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

    • A photometric study of globular clusters observed by the APOGEE survey
      In this paper, we describe the photometric and spectroscopic properties of multiple populations in seven northern globular clusters. In this study, we employ precise ground-based photometry from the private collection of Stetson, space photometry from the Hubble Space Telescope (HST), literature abundances of Na and O, and Apache Point Observatory
      Mészáros, Sz. et al.

      Advertised on:

      4
      2018
      Citations
      6
    • Disentangling the Galactic Halo with APOGEE. I. Chemical and Kinematical Investigation of Distinct Metal-poor Populations
      We find two chemically distinct populations separated relatively cleanly in the [Fe/H]–[Mg/Fe] plane, but also distinguished in other chemical planes, among metal-poor stars (primarily with metallicities [{Fe}/{{H}}] -0.9) observed by the Apache Point Observatory Galactic Evolution Experiment (APOGEE) and analyzed for Data Release 13 (DR13) of the
      Hayes, C. R. et al.

      Advertised on:

      1
      2018
      Citations
      135
    • Disentangling the Galactic Halo with APOGEE. II. Chemical and Star Formation Histories for the Two Distinct Populations
      The formation processes that led to the current Galactic stellar halo are still under debate. Previous studies have provided evidence for different stellar populations in terms of elemental abundances and kinematics, pointing to different chemical and star formation histories (SFHs). In the present work, we explore, over a broader range in
      Fernández-Alvar, E. et al.

      Advertised on:

      1
      2018
      Citations
      58
    • The Bulge Metallicity Distribution from the APOGEE Survey
      The Apache Point Observatory Galactic Evolution Experiment (APOGEE) provides spectroscopic information of regions of the inner Milky Way, which are inaccessible to optical surveys. We present the first large study of the metallicity distribution of the innermost Galactic regions based on high-quality measurements for 7545 red giant stars within 4.5
      García Pérez, A. E. et al.

      Advertised on:

      1
      2018
      Citations
      38
    • J0815+4729: A Chemically Primitive Dwarf Star in the Galactic Halo Observed with Gran Telescopio Canarias
      We report the discovery of the carbon-rich hyper metal-poor unevolved star J0815+4729. This dwarf star was selected from SDSS/BOSS as a metal-poor candidate and follow-up spectroscopic observations at medium resolution were obtained with the Intermediate dispersion Spectrograph and Imaging System (ISIS) at William Herschel Telescope and the Optical
      Aguado, D. S. et al.

      Advertised on:

      1
      2018
      Citations
      31
    • Metallicity gradient of the thick disc progenitor at high redshift
      We have developed a novel Markov Chain Monte Carlo chemical 'painting' technique to explore possible radial and vertical metallicity gradients for the thick disc progenitor. In our analysis, we match an N-body simulation to the data from the Apache Point Observatory Galactic Evolution Experiment survey. We assume that the thick disc has a constant
      Kawata, D. et al.

      Advertised on:

      1
      2018
      Citations
      17
    • Elemental Abundances of Kepler Objects of Interest in APOGEE. I. Two Distinct Orbital Period Regimes Inferred from Host Star Iron Abundances
      The Apache Point Observatory Galactic Evolution Experiment (APOGEE) has observed ∼600 transiting exoplanets and exoplanet candidates from Kepler (Kepler Objects of Interest, KOIs), most with ≥18 epochs. The combined multi-epoch spectra are of high signal-to-noise ratio (typically ≥100) and yield precise stellar parameters and chemical abundances
      Wilson, R. F. et al.

      Advertised on:

      2
      2018
      Citations
      40
    • 12C/13C isotopic ratios in red-giant stars of the open cluster NGC 6791
      Carbon isotope ratios, along with carbon and nitrogen abundances, are derived in a sample of 11 red-giant members of one of the most metal-rich clusters in the Milky Way, NGC 6791. The selected red-giants have a mean metallicity and standard deviation of [Fe/H] = +0.39 ± 0.06 (Cunha et al. 2015). We used high-resolution H-band spectra obtained by
      Szigeti, L. et al.

      Advertised on:

      3
      2018
      Citations
      15
    • The Pristine survey - III. Spectroscopic confirmation of an efficient search for extremely metal-poor stars
      The Pristine survey is a narrow-band, photometric survey focused around the wavelength region of the Ca II H&K absorption lines, designed to efficiently search for extremely metal-poor stars. In this work, we use the first results of a medium-resolution spectroscopic follow-up to refine the selection criteria for finding extremely metal-poor stars
      Youakim, K. et al.

      Advertised on:

      12
      2017
      Citations
      53
    • The 13th Data Release of the Sloan Digital Sky Survey: First Spectroscopic Data from the SDSS-IV Survey Mapping Nearby Galaxies at Apache Point Observatory
      The fourth generation of the Sloan Digital Sky Survey (SDSS-IV) began observations in 2014 July. It pursues three core programs: the Apache Point Observatory Galactic Evolution Experiment 2 (APOGEE-2), Mapping Nearby Galaxies at APO (MaNGA), and the Extended Baryon Oscillation Spectroscopic Survey (eBOSS). As well as its core program, eBOSS
      Albareti, F. D. et al.

      Advertised on:

      12
      2017
      Citations
      580
    • Gaia Data Release 1. Testing parallaxes with local Cepheids and RR Lyrae stars
      Context. Parallaxes for 331 classical Cepheids, 31 Type II Cepheids, and 364 RR Lyrae stars in common between Gaia and the Hipparcos and Tycho-2 catalogues are published in Gaia Data Release 1 (DR1) as part of the Tycho-Gaia Astrometric Solution (TGAS). Aims: In order to test these first parallax measurements of the primary standard candles of the
      Gaia Collaboration et al.

      Advertised on:

      9
      2017
      Citations
      98
    • Adding the s-Process Element Cerium to the APOGEE Survey: Identification and Characterization of Ce ii Lines in the H-band Spectral Window
      Nine Ce ii lines have been identified and characterized within the spectral window observed by the Apache Point Observatory Galactic Evolution Experiment (APOGEE) survey (between λ1.51 and 1.69 μm). At solar metallicities, cerium is an element that is produced predominantly as a result of the slow capture of neutrons (the s-process) during
      Cunha, K.a et al.

      Advertised on:

      8
      2017
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      81
    • APOGEE Chemical Abundances of the Sagittarius Dwarf Galaxy
      The Apache Point Observatory Galactic Evolution Experiment provides the opportunity of measuring elemental abundances for C, N, O, Na, Mg, Al, Si, P, K, Ca, V, Cr, Mn, Fe, Co, and Ni in vast numbers of stars. We analyze thechemical-abundance patterns of these elements for 158 red giant stars belonging to the Sagittarius dwarf galaxy (Sgr). This is
      Hasselquist, S. et al.

      Advertised on:

      8
      2017
      Citations
      74
    • The Apache Point Observatory Galactic Evolution Experiment (APOGEE)
      The Apache Point Observatory Galactic Evolution Experiment (APOGEE), one of the programs in the Sloan Digital Sky Survey III (SDSS-III), has now completed its systematic, homogeneous spectroscopic survey sampling all major populations of the Milky Way. After a three-year observing campaign on the Sloan 2.5 m Telescope, APOGEE has collected a half
      Majewski, S. R. et al.

      Advertised on:

      9
      2017
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      1000
    • Atypical Mg-poor Milky Way Field Stars with Globular Cluster Second-generation-like Chemical Patterns
      We report the peculiar chemical abundance patterns of 11 atypical Milky Way (MW) field red giant stars observed by the Apache Point Observatory Galactic Evolution Experiment (APOGEE). These atypical giants exhibit strong Al and N enhancements accompanied by C and Mg depletions, strikingly similar to those observed in the so-called second-generation
      Fernández-Trincado, J. G. et al.

      Advertised on:

      9
      2017
      Citations
      73
    • The open cluster King 1 in the second quadrant
      We analyse the poorly studied open cluster King 1 in the second Galactic quadrant. From wide-field photometry, we have studied the spatial distribution of this cluster. We determined that the centre of King 1 is located at α2000 = 00h22m and δ2000 = +64°23΄. By parameterizing the stellar density with a King profile, we have obtained a central
      Carrera, R. et al.

      Advertised on:

      10
      2017
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      8
    • Ultracool dwarf benchmarks with Gaia primaries
      We explore the potential of Gaia for the field of benchmark ultracool/brown dwarf companions, and present the results of an initial search for metal-rich/metal-poor systems. A simulated population of resolved ultracool dwarf companions to Gaia primary stars is generated and assessed. Of the order of ˜24 000 companions should be identifiable outside
      Marocco, F. et al.

      Advertised on:

      10
      2017
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    • The Pristine survey - I. Mining the Galaxy for the most metal-poor stars
      We present the Pristine survey, a new narrow-band photometric survey focused on the metallicity-sensitive Ca H&K lines and conducted in the Northern hemisphere with the wide-field imager MegaCam on the Canada-France-Hawaii Telescope. This paper reviews our overall survey strategy and discusses the data processing and metallicity calibration
      Venn, Kim A. et al.

      Advertised on:

      11
      2017
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      195
    • A Gemini snapshot survey for double degenerates
      We present the results from a Gemini snapshot radial-velocity survey of 44 low-mass white-dwarf candidates selected from the Sloan Digital Sky Survey (SDSS) spectroscopy. To find sub-hour orbital period binary systems, our time-series spectroscopy had cadences of 2-8 min over a period of 20-30 min. Through follow-up observations at Gemini and the
      Bell, Keaton J. et al.

      Advertised on:

      11
      2017
      Citations
      13
    • The puzzling interpretation of NIR indices: The case of NaI2.21
      We present a detailed study of the Na I line strength index centred in the K band at 22 100 Å (NaI2.21 hereafter) relying on different samples of early-type galaxies. Consistent with previous studies, we find that the observed line strength indices cannot be fit by state-of-the-art scaled-solar stellar population models, even using our newly
      Aguado, D. S. et al.

      Advertised on:

      11
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    Related talks

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    Related conferences

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    Related projects
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