Similar Metallicity Research Articles

GA-NIFS: an extremely nitrogen-loud and chemically stratified galaxy at z ~ 5.55

ABSTRACT We report the chemical abundance pattern of GS_3073, a galaxy hosting an overmassive active black hole at $z=5.55$, by leveraging observations from JWST/NIRSpec and Very Large Telescope/VIsible Multi-Object Spectrograph. Based on the rest-frame ultraviolet (UV) emission lines, which trace high-density ($\sim 10^5~{\rm cm^{-3}}$) and highly ionized gas, we derive $\rm \log (N/O) = 0.42^{+0.13}_{-0.10}$. At an estimated metallicity of $0.2~Z_{\odot }$, this is the most extreme nitrogen-rich object found by JWST thus far. In comparison, the relative carbon abundance derived is $\rm \log (C/O) = -0.38^{+0.13}_{-0.11}$, which is not significantly higher than those in local galaxies and stars with similar metallicities. We also found potential detection of [Fe vii]$\lambda 6087$ and [Fe xiv]$\lambda 5303$, both blended with [Ca v]. We inferred a range of Fe abundances compatible with those in local stars and galaxies. Overall, the chemical abundance pattern of GS_3073 is compatible with enrichment by supermassive stars with $M_* \gtrsim 1000~M_\odot$, asymptotic giant branch stars, or Wolf–Rayet stars. Interestingly, when using optical emission lines that trace lower density ($\sim 10^3~{\rm cm}^{-3}$) and lower ionization gas, we found a sub-solar N/O ratio, consistent with local galaxies at the same metallicity. We interpret the difference in N/O derived from UV lines and optical lines as evidence for a stratified system, where the inner and denser region is both more chemically enriched and more ionized. Our results suggest that nitrogen loudness in high-z galaxies might be confined to the central, dense, and highly ionized regions of the galaxies, while the bulk of the galaxies evolves more normally.

Direct estimates of nitrogen abundance for Seyfert 2 nuclei

Abstract We derive the nitrogen and oxygen abundances in the Narrow Line Regions (NLRs) of a sample of 38 local (z < 0.4) Seyfert 2 nuclei. For that, we consider narrow optical emission line intensities and direct estimates of the electron temperatures (Te-method). We obtain a new theoretical expression for the nitrogen Ionization Correction Factor [ICF($\rm N^{+}$)] for NLRs. Applying this new ICF, we unexpectedly find that NLRs and disk H ii regions exhibit similar ICF distributions. We find nitrogen abundances in the range $7.6 \: < \: \rm 12+log(N/H) \: < \: 8.6$ (mean value 8.06 ± 0.22) or $\rm 0.4 \: < \: (N/N_{\odot }) \: < 4.7$, in the metallicity regime $8.3 \: < \: \rm 12+log(O/H) \: < \: 9.0$. Our results indicate that the dispersion in N/H abundance for a fixed O/H value in AGNs of ∼0.2 dex agrees with that for disc H ii regions with similar metallicity. We show that Seyfert 2 nuclei follow a similar (N/O)-(O/H) relation to the one followed by star-forming objects. Finally, we find that active galaxies called as ”nitrogen-loud” observed at very high redshift (z > 5) show N/O values in consonance with those derived for local NLRs. This result indicates that the main star-formation event is completed in the early evolution stages of active galaxies.

The Sunburst Arc with JWST

We report the detection of a population of Wolf-Rayet (WR) stars in the Sunburst Arc, a strongly gravitationally lensed galaxy at redshift z = 2.37. As the brightest known lensed galaxy, the Sunburst Arc has become an important cosmic laboratory for studying star and cluster formation, Lyman α (Lyα) radiative transfer, and Lyman continuum (LyC) escape. Here, we present the first results of JWST/NIRSpec IFU observations of the Sunburst Arc, focusing on a stacked spectrum of the 12-fold imaged Sunburst LyC-emitting (LCE) cluster. In agreement with previous studies, we find that the Sunburst LCE cluster is a very massive, compact star cluster with Mdyn = (9 ± 1)×106 M⊙. Our age estimate of 4.2–4.5 Myr is much larger than the crossing time of tcross = 183 ± 9 kyr, indicating that the cluster is dynamically evolved and consistent with it being gravitationally bound. We find a significant nitrogen enhancement of the low ionization state interstellar medium (ISM), with log(N/O) = − 0.74 ± 0.09, which is ≈0.8 dex above typical values for H II regions of a similar metallicity in the local Universe. We find broad stellar emission complexes around He IIλ4686 and C IVλ5808 with associated nitrogen emission; this is the first time WR signatures have been directly observed at redshifts above ∼0.5. The strength of the WR signatures cannot be reproduced by stellar population models that only include single-star evolution. While models with binary evolution better match the WR features, they still struggle to reproduce the nitrogen-enhanced WR features. JWST reveals the Sunburst LCE cluster to be a highly ionized proto-globular cluster with low oxygen abundance and extreme nitrogen enhancement that hosts a population of WR stars, likely including a previously suggested population of very massive stars (VMSs), which together are rapidly enriching the surrounding medium.

Combined Gemini-South and HST photometric analysis of the globular cluster NGC 6558

Context. NGC 6558 is a low-galactic-latitude globular cluster projected in the direction of the Galactic bulge. Due to high reddening, this region presents challenges in deriving accurate parameters, which require meticulous photometric analysis. We present a combined analysis of near-infrared and optical photometry from multi-epoch high-resolution images collected with Gemini-South/GSAOI+GeMS (in the J and KS filters) and HST/ACS (in the F606W and F814W filters). Aims. We aim to refine the fundamental parameters of NGC 6558, utilising high-quality Gemini-South/GSAOI and HST/ACS photometries. Additionally, we intend to investigate its role in the formation of the Galactic bulge. Methods. We performed a meticulous differential reddening correction to investigate the effect of contamination from Galactic bulge field stars. To derive the fundamental parameters – age, distance, reddening, and the total-to-selective coefficient – we employed a Bayesian isochrone fitting. The results from high-resolution spectroscopy and RR Lyrae stars were implemented as priors. For the orbital parameters, we employed a barred Galactic mass model. Furthermore, we analysed the age-metallicity relation to contextualise NGC 6558 within the Galactic bulge’s history. Results. We studied the impact of two differential reddening corrections on the age derivation. When removing as much as possible of the Galactic bulge field star contamination, the isochrone fitting combined with synthetic colour-magnitude diagrams gives a distance of 8.41−0.10+0.11 kpc, an age of 13.0 ± 0.9 Gyr, and a reddening of E(B − V) = 0.34 ± 0.02. We derived a total-to-selective coefficient of RV = 3.2 ± 0.2 thanks to the simultaneous near-infrared–optical synthetic colour-magnitude diagram fitting, which, aside from errors, agrees with the commonly used value. The orbital parameters showed that NGC 6558 is confined within the inner Galaxy and it is not compatible with a bar-shape orbit, indicating that it is a bulge member. Assembling the old and moderately metal-poor ([Fe/H] ∼ −1.1) clusters in the Galactic bulge, we derived their age-metallicity relation with star formation starting at 13.6 ± 0.2 Gyr and effective yields of ρ = 0.05 ± 0.01 Z⊙. Conclusions. The old age derived for NGC 6558 is compatible with other clusters with similar metallicity and a blue horizontal branch in the Galactic bulge, which constitute the moderately metal-poor globular clusters. The age-metallicity relation shows that the starting age of star formation is compatible with the age of NGC 6558, and the chemical enrichment is ten times faster than the ex situ globular cluster branch.

Peculiarities of the chemical enrichment of metal-poor stars in the Milky Way Galaxy

The oldest stars in the Milky Way are metal-poor with Fe/H $<$ -- 1.0, displaying peculiar elemental abundances compared to solar values. The relative variations in the chemical compositions among stars is also increasing with decreasing stellar metallicity, allowing for the pure signature of unique nucleosynthesis processes to be revealed. The study of the $r$-process is, for instance, one of the main goals of stellar archaeology and metal-poor stars exhibit an unexpected complexity in the stellar production of the $r$-process elements in the early Galaxy. In this work, we report the atmospheric parameters, main dynamic properties, and the abundances of four metal-poor stars: HE 1523-–0901, HD 6268, HD 121135, and HD 195636 (--1.5 $>$ Fe/H The abundances were derived from spectra obtained with the HRS echelle spectrograph at the Southern African Large Telescope, using both local and non-local thermodynamic equilibrium (LTE and NLTE) approaches, with the average error between 0.10 and 0.20 dex. Based on their kinematical properties, we show that HE 1523--0901 and HD 195636 are halo stars with typical high velocities. In particular, HD 121135 displays a peculiar kinematical behaviour, making it unclear whether it is a halo or an accreted star. Furthermore, HD 6268 is possibly a rare prototype of very metal-poor thick disk stars. The abundances derived for our stars are compared with theoretical stellar models and with other stars with similar metallicity values from the literature. HD 121135 is Al-poor and Sc-poor, compared to stars observed in the same metallicity range (--1.62 $>$ Fe/H $>$--1.12). The most metal-poor stars in our sample, HE 1523 -- 0901, HD 6268, and HD 195636, exhibit anomalies that are better explained by supernova models from fast-rotating stellar progenitors for elements up to the Fe group. Compared to other stars in the same metallicity range, their common biggest anomaly is represented by the low Sc abundances. If we consider the elements beyond Zn, HE 1523--0901 can be classified as an r-II star, HD 6268 as an r-I candidate, and HD 195636 and HD 121135 exhibiting a borderline $r$-process enrichment between limited-r and r-I star. Significant relative differences are observed between the $r$-process signatures in these stars.

α-element enhancements in the ISM of the LMC and SMC: Evidence of recent star formation

Context. Important questions regarding the chemical composition of the neutral interstellar medium (ISM) in the Large Magellanic Cloud (LMC) and Small Magellanic Cloud (SMC) are still open. It is usually assumed that their metallicity is uniform and equal to that measured in hot stars and H II regions, but direct measurements of the neutral ISM metallicity had not been performed until now. Deriving the metallicity from the observed metal abundances is not straightforward because the abundances depend on the depletion of metals into dust and on nucleosynthesis effects such as α-element enhancement. Aims. Our aim is to measure the metallicity of the neutral ISM in the LMC and SMC, dust depletion, and any nucleosynthesis effects. Methods. We collected literature column densities of Ti II, Ni II, Cr II, Fe II, Mn II, Si II, Cu II, Mg II, S II, P II, Zn II, and O I in the neutral ISM towards 32 hot stars in the LMC and 22 in the SMC. We determined dust depletion from the relative abundances of different metals because they deplete with different strengths. This includes a ‘golden sample’ of sightlines where Ti and other α-elements are available. We fit linear relations to the observed abundance patterns so that the slopes determined the strengths of dust depletion and the normalizations determined the metallicities. We investigated α-element enhancements in the gas from the deviations from the linear fits and compared them with stars. Results. In our golden sample we find α-element enhancement in the neutral ISM in most systems, on average 0.26 dex (0.35 dex) for the LMC (SMC), and an Mn underabundance in the SMC (on average −0.35 dex). Measurements of Mn II are not available for the LMC. These are higher than for stars at similar metallicities. We find total neutral ISM metallicities that are mostly consistent with hot star metallicity values, on average [M/H]tot = −0.33 (−0.83), with standard deviations of 0.30 (0.30), in the LMC (the SMC). In six systems, however, we find significantly lower metallicities, 2 out of 32 in the LMC (with ~16% solar) and 4 out of 22 in the SMC (3 and 10% solar), two of which are in the outskirts of the SMC near the Magellanic Bridge, a region known for having a lower metallicity. Conclusions. The observed a-element enhancements and Mn underabundance are likely due to bursts of star formation, more recently than ~1 Gyr ago, that enriched the ISM from core-collapse supernovae. With the exception of lines of sight towards the Magellanic Bridge, the neutral gas in the LMC and SMC appears fairly well mixed in terms of metallicity.

ALMA-LEGUS. I. The Influence of Galaxy Morphology on Molecular Cloud Properties

We present a comparative study of the molecular gas in two galaxies from the Legacy ExtraGalactic UV Survey (LEGUS) sample: barred spiral NGC 1313 and flocculent spiral NGC 7793. These two galaxies have similar masses, metallicities, and star formation rates, but NGC 1313 is forming significantly more massive star clusters than NGC 7793, especially young massive clusters (<10 Myr, >104 M ⊙). Using Atacama Large Millimeter/submillimeter Array (ALMA) CO(2–1) observations of the two galaxies with the same sensitivity and resolution (13 pc), we directly compare the molecular gas in these two similar galaxies to determine the physical conditions responsible for their large disparity in cluster formation. By fitting size–line width relations for the clouds in each galaxy, we find that NGC 1313 has a higher intercept than NGC 7793, implying that its clouds have higher kinetic energies at a given size scale. NGC 1313 also has more clouds near virial equilibrium than NGC 7793, which may be connected to its higher rate of massive cluster formation. However, these virially bound clouds do not show a stronger correlation with young clusters than with the general cloud population. We find surprisingly small differences between the distributions of molecular cloud populations in the two galaxies, though the largest of those differences is that NGC 1313 has higher surface densities and lower freefall times.

Production of s-process elements in asymptotic giant branch stars as revealed by Gaia/GSP-Spec abundances

Context. The recent parameterisation by the GSP-Spec module of Gaia/Radial Velocity Spectrometer stellar spectra has produced an homogeneous catalogue of about 174 000 asymptotic giant branch (AGB) stars. Among the 13 chemical elements presented in this Gaia third data release, the abundance of two of them (cerium and neodymium) have been estimated in most of these AGB stars. These two species are formed by slow neutron captures (s-process) in the interior of low- and intermediate-mass stars. They belong to the family of second-peak s-process elements. Aims. We study the content and production rate of Ce and Nd in AGB stars, using the atmospheric parameters and chemical abundances derived by the GSP-Spec module. Methods. We defined a working sample of 19 544 AGB stars with high-quality Ce and/or Nd abundances, selected by applying a specific combination of the GSP-Spec quality flags. We compared these abundances with the yield production predicted by AGB evolutionary models. Results. We first confirmed that the majority of the working sample is composed of AGB stars by estimating their absolute magnitude in the K-band and their properties in a Gaia-2MASS diagram. We also checked that these stars are oxygen-rich AGB stars, as assumed during the GSP-Spec parameterisation. We found a good correlation between the Ce and Nd abundances, confirming the high quality of the derived abundances and that these species indeed belong to the same s-process family. We also found higher Ce and Nd abundances for more evolved AGB stars of similar metallicity, illustrating the successive mixing episodes enriching the AGB star surface in s-process elements formed deeper in their stellar interior. We then compared the observed Ce and Nd abundances with the FRUITY and Monash AGB yields and found that the higher Ce and Nd abundances cannot be explained by AGB stars of masses higher than 5 M⊙. In contrast, the yields predicted by both models for AGB stars with an initial mass between ∼1.5 and ∼2.5 M⊙ and metallicities between ∼−0.5 and ∼0.0 dex are fully compatible with the observed GSP-Spec abundances. Conclusions. This work based on the largest catalogue of high-quality second-peak s-element abundances in oxygen-rich AGB stars allows evolutionary models to be constrained and confirms the fundamental role played by low- and intermediate-mass stars in the enrichment of the Universe in these chemical species.

The stellar ‘Snake’ – II. The mass function

ABSTRACT We present a comprehensive investigation on the mass function (MF) of a snake-like stellar structure in the solar neighbourhood, building on our previous discovery. To ensure the reliability of the data, we reselect the member stars of the Stellar ‘Snake’ in the latest Gaia Data Release 3 using the same approach as the initial series of articles. We also precisely measure the physical parameters of the clusters within the Stellar Snake. In light of the high completeness of the member stars in the cluster regions, we develop a simulated model colour–magnitude diagram-based inference method to derive the mass function, binary fraction, and mass-ratio distribution of the clusters in the Stellar Snake. Notably, despite their similar ages and metallicity, we discover systematic variations in the MFs along the elongation direction of the Snake in the mass range of 0.5 to 2.0 M⊙. The ‘head’ of the Snake conforms to a canonical initial mass function with a power-law slope of α ∼ −2.3. Extending towards the ‘tail’, the MF becomes more top-light, indicating a deficiency of massive stars within these clusters. This result provides evidence for the delayed formation of massive stars in the clusters. Such clues give support to the hypothesis that the Stellar Snake constitutes as a hierarchically primordial structure.

Abundance of strontium in the Galactic globular cluster 47 Tuc

Aims. We have determined Sr abundance in a sample of 31 red giant branch stars located in the Galactic globular cluster 47 Tuc with the aim to identify potential differences in the Sr abundance between first population (1P, Na-poor) and second population (2P, Na-rich) stars. Methods. We derived the Na and Sr abundances from the archival spectra obtained with the UVES spectrograph. To do this, we used 1D ATLAS9 model atmospheres and a 1D local thermodynamic equilibrium spectral synthesis method. Particular attention was paid to assessing the potential impact of CN line blending on the obtained Sr abundances. Furthermore, we evaluated the potential influence of convection on the Sr line formation by using 3D hydrodynamical model atmospheres computed with the CO5 BOLD code. Results. Our results suggest a weak correlation between the abundances of Sr and Na. Together with a similar correlation between the abundances of Zr and Na determined in our previous study, our analysis of Sr suggests that polluters that have enriched 2P stars with light elements may have produced some s-process elements as well. The mean Sr abundance determined in 31 red giant branch stars of 47 Tuc is ⟨[Sr/Fe]⟩ = 0.18 ± 0.08 (the error denotes the standard deviation due to the star-to-star abundance scatter). This value is within the range of the Sr abundance variation that is observed in Galactic field stars of similar metallicity. The mean [Sr/Zr] abundance ratio in our sample stars suggests that the two s-process elements could have been synthesized by either low-mass asymptotic giant branch stars (M = 1 − 4 M⊙) or massive (M = 10 − 20 M⊙) fast-rotating (vrot = 200 − 300 km s−1) stars.

A Comparative Study between M30 and M92: M92 is a Merger Remnant with a Large Helium Enhancement

We perform a comparative study of the ex situ second-parameter pair globular clusters (GCs) M30 and M92, having similar metallicities but different horizontal branch morphologies. We obtain similar mean primordial carbon abundances for both clusters. However, M92 shows a large dispersion in carbon due to a more extended C–N anticorrelation, while M30 exhibits a higher primordial nitrogen abundance, suggesting that they have different chemical enrichment histories. Our new results confirm our previous result that M92 is a metal-complex GC showing a bimodal metallicity distribution. We also find that the metal-rich group of stars in M92 shows a helium enhancement as large as ΔY ∼ 0.05 from the red giant branch bump V magnitudes, which can also be supported by (i) a lack of bright red giant branch stars, (ii) synthetic evolutionary horizontal branch population models and (iii) the more extended spatial distribution due to different degree of the diffusion process from their lower masses. We reinterpret the [Eu/Fe] measurements by others, finding that the two metallicity groups of stars in M92 have significantly different [Eu/Fe] abundances with small scatters. This strongly suggests that they formed independently out of well-mixed interstellar media in different environments. We suggest that M92 is a more complex system than a normal GC, most likely a merger remnant of two GCs or an even more complex system. In the Appendix, we address the problems with the recently developed color–temperature relations and the usage of broadband photometry in the populational taggings.

Chemodynamical Nature of the Anticenter Stream and Monoceros Ring

In the epoch of deep photometric surveys, a large number of substructures—e.g., overdensities and streams—have been identified. With the help of astrometry and spectroscopy, the community has revealed a complex picture of our Milky Way (MW) after investigating their origins. The off-plane substructures the Anticenter Stream (ACS) and Monoceros Ring (MNC), once considered as dissolving dwarf galaxies, were later found to share similar kinematics and metallicity with the Galactic outer thin disk. In this work, we aim to chemically tag ACS and MNC with high-accuracy abundances from the APOGEE survey. By extrapolating chemical abundance trends in the outer thin-disk region (10 < R GC < 18 kpc, 0 < ∣Z GC∣ < 3 kpc), we found that ACS and MNC stars show consistent chemical abundances as the extrapolating values for 12 elements, including C, N, O, Mg, Al, Si, K, Ca, Cr, Mn, Co, and Ni. The similar chemical patterns indicate that ACS and MNC have a similar star formation history as the MW outer thin disk, while we also excluded their dwarf galaxy association, as they are distinctive in multiple chemical spaces. The ages of ACS and MNC stars are consistent with the time of the first Sagittarius dSph passage, indicating their possible connection.

Abundances of Extreme r-Process Elements in a Sample of CEMP-rs Stars

We analyze high-resolution spectra of five carbon-enhanced metal-poor (CEMP) stars acquired using Ultraviolet and Visual Echelle Spectrograph (UVES). Assuming local thermodynamic equilibrium (LTE), we derive the abundances of extreme r-process elements such as Tb, Ho, Tm, and Yb using TURBOSPECTRUM radiative transfer code with MARCS model atmospheres. Four of the program stars have their atmospheric parameters adopted from our previous studies, while for CS 22947-187, we determine the atmospheric parameters (Teff = 5200 K, log g = 1.5, ξ = 1.70 km s−1, and [Fe/H] = −2.55) using the BACCHUS code in semi-automated mode. These stars are already classified as CEMP-rs stars (i.e., carbon-enhanced metal-poor stars with enrichment of elements from both slow and rapid neutron-capture processes), using our new classification criteria for CEMP stars. The derived r-process abundances for our program stars are similar to those for rI and rII stars of similar metallicity.

FUNDAMENTAL PARAMETERS OF SUPERGIANT STAR HD 40589 (A0Iab)

The atmosphere of HD 40589 (A0Iab) supergiant star of A spectral class was studied using the model atmosphere and parallax methods. The effective temperatures (Teff) and surface of gravity (log g) were determined using a comparison of the observed and calculated values of the photometric quantities [c1], Q and the equivalent widths of the hydrogen Balmer lines and parallax. Based on the Fe II lines the microturbulent velocity and metallicity [Fe/H] were determined. Metallicity of the program star is close to the metallicity of the Sun. This shows that our program star and the Sun are formed from the interstellar medium of a similar metallicity.

Chemical Analysis of the Brightest Star of the Cetus II Ultrafaint Dwarf Galaxy Candidate* * This paper includes data gathered with the 6.5 m Magellan Telescopes located at Las Campanas Observatory, Chile.

We present a detailed chemical abundance analysis of the brightest star in the ultrafaint dwarf (UFD) galaxy candidate Cetus II from high-resolution Magellan/MIKE spectra. For this star, DES J011740.53-173053, abundances or upper limits of 18 elements from carbon to europium are derived. Its chemical abundances generally follow those of other UFD galaxy stars, with a slight enhancement of the α-elements (Mg, Si, and Ca) and low neutron-capture element (Sr, Ba, and Eu) abundances supporting the classification of Cetus II as a likely UFD. The star exhibits lower Sc, Ti, and V abundances than Milky Way (MW) halo stars with similar metallicity. This signature is consistent with yields from a supernova originating from a star with a mass of ∼11.2 M ⊙. In addition, the star has a potassium abundance of [K/Fe] = 0.81, which is somewhat higher than the K abundances of MW halo stars with similar metallicity, a signature that is also present in a number of UFD galaxies. A comparison including globular clusters and stellar stream stars suggests that high K is a specific characteristic of some UFD galaxy stars and can thus be used to help classify objects as UFD galaxies.

Zero-age horizontal branch models for −2.5 ≤ [Fe/H] ≤−0.5 and their implications for the apparent distance moduli of globular clusters

ABSTRACT Grids of zero-age horizontal branch (ZAHB) models are presented, along with a suitable interpolation code, for −2.5 ≤ [Fe/H] ≤ −0.5, in steps of 0.2 dex, assuming Y = 0.25 and 0.29, [O/Fe] = +0.4 and +0.6, and [m/Fe] = +0.4 for all of the other α-elements. The HB populations of 37 globular clusters (GCs) are fitted to these ZAHBs to derive their apparent distance moduli, (m − M)V. With few exceptions, the best estimates of their reddenings from dust maps are adopted. The distance moduli are constrained using the prediction that (MF606W − MF814W)0 colours of metal-poor, main-sequence stars at $M_{F606W} \mathrel {\rm{{\gt }\lower.5 ex\rm{\sim }}}5.0$ have very little sensitivity to [Fe/H]. Intrinsic (MF336W − MF606W)0 colours of blue HB stars, which provide valuable connections between GCs with exclusively blue HBs and other clusters of similar metallicity that also have red HB components, limit the uncertainties of relative (m − M)V values to within ±0.03–0.04 mag. The ZAHB-based distances agree quite well with the distances derived by Baumgardt &amp; Vasiliev. Their implications for GC ages are briefly discussed. Stellar rotation and mass loss appear to be more important than helium abundance variations in explaining the colour–magnitude diagrams of second-parameter GCs (those with anomalously very blue HBs for their metallicities).

The role of radial migration in open cluster and field star populations withGaiaDR3

Context.The survival time of a star cluster depends on its total mass, density, and thus size, as well as on the environment in which it was born and in which lies. Its dynamical evolution is influenced by various factors such as gravitational effects of the Galactic bar, spiral structures, and molecular clouds. Overall, the factors that determine the longevity of a cluster are complex and not fully understood.Aims.This study aims to investigate whether open clusters and field stars respond differently to the perturbations that cause radial migration. In particular, we aim to understand the nature of the oldest surviving clusters.Methods.We compared the time evolution of the kinematic properties of twoGaiaDR3 samples. The first sample is composed of ∼40 open clusters and the second one of ∼66 000 main sequence turn off field stars. Both of the samples are composed of stars selected with the same quality criterion, and they belong to the thin disc, are in a similar metallicity range, are located in the same Galactocentric region [7.5–9 kpc], and have ages greater than 1 Gyr. We performed a statistical analysis comparing the properties of the samples of the field stars and of the open clusters.Results.A qualitative comparison of kinematic and orbital properties revealed that clusters younger than 2–3 Gyr are more resistant to perturbations than field stars, and they move along quasi-circular orbits. Conversely, clusters older than approximately 3 Gyr have more eccentric and inclined orbits than isolated stars in the same age range. Such orbits lead the older clusters to reach higher elevations on the Galactic plane, maximising their probability to survive several more gigayears. A formal statistical analysis revealed that there are differences among the time evolution of most of the kinematic and orbital properties of the field stars and open clusters. However, the comparison between some properties (e.g.,VϕandLZ) do not reach a sufficient statistical significance.Conclusions.Our results suggest that the oldest surviving clusters are usually more massive and move on orbits with a higher eccentricity. Although they are still reliable tracers of the Galaxy’s past composition, they do not reflect the composition of the place where they are currently found. Therefore, we cannot avoid considering kinematic properties when comparing data and models of chemical evolution and also taking into account the intrinsic differences between clusters and isolated stars. To validate the results, new studies that increase the sample of open clusters, especially at older ages, are needed.

Initial mass function variability from the integrated light of diverse stellar systems

ABSTRACT We present a uniform analysis of the stellar initial mass function (IMF) from integrated light spectroscopy of 15 compact stellar systems (11 globular clusters in M31 and 4 ultra compact dwarfs in the Virgo cluster, UCDs) and two brightest Coma cluster galaxies (BCGs), covering a wide range of metallicities (−1.7 &amp;lt; [Fe/H] &amp;lt; 0.01) and velocity dispersions (7.4 km s−1 &amp;lt;σ &amp;lt; 275 km s−1). The S/N ∼100 Å−1 Keck LRIS spectra are fitted over the range 4000 &amp;lt; λ/Å &amp;lt; 10 000 with flexible full-spectrum stellar population synthesis models. We use the models to fit simultaneously for ages, metallicities, and individual elemental abundances of the population, allowing us to decouple abundance variations from variations in IMF slope. We show that compact stellar systems do not follow the same trends with physical parameters that have been found for early-type galaxies. Most globular clusters in our sample have an IMF consistent with that of the Milky Way, over a wide range of [Fe/H] and [Mg/Fe]. There is more diversity among the UCDs, with some showing evidence for a bottom-heavy IMF, but with no clear correlation with metallicity, abundance, or velocity dispersion. The two Coma BCGs have similar velocity dispersion and metallicity, but we find the IMF of NGC 4874 is consistent with that of the Milky Way while NGC 4889 presents evidence for a significantly bottom-heavy IMF. For this sample, the IMF appears to vary between objects in a way that is not explained by a single metallicity-dependent prescription.

Chemical abundances of the young inner-disc open cluster NGC 6705 observed by APOGEE: sodium-rich and not α-enhanced

ABSTRACT Previous results in the literature have found the young inner-disc open cluster NGC 6705 to be mildly α-enhanced. We examined this possibility via an independent chemical abundance analysis for 11 red-giant members of NGC 6705. The analysis is based on near-infrared APOGEE spectra and relies on LTE calculations using spherical model atmospheres and radiative transfer. We find a mean cluster metallicity of $\rm [Fe/H] = +0.13 \pm 0.04$, indicating that NGC 6705 is metal-rich, as may be expected for a young inner-disc cluster. The mean α-element abundance relative to iron is $\rm \langle [\alpha /Fe]\rangle =-0.03 \pm 0.05$, which is not at odds with expectations from general Galactic abundance trends. NGC 6705 also provides important probes for studying stellar mixing, given its turn-off mass of M ∼ 3.3 M⊙. Its red giants have low 12C abundances ([12C/Fe] = −0.16) and enhanced 14N abundances ([14N/Fe] = +0.51), which are key signatures of the first dredge-up on the red giant branch. An additional signature of dredge-up was found in the Na abundances, which are enhanced by [Na/Fe] = +0.29, with a very small non-LTE correction. The 16O and Al abundances are found to be near-solar. All of the derived mixing-sensitive abundances are in agreement with stellar models of approximately 3.3 M⊙ evolving along the red giant branch and onto the red clump. As found in young open clusters with similar metallicities, NGC 6705 exhibits a mild excess in the s-process element cerium with $\rm [Ce/Fe] = +0.13\pm 0.07$.

A Massive Hot Jupiter Orbiting a Metal-rich Early M Star Discovered in the TESS Full-frame Images

Observations and statistical studies have shown that giant planets are rare around M dwarfs compared with Sun-like stars. The formation mechanism of these extreme systems has remained under debate for decades. With the help of the TESS mission and ground-based follow-up observations, we report the discovery of TOI-4201b, the most massive and densest hot Jupiter around an M dwarf known so far with a radius of 1.22 ± 0.04 R J and a mass of 2.48 ± 0.09 M J, about 5 times heavier than most other giant planets around M dwarfs. It also has the highest planet-to-star mass ratio (q ∼ 4 × 10−3) among such systems. The host star is an early M dwarf with a mass of 0.61 ± 0.02 M ⊙ and a radius of 0.63 ± 0.02 R ⊙. It has significant supersolar iron abundance ([Fe/H] = 0.52 ± 0.08 dex). However, interior structure modeling suggests that its planet TOI-4201b is metal-poor, which challenges the classical core-accretion correlation of stellar−planet metallicity, unless the planet is inflated by additional energy sources. Building on the detection of this planet, we compare the stellar metallicity distribution of four planetary groups: hot/warm Jupiters around G/M dwarfs. We find that hot/warm Jupiters show a similar metallicity dependence around G-type stars. For M-dwarf host stars, the occurrence of hot Jupiters shows a much stronger correlation with iron abundance, while warm Jupiters display a weaker preference, indicating possible different formation histories.