude diagrams of the associations in N~11 and of the foreground field population. These data are complemented by archive IR Spitzer data which allow the detection of young embedded stellar objects. The spatial distribution of the pre-main sequence candidates and young embedded stellar objects is compared with literature data observed at different wavelengths, such as H$_α$ and CO maps, and with the distribution of OB and Herbig Ae/Be stars. The degree of clustering is derived using the Minimal Spanning Tree method and the two point correlation function to get insights about the formation process. A large population of pre-main sequence candidates is found in N11. Their masses are in the range of 1.3-2 MSun for ages from 2 to 10 Myr. Young embedded stellar objects having ages of 0.1-1 Myr are found to be intermixed with the candidate pre-main sequence stars. The spatial distribution of the stars shows that this region is the product of clustered star formation. No significant difference is found in the clustering degree of young blue main sequence stars and faint pre-main sequence candidates, suggesting that they might be part of the same formation process. The data suggest that the star formation in the region is a long-lasting process where stars from 0.1 to 10 Myr are widely distributed.

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arXiv2008

The Gaia satellite: a tool for Emission Line Stars and Hot Stars

The Gaia satellite will be launched at the end of 2011. It will observe at least 1 billion stars, and among them several million emission line stars and hot stars. Gaia will provide parallaxes for each star and spectra for stars till V magnitude equal to 17. After a general description of Gaia, we present the codes and methods, which are currently developed by our team. They will provide automatically the astrophysical parameters and spectral classification for the hot and emission line stars in the Milky Way and other close Local Group galaxies such as the Magellanic Clouds.

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arXiv2002

High resolution spectral survey of symbiotic stars in the near-IR over the GAIA wavelength range

High resolution (R~20,000), high signal-to-noise (S/N~100) spectra were collected for ~40 symbiotic stars with the Asiago echelle spectrograph over the same 8480-8740 Ang wavelength range covered by the ESA Cornerstone mission GAIA, centered on the near-IR CaII triplet and the head of the Paschen series. A large number (~140) of cool MKK giant and supergiant templates were observed with the same instrumentation to serve as a reference and classification grid. The spectra offer bright prospects in classifying and addressing the nature of the cool component of symbiotic stars (deriving T(eff), log g, [Fe/H], [alpha/Fe], V(rot)sin i both via MDM-like methods and syntetic atmosphere modeling) and mapping the physical condition and kinematics of the gas regions responsible for the emission lines.

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