arXiv subjects

E. Brugaletta

Publications and source records attributed to E. Brugaletta.

16 recordsLinked to original sources

arXiv2022

Gaia Data Release 3. Rotational modulation and patterns of colour variations in solar-like variables

The Gaia third Data Release (DR3) presents a catalogue of 474\,026 stars with variability induced by magnetic activity. For each star, the catalogue provides a list of about 70 parameters among which the most important are the stellar rotation period $P$, the photometric amplitude $A$ of the rotational signal and the Pearson Correlation Coefficient $r_0$ between brightness and magnitude variations. The Specific Objects Study (SOS) pipeline, developed to characterise magnetically active stars with Gaia Data, has been described in the paper accompanying the Gaia second Data Release. Here we describe the changes made to the pipeline and a new method developed to analyze Gaia time-series and to reveal spurious signals induced by instrumental effects or by the peculiar nature of the investigated stellar source. The period-amplitude diagram obtained with the DR3 data confirms the bimodal distribution of fast rotating stars seen in the DR2 release. The DR3 data permitted, for the first time, to analyze the patterns of magnitude-color variations for thousands of magnetically active stars. The measured $r_0$ values are tightly correlated with the stars position in the period-amplitude diagram. The relationship between the $P$, $A$ and $r_0$ parameters inferred for thousands of stars could be very useful to improve the understanding of stellar magnetic fields and to improve theoretical models. The method developed to reveal the spurious signals can be applied to each of the released Gaia photometric time-series and can be exploited by anyone interested in working directly with Gaia time-series.

astro-ph.SR↗

arXiv2022

Gaia DR3: Apsis III -- Non-stellar content and source classification

Context. As part of the third Gaia data release, we present the contributions of the non-stellar and classification modules from the eighth coordination unit (CU8) of the Data Processing and Analysis Consortium, which is responsible for the determination of source astrophysical parameters using Gaia data. This is the third in a series of three papers describing the work done within CU8 for this release. Aims. For each of the five relevant modules from CU8, we summarise their objectives, the methods they employ, their performance, and the results they produce for Gaia DR3. We further advise how to use these data products and highlight some limitations. Methods. The Discrete Source Classifier (DSC) module provides classification probabilities associated with five types of sources: quasars, galaxies, stars, white dwarfs, and physical binary stars. A subset of these sources are processed by the Outlier Analysis (OA) module, which performs an unsupervised clustering analysis, and then associates labels with the clusters to complement the DSC classification. The Quasi Stellar Object Classifier (QSOC) and the Unresolved Galaxy Classifier (UGC) determine the redshifts of the sources classified as quasar and galaxy by the DSC module. Finally, the Total Galactic Extinction (TGE) module uses the extinctions of individual stars determined by another CU8 module to determine the asymptotic extinction along all lines of sight for Galactic latitudes |b| > 5 deg. Results. Gaia DR3 includes 1591 million sources with DSC classifications; 56 million sources to which the OA clustering is applied; 1.4 million sources with redshift estimates from UGC; 6.4 million sources with QSOC redshift; and 3.1 million level 9 HEALPixes of size 0.013 squared degree, where the extinction is evaluated by TGE.

astro-ph.GA↗

arXiv2022

Gaia Data Release 3: Analysis of the Gaia BP/RP spectra using the General Stellar Parameterizer from Photometry

We present the General Stellar Parameterizer from Photometry (GSP-Phot), which is part of the astrophysical parameters inference system (Apsis). GSP-Phot is designed to produce a homogeneous catalogue of parameters for hundreds of millions of single non-variable stars based on their astrometry, photometry, and low-resolution BP/RP spectra. These parameters are effective temperature, surface gravity, metallicity, absolute $M_G$ magnitude, radius, distance, and extinction for each star. GSP-Phot uses a Bayesian forward-modelling approach to simultaneously fit the BP/RP spectrum, parallax, and apparent $G$ magnitude. A major design feature of GSP-Phot is the use of the apparent flux levels of BP/RP spectra to derive, in combination with isochrone models, tight observational constraints on radii and distances. We carefully validate the uncertainty estimates by exploiting repeat Gaia observations of the same source. The data release includes GSP-Phot results for 471 million sources with $G<19$. Typical differences to literature values are 110 K for $T_{\rm eff}$ and 0.2-0.25 for $\log g$, but these depend strongly on data quality. In particular, GSP-Phot results are significantly better for stars with good parallax measurements ($\varpi/σ_varpi>20$), mostly within 2kpc. Metallicity estimates exhibit substantial biases compared to literature values and are only useful at a qualitative level. However, we provide an empirical calibration of our metallicity estimates that largely removes these biases. Extinctions $A_0$ and $A_{\rm BP}$ show typical differences from reference values of 0.07-0.09 mag. MCMC samples of the parameters are also available for 95% of the sources. GSP-Phot provides a homogeneous catalogue of stellar parameters, distances, and extinctions that can be used for various purposes, such as sample selections (OB stars, red giants, solar analogues etc.).

astro-ph.SR↗

arXiv2022

Gaia Data Release 3: Astrophysical parameters inference system (Apsis) I -- methods and content overview

Gaia Data Release 3 contains a wealth of new data products for the community. Astrophysical parameters are a major component of this release. They were produced by the Astrophysical parameters inference system (Apsis) within the Gaia Data Processing and Analysis Consortium. The aim of this paper is to describe the overall content of the astrophysical parameters in Gaia Data Release 3 and how they were produced. In Apsis we use the mean BP/RP and mean RVS spectra along with astrometry and photometry, and we derive the following parameters: source classification and probabilities for 1.6 billion objects, interstellar medium characterisation and distances for up to 470 million sources, including a 2D total Galactic extinction map, 6 million redshifts of quasar candidates and 1.4 million redshifts of galaxy candidates, along with an analysis of 50 million outlier sources through an unsupervised classification. The astrophysical parameters also include many stellar spectroscopic and evolutionary parameters for up to 470 million sources. These comprise Teff, logg, and m_h (470 million using BP/RP, 6 million using RVS), radius (470 million), mass (140 million), age (120 million), chemical abundances (up to 5 million), diffuse interstellar band analysis (0.5 million), activity indices (2 million), H-alpha equivalent widths (200 million), and further classification of spectral types (220 million) and emission-line stars (50 thousand). This catalogue is the most extensive homogeneous database of astrophysical parameters to date, and it is based uniquely on Gaia data.

astro-ph.GA↗

arXiv2022

Gaia Data Release 3: Apsis II -- Stellar Parameters

The third Gaia data release contains, beyond the astrometry and photometry, dispersed light for hundreds of millions of sources from the Gaia prism spectra (BP and RP) and the spectrograph (RVS). This data release opens a new window on the chemo-dynamical properties of stars in our Galaxy, essential knowledge for understanding the structure, formation, and evolution of the Milky Way. To provide insight into the physical properties of Milky Way stars, we used these data to produce a uniformly-derived, all-sky catalog of stellar astrophysical parameters (APs): Teff, logg, [M/H], [$α$/Fe], activity index, emission lines, rotation, 13 chemical abundance estimates, radius, age, mass, bolometric luminosity, distance, and dust extinction. We developed the Apsis pipeline to infer APs of Gaia objects by analyzing their astrometry, photometry, BP/RP, and RVS spectra. We validate our results against other literature works, including benchmark stars, interferometry, and asteroseismology. Here we assessed the stellar analysis performance from Apsis statistically. We describe the quantities we obtained, including our results' underlying assumptions and limitations. We provide guidance and identify regimes in which our parameters should and should not be used. Despite some limitations, this is the most extensive catalog of uniformly-inferred stellar parameters to date. These comprise Teff, logg, and [M/H] (470 million using BP/RP, 6 million using RVS), radius (470 million), mass (140 million), age (120 million), chemical abundances (5 million), diffuse interstellar band analysis (1/2 million), activity indices (2 million), H{$α$} equivalent widths (200 million), and further classification of spectral types (220 million) and emission-line stars (50 thousand). More precise and detailed astrophysical parameters based on epoch BP, RP, and RVS are planned for the next Gaia data release.

astro-ph.SR↗

arXiv2022

Gaia Data Release 3. Stellar chromospheric activity and mass accretion from Ca II IRT observed by the Radial Velocity Spectrometer

The Gaia Radial Velocity Spectrometer provides the unique opportunity of a spectroscopic analysis of millions of stars at medium-resolution in the near-infrared. This wavelength range includes the Ca II infrared triplet (IRT), which is a good diagnostics of magnetic activity in the chromosphere of late-type stars. Here we present the method devised for inferring the Gaia stellar activity index together with its scientific validation. A sample of well studied PMS stars is considered to identify the regime in which the Gaia stellar activity index may be affected by mass accretion. The position of these stars in the colour-magnitude diagram and the correlation with the amplitude of the photometric rotational modulation is also scrutinised. Three regimes of the chromospheric stellar activity are identified, confirming suggestions made by previous authors on much smaller $R'_{\rm HK}$ datasets. The highest stellar activity regime is associated with PMS stars and RS CVn systems, in which activity is enhanced by tidal interaction. Some evidence of a bimodal distribution in MS stars with $T_{\rm eff}\ge$ 5000 K is also found, which defines the two other regimes, without a clear gap in between. Stars with 3500 K$\le T_{\rm eff} \le$ 5000 K are found to be either very active PMS stars or active MS stars with a unimodal distribution in chromospheric activity. A dramatic change in the activity distribution is found for $T_{\rm eff}\le$3500 K, with a dominance of low activity stars close to the transition between partially- and fully-convective stars and a rise in activity down into the fully-convective regime.

astro-ph.SR↗

arXiv2022

Gaia Data Release 3: Analysis of RVS spectra using the General Stellar Parametriser from spectroscopy

The chemo-physical parametrisation of stellar spectra is essential for understanding the nature and evolution of stars and of Galactic stellar populations. Gaia DR3 contains the parametrisation of RVS data performed by the General Stellar Parametriser-spectroscopy, module. Here we describe the parametrisation of the first 34 months of RVS observations. GSP-spec estimates the chemo-physical parameters from combined RVS spectra of single stars. The main analysis workflow described here, MatisseGauguin, is based on projection and optimisation methods and provides the stellar atmospheric parameters; the individual chemical abundances of N, Mg, Si, S, Ca, Ti, Cr, FeI, FeII, Ni, Zr, Ce and Nd; the differential equivalent width of a cyanogen line; and the parameters of a DIB feature. Another workflow, based on an artificial neural network, provides a second set of atmospheric parameters that are useful for classification control. We implement a detailed quality flag chain considering different error sources. With about 5.6 million stars, the Gaia DR3 GSP-spec all-sky catalogue is the largest compilation of stellar chemo-physical parameters ever published and the first one from space data. Internal and external biases have been studied taking into account the implemented flags. In some cases, simple calibrations with low degree polynomials are suggested. The homogeneity and quality of the estimated parameters enables chemo-dynamical studies of Galactic stellar populations, interstellar extinction studies from individual spectra, and clear constraints on stellar evolution models. We highly recommend that users adopt the provided quality flags for scientific exploitation . The Gaia DR3 GSP-spec catalogue is a major step in the scientific exploration of Milky Way stellar populations, confirming the Gaia promise of a new Galactic vision (abridged).

astro-ph.GA↗

arXiv2021

Gaia Early Data Release 3: Summary of the contents and survey properties

We present the early installment of the third Gaia data release, Gaia EDR3, consisting of astrometry and photometry for 1.8 billion sources brighter than magnitude 21, complemented with the list of radial velocities from Gaia DR2. Gaia EDR3 contains celestial positions and the apparent brightness in G for approximately 1.8 billion sources. For 1.5 billion of those sources, parallaxes, proper motions, and the (G_BP-G_RP) colour are also available. The passbands for G, G_BP, and G_RP are provided as part of the release. For ease of use, the 7 million radial velocities from Gaia DR2 are included in this release, after the removal of a small number of spurious values. New radial velocities will appear as part of Gaia DR3. Finally, Gaia EDR3 represents an updated materialisation of the celestial reference frame (CRF) in the optical, the Gaia-CRF3, which is based solely on extragalactic sources. The creation of the source list for Gaia EDR3 includes enhancements that make it more robust with respect to high proper motion stars, and the disturbing effects of spurious and partially resolved sources. The source list is largely the same as that for Gaia DR2, but it does feature new sources and there are some notable changes. The source list will not change for Gaia DR3. Gaia EDR3 represents a significant advance over Gaia DR2, with parallax precisions increased by 30 percent, proper motion precisions increased by a factor of 2, and the systematic errors in the astrometry suppressed by 30--40 percent for the parallaxes and by a factor ~2.5 for the proper motions. The photometry also features increased precision, but above all much better homogeneity across colour, magnitude, and celestial position. A single passband for G, G_BP, and G_RP is valid over the entire magnitude and colour range, with no systematics above the 1 percent level.

astro-ph.GA↗

arXiv2021

Gaia Early Data Release 3: The Galactic anticentre

We aim to demonstrate the scientific potential of the Gaia Early Data Release 3 (EDR3) for the study of the Milky Way structure and evolution. We used astrometric positions, proper motions, parallaxes, and photometry from EDR3 to select different populations and components and to calculate the distances and velocities in the direction of the anticentre. We explore the disturbances of the current disc, the spatial and kinematical distributions of early accreted versus in-situ stars, the structures in the outer parts of the disc, and the orbits of open clusters Berkeley 29 and Saurer 1. We find that: i) the dynamics of the Galactic disc are very complex with vertical asymmetries, and new correlations, including a bimodality with disc stars with large angular momentum moving vertically upwards from below the plane, and disc stars with slightly lower angular momentum moving preferentially downwards; ii) we resolve the kinematic substructure (diagonal ridges) in the outer parts of the disc for the first time; iii) the red sequence that has been associated with the proto-Galactic disc that was present at the time of the merger with Gaia-Enceladus-Sausage is currently radially concentrated up to around 14 kpc, while the blue sequence that has been associated with debris of the satellite extends beyond that; iv) there are density structures in the outer disc, both above and below the plane, most probably related to Monoceros, the Anticentre Stream, and TriAnd, for which the Gaia data allow an exhaustive selection of candidate member stars and dynamical study; and v) the open clusters Berkeley~29 and Saurer~1, despite being located at large distances from the Galactic centre, are on nearly circular disc-like orbits. We demonstrate how, once again, the Gaia are crucial for our understanding of the different pieces of our Galaxy and their connection to its global structure and history.

astro-ph.GA↗

arXiv2021

Gaia Early Data Release 3: Structure and properties of the Magellanic Clouds

We compare the Gaia DR2 and Gaia EDR3 performances in the study of the Magellanic Clouds and show the clear improvements in precision and accuracy in the new release. We also show that the systematics still present in the data make the determination of the 3D geometry of the LMC a difficult endeavour; this is at the very limit of the usefulness of the Gaia EDR3 astrometry, but it may become feasible with the use of additional external data. We derive radial and tangential velocity maps and global profiles for the LMC for the several subsamples we defined. To our knowledge, this is the first time that the two planar components of the ordered and random motions are derived for multiple stellar evolutionary phases in a galactic disc outside the Milky Way, showing the differences between younger and older phases. We also analyse the spatial structure and motions in the central region, the bar, and the disc, providing new insights into features and kinematics. Finally, we show that the Gaia EDR3 data allows clearly resolving the Magellanic Bridge, and we trace the density and velocity flow of the stars from the SMC towards the LMC not only globally, but also separately for young and evolved populations. This allows us to confirm an evolved population in the Bridge that is slightly shift from the younger population. Additionally, we were able to study the outskirts of both Magellanic Clouds, in which we detected some well-known features and indications of new ones.

astro-ph.GA↗

arXiv2020

Gaia Early Data Release 3: The Gaia Catalogue of Nearby Stars

We produce a clean and well-characterised catalogue of objects within 100\,pc of the Sun from the \G\ Early Data Release 3. We characterise the catalogue through comparisons to the full data release, external catalogues, and simulations. We carry out a first analysis of the science that is possible with this sample to demonstrate its potential and best practices for its use. The selection of objects within 100\,pc from the full catalogue used selected training sets, machine-learning procedures, astrometric quantities, and solution quality indicators to determine a probability that the astrometric solution is reliable. The training set construction exploited the astrometric data, quality flags, and external photometry. For all candidates we calculated distance posterior probability densities using Bayesian procedures and mock catalogues to define priors. Any object with reliable astrometry and a non-zero probability of being within 100\,pc is included in the catalogue. We have produced a catalogue of \NFINAL\ objects that we estimate contains at least 92\% of stars of stellar type M9 within 100\,pc of the Sun. We estimate that 9\% of the stars in this catalogue probably lie outside 100\,pc, but when the distance probability function is used, a correct treatment of this contamination is possible. We produced luminosity functions with a high signal-to-noise ratio for the main-sequence stars, giants, and white dwarfs. We examined in detail the Hyades cluster, the white dwarf population, and wide-binary systems and produced candidate lists for all three samples. We detected local manifestations of several streams, superclusters, and halo objects, in which we identified 12 members of \G\ Enceladus. We present the first direct parallaxes of five objects in multiple systems within 10\,pc of the Sun.

astro-ph.SR↗

arXiv2020

Gaia Early Data Release 3: Acceleration of the solar system from Gaia astrometry

Context. Gaia Early Data Release 3 (Gaia EDR3) provides accurate astrometry for about 1.6 million compact (QSO-like) extragalactic sources, 1.2 million of which have the best-quality five-parameter astrometric solutions. Aims. The proper motions of QSO-like sources are used to reveal a systematic pattern due to the acceleration of the solar system barycentre with respect to the rest frame of the Universe. Apart from being an important scientific result by itself, the acceleration measured in this way is a good quality indicator of the Gaia astrometric solution. Methods. The effect of the acceleration is obtained as a part of the general expansion of the vector field of proper motions in Vector Spherical Harmonics (VSH). Various versions of the VSH fit and various subsets of the sources are tried and compared to get the most consistent result and a realistic estimate of its uncertainty. Additional tests with the Gaia astrometric solution are used to get a better idea on possible systematic errors in the estimate. Results. Our best estimate of the acceleration based on Gaia EDR3 is $(2.32 \pm 0.16) \times 10^{-10}$ m s${}^{-2}$ (or $7.33 \pm 0.51$ km s$^{-1}$ Myr${}^{-1}$) towards $α= 269.1^\circ \pm 5.4^\circ$, $δ= -31.6^\circ \pm 4.1^\circ$, corresponding to a proper motion amplitude of $5.05 \pm 0.35$ $μ$as yr${}^{-1}$. This is in good agreement with the acceleration expected from current models of the Galactic gravitational potential. We expect that future Gaia data releases will provide estimates of the acceleration with uncertainties substantially below 0.1 $μ$as yr${}^{-1}$.

astro-ph.GA↗

arXiv2015

Gaia-ESO Survey: The analysis of pre-main sequence stellar spectra

This paper describes the analysis of UVES and GIRAFFE spectra acquired by the Gaia-ESO Public Spectroscopic Survey in the fields of young clusters whose population includes pre-main sequence (PMS) stars. Both methods that have been extensively used in the past and new ones developed in the contest of the Gaia-ESO survey enterprise are available and used. The internal precision of these quantities is estimated by inter-comparing the results obtained by such different methods, while the accuracy is estimated by comparison with independent external data, like effective temperature and surface gravity derived from angular diameter measurements, on a sample of benchmarks stars. Specific strategies are implemented to deal with fast rotation, accretion signatures, chromospheric activity, and veiling. The analysis carried out on spectra acquired in young clusters' fields during the first 18 months of observations, up to June 2013, is presented in preparation of the first release of advanced data products. Stellar parameters obtained with the higher resolution and larger wavelength coverage from UVES are reproduced with comparable accuracy and precision using the smaller wavelength range and lower resolution of the GIRAFFE setup adopted for young stars, which allows us to provide with confidence stellar parameters for the much larger GIRAFFE sample. Precisions are estimated to be $\approx$ 120 K r.m.s. in Teff, $\approx$0.3 dex r.m.s. in logg, and $\approx$0.15 dex r.m.s. in [Fe/H], for both the UVES and GIRAFFE setups.

astro-ph.SR↗

arXiv2014

The Gaia-ESO Survey: Chromospheric Emission, Accretion Properties, and Rotation in $γ$ Velorum and Chamaeleon I

We use the fundamental parameters delivered by the GES consortium in the first internal data release to select the members of $γ$ Vel and Cha I among the UVES and GIRAFFE spectroscopic observations. A total of 140 $γ$ Vel members and 74 Cha I members were studied. We calculated stellar luminosities through spectral energy distributions, while stellar masses were derived by comparison with evolutionary tracks. The spectral subtraction of low-activity and slowly rotating templates, which are rotationally broadened to match the $v\sin i$ of the targets, enabled us to measure the equivalent widths (EWs) and the fluxes in the H$α$ and H$β$ lines. The H$α$ line was also used for identifying accreting objects and for evaluating the mass accretion rate ($\dot M_{\rm acc}$). The distribution of $v\sin i$ for the members of $γ$ Vel displays a peak at about 10 km s$^{-1}$ with a tail toward faster rotators. There is also some indication of a different $v\sin i$ distribution for the members of its two kinematical populations. Only a handful of stars in $γ$ Vel display signatures of accretion, while many more accretors were detected in the younger Cha~I. Accreting and active stars occupy two different regions in a $T_{\rm eff}$-flux diagram and we propose a criterion for distinguishing them. We derive $\dot M_{\rm acc}$ in the ranges $10^{-11}$-$10^{-9} M_\odot$yr$^{-1}$ and $10^{-10}$-$10^{-7} M_\odot$yr$^{-1}$ for $γ$ Vel and Cha I accretors, respectively. We find less scatter in the $\dot M_{\rm acc}-M_\star$ relation derived through the H$α$ EWs, when compared to the H$α$ $10\%W$ diagnostics, in agreement with other authors.

astro-ph.SR↗

arXiv2014

The Gaia-ESO Survey: Kinematic structure in the Gamma Velorum Cluster

Context: A key science goal of the Gaia-ESO survey (GES) is to use the kinematics of low-mass stars in young clusters to probe their dynamical histories and how they populate the field as they become unbound. The clustering of low-mass stars around the massive W-R binary gamma^2 Velorum was one of the first GES targets. Aims: To empirically determine the radial velocity (RV) precision of GES data, construct a kinematically unbiased sample of cluster members and characterise their dynamical state. Methods: Targets were selected from colour-magnitude diagrams and intermediate resolution spectroscopy used to derive RVs and assess membership from the strength of the Li6708A line. The RV distribution was analysed using a maximum likelihood technique that accounts for unresolved binaries. Results: The GES RV precision is about 0.25km/s and sufficient to resolve velocity structure in the low-mass population around gamma^2 Vel. The structure is well fitted by two kinematic components with roughly equal numbers of stars; the first has an intrinsic dispersion of 0.34+/-0.16km/s, consistent with virial equilibrium. The second has a broader dispersion of 1.60+/-0.37km/s and is offset from the first by ~2km/s. The first population is older by 1-2Myr based on a greater level of Li depletion seen among its M-stars and is probably more centrally concentrated around gamma^2 Vel. Conclusions: We consider several formation scenarios, concluding that the two kinematic components are a bound remnant of the original, denser cluster that formed gamma^2 Vel, and a dispersed population from the wider Vela OB2 association, of which gamma^2 Vel is the most massive member. The apparent youth of gamma^2 Vel compared to the older (>=10Myr) low-mass population surrounding it suggests a scenario where the massive binary formed in a clustered environment after the formation of the bulk of the low-mass stars.[abridged]

astro-ph.SR↗

arXiv2011

The debris disk host star HD 61005: a member of the Argus Association?

HD 61005 is a nearby young solar type star that shows a large infrared excess due to a debris disk. The disk has been recently imaged from ground and space, with indications of several components. Some characteristics of the disk suggest the presence of planetary companions around the star, that remain undetected in deep adaptive optics imaging. For a better understanding of the system we aim to refine the determination of the stellar parameters, with emphasis on the stellar age and system orientation. We used ASAS and Hipparcos photometry and FEROS spectra to determine the rotation period, radial and rotational velocity, chromospheric emission, effective temperature, and chemical composition. We find no indication of any misalignment between the star rotation axis and the disk. The standard age calibrations applied to several indicators yield an age close to that of the Pleiades (120 Myr); however the kinematic properties strongly support its membership in the younger (40 Myr) Argus association, which also includes the IC 2391 open cluster. Detailed comparison of the properties of HD 61005 and IC 2391 members shows that the characteristics of HD 61005 are compatible with membership to the Argus association, once its rather slow rotation is taken into account, because lithium and other age indicators are somewhat correlated with stellar rotation at a fixed age. We also identify systematic differences between the field and cluster population of the Argus association, which are probably selection effects, so we suggest that additional members with slower rotation and lower activity level are waiting to be identified.

astro-ph.SR↗