Showing 1–50 of 357 results for author: Cassisi, S

A critical analysis of main-sequence fitting in open clusters to derive the helium-to-metal enrichment ratio $ΔY/ΔZ$

Authors: G. Valle, N. Ricci, M. Dell'Omodarme, P. G. Prada Moroni, S. Degl'Innocenti, S. Cassisi

Abstract: We aim to investigate the feasibility of accurately determining the helium-to-metal enrichment ratio $ΔY/ΔZ$ for open clusters using Gaia DR3 photometry. To test the reliability of this calibration, we performed a theoretical investigation using mock open clusters. We generated synthetic photometric data from isochrones calculated by five different stellar evolution codes (FRANEC, PARSEC 1.2s, PAR… ▽ More We aim to investigate the feasibility of accurately determining the helium-to-metal enrichment ratio $ΔY/ΔZ$ for open clusters using Gaia DR3 photometry. To test the reliability of this calibration, we performed a theoretical investigation using mock open clusters. We generated synthetic photometric data from isochrones calculated by five different stellar evolution codes (FRANEC, PARSEC 1.2s, PARSEC 2.0, BASTI, and MIST), for which the true $ΔY/ΔZ$ is known. We then fitted these mock clusters with two sets of isochrones calculated with the FRANEC code, differing only in the implementation of bolometric corrections (BCs). The analysis focused on the G-band absolute magnitude range (4.3 to 6.5 mag) to minimise the impact of poorly constrained physics. Synthetic clusters were generated at [Fe/H] values from 0.0 to 0.15 dex, for different numbers of populating stars and different levels of photometric uncertainties. The Monte Carlo experiments revealed significant and code-dependent biases. Unbiased results were achieved only when the stellar models used for synthetic-cluster generation and fitting were identical. Using identical FRANEC stellar models but different BCs introduced a significant bias of up to 0.6. Furthermore, using different stellar models for synthetic cluster generations resulted in even larger biases: $ΔY/ΔZ$ was underestimated by up to 0.8 for PARSEC target isochrones, while it was overestimated for BASTI and MIST isochrones by up to 0.6 and 1.5, respectively. The magnitude and the inconsistency of these biases strongly suggest that the photometric calibration of $ΔY/ΔZ$ using open clusters is not reliably robust. △ Less

Submitted 6 April, 2026; originally announced April 2026.

Comments: Accepted for publication in A&A

The Hubble Missing Globular Cluster Survey. III. Astro-photometric catalogs, artificial-star tests, and improved absolute proper motions

Authors: M. Libralato, A. Bellini, D. Massari, M. Bellazzini, F. Aguado-Agelet, S. Cassisi, E. Ceccarelli, E. Dalessandro, E. Dodd, F. R. Ferraro, C. Gallart, B. Lanzoni, M. Monelli, A. Mucciarelli, E. Pancino, R. Pascale, L. Rosignoli, M. Salaris, S. Saracino, C. Zerbinati

Abstract: The Hubble Missing Globular Cluster Survey (MGCS) has taken one of the last opportunities to complete the census of Galactic globular clusters (GCs) started by past Hubble Space Telescope (HST) programs, securing high-resolution data for 34 GCs never observed before by HST. The previous papers of the series have highlighted the astrometric and photometric potential of the project by analyzing a su… ▽ More The Hubble Missing Globular Cluster Survey (MGCS) has taken one of the last opportunities to complete the census of Galactic globular clusters (GCs) started by past Hubble Space Telescope (HST) programs, securing high-resolution data for 34 GCs never observed before by HST. The previous papers of the series have highlighted the astrometric and photometric potential of the project by analyzing a subsample of targets. We present, and release to the community, the official astro-photometric catalogs of the MGCS for all GCs imaged by this project. We describe the data reduction using state-of-the-art techniques designed for HST. We discuss the photometric calibration and show, for the first time, the synergy with the Gaia catalog to ensure homogeneous photometry across our data set. We compute artificial-star tests that can be used to assess systematics and the completeness level of our data. We combined HST and Gaia data to refine the absolute PMs of our GCs, reaching a precision $\sim$3 times better than that of Gaia alone. We used these new PMs to update (and to determine for the first time for six systems) the associations between GCs and their putative galaxy progenitors. This work continues decades-long efforts of large Treasury programs in sharing precise and accurate atlases to the community for studying GCs across a wide range of scientific endeavors. △ Less

Submitted 26 March, 2026; originally announced March 2026.

Comments: 12 pages, 9 figures, 6 tables. Accepted for publication in A&A. Catalogs available upon publication

Proof that the Milky Way experienced a significant merger only 1.5 billion years after the Big Bang

Authors: Davide Massari, Chiara Zerbinati, Cristiano Fanelli, Amina Helmi, Edoardo Ceccarelli, Fernando Aguado-Agelet, Santi Cassisi, Ewoud Wempe, Matteo Monelli, Andrea Bellini, Thomas Callingham, Hanneke C. Woudenberg, Roger Cohen, Carme Gallart, Elena Pancino, Sara Saracino, Maurizio Salaris, Alessio Mucciarelli

Abstract: The merger history of the Galaxy has been traced back firmly to redshift 2 (10 Billion years ago). While there have been claims of the existence of at least one more significant merger before this time, supporting evidence has been indirect and contentious. Here we show that the population of globular clusters around the Galaxy depicts three distinct age-metallicity sequences, one associated with… ▽ More The merger history of the Galaxy has been traced back firmly to redshift 2 (10 Billion years ago). While there have been claims of the existence of at least one more significant merger before this time, supporting evidence has been indirect and contentious. Here we show that the population of globular clusters around the Galaxy depicts three distinct age-metallicity sequences, one associated with the merger with Gaia-Enceladus 10 billion years ago, one to the progenitor of the Milky Way and a third intermediate sequence associated to at least one merger which we estimate took place merely 1.5 billion years after the Big Bang. This discovery has been possible thanks to exquisite Hubble Space Telescope data and sophisticated analysis that enables very precise relative age determination of globular clusters. The newly identified sequence reveals that this merger took place with an object of stellar mass similar to that of Gaia-Enceladus (~5x10$^8$ M$_{\odot}$), and which deposited most of its mass in the inner 6 kpc of the Milky Way. The unambiguous identification of a third merger event in the inner Galaxy puts to rest earlier debates, and honoring previous work we name the progenitor system Low-energy-Kraken-Heracles, or LKH for short. △ Less

Submitted 26 January, 2026; originally announced January 2026.

Comments: Revised version of a paper under review, 26 pages, 8 figures, 2 tables

Why the Northern Hemisphere Needs a 30-40 m Telescope and the Science at Stake: Resolved Stellar Populations Studies in M31 and its Satellites

Authors: C. Gallart, E. Fernández-Alvar, A. B. A. Queiroz, A. Aparicio, B. Anguiano, G. Battaglia, M. Beasley, T. Bensby, G. Bono, V. Braga, L. Carigi, L. Casamiquela, S. Cassisi, C. Chiappini, V. P. Debattista, A. del Pino, I. Escala, A. M. N. Ferguson, G. Fiorentino, K. M. Gilbert, P. Guhathakurta, R. Ibata, E. N. Kirby, K. Kuijken, S. Larsen , et al. (26 additional authors not shown)

Abstract: A 30 m class optical/near-IR telescope in the Northern Hemisphere, equipped for diffraction-limited imaging and high-resolution, multi-object spectroscopy of faint stars, would enable a transformational investigation of the formation and evolution of M31 and its satellite system - on par with what Gaia, the HST, and other major photometric and spectroscopic facilities have achieved for the Milky W… ▽ More A 30 m class optical/near-IR telescope in the Northern Hemisphere, equipped for diffraction-limited imaging and high-resolution, multi-object spectroscopy of faint stars, would enable a transformational investigation of the formation and evolution of M31 and its satellite system - on par with what Gaia, the HST, and other major photometric and spectroscopic facilities have achieved for the Milky Way (MW) and its satellites. The unprecedented detail obtained for our home system has reshaped our understanding of the assembly of the MW disk, halo, and bulge, and that of its satellites, which now serve as a benchmark for galaxy formation and evolution models. Extending this level of insight to the M31 system - that of the nearest massive spiral and the only one for which such a comprehensive, resolved stellar population study is feasible - will allow us to address a fundamental question: how representative is the MW and its satellite system within the broader context of galaxy evolution? △ Less

Submitted 16 December, 2025; originally announced December 2025.

Comments: White Paper submitted to "ESO Expanding Horizons: Transforming Astronomy in the 2040s"

Selection and characterisation of the M-dwarf targets in the PLATO Input Catalogue

Authors: L. Prisinzano, M. Montalto, G. Piotto, P. M. Marrese, S. Marinoni, V. Nascimbeni, V. Granata, J. Cabrera, K. Belkacem, M. Deleuil, L. Gizon, M. J. Goupil, I. Pagano, D. Pollacco, R. Ragazzoni, H. Rauer, S. Udry, J. Maldonado, G. Micela, F. Damiani, L. Affer, G. Altavilla, C. Argiroffi, S. Benatti, S. Cassisi , et al. (11 additional authors not shown)

Abstract: The ESA's PLAnetary Transits and Oscillations of Stars (PLATO) mission aims to detect planets orbiting around dwarfs and subgiant stars with spectral type F5 or later, including M-dwarfs. The PLATO Input Catalogue (PIC) contains all targets available for observation by the nominal science. The latest version, PIC2.1.0.1, focuses on the Southern PLATO field, named LOPS2, selected as the first long… ▽ More The ESA's PLAnetary Transits and Oscillations of Stars (PLATO) mission aims to detect planets orbiting around dwarfs and subgiant stars with spectral type F5 or later, including M-dwarfs. The PLATO Input Catalogue (PIC) contains all targets available for observation by the nominal science. The latest version, PIC2.1.0.1, focuses on the Southern PLATO field, named LOPS2, selected as the first long observation field, and includes the P4 sample, one of the four target samples outlined in the Science Requirement Document. P4 includes the M-dwarfs with magnitudes V < 16 located within LOPS2. A characterisation of the M-dwarfs in the PIC is essential for assessing their potentiality to host exoplanets, and eventually estimate the hosted planet(s) properties. The purpose of this paper is to describe how we selected the P4 M-dwarf targets, and obtained their fundamental parameters and properties. In this work, we introduce the P4 sample and detail the methodologies adopted for the measurement of their stellar parameters. Based on a statistical analysis of the P4 sample, we assess both the photometric and volume completeness, and classify the stellar populations according to their Galactic spatial-velocity components. The adopted stellar parameters are validated by comparison with independent methods from the literature used to estimate stellar radii. The P4 sample is compliant with the PLATO science requirements. Being magnitude limited, its volume completeness decreases going towards distances larger than 30 pc, where late-type targets are progressively less covered. The observed large spread in the colour-magnitude diagram is likely due to the combination of several effects such as metallicity, age, binarity and activity. The strategy we adopted for deriving stellar parameters provides results consistent with those obtained in the literature with different and independent methods. △ Less

Submitted 16 December, 2025; originally announced December 2025.

Comments: 15 pages,, 15 figures

The Hubble Missing Globular Cluster Survey. II. Survey membership tools and kinematic analysis of NGC 6749

Authors: L. Rosignoli, M. Libralato, R. Pascale, D. Massari, E. Dalessandro, E. Ceccarelli, H. Baumgardt, M. Bellazzini, A. Bellini, F. Aguado-Agelet, S. Cassisi, M. Monelli, A. Mucciarelli, E. Pancino, M. Salaris, E. Dodd, F. R. Ferraro, B. Lanzoni

Abstract: The Hubble Missing Globular Cluster Survey has secured high quality astro photometric data in two bands for 34 clusters never observed with HST. When combined with Gaia positional measurements, this data set enables the investigation of the bulk motion and the internal kinematics of these poorly studied clusters to an unprecedented level of detail. Focusing on the case of NGC 6749, we here showcas… ▽ More The Hubble Missing Globular Cluster Survey has secured high quality astro photometric data in two bands for 34 clusters never observed with HST. When combined with Gaia positional measurements, this data set enables the investigation of the bulk motion and the internal kinematics of these poorly studied clusters to an unprecedented level of detail. Focusing on the case of NGC 6749, we here showcase how the combined Gaia HST proper motions have a quality sufficient to accurately assess the cluster stellar membership, determine its absolute proper motion with a precision superior to Gaia, and to investigate its kinematic profile for the first time. Proper motions are determined using the public code GAIAHUB, which for NGC 6749 combines data sets separated in time by 8 years. The resulting measurements improve the precision of Gaia proper motions by a factor of 10 at the faint end, and enable recovering the proper motion for 662 stars for which Gaia could only measure the positions. These proper motions are efficient in decontaminating the colour magnitude diagram of NGC 6749, and make it possible to compare the efficacy of a method of statistical decontamination that relies only on the photometric information extracted from the HST parallel fields. Finally, using the sample of best measured proper motions we determine the velocity dispersion and anisotropy profiles of NGC 6749, that reveal an isotropic behaviour in the cluster inner regions and a slight radial anisotropy outside 1.5 half light radii. The proper motions and the code to statistically decontaminate the clusters color magnitude diagram are made available as public products of the survey. △ Less

Submitted 1 December, 2025; originally announced December 2025.

Journal ref: A&A 707, A258 (2026)

Hubble Space Telescope proper motions of Large Magellanic Cloud star clusters -- II. Kinematic structure of young and intermediate-age clusters

Authors: F. Niederhofer, L. Cullinane, D. Massari, N. Bastian, A. Bellini, F. Aguado-Agelet, S. Cassisi, D. Erkal, M. Libralato, N. Kacharov, I. Cabrera-Ziri, E. Ceccarelli, M. -R. L. Cioni, F. Dresbach, M. Häberle, S. Martocchia, S. Saracino

Abstract: In this paper, we explore the kinematic properties of a sample of 19 young (<1 Gyr) and intermediate-age (1-2.5 Gyr) massive star clusters within the Large Magellanic Cloud (LMC). We analyse the proper motions of the clusters, which have been measured based on multi-epoch Hubble Space Telescope (HST) observations. Additionally, we infer from the HST data homogeneous and robust estimates for the di… ▽ More In this paper, we explore the kinematic properties of a sample of 19 young (<1 Gyr) and intermediate-age (1-2.5 Gyr) massive star clusters within the Large Magellanic Cloud (LMC). We analyse the proper motions of the clusters, which have been measured based on multi-epoch Hubble Space Telescope (HST) observations. Additionally, we infer from the HST data homogeneous and robust estimates for the distances, ages and metallicities of the clusters. This collection of information, in combination with literature line-of-sight velocities, allows us to investigate the full 3D dynamics of our sample of clusters within the frame of the LMC in a self-consistent way. While most young clusters orbit the LMC close to the stellar disc plane, NGC 1850 (~100 Myr old) depicts a peculiar case. Depending on the exact distance from the disc, it follows either a highly inclined, retrograde orbit or an eccentric orbit along the bar structure. The orbits of young clusters that formed North of the LMC centre show signs that might be connected to the resettling motion of the LMC bar structure. Based on the dynamic properties in combination with the positions of the clusters in the age-metallicity space, we find no clear-cut evidence for clusters in our sample that could have been stripped from the Small Magellanic Cloud (SMC) onto the LMC. We finally compare the kinematics of the intermediate-age clusters with a suite of simple numerical simulations of the Magellanic system to interpret the cluster motions. A possible interaction history of the LMC with the SMC, where the SMC had two past crossings of the LMC disc plane (about 300 and 900 Myr ago), in combination with the recent SMC pericentre passage, can qualitatively explain the observed kinematic structure of the clusters analysed in this work. △ Less

Submitted 18 November, 2025; originally announced November 2025.

Comments: Accepted for publication in A&A, 21 pages, 9 figures, 7 tables

Journal ref: A&A 705, A94 (2026)

Chronology of our Galaxy from Gaia colour-magnitude diagram fitting (ChronoGal): IV. On the inner Milky Way stellar age distribution

Authors: Tomás Ruiz-Lara, David Mirabal, Carme Gallart, Robert Grand, Francesca Fragkoudi, Isabel Pérez, Santi Cassisi, Emma Fernández-Alvar, Anna B. Queiroz, Guillem Aznar-Menargues, Yllari K. González-Koda, Alicia Rivero, Francisco Surot, Guillaume F. Thomas, Rebekka Bieri, Facundo A. Gomez, Rüdiger Pakmor, Freeke van de Voort

Abstract: The Milky Way's inner region is dominated by a stellar bar and a boxy-peanut shaped bulge. However, which stellar populations inhabit the inner Galaxy or how star formation proceeded there is still unknown. The difficulty in studying these stars stems from their location in dense regions that are strongly impacted by extinction and crowding effects. In this work, we use star formation histories co… ▽ More The Milky Way's inner region is dominated by a stellar bar and a boxy-peanut shaped bulge. However, which stellar populations inhabit the inner Galaxy or how star formation proceeded there is still unknown. The difficulty in studying these stars stems from their location in dense regions that are strongly impacted by extinction and crowding effects. In this work, we use star formation histories computed in the solar neighbourhood using Gaia Colour-Magnitude Diagram fitting to shed light onto the evolution of the central regions of our Galaxy. For that, we have obtained precise age distributions for the non-negligible amount of super metal-rich stars ([M/H] $\sim$ 0.5) in the solar neighbourhood (more than 5$\%$ of the total stars within 400 pc of the plane). Assuming that these stars were born in the inner Galaxy and migrated outwards, those distributions should be indicative of the true stellar age distribution in the inner Galaxy. Surprisingly, we find that these age distributions are not continuous but show clear signs of episodic star formation ($\sim$~13.5, 10.0, 7.0, 4.0, 2.0 and less than 1~Gyr ago). Interestingly, with the exception of the 4~Gyr event, the timings of the detected events coincide with the formation of the primitive Milky Way and with known merging events or satellite encounters (Gaia-Enceladus-Sausage, Sagittarius dwarf galaxy, and the Magellanic Clouds), suggesting that these could have induced enhanced and global star-forming episodes. These results are compatible with a scenario in which Gaia-Enceladus-Sausage is responsible for the formation of the bar 10 Gyr ago. However, we cannot associate any accretion counterpart with the 4-Gyr-ago event, leaving room for a late formation of the bar, as previously proposed. A qualitative comparison with the Auriga Superstars simulations suggesting a possible link to bar dynamics and satellite accretion. [Abridged] △ Less

Submitted 2 October, 2025; originally announced October 2025.

Comments: 10 pages, 6 figures, accepted for publication in A&A

Cluster Ages to Reconstruct the Milky Way Assembly (CARMA) IV. Chrono-dynamics of seven old star clusters in the Large Magellanic Cloud and the peculiar origin of NGC 1841

Authors: F. Niederhofer, D. Massari, F. Aguado-Agelet, S. Cassisi, A. Bellini, V. Kozhurina-Platais, M. Libralato, N. Kacharov, A. Mucciarelli, M. Monelli, N. Bastian, I. Cabrera-Ziri, E. Ceccarelli, M. -R. L. Cioni, F. Dresbach, M. Häberle, S. Martocchia, S. Saracino

Abstract: In this study, we report conclusive evidence for an ancient star cluster that has been accreted by the Large Magellanic Cloud (LMC). By leveraging observations from the Hubble Space Telescope (HST), we investigate the chrono-dynamical structure of a sample of seven old star clusters within the LMC in a self-consistent way. The multi-epoch nature of the dataset allowed the determination of high-pre… ▽ More In this study, we report conclusive evidence for an ancient star cluster that has been accreted by the Large Magellanic Cloud (LMC). By leveraging observations from the Hubble Space Telescope (HST), we investigate the chrono-dynamical structure of a sample of seven old star clusters within the LMC in a self-consistent way. The multi-epoch nature of the dataset allowed the determination of high-precision proper motions for the clusters. Employing an isochrone-fitting methodology, we additionally infer from the deep high-resolution HST data homogeneous and robust estimates for their distances, ages and metallicities. Supplementing these data with literature line-of-sight velocities, we investigate the full 3-dimensional dynamics of the clusters within the frame of the LMC. With respect to the other clusters in our sample, NGC 1841 depicts a peculiar case. Its position in the age-metallicity plane, that makes it about 1 Gyr younger than the other metal-poor LMC clusters, but also its dynamical properties with a radial orbit almost perpendicular to the LMC disc plane, clearly advocates for a different origin. We thus conclude that NGC 1841 has likely been accreted by the LMC from a smaller galaxy. The other clusters in our sample show disc-like kinematics, with the case of NGC 2210 being peculiar, based on its inclined orbit. Their coherent age-metallicity relation closely resembles that of Gaia-Sausage-Enceladus globular clusters, thus suggesting a similar early evolution for the two dwarf galaxies. We do not find clear-cut chrono-kinematic evidence that NGC 2005 has been accreted by the LMC as suggested by a previous study based on its chemical abundance pattern. Regardless of its nature, its very old age illustrates that peculiar chemical evolutions already emerge at very early times. △ Less

Submitted 12 September, 2025; originally announced September 2025.

Comments: Accepted for publication in A&A, 22 pages, 13 figures, 4 tables

Wide binaries in an ultra-faint dwarf galaxy: discovery, population modeling, and a nail in the coffin of primordial black hole dark matter

Authors: Cheyanne Shariat, Kareem El-Badry, Mario Gennaro, Keyi Ding, Joshua D. Simon, Roberto J. Avila, Annalisa Calamida, Santi Cassisi, Matteo Correnti, Daniel R. Weisz, Marla Geha, Evan N. Kirby, Thomas M. Brown, Massimo Ricotti, Kristen B. W. McQuinn, Nitya Kallivayalil, Karoline Gilbert, Camilla Pacifici, Puragra Guhathakurta, Denija Crnojević, Martha L. Boyer, Rachael L. Beaton, Vedant Chandra, Roger E. Cohen, Alvio Renzini , et al. (2 additional authors not shown)

Abstract: We report the discovery and characterization of a wide binary population in the ultrafaint dwarf galaxy Boötes I using deep JWST/NIRCam imaging. Our sample consists of 52 candidate binaries with projected separations of 7,000 - 16,000 au and stellar masses from near the hydrogen-burning limit to the main-sequence turnoff ($\sim0.1$ - $0.8~{\rm M_\odot}$). By forward-modeling selection biases and c… ▽ More We report the discovery and characterization of a wide binary population in the ultrafaint dwarf galaxy Boötes I using deep JWST/NIRCam imaging. Our sample consists of 52 candidate binaries with projected separations of 7,000 - 16,000 au and stellar masses from near the hydrogen-burning limit to the main-sequence turnoff ($\sim0.1$ - $0.8~{\rm M_\odot}$). By forward-modeling selection biases and chance alignments, we find that $1.25\pm0.25\%$ of Boötes I stars are members of wide binaries with separations beyond 5,000 au. This fraction, along with the distributions of separations and mass ratios, matches that in the Solar neighborhood, suggesting that wide binary formation is largely insensitive to metallicity, even down to [Fe/H] $\approx -2.5$. The observed truncation in the separation distribution near 16,000 au is well explained by stellar flyby disruptions. We also discuss how the binaries can be used to constrain the galaxy's dark matter properties. We show that our detection places new limits on primordial black hole dark matter, finding that compact objects with $M \gtrsim 5~{\rm M_\odot}$ cannot constitute more than $\sim1\%$ of the dark matter content. In contrast to previous work, we find that wide binaries are unlikely to provide robust constraints on the dark matter profile of ultrafaint galaxies given the uncertainties in the initial binary population, flyby disruptions, and contamination from chance alignments. These findings represent the most robust detection of wide binaries in an external galaxy to date, opening a new avenue for studying binary star formation and survival in extreme environments. △ Less

Submitted 1 October, 2025; v1 submitted 4 September, 2025; originally announced September 2025.

Comments: re-submitted to PASP after minor changes

James Webb Space Telescope observations of the white dwarf cooling sequence of 47 Tucanae

Authors: M. Salaris, M. Scalco, L. R. Bedin, S. Cassisi

Abstract: We present a study of the white dwarf (WD) cooling sequence of the globular cluster 47 Tucanae (47 Tuc or NGC 104) using deep infrared observations with the James Webb Space Telescope (JWST). By combining these data with ultra-deep optical imaging from the Hubble Space Telescope (HST) taken ~12 years earlier, we derived precise proper motions (PMs) and isolated a clean sample of WD cluster members… ▽ More We present a study of the white dwarf (WD) cooling sequence of the globular cluster 47 Tucanae (47 Tuc or NGC 104) using deep infrared observations with the James Webb Space Telescope (JWST). By combining these data with ultra-deep optical imaging from the Hubble Space Telescope (HST) taken ~12 years earlier, we derived precise proper motions (PMs) and isolated a clean sample of WD cluster members. We estimated the cluster's age by comparing the observed WD cooling sequence luminosity function (LF), derived from JWST photometry, with theoretical models, obtaining a value of 11.8 +/- 0.5 Gyr, in agreement with main sequence turn-off ages, and ages determined from the masses and radii of two eclipsing binaries in the cluster. The age determined from the infrared LF is consistent with the optical LF based on the HST photometry. However, small discrepancies exist between the shape of the observed and theoretical LFs. To investigate these differences, we tested the cooling times of WD models populating the bright part of the observed cooling sequence against a semi-empirical calibration from the literature, based on bright WDs in 47 Tuc, finding agreement within less than 2 sigma. A more detailed analysis of dynamical effects and the impact of multiple stellar populations on the WD mass distribution in the observed field will be essential for addressing this discrepancy in future studies. △ Less

Submitted 25 June, 2025; originally announced June 2025.

Comments: 13 pages, 14 figures, 2 tables (3 figures and 2 tables in Appendices A-C). Accepted for publication in MNRAS on 24 June 2025. Manuscript ID: MN-25-0662-MJ

Spatial Age Distribution of Classical Cepheids in Spiral Galaxies: The Cases of M31 and M33

Authors: Giulia De Somma, Marcella Marconi, Vincenzo Ripepi, Santi Cassisi, Roberto Molinaro, Ilaria Musella, Teresa Sicignano, Erasmo Trentin

Abstract: Classical Cepheids can be used as age indicators due to well-established period-age and period-age-color relations. \citet{Desomma2021} refined these relations by including a metallicity term and different Mass-Luminosity assumptions. In this study, we apply the period-age-metallicity relation for the first time to samples of Classical Cepheids in M31 and M33. For both galaxies, we consider Ceph… ▽ More Classical Cepheids can be used as age indicators due to well-established period-age and period-age-color relations. \citet{Desomma2021} refined these relations by including a metallicity term and different Mass-Luminosity assumptions. In this study, we apply the period-age-metallicity relation for the first time to samples of Classical Cepheids in M31 and M33. For both galaxies, we consider Cepheid coordinates and spatial distributions, along with the metallicity gradients by \citet{Zaritsky1994} and \citet{Magrini2007}, to provide a metallicity estimate for each pulsator. By applying the period-age-metallicity relation, we derive individual ages for each Cepheid. Combining these ages and spatial distributions, we construct detailed age maps for both galaxies. Our analysis confirms a radial age gradient, with younger Cepheids preferentially found toward the galactic centers. In M31, we confirm an outer ring at $\sim 11$ kpc, consistent with previous studies, and identify for the first time an inner ring at $\sim 7$ kpc, possibly associated with star formation episodes. Comparing age gradients at different angles, we find a consistent general trend of ages increasing monotonically with radius. At the same time, we observe smaller-scale differences, particularly in the $90^\circ$-$180^\circ$ quadrant, suggesting asymmetric star formation and possible dynamical influences. In contrast, M33 displays a steeper global age gradient, indicating a higher concentration of young stars toward its center. This study highlights the utility of Cepheids as stellar population tracers, providing insights into the star formation and dynamical evolution of spiral galaxies. Future works will extend this methodology to additional galaxies. △ Less

Submitted 17 April, 2025; originally announced April 2025.

Comments: 11 pages, 6 figures, 2 tables. Accepted for publication in the Astrophysical Journal Letters

Chronology of our Galaxy from Gaia colour-magnitude diagram fitting (ChronoGal) II. Unveiling the formation and evolution of the kinematically selected Thick and Thin Discs

Authors: Emma Fernández-Alvar, Tomás Ruiz-Lara, Carme Gallart, Santi Cassisi, Francisco Surot, Yllari K. González-Koda, Thomas M. Callingham, Anna B. Queiroz, Giuseppina Battaglia, Guillaume Thomas, Cristina Chiappini, Vanessa Hill, Emma Dodd, Amina Helmi, Guillem Aznar-Menargues, Alejandro de la Cueva, David Mirabla, Mónica Quintana-Ansaldo, Alicia Rivero

Abstract: Understanding the formation and evolution of the Milky Way's thin and thick discs is crucial to galaxy formation studies. We derive age and metallicity distributions of the kinematic thick and thin discs using the CMDft.Gaia pipeline and Gaia DR3 data within 250 pc of the Sun, covering 1 kpc in height. Our results show that the kinematic thick disc is mostly older than 10 Gyr, undergoing three mai… ▽ More Understanding the formation and evolution of the Milky Way's thin and thick discs is crucial to galaxy formation studies. We derive age and metallicity distributions of the kinematic thick and thin discs using the CMDft.Gaia pipeline and Gaia DR3 data within 250 pc of the Sun, covering 1 kpc in height. Our results show that the kinematic thick disc is mostly older than 10 Gyr, undergoing three main metallicity enrichment episodes: (1) over 12 Gyr ago, peaking at [M/H] $\sim$ -0.5 dex, (2) $\sim$11 Gyr ago, rapidly increasing to solar [M/H] and spanning [$α$/Fe] from 0.3 to solar, and (3) just over 10 Gyr ago, reaching supersolar metallicities. Meanwhile, the kinematic thin disc began forming $\sim$10 Gyr ago, just as thick disc star formation ended, characterized by supersolar metallicities and low [$α$/Fe]. This transition coincides with the Milky Way's last major merger: Gaia-Sausage Enceladus (GSE). We also identify a subset of kinematic thin disc stars older than 10 Gyr with high/intermediate [$α$/Fe], indicating a transition phase. The age-metallicity relation of the thin disc suggests overlapping star formation episodes and radial mixing in the solar neighborhood, with the greatest spread $\sim$6 Gyr ago. Additionally, we detect an isolated thick disc star formation event at solar metallicity, coinciding with Sagittarius' first pericenter passage. These findings provide precise age-metallicity distributions and star formation rates, offering key insights for chemical evolution models and cosmological simulations. △ Less

Submitted 25 March, 2025; originally announced March 2025.

Comments: Submitted to A&A

Journal ref: A&A 704, A258 (2025)

Chronology of our Galaxy from Gaia CMD-fitting (ChronoGal): the early formation of the Milky Way disk and the impact of Gaia-Sausage-Enceladus

Authors: C. Gallart, E. Fernández-Alvar, S. Cassisi, T. Ruiz-Lara, F. Surot, G. Aznar-Menargues, Y. González-Koda, D. Mirabal, A. B. Queiroz, A. Rivero

Abstract: The derivation of precise stellar ages is considered the current major challenge to reconstruct the chronology of the Milky Way. Color-magnitude diagram (CMD)-fitting offers a robust alternative to individual age determinations via the derivation of dynamically evolved star formation histories (deSFH) and age-metallicity distributions (Gallart et al. 2024). Our new suite of routines, CMDft.Gaia, s… ▽ More The derivation of precise stellar ages is considered the current major challenge to reconstruct the chronology of the Milky Way. Color-magnitude diagram (CMD)-fitting offers a robust alternative to individual age determinations via the derivation of dynamically evolved star formation histories (deSFH) and age-metallicity distributions (Gallart et al. 2024). Our new suite of routines, CMDft.Gaia, specifically developed to analyse Gaia CMDs, produce deSFHs which are robust against sensible changes in the input parameters and extremely precise, providing an unprecedentedly detailed characterization of the successive events of star formation that, since its early evolution, have shaped the current Milky Way. Also important is the fact that, thanks to the high completeness of the Gaia photometric data, CMDft.Gaia provides the actual number of stars and the mass involved in the different events of star formation. The current analysis of the deSFH for stellar populations within 100 pc of the Sun, as well as for kinematically selected stars in the thin disk, thick disk, and halo, allows us to sketch a tentative picture of Milky Way evolution. The findings indicate that star formation commenced very early in a thick disk, with a small fraction of stars having [M/H]<-0.5 forming more than 12 Gyr ago. This phase culminated in a more prominent 12 Gyr old population with [M/H]~-0.5. Approximately 11 Gyr ago, the merger with GSE triggered an intense burst of star formation, generating most of the thick disk mass and enriching its metallicity to solar levels. Subsequently, the bulk of the star formation in the thin disk started and continues with a somewhat episodic behaviour up to the present time. △ Less

Submitted 21 March, 2025; originally announced March 2025.

Comments: 7 pages, 3 figures, to appear in the proceedings of IAU Symposium 395 "Stellar populations in the Milky Way and beyond" (eds. J. Meléndez, C. Chiappini, R. Schiavon, M. Trevisan)

Cluster Ages to Reconstruct the Milky Way Assembly (CARMA). III. NGC 288 as the first Splashed globular cluster

Authors: E. Ceccarelli, D. Massari, F. Aguado-Agelet, A. Mucciarelli, S. Cassisi, M. Monelli, E. Pancino, M. Salaris, S. Saracino

Abstract: The system of globular clusters (GCs) in the Milky Way (MW) comprises a mixture of both in situ and accreted clusters. Tracing the origin of GCs provides invaluable insights into the formation history of the MW. However, reconciling diverse strands of evidence is often challenging. A notable example is NGC 288, where despite significant efforts in the literature, the available chrono-chemodynamica… ▽ More The system of globular clusters (GCs) in the Milky Way (MW) comprises a mixture of both in situ and accreted clusters. Tracing the origin of GCs provides invaluable insights into the formation history of the MW. However, reconciling diverse strands of evidence is often challenging. A notable example is NGC 288, where despite significant efforts in the literature, the available chrono-chemodynamical data have yet to provide a definitive conclusion regarding its origin. On the one hand, all post-Gaia dynamical studies indicate an accreted origin for NGC 288 from the Gaia-Sausage-Enceladus (GSE) dwarf galaxy. On the other hand, NGC 288 has been found to be 2.5 Gyr older than other GSE GCs at the same metallicity, this suggesting a different (and possibly in situ) origin. In this work, we address the unresolved question on the origin of NGC 288 by analyzing its chrono-chemical properties in an unprecedentedly homogeneous framework. First, we compare the location of NGC 288 in the age-metallicity plane with that of other two in situ GCs at similar metallicity, namely NGC 6218 and NGC 6362. The age estimates obtained within the homogeneous framework of the CARMA collaboration show that the three clusters are coeval, reinforcing the contrast with the dynamical interpretation. Then, we compare the abundances with a sample of in situ and accreted clusters at similar metallicity, finding again consistency with the chemistry of in situ systems. To reconcile these results with its orbital properties, we propose a scenario where NGC 288 formed in the proto-disc of the MW, and then was dynamically heated by the interaction with the GSE merger. This is a fate that resembles that of proto-disc stars undergoing the so-called Splash event. Therefore, NGC 288 demonstrates the importance of a homogeneous chrono-chemodynamical information in the interpretation of the origin of MW GCs. △ Less

Submitted 1 August, 2025; v1 submitted 4 March, 2025; originally announced March 2025.

Comments: Main paper: 7 pages and 5 figures. Appendix: 2 pages and 2 figures. Shortened abstract to meet arXiv's length requirements. Accepted for publication in A&A

Chronology of our Galaxy from Gaia colour-magnitude diagram fitting (ChronoGal) -- III. Age and metallicity distribution of Gaia-Sausage-Enceladus stars near the Sun

Authors: Yllari K. González-Koda, Tomás Ruiz-Lara, Carme Gallart, Edoardo Ceccarelli, Emma Dodd, Emma Fernández-Alvar, Santi Cassisi, Francisco Surot, Fernando Aguado-Agelet, Davide Massari, Matteo Monelli, Thomas M. Callingham, Amina Helmi, Guillem Aznar-Menargues, David Mirabal, Alicia Rivero, Anna B. Queiroz

Abstract: Context. Gaia-Sausage-Enceladus is considered the last major merger that contributed to the formation of the Milky Way. Its remnants dominate the nearby accreted stellar halo of the Milky Way. Aim. We aim to characterise the star formation history of Gaia-Sausage-Enceladus through the age and metallicity of its stellar populations. Methods. From Gaia DR3 data, we dynamically define three Gaia-Saus… ▽ More Context. Gaia-Sausage-Enceladus is considered the last major merger that contributed to the formation of the Milky Way. Its remnants dominate the nearby accreted stellar halo of the Milky Way. Aim. We aim to characterise the star formation history of Gaia-Sausage-Enceladus through the age and metallicity of its stellar populations. Methods. From Gaia DR3 data, we dynamically define three Gaia-Sausage-Enceladus samples with different criteria and possible degrees of contamination from other substructures in the halo. Then, we derive the stellar age and metallicity distributions using the CMDfit.Gaia package. Results. We identify three main populations of stars and a fourth smaller one following an almost linear age-[M/H] relation. The three oldest populations correspond to the bulk of the star formation that lasted for, at least, $\sim$3-4 Gyr and ended about 10 Gyr ago, its metallicities ranging from $-$1.7 to $-$0.8. We categorise these populations into two main epochs: the evolution of GSE in isolation and the merger event. This separation finds independent support from the age-metallicty relation of GSE globular clusters (Aguado-Agelet et al., subm.). The fourth population is younger and more metal-rich, at $\sim$8.5 Gyr and [M/H]$\sim-0.4$; its link to GSE is unclear. △ Less

Submitted 27 February, 2025; originally announced February 2025.

Comments: See companion paper by Aguado-Agelet et al. 14 pages, 14 figures, 4 appendices. Submitted for publication in A&A

Journal ref: A&A 704, A259 (2025)

Cluster Ages to Reconstruct the Milky Way Assembly (CARMA). II. The age-metallicity relation of Gaia-Sausage-Enceladus globular clusters

Authors: Fernando Aguado-Agelet, Davide Massari, Matteo Monelli, Santi Cassisi, Carme Gallart, Edoardo Ceccarelli, Yllari Kay González-Koda, Tomás Ruiz-Lara, Elena Pancino, Sara Saracino, Maurizio Salaris

Abstract: We present the age determination of 13 globular clusters dynamically associated with the Gaia-Sausage-Enceladus (GSE) merger event, as part of the CARMA project effort to trace the Milky Way assembly history. We used deep and homogeneous archival $Hubble$ $Space$ $Telescope$ data, and applied isochrone-fitting to derive homogeneous age estimates. We find that the majority of the selected clusters… ▽ More We present the age determination of 13 globular clusters dynamically associated with the Gaia-Sausage-Enceladus (GSE) merger event, as part of the CARMA project effort to trace the Milky Way assembly history. We used deep and homogeneous archival $Hubble$ $Space$ $Telescope$ data, and applied isochrone-fitting to derive homogeneous age estimates. We find that the majority of the selected clusters form a well-defined age-metallicity relation, with a few outliers. Among these, NGC 288 and NGC 6205 are more than 2 Gyr older than the other GSE globular clusters at similar metallicity, and are therefore interpreted as of likely in-situ origin. Moreover, NGC 7099 is somewhat younger than the average GSE trend, this suggesting a possible alternative dwarf galaxy progenitor, while NGC 5286 is mildly older, as if its progenitor was characterised by an higher star-formation efficiency. Another remarkable feature of the resulting age-metallicity relation is the presence of two epochs of globular cluster formation, with a duration of $\sim0.3$ Gyr each and separated by $\sim2$ Gyr. These findings are in excellent agreement with the age-metallicity relation of halo field stars found by González-Koda et al., clearly hinting at episodic star-formation in GSE. The age of the two formation epochs is similar to the mean age of the two groups of in-situ globular clusters previously studied by CARMA. These epochs might therefore be precisely pinpointing two important dynamical events that GSE had with the Milky Way during its evolutionary history. Finally, we discuss the correlation between the recent determination of Si and Eu with the clusters age and origin. △ Less

Submitted 15 July, 2025; v1 submitted 27 February, 2025; originally announced February 2025.

Comments: Accepted for publication by A&A. Main paper: 10 pages and 5 figures. Appendix: 13 pages and 12 figures. See the companion paper by Gonzalez-Koda et al. 2025

Journal ref: A&A 704, A255 (2025)

Performance of the Stellar Abundances and atmospheric Parameters Pipeline adapted for M dwarfs I. Atmospheric parameters from the spectroscopic module

Authors: Terese Olander, Matthew R. Gent, Ulrike Heiter, Oleg Kochukhov, Maria Bergemann, Ekaterina Magg, Santi Cassisi, Mikhail Kovalev, Thierry Morel, Nicola J. Miller, Diogo Souto, Yutong Shan, Bárbara Rojas-Ayala, Elisa Delgado-Mena, Haiyang S. Wang

Abstract: M dwarfs are important targets in the search for Earth-like exoplanets due to their small masses and low luminosities. Several ongoing and upcoming space missions are targeting M dwarfs for this reason, and the ESA PLATO mission is one of these. In order to fully characterise a planetary system the properties of the host star must be known. For M dwarfs we can derive effective temperature, surface… ▽ More M dwarfs are important targets in the search for Earth-like exoplanets due to their small masses and low luminosities. Several ongoing and upcoming space missions are targeting M dwarfs for this reason, and the ESA PLATO mission is one of these. In order to fully characterise a planetary system the properties of the host star must be known. For M dwarfs we can derive effective temperature, surface gravity, metallicity, and abundances of various elements from spectroscopic observations in combination with photometric data. The Stellar Abundances and atmospheric Parameters Pipeline (SAPP) has been developed as a prototype for one of the stellar science softwares within the PLATO consortium, it is aimed at FGK stars. We have modified it to be able to analyse the M dwarf among the PLATO targets. The current version of the pipeline for M dwarfs mostly relies on spectroscopic observations. The data processing is based on the machine learning algorithm The Payne and fits a grid of model spectra to an observed spectrum to derive effective temperature and metallicity. We use spectra in the H-band, as the near-infrared region is beneficial for M dwarfs. A method based on synthetic spectra was developed for the continuum normalisation of the spectra, taking into account the pseudo-continuum formed by numerous lines of the water molecule. Photometry is used to constrain the surface gravity. We tested the modified SAPP on spectra of M dwarfs from the APOGEE survey. Our validation sample of 26 stars includes stars with interferometric observations and binaries. We found a good agreement between our values and reference values from a range of studies. The overall uncertainties in the derived effective temperature, surface gravity, and metallicity is 100 K, 0.1 dex, and 0.15 dex, respectively. We find that the modified SAPP performs well on M dwarfs and identify possible areas of future development. △ Less

Submitted 13 February, 2025; originally announced February 2025.

Comments: Accepted in A&A

Journal ref: A&A 696, A62 (2025)

The $Hubble$ Missing Globular Cluster Survey. I. Survey overview and the first precise age estimate for ESO452-11 and 2MASS-GC01

Authors: D. Massari, M. Bellazzini, M. Libralato, A. Bellini, E. Dalessandro, E. Ceccarelli, F. Aguado-Agelet, S. Cassisi, C. Gallart, M. Monelli, A. Mucciarelli, E. Pancino, M. Salaris, S. Saracino, E. Dodd, F. R. Ferraro, E. R. Garro, B. Lanzoni, R. Pascale, L. Rosignoli

Abstract: We present the $Hubble$ Missing Globular Cluster Survey (MGCS), a $Hubble$ $Space$ $Telescope$ Treasury Program dedicated to the observation of all kinematically confirmed Milky Way globular clusters that missed previous $Hubble$ imaging. After introducing the aims of the programme and describing its target clusters, we showcase the first results of the survey. These are related to two clusters, o… ▽ More We present the $Hubble$ Missing Globular Cluster Survey (MGCS), a $Hubble$ $Space$ $Telescope$ Treasury Program dedicated to the observation of all kinematically confirmed Milky Way globular clusters that missed previous $Hubble$ imaging. After introducing the aims of the programme and describing its target clusters, we showcase the first results of the survey. These are related to two clusters, one located at the edge of the Milky Way bulge and observed in optical bands, namely ESO452-11, and one located in the Galactic disc observed in the near-IR, namely 2MASS-GC01. For both clusters, the deep colour-magnitude diagrams obtained from the MGCS observations reach several magnitudes below their main-sequence turn-off and thus enable the first precise estimate of their age. By using the methods developed in the Cluster Ages to Reconstruct the Milky Way Assembly (CARMA) project, we find ESO452-11 to be an old metal-intermediate globular cluster, with ${\rm [M/H]}\simeq-0.80^{+0.08}_{-0.11}$ and an age of ${\rm t}=13.59^{+0.48}_{-0.69}$ Gyr. Its location on the age-metallicity relation makes it consistent with an in situ origin, in agreement with its dynamical properties. On the other hand, the results for 2MASS-GC01 highlight it as a young metal-intermediate cluster, with an age of ${\rm t}=7.22^{+0.93}_{-1.11}$ Gyr at ${\rm [M/H]}=-0.73^{+0.06}_{-0.06}$. Despite the large associated uncertainty, our age estimate for this extremely extincted cluster indicates it to be either the youngest globular cluster known to date or a massive and compact open cluster, which is consistent with its almost circular, disc-like orbit △ Less

Submitted 8 May, 2025; v1 submitted 3 February, 2025; originally announced February 2025.

Comments: 14 pages, 6 figures, 2 tables, accepted by A&A. Cluster catalogues will be presented and made public in a forthcoming paper by Libralato et al

Journal ref: A&A 698, A197 (2025)

Improving the stellar age determination through joint modeling of binarity and asteroseismology -- Grid modeling of the seismic red-giant binary KIC 9163796

Authors: D. H. Grossmann, P. G. Beck, S. Mathur, C. Johnston, D. Godoy-Rivera, J. C. Zinn, S. Cassisi, B. Liagre, T. Masseron, R. A. Garcia, A. Hanslmeier, N. Muntean, L. S. Schimak, L. Steinwender, D. Stello

Abstract: Context. Typical uncertainties of ages determined for single star giants from isochrone fitting using single-epoch spectroscopy and photometry without any additional constraints are 30-50 %. Binary systems, particularly double-lined spectroscopic (SB2) binaries, provide an opportunity to study the intricacies of internal stellar physics and better determine stellar parameters, particularly the ste… ▽ More Context. Typical uncertainties of ages determined for single star giants from isochrone fitting using single-epoch spectroscopy and photometry without any additional constraints are 30-50 %. Binary systems, particularly double-lined spectroscopic (SB2) binaries, provide an opportunity to study the intricacies of internal stellar physics and better determine stellar parameters, particularly the stellar age. Aims. By using the constraints from binarity and asteroseismology, we aim to obtain precise age and stellar parameters for the red giant-subgiant binary system KIC 9163796, a system with a mass ratio of 1.015 but distinctly different positions in the Hertzsprung-Russell diagram (HRD). Methods. We compute a multidimensional model grid of individual stellar models. From different combinations of figures of merit, we use the constraints drawn from binarity, spectroscopy, and asteroseismology to determine the stellar mass, chemical composition, and age of KIC 9163796. Results. Our combined-modeling approach leads to an age estimation of the binary system KIC 9163796 of 2.44$^{+0.25}_{-0.20}$ Gyr, which corresponds to a relative error in the age of 9 %. Furthermore, we found both components exhibiting equal initial helium abundance of 0.27 to 0.30, significantly higher than the primordial helium abundance, and an initial heavy metal abundance below the spectroscopic value. The masses of our models are in agreement with masses derived from the asteroseismic scaling relations. Conclusions. By exploiting the unique, distinct positions of KIC 9163796, we successfully demonstrated that combining asteroseismic and binary constraints leads to a significant improvement of precision in age estimation, that have a relative error below 10% for a giant star. △ Less

Submitted 15 January, 2025; originally announced January 2025.

Comments: Accepted for publication in Astronomy & Astrophysics (18 pages, 14 figures)

Stellar Pulsation and Evolution: a Combined Theoretical Renewal and Updated Models (SPECTRUM) -- I: Updating radiative opacities for pulsation models of Classical Cepheid and RR-Lyrae

Authors: Giulia De Somma, Marcella Marconi, Santi Cassisi, Roberto Molinaro

Abstract: Pulsating stars are universally recognized as precise distance indicators and tracers of stellar populations. Their variability, combined with well-defined relationships between pulsation properties and intrinsic evolutionary parameters such as luminosity, mass, and age, makes them essential for understanding galactic evolution and retrieving star formation histories. Therefore, accurate modeling… ▽ More Pulsating stars are universally recognized as precise distance indicators and tracers of stellar populations. Their variability, combined with well-defined relationships between pulsation properties and intrinsic evolutionary parameters such as luminosity, mass, and age, makes them essential for understanding galactic evolution and retrieving star formation histories. Therefore, accurate modeling of pulsating stars is crucial for using them as standard candles and stellar population tracers. This is the first paper in the "Stellar Pulsation and Evolution: a Combined Theoretical Renewal and Updated Models" (SPECTRUM) project, which aims to present an update of Stellingwerf's hydrodynamical pulsation code, by adopting the latest radiative opacity tables commonly used in stellar evolution community. We assess the impact of this update on pulsation properties, such as periods, instability strip topology, and light curve shapes, as well as on Period Wesenheit and Period-Luminosity relations for Classical Cepheids and RR Lyrae stars, comparing the results with those derived using older opacity data. Our results indicate that the opacity update introduces only minor changes: instability strip boundary locations shift by no more than $100K$ in effective temperature, and pulsation periods vary within $1σ$ compared to previous evaluations. Light curves exhibit slight differences in shape and amplitude. Consequently, the theoretical calibration of the Cepheid or RRL-based extragalactic distance scale remains largely unaffected by the opacity changes. However, achieving consistency in opacity tables between stellar evolution and pulsation codes is a significant step toward a homogeneous and self-consistent stellar evolution and pulsation framework. △ Less

Submitted 2 November, 2024; originally announced November 2024.

Comments: Accepted for Publication in the Astrophysical Journal. 17 pages, 11 figures, 4 tables

Characterisation of local halo building blocks: Thamnos and Sequoia

Authors: Emma Dodd, Tomás Ruiz-Lara, Amina Helmi, Carme Gallart, Thomas M. Callingham, Santi Cassisi, Emma Fernández-Alvar, Fransisco Surot

Abstract: A crucial aspect of galaxy evolution is the pace at which galaxies build up their mass. We investigate this hierarchical assembly by uncovering and timing accretion events experienced by our Galaxy. In the Milky Way, accreted debris has been identified in the local halo, thanks to Gaia. We combine this dataset with advances in colour-magnitude diagram (CMD) fitting to characterise the Galaxy's bui… ▽ More A crucial aspect of galaxy evolution is the pace at which galaxies build up their mass. We investigate this hierarchical assembly by uncovering and timing accretion events experienced by our Galaxy. In the Milky Way, accreted debris has been identified in the local halo, thanks to Gaia. We combine this dataset with advances in colour-magnitude diagram (CMD) fitting to characterise the Galaxy's building blocks based on their age and metallicity distributions. Here, we focus on the retrograde halo, specifically Thamnos and Sequoia. This study, part of the ChronoGal project, uses CMDft.Gaia to fit absolute CMDs of stars from these sub-structures, extracted from a local 5D Gaia DR3 dataset. By comparing their age and metallicity distributions with expected contamination from Gaia Enceladus (GE) and low-energy (LE) in situ populations, we identify distinct stellar population signatures for Sequoia and Thamnos. Both have metal-poor populations ([Fe/H] -2.5 to -1.5 dex) distinct from contamination. Their age distributions reveal the build-up pace of their progenitors: half of Sequoia's stars formed by 12 Gyr ago, while Thamnos appears slightly older and declines faster, forming half its stars by 12.3 Gyr. GE and LE populations formed half their stars by 12.1 Gyr and 12.9 Gyr, respectively. Caution is needed interpreting these distributions, especially for Sequoia, due to small sample sizes that can shift ages younger by up to 1 Gyr. Nonetheless, accounting for this and residual contamination, we conclude Thamnos, Gaia Enceladus, and Sequoia are predominantly old and were accreted within 1-2 Gyr of each other. We present, for the first time, age distributions for the retrograde halo sub-structures Sequoia and Thamnos, derived from photometric data using CMD fitting that also yields metallicity distributions consistent with spectroscopy. △ Less

Submitted 30 June, 2025; v1 submitted 25 August, 2024; originally announced August 2024.

Comments: 22 pages, 18 figures, accepted in A&A

Journal ref: A&A 698, A277 (2025)

Unveiling the purely young star formation history of the SMC's northeastern shell from colour-magnitude diagram fitting

Authors: Joanna D. Sakowska, Noelia E. D. Noël, Tomás Ruiz-Lara, Carme Gallart, Pol Massana, David L. Nidever, Santi Cassisi, Patricio Correa-Amaro, Yumi Choi, Gurtina Besla, Denis Erkal, David Martínez-Delgado, Matteo Monelli, Knut A. G. Olsen, Guy S. Stringfellow

Abstract: We obtain a quantitative star formation history (SFH) of a shell-like structure ('shell') located in the northeastern part of the Small Magellanic Cloud (SMC). We use the Survey of the MAgellanic Stellar History (SMASH) to derive colour-magnitude diagrams (CMDs), reaching below the oldest main-sequence turnoff, from which we compute the SFHs with CMD fitting techniques. We present, for the first t… ▽ More We obtain a quantitative star formation history (SFH) of a shell-like structure ('shell') located in the northeastern part of the Small Magellanic Cloud (SMC). We use the Survey of the MAgellanic Stellar History (SMASH) to derive colour-magnitude diagrams (CMDs), reaching below the oldest main-sequence turnoff, from which we compute the SFHs with CMD fitting techniques. We present, for the first time, a novel technique that uses red clump (RC) stars from the CMDs to assess and account for the SMC's line-of-sight depth effect present during the SFH derivation. We find that accounting for this effect recovers a more accurate SFH. We quantify a 7 kpc line-of-sight depth present in the CMDs, in good agreement with depth estimates from RC stars in the northeastern SMC. By isolating the stellar content of the northeastern shell and incorporating the line-of-sight depth into our calculations, we obtain an unprecedentedly detailed SFH. We find that the northeastern shell is primarily composed of stars younger than 500 Myrs, with significant star formation enhancements around 250 Myr and 450 Myr. These young stars are the main contributors to the shell's structure. We show synchronicity between the northeastern shell's SFH with the Large Magellanic Cloud's (LMC) northern arm, which we attribute to the interaction history of the SMC with the LMC and the Milky Way (MW) over the past 500 Myr. Our results highlight the complex interplay of ram pressure stripping and the influence of the MW's circumgalactic medium in shaping the SMC's northeastern shell. △ Less

Submitted 18 July, 2024; originally announced July 2024.

Comments: 17 pages, 13 figures. Accepted to MNRAS for publication

The PLATO Mission

Authors: Heike Rauer, Conny Aerts, Juan Cabrera, Magali Deleuil, Anders Erikson, Laurent Gizon, Mariejo Goupil, Ana Heras, Jose Lorenzo-Alvarez, Filippo Marliani, César Martin-Garcia, J. Miguel Mas-Hesse, Laurence O'Rourke, Hugh Osborn, Isabella Pagano, Giampaolo Piotto, Don Pollacco, Roberto Ragazzoni, Gavin Ramsay, Stéphane Udry, Thierry Appourchaux, Willy Benz, Alexis Brandeker, Manuel Güdel, Eduardo Janot-Pacheco , et al. (820 additional authors not shown)

Abstract: PLATO (PLAnetary Transits and Oscillations of stars) is ESA's M3 mission designed to detect and characterise extrasolar planets and perform asteroseismic monitoring of a large number of stars. PLATO will detect small planets (down to <2 R_(Earth)) around bright stars (<11 mag), including terrestrial planets in the habitable zone of solar-like stars. With the complement of radial velocity observati… ▽ More PLATO (PLAnetary Transits and Oscillations of stars) is ESA's M3 mission designed to detect and characterise extrasolar planets and perform asteroseismic monitoring of a large number of stars. PLATO will detect small planets (down to <2 R_(Earth)) around bright stars (<11 mag), including terrestrial planets in the habitable zone of solar-like stars. With the complement of radial velocity observations from the ground, planets will be characterised for their radius, mass, and age with high accuracy (5 %, 10 %, 10 % for an Earth-Sun combination respectively). PLATO will provide us with a large-scale catalogue of well-characterised small planets up to intermediate orbital periods, relevant for a meaningful comparison to planet formation theories and to better understand planet evolution. It will make possible comparative exoplanetology to place our Solar System planets in a broader context. In parallel, PLATO will study (host) stars using asteroseismology, allowing us to determine the stellar properties with high accuracy, substantially enhancing our knowledge of stellar structure and evolution. The payload instrument consists of 26 cameras with 12cm aperture each. For at least four years, the mission will perform high-precision photometric measurements. Here we review the science objectives, present PLATO's target samples and fields, provide an overview of expected core science performance as well as a description of the instrument and the mission profile at the beginning of the serial production of the flight cameras. PLATO is scheduled for a launch date end 2026. This overview therefore provides a summary of the mission to the community in preparation of the upcoming operational phases. △ Less

Submitted 18 November, 2024; v1 submitted 8 June, 2024; originally announced June 2024.

Benchmarking the effective temperature scale of red giant branch stellar models: the case of the metal-poor halo giant HD 122563

Authors: O. L. Creevey, S. Cassisi, F. Thévenin, M. Salaris, A. Pietrinferni

Abstract: There is plenty of evidence in the literature of significant discrepancies between the observations and models of metal-poor red giant branch stars, in particular regarding the effective temperature, teff, scale. We revisit the benchmark star HD 122563 using the most recent observations from Gaia Data Release 3, to investigate if these new constraints may help in resolving this discrepancy. We rev… ▽ More There is plenty of evidence in the literature of significant discrepancies between the observations and models of metal-poor red giant branch stars, in particular regarding the effective temperature, teff, scale. We revisit the benchmark star HD 122563 using the most recent observations from Gaia Data Release 3, to investigate if these new constraints may help in resolving this discrepancy. We review the most recent spectroscopic determinations of the metallicity of HD 122563 [Fe/H], and provide a new assessment of its fundamental parameters, i.e. bolometric luminosity, teff, surface gravity, plus a photometric determination of its metal content. Using these constraints, we compare the position of the star in the Hertzsprung-Russell (H-R) diagram with various recent sets of stellar evolution tracks. The H-R diagram analysis reveals a significant disagreement between observed and theoretical teff values, when adopting the most recent spectroscopic estimate of [Fe/H]. On the other hand, by using the photometric determination of [Fe/H] some of the selected sets of stellar tracks appear in fair agreement with observations. The sets with discrepant teff can be made to agree with observations either by modifying the prescription adopted to calculate the models' outer boundary conditions, and/or by reducing the adopted value of the mixing length parameter with respect to the solar-calibration. A definitive assessment of whether the teff scale of metal-poor stellar red giant branch models is consistent with observations requires an even more accurate determination of the fundamental parameters of HD 122563 and also a larger sample of calibrators. From the theoretical side, it is crucial to minimise the current uncertainties in the treatment (boundary conditions, temperature gradient) of the outer layers of stellar models with convective envelopes. △ Less

Submitted 5 April, 2024; originally announced April 2024.

Comments: accepted for publication in A&A

Journal ref: A&A 689, A243 (2024)

Ne22 distillation and the cooling sequence of the old metal-rich open cluster NGC 6791

Authors: Maurizio Salaris, Simon Blouin, Santi Cassisi, Luigi R. Bedin

Abstract: Recent Monte Carlo plasma simulations to study in crystallizing carbon-oxygen (CO) white dwarfs (WDs) the phase separation of Ne22 (the most abundant metal after carbon and oxygen) have shown that, under the right conditions, a distillation process that transports Ne22 toward the WD centre is efficient and releases a considerable amount of gravitational energy that can lead to cooling delays of up… ▽ More Recent Monte Carlo plasma simulations to study in crystallizing carbon-oxygen (CO) white dwarfs (WDs) the phase separation of Ne22 (the most abundant metal after carbon and oxygen) have shown that, under the right conditions, a distillation process that transports Ne22 toward the WD centre is efficient and releases a considerable amount of gravitational energy that can lead to cooling delays of up to several Gyr. Here we present the first CO WD stellar evolution models that self-consistently include the effect of neon distillation, and cover the full range of CO WD masses, for a progenitor metallicity twice-solar appropriate for the old open cluster NGC 6791. The old age (about 8.5 Gyr) and high metallicity of this cluster -- hence the high neon content (about 3% by mass) in the cores of its WDs -- maximize the effect of neon distillation in the models to be compared with the observed cooling sequence. We discuss the effect of distillation on the internal chemical stratification and cooling time of the models, confirming that distillation causes cooling delays up to several Gyr, that depend in a non-monotonic way on the mass. We also show how our models produce luminosity functions (LFs) that can match the faint end of the observed WD LF in NGC 6791, for ages consistent with the range determined from a sample of cluster's eclipsing binary stars, and the main sequence turn-off. Without the inclusion of distillation the theoretical WD cooling sequences reach too faint magnitudes compared to the observations. We also propose James Webb Space Telescope observations that can independently demonstrate the efficiency of neon distillation in the interiors of NGC 6791 WDs, and help resolve the current uncertainty on the treatment of the electron conduction opacities for the hydrogen-helium envelope of the WD models. △ Less

Submitted 5 March, 2024; originally announced March 2024.

Comments: 10 pages, 10 figures, accepted for publication in A&A

Journal ref: A&A 686, A153 (2024)

Chronology of our Galaxy from Gaia Colour-Magnitude Diagram-fitting (ChronoGal). I. The formation and evolution of the thin disk from the Gaia Catalogue of Nearby Stars

Authors: C. Gallart, F. Surot, S. Cassisi, E. Fernández-Alvar, D. Mirabal, A. Rivero, T. Ruiz-Lara, J. Santos-Torres, G. Aznar-Menargues, G. Battaglia, A. B. Queiroz, M. Monelli, E. Vasiliev, C. Chiappini, A. Helmi, V. Hill, D. Massari, G. F. Thomas

Abstract: The current major challenge to reconstruct the chronology of the Milky Way (MW) is the difficulty to derive precise stellar ages. CMD-fitting offers an alternative to individual age determinations to derive the star formation history (SFH). We present CMDft.Gaia and use it to analyse the CMD of the Gaia Catalogue of Nearby Stars (GCNS), which contains a census of the stars within 100 pc of the Sun… ▽ More The current major challenge to reconstruct the chronology of the Milky Way (MW) is the difficulty to derive precise stellar ages. CMD-fitting offers an alternative to individual age determinations to derive the star formation history (SFH). We present CMDft.Gaia and use it to analyse the CMD of the Gaia Catalogue of Nearby Stars (GCNS), which contains a census of the stars within 100 pc of the Sun. The result is an unprecedented detailed view of the evolution of the MW disk. The bulk of star formation started 11-10.5 Gyr ago at [Fe/H]~solar and continued with a slightly decreasing metallicity trend until 6 Gyr ago. Between 6-4 Gyr ago, a break in the age-metallicity distribution is observed, with 3 stellar populations with distinct metallicities (sub-solar, solar, and super-solar), possibly indicating some dramatic event in the Galaxy. Star formation resumed 4 Gyr ago with a bursty behaviour, metallicity near solar and higher average SFR. The derived metallicity distribution closely matches precise spectroscopic data, which also show stellar populations deviating from solar metallicity. Interestingly, our results reveal the presence of intermediate-age populations with both a metallicity typical of the thick disk and supersolar metallicity. Our many tests indicate that, with high precision Gaia photometric and distance data, CMDft.Gaia can achieve a precision ~10% and an accuracy better than 6% in the dating of even old stellar populations. The comparison with independent spectroscopic data shows that metallicity distributions are determined with high precision, without imposing a-priory metallicity information. This opens the door to obtaining detailed and robust information on the evolution of the stellar populations of the MW over cosmic time. As an example we provide an unprecedented detailed view of the age and metallicity distributions of the stars within 100 pc of the Sun. △ Less

Submitted 14 February, 2024; originally announced February 2024.

Comments: 35 pages, 30 figures; to be published in A&A; revised version after minor referee comments

Journal ref: A&A 687, A168 (2024)

Classical Cepheid Pulsation properties in the Rubin-LSST filters

Authors: Giulia De Somma, Marcella Marconi, Santi Cassisi, Roberto Molinaro, Anupam Bhardwaj, Vincenzo Ripepi, Ilaria Musella, Adriano Pietrinferni, Teresa Sicignano, Erasmo Trentin, Silvio Leccia

Abstract: Homogeneous multi-wavelength observations of classical Cepheids from the forthcoming Rubin-LSST have the potential to significantly contribute to our understanding of the evolutionary and pulsation properties of these pulsating stars. Updated pulsation models for Classical Cepheid stars have been computed under various assumptions about chemical compositions, including relatively low metallicity (… ▽ More Homogeneous multi-wavelength observations of classical Cepheids from the forthcoming Rubin-LSST have the potential to significantly contribute to our understanding of the evolutionary and pulsation properties of these pulsating stars. Updated pulsation models for Classical Cepheid stars have been computed under various assumptions about chemical compositions, including relatively low metallicity ($Z$ = $0.004$ with $Y$ =$0.25$ and $Z$=$0.008$ with $Y$ =$0.25$), solar metallicity ($Z$=$0.02$ with $Y$=$0.28$), and supersolar metallicity environments ($Z$ = $0.03$ with $Y$ = $0.28$). From the predicted periods, intensity-weighted mean magnitudes, and colors, we have derived the first theoretical pulsation relations in the Rubin-LSST filters (ugrizy), including period-luminosity-color, period-Wesenheit, and period-age-color relations. We find that the coefficients of these relations are almost insensitive to the efficiency of superadiabatic convection but are significantly affected by the assumption of the mass-luminosity relation and the adopted chemical composition. Metal-dependent versions of these relations are also derived, representing valuable tools for individual distance determinations and correction for metallicity effects on the cosmic distance scale. △ Less

Submitted 8 February, 2024; originally announced February 2024.

Comments: 23 pages, 6 figures, and 11 tables; accepted for publication in MNRAS

Double Red Giant Branch and Red Clump features of Galactic disc stellar populations with Gaia GSPspec

Authors: Alejandra Recio-Blanco, P. de Laverny, P. A. Palicio, S. Cassisi, A. Pietrinferni, N. Lagarde, C. Navarrete

Abstract: To disentangle the different competing physical processes at play in Galactic evolution, a detailed chrono chemicalkinematical, and dynamical characterisation of the disc bimodality is necessary, including high number statistics. Here we make use of an extremely precise subsample of the Gaia DR3 GSP-Spec catalogue of stellar chemophysical parameters. The selected database is composed of 408 800 st… ▽ More To disentangle the different competing physical processes at play in Galactic evolution, a detailed chrono chemicalkinematical, and dynamical characterisation of the disc bimodality is necessary, including high number statistics. Here we make use of an extremely precise subsample of the Gaia DR3 GSP-Spec catalogue of stellar chemophysical parameters. The selected database is composed of 408 800 stars with a median uncertainty of 10 K, 0.03 and 0.01 dex in Teff , log(g) and [M/H], respectively. The stellar parameter precision allows to break the age-metallicity degeneracy of disc stars. For the first time, the disc bimodality in the Kiel diagramme of giant stars is observed, getting rid of interstellar absortion issues. This bimodality produces double Red Giant Branch sequences and Red Clump features for mono-metallicity populations. A comparison with BaSTI isochrones allows to demonstrate that an age gap is needed to explain the evolutionary sequences separation, in agreement with previous age-metallicity relations obtained using sub-giant stars. A bimodal distribution in the stellar mass-[alpha/Fe] plane is observed at constant metallicity. Finally, a selection of stars with [M/H]=0.45 \pm 0.03 dex shows that the most metal-rich population in the Milky Way disc presents an important proportion of stars with ages in the range 5-13 Gyr. This old, extremely metal-rich population is possibly a mix of migrated stars from the internal Galactic regions, and old disc stars formed before the last major merger of the Milky Way. The Gaia GSP-Spec Kiel diagrammes of disc mono-abundance stellar populations reveal a complex, non linear age-metallicity relation crafted by internal and external processes of Galactic evolution. Their detailed analysis opens new opportunities to reconstruct the puzzle of the Milky Way disc bimodality. △ Less

Submitted 12 November, 2024; v1 submitted 2 February, 2024; originally announced February 2024.

Comments: Accepted for publication in A&A

Journal ref: A&A 692, A235 (2024)

The updated BaSTI stellar evolution models and isochrones.IV. alpha-depleted calculations

Authors: Adriano Pietrinferni, Maurizio Salaris, Santi Cassisi, Alessandro Savino, Alessio Mucciarelli, David Hyder, Sebastian Hidalgo

Abstract: This is the fourth paper of our new release of the BaSTI (a Bag of Stellar Tracks and Isochrones) stellar model and isochrone library. Following the updated solar-scaled, alpha-enhanced, and white dwarf model libraries, we present here alpha-depleted ([alpha/Fe] = -0.2) evolutionary tracks and isochrones, suitable to study the alpha-depleted stars discovered in Local Group dwarf galaxies and in th… ▽ More This is the fourth paper of our new release of the BaSTI (a Bag of Stellar Tracks and Isochrones) stellar model and isochrone library. Following the updated solar-scaled, alpha-enhanced, and white dwarf model libraries, we present here alpha-depleted ([alpha/Fe] = -0.2) evolutionary tracks and isochrones, suitable to study the alpha-depleted stars discovered in Local Group dwarf galaxies and in the Milky Way. These calculations include all improvements and updates of the solar-scaled and alpha-enhanced models, and span a mass range between 0.1 and 15 Msun, 21 metallicities between [Fe/H] = -3.20 and +0.45 with a helium-to-metal enrichment ratio dY/dZ = 1.31, homogeneous with the solar-scaled and alpha-enhanced models. The isochrones -- available in several photometric filters -- cover an age range between 20 Myr and 14.5 Gyr, including the pre-main-sequence phase. We have compared our isochrones with independent calculations of alpha-depleted stellar models, available for the same alpha-element depletion adopted in present investigation. We have also discussed the effect of an alpha-depleted heavy element distribution on the bolometric corrections in different wavelength regimes. Our alpha-depleted evolutionary tracks and isochrones are publicly available at the BaSTI website. △ Less

Submitted 10 November, 2023; originally announced November 2023.

Comments: 7 pages, 4 figures, 3 tables. Accepted for publication in MNRAS

The JWST Galactic Center Survey -- A White Paper

Authors: Rainer Schoedel, Steve Longmore, Jonny Henshaw, Adam Ginsburg, John Bally, Anja Feldmeier, Matt Hosek, Francisco Nogueras Lara, Anna Ciurlo, Mélanie Chevance, J. M. Diederik Kruijssen, Ralf Klessen, Gabriele Ponti, Pau Amaro-Seoane, Konstantina Anastasopoulou, Jay Anderson, Maria Arias, Ashley T. Barnes, Cara Battersby, Giuseppe Bono, Lucía Bravo Ferres, Aaron Bryant, Miguel Cano Gonzáalez, Santi Cassisi, Leonardo Chaves-Velasquez , et al. (89 additional authors not shown)

Abstract: The inner hundred parsecs of the Milky Way hosts the nearest supermassive black hole, largest reservoir of dense gas, greatest stellar density, hundreds of massive main and post main sequence stars, and the highest volume density of supernovae in the Galaxy. As the nearest environment in which it is possible to simultaneously observe many of the extreme processes shaping the Universe, it is one of… ▽ More The inner hundred parsecs of the Milky Way hosts the nearest supermassive black hole, largest reservoir of dense gas, greatest stellar density, hundreds of massive main and post main sequence stars, and the highest volume density of supernovae in the Galaxy. As the nearest environment in which it is possible to simultaneously observe many of the extreme processes shaping the Universe, it is one of the most well-studied regions in astrophysics. Due to its proximity, we can study the center of our Galaxy on scales down to a few hundred AU, a hundred times better than in similar Local Group galaxies and thousands of times better than in the nearest active galaxies. The Galactic Center (GC) is therefore of outstanding astrophysical interest. However, in spite of intense observational work over the past decades, there are still fundamental things unknown about the GC. JWST has the unique capability to provide us with the necessary, game-changing data. In this White Paper, we advocate for a JWST NIRCam survey that aims at solving central questions, that we have identified as a community: i) the 3D structure and kinematics of gas and stars; ii) ancient star formation and its relation with the overall history of the Milky Way, as well as recent star formation and its implications for the overall energetics of our galaxy's nucleus; and iii) the (non-)universality of star formation and the stellar initial mass function. We advocate for a large-area, multi-epoch, multi-wavelength NIRCam survey of the inner 100\,pc of the Galaxy in the form of a Treasury GO JWST Large Program that is open to the community. We describe how this survey will derive the physical and kinematic properties of ~10,000,000 stars, how this will solve the key unknowns and provide a valuable resource for the community with long-lasting legacy value. △ Less

Submitted 14 October, 2025; v1 submitted 18 October, 2023; originally announced October 2023.

Comments: This White Paper will be updated when required (e.g. new authors joining, editing of content). Most recent update: 14 Oct 2025

Cluster Ages to Reconstruct the Milky Way Assembly (CARMA) I. The final word on the origin of NGC6388 and NGC6441

Authors: Davide Massari, Fernando Aguado-Agelet, Matteo Monelli, Santi Cassisi, Elena Pancino, Sara Saracino, Carme Gallart, Tomás Ruiz-Lara, Emma Fernández-Alvar, Francisco Surot, Amalie Stokholm, Maurizio Salaris, Andrea Miglio, Edoardo Ceccarelli

Abstract: We present CARMA, the Cluster Ages to Reconstruct the Milky Way Assembly project, that aims at determining precise and accurate age measurements for the entire system of known Galactic globular clusters and at using them to trace the most significant merger events experienced by the Milky Way. The strength of CARMA relies on the use of homogeneous photometry, theoretical isochrones, and statistica… ▽ More We present CARMA, the Cluster Ages to Reconstruct the Milky Way Assembly project, that aims at determining precise and accurate age measurements for the entire system of known Galactic globular clusters and at using them to trace the most significant merger events experienced by the Milky Way. The strength of CARMA relies on the use of homogeneous photometry, theoretical isochrones, and statistical methods, that will enable to define a systematic-free chronological scale for the complete sample of Milky Way globulars. In this paper we describe the CARMA framework in detail, and present a first application on a sample of six metal-rich globular clusters with the aim of putting the final word on the debated origin of NGC6388 and NGC6441. Our results demonstrate that this pair of clusters is coeval with other four systems having a clear in-situ origin. Moreover, their location in the age-metallicity plane matches the one occupied by in-situ field stars. Such an accurate age comparison enabled by the CARMA methodology rules out the possibility that NGC6388 and NGC6441 have been accreted as part of a past merger event. △ Less

Submitted 2 October, 2023; originally announced October 2023.

Comments: 11 pages + Appendix, 13 figures, accepted for publication by A&A

Journal ref: A&A 680, A20 (2023)

Photometry and astrometry with JWST -- III. A NIRCam-Gaia DR3 analysis of the open cluster NGC 2506

Authors: D. Nardiello, L. R. Bedin, M. Griggio, M. Salaris, M. Scalco, S. Cassisi

Abstract: In the third paper of this series aimed at developing the tools for analysing resolved stellar populations using the cameras on board of the James Webb Space Telescope (JWST), we present a detailed multi-band study of the 2 Gyr Galactic open cluster NGC 2506. We employ public calibration data-sets collected in multiple filters to: (i) derive improved effective Point Spread Functions (ePSFs) for te… ▽ More In the third paper of this series aimed at developing the tools for analysing resolved stellar populations using the cameras on board of the James Webb Space Telescope (JWST), we present a detailed multi-band study of the 2 Gyr Galactic open cluster NGC 2506. We employ public calibration data-sets collected in multiple filters to: (i) derive improved effective Point Spread Functions (ePSFs) for ten NIRCam filters; (ii) extract high-precision photometry and astrometry for stars in the cluster, approaching the main-sequence (MS) lower mass of ~0.1 Msun; and (iii) take advantage of the synergy between JWST and Gaia DR3 to perform a comprehensive analysis of the cluster's global and local properties. We derived a MS binary fraction of ~57.5 %, extending the Gaia limit (~0.8 Msun) to lower masses (~0.4 Msun) with JWST. We conducted a study on the mass functions (MFs) of NGC 2506, mapping the mass segregation with Gaia data, and extending MFs to lower masses with the JWST field. We also combined information on the derived MFs to infer an estimate of the cluster present-day total mass. Lastly, we investigated the presence of white dwarfs (WDs) and identified a strong candidate. However, to firmly establish its cluster membership, as well as that of four other WD candidates and of the majority of faint low-mass MS stars, further JWST equally deep observations will be required. We make publicly available catalogues, atlases, and the improved ePSFs. △ Less

Submitted 21 August, 2023; originally announced August 2023.

Comments: 20 pages, 17 figures (5 in low resolution), 4 tables. Accepted for publication in MNRAS on August 5, 2023. PSF models, catalogs and stacked images are publicly available at https://web.oapd.inaf.it/bedin/files/PAPERs_eMATERIALs/JWST/Paper_03/

Roman Early-Definition Astrophysics Survey Opportunity: Galactic Roman Infrared Plane Survey (GRIPS)

Authors: Roberta Paladini, Catherine Zucker, Robert Benjamin, David Nataf, Dante Minniti, Gail Zasowski, Joshua Peek, Sean Carey, Lori Allen, Javier Alonso-Garcia, Joao Alves, Friederich Anders, Evangelie Athanassoula, Timothy C. Beers, Jonathan Bird, Joss Bland-Hwathorn, Anthony Brown, Sven Buder, Luca Casagrande, Andrew Casey, Santi Cassisi, Marcio Catelan, Ranga-Ram Chary, Andre-Nicolas Chene, David Ciardi , et al. (45 additional authors not shown)

Abstract: A wide-field near-infrared survey of the Galactic disk and bulge/bar(s) is supported by a large representation of the community of Galactic astronomers. The combination of sensitivity, angular resolution and large field of view make Roman uniquely able to study the crowded and highly extincted lines of sight in the Galactic plane. A ~1000 deg2 survey of the bulge and inner Galactic disk would yiel… ▽ More A wide-field near-infrared survey of the Galactic disk and bulge/bar(s) is supported by a large representation of the community of Galactic astronomers. The combination of sensitivity, angular resolution and large field of view make Roman uniquely able to study the crowded and highly extincted lines of sight in the Galactic plane. A ~1000 deg2 survey of the bulge and inner Galactic disk would yield an impressive dataset of ~120 billion sources and map the structure of our Galaxy. The effort would foster subsequent expansions in numerous dimensions (spatial, depth, wavelengths, epochs). Importantly, the survey would benefit from early defintion by the community, namely because the Galactic disk is a complex environment, and different science goals will require trade offs. △ Less

Submitted 14 July, 2023; originally announced July 2023.

Comments: Submitted to the Roman Project on October 22 2021 in response to a call for white papers on early-definition Astrophysics opportunity

Exploring the origin of the extended main sequence turn off in M37 through the white dwarf cooling sequence

Authors: M. Griggio, M. Salaris, D. Nardiello, L. R. Bedin, S. Cassisi, J. Anderson

Abstract: We use new observations from the Canada-France-Hawaii Telescope to study the white dwarf cooling sequence of the open cluster M37, a cluster that displays an extended main sequence turn-off and, according to a recent photometric analysis, also a spread of initial chemical composition. By taking advantage of a first epoch collected in 1999 with the same telescope, we have been able to calculate pro… ▽ More We use new observations from the Canada-France-Hawaii Telescope to study the white dwarf cooling sequence of the open cluster M37, a cluster that displays an extended main sequence turn-off and, according to a recent photometric analysis, also a spread of initial chemical composition. By taking advantage of a first epoch collected in 1999 with the same telescope, we have been able to calculate proper motions for sources as faint as g ~ 26 (about ~ 6 magnitudes fainter than the Gaia limit), allowing us to separate cluster members from field stars. This has enabled us to isolate a sample of the white dwarf population of M37, reaching the end of the cooling sequence (at g ~ 23.5). The here-derived atlas and calibrated catalogue of the sources in the field of view is publicly released as supplementary on-line material. Finally, we present an exhaustive comparison of the white dwarf luminosity function with theoretical models, which has allowed us to exclude the age-spread scenario as the main responsible for the extended turnoff seen in the cluster colour-magnitude-diagram. △ Less

Submitted 16 June, 2023; originally announced June 2023.

Comments: 10 pages, 13 figures. Accepted for publication in MNRAS on 2023, June 15

The broadening of the main sequence in the open cluster M38

Authors: M. Griggio, M. Salaris, L. R. Bedin, S. Cassisi

Abstract: Our recent multi-band photometric study of the colour width of the lower main sequence of the open cluster M37 has revealed the presence of a sizeable initial chemical composition spread in the cluster. If initial chemical composition spreads are common amongst open clusters, this would have major implications for cluster formation models and the foundation of the chemical tagging technique. Here… ▽ More Our recent multi-band photometric study of the colour width of the lower main sequence of the open cluster M37 has revealed the presence of a sizeable initial chemical composition spread in the cluster. If initial chemical composition spreads are common amongst open clusters, this would have major implications for cluster formation models and the foundation of the chemical tagging technique. Here we present a study of the unevolved main sequence of the open cluster M38, employing Gaia DR3 photometry and astrometry, together with newly acquired Sloan photometry. We have analysed the distribution of the cluster's lower main sequence stars with a differential colour-colour diagram made of combinations of Gaia and Sloan magnitudes, like in the study of M37. We employed synthetic stellar populations to reproduce the observed trend of M38 stars in this diagram, and found that the observed colour spreads can be explained simply by the combined effect of differential reddening across the face of the cluster and the presence of unresolved binaries. There is no need to include in the synthetic sample a spread of initial chemical composition as instead necessary to explain the main sequence of M37. Further photometric investigations like ours, as well as accurate differential spectroscopic analyses on large samples of open clusters, are necessary to understand whether chemical abundance spreads are common among the open cluster population. △ Less

Submitted 9 June, 2023; originally announced June 2023.

Comments: 8 pages, 10 figures. Accepted for publication in MNRAS on 2023, June 07

The "canonical" White Dwarf Cooling Sequence of M5

Authors: Jianxing Chen, Francesco R. Ferraro, Maurizio Salaris, Mario Cadelano, Barbara Lanzoni, Cristina Pallanca, Leandro G. Althaus, Santi Cassisi

Abstract: Recently, a new class of white dwarfs (dubbed ``slowly cooling WDs'') has been identified in two globular clusters (namely M13 and NGC 6752) showing a horizontal branch (HB) morphology with an extended blue tail. The cooling rate of these WDs is reduced by stable thermonuclear hydrogen burning in their residual envelope, and they are thought to be originated by stars that populate the blue tail of… ▽ More Recently, a new class of white dwarfs (dubbed ``slowly cooling WDs'') has been identified in two globular clusters (namely M13 and NGC 6752) showing a horizontal branch (HB) morphology with an extended blue tail. The cooling rate of these WDs is reduced by stable thermonuclear hydrogen burning in their residual envelope, and they are thought to be originated by stars that populate the blue tail of the HB and then skip the asymptotic giant branch phase. Consistently, no evidence of such kind of WDs has been found in M3, a similar cluster with no blue extension of the HB. To further explore this phenomenon, we took advantage of deep photometric data acquired with the Hubble Space Telescope in the near-ultraviolet and investigate the bright portion of the WD cooling sequence in M5, another Galactic globular cluster with HB morphology similar to M3. The normalized WD luminosity function derived in M5 turns out to be impressively similar to that observed in M3, in agreement with the fact that the stellar mass distribution along the HB of these two systems is almost identical. The comparison with theoretical predictions is consistent with the fact that the cooling sequence in this cluster is populated by canonical (fast cooling) WDs. Thus, the results presented in this paper provide further support to the scenario proposing a direct causal connection between the slow cooling WD phenomenon and the horizontal branch morphology of the host stellar cluster. △ Less

Submitted 28 April, 2023; originally announced April 2023.

Comments: 12 pages, 8 figures, accepted in the ApJ

The GeMS/GSAOI Galactic Globular Cluster Survey (G4CS) II: Characterization of 47 Tuc with Bayesian Statistics

Authors: Mirko Simunovic, Thomas H. Puzia, Bryan Miller, Eleazar R. Carrasco, Aaron Dotter, Santi Cassisi, Stephanie Monty, Peter Stetson

Abstract: We present a photometric analysis of globular cluster 47 Tuc (NGC\,104), using near-IR imaging data from the GeMS/GSAOI Galactic Globular Cluster Survey (G4CS) which is in operation at Gemini-South telescope.~Our survey is designed to obtain AO-assisted deep imaging with near diffraction-limited spatial resolution of the central fields of Milky Way globular clusters.~The G4CS near-IR photometry wa… ▽ More We present a photometric analysis of globular cluster 47 Tuc (NGC\,104), using near-IR imaging data from the GeMS/GSAOI Galactic Globular Cluster Survey (G4CS) which is in operation at Gemini-South telescope.~Our survey is designed to obtain AO-assisted deep imaging with near diffraction-limited spatial resolution of the central fields of Milky Way globular clusters.~The G4CS near-IR photometry was combined with an optical photometry catalog obtained from Hubble Space Telescope survey data to produce a high-quality color-magnitude diagram that reaches down to K$_s\approx$ 21 Vega mag.~We used the software suite BASE-9, which uses an adaptive Metropolis sampling algorithm to perform a Markov chain Monte Carlo (MCMC) Bayesian analysis, and obtained probability distributions and precise estimates for the age, distance and extinction cluster parameters.~Our best estimate for the age of 47 Tuc is 12.42$^{+0.05}_{-0.05}$ $\pm$ 0.08 Gyr, and our true distance modulus estimate is (m$-$M)$_0$=13.250$^{+0.003}_{-0.003}$ $\pm$ 0.028 mag, in tight agreement with previous studies using Gaia DR2 parallax and detached eclipsing binaries. △ Less

Submitted 25 April, 2023; v1 submitted 21 April, 2023; originally announced April 2023.

Comments: 25 pages, 15 figures. Accepted for publication in The Astrophysical Journal

Globular Cluster UVIT Legacy Survey (GlobULeS) $-$ II. Evolutionary status of hot stars in M3 and M13

Authors: Ranjan Kumar, Ananta C. Pradhan, Snehalata Sahu, Annapurni Subramaniam, Sonika Piridi, Santi Cassisi, Devendra K. Ojha

Abstract: We present a far-ultraviolet (FUV) study of hot stellar populations in the second parameter pair globular clusters (GCs) M3 and M13, as a part of the Globular cluster UVIT Legacy Survey program (GlobULeS). We use observations made with F148W and F169M filters of the Ultraviolet Imaging Telescope (UVIT) onboard {\em AstroSat} along with ground-based data (UBVRI filters), {\em Hubble Space Telescope… ▽ More We present a far-ultraviolet (FUV) study of hot stellar populations in the second parameter pair globular clusters (GCs) M3 and M13, as a part of the Globular cluster UVIT Legacy Survey program (GlobULeS). We use observations made with F148W and F169M filters of the Ultraviolet Imaging Telescope (UVIT) onboard {\em AstroSat} along with ground-based data (UBVRI filters), {\em Hubble Space Telescope (HST)} GC catalogue, and {\em Gaia} EDR3 catalogue. Based on the FUV-optical colour-magnitude diagrams, we classify the sources into the horizontal branch (HB) stars, post-HB stars, and hot white dwarfs (WDs) in both the GCs. The comparison of synthetic and observed colours of the observed HB stars suggests that the mass-loss at the red giant branch (RGB) and He spread in both clusters have a simultaneous effect on the different HB distributions detected in M3 and M13, such that, HB stars of M13 require a larger spread in He (${\rm 0.247-0.310}$) than those of M3 (${\rm Y= 0.252-0.266}$). The evolutionary status of HB stars, post-HB stars, and WDs are studied using SED fit parameters and theoretical evolutionary tracks on the H-R diagram. We found that the observed post-HB stars have evolved from zero-age HB (ZAHB) stars of the mass range $0.48-0.55$ \Msun\ in M3 and M13. We detect 24 WD candidates in each cluster having ${\rm \log(L_{bol}/L_\odot)}$ in the range $-0.8$ to $+0.6$ and ${\rm \log(T_{eff}/K)}$ in the range of 4.2 to 5.0. Placing the WDs on the H-R diagram and comparing them with models suggest that M13 has a population of low-mass WDs, probably originating from binary evolution. △ Less

Submitted 3 April, 2023; originally announced April 2023.

Comments: Accepted for publication in MNRAS main journal

Journal ref: 2023, Monthly Notices of the Royal Astronomical Society

The Hubble Space Telescope UV Legacy Survey of Galactic Globular Clusters. XXIV. Differences in internal kinematics of multiple stellar populations

Authors: M. Libralato, E. Vesperini, A. Bellini, A. P. Milone, R. P. van der Marel, G. Piotto, J. Anderson, A. Aparicio, B. Barbuy, L. R. Bedin, T. M. Brown, S. Cassisi, D. Nardiello, A. Sarajedini, M. Scalco

Abstract: Our understanding of the kinematic properties of multiple stellar populations (mPOPs) in Galactic globular clusters (GCs) is still limited compared to what we know about their chemical and photometric characteristics. Such limitation arises from the lack of a comprehensive observational investigation of this topic. Here we present the first homogeneous kinematic analysis of mPOPs in 56 GCs based o… ▽ More Our understanding of the kinematic properties of multiple stellar populations (mPOPs) in Galactic globular clusters (GCs) is still limited compared to what we know about their chemical and photometric characteristics. Such limitation arises from the lack of a comprehensive observational investigation of this topic. Here we present the first homogeneous kinematic analysis of mPOPs in 56 GCs based on high-precision proper motions computed with Hubble Space Telescope data. We focused on red-giant-branch stars, for which the mPOP tagging is clearer, and measured the velocity dispersion of stars belonging to first (1G) and second generations (2G). We find that 1G stars are generally kinematically isotropic even at the half-light radius, whereas 2G stars are isotropic at the center and become radially anisotropic before the half-light radius. The radial anisotropy is induced by a lower tangential velocity dispersion of 2G stars with respect to the 1G population, while the radial component of the motion is comparable. We also show possible evidence that the kinematic properties of mPOPs are affected by the Galactic tidal field, corroborating previous observational and theoretical results suggesting a relation between the strength of the external tidal field and some properties of mPOPs. Although limited to the GCs' central regions, our analysis leads to new insights into the mPOP phenomenon, and provides the motivation for future observational studies of the internal kinematics of mPOPs. △ Less

Submitted 12 January, 2023; v1 submitted 10 January, 2023; originally announced January 2023.

Comments: 10 pages, 4 figures, 2 tables. Accepted for publication on ApJ

CUBES: a UV spectrograph for the future

Authors: S. Covino, S. Cristiani, J. M. Alcala', S. H. P. Alencar, S. A. Balashev, B. Barbuy, N. Bastian, U. Battino, L. Bissell, P. Bristow, A. Calcines, G. Calderone, P. Cambianica, R. Carini, B. Carter, S. Cassisi, B. V. Castilho, G. Cescutti, N. Christlieb, R. Cirami, R. Conzelmann, I. Coretti, R. Cooke, G. Cremonese, K. Cunha , et al. (64 additional authors not shown)

Abstract: In spite of the advent of extremely large telescopes in the UV/optical/NIR range, the current generation of 8-10m facilities is likely to remain competitive at ground-UV wavelengths for the foreseeable future. The Cassegrain U-Band Efficient Spectrograph (CUBES) has been designed to provide high-efficiency (>40%) observations in the near UV (305-400 nm requirement, 300-420 nm goal) at a spectral r… ▽ More In spite of the advent of extremely large telescopes in the UV/optical/NIR range, the current generation of 8-10m facilities is likely to remain competitive at ground-UV wavelengths for the foreseeable future. The Cassegrain U-Band Efficient Spectrograph (CUBES) has been designed to provide high-efficiency (>40%) observations in the near UV (305-400 nm requirement, 300-420 nm goal) at a spectral resolving power of R>20,000, although a lower-resolution, sky-limited mode of R ~ 7,000 is also planned. CUBES will offer new possibilities in many fields of astrophysics, providing access to key lines of stellar spectra: a tremendous diversity of iron-peak and heavy elements, lighter elements (in particular Beryllium) and light-element molecules (CO, CN, OH), as well as Balmer lines and the Balmer jump (particularly important for young stellar objects). The UV range is also critical in extragalactic studies: the circumgalactic medium of distant galaxies, the contribution of different types of sources to the cosmic UV background, the measurement of H2 and primordial Deuterium in a regime of relatively transparent intergalactic medium, and follow-up of explosive transients. The CUBES project completed a Phase A conceptual design in June 2021 and has now entered the Phase B dedicated to detailed design and construction. First science operations are planned for 2028. In this paper, we briefly describe the CUBES project development and goals, the main science cases, the instrument design and the project organization and management. △ Less

Submitted 24 December, 2022; originally announced December 2022.

Comments: Proceedings for the HACK100 conference, Trieste, June 2022. arXiv admin note: substantial text overlap with arXiv:2208.01672

High-precision abundances of first population stars in NGC 2808: confirmation of a metallicity spread

Authors: C. Lardo, M. Salaris, S. Cassisi, N. Bastian, A. Mucciarelli, I. Cabrera-Ziri, E. Dalessandro

Abstract: Photometric investigations have revealed that Galactic globular clusters exhibit internal metallicity variations amongst the so-called first-population stars, until now considered to have a homogeneous initial chemical composition. This is not fully supported by the sparse spectroscopic evidence, which so far gives conflicting results. Here, we present a high-resolution re-analysis of five stars i… ▽ More Photometric investigations have revealed that Galactic globular clusters exhibit internal metallicity variations amongst the so-called first-population stars, until now considered to have a homogeneous initial chemical composition. This is not fully supported by the sparse spectroscopic evidence, which so far gives conflicting results. Here, we present a high-resolution re-analysis of five stars in the Galactic globular cluster NGC 2808 taken from the literature. Target stars are bright red giants with nearly identical atmospheric parameters belonging to the first population according to their identification in the chromosome map of the cluster, and we have measured precise differential abundances for Fe, Si, Ca, Ti, and Ni to the ~0.03 dex level. Thanks to the very small uncertainties associated to the differential atmospheric parameters and abundance measurements, we find that target stars span a range of iron abundance equal to 0.25 +/- 0.06 dex. The individual elemental abundances are highly correlated with the position of the star along the extended sequence described by first population objects in the cluster chromosome map: bluer stars have a lower iron content. This agrees with inferences from the photometric analysis. The differential abundances for all other elements also show statistically significant ranges that point to intrinsic abundance spreads. The Si, Ca, Ti, and Ni variations are highly correlated with iron variations and the total abundance spreads for all elements are consistent within the error bars. This suggests a scenario in which short-lived massive stars exploding as supernovae contributed to the self-enrichment of the gas in the natal cloud while star formation was still ongoing. △ Less

Submitted 24 October, 2022; originally announced October 2022.

Comments: 9 pages, 9 figures. Accepted for publication in A&A

Journal ref: A&A 669, A19 (2023)

Photometry and astrometry with JWST -- I. NIRCam Point Spread Functions and the first JWST colour-magnitude diagrams of a globular cluster

Authors: D. Nardiello, L. R. Bedin, A. Burgasser, M. Salaris, S. Cassisi, M. Griggio, M. Scalco

Abstract: As the James Webb Space Telescope (JWST) has become fully operational, early-release data are now available to begin building the tools and calibrations for precision point-source photometry and astrometry in crowded cluster environments. Here, we present our independent reduction of NIRCam imaging of the metal-poor globular cluster M92, which were collected under Director's Discretionary Early Re… ▽ More As the James Webb Space Telescope (JWST) has become fully operational, early-release data are now available to begin building the tools and calibrations for precision point-source photometry and astrometry in crowded cluster environments. Here, we present our independent reduction of NIRCam imaging of the metal-poor globular cluster M92, which were collected under Director's Discretionary Early Release Science programme ERS-1334. We derived empirical models of the Point Spread Function (PSF) for filters F090W, F150W, F277W, and F444W, and find that these PSFs: (i) are generally under-sampled (FWHM~2 pixel) in F150W and F444W and severely under-sampled (FWHM~1 pixel) in F090W and F277W; (ii) have significant variation across the field of view, up to ~15-20 %; and (iii) have temporal variations of ~3-4 % across multi-epoch exposures. We deployed our PSFs to determine the photometric precision of NIRCam for stars in the crowded, central regions of M92, measured to be at the ~0.01 mag level. We use these data to construct the first JWST colour-magnitude diagrams of a globular cluster. Employing existing stellar models, we find that the data reach almost the bottom of the M92 main sequence (~0.1 M$_{\odot}$), and reveal 24 white dwarf candidate members of M92 in the brightest portion of the white dwarf cooling sequence. The latter are confirmed through a cross-match with archival HST UV and optical data. We also detect the presence of multiple stellar populations along the low-mass main sequence of M92. △ Less

Submitted 14 September, 2022; originally announced September 2022.

Comments: 14 pages, 11 figures, 2 tables. Accepted for publication in MNRAS on September 13, 2022. PSF models, catalogs and stacked images are publicly available at https://web.oapd.inaf.it/bedin/files/PAPERs_eMATERIALs/JWST/Paper_01/

Signature of a chemical spread in the open cluster M37

Authors: M. Griggio, M. Salaris, S. Cassisi, A. Pietrinferni, L. R. Bedin

Abstract: Recent Gaia photometry of the open cluster M37 have disclosed the existence of an extended main-sequence turn off -- like in Magellanic clusters younger than about 2 Gyr -- and a main sequence that is broadened in colour beyond what is expected from the photometric errors, at magnitudes well below the region of the extended turn off, where neither age differences nor rotation rates (the candidates… ▽ More Recent Gaia photometry of the open cluster M37 have disclosed the existence of an extended main-sequence turn off -- like in Magellanic clusters younger than about 2 Gyr -- and a main sequence that is broadened in colour beyond what is expected from the photometric errors, at magnitudes well below the region of the extended turn off, where neither age differences nor rotation rates (the candidates to explain the extended turn off phenomenon) are expected to play a role. Moreover, not even the contribution of unresolved binaries can fully explain the observed broadening. We investigated the reasons behind this broadening by making use of synthetic stellar populations and differential colour-colour diagrams using a combination of Gaia and Sloan filters. From our analysis we have concluded that the observed colour spread in the Gaia colour-magnitude diagram can be reproduced by a combination of either a metallicity spread Delta[Fe/H] ~ 0.15 plus a differential reddening across the face of the cluster spanning a total range DeltaE (B - V) ~ 0.06, or a spread of the initial helium mass fraction DeltaY ~ 0.10 plus a smaller range of reddening DeltaE (B - V) ~ 0.03. High-resolution differential abundance determinations of a sizeable sample of cluster stars are necessary to confirm or exclude the presence of a metal abundance spread. Our results raise the possibility that also individual open clusters, like globular clusters and massive star clusters, host stars born with different initial chemical compositions. △ Less

Submitted 1 September, 2022; originally announced September 2022.

Comments: 10 pages, 10 figures. Accepted for publication in MNRAS on 2022, August 31, manuscript ID. MN-22-2637-MJ

The CUBES Science Case

Authors: Chris Evans, Stefano Cristiani, Cyrielle Opitom, Gabriele Cescutti, Valentina D'Odorico, Juan Manuel Alcalá, Silvia H. P. Alencar, Sergei Balashev, Beatriz Barbuy, Nate Bastian, Umberto Battino, Pamela Cambianica, Roberta Carini, Brad Carter, Santi Cassisi, Bruno Vaz Castilho, Norbert Christlieb, Ryan Cooke, Stefano Covino, Gabriele Cremonese, Katia Cunha, André R. da Silva, Valerio D'Elia, Annalisa De Cia, Gayandhi De Silva , et al. (29 additional authors not shown)

Abstract: We introduce the scientific motivations for the development of the Cassegrain U-Band Efficient Spectrograph (CUBES) that is now in construction for the Very Large Telescope. The assembled cases span a broad range of contemporary topics across Solar System, Galactic and extragalactic astronomy, where observations are limited by the performance of current ground-based spectrographs shortwards of 400… ▽ More We introduce the scientific motivations for the development of the Cassegrain U-Band Efficient Spectrograph (CUBES) that is now in construction for the Very Large Telescope. The assembled cases span a broad range of contemporary topics across Solar System, Galactic and extragalactic astronomy, where observations are limited by the performance of current ground-based spectrographs shortwards of 400nm. A brief background to each case is presented and specific technical requirements on the instrument design that flow-down from each case are identified. These were used as inputs to the CUBES design, that will provide a factor of ten gain in efficiency for astronomical spectroscopy over 300-405nm, at resolving powers of R~24,000 and ~7,000. We include performance estimates that demonstrate the ability of CUBES to observe sources that are up to three magnitudes fainter than currently possible at ground-ultraviolet wavelengths, and we place its predicted performance in the context of existing facillities. △ Less

Submitted 30 September, 2022; v1 submitted 2 August, 2022; originally announced August 2022.

Comments: Accepted for publication in Experimental Astronomy

CUBES, the Cassegrain U-Band Efficient Spectrograph

Authors: S. Cristiani, J. M. Alcalá, S. H. P. Alencar, S. A. Balashev, N. Bastian, B. Barbuy, U. Battino, A. Calcines, G. Calderone, P. Cambianica, R. Carini, B. Carter, S. Cassisi, B. V. Castilho, G. Cescutti, N. Christlieb, R. Cirami, I. Coretti, R. Cooke, S. Covino, G. Cremonese, K. Cunha, G. Cupani, A. R. da Silva, V. De Caprio , et al. (52 additional authors not shown)

Abstract: In the era of Extremely Large Telescopes, the current generation of 8-10m facilities are likely to remain competitive at ground-UV wavelengths for the foreseeable future. The Cassegrain U-Band Efficient Spectrograph (CUBES) has been designed to provide high-efficiency (>40%) observations in the near UV (305-400 nm requirement, 300-420 nm goal) at a spectral resolving power of R>20,000 (with a lowe… ▽ More In the era of Extremely Large Telescopes, the current generation of 8-10m facilities are likely to remain competitive at ground-UV wavelengths for the foreseeable future. The Cassegrain U-Band Efficient Spectrograph (CUBES) has been designed to provide high-efficiency (>40%) observations in the near UV (305-400 nm requirement, 300-420 nm goal) at a spectral resolving power of R>20,000 (with a lower-resolution, sky-limited mode of R ~ 7,000). With the design focusing on maximizing the instrument throughput (ensuring a Signal to Noise Ratio (SNR) ~20 per high-resolution element at 313 nm for U ~18.5 mag objects in 1h of observations), it will offer new possibilities in many fields of astrophysics, providing access to key lines of stellar spectra: a tremendous diversity of iron-peak and heavy elements, lighter elements (in particular Beryllium) and light-element molecules (CO, CN, OH), as well as Balmer lines and the Balmer jump (particularly important for young stellar objects). The UV range is also critical in extragalactic studies: the circumgalactic medium of distant galaxies, the contribution of different types of sources to the cosmic UV background, the measurement of H2 and primordial Deuterium in a regime of relatively transparent intergalactic medium, and follow-up of explosive transients. The CUBES project completed a Phase A conceptual design in June 2021 and has now entered the detailed design and construction phase. First science operations are planned for 2028. △ Less

Submitted 2 August, 2022; originally announced August 2022.

Comments: SPIE proceedings, SPIE Astronomical Telescopes + Instrumentation 2022, Montréal, Canada; 20 pages, 13 figures, 2 tables

Astro-photometric study of M37 with Gaia and wide-field ugi-imaging

Authors: M. Griggio, L. R. Bedin, R. Raddi, N. Reindl, L. Tomasella, M. Scalco, M. Salaris, S. Cassisi, P. Ochner, S. Ciroi, P. Rosati, D. Nardiello, J. Anderson, M. Libralato, A. Bellini, A. Vallenari, L. Spina, M. Pedani

Abstract: We present an astrometric and photometric wide-field study of the Galactic open star cluster M37 (NGC 2099). The studied field was observed with ground-based images covering a region of about four square degrees in the Sloan-like filters ugi. We exploited the Gaia catalogue to calibrate the geometric distortion of the large field mosaics, developing software routines that can be also applied to ot… ▽ More We present an astrometric and photometric wide-field study of the Galactic open star cluster M37 (NGC 2099). The studied field was observed with ground-based images covering a region of about four square degrees in the Sloan-like filters ugi. We exploited the Gaia catalogue to calibrate the geometric distortion of the large field mosaics, developing software routines that can be also applied to other wide-field instruments. The data are used to identify the hottest white dwarf (WD) member candidates of M37. Thanks to the Gaia EDR3 exquisite astrometry we identified seven such WD candidates, one of which, besides being a high-probability astrometric member, is the putative central star of a planetary nebula. To our knowledge, this is a unique object in an open cluster, and we have obtained follow-up low-resolution spectra that are used for a qualitative characterisation of this young WD. Finally, we publicly release a three-colour atlas and a catalogue of the sources in the field of view, which represents a complement of existing material. △ Less

Submitted 7 July, 2022; originally announced July 2022.

Comments: 13 pages, 4 table, 13 figures. Accepted for publication in MNRAS on 2022, July 6, manuscript ID. MN-22-2264-MJ

Slowly cooling white dwarfs in NGC 6752

Authors: J. Chen, F. R. Ferraro, M. Cadelano, M. Salaris, B. Lanzoni, C. Pallanca, L. G. Althaus, S. Cassisi, E. Dalessandro

Abstract: Recently, a new class of white dwarfs (``slowly cooling WDs'') has been identified in the globular cluster M13. The cooling time of these stars is increased by stable thermonuclear hydrogen burning in their residual envelope. These WDs are thought to be originated by horizontal branch (HB) stars populating the HB blue tail, which skipped the asymptotic giant branch phase. To further explore this p… ▽ More Recently, a new class of white dwarfs (``slowly cooling WDs'') has been identified in the globular cluster M13. The cooling time of these stars is increased by stable thermonuclear hydrogen burning in their residual envelope. These WDs are thought to be originated by horizontal branch (HB) stars populating the HB blue tail, which skipped the asymptotic giant branch phase. To further explore this phenomenon, we took advantage of deep photometric data acquired with the Hubble Space Telescope in the near-ultraviolet and investigate the bright portion of the WD cooling sequence in NGC 6752, another Galactic globular cluster with metallicity, age and HB morphology similar to M13. The normalized WD luminosity function derived in NGC 6752 turns out to be impressively similar to that observed in M13, in agreement with the fact that the stellar mass distribution along the HB of these two systems is almost identical. As in the case of M13, the comparison with theoretical predictions is consistent with $\sim 70\%$ of the investigated WDs evolving at slower rates than standard, purely cooling WDs. Thanks to its relatively short distance from Earth, NGC 6752 photometry reaches a luminosity one order of a magnitude fainter than the case of M13, allowing us to sample a regime where the cooling time delay, with respect to standard WD models, reaches $\sim 300$ Myr. The results presented in this paper provide new evidence for the existence of slowly cooling WDs and further support to the scenario proposing a direct causal connection between this phenomenon and the horizontal branch morphology of the host stellar cluster. △ Less

Submitted 20 June, 2022; originally announced June 2022.

Comments: 14 pages, 9 figures, accepted for publication in ApJ

The Hubble Space Telescope UV Legacy Survey of Galactic Globular Clusters. XXIII. Proper-motion catalogs and internal kinematics

Authors: M. Libralato, A. Bellini, E. Vesperini, G. Piotto, A. P. Milone, R. P. van der Marel, J. Anderson, A. Aparicio, B. Barbuy, L. R. Bedin, L. Borsato, S. Cassisi, E. Dalessandro, F. R. Ferraro, I. R. King, B. Lanzoni, D. Nardiello, S. Ortolani, A. Sarajedini, S. T. Sohn

Abstract: A number of studies based on data collected by the $\textit{Hubble Space Telescope}$ ($\textit{HST}$) GO-13297 program "HST Legacy Survey of Galactic Globular Clusters: Shedding UV Light on Their Populations and Formation" have investigated the photometric properties of a large sample of Galactic globular clusters and revolutionized our understanding of their stellar populations. In this paper, we… ▽ More A number of studies based on data collected by the $\textit{Hubble Space Telescope}$ ($\textit{HST}$) GO-13297 program "HST Legacy Survey of Galactic Globular Clusters: Shedding UV Light on Their Populations and Formation" have investigated the photometric properties of a large sample of Galactic globular clusters and revolutionized our understanding of their stellar populations. In this paper, we expand previous studies by focusing our attention on the stellar clusters' internal kinematics. We computed proper motions for stars in 56 globular and one open clusters by combining the GO-13297 images with archival $\textit{HST}$ data. The astro-photometric catalogs released with this paper represent the most complete and homogeneous collection of proper motions of stars in the cores of stellar clusters to date, and expand the information provided by the current (and future) $\textit{Gaia}$ data releases to much fainter stars and into the crowded central regions. We also census the general kinematic properties of stellar clusters by computing the velocity-dispersion and anisotropy radial profiles of their bright members. We study the dependence on concentration and relaxation time, and derive dynamical distances. Finally, we present an in-depth kinematic analysis of the globular cluster NGC 5904. △ Less

Submitted 5 July, 2022; v1 submitted 20 June, 2022; originally announced June 2022.

Comments: 33 pages, 19 figures, 6 tables. Accepted for publication on ApJ. Astro-photometric catalogs, velocity-dispersion values and profiles are available at https://archive.stsci.edu/hlsp/hacks

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

Authors: O. L. Creevey, R. Sordo, F. Pailler, Y. Frémat, U. Heiter, F. Thévenin, R. Andrae, M. Fouesneau, A. Lobel, C. A. L. Bailer-Jones, D. Garabato, I. Bellas-Velidis, E. Brugaletta, A. Lorca, C. Ordenovic, P. A. Palicio, L. M. Sarro, L. Delchambre, R. Drimmel, J. Rybizki, G. Torralba Elipe, A. J. Korn, A. Recio-Blanco, M. S. Schultheis, F. De Angeli , et al. (64 additional authors not shown)

Abstract: 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… ▽ More 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. △ Less

Submitted 12 June, 2022; originally announced June 2022.

Comments: 35 pages (incl 7 pages references, appendix, affiliations, acknowledgements), 29 figures, A&A, accepted

Journal ref: A&A 674, A26 (2023)