arXiv subjects

E. Dalessandro

Publications and source records attributed to E. Dalessandro.

At least 37 records · Page 2Linked to original sources

arXiv2025

Tracing the W3/W4/W5 and Perseus complex dynamical evolution with star clusters

The Perseus complex offers an ideal testbed to study cluster formation and early evolution as it hosts two major hierarchical structures (namely LISCA I and LISCA II) and the W3/W4/W5 (W345) region characterized by recent star formation. This work aims to provide a full characterization of the population of star clusters in the W345 region, in terms of their structural, photometric, and kinematic properties. Clusters are then used to probe the dynamical properties of the W345 region and, on a larger scale, to investigate the evolution of the Perseus complex. We used Gaia DR3 data to search for star clusters in the W345 region and characterize them in terms of their density structure, ellipticity, internal dynamical state, and ages. We identified five stellar clusters belonging to the W345 complex. The three younger clusters are still partially embedded in the gas and show evidence of expansion, while the older ones cleared the surrounding gas. We also found that YSOs trace the parent gas structure and possibly its kinematics. Thanks to the 6D information available for star clusters, we followed their orbital evolution to assess the formation conditions and evolution of the complex. When accounting for the Galactic potential, we find that the Perseus complex is not dispersing. The observed expansion might be a projection effect due to stars orbiting the Galaxy at different velocities. In addition, we find that the LISCA I and W345 systems formed some $20-30$ Myr ago just a few hundred parsecs away, while LISCA II was originally $\simeq 0.75-1$ kpc apart. Finally, we also assessed the impact of spiral arm perturbations by constructing tailored Galactic potential which matches the observed Galactic spiral arm structure. We find spiral structures drag star clusters toward higher-density regions, possibly keeping clusters closer for longer than the unperturbed, axisymmetric case.

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arXiv2025

On the manifest link between Terzan 5 and the Galactic bulge

We address the chemical link between Terzan 5 (hereafter Ter5) and the Bulge, as probed by the observed distributions of [$α$/Fe] abundance ratios with varying [Fe/H] and by suitable statistical tests to evaluate their significance. We also present a comprehensive review of the kinematic and evolutionary properties of Ter5, based on all the available observational signatures and the scenarios proposed so far in the literature for the formation and evolution of Ter5, based on these observational facts and the recent modeling of its star formation and chemical enrichment history. This analysis confirms the complex nature of this massive stellar system, with robust evidences of a bulge in-situ formation and of a subsequent evolution that cannot be simply explained by a single merging/accretion event of two globulars or a globular and a giant molecular cloud, as proposed in the literature, but it requires a more complex star formation likely accompanied by some self-enrichment.

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arXiv2025

The Bulge Cluster Origin (BulCO) survey at the ESO-VLT: probing the early history of the Milky Way assembling. Design and first results in Liller1

We present the scientific goals and the very first results of the Bulge Cluster Origin (BulCO) survey. This survey has been specifically designed to perform an unprecedented chemical screening of stellar systems orbiting the Milky Way bulge, with the aim to unveil their true origin. It takes advantage of the improved performances of the spectrograph CRIRES+ operating at the ESO Very Large telescope, in the near-infrared domain. Due to the complex evolutionary history of the Milky Way, a variety of relics tracing different phenomena is expected to populate the Bulge: globular clusters formed in-situ or accreted from outside the Galaxy, nuclear star clusters of cannibalized structures, and possibly a few remnants of the proto-bulge formation process (the so-called ``bulge fossil fragments"). The signatures of the different origins are imprinted in the chemical properties of these stellar systems because specific abundance patterns provide authentic "chemical DNA" tests univocally tracing the enrichment process and, therefore, the environment where the stellar population formed. Thus, each system can provide a new piece of information on the bulge formation and evolutionary history. As first results of the survey, here we discuss the alpha-element and iron abundances of a sample of stars observed in the stellar system Liller 1, which is proposed to be a bulge fossil fragment. By combining this dataset with a recently published sample of high/mid-resolution spectra, we discuss the overall chemical properties of the stellar populations in Liller1, proving its link with the Galactic bulge and providing new constraints on its star formation history.

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arXiv2024

Euclid: High-precision imaging astrometry and photometry from Early Release Observations. I. Internal kinematics of NGC 6397 by combining Euclid and Gaia data

The instruments at the focus of the Euclid space observatory offer superb, diffraction-limited imaging over an unprecedented (from space) wide field of view of 0.57 deg$^2$. This exquisite image quality has the potential to produce high-precision astrometry for point sources once the undersampling of Euclid's cameras is taken into account by means of accurate, effective point spread function (ePSF) modelling. We present a complex, detailed workflow to simultaneously solve for the geometric distortion (GD) and model the undersampled ePSFs of the Euclid detectors. Our procedure was successfully developed and tested with data from the Early Release Observations (ERO) programme focused on the nearby globular cluster NGC 6397. Our final one-dimensional astrometric precision for a well-measured star just below saturation is 0.7 mas (0.007 pixel) for the Visible Instrument (VIS) and 3 mas (0.01 pixel) for the Near-Infrared Spectrometer and Photometer (NISP). Finally, we present a specific scientific application of this high-precision astrometry: the combination of Euclid and Gaia data to compute proper motions and study the internal kinematics of NGC 6397. Future work, when more data become available, will allow for a better characterisation of the ePSFs and GD corrections that are derived here, along with assessment of their temporal stability, and their dependencies on the spectral energy distribution of the sources as seen through the wide-band filters of Euclid.

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arXiv2024

A 3D view of multiple populations kinematics in Galactic globular clusters

We present the first 3D kinematic analysis of multiple stellar populations (MPs) in a representative sample of 16 Galactic globular clusters (GCs). For each GC in the sample we studied the MP line-of-sight, plane-of-the-sky and 3D rotation as well as the velocity distribution anisotropy. The differences between first- (FP) and second-population (SP) kinematic patterns were constrained by means of parameters specifically defined to provide a global measure of the relevant physical quantities and to enable a meaningful comparison among different clusters. Our analysis provides the first observational description of the MP kinematic properties and of the path they follow during the long-term dynamical evolution. In particular, we find evidence of differences between the rotation of MPs along all velocity components with the SP preferentially rotating faster than the FP. The difference between the rotation strength of MPs is anti-correlated with the cluster dynamical age. We observe also that FPs are characterized by isotropic velocity distributions at any dynamical age probed by our sample. On the contrary, the velocity distribution of SP stars is found to be radially anisotropic in dynamically young clusters and isotropic at later evolutionary stages. The comparison with a set of numerical simulations shows that these observational results are consistent with the long-term evolution of clusters forming with an initially more centrally concentrated and more rapidly rotating SP subsystem. We discuss the possible implications these findings have on our understanding of MP formation and early evolution.

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arXiv2024

Inference of black-hole mass fraction in Galactic globular clusters. A multi-dimensional approach to break the initial-condition degeneracies

Context. Globular clusters (GCs) are suggested to host many stellar-mass black holes (BHs) at their centers, thus resulting in ideal testbeds for BH formation and retention theories. BHs are expected to play a major role in GC structural and dynamical evolution and their study has attracted a lot of attention. In recent years, several works attempted to constrain the BH mass fraction in GCs typically by comparing a single observable (for example mass segregation proxies) with scaling relations obtained from numerical simulations. Aims. We aim to uncover the possible intrinsic degeneracies in determining the BH mass fraction from single dynamical parameters and identify the possible parameter combinations that are able to break these degeneracies. Methods. We used a set of 101 Monte Carlo simulations sampling a large grid of initial conditions. In particular, we explored the impact of different BH natal kick prescriptions on widely adopted scaling relations. We then compared the results of our simulations with observations obtained using state-of-the-art HST photometric and astrometric catalogs for a sample of 30 Galactic GCs. Results. We find that using a single observable to infer the present-day BH mass fraction in GCs is degenerate, as similar values could be attained by simulations including different BH mass fractions. We argue that the combination of mass-segregation indicators with GC velocity dispersion ratios could help us to break this degeneracy efficiently. We show that such a combination of parameters can be derived with currently available data. However, the limited sample of stars with accurate kinematic measures and its impact on the overall errors do not allow us to discern fully different scenarios yet.

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arXiv2024

Multi-iron subpopulations in Liller 1 from high resolution H-band spectroscopy

We present a high resolution chemical study of a representative sample of 21 luminous giant stars of Liller~1, a complex stellar system in the Galactic bulge, based on H band spectra acquired with the Near InfraRed Spectrograph at KeckII. 15 stars turn out to have a subsolar iron abundance and enhanced [$α$/Fe] and [Al/Fe], likely old that formed early and quickly from gas mainly enriched by type~II supernovae, and 6 stars with supersolar iron and roughly solar-scaled [$α$/Fe] and [Al/Fe], likely younger, thus formed at later epochs from gas also enriched by type~Ia supernovae. Moreover, both subpopulations show enhanced [N/Fe], as in the bulge field, about solar-scaled [V/Fe], and depletion of [C/Fe] and $^{12}$C/$^{13}$C with respect to the solar values, indicating the occurrence of significant mixing in the stellar interiors of these evolved stars. The current study has also made evident that the sub-solar subpopulation shows some structuring, and the presence of a third subcomponent with iron content and [$α$/Fe] enhancement somewhat intermediate between the metal-poor and metal-rich main subpopulations, has been statistically assessed, providing the chemical signature of an extended star formation with multiple bursts and of some self-enrichment.

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arXiv2024

Detailed chemical abundances of the globular cluster Terzan 6 in the inner bulge

We used near-infrared spectroscopy at medium-high resolution (R=8,000$-$25,000) to perform the first comprehensive chemical study of the intermediate luminosity bulge globular cluster Terzan~6. We derived detailed abundances and abundance patterns of 27 giant stars, likely members of Terzan~6, based on their accurate Hubble Space Telescope proper motions and line-of-sight radial velocities. From the spectral analysis of these stars, we determined an average heliocentric radial velocity of 143.3$\pm$1.0 km s$^{-1}$ with a velocity dispersion of 5.1$\pm$0.7 km s$^{-1}$ and an average [Fe/H]=$-0.65\pm0.01$ and a low 1$σ$ dispersion of 0.03 dex. We also measured some depletion of [Mn/Fe] with respect to the solar-scaled values and enhancement of for [Ca/Fe], [Si/Fe], [Mg/Fe], [Ti/Fe], [O/Fe], [Al/Fe], [Na/Fe], and, to a lower extent, for [K/Fe], consistent with previous measurements of other bulge globular clusters and favoring the scenario of a rapid bulge formation and chemical enrichment. Some spread in the light element abundances suggest the presence of first- and second-generation stars, typical of genuine globulars. Finally, we measured some depletion of carbon and low $\rm ^{12}C/^{13}C$ isotopic ratios, as in previous studies of field and cluster bulge giants, indicating that extra-mixing mechanisms should be at work during the post main sequence evolution in the high metallicity regime as well.

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arXiv2024

Euclid: Early Release Observations -- Unveiling the morphology of two Milky Way globular clusters out to their periphery

As part of the Euclid Early Release Observations (ERO) programme, we analyse deep, wide-field imaging from the VIS and NISP instruments of two Milky Way globular clusters (GCs), namely NGC 6254 (M10) and NGC 6397, to look for observational evidence of their dynamical interaction with the Milky Way. We search for such an interaction in the form of structural and morphological features in the clusters' outermost regions, which are suggestive of the development of tidal tails on scales larger than those sampled by the ERO programme. Our multi-band photometric analysis results in deep and well-behaved colour-magnitude diagrams that, in turn, enable an accurate membership selection. The surface brightness profiles built from these samples of member stars are the deepest ever obtained for these two Milky Way GCs, reaching down to $\sim30.0$ mag~arcsec$^{-2}$, which is about $1.5$ mag arcsec$^{-2}$ below the current limit. The investigation of the two-dimensional density map of NGC 6254 reveals an elongated morphology of the cluster peripheries in the direction and with the amplitude predicted by $N$-body simulations of the cluster's dynamical evolution, at high statistical significance. We interpret this as strong evidence for the first detection of tidally induced morphological distortion around this cluster. The density map of NGC 6397 reveals a slightly elliptical morphology, in agreement with previous studies, which requires further investigation on larger scales to be properly interpreted. This ERO project thus demonstrates the power of Euclid in studying the outer regions of GCs at an unprecedented level of detail, thanks to the combination of large field of view, high spatial resolution, and depth enabled by the telescope. Our results highlight the future Euclid survey as the ideal data set to investigate GC tidal tails and stellar streams.

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arXiv2024

Euclid: Early Release Observations -- Programme overview and pipeline for compact- and diffuse-emission photometry

The Euclid ERO showcase Euclid's capabilities in advance of its main mission, targeting 17 astronomical objects, from galaxy clusters, nearby galaxies, globular clusters, to star-forming regions. A total of 24 hours observing time was allocated in the early months of operation, engaging the scientific community through an early public data release. We describe the development of the ERO pipeline to create visually compelling images while simultaneously meeting the scientific demands within months of launch, leveraging a pragmatic, data-driven development strategy. The pipeline's key requirements are to preserve the image quality and to provide flux calibration and photometry for compact and extended sources. The pipeline's five pillars are: removal of instrumental signatures; astrometric calibration; photometric calibration; image stacking; and the production of science-ready catalogues for both the VIS and NISP instruments. We report a PSF with a full width at half maximum of 0.16" in the optical and 0.49" in the three NIR bands. Our VIS mean absolute flux calibration is accurate to about 1%, and 10% for NISP due to a limited calibration set; both instruments have considerable colour terms. The median depth is 25.3 and 23.2 AB mag with a SNR of 10 for galaxies, and 27.1 and 24.5 AB mag at an SNR of 5 for point sources for VIS and NISP, respectively. Euclid's ability to observe diffuse emission is exceptional due to its extended PSF nearly matching a pure diffraction halo, the best ever achieved by a wide-field, high-resolution imaging telescope. Euclid offers unparalleled capabilities for exploring the LSB Universe across all scales, also opening a new observational window in the NIR. Median surface-brightness levels of 29.9 and 28.3 AB mag per square arcsec are achieved for VIS and NISP, respectively, for detecting a 10 arcsec x 10 arcsec extended feature at the 1 sigma level.

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arXiv2024

X-shooter spectroscopy of Liller1 giant stars

We present the first comprehensive chemical study of a representative sample of 27 luminous red giant branch (RGB) stars belonging to Liller 1, a complex stellar system in the Galactic bulge. This study is based on medium-resolution near-infrared spectra acquired with X-shooter at the Very Large Telescope. We found a subpopulation counting 22 stars with subsolar metallicity ($<$[Fe/H]$>=-0.31\pm0.02$ and 1$σ$ dispersion of 0.08 dex) and with enhanced [$α$/Fe], [Al/Fe], and [K/Fe] that likely formed early and quickly from gas that was mainly enriched by type II supernovae, and a metal-rich population counting 5 stars with supersolar metallicity ($<$[Fe/H]$>$=+0.22$\pm$0.03 and 1$σ$ dispersion of 0.06 dex) and roughly solar-scaled [$α$/Fe], [Al/Fe], and [K/Fe] that formed at later epochs from gas that was also enriched by type Ia supernovae. Moreover, both subpopulations show enhanced [Na/Fe], as in the bulge field, about solar-scaled [V/Fe], and depletion of [C/Fe] and $^{12}$C/$^{13}$C with respect to the solar values. This indicates that mixing and extra-mixing processes during the RGB evolution also occur at very high metallicities. Notably, no evidence of a Na-O anticorrelation, which is considered the fingerprint of genuine globular clusters, has been found. This challenges any formation scenarios that invoke the accretion of a molecular cloud or an additional stellar system onto a genuine globular cluster. The results of this study underline the strong chemical similarity between Liller 1 and Terzan 5 and support the hypothesis that these complex stellar systems might be fossil fragments of the epoch of Galactic bulge formation.

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arXiv2023

Ongoing hierarchical massive cluster assembly: the LISCA II structure in the Perseus complex

We report on the identification of a massive ($\sim10^5$ M$_\odot$) sub-structured stellar system in the Galactic Perseus complex likely undergoing hierarchical cluster assembly. Such a system comprises nine star clusters (including the well-known clusters NGC 654 and NGC 663) and an extended and low-density stellar halo. Gaia-DR3 and available spectroscopic data show that all its components are physically consistent in the 6D phase-space (position, parallax, and 3D motion), homogeneous in age (14 $-$ 44 Myr), and chemical content (half-solar metallicity). In addition, the system's global stellar density distribution is that of typical star clusters and shows clear evidence of mass segregation. We find that the hierarchical structure is mostly contracting towards the center with a speed of up to $\simeq4-5$ km s$^{-1}$, while the innermost regions expand at a lower rate (about $\simeq1$ km s$^{-1}$) and are dominated by random motions. Interestingly, this pattern is dominated by the kinematics of massive stars, while low-mass stars ($M<2$ M$_\odot$) are characterized by contraction across the entire cluster. Finally, the nine star clusters in the system are all characterized by a relatively flat velocity dispersion profile possibly resulting from ongoing interactions and tidal heating. We show that the observational results are generally consistent with those found in $N$-body simulations following the cluster violent relaxation phase strongly suggesting that the system is a massive cluster in the early assembly stages. This is the second structure with these properties identified in our Galaxy and, following the nomenclature of our previous work, we named it LISCA II.

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arXiv2022

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

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.

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arXiv2022

Clues to the formation of Liller 1 from modeling its complex star formation history

Liller 1 and Terzan 5 are two massive systems in the Milky-Way bulge hosting populations characterized by significantly different ages ($Δt>7-8$ Gyr) and metallicities ($Δ$[Fe/H]$\sim1$ dex). Their origin is still strongly debated in the literature and all formation scenarios proposed so far require some level of fine-tuning. The detailed star formation histories (SFHs) of these systems may represent an important piece of information to assess their origin. Here we present the first attempt to perform such an analysis for Liller 1. The first key result we find is that Liller 1 has been forming stars over its entire lifetime. More specifically, three broad SF episodes are clearly detected: 1) a dominant one, occurred some 12-13 Gyr ago with a tail extending for up to $\sim3$ Gyr, 2) an intermediate burst, between 6 and 9 Gyr ago, 3) and a recent one, occurred between 1 and 3 Gyr ago. The old population contributes to about $70\%$ of the total stellar mass and the remaining fraction is almost equally split between the intermediate and young populations. If we take these results at a face value, they would suggest that this system unlikely formed through the merger between an old globular cluster and a Giant Molecular Cloud, as recently proposed. On the contrary, our findings provide further support to the idea that Liller 1 is the surviving relic of a massive primordial structure that contributed to the Galactic bulge formation, similarly to the giant clumps observed in star-forming high-redshift galaxies.

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arXiv2022

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

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.

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arXiv2022

Slowly cooling white dwarfs in NGC 6752

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.

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arXiv2022

Lithium detection in red supergiant stars of the Perseus complex

We present the first systematic study of lithium abundance in a chemically homogeneous sample of 27 red supergiants (RSGs) in the young Perseus complex. For these stars, accurate stellar parameters and detailed chemical abundances of iron and iron peak, CNO, alpha, light and neutron-capture elements have been already obtained by means of high resolution optical and near-infrared spectroscopy. The observed RSGs have half-solar metallicity, 10-30 Myr age, bolometric luminosities in the 10$^4$-10$^5$ L$_{\odot}$ range and likely mass progenitors in the 9-14 M$_{\odot}$ range. We detected the optical Li I doublet in eight out of the 27 observed K and M type RSGs, finding relatively low A(Li)$<$1.0 dex abundances, while for the remaining 19 RSGs upper limits of A(Li)$<$-0.2 dex have been set. Warmer and less luminous (i.e. likely less massive) as well as less mixed (i.e. with lower [C/N] and $^{12}$C/$^{13}$C depletion) RSGs with Li detection show somewhat higher Li abundances. In order to explain Li detection in $\sim$30\% of the observed RSGs, we speculate that some stochasticity and a scenario where Li was not completely destroyed in the convective atmospheres and/or a secondary production took place during the post-Main Sequence evolution, should be at work.

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arXiv2022

The ESO-VLT MIKiS survey reloaded: velocity dispersion profile and rotation curve of NGC 1904

We present an investigation of the internal kinematic properties of M79 (NGC 1904). Our study is based on radial velocity measurements obtained from the ESO-VLT Multi-Instrument Kinematic Survey (MIKiS) of Galactic globular clusters for more than 1700 individual stars distributed between $\sim 0.3^{\prime\prime}$ and $770^{\prime\prime}$ ($\sim14$ three-dimensional half-mass radii), from the center. Our analysis reveals the presence of ordered line-of-sight rotation with a rotation axis almost aligned along the East-West direction and a velocity peak of $1.5$ km s$^{-1}$ at $\sim 70^{\prime\prime}$ from the rotation axis. The velocity dispersion profile is well described by the same King model that best fits the projected density distribution, with a constant central plateau at $σ_0\sim 6$ km s$^{-1}$. To investigate the cluster rotation in the plane of the sky, we have analyzed the proper motions provided by the Gaia EDR3, finding a signature of rotation with a maximum amplitude of $\sim 2.0$ km s$^{-1}$ at $\sim 80^{\prime\prime}$ from the cluster center. Analyzing the three-dimensional velocity distribution, for a sub-sample of 130 stars, we confirm the presence of systemic rotation and find a rotation axis inclination angle of $37$° with respect to the line-of-sight. As a final result, the comparison of the observed rotation curves with the results of a representative N-body simulation of a rotating star cluster shows that the present-day kinematic properties of NGC 1904 are consistent with those of a dynamically old system that has lost a significant fraction of its initial angular momentum.

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