Stellar evolution along the HR diagram with Gaia

19 Sept 2022, 18:30 → 23 Sept 2022, 20:00 Europe/Rome

INAF-Osservatorio Astronomico di Capodimonte

MW-Gaia WG2/1 Hybrid Workshop

Monday, 19 September

18:30 → 20:00 Opening Reception

Opening Reception at the Observatory of Capodimonte. Please, note that the bus is only provided for the return downtown

Tuesday, 20 September

08:30 → 09:00 Registration

09:00 → 09:20 Welcome+infos (M. Marconi - G. Clementini - I. Musella)

09:20 → 10:40 Overview on Gaia data/products and their use: I Session - Chair: G. Clementini

09:20 The Gaia mission and stellar physics (Invited)

I will present and overview of the Gaia mission and its most recent data release. The presentation will focus on the Gaia mission status and the plans for the extended mission, as well as the astrometric and photometric data in relation to stellar physics research.

Speaker: A. Brown

Brown_Anthony.pdf

09:50 Gaia stellar parameters in Data Release 3 (Invited)

As part of Gaia DR3, an extensive astrophysical characterisation of Galactic and extra-galactic sources has been published. In my presentation, I will provide an overview of the various different types of stellar-parameter estimates included in Gaia DR3. Some of these apply to specific types of stars while other parameterisations are general.
These stellar-parameter estimates also make use of different types of Gaia data. I will highlight interesting results but also limitations.
Lastly, using examples from the literature, I will show how to use these results in practice.

Speaker: R. Andrae

10:20 Transferring spectroscopic stellar labels to Gaia DR3 stars with supervised learning

The Gaia Data Release 3 (DR3, published in June 2022) has delivered astrometric, photometric, and spectroscopic measurements for more than a billion stars. The wealth and complexity of the data makes traditional approaches for estimating stellar parameters for the full Gaia dataset prohibitive. We have explored different supervised learning methods for extracting basic stellar parameters as well as distances and line-of-sight extinctions, given spectro-photo-astrometric data, taking advantage of the newly released Gaia BP/RP spectra. For training we use an enhanced high-quality dataset compiled from Gaia DR3 and ground-based spectroscopic survey data covering the whole sky and all Galactic components. We present first results obtained using the full wealth of Gaia DR3 data, demonstrating that thanks to the BP/RP spectra we can now deliver more reliable stellar parameters, especially metallicities. It also allows us to extend the covered parameter space to regions that are difficult for classical isochrone-based methods such as StarHorse (e.g. white dwarfs or hot stars).

Speaker: F. Anders

10:40 → 11:10 Coffe-Break

11:10 → 12:30 Overview on Gaia data/products and their use: II Session - Chair: S. Randich

11:10 Gaia chemical abundances from the Radial Velocity Spectrograph (Invited)

The chemo-physical parametrization of stellar spectra is essential to understand the nature and evolution of stars and of Galactic stellar populations.

The Gaia third data release contains the parametrization of the Radial Velocity Spectrometer data, performed by the General Stellar Parametrizer-spectroscopy, GSP-Spec, module.

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.

The homogeneity and quality of the estimated parameters enables chemo-dynamical studies of Galactic stellar populations and clear constraints to stellar evolution models. In this talk, the DR3 GSPspec catalogue will be presented, and several examples concerning its application to stellar evolution studies will be shown.

Speaker: A. Recio-Blanco

11:40 Variable stars in Gaia Data Release 3 (Invited)

Pulsating variable stars have been used for a long time both as fundamental distance indicators and as stellar population tracers. But, thanks to the availability of additional observables such as periods and amplitudes, they also represent an independent check for the stellar evolution theory. Also, non-intrinsic variables, like binaries, rotational etc. provide important constraints to evolutionary models.
In this context, the contribution of the recent Gaia mission data release 3 (DR3) represents an impressive step forward whose outcomes will be valuable for many years to come.
In this talk, I review the main properties of the variable stars in DR3 which are most relevant for the stellar evolutionary studies, focusing in particular on the pulsating stars such as RR Lyrae, Cepheids and main-sequence oscillators.

Speaker: V. Ripepi

12:10 Absolute calibration of Type II Cepheid and RR Lyrae distance scales using Gaia DR3

RR Lyrae and Type II Cepheid variables are sensitive probes for the precision stellar astrophysics and the distance scale. These population II variables are known to follow well-defined Period-Luminosity relation at NIR wavelengths and can provide an independent primary calibration of the cosmic distance ladder. We present an absolute calibration of Period-Luminosity-Metallicity relations (PLZR) for the Milky Way field and globular cluster Type II Cepheid and RR Lyrae variables at NIR wavelengths. The spectroscopic metallicities from Gaia-RVS and Gaia parallaxes together with multiband photometry are used to obtain an independent calibration of PLZR for Galactic field variables. Our new NIR photometry of globular clusters with CFHT/Gemini for a wide range of metallicities and the Gaia data are utilized to quantify metallicity dependence on pulsation properties of globular cluster variables. NIR observations of population II variables in peculiar globular clusters NGC 6441 and NGC 6388 are used to investigate the effect of possible helium enhancement on their pulsation properties. We also provide a comparison of RR Lyrae and Type II Cepheid pulsation properties with the theoretical predictions and explore stringent constraints on the impact of metallicity and helium on both evolutionary and pulsation models for helium burning horizontal-branch and post-horizontal-branch low-mass stars.

Speaker: A. Bhardway

Bhardwaj_Anupam.pdf

12:30 → 14:30 Lunch Break

14:30 → 16:10 Overview on Gaia data/products and their use: III Session - Chair: L. Eyer

14:30 Multiple stellar systems in Gaia DR3 (Invited)

The Gaia DR3 catalogue is the first release from the mission to contain the detailed solutions for multiple star systems. These have been identified by Gaia’s unique range of observational techniques providing orbital elements or trend parameters for astrometric, spectroscopic and photometric (eclipsing) binaries and combinations of them.

This is a hugely important data resource containing approximately 800,000 objects which increases the number of known binary orbits by an order of magnitude. These systems are distributed across the H-R diagram allowing studies of binarity on the main sequence and along the RGB/AGB. The large sample also allows the discovery of significant samples of more exotic and scarce systems. A combination of variability and binary catalogues reveals a number of new EL CVn systems. There are also many systems that appear to contain a compact object – the so-called Sirius-like systems, comprising a main sequence star and a hidden white dwarf companion, together with new examples of double degenerate, binary white dwarfs. The Gaia catalogue is also able to probe the bottom of the main sequence, determining the orbits of previously-suspected binary ultracool dwarfs and highlighting completely new examples. In the substellar regime Gaia provides important constraints on the occurrence rates of substellar companions to M dwarfs and detects several dozen new exoplanet candidates, including two with validated orbital solutions and one super-Jupiter orbiting a white dwarf, which require confirmation. This talk will survey the wealth of data included in the binary star catalogues and present some of the highlights of the early analyses.

Speaker: M. Barstow

Barstow_Martin.pdf

15:00 White dwarfs and the Gaia revolution (Invited)

Over 95% of all the stars in the Galaxy will, one day, evolve into white dwarfs: small stellar remnants slowly cooling and fading over billions of years. The unique properties of these objects make them powerful tools with applications in diverse areas of astrophysics, from cosmochronology to exo-planetary science.

However, because of their sparse sky density and intrinsic low luminosity, identifying large numbers of white dwarfs has historically been an extremely challenging task.

Until 4 years ago we could only rely on small and severely biased samples, often constructed from serendipitous discoveries.

Then, Gaia changed everything…

This talk will describe the transformative impact that Gaia had in the field of white dwarfs by enabling the identification of over 359,000 of these stars, nearly ten times more than what was known before. It will briefly outline the process that led to the identification of the Gaia white dwarfs and illustrate the properties of this unprecedented sample highlighting some of the most impactful discoveries enabled by it. It will then conclude with an overview of the latest additions brought by the recent DR3 and with a look at future perspectives.

Speaker: N. Gentile Fusillo

15:30 Gaia : An efficient black-hole hunter

Understanding the connection between the properties of BHs and their progenitors is interesting in many branches of astrophysics. Traditional methods such as detection through X-ray, radio, or gravitational-wave emission are sensitive towards a small subset of all BH binaries expected to form in nature. In my talk I will explore the exciting possibilities for detecting BHs in detached binary systems with luminous companions (LCs) via astrometric and photometric measurements. We create highly realistic models of BH-LC binaries expected to be there at present in the Milky Way (MW) using the binary population synthesis code COSMIC for two adopted supernovae models. Taking into account Gaia's astrometric precision, spectroscopic resolution, and interstellar extinction and reddening, we find that Gaia in its 10 year mission should detect around 30-300 BH candidates of which 10-100 will have clear mass constraints. These potentially detectable BHs constitute a set complementary to those detected by other traditional methods. Furthermore, since the LC's properties, such as age and metallicity, can be constrained relatively easily, and it is expected that the BH's progenitor must have had the same zero-age properties as the LC, if detected in large numbers as our models suggest, for the first time, we will be able to constrain the highly uncertain map connecting BH properties with those of their progenitors.

Speaker: C. Chawla

15:50 The white dwarf population within 100pc as seen by Gaia-DR3 and the VO

The recent Gaia data release 3 has provided BP/RP spectra for most of the white dwarfs (WD) located closer than 100 pc from the Sun. This volume-limited sample of WDs within 100pc is the most complete sample of WDs defined so far (Jiménez-Esteban et al. 2018). We have used the Gaia-DR3 spectra, the Virtual Observatory (VO), and a new collection of emission model spectra, to classify the WDs into H-rich (DA) or He-rich (DB) atmosphere. Our method has demonstrated to be an excellent classifier, reaching both an accuracy and a precision higher than 90%. This has allowed to study the population of DA and DB WDs within 100pc as never before. In this talk we will explain the methodology used for classification, and we will present the result of the comparative study of DA and DB WD populations in the vicinity of the Sun.

Speaker: F. Jiménez-Esteban

Jiménez-Esteban_Fran.pdf

16:10 → 16:40 Coffe-Break

16:40 → 18:20 Overview on Gaia data/products and their use: IV Session - Chair: S. Van Eck

16:40 Star clusters as laboratories for stellar evolution (Invited)

As groups of co-eval stars sharing the same initial chemical composition, star clusters are ideal laboratories to test stellar evolution models. The Gaia data has been especially useful in showing the limits and inconsistencies of pre-main-sequence star models and the resulting uncertainty in isochronal ages of young clusters. In this talk I will review results obtained with Gaia and combinations of asteroseismology and ground-based spectroscopy of cluster stars to constrain the physical processes governing the evolution of stars.

Speaker: T. Cantat-Gaudin

17:10 OB stars and associations with Gaia (Invited)

OB stars are the luminaries of the Milky Way but their lives are brief. As such, they provide unique problems and opportunities for their analysis with Gaia, as their luminosities, intrinsic colors, and spatial distribution are quite different from the dominant cooler populations. In particular, most OB stars are born in (unbound) OB associations and Gaia can be used to address two issues: [a] is that "most" an "all"? and [b] are associations dissolved clusters? In this talk I will present recent studies of OB stars, clusters, and associations with Gaia that address those issues and others, such as the IMF for massive stars, the tracing of spiral arms, the origin of runaway stars, and how to (correctly) deal with extinction.

Speaker: J. Maiz Apellaniz

Maíz_Apellániz_Jesús.pdf

17:40 A Gaia 4D panoramic of the clustered star formation in the solar neighborhood.

Gaia data has tailored a very complete sample of open clusters, within 3.5 kpc around the Sun, with homogeneous data. The clusters with ages less than 50 Ma (YOCs) provide a taster of how clustered star formation takes place in the extended solar neighborhood. From the Gaia-YOC sample we analyze the hierarchy of star formation in this Galactic region and the 4D (X,Y,Z,Vz) structure in the solar vicinity. Warp, corrugations and local high displacements seem to coexist in this Galactic area that challenges us to look for a unique scenario able to fit all the pieces of the puzzle.

Speaker: E. Alfaro

Wednesday, 21 September

09:00 → 10:40 Stellar evolution and pulsation models: I Session - Chair: J. Montalban

09:00 The galaxy in your preferred colour: synthetic photometry from Gaia XP spectra (Invited)

The release of BP/RP spectrophotometry for 220 M stars in Gaia DR3 allows for the first time to obtain synthetic photometry in any passband enclosed in the range 330-1050 nm.
This photometry is (a) obtained from data acquired beyond the Earth’s atmosphere, (b) all sky, (c) directly tied to fluxes in physical units, (d) precise to the limits enforced by the internal calibration of Gaia spectrophotometry. I summarise the properties and limitation of synthetic photometry from DR3 data, briefly discussing future developments and showing some examples of application.

Speaker: M. Bellazzini

Napoli2022_MB_final.pdf

09:30 Low-mass star modelling: constraints from Gaia (Invited)

Despite the huge progress made in these last decades in the modelling of low-mass stars, there are still important uncertainties affecting their stellar models. In this talk, we'll review some important aspects related to the evolutionary and structural properties of low-mass stars, and discuss the constraints/benchmarks provided by Gaia data.

Speaker: S. Cassisi

cassisi_santi.pdf

10:00 Single star sequences of the Hyades and Pleiades open clusters

Based on GAIA DR3 we have identified bonafide single stars and likely binary and multiple systems in the Hyades and Pleiades open clusters. We fit fiducial isochrones in the GAIA photometric system for more than 600 single stars in the Hyades, and more than 800 single stars in the Pleiades. The fiducial isochrones serve as benchmarks for the MESA/MIST and PARSEC evolutionary models and isochrones. While PARSEC isochrone overall provide a very good fit to the observed sequences, MESA isochrones systematically under predict the observed stellar luminosity for stars with masses between 0.25 and 0.85 M_sun. The PARSEC evolutionary models enable us to assign mass, effective temperature, luminosity, and surface gravity to each of the single stars, making these some of the largest homogeneous samples of stars with slightly supersolar metallicity at ages of ~140 and 700 Myr, respectively, and masses in the range 0.1 to 3 M_sun. We compare PARSEC derived parameters assuming a fixed metallicity for each of the clusters with the parameters provided by the GAIA Astrophysical parameters interference system (APSIS) of DR3, and discuss systematic trends.

Speaker: W. Brandner

10:20 Solving the puzzle of mixing in giant stars with the Besançon Galaxy Model

The current (and future) large Galactic surveys are revolutionising our knowledge of Galactic and stellar physics, providing kinematics, chemical and global properties for a very large number of stars across the Milky Way. The Gaia and Kepler space-missions, along with ground-based spectroscopic surveys paves the way to a better understanding of stellar interiors, providing valuable and independent constraints on current stellar evolution models and on the physics of different transport processes.

This incredible large number of data motivates the development of statistical analysis of Galactic stellar populations improving our understanding of the Milky Way and its stars. The so-called population synthesis approach is a powerful tool for such analysis, allowing the computation of mock catalogues under various model hypothesis, to provide a forward modelling, and to statistical compare them with any type of large survey data.

In this talk, I will present some results from Lagarde et al. (2019) where we investigate the effects of extra-mixing on C and N abundances using the first comparison between the Gaia-ESO survey abundances with simulations of the observed fields using the Besançon stellar population synthesis model. In a second part of the talk, I will present a recent study of a sample of Kepler giants for which we have performed a high-resolution spectroscopic follow-up (Lagarde et al. in prep.). In this study we demonstrate the power of the combination of seismic and spectroscopic data to constrain the efficiency of extra-mixing on the red-giant branch.

Speaker: N. Lagarde

Lagarde_Nadege.pdf

10:40 → 11:10 Coffe-Break

11:10 → 12:40 Stellar evolution and pulsation models: II Session - Chair: M. Limongi

11:10 Constraints on AGB stellar models from GAIA (Invited)

In this review I will present some Gaia highlights concerning AGB stars. Gaia parallaxes of the most evolved AGB stars suffer from surface brightness and color variations. Binarity diagnostics are also less precise due to such jitter. Despite these difficulties, Gaia data are able to bring strong constraints on stellar evolution by allowing to clearly constrain the luminosities of several classes of key AGB objects.

Speaker: S. Van Eck

11:40 Constraining the Evolution of Milky Way AGB stars and Their White Dwarf Progeny with GAIA (Invited)

We examine the population of asymptotic giant branch (AGB) stars that appear in the fields of intermediate-age and young open star clusters using GAIA DR2 and EDR3 photometric and astrometric data. For the first time, thanks to GAIA, we identify 49 AGB star candidates brighter than the tip of the red giant branch, with a good to high cluster membership probability. There are 19 TP-AGB stars with known spectral types among them: 4 M stars, 3 MS/S stars, and 12 C stars. We characterize each star in terms of initial mass, luminosity, mass-loss rate, core mass, period, and mode of pulsation by combining observations, stellar models, and radiative transfer calculations that include the effect of circumstellar dust. The data collected allows us to shed light on the TP-AGB evolution at solar-like metallicity, constraining the third dredge-up process, the initial masses of carbon stars, stellar winds, pulsation, and the initial-final mass relation (IFMR). We discover that two bright carbon stars, MSB 75 and BM IV 90,members of the clusters NGC 7789 and NGC 2660 (with similar ages of 1.2-1.6 Gyr and initial masses of 2.1 > Mi/Msun > 1.9), have unusually high core masses, Mc~ 0.7 Msun. These results support the findings of a recent work that identified a kink in the IFMR, which suddenly interrupts its monotonic trend just at the same initial masses. Interestingly, the ages of the host clusters NGC 7789 and NGC 2660 correspond to the transition between low-mass stars that undergo the helium flash at the RGB tip and those just massive enough to avoid electron degeneracy in their helium cores. The intriguing implications for stellar and galaxy evolution are discussed.

Speaker: P. Marigo

12:10 Stellar models of Massive Stars and GAIA (Invited)

In this talk, I shall discuss the main challenges faced by massive star modelling and how the data collected by Gaia may help in overcoming these challenges.
We shall begin by addressing questions related to massive star formation, then discuss the impacts of the physics of transport processes both in convective and radiative layers. We shall comment on the questions of the impact of mass losses and of a surface magnetic field both in single and multiple systems.

Speaker: G. Meynet

12:40 → 14:30 Lunch-Break

14:30 → 15:40 Stellar evolution and pulsation models: III Session - Chair: J. Isern

14:30 Mind the gaps: a massive empirical approach to high-mass stellar evolution with the aid of IACOB, WEAVE, Gaia and TESS

IACOB is an ambitious long-term observational project which is contributing to the so-called new era of investigation of massive stars by concentrating on Galactic OB stars. More specifically, the main scientific goal of the project is to provide a complete empirical overview of the physical properties of a statistically significant sample of Galactic OB stars. In particular, the ultimate driver of the project is that the compiled information can be used as a strong and long-lasting empirical anchor point for our theories of stellar atmospheres, winds, interiors and evolution of massive stars. In this endeavor, we are benefiting from: (a) optical, high-resolution spectroscopic instruments attached to 1-5~m telescopes, mostly in the Canary Islands observatories; (b) state-of-the-art tools and techniques to perform single snap-shot and multi-epoch quantitative spectroscopic analyses (providing accurate estimates for the stellar/wind parameters, rotational velocities, abundances, as well as information about stellar phenomena giving rise to spectroscopic variability/peculiarity such as binarity, pulsations, rotational modulation, peculiar emission and/or wind variability); (c) parallaxes and proper motions provided by the Gaia mission; and (d) high-cadence, uninterrupted photometry provided by the TESS mission.

In this talk, I will provide an overview of how the incorporation of Gaia data to the IACOB project is helping us to solve some of the long-standing questions and problems about the first stages of evolution of stars born with masses in the range between 15 and 80 Msol. Special emphasis will be put in the critical importance of supporting Gaia observations with ground-based spectroscopic surveys to be able to investigating stellar evolution along the upper right region of the HRD with Gaia.

Speaker: S. Simon-Diaz

SimonDiaz_Sergio.pdf

14:50 On the s-elements content of the Milky Way as revealed by Gaia/DR3 data

Understanding the formation and evolution history of the Milky Way is still quite challenging. Combining kinematic and dynamical studies together with the chemical analysis of large number of stars allows us to well characterize the Galactic stellar populations and, hence, unveil their formation histories. Especially, abundances of neutron-capture elements are particularly important to understand the Galactic chemical evolution history.

Within this context, the Gaia DR3 offers a huge step forward since such chemical abundances associated with accurate astrometric have been published for an unprecedented number of stars. Thanks to such data derived from the analysis of RVS spectra by the GSP-spec module, we have explored the Galactic content in neutron-capture elements (Ce, Nd, Zr). We remind that these species are formed in the late stages of low and intermediate stars by slow-neutron captures. As they do not belong to the same s-process peaks and hence are produced under different physical conditions), the Gaia data allow us to disentangle the stellar sites of their production better and help to better understand their Galactic chemical evolution. For instance, Gaia DR3 Cerium abundances have shown a flat trend in [Ce/Fe] vs [M/H] in the Milky way disc. We also computed horizontal gradient from field stars as well as from open clusters. We also found cerium in the halo within accreted systems and one globular cluster.

Speaker: G. Contursi

15:10 Classical Cepheids as Distance Indicators and Stellar Population Tracers in the Gaia Era (Invited)

Modeling of radially pulsating stars, specifically Classical Cepheids, is fundamental to constrain the physical properties of these stars and their role as stellar population tracers, as well as to calibrate the extragalactic distance scale. In particular, the investigation of the dependence of their predicted properties on the various physical and numerical assumptions can help understand residual systematic errors in the local determination of the Hubble constant.
We recently provided a detailed homogeneous nonlinear pulsation model grid of Classical Cepheids taking into account variations of chemical composition, mass-luminosity (ML) relation, and efficiency of super-adiabatic convection.
The predicted observables included the instability strips, multi-filter light curves, and the corresponding mean magnitudes and colors; which were used to derive metal-dependent period-luminosity-color (PLC) and period-Wesenheit (PW) relations. The latter were applied to a sample of Gaia Early Data Release 3 (DR3) Galactic Cepheids and the inferred theoretical parallaxes were tested against Gaia astrometric results. Moreover, by combining this pulsational scenario with updated stellar evolution predictions, we derived new and accurate metal-dependent Period-Age and Period-Age-Color relations, which were applied to the same sample of Galactic Cepheids in the Gaia DR3 to constrain their age distribution.

Speaker: G. De Somma

15:40 → 16:10 Coffe-Break

16:10 → 17:20 Stellar evolution and pulsation models: IV Session - Chair: M. Marconi

16:10 RR Lyrae pulsation and evolutionary models tested against Gaia EDR3 (Invited)

The Gaia mission not only leads to new discoveries in nearly all disciplines in astronomy and astrophysics but also offers a unique opportunity for testing the coherence of the parameters derived for various physical systems. Furthermore, these tests help to investigate the possible systematics left in the Gaia
parallaxes.

In this talk we focus on the Galactic field RR Lyrae stars that are capable of providing full (mass, effective temperature and luminosity) solution by using pulsation and evolution theories, together with stellar atmosphere models and multi-band photometry.
We find good overall agreement with the independent Gaia/EDR3 parallaxes, indicating no significant flaws on both sides.
These results will be confronted with other similar studies, including Cepheids, binary stars and HST parallaxes.

Speaker: G. Kovacs

kovacs_geza.pdf

16:40 Ultra Long Period Cepheids in the HR diagram: new insights from Gaia DR3

Thanks to the well known Period-Luminosity relation, Ultra Long Period (ULP) Cepheids, characterized by periods longer than about 80 days, are among the brightest primary indicators to calibrate the cosmic distance ladder, currently at the center of the debate on the Hubble constant tension. In principle, with the advent of next generation facilities, these bright pulsating variables will be observable up to cosmological distances (larger than 100 Mpc) allowing us to measure the Hubble constant without the need for secondary distance indicators. This occurrence would significantly reduce the error budget in the final Hubble constant value. In spite of this challenging property, the ULPs are not completely understood from the theoretical point of view. On one side, they have been hypothesised to be the extension of Classical cepheids at longer periods and higher masses, on the other side current stellar evolution and pulsation models do not predict such long periods in the corresponding color-magnitude diagrams, in particular in the lowest metal regime,
Unfortunately the number of known ULPs is small, 72 objects, with a photometry that is not always homogeneous and often without the possibility of having accurate light curves for a reliable comparison with evolutionary and pulsation models. In this context, Thanks to Gaia DR3 we have the opportunity to have homogeneous photometry and a number of well sampled light curves for 14 already known ULPs in the various galaxies, namely SMC, LMC, M31 and M33. These data are compared with updated evolutionary tracks in the Color-Magnitude diagram to provide constraints on the evolutionary properties. Moreover, the model fitting of observed multi-filter light curves, based on ad hoc computed pulsation models provide independent information on the intrinsic stellar parameters.

Speaker: I. Musella

ULPnew_IMusella.pdf

17:00 Gaia distances: an opportunity for gauging the asteroseismic accuracy of beta Cephei pulsators

The β Cephei pulsators are massive main-sequence stars presenting low radial-order oscillations. These latter bear a powerful signature of physical processes at the edge of the convective core and in the radiative envelope, as for e.g. convective overshooting, hydrodynamic or magnetic instabilities. Yet, it is not clear to what extent the seismic inferences describe accurately the structure of these massive stars. However, a novel interferometric approach has recently been shown able to measure the angular diameter of these bright objects. We have developed and tested new methods for the seismic modelling of β Cephei pulsators, including inversions of the mean stellar density. Inferred density combined with an independently determined stellar radius would allow for accurate estimation of the mass ; and would be a direct test of the accuracy of the results from asteroseismic forward modelling. In that regards, improvement in the distance determination of bright stars by Gaia, presently or in the future, is the key to determine accurate radius from the recent interferometric measurements of β Cephei stars.

Speaker: S. Salmon

20:00 → 22:30 Social Dinner

Thursday, 22 September

09:00 → 10:40 White dwarfs - Asteroseismology - Binaries: I Session - Chair: S. Simon-Diaz

09:00 Understanding binary stars with Gaia (Invited)

Binary stars are vital to most of astrophysics. Both historically and still today they provide key measurements of stellar masses and radii. Many binaries interact, hence transfer and lose mass and angular momentum leading to the formation of exotic stars like blue stragglers, R-type carbon stars, Wolf-Rayet stars and barium/CH/CEMP stars, and also unique phenomena such as novae, X-ray binaries, type Ia supernovae and gravitational-wave sources. In the context of Gaia and the Gaia HRD, binaries are (almost) everywhere, and where they are not we find probably only merged binaries. I will review the number of, and properties of, binaries in the HRD, linking this to work that has been done using Gaia. Modelling of binaries has come a long way since they became trendy (again?) about a decade ago, and I will describe how stellar-population modelling now includes binaries and how we are dealing with the large datasets required by a mission such as Gaia. I will end with a discussion of the big questions in binary-stellar evolution, and how Gaia can/will/may help us to pin down the many – still large! – uncertainties in binary stellar modelling.

Speaker: R. Izzard

09:30 White dwarf cosmochronology (Invited)

The evolution of white dwarfs is a gravothermal process of cooling that allows them to be be used for reconstructing or at least for constraining the evolution of several Galactic populations of stars. At present, the number of white dwarfs with reasonably good parallaxes and photometric data is ~300,000 thanks to the Gaia mission. These data together with the spectroscopic information obtained by different surveys have shown the existence of structures in the HR-domain of white dwarfs and have provided luminosity functions of unprecedented precision that open new perspectives about the evolution of white dwarfs. One of them is crystallization. This process releases energy via latent heat and through the sedimentation of heavier chemical species by a change of solubility during the transition liquid-solid and consequently it slows down the cooling evoution. This effect raises a new problem, the dependence on the initial metallicity, an aspect that cannot be longer neglected and that it is hard to include since it is impossible to estimate the original metallicity of the parent star of isolated white dwarfs. One possible way to solve or to palliate this problem is to obtain the luminosity function of white dwarfs that are members of non-interacting binaries.

Speaker: J. Isern

Isern_Jordi.pdf

10:00 Accurate masses of Hyades White Dwarfs

Accurate measurements of white dwarfs masses are needed for determining the amount of gas recycled in the Galaxy, and, when measured through gravitational
redshift, establish a firm comparison between quantum mechanics and general relativity predictions.
We use the accurate ESPRESSO spectrograph at the VLT to determine Doppler shifts and gravitational redshifts for 8 bona fide Hyades white dwarfs, with an
accuracy of better than 1.5$\%$. By comparing the gravitational redshift M/R measurements with those derived by fitting the Gaia color - magnitude
diagram with theoretical models, we find that the models and the observed M/R ratios globally agree extremely well, to better than 1%. By comparing photometric and spectroscopic Teff, we confirm that spectroscopic Teff are systematically larger, producing larger masses and smaller radii than what
found in our analysis.

Speaker: L. Pasquini

Pasquini_Luca.pdf

10:20 Seismic cartography of white-dwarf interiors: how well can we constrain convective mixing?

Probing internal properties of white-dwarf stars has been amongst the earliest objectives of asteroseismology. White-dwarf pulsators offer exciting opportunities to unravel their inner structure and dynamics from the observed low-degree, low-order gravity (g-)modes. We review the most recent efforts from our group to perform a complete seismic cartography of white-dwarf interiors of DB and DA pulsators. Such results constitute precious guidelines for modeling late stages of stellar evolution and better understanding their constitutive physics. We show how Gaia's input is essential in this context to validate any physical solution found.

Speaker: N. Giammichele

10:40 → 11:10 Coffe-Break

11:10 → 12:30 White dwarfs - Asteroseismology - Binaries: II Session - Chair: L. Girardi

11:10 Photometric Determination of Main-Sequence Binaries

The brightness and colour of a star are determined by factors such as mass, age and metallicity but can also be affected by the presence of an unresolved companion. Any discussion of stellar evolution on the H-R diagram must involve a consideration stellar multiplicity. For example, a young binary system at low metallicity may be bright enough such that it resembles an evolved single star at high metallicity. Using simulation-based inference, we show how observations of stars in multiple photometric bands can be used to constrain stellar properties such as mass, age, and metallicity, as well as identify the presence of an unresolved companion and infer its mass. We present preliminary results on a sample of Gaia sources and demonstrate how we can identify binaries based on their positions on the H-R diagram.

Speaker: A. Wallace

Wallace_Alexander.pdf

11:30 Hunting for massive degenerate binaries with a black hole using Gaia

Single-degenerate massive binaries containing a black hole (OB+BH) represent an important evolutionary phase on the pathway of becoming BH mergers. In the past two years, several OB+BHs were reported to exist on the basis of spectroscopic investigations. However, most reported OB+BH systems were later challenged by follow-up studies, demonstrating the extreme difficulty to identify BHs using spectroscopic data alone.
On June 13th, the full third Gaia data release (DR3) was publicly released, providing us with the first Gaia astrometric orbits of binary systems.

In preparation for DR3, we have developed a unique method that allows for the identification of OB+BH systems in the Gaia binary catalogue. Assuming a direct collapse and no kick upon BH formation, we estimated that 200 OB+BHs could be identified using Gaia. Moreover, we showed that different BH-formation scenarios could lead to distinct period and eccentricity distributions. However, so far, we retrieved no OB+BH binaries in DR3 from the astrometric solutions.

In my talk, I will describe our methodology of extracting OB+BH binaries using Gaia DR3 solutions. I will demonstrate why the highly conservative filtering imposed by the Gaia collaboration led to a null detection, and how this can be remedied in the future.

Speaker: S. Janssens

Janssens_Soetkin.pdf

11:50 Triage of Gaia astrometric binaries

In preparation for the release of the astrometric orbits of Gaia, Shahaf, Mazeh, Faigler, and Holl (2019) proposed a triage technique to identify hierarchical triples and astrometric binaries that have compact companions. The classification is done based on the astrometric semi-major axis, the parallax, and the primary mass, and relies upon the use of an appropriate mass-luminosity relation. Having the astrometric orbits of Gaia at hand, we analyzed a sample of binaries with main-sequence stars primaries less massive than ~3 Solar masses. We identified a large sample of hierarchical triples; hundreds of main-sequence stars with a white dwarf companion; and, dozens of systems with neutron star or black-hole candidates as their faint massive secondaries. We discuss the sensitivity of the method to the age and composition of the primary star and use the classification to discuss the emerging properties of their populations as a whole.

Speaker: S. Shahaf

Shahaf_Sahar.pdf

12:10 Gaia Spectroscopic Orbits Validation with external Radial Velocity Surveys

The recently published Gaia DR3 catalog of 181,327 spectroscopic binaries (SB) includes the Keplerian elements of each orbit, but not the measured radial velocities (RVs) and their epochs themselves. In this work, we used two external sources to validate the orbits - LAMOST DR6 and GALAH DR3 stars with measured RVs that have Gaia-SB orbits.
We compared the expected RVs, based on the Gaia orbits, with the LAMOST and GALAH measurements. Finding some orbits that are not consistent with these measurements, we constructed a function that estimates the probability of each of the Gaia orbits to be correct, using the Gaia period and robustness parameters. Choosing a working point that allows for an order of 20% contamination, we put up a 'clean' catalog consisting of almost 90K orbits, which does not include any short-period binaries with high eccentricity. The clean SB1 sample can be used for a thorough study of the statistical features of short-period binaries. As a first step, we point to two possible emerging features - a circularized main-sequence sub-sample, and a paucity of short-period low-mass primary binaries. One should find out whether these features are genuine, or might come from some observational biases.

Speaker: D. Bashi

12:30 → 14:30 Lunch-Breack

14:30 → 16:00 White dwarfs - Asteroseismology - Binaries: III Session - Chair: I. Negueruela

14:30 Asteroseismology and Gaia: pulsators on the main sequence and red-giant stars (Invited)

With the advent of high-precision photometry missions such as CoRoT, Kepler and TESS it has been possible to detect oscillations similar to those observed in the Sun in a huge number of G-K type stars, dwarfs and giant stars. The simple link between the global features of the their oscillation spectra ($\Delta \nu$ y $\nu_{\rm max}$) and stellar parameters (Mass and Radius) open the door to the “ensemble asteroseismology”, that is, the characterisation of multiple stellar populations without the need (or nearly so) for stellar models.
Asteroseismology appears hence as an independent method of estimating precise radii (or distances, included outside the solar neighbourhood ) and provides a unique set for calibration/ comparison to Gaia astrometry. In the opposite sense, the scaling relations between $\Delta \nu$ y $\nu_{\rm max}$ and the global properties of the stars needs for validation and calibration, and for this purpose Gaia is fundamental.
Here I will present how the combination of asteroseismology and astrometry contributes, first, to characterise the systematics affecting both, and second, to achieving an amazing sharpness in our vision of the Milky Way.

Speaker: Montalban

15:00 Milky Way helium enrichment constrained by red clump stars

The helium mass fraction, Y, is an important constraint in stellar models. For low mass stars, its value is usually estimated by assuming a linear helium-to-metal enrichment ratio, DY/DZ, and so obtaining Y from the measured metal mass fraction, Z. However, the behaviour of DY/DZ is uncertain, and varies significantly between methods presented in the literature.
We use the luminosity of red clump (low-mass, core helium-burning) stars as a proxy for Y, and so investigate the helium enrichment history. The approach combines asteroseismic results from Kepler with spectroscopy from APOGEE and astrometry from Gaia to allow red clump stars to be used in this way for the first time.

Speaker: E. Willett

Willett_Emma.pdf

15:20 Precise asteroseismic ages from pulsating pre-main-sequence stars

The ages of stars are notoriously difficult to determine, especially for young stars that are still shrouded in dust or surrounded by discs. Here, every Myr matters, as we try to probe the processes of planet formation and stellar composition build-up. We typically rely on ensemble ages determined for clusters or associations, but age gradients and age dispersion limit the accuracy of this method. I will discuss recent results from asteroseismology of pre-main-sequence delta Scuti pulsators, where age precisions of ~10% (~1 Myr) can be achieved. I will describe the evolution of pulsation frequencies in pre-main-sequence stars and how this allows masses and metallicities to be determined in a degeneracy-free way, permitting stellar associations to be dated with much better precision.

Speaker: S. Murphy

Murphy_Simon.pdf

15:40 Very young low mass stars in the Milky Way unveiled by DBSCAN and Gaia EDR3. Mapping the young clusters within 1.5 Kpc

With an unprecedented astrometric and photometric data precision, Gaia EDR3 gives us the opportunity to systematically and homogeneously detect and map the low mass populations of the star forming regions (SFRs)/very young clusters in the Milky Way in the optical bands.
We present a catalogue of the young stellar objects (YSOs) identified with Gaia EDR3 data in the solar neighbourhood (within about 1.5 kpc), and of the very young clusters to which they belong.
Our main goal is to study the properties of the very young clusters and put them in the context of the structure of the Milky way galaxy.
In this talk we will describe the application of a machine learning unsupervised clustering algorithm namely DBSCAN on a sample of data photometrically selected on the region where very young stars (<10 Myr) are expected to be found, with the aim to identify putative young stellar clusters based on proper motions and positions.In a subsequent step, a subsample of 51 clusters, selected among the 7323 found with DBSCAN, and whose properties are already well known, has been used as template data set, to identify very young clusters from the pattern of the observed color-absolute magnitude diagrams through a data mining procedure. We find more than 100K candidate YSOs around SFRs and stellar clusters younger than 10 Myr and within a distance of 1.5 Kpc.
In addition, about 50K low mass members of up to 100 Myr old stellar clusters located within about 500 pc were also found. These latter appear very diffuse on the sky and are mainly distributed around the regions of Sco-Cen, Vela OB2 and Orion. The selected YSOs are spatially correlated with
the well known SFRs. Most of them are associated with well concentrated regions or complex structures of the Galaxy. We find evidence of a structure traced by the massive SFRs, as, for example, Orion, Sco-Cen and Vela OB2, located within 600-700\,pc and belonging to a very complex three-dimensional structure inclined with respect to the Galactic Plane.
The farthermost clusters seem to follow a more regular pattern along the Galactic Plane.

Speaker: L. Prisinzano

prisinzano_loredana.pdf

16:00 → 16:30 Coffe-Break

16:30 → 17:00 White dwarfs - Asteroseismology - Binaries: IV Session - Chair: P. Marigo

16:30 Testing models of ultimate stages of stellar evolution with asteroseismology of evolved compact pulsators: achievements and prospects in the Gaia era (Invited)

Evolved compact pulsators found primarily amongst the white dwarf and hot subdwarf populations provide important seismic windows over the late stages of stellar evolution of low-to-intermediate mass stars, past the red-giant branch. These windows are particularly welcomed as uncertainties in modeling the core helium-burning phase and beyond are still prominent and pile-up, impacting strongly the inner structure of the final products (the white dwarfs). In this review,
I briefly recall the status of asteroseismology of evolved compact stars from the observational point of view (using in particular space-based observatories, such as Kepler, TESS, and the contribution of GAIA to this respect). Then I focus on recent attempts to exploit the seismic information contained in pulsating hot B subdwarf (sdB) stars (core helium-burning objects populating the Extreme Horizontal Branch) and pulsating white dwarfs to provide insight on their internal structure, and confront seismic measurements with predictions from stellar evolution models. In this quest, GAIA also has an important role to play.

Speaker: S. Charpinet

17:00 → 18:30 Poster Session: - Chair: P. Marigo

17:00 Refined Ephemeris for Four Hot Jupiters using Ground-Based and TESS Observations

Speaker: R. Foroughi

17:05 3D Time-dependent convection model for asteroseismology

Speaker: S. Lizin

17:10 The evolution of the Galactic discs revealed by the Gaia-APOGEE-Kepler giant stars

Speaker: N. Lagarde

17:15 3D static models of close binaries in hydrostatic equilibrium with MoBiDICT

Speaker: L. Fellay

17:20 Spectroscopic VUES and photometric TESS survey of single and binary variable stars

Speaker: R. Urbonaviciute

17:25 Spectroscopic analysis of A- and F-type stars observed by Kepler

Speaker: J. Krüger

17:30 H-R diagrams of 1,656 CWNU new star clusters

Speaker: Z. He

17:35 The electron scattering on H2+and HD+ molecular cations: Dissociative recombination and ro-vibrational transitions. Application in astrophysics (Pitch Talk)

Speaker: N. Pop

17:40 VO tools and services for Gaia and the stellar evolution. (Pitch Talk)

Speaker: E. Solano

17:45 The upper HR diagram of young clusters is dominated by binary interaction (Pitch Talk)

Speaker: I. Negueruela

17:50 Star Formation in Serpens (Pitch Talk)

Speaker: P. Hasan

17:55 Detection of double-lined spectroscopic binaries in LAMOST-MRS using vsini variation (Pitch Talk)

Speaker: M. Kovalev

Friday, 23 September

09:00 → 10:20 Synergies: I Session - Chair: A. Recio-Blanco

09:00 The impact of the Gaia-ESO Survey on Stellar Physics and Evolution (Invited)

The Gaia-ESO Survey (GES) is a Large Public Spectroscopic Survey carried out with FLAMES on the ESO/VLT and whose final catalogue has been released to the community through the ESO Archive last Spring. GES has delivered precise radial velocities, stellar parameters, and abundances for more than 100,000 stars in the Milky Way, including members of more than 60 open star clusters. I will briefly summarise the main characteristics of GES, its target sample and advanced products; I will then discuss the impact and legacy of GES for stellar physics and evolution.

Speaker: S. Randich

09:30 Coupling WEAVE observations with Gaia (Invited)

With its 2 degrees field-of-view and its nearly 1000 fibers feeding a dual-beam spectrograph that covers the wavelength range 366-959nm at R~5000 or two shorter ranges at R~20 000, WEAVE, installed at the WHT in La Palma, will be the first large galactic survey with a target selection from Gaia DR3. It will complement Gaia with accurate radial velocities and metallicities for faint stars (G>15) and enrich the Gaia catalogue with precise abundances coming from different nucleosynthetic families for stars for which Gaia RVS has obtained only moderate resolution spectra. Simultaneously, it will enlarge the volume in which Gaia's transverse motions are useful and also allow to get well constrained, spectroscopically derived, ages for a significant fraction of the surveyed stars.
In this talk I will present an overview of the WEAVE Galactic archeology surveys and the way they will help improving our understanding of Milky Way formation.

Speaker: G. Kordopatis

10:00 X-Shooter characterization of YSOs selected with Gaia DR2

I will speak about the full characterization of the young stellar objects (YSOs) with VLT/X-Shooter that were originally selected based on their consistent kinematic properties with either a stellar system or a stellar association. I will discuss the essential role that Gaia DR2 played in selecting our candidates and how the catalog further contributed to our final analysis (with flags such as RUWE for hints on binarity or passing maximum velocity difference tests indicated in Majidi et al. 2020 & 2022). Interestingly, we found both cases where the consistent kinematic properties hinted at finding new members of a stellar association or wide companion candidates of a stellar system and cases that failed to do so. For determining the genuine members of spatially overlapped stellar associations at young ages, the criterion of consistent kinematic properties is essential but the follow-up spectroscopy is indispensable for obtaining the stellar properties of the candidate members and approving their membership. I will thus focus on what we can learn from selecting candidates resolved by Gaia, and how combined with other powerful facilities such as OmegaCAM, identifying YSOs can be substantially facilitated.

Speaker: F. Majidi

Majidi_Fatemehzahra.pdf

10:20 → 10:50 Coffe-Break

10:50 → 12:10 Synergies: II Session - Chair: G. Meynet

10:50 4MOST revolution and the synergy with Gaia (Invited)

I will review some of planned science cases relevant to studies of stellar structure and evolution with 4MOST. In particular, I will focus on the questions that highlight the spectroscopic capabilities of the 4MOST high-resolution spectrograph and capitalise on synergies with Gaia and time-domain photometry missions. The topics that I will address include fundamental stellar parameters, chemical abundance trends in stellar populations, and synergies with asteroseismology, studies of stellar activity, and multiplicity.

Speaker: M. Bergemann

11:20 VLT-MOONS: near-IR multi-object spectroscopy with the VLT and synergies with Gaia (Invited)

The Multi Object Optical and Near-infrared Spectrograph (MOONS) instrument is the next generation multi-object spectrograph for the VLT. This powerful instrument will combine for the first time the large collecting power of the VLT with a high multiplexing capability offered by 1000 optical fibres moved with individual robotic positioners and a novel, very fast spectrograph able to provide both low- and high-resolution spectroscopy simultaneously across the wavelength range 0.64μm - 1.8μm. In particular, the high-resolution modes of MOONS are specifically tailored for a variety of key Galactic science cases. In this talk I will give an overview of the instrument, GTO surveys plans, and capabilities offered to the community with an emphasis in the great complementarity between MOONS and Gaia.

Speaker: O. Gonzalez

11:50 Gaia and the upcoming WEAVE Cygnus-X Survey: disentangling the evolutionary status of one of the most massive star-forming regions of the Galaxy

In this contribution I introduce current work and future perspectives for the upcoming WEAVE high-resolution survey in the Cygnus-X complex. WEAVE, the next multi-object spectrograph at the 4.2m William Herschel Telescope, will provide high-quality spectra over the coming years for thousands of massive stars in the northern Galactic plane and, specifically, in several rich Cygnus OB associations. Using previous spectroscopic studies focused on Cygnus OB2 as a template, and combining WEAVE data and the expected accuracy that Gaia will reach in Cygnus-X (DR3 and forthcoming releases) we will be able to disentangle the global evolutionary status of the region and inspect the position of their most massive members in the Hertzsprung-Russell Diagram, considering the possibility that some of them were born with a different initial rotational velocity than the rest or have followed peculiar (e.g., not single) evolutionary paths.

Speaker: S. R. Berlanas

12:10 → 12:50 Final Remarks (L. Eyer)

12:50 → 15:00 Lunch-Break

15:00 → 20:00 Guided Tour