GRANULATION SIGNATURES IN THE SPECTRUM OF THE VERY METAL-POOR RED GIANT HD 122563

Journal Article · Mon Dec 20 00:00:00 EST 2010 · Astrophysical Journal Letters

DOI:https://doi.org/10.1088/2041-8205/725/2/L223· OSTI ID:21454874

RamIrez, I ^[1]; Collet, R; Asplund, M ^[2]; Lambert, D L ^[3]; Allende Prieto, C ^[4]

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1. Observatories of the Carnegie Institution for Science, 813 Santa Barbara Street, Pasadena, CA 91101 (United States)
2. Max Planck Institut fuer Astrophysik, Postfach 1317, 85741 Garching (Germany)
3. McDonald Observatory and Department of Astronomy, University of Texas, Austin, TX 78712-0259 (United States)
4. Instituto de Astrofisica de Canarias, 38205, La Laguna, Tenerife (Spain)

A very high resolution (R = {lambda}/{Delta}{lambda} = 200, 000), high signal-to-noise ratio (S/N {approx_equal} 340) blue-green spectrum of the very metal-poor ([Fe/H] {approx_equal} -2.6) red giant star HD 122563 has been obtained by us at McDonald Observatory. We measure the asymmetries and core wavelengths of a set of unblended Fe I lines covering a wide range of line strength. Line bisectors exhibit the characteristic C-shape signature of surface convection (granulation) and they span from about 100 m s{sup -1} in the strongest Fe I features to 800 m s{sup -1} in the weakest ones. Core wavelength shifts range from about -100 to -900 m s{sup -1}, depending on line strength. In general, larger blueshifts are observed in weaker lines, but there is increasing scatter with increasing residual flux. Assuming local thermodynamic equilibrium (LTE), we synthesize the same set of spectral lines using a state-of-the-art three-dimensional (3D) hydrodynamic simulation for a stellar atmosphere of fundamental parameters similar to those of HD 122563. We find good agreement between model predictions and observations. This allows us to infer an absolute zero point for the line shifts and radial velocity. Moreover, it indicates that the structure and dynamics of the simulation are realistic, thus providing support to previous claims of large 3D-LTE corrections to elemental abundances and fundamental parameters of very metal-poor red giant stars obtained with standard 1D-LTE spectroscopic analyses, as suggested by the hydrodynamic model used here.

• OSTI ID: 21454874
• Journal Information: Astrophysical Journal Letters, Vol. 725, Issue 2; Other Information: DOI: 10.1088/2041-8205/725/2/L223; ISSN 2041-8205
• Country of Publication: United States
• Language: English

Related Subjects

79 ASTROPHYSICS
COSMOLOGY AND ASTRONOMY
ABUNDANCE
GRANULATION
HYDRODYNAMIC MODEL
LTE
METALS
RADIAL VELOCITY
RED GIANT STARS
SIGNAL-TO-NOISE RATIO
STELLAR ATMOSPHERES
THREE-DIMENSIONAL CALCULATIONS
ATMOSPHERES
DIMENSIONLESS NUMBERS
ELEMENTS
EQUILIBRIUM
FABRICATION
GIANT STARS
MATHEMATICAL MODELS
PARTICLE MODELS
STARS
STATISTICAL MODELS
THERMODYNAMIC MODEL
VELOCITY