Context.
Well studied open clusters (OCs) of the solar neighborhood are frequently used as reference objects to test galactic and stellar theories. For that purpose, their chemical composition needs ...to be known with a high level of confidence. It is also important to clarify if each OC is chemically homogeneous and if it has a unique chemical signature.
Aims.
The aims of this work are (1) to determine accurate and precise abundances of 22 chemical species (from Na to Eu) in the Hyades, Praesepe, and Rupecht 147 by using a large number of stars at different evolutionary states, (2) to evaluate the level of chemical homogeneity of these OCs, and (3) to compare their chemical signatures.
Methods.
We gathered ∼800 high resolution and high signal-to-noise spectra of ∼100 members in the three clusters, which were obtained with the latest memberships based on
Gaia
DR2 data. We built a pipeline, which computes atmospheric parameters and strictly line-by-line differential abundances among twin stars in our sample. With this method, we were able to reach a very high precision in the abundances (0.01–0.02 dex in most of the elements).
Results.
We find large differences in the absolute abundances in some elements, which can be attributed to diffusion, non-local thermodynamic equilibrium (non-LTE) effects, or systematics in the analysis. For the three OCs, we find strong correlations in the differential abundances between different pairs of elements. According to our experiment with synthetic data, this can be explained by some level of chemical inhomogeneity. We compare differential abundances of several stars from the Hyades and Praesepe tails: The stars that differ more in chemical abundances also have distinct kinematics, even though they have been identified as members of the tail.
Conclusions.
It is possible to obtain high precision abundances using a differential analysis even when mixing spectra from different instruments. With this technique, we find that the Hyades and Preasepe have the same chemical signature when G dwarfs and K giants are considered. Despite a certain level of inhomogeneity in each cluster, it is still possible to clearly distinguish the chemical signature of the older cluster Ruprecht 147 when compared to the Hyades and Praesepe.
Context.
Precise chemical abundances coupled with reliable ages are key ingredients to understanding the chemical history of our Galaxy. Open clusters (OCs) are useful for this purpose because they ...provide ages with good precision.
Aims.
The aim of this work is to investigate the relation between different chemical abundance ratios and age traced by red clump (RC) stars in OCs.
Methods.
We analyzed a large sample of 209 reliable members in 47 OCs with available high-resolution spectroscopy. We applied a differential line-by-line analysis, performing a comprehensive chemical study of 25 chemical species. This sample is among the largest samples of OCs homogeneously characterized in terms of atmospheric parameters, detailed chemistry, and age.
Results.
In our metallicity range (−0.2 < M/H < +0.2) we find that while most Fe-peak and
α
elements show a flat dependence on age, the
s
-process elements show a decreasing trend with increasing age with a remarkable knee at 1 Gyr. For Ba, Ce, Y, Mo, and Zr, we find a plateau at young ages (< 1 Gyr). We investigate the relations between all possible combinations among the computed chemical species and age. We find 19 combinations with significant slopes, including Y/Mg and Y/Al. The ratio Ba/
α
shows the most significant correlation.
Conclusions.
We find that the Y/Mg relation found in the literature using solar twins is compatible with the one found here in the solar neighborhood. The age–abundance relations in clusters at large distances(
d
> 1 kpc) show larger scatter than those in clusters in the solar neighborhood, particularly in the outer disk. We conclude that, in addition to pure nucleosynthetic arguments, the complexity of the chemical space introduced by the Galactic dynamics must be taken into account in order to understand these relations, especially outside of the local bubble.
The binary system 16 Cygni is key in studies of the planet-star chemical composition connection, as only one of the stars is known to host a planet. This allows us to better assess the possible ...influence of planet interactions on the chemical composition of stars that are born from the same cloud and thus should have a similar abundance pattern. In our previous work, we found clear abundance differences for elements with Z ≤ 30 between both components of this system and a trend of these abundances as a function of the condensation temperature (Tc), which suggests a spectral chemical signature related to planet formation. In this work we show that our previous findings are still consistent even if we include more species, such as the volatile N and neutron capture elements (Z > 30). We report a slope with Tc of 1.56 ± 0.24 × 10−5 dex K−1, that is good agreement with our previous work. We also performed some tests using ARES and iSpec to measure automatically the equivalent width and found Tc slopes in reasonable agreement with our results as well. In addition, we determined abundances for Li and Be by spectral synthesis, finding that 16 Cyg A is richer not only in Li but also in Be, when compared to its companion. This may be evidence of planet engulfment, indicating that the Tc trend found in this binary system may be a chemical signature of planet accretion in the A component, rather than an imprint of the giant planet rocky core formation on 16 Cyg B.
Gaia and its complementary spectroscopic surveys combined will yield the most comprehensive database of kinematic and chemical information of stars in the Milky Way. The Gaia FGK benchmark stars play ...a central role in this matter as they are calibration pillars for the atmospheric parameters and chemical abundances for various surveys. The spectroscopic analyses of the benchmark stars are done by combining different methods, and the results will be affected by the systematic uncertainties inherent in each method. In this paper, we explore some of these systematic uncertainties. We determined line abundances of Ca, Cr, Mn and Co for four benchmark stars using six different methods. We changed the default input parameters of the different codes in a systematic way and found, in some cases, significant differences between the results. Since there is no consensus on the correct values for many of these default parameters, we urge the community to raise discussions towards standard input parameters that could alleviate the difference in abundances obtained by different methods. In this work, we provide quantitative estimates of uncertainties in elemental abundances due to the effect of differing technical assumptions in spectrum modelling.
We present a chemical abundance distribution study in 14 α, odd-Z, even-Z, light, and Fe-peak elements of approximately 3200 intermediate-metallicity giant stars from the Apache Point Observatory ...Galactic Evolution Experiment (APOGEE) survey. The main aim of our analysis is to explore the Galactic disc–halo transition region within −1.20 < Fe/H < −0.55 as a means to study chemical difference (and similarities) between these components. In this paper, we show that there is an α-poor and α-rich sequence within both the metal-poor and intermediate-metallicity regions. Using the Galactic rest-frame radial velocity and spatial positions, we further separate our sample into the canonical Galactic components. We then studied the abundances ratios of Mg, Ti, Si, Ca, O, S, Al, C+N, Na, Ni, Mn, V, and K for each of the components and found the following: (1) the α-poor halo subgroup is chemically distinct in the α-elements, particularly O, Mg, S, Al, C+N, and Ni, from the α-rich halo, consistent with the literature confirming the existence of an α-poor accreted halo population; (2) the canonical thick disc and halo are not chemically distinct in all elements indicating a smooth transition between the thick disc and halo; (3) a subsample of the α-poor stars at metallicities as low as Fe/H ∼ −0.85 dex are chemically and dynamically consistent with the thin disc indicating that the thin disc may extend to lower metallicities than previously thought; and (4) the locations of the most metal-poor thin disc stars are consistent with a negative radial metallicity gradient. Finally, we used our analysis to suggest a new set of chemical abundance planes (α/Fe, C+N/Fe, Al/Fe, and Mg/Mn) that may be able to chemically label the Galactic components in a clean and efficient way independent of kinematics.
ABSTRACT
Astrometry and photometry from Gaia and spectroscopic data from the Gaia-ESO Survey (GES) are used to identify the lithium depletion boundary (LDB) in the young cluster NGC 2232. A ...specialized spectral line analysis procedure was used to recover the signature of undepleted lithium in very low luminosity cluster members. An age of 38 ± 3 Myr is inferred by comparing the LDB location in absolute colour−magnitude diagrams (CMDs) with the predictions of standard models. This is more than twice the age derived from fitting isochrones to low-mass stars in the CMD with the same models. Much closer agreement between LDB and CMD ages is obtained from models that incorporate magnetically suppressed convection or flux-blocking by dark, magnetic starspots. The best agreement is found at ages of 45−50 Myr for models with high levels of magnetic activity and starspot coverage fractions >50 per cent, although a uniformly high spot coverage does not match the CMD well across the full luminosity range considered.
Context. Large spectroscopic surveys devoted to the study of the Milky Way, including Gaia, use automated pipelines to determine the atmospheric parameters of millions of stars. The Gaia FGK ...benchmark stars are reference stars with Teff and log ?? derived through fundamental relations, independently of spectroscopy, to be used as anchors for the parameter scale. The first and second versions of the sample have been extensively used for that purpose, and more generally to help constrain stellar models. Aims. We provide the third version of the Gaia FGK benchmark stars, an extended set intended to improve the calibration of spectroscopic surveys, and their interconnection. Methods. We have compiled about 200 candidates that have precise measurements of angular diameters and parallaxes. We determined their bolometric fluxes by fitting their spectral energy distribution. Masses were determined using two sets of stellar evolution models. In a companion paper, we describe the determination of metallicities and detailed abundances. Results. We provide a new set of 192 Gaia FGK benchmark stars with their fundamental Teff and log ??, and with uncertainties lower than 2% for most stars. Compared to the previous versions, the homogeneity and accuracy of the fundamental parameters are significantly improved thanks to the high quality of the Gaia photometric and astrometric data.
We take advantage of the Gaia-ESO Survey iDR4 bulge data to search for abundance anomalies that could shed light on the composite nature of the Milky Way bulge. The α-element (Mg, Si, and whenever ...available, Ca) abundances, and their trends with Fe abundances have been analysed for a total of 776 bulge stars. In addition, the aluminum abundances and their ratio to Fe and Mg have also been examined. Our analysis reveals the existence of low-α element abundance stars with respect to the standard bulge sequence in the α/ Fe versus Fe/H plane. Eighteen objects present deviations in α/ Fe ranging from 2.1 to 5.3σ with respect to the median standard value. Those stars do not show Mg-Al anti-correlation patterns. Incidentally, this sign of the existence of multiple stellar populations is reported firmly for the first time for the bulge globular cluster NGC 6522. The identified low-α abundance stars have chemical patterns that are compatible with those of the thin disc. Their link with massive dwarf galaxies accretion seems unlikely, as larger deviations in α abundance and Al would be expected. The vision of a bulge composite nature and a complex formation process is reinforced by our results. The approach used, which is a multi-method and model-driven analysis of high resolution data, seems crucial to reveal this complexity.
Context.
To take full advantage of upcoming large-scale spectroscopic surveys, it will be necessary to parameterize millions of stellar spectra in an efficient way. Machine learning methods, ...especially convolutional neural networks (CNNs), will be among the main tools geared at achieving this task.
Aims.
We aim to prepare the groundwork for machine learning techniques for the next generation of spectroscopic surveys, such as 4MOST and WEAVE. Our goal is to show that CNNs can predict accurate stellar labels from relevant spectral features in a physically meaningful way. The predicted labels can be used to investigate properties of the Milky Way galaxy.
Methods.
We built a neural network and trained it on GIRAFFE spectra with their associated stellar labels from the sixth internal
Gaia
-ESO data release. Our network architecture contains several convolutional layers that allow the network to identify absorption features in the input spectra. The internal uncertainty was estimated from multiple network models. We used the t-distributed stochastic neighbor embedding tool to remove bad spectra from our training sample.
Results.
Our neural network is able to predict the atmospheric parameters
T
eff
and log(
g
) as well as the chemical abundances Mg/Fe, Al/Fe, and Fe/H for 36 904 stellar spectra. The training precision is 37 K for
T
eff
, 0.06 dex for log(
g
), 0.05 dex for Mg/Fe, 0.08 dex for Al/Fe, and 0.04 dex for Fe/H. Network gradients reveal that the network is inferring the labels in a physically meaningful way from spectral features. We validated our methodology using benchmark stars and recovered the properties of different stellar populations in the Milky Way galaxy.
Conclusions.
Such a study provides very good insights into the application of machine learning for the analysis of large-scale spectroscopic surveys, such as WEAVE and 4MOST Milky Way disk and bulge low- and high-resolution (4MIDABLE-LR and -HR). The community will have to put substantial efforts into building proactive training sets for machine learning methods to minimize any possible systematics.
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