Chemical Abundances in Stars

Start year
2010
Organizational Unit

Grants related:

    General
    Description

    Stellar spectroscopy allows us to determine the properties and chemical compositions of stars. From this information for stars of different ages in the Milky Way, it is possible to reconstruct the chemical evolution of the Galaxy, as well as the origin of the elements heavier than boron, created mainly in stellar interiors. It is also possible to study stellar formation, and the formation of the Galaxy, from the signature of the Galactic potential on the stellar orbits, and the distributions of mass, ages, and the abundance of heavy elements.

    Obtaining high-resolution spectra, as necessary for studies of chemical compositions, requires advanced and efficient instrumentation. This is particularly true for research that calls for large stellar samples, which demands the observation of hundreds or thousands of sources simultaneously. Efficiency requires that the data processing and analysis are performed in an automated way.

    The interpretation of spectra is based on physical models of the atmospheres of the stars, from where the light that we observe escapes the stars. The main ingredients for building such models are the fluid dynamics, and the properties of the atoms, ions, and molecules, especially regarding their interactions with the radiation coming from the stellar interior.

    Once we have a plausible model, it is possible to compute in detail how the radiation propagates through the stellar atmosphere, and the emergent spectrum, which can then be iteratively compared with the observations to refine the model.

    This project covers three different research fronts:

    - Improving model atmospheres and simulations of stellar spectra.

    - Developing tools for acquisition, reduction, and analysis of spectroscopic observations, in particular for the determination of chemical abundances in stars.

    - Designing, preparing, and executing spectroscopic studies of stars aimed at understanding a) the most relevant aspects of the physics of stellar atmospheres, b) the formation and evolution of stars, c) the origin of the chemical elements, and d) the formation, structure, and evolution of the Milky Way galaxy.

    Principal investigator
    Project staff
    Collaborators
    Dr.
    I. Hubeny
    Dr.
    B. Castanheira
    Dr.
    M. Kilic
    Dr.
    S. Majewski
    Dr.
    H.G. Ludwig
    Dr.
    M. Cropper
    Dr.
    M. P. Ruffoni
    Dr.
    J. C. Pickering
    Dr.
    K. Cunha
    Dr.
    Andrew Cooper
    Dr.
    Boris Gaensicke
    1. Complete the installation and commissioning of HORuS on GTC
    2. Discover two new stars with more than 100,000 times less iron than the Sun
    3. Complete the classification of all the APOGEE spectra with K-means
    4. Publish a complete collection of model stellar spectra for stars O to M
    5. Identify the signature of chemical diffusion in the atmospheres of the stars in the cluster M67

    Related publications

    • New ultra metal-poor stars from SDSS: follow-up GTC medium-resolution spectroscopy
      Context. The first generation of stars formed in the Galaxy left behind the chemical signatures of their nucleosynthesis in the interstellar medium, visible today in the atmospheres of low-mass stars that formed afterwards. Sampling the chemistry of those low-mass provides insight into the first stars. Aims: We aim to increase the samples of stars
      Aguado, D. S. et al.

      Advertised on:

      7
      2017
      Citations
      23
    • WHT follow-up observations of extremely metal-poor stars identified from SDSS and LAMOST
      Aims: We have identified several tens of extremely metal-poor star candidates from SDSS and LAMOST, which we follow up with the 4.2 m William Herschel Telescope (WHT) telescope to confirm their metallicity. Methods: We followed a robust two-step methodology. We first analyzed the SDSS and LAMOST spectra. A first set of stellar parameters was
      Aguado, D. S. et al.

      Advertised on:

      9
      2017
      Citations
      37
    • Sloan Digital Sky Survey IV: Mapping the Milky Way, Nearby Galaxies, and the Distant Universe
      We describe the Sloan Digital Sky Survey IV (SDSS-IV), a project encompassing three major spectroscopic programs. The Apache Point Observatory Galactic Evolution Experiment 2 (APOGEE-2) is observing hundreds of thousands of Milky Way stars at high resolution and high signal-to-noise ratios in the near-infrared. The Mapping Nearby Galaxies at Apache
      Mao, Shude et al.

      Advertised on:

      7
      2017
      Citations
      1000
    • The Gaia-ESO Survey: Low-α element stars in the Galactic bulge
      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
      Zaggia, S. et al.

      Advertised on:

      6
      2017
      Citations
      36
    • Gaia Data Release 1. Open cluster astrometry: performance, limitations, and future prospects
      Context. The first Gaia Data Release contains the Tycho-Gaia Astrometric Solution (TGAS). This is a subset of about 2 million stars for which, besides the position and photometry, the proper motion and parallax are calculated using Hipparcos and Tycho-2 positions in 1991.25 as prior information. Aims: We investigate the scientific potential and
      Zschocke, S. et al.

      Advertised on:

      5
      2017
      Citations
      92
    • Monitoring luminous yellow massive stars in M 33: new yellow hypergiant candidates
      Context. The evolution of massive stars surviving the red supergiant (RSG) stage remains unexplored due to the rarity of such objects. The yellow hypergiants (YHGs) appear to be the warm counterparts of post-RSG classes located near the Humphreys-Davidson upper luminosity limit, which are characterized by atmospheric instability and high mass-loss
      Kourniotis, M. et al.

      Advertised on:

      5
      2017
      Citations
      12
    • The Correlation between Mixing Length and Metallicity on the Giant Branch: Implications for Ages in the Gaia Era
      In the updated APOGEE-Kepler catalog, we have asteroseismic and spectroscopic data for over 3000 first ascent red giants. Given the size and accuracy of this sample, these data offer an unprecedented test of the accuracy of stellar models on the post-main-sequence. When we compare these data to theoretical predictions, we find a metallicity
      Tayar, Jamie et al.

      Advertised on:

      5
      2017
      Citations
      94
    • Timing the Evolution of the Galactic Disk with NGC 6791: An Open Cluster with Peculiar High-α Chemistry as Seen by APOGEE
      We utilize elemental-abundance information for Galactic red giant stars in five open clusters (NGC 7789, NGC 6819, M67, NGC 188, and NGC 6791) from the Apache Point Observatory Galactic Evolution Experiment (APOGEE) DR13 data set to age-date the chemical evolution of the high- and low-α element sequences of the Milky Way (MW). Key to this time
      Linden, Sean T. et al.

      Advertised on:

      6
      2017
      Citations
      22
    • Four new massive pulsating white dwarfs including an ultramassive DAV
      We report the discovery of four massive (M > 0.8 M⊙) ZZ Ceti white dwarfs, including an ultramassive 1.16 M⊙ star. We obtained ground-based, time series photometry for 13 white dwarfs from the Sloan Digital Sky Survey Data Release 7 and Data Release 10 whose atmospheric parameters place them within the ZZ Ceti instability strip. We detect
      Curd, B. et al.

      Advertised on:

      2
      2017
      Citations
      30
    • Baade's window and APOGEE. Metallicities, ages, and chemical abundances
      Context. Baade's window (BW) is one of the most observed Galactic bulge fields in terms of chemical abundances. Owing to its low and homogeneous interstellar absorption it is considered the perfect calibration field for Galactic bulge studies. Aims: In the era of large spectroscopic surveys, calibration fields such as BW are necessary for cross
      Schultheis, M. et al.

      Advertised on:

      3
      2017
      Citations
      66
    • Chemical tagging with APOGEE: discovery of a large population of N-rich stars in the inner Galaxy
      Formation of globular clusters (GCs), the Galactic bulge, or galaxy bulges in general is an important unsolved problem in Galactic astronomy. Homogeneous infrared observations of large samples of stars belonging to GCs and the Galactic bulge field are one of the best ways to study these problems. We report the discovery by APOGEE (Apache Point
      Schiavon, R. P. et al.

      Advertised on:

      2
      2017
      Citations
      175
    • Chemical Abundances of M-dwarfs from the APOGEE Survey. I. The Exoplanet Hosting Stars Kepler-138 and Kepler-186
      We report the first detailed chemical abundance analysis of the exoplanet-hosting M-dwarf stars Kepler-138 and Kepler-186 from the analysis of high-resolution (R ∼ 22,500) H-band spectra from the SDSS-IV–APOGEE survey. Chemical abundances of 13 elements—C, O, Na, Mg, Al, Si, K, Ca, Ti, V, Cr, Mn, and Fe—are extracted from the APOGEE spectra of
      Souto, D. et al.

      Advertised on:

      2
      2017
      Citations
      46
    • The Gaia-ESO Survey: Calibration strategy
      The Gaia-ESO survey (GES) is now in its fifth and last year of observations and has produced tens of thousands of high-quality spectra of stars in all Milky Way components. This paper presents the strategy behind the selection of astrophysical calibration targets, ensuring that all GES results on radial velocities, atmospheric parameters, and
      Pancino, E. et al.

      Advertised on:

      1
      2017
      Citations
      60
    • NLTE Analysis of High-resolution H-band Spectra. II. Neutral Magnesium
      Aiming at testing the validity of our magnesium atomic model and investigating the effects of non-local thermodynamical equilibrium (NLTE) on the formation of the H-band neutral magnesium lines, we derive the differential Mg abundances from selected transitions for 13 stars either adopting or relaxing the assumption of local thermodynamical
      Zhang, J. et al.

      Advertised on:

      1
      2017
      Citations
      17
    • Chemical trends in the Galactic halo from APOGEE data
      The galaxy formation process in the Λ cold dark matter scenario can be constrained from the analysis of stars in the Milky Way's halo system. We examine the variation of chemical abundances in distant halo stars observed by the Apache Point Observatory Galactic Evolution Experiment (APOGEE), as a function of distance from the Galactic Centre (r)
      Fernández-Alvar, E. et al.

      Advertised on:

      2
      2017
      Citations
      29
    • Galactic archaeology with asteroseismology and spectroscopy: Red giants observed by CoRoT and APOGEE
      With the advent of the space missions CoRoT and Kepler, it has recently become feasible to determine precise asteroseismic masses and relative ages for large samples of red giant stars. We present the CoRoGEE dataset, obtained from CoRoT light curves for 606 red giants in two fields of the Galactic disc that have been co-observed by the Apache
      Anders, F. et al.

      Advertised on:

      1
      2017
      Citations
      101
    • IMF and [Na/Fe] abundance ratios from optical and NIR spectral features in early-type galaxies
      We present a joint analysis of the four most prominent sodium-sensitive features (Na D, Na I λ8190Å, Na I λ1.14 μm, and Na I λ2.21 μm), in the optical and near-infrared spectral ranges, of two nearby, massive (σ ˜ 300 km s-1), early-type galaxies (named XSG1 and XSG2). Our analysis relies on deep Very Large Telescope/X-Shooter long-slit spectra
      La Barbera, F. et al.

      Advertised on:

      1
      2017
      Citations
      63
    • Evidence for a metal-poor population in the inner Galactic bulge
      The inner Galactic bulge has, until recently, been avoided in chemical evolution studies because of extreme extinction and stellar crowding. Large, near-IR spectroscopic surveys, such as the Apache Point Observatory Galactic Evolution Experiment (APOGEE), for the first time allow the measurement of metallicities in the inner region of our Galaxy
      Schultheis, M. et al.

      Advertised on:

      12
      2015
      Citations
      26
    • The SDSS-III APOGEE Spectral Line List for H-band Spectroscopy
      We present the H-band spectral line lists adopted by the Apache Point Observatory Galactic Evolution Experiment (APOGEE). The APOGEE line lists comprise astrophysical, theoretical, and laboratory sources from the literature, as well as newly evaluated astrophysical oscillator strengths and damping parameters. We discuss the construction of the
      Shetrone, M. et al.

      Advertised on:

      12
      2015
      Citations
      157
    • The Data Reduction Pipeline for the Apache Point Observatory Galactic Evolution Experiment
      The Apache Point Observatory Galactic Evolution Experiment (APOGEE), part of the Sloan Digital Sky Survey III, explores the stellar populations of the Milky Way using the Sloan 2.5-m telescope linked to a high resolution (R ∼ 22,500), near-infrared (1.51–1.70 μm) spectrograph with 300 optical fibers. For over 150,000 predominantly red giant branch
      Nidever, D. L. et al.

      Advertised on:

      12
      2015
      Citations
      355

    Related talks

    No related talks were found.

    Related conferences

    No related conferences were found.
    Related projects
    Optical bench
    HORuS - High Optical Resolution Spectrograph
    High-resolution spectrograph for the 10-m Gran Telescopio Canarias (GTC) based on components from UES, a spectrograph which was in use at the 4.2-m William Herschel Telescope (WHT) between 1992 and 2001.
    Carlos
    Allende Prieto
    Gran Telescopio Canarias (GTC)
    SEVERO OCHOA 2016 - 2019
    The IAC is an internationalized Spanish research centre aiming to achieve major advances in the understanding of the laws that govern the origin and evolution of the various forms of matter/energy in the Universe. Outstanding results are expected in key areas of research such as Solar physics, Sun-Earth connections, Exoplanetary systems, Solar
    Rafael
    Rebolo López