We show that the masses of red giant stars can be well predicted from their photospheric carbon and nitrogen abundances, in conjunction with their spectroscopic stellar labels log g, T
eff, and Fe/H. ...This is qualitatively expected from mass-dependent post-main-sequence evolution. We here establish an empirical relation between these quantities by drawing on 1475 red giants with asteroseismic mass estimates from Kepler that also have spectroscopic labels from Apache Point Observatory Galactic Evolution Experiment (APOGEE) DR12. We assess the accuracy of our model, and find that it predicts stellar masses with fractional rms errors of about 14 per cent (typically 0.2 M⊙). From these masses, we derive ages with rms errors of 40 per cent. This empirical model allows us for the first time to make age determinations (in the range 1–13 Gyr) for vast numbers of giant stars across the Galaxy. We apply our model to ∼52 000 stars in APOGEE DR12, for which no direct mass and age information was previously available. We find that these estimates highlight the vertical age structure of the Milky Way disc, and that the relation of age with α/M and metallicity is broadly consistent with established expectations based on detailed studies of the solar neighbourhood.
We report chemical abundances obtained by Sloan Digital Sky Survey (SDSS)-III/Apache Point Observatory Galactic Evolution Experiment for giant stars in five globular clusters located within 2.2 kpc ...of the Galactic Centre. We detect the presence of multiple stellar populations in four of those clusters (NGC 6553, NGC 6528, Terzan 5 and Palomar 6) and find strong evidence for their presence in NGC 6522. All clusters with a large enough sample present a significant spread in the abundances of N, C, Na and Al, with the usual correlations and anticorrelations between various abundances seen in other globular clusters. Our results provide important quantitative constraints on theoretical models for self-enrichment of globular clusters, by testing their predictions for the dependence of yields of elements such as Na, N, C and Al on metallicity. They also confirm that, under the assumption that field N-rich stars originate from globular cluster destruction, they can be used as tracers of their parental systems in the high-metallicity regime.
Data from the SDSS-IV/Apache Point Observatory Galactic Evolution Experiment (APOGEE-2) have been released as part of SDSS Data Releases 13 (DR13) and 14 (DR14). These include high-resolution H-band ...spectra, radial velocities, and derived stellar parameters and abundances. DR13, released in 2016 August, contained APOGEE data for roughly 150,000 stars, and DR14, released in 2017 August, added about 110,000 more. Stellar parameters and abundances have been derived with an automated pipeline, the APOGEE Stellar Parameter and Chemical Abundance Pipeline (ASPCAP). We evaluate the performance of this pipeline by comparing the derived stellar parameters and abundances to those inferred from optical spectra and analysis for several hundred stars. For most elements-C, Na, Mg, Al, Si, S, Ca, Cr, Mn, Ni-the DR14 ASPCAP analyses have systematic differences with the comparisons samples of less than 0.05 dex (median), and random differences of less than 0.15 dex (standard deviation). These differences are a combination of the uncertainties in both the comparison samples as well as the ASPCAP analysis. Compared to the references, magnesium is the most accurate alpha-element derived by ASPCAP, and shows a very clear thin/thick disk separation, while nickel is the most accurate iron-peak element (besides iron itself).
We derive age constraints for 1639 red giants in the APOKASC sample for which seismic parameters from Kepler, as well as effective temperatures, metallicities and α/Fe values from APOGEE DR12 (Apache ...Point Observatory Galactic Evolution Experiment Data Release 12) are available. We investigate the relation between age and chemical abundances for these stars, using a simple and robust approach to obtain ages. We first derive stellar masses using standard seismic scaling relations, then determine the maximum possible age for each star as function of its mass and metallicity, independently of its evolutionary stage. While the overall trend between maximum age and chemical abundances is a declining fraction of young stars with increasing α/Fe, at least 14 out of 241 stars with α/Fe >0.13 are younger than 6 Gyr. Five stars with α/Fe ≥0.2 have ages below 4 Gyr. We examine the effect of modifications in the standard seismic scaling relations, as well as the effect of very low helium fractions, but these changes are not enough to make these stars as old as usually expected for α-rich stars (i.e. ages greater than 8–9 Gyr). Such unusual α-rich young stars have also been detected by other surveys, but defy simple explanations in a galaxy evolution context.
The Open Cluster Chemical Abundances and Mapping (OCCAM) survey aims to produce a comprehensive, uniform, infrared-based spectroscopic data set for hundreds of open clusters, and to constrain key ...Galactic dynamical and chemical parameters from this sample. This second contribution from the OCCAM survey presents analysis of 259 member stars with Fe/H determinations in 19 open clusters, using Sloan Digital Sky Survey Data Release 14 (SDSS/DR14) data from the Apache Point Observatory Galactic Evolution Experiment and ESA Gaia. This analysis, which includes clusters with RGC ranging from 7 to 13 kpc, measures an Fe/H gradient of −0.061 0.004 dex kpc−1. We also confirm evidence of a significant positive gradient in the -elements (O/Fe, Mg/Fe, and Si/Fe) and present evidence for a significant negative gradient in iron-peak elements (Mn/Fe and Ni/Fe).
The SDSS-IV Apache Point Observatory Galactic Evolution Experiment (APOGEE) survey provides precise chemical abundances of 18 chemical elements for ∼176,000 red giant stars distributed over much of ...the Milky Way Galaxy (MW), and includes observations of the core of the Sagittarius dwarf spheroidal galaxy (Sgr). The APOGEE chemical abundance patterns of Sgr have revealed that it is chemically distinct from the MW in most chemical elements. We employ a k-means clustering algorithm to six-dimensional chemical space defined by (C+N)/Fe, O/Fe, Mg/Fe, Al/Fe, Mn/Fe, and Ni/Fe to identify 62 MW stars in the APOGEE sample that have Sgr-like chemical abundances. Of the 62 stars, 35 have Gaia kinematics and positions consistent with those predicted by N-body simulations of the Sgr stream, and are likely stars that have been stripped from Sgr during the last two pericenter passages (<2 Gyr ago). Another 20 of the 62 stars exhibit chemical abundances indistinguishable from the Sgr stream stars, but are on highly eccentric orbits with median rapo ∼ 25 kpc. These stars are likely the "accreted" halo population thought to be the result of a separate merger with the MW 8-11 Gyr ago. We also find one hypervelocity star candidate. We conclude that Sgr was enriched to Fe/H ∼ −0.2 before its most recent pericenter passage. If the "accreted halo" population is from one major accretion event, then this progenitor galaxy was enriched to at least Fe/H ∼ −0.6, and had a similar star formation history to Sgr before merging.
Coenzyme Q (CoQ) is an essential component of the mitochondrial electron transport chain and an antioxidant in plasma membranes and lipoproteins. It is endogenously produced in all cells by a highly ...regulated pathway that involves a mitochondrial multiprotein complex. Defects in either the structural and/or regulatory components of CoQ complex or in non-CoQ biosynthetic mitochondrial proteins can result in a decrease in CoQ concentration and/or an increase in oxidative stress. Besides CoQ
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deficiency syndrome and aging, there are chronic diseases in which lower levels of CoQ
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are detected in tissues and organs providing the hypothesis that CoQ
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supplementation could alleviate aging symptoms and/or retard the onset of these diseases. Here, we review the current knowledge of CoQ
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biosynthesis and primary CoQ
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deficiency syndrome, and have collected published results from clinical trials based on CoQ
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supplementation. There is evidence that supplementation positively affects mitochondrial deficiency syndrome and the symptoms of aging based mainly on improvements in bioenergetics. Cardiovascular disease and inflammation are alleviated by the antioxidant effect of CoQ
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. There is a need for further studies and clinical trials involving a greater number of participants undergoing longer treatments in order to assess the benefits of CoQ
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treatment in metabolic syndrome and diabetes, neurodegenerative disorders, kidney diseases, and human fertility.
We present C/N-Fe/H abundance trends from the SDSS-IV Apache Point Observatory Galactic Evolution Experiment survey, Data Release 14 (DR14), for red giant branch stars across the Milky Way (3 kpc < R ...< 15 kpc). The carbon-to-nitrogen ratio (often expressed as C/N) can indicate the mass of a red giant star, from which an age can be inferred. Using masses and ages derived by Martig et al., we demonstrate that we are able to interpret the DR14 C/N-Fe/H abundance distributions as trends in age-Fe/H space. Our results show that an anticorrelation between age and metallicity, which is predicted by simple chemical evolution models, is not present at any Galactic zone. Stars far from the plane ( kpc) exhibit a radial gradient in C/N (∼−0.04 dex kpc−1). The C/N dispersion increases toward the plane ( C/N = 0.13 at kpc to C/N = 0.18 dex at Z < 0.5 kpc). We measure a disk metallicity gradient for the youngest stars (age < 2.5 Gyr) of −0.060 dex kpc−1 from 6 to 12 kpc, which is in agreement with the gradient found using young CoRoGEE stars by Anders et al. Older stars exhibit a flatter gradient (−0.016 dex kpc−1), which is predicted by simulations in which stars migrate from their birth radii. We also find that radial migration is a plausible explanation for the observed upturn of the C/N-Fe/H abundance trends in the outer Galaxy, where the metal-rich stars are relatively enhanced in C/N.
ABSTRACT We present new identifications of five red giant stars in the Galactic halo with chemical abundance patterns that indicate they originally formed in globular clusters. Using data from the ...Apache Point Observatory Galactic Evolution Experiment (APOGEE) Survey available through Sloan Digital Sky Survey (SDSS) Data Release 12, we first identify likely halo giants, and then search those for the well-known chemical tags associated with globular clusters, specifically enrichment in nitrogen and aluminum. We find that 2% of the halo giants in our sample have this chemical signature, in agreement with previous results. Following the interpretation in our previous work on this topic, this would imply that at least 13% of halo stars originally formed in globular clusters. Recent developments in the theoretical understanding of globular cluster formation raise questions about that interpretation, and we concede the possibility that these migrants represent a small fraction of the halo field. There are roughly as many stars with the chemical tags of globular clusters in the halo field as there are in globular clusters, whether or not they are accompanied by a much larger chemically untaggable population of former globular cluster stars.
ABSTRACT
Stellar ages are a crucial component to studying the evolution of the Milky Way. Using Gaia DR2 distance estimates, it is now possible to estimate stellar ages for a larger volume of evolved ...stars through isochrone matching. This work presents M/H–age and α/M–age relations derived for different spatial locations in the Milky Way disc. These relations are derived by hierarchically modelling the star formation history of stars within a given chemical abundance bin. For the first time, we directly observe that significant variation is apparent in the M/H–age relation as a function of both Galactocentric radius and distance from the disc mid-plane. The M/H–age relations support claims that radial migration has a significant effect in the plane of the disc. Using the M/H bin with the youngest mean age at each radial zone in the plane of the disc, the present-day metallicity gradient is measured to be −0.059 ± 0.010 dex kpc−1, in agreement with Cepheids and young field stars. We find a vertically flared distribution of young stars in the outer disc, confirming predictions of models and previous observations. The mean age of the M/H–α/M distribution of the solar neighbourhood suggests that the high-M/H stars are not an evolutionary extension of the low-α sequence. Our observational results are important constraints to Galactic simulations and models of chemical evolution.
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