Search for: All records

Open-star clusters are the essential building blocks of the Galactic disk; “strong chemical tagging”—the premise that all star clusters can be reconstructed given chemistry information alone—is a driving force behind many current and upcoming large Galactic spectroscopic surveys. In this work, we characterize the abundance patterns for nine elements (C, N, O, Ne, Mg, Si, S, Ca, and Fe) in open clusters (OCs) in three galaxies (m12i, m12f, and m12m) from the Latte suite of FIRE-2 simulations, to investigate the feasibility of strong chemical tagging in these simulations. We select young massive (≥10^4.6M_⊙) OCs formed in the last ∼100 Myr and calculate the intra- and intercluster abundance scatter for these clusters. We compare these results with analogous calculations drawn from observations of OCs in the Milky Way. We find the intracluster scatter of the observations and simulations to be comparable. While the abundance scatter within each cluster is minimal (≲0.020 dex), the mean abundance patterns of different clusters are not unique. We also calculate the chemical difference in intra- and intercluster star pairs and find it, in general, to be so small that it is difficult to distinguish between stars drawn from the same OC or from different OCs. Despite tracing three distinct nucleosynthetic families (core-collapse supernovae, white dwarf supernovae, and stellar winds), we conclude that these elemental abundances do not provide enough discriminating information to use strong chemical tagging for reliable OC membership. 

Abstract The observed chemical diversity of Milky Way stars places important constraints on Galactic chemical evolution and the mixing processes that operate within the interstellar medium. Recent works have found that the chemical diversity of disk stars is low. For example, the Apache Point Observatory Galactic Evolution Experiment (APOGEE) “chemical doppelganger rate,” or the rate at which random pairs of field stars appear as chemically similar as stars born together, is high, and the chemical distributions of APOGEE stars in some Galactic populations are well-described by two-dimensional models. However, limited attention has been paid to the heavy elements (Z> 30) in this context. In this work, we probe the potential for neutron-capture elements to enhance the chemical diversity of stars by determining their effect on the chemical doppelganger rate. We measure the doppelganger rate in GALactic Archaeology with HERMES DR3, with abundances rederived usingThe Cannon, and find that considering the neutron-capture elements decreases the doppelganger rate from ∼2.2% to 0.4%, nearly a factor of 6, for stars with −0.1 < [Fe/H] < 0.1. While chemical similarity correlates with similarity in age and dynamics, including neutron-capture elements does not appear to select stars that aremoresimilar in these characteristics. Our results highlight that the neutron-capture elements contain information that is distinct from that of the lighter elements and thus add at least one dimension to Milky Way abundance space. This work illustrates the importance of considering the neutron-capture elements when chemically characterizing stars and motivates ongoing work to improve their atomic data and measurements in spectroscopic surveys. 

ABSTRACT Chemical abundance anomalies in twin stars have recently been considered tell-tale signs of interactions between stars and planets. While such signals are prevalent, their nature remains a subject of debate. On the one hand, exoplanet formation may induce chemical depletion in host stars by locking up refractory elements. On the other hand, exoplanet engulfment can result in chemical enrichment, and both processes potentially produce similar differential signals. In this study, we aim to observationally disentangle these processes by using the Ca ii infrared triplet to measure the magnetic activity of 125 co-moving star pairs with high signal-to-noise ratio, and high-resolution spectra from the Magellan, Keck, and VLT (Very Large Telescope) telescopes. We find that co-natal star pairs in which the two stars exhibit significant chemical abundance differences also show differences in their magnetic activity, with stars depleted in refractories being magnetically more active. Furthermore, the strength of this correlation between differential chemical abundances and differential magnetic activity increases with condensation temperature. One possible explanation is that the chemical anomaly signature may be linked to planet formation, wherein refractory elements are locked into planets, and the host stars become more active due to more efficient contraction during the pre-main-sequence phase or star–planet tidal and magnetic interactions. 

ABSTRACT The element abundances of local group galaxies connect enrichment mechanisms to galactic properties and serve to contextualize the Milky Way’s abundance distributions. Individual stellar spectra in nearby galaxies can be extracted from integral field unit (IFU) data, and provide a means to take an abundance census of the local group. We introduce a programme that leverages $R=1800$, $$\mathrm{SNR}=15$$, IFU resolved spectra from the multi unit spectroscopic explorer . We deploy the data-driven modelling approach for labelling stellar spectra with stellar parameters and abundances, of The Cannon, on resolved stars in NGC 6822. We construct our model for The Cannon using $$\approx$$19 000 Milky Way lamost spectra with apogee labels. We report six inferred abundance labels (denoted $$\ell _\mathrm{X}$$), for 192 NGC 6822 disc stars, precise to $$\approx$$0.15 dex. We validate our generated spectral models provide a good fit to the data, including at individual atomic line features. We infer mean abundances of $$\ell _\mathrm{[Fe/H]} = -0.90 \pm 0.03$$, $$\ell _\mathrm{[Mg/Fe]} = -0.01 \pm 0.01$$, $$\ell _\mathrm{[Mn/Fe]} = -0.22 \pm 0.02$$, $$\ell _\mathrm{[Al/Fe]} = -0.33 \pm 0.03$$, $$\ell _\mathrm{[C/Fe]} =-0.43 \pm 0.03$$, $$\ell _\mathrm{[N/Fe]} =0.18 \pm 0.03$$. These abundance labels are similar to those of dwarf galaxies observed by apogee, and the lower enhancements for NGC 6822 compared to the Milky Way are consistent with expectations. This approach supports a new era in extragalactic archaeology of characterizing the local group enrichment diversity using low-resolution, low signal to noise ratio IFU resolved spectra. Furthermore, we conclude that it is feasible to build a model based on spectra observed with one instrument and apply it to spectra obtained with another. 

Abstract The goal of this paper is to describe the science verification of Milky Way Mapper (MWM) APOGEE Stellar Parameter and Chemical Abundances Pipeline (ASPCAP) data products published in Data Release 19 (DR19) of the fifth phase of the Sloan Digital Sky Survey (SDSS-V). We compare MWM ASPCAP atmospheric parametersT_eff, logg, 24 abundances of 21 elements (carbon, nitrogen, and oxygen have multiple sources for deriving their abundance values) and their uncertainties determined from Apache Point Observatory Galactic Evolution Experiment (APOGEE) spectrograph spectra with those of the literature and evaluate their accuracy and precision. We also test the zero-point calibration of thev_radderived by the APOGEE Data Reduction Pipeline. This data release contains ASPCAP parameters for 964,989 stars, including all APOGEE-2 targets expanded with new observations of 336,511 stars from the Apache Point Observatory observed until 2023 July 4. Overall, the newT_effvalues show excellent agreement with the IRFM scale, while the surface gravities exhibit slight systematic offsets compared to asteroseisimic gravities. The estimated precision ofT_effis between 50 and 70 K for giants and 70–100 K for dwarfs, while surface gravities are measured with a precision of 0.07–0.09 dex for giants. We achieve an estimated precision of 0.02–0.04 dex for multiple elements, including metallicity,α, Mg, and Si, while the precision of at least 10 elements is better than 0.1 dex. 

Abstract The element abundances of stars, particularly the refractory elements (e.g., Fe, Si, and Mg), play an important role in connecting stars to their planets. Most Sun-like stars do not have refractory abundance measurements since obtaining a large sample of high-resolution spectra is difficult with oversubscribed observing resources. In this work we infer abundances for C, N, O, Na, Mn, Cr, Si, Fe, Ni, Mg, V, Ca, Ti, Al, and Y for solar analogs with Gaia Radial Velocity Spectrometer (RVS) spectra (R= 11,200) usingTheCannon, a data-driven method. We train a linear model on a reference set of 34 stars observed by Gaia RVS with precise abundances measured from previous high-resolution spectroscopic efforts (R> 30,000–110,000). We then apply this model to several thousand Gaia RVS solar analogs. This yields abundances with average upper limit precisions of 0.04–0.1 dex for 17,412 stars, 50 of which are identified planet (candidate) hosts. We subsequently test the relative refractory depletion of these stars with increasing element condensation temperature compared to the Sun. The Sun remains refractory depleted compared to other Sun-like stars regardless of our current knowledge of the planets they host. This is inconsistent with theories of various types of planets locking up or sequestering refractories. Furthermore, we find no significant abundance differences between identified close-in giant planet hosts, giant planet hosts, and terrestrial/small planet hosts with the rest of the sample within our precision limits. This work demonstrates the utility of data-driven learning for future exoplanet composition and demographics studies. 

ABSTRACT Stars born on near-circular orbits in spiral galaxies can subsequently migrate to different orbits due to interactions with non-axisymmetric disturbances within the disc such as bars or spiral arms. This paper extends the study of migration to examine the role of external influences using the example of the interaction of the Sagittarius dwarf galaxy (Sgr) with the Milky Way (MW). We first make impulse approximation estimates to characterize the influence of Sgr disc passages. The tidal forcing from Sgr can produce changes in both guiding radius ΔRg and orbital eccentricity, as quantified by the maximum radial excursion ΔRmax. These changes follow a quadrupole-like pattern across the face of the disc, with amplitude increasing with Galactocentric radius. We next examine a collisionless N-body simulation of a Sgr-like satellite interacting with an MW-like galaxy and find that Sgr’s influence in the outer disc dominates the secular evolution of orbits between disc passages. Finally, we use the same simulation to explore possible observable signatures of Sgr-induced migration by painting the simulation with different age stellar populations. We find that following Sgr disc passages, the migration it induces manifests within an annulus as an approximate quadrupole in azimuthal metallicity variations (δ[Fe/H]), along with systematic variations in orbital eccentricity, ΔRmax. These systematic variations can persist for several rotational periods. We conclude that this combination of signatures may be used to distinguish between the different migration mechanisms shaping the chemical abundance patterns of the MW’s thin disc. 

Abstract Observations of the Milky Way’s low- α disk show that several element abundances correlate with age at fixed metallicity, with unique slopes and small scatters around the age–[X/Fe] relations. In this study, we turn to simulations to explore the age–[X/Fe] relations for the elements C, N, O, Mg, Si, S, and Ca that are traced in a FIRE-2 cosmological zoom-in simulation of a Milky Way–like galaxy, m12i, and understand what physical conditions give rise to the observed age–[X/Fe] trends. We first explore the distributions of mono-age populations in their birth and current locations, [Fe/H], and [X/Fe], and find evidence for inside-out radial growth for stars with ages <7 Gyr. We then examine the age–[X/Fe] relations across m12i’s disk and find that the direction of the trends agrees with observations, apart from C, O, and Ca, with remarkably small intrinsic scatters, σ int (0.01 − 0.04 dex). This σ int measured in the simulations is also metallicity dependent, with σ int ≈ 0.025 dex at [Fe/H] = −0.25 dex versus σ int ≈ 0.015 dex at [Fe/H] = 0 dex, and a similar metallicity dependence is seen in the GALAH survey for the elements in common. Additionally, we find that σ int is higher in the inner galaxy, where stars are older and formed in less chemically homogeneous environments. The age–[X/Fe] relations and the small scatter around them indicate that simulations capture similar chemical enrichment variance as observed in the Milky Way, arising from stars sharing similar element abundances at a given birth place and time. 

Abstract Planetary engulfment events have long been proposed as a lithium (Li) enrichment mechanism contributing to the population of Li-rich giants ( A (Li) ≥ 1.5 dex). Using MESA stellar models and A (Li) abundance measurements obtained by the GALAH survey, we calculate the strength and observability of the surface Li enrichment signature produced by the engulfment of a hot Jupiter (HJ). We consider solar-metallicity stars in the mass range of 1–2 M ⊙ and the Li supplied by a HJ of 1.0 M J . We explore engulfment events that occur near the main-sequence turn-off (MSTO) and out to orbital separations of R ⋆ ∼ 0.1 au = 22 R ⊙ . We map our results onto the Hertzsprung–Russell Diagram, revealing the statistical significance and survival time of Li enrichment. We identify the parameter space of masses and evolutionary phases where the engulfment of a HJ can lead to Li enrichment signatures at a 5 σ confidence level and with meteoritic abundance strengths. The most compelling strengths and survival times of engulfment-derived Li enrichment are found among host stars of 1.4 M ⊙ near the MSTO. Our calculations indicate that planetary engulfment is not a viable enrichment pathway for stars that have evolved beyond the subgiant branch. For these sources, observed Li enhancements are likely to be produced by other mechanisms, such as the Cameron–Fowler process or the accretion of material from an asymptotic giant branch companion. Our results do not account for second-order effects, such as extra mixing processes, which can further dilute Li enrichment signatures. 

ABSTRACT The detailed age-chemical abundance relations of stars measure time-dependent chemical evolution. These trends offer strong empirical constraints on nucleosynthetic processes, as well as the homogeneity of star-forming gas. Characterizing chemical abundances of stars across the Milky Way over time has been made possible very recently, thanks to surveys like Gaia, APOGEE, and Kepler. Studies of the low-α disc have shown that individual elements have unique age–abundance trends and the intrinsic dispersion around these relations is small. In this study, we examine and compare the age distribution of stars across both the high and low-α disc and quantify the intrinsic dispersion of 16 elements around their age–abundance relations at [Fe/H] = 0 using APOGEE DR16. We examine the age–metallicity relation and visualize the temporal and spatial distribution of disc stars in small chemical cells. We find: (1) the high-α disc has shallower age–abundance relations compared to the low-α disc, but similar median intrinsic dispersions of ∼0.03 dex; (2) turnover points in the age-[Fe/H] relations across radius for both the high- and low-α disc. The former constrains the mechanisms that set similar intrinsic dispersions, regardless of differences in the enrichment history, for stars in both disc, and the latter indicates the presence of radial migration in both disc. Our study is accompanied by an age catalogue for 64 317 stars in APOGEE derived using the cannon with a median uncertainty of 1.5 Gyr (26 per cent; APO-CAN stars), and a red clump catalogue of 22 031 stars with a contamination rate of 2.7 per cent.