Elena Valenti

We present the largest and most homogeneous catalog of radial velocity (RV) measurements for field RR Lyrae (RRL) variables, based on both proprietary and publicly available spectroscopic data. The sample includes 17 563 RRLs pulsating in the fundamental mode (12 353 RRab), in the first overtone (5011 RRc), and in double-mode (199 RRd). The RV curve (RVC) templates for metallic and Balmer lines were used to derive RV amplitudes and V _γ velocities, defined as the RV of the stellar barycenter with respect to the Sun. The typical accuracy across the catalog is on average 3.8 km s ⁻¹ for well-sampled RVCs, 6.5 km s ⁻¹ for RVCs with 3–7 phase points and 11.3 km s ⁻¹ for RVCs with fewer than three phase points. The use of different spectroscopic diagnostics and RVC templates provides, within the errors, very similar V _γ velocities. We found that the metallicity dependence of RV amplitudes is vanishing for metallic lines, but becomes increasingly significant for H γ and H δ . Moreover, the scaling relations between photometric (V, G _BP , G, G _RP ) and RV amplitudes are linear for RRc and nonlinear for RRab variables, independently of the adopted diagnostic. This circumstantial evidence indicates that convection affects more luminosity than RV amplitudes when moving from the blue (hot) to the red (cool) edge of the instability strip. The spectroscopic Bailey diagram (RV amplitude versus period) shows a smooth transition and a reduced spread at a fixed period, when moving from metal-poor to metal-rich RRLs. Finally, we also found evidence that the metallicity distribution function of Blazhko RRLs is skewed toward the metal-intermediate and metal-rich regimes.

In this paper, we present the chemical screening of the complex stellar population discovered in the Bulge Fossil Fragment Liller 1. This study is part of the Bulge Cluster Origin (BulCO) survey based on a Large Program at the ESO-Very Large Telescope with the high-resolution spectrograph CRIRES+. The survey is aimed at performing an unprecedented chemical screening of 17 stellar systems orbiting the Milky Way bulge, with the ultimate goal of unveiling their origin and true nature. We measured precise chemical abundances of iron, CNO, iron-peak, α-elements, a few other light elements, and neutron-capture elements for a sample of 30 red giant branch stars, kinematic members of Liller 1. The presented analysis provides the high-resolution spectroscopic proof of the complex chemistry of this massive stellar system, with multimetallicity subpopulations of different ages that nicely fit into a self-enrichment scenario. We find no evidence for the Na–O anticorrelation associated with genuine globular clusters; rather, the overall abundance trends are similar to those seen in the bulge field and in Terzan 5, providing definitive evidence of an in situ formation of Liller 1 within the Galactic bulge.

The shape and kinematics of the metal-poor stellar component of the Galactic bulge are still poorly characterized, and, therefore, the origin of this component is not yet strongly constrained. RR Lyrae stars in the bulge have been reported to be associated with the spheroidal, relatively metal-poor component. They offer a way to trace this component with precise distances and therefore the possibility to calculate orbits and minimize contaminations. While a few studies of RR Lyrae spectra with medium and/or high resolution are now available, none target stars in the Galactic bulge. We present here a spectroscopic determination of Fe and α-element abundances for RR Lyrae stars in the Galactic bulge, with the main goal of providing a benchmark to calibrate other metallicity indicators, appropriate for this specific stellar population. We analyzed FLAMES/GIRAFEE spectra of 78 RR Lyrae stars (60 ab-type and 18 c-type). We applied a full-spectrum fitting technique to obtain the spectroscopic metallicity and overall α-element abundance. Distances were derived by means of a period-luminosity-metallicity relation, and orbits were computed by combining the radial velocities derived in our study with the proper motions from DR3. Gaia The resulting metallicities peak at ̊m Fe/H _ median = -1.34 ± 0.04 and -1.44 ± 0.08 dex for ab and c-types, respectively. The majority of the bulge RR Lyrae are metal-poor stars with relatively high α-element abundances around ̊m α/Fe ± 0.03 dex. We used our spectroscopic measurements to test different methods for deriving metallicities based on photometry, which utilize Fourier parameters in the light curves of the RR Lyrae. The data suggest a possible correlation between the metallicity difference and the α/Fe ratio, which requires further investigation. There are some ab-type RR Lyrae that show metallicities higher than -1 dex and low ̊m α/Fe values. We kinematically studied these stars and find a difference between three stars with similar α/Fe values and the main group, indicating that they may be slightly younger and correspond to the disk population.

The nuclear bulge of the Milky Way harbors stellar populations that provide crucial insights into galaxy formation processes and serve as a nearby analog for understanding bulge formation in external galaxies. However, detailed studies of this region are severely hampered by extreme and highly variable interstellar extinction, which obscures the intrinsic stellar properties and impedes accurate stellar mass determinations. Our goal is to measure the extinction law toward the nuclear bulge and to estimate its stellar density. We developed a method for determining the extinction law toward the nuclear bulge by kinematically selecting red clump stars that belong to this region. We created a reddening map with a high spatial resolution and computed stellar mass with completeness-corrected red clump star counts, scaled from empirical measurements. We find a total-to-selective extinction ratio of mathrm A_K/ E_ H-K = 1.259 ± 0.074 and an extinction ratio of = 1.794 ± 0.046, which are consistent with previous works. The reddending map with the high spatial resolution shows clear filamentary structures and a gradient in the extinction over the giant molecular cloud G0.253+0.016 (i.e., the Brick). From the star counts, we measured a stellar mass of M_⊙ for the nuclear bulge, in agreement with other mass estimates.

In this paper, we present the chemical screening of the stellar population belonging to the globular cluster NGC 6553 in the Galactic bulge. This study has been conducted in the contest of the Bulge Cluster Origin (BulCO) survey, an ESO-VLT Large Program that is currently ongoing with CRIRES in the near-infrared (NIR) domain. This survey is performing an unprecedented chemical screening of 17 stellar systems orbiting the Milky Way bulge, with the aim of unveiling their origin and true nature. Here we present and discuss the abundances of 18 elements produced via distinct nucleosynthetic channels for 14 red giant branch stars belonging to NGC 6553. We found a mean [Fe/H] = −0.20 ± 0.01 deX, and about solar-scaled iron-peak elements, confirming that this is one of the most metal-rich globular clusters in the Milky Way. We also found [X/Fe] enhancement of α and several other light elements. Furthermore, we assessed the presence of multiple populations typical of genuine globular clusters from the significant spreads in Na, N, and C, along with an almost vertical Na-O anticorrelation. Finally, by using classical ([α/Fe] versus [Fe/H]) and newly-defined ([V/Fe] and [Zn/Fe] versus [Fe/H]) “chemical DNA tests”, we have proven its in situ formation within the Galactic bulge.

The James Webb Space Telescope (JWST) provides an exciting opportunity to investigate stellar systems located in heavily obscured regions such as the Galactic bulge. Possibly the most enigmatic among them is Terzan 5; long classified as a globular cluster, it is now known to host distinct stellar populations with different iron abundances (ranging from approximately [Fe/H]=-0.8 to [Fe/H]=+0.3 dex). Indeed, the chemical and structural properties collected so far suggest that it is the remnant of one of the primordial clumps that contributed to the early assembly of the bulge, a so-called “Bulge Fossil Fragment.” Here we present a new photometric analysis of Terzan 5 based on JWST/NIRCam observations in the F115W and F200W filters, as well as archival HST/ACS optical (F606W and F814W) data. The dataset overcomes the severe and spatially variable extinction along the line of sight and yields the deepest color-magnitude diagram ever obtained for Terzan 5. Proper motion selections and high-resolution differential reddening corrections allowed us to isolate bona fide cluster members and to provide an unprecedented view of the main-sequence turn-off region. We clearly identify two main components and determine their respective ages: the old, sub-solar component has an age of 12.5 ± 0.5 Gyr, while the super-solar component is significantly younger with an age of 4.7 ± 0.5 Gyr. Interestingly, we also find hints of an even younger main sequence turn-off and sub-giant branch, consistent with the presence of a further stellar component with an age of 3.8 ± 0.5 Gyr. There is also evidence of a blue plume populated by stars as bright as m _F115W ~ 17.4, suggesting a prolonged period of star formation extending up to 2.5 Gyr ago.

Einstein Telescope (ET) is the European project for a gravitational-wave (GW) observatory of third-generation. In this paper we present a comprehensive discussion of its science objectives, providing state-of-the-art predictions for the capabilities of ET in both geometries currently under consideration, a single-site triangular configuration or two L-shaped detectors. We discuss the impact that ET will have on domains as broad and diverse as fundamental physics, cosmology, early Universe, astrophysics of compact objects, physics of matter in extreme conditions, and dynamics of stellar collapse. We discuss how the study of extreme astrophysical events will be enhanced by multi-messenger observations. We highlight the ET synergies with ground-based and space-borne GW observatories, including multi-band investigations of the same sources, improved parameter estimation, and complementary information on astrophysical or cosmological mechanisms obtained combining observations from different frequency bands. We present advancements in waveform modeling dedicated to third-generation observatories, along with open tools developed within the ET Collaboration for assessing the scientific potentials of different detector configurations. We finally discuss the data analysis challenges posed by third-generation observatories, which will enable access to large populations of sources and provide unprecedented precision.

We introduce a new photometric catalog of RR Lyrae (RRL) variables (∼300,000) mainly based on data available in public datasets. We also present the largest and most homogeneous spectroscopic dataset of RRLs and blue horizontal branch (BHB) stars ever collected. This includes radial velocity measurements (∼16,000) and iron abundances (Δ S method for 8140 RRLs, plus 547 from literature). Elemental abundances based on high-resolution spectra are provided for 487 RRLs and 64 BHB stars. We identified candidate RRLs associated with the main Galactic components and their iron distribution function (IDF) becomes more metal rich when moving from the halo ([Fe/H] = −1.56) to the thick disk (TCD; [Fe/H] = −1.47) and thin disk (TND; [Fe/H] = −0.73). Furthermore, halo RRLs and RRLs in retrograde orbits are α enhanced ([ α /Fe]=0.27, σ = 0.18), while TCD RRLs are either α enhanced ([Fe/H] ≤ −1.0) or α poor ([Fe/H] > −1.0), and TND RRLs are mainly α poor ([ α /Fe] = −0.01, σ = 0.20). We also identified RRLs associated with the main stellar streams—Gaia–Sausage–Enceladus (GSE); Sequoia, Helmi, and Sagittarius—and we found that their IDFs are quite similar to halo RRLs. However, GSE RRLs lack the metal-poor/metal-rich tails and their α -element distribution is quite compact. The iron radial gradient in Galactocentric distance for TND, TCD, and halo RRLs is negative and it decreases from −0.026, to −0.010, and to −0.002 dex kpc ⁻¹ . The iron radial gradient based on dry halo (halo without substructures) RRLs is, within the errors, equal to the global halo. We also found a strong similarity between iron and [ α /Fe] radial gradients of Milky Way RRLs and M31 globular clusters throughout the full range of galactocentric distances covered by the two samples.

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 that unequivocally trace the enrichment process, and therefore, the environment in which 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, we discuss the α−element and iron abundances of a sample of stars that was 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- to medium-resolution spectra, we show that the overall chemical properties of the stellar populations in Liller1 prove its tight link with the Galactic bulge and provide new constraints on its star formation history.