The GIRAFFE Inner Bulge Survey (GIBS): II. Metallicity distributions and alpha element abundances at fixed Galactic latitude

O. A. Gonzalez, M. Zoccali, S. Vasquez, V. Hill, M. Rejkuba, E. Valenti, A. Rojas-Arriagada, A. Renzini, C. Babusiaux, D. Minniti, T. M. Brown

Resultado de la investigación: Article

32 Citas (Scopus)

Resumen

Aims. We investigate metallicity and α-element abundance gradients along a Galactic longitude strip, at latitude b -4°, with the aim of providing observational constraints for the structure and origin of the Milky Way bulge. Methods. High-resolution (R ∼ 22 500) spectra for 400 K giants, in four fields within-4.8° ≤ b ≤-3.4° and-10° ≤ l ≤ +10°, were obtained within the GIRAFFE Inner Bulge Survey (GIBS) project. To this sample we added another ∼400 stars in Baade's Window at (l,b) = (1°,-4°), observed with the identical instrumental configuration: FLAMES GIRAFFE in Medusa mode with HR13 setup. All target stars lie within the red clump of the bulge colour-magnitude diagram, thus minimising contamination from the disc or halo stars. The spectroscopic stellar surface parameters were derived with an automatic method based on the GALA code, while the [Ca/Fe] and [Mg/Fe] abundances as a function of [Fe/H] were derived through a comparison with the synthetic spectra using MOOG. We constructed the metallicity distributions for the entire sample, and for each field individually, in order to investigate the presence of gradients or field-to-field variations in the shape of the distributions. Results. The metallicity distributions in the five fields are consistent with being drawn from a single parent population, indicating the absence of a gradient along the major axis of the Galactic bar. The global metallicity distribution is nicely fitted by two Gaussians. The metal-poor component is rather broad, with a mean at [Fe/H] =-0.31 dex and σ = 0.31 dex. The metal-rich component is narrower, with mean [Fe/H] = + 0.26 and σ = 0.2 dex. The [Mg/Fe] ratio follows a tight trend with [Fe/H], with enhancement with respect to solar in the metal-poor regime similar to the value observed for giant stars in the local thick disc. [Ca/Fe] abundances follow a similar trend, but with a considerably larger scatter than [Mg/Fe]. A decrease in [Mg/Fe] is observed at [Fe/H] =-0.44 dex. This knee is in agreement with our previous bulge study of K-giants along the minor axis, but is 0.1 dex lower in metallicity than the value reported for the microlensed dwarf and subgiant stars in the bulge. We found no variation in α-element abundance distributions between different fields.

Idioma originalEnglish
Número de artículoA46
PublicaciónAstronomy and Astrophysics
Volumen584
DOI
EstadoPublished - 1 dic 2015

Huella dactilar

metallicity
stars
gradients
metal
subgiant stars
metals
single parent
trends
dwarf stars
giant stars
color-magnitude diagram
clumps
longitude
halos
strip
contamination
diagram
distribution
augmentation
high resolution

ASJC Scopus subject areas

  • Astronomy and Astrophysics
  • Space and Planetary Science

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Gonzalez, O. A. ; Zoccali, M. ; Vasquez, S. ; Hill, V. ; Rejkuba, M. ; Valenti, E. ; Rojas-Arriagada, A. ; Renzini, A. ; Babusiaux, C. ; Minniti, D. ; Brown, T. M. / The GIRAFFE Inner Bulge Survey (GIBS) : II. Metallicity distributions and alpha element abundances at fixed Galactic latitude. En: Astronomy and Astrophysics. 2015 ; Vol. 584.
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abstract = "Aims. We investigate metallicity and α-element abundance gradients along a Galactic longitude strip, at latitude b -4°, with the aim of providing observational constraints for the structure and origin of the Milky Way bulge. Methods. High-resolution (R ∼ 22 500) spectra for 400 K giants, in four fields within-4.8° ≤ b ≤-3.4° and-10° ≤ l ≤ +10°, were obtained within the GIRAFFE Inner Bulge Survey (GIBS) project. To this sample we added another ∼400 stars in Baade's Window at (l,b) = (1°,-4°), observed with the identical instrumental configuration: FLAMES GIRAFFE in Medusa mode with HR13 setup. All target stars lie within the red clump of the bulge colour-magnitude diagram, thus minimising contamination from the disc or halo stars. The spectroscopic stellar surface parameters were derived with an automatic method based on the GALA code, while the [Ca/Fe] and [Mg/Fe] abundances as a function of [Fe/H] were derived through a comparison with the synthetic spectra using MOOG. We constructed the metallicity distributions for the entire sample, and for each field individually, in order to investigate the presence of gradients or field-to-field variations in the shape of the distributions. Results. The metallicity distributions in the five fields are consistent with being drawn from a single parent population, indicating the absence of a gradient along the major axis of the Galactic bar. The global metallicity distribution is nicely fitted by two Gaussians. The metal-poor component is rather broad, with a mean at [Fe/H] =-0.31 dex and σ = 0.31 dex. The metal-rich component is narrower, with mean [Fe/H] = + 0.26 and σ = 0.2 dex. The [Mg/Fe] ratio follows a tight trend with [Fe/H], with enhancement with respect to solar in the metal-poor regime similar to the value observed for giant stars in the local thick disc. [Ca/Fe] abundances follow a similar trend, but with a considerably larger scatter than [Mg/Fe]. A decrease in [Mg/Fe] is observed at [Fe/H] =-0.44 dex. This knee is in agreement with our previous bulge study of K-giants along the minor axis, but is 0.1 dex lower in metallicity than the value reported for the microlensed dwarf and subgiant stars in the bulge. We found no variation in α-element abundance distributions between different fields.",
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author = "Gonzalez, {O. A.} and M. Zoccali and S. Vasquez and V. Hill and M. Rejkuba and E. Valenti and A. Rojas-Arriagada and A. Renzini and C. Babusiaux and D. Minniti and Brown, {T. M.}",
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Gonzalez, OA, Zoccali, M, Vasquez, S, Hill, V, Rejkuba, M, Valenti, E, Rojas-Arriagada, A, Renzini, A, Babusiaux, C, Minniti, D & Brown, TM 2015, 'The GIRAFFE Inner Bulge Survey (GIBS): II. Metallicity distributions and alpha element abundances at fixed Galactic latitude', Astronomy and Astrophysics, vol. 584, A46. https://doi.org/10.1051/0004-6361/201526737

The GIRAFFE Inner Bulge Survey (GIBS) : II. Metallicity distributions and alpha element abundances at fixed Galactic latitude. / Gonzalez, O. A.; Zoccali, M.; Vasquez, S.; Hill, V.; Rejkuba, M.; Valenti, E.; Rojas-Arriagada, A.; Renzini, A.; Babusiaux, C.; Minniti, D.; Brown, T. M.

En: Astronomy and Astrophysics, Vol. 584, A46, 01.12.2015.

Resultado de la investigación: Article

TY - JOUR

T1 - The GIRAFFE Inner Bulge Survey (GIBS)

T2 - II. Metallicity distributions and alpha element abundances at fixed Galactic latitude

AU - Gonzalez, O. A.

AU - Zoccali, M.

AU - Vasquez, S.

AU - Hill, V.

AU - Rejkuba, M.

AU - Valenti, E.

AU - Rojas-Arriagada, A.

AU - Renzini, A.

AU - Babusiaux, C.

AU - Minniti, D.

AU - Brown, T. M.

PY - 2015/12/1

Y1 - 2015/12/1

N2 - Aims. We investigate metallicity and α-element abundance gradients along a Galactic longitude strip, at latitude b -4°, with the aim of providing observational constraints for the structure and origin of the Milky Way bulge. Methods. High-resolution (R ∼ 22 500) spectra for 400 K giants, in four fields within-4.8° ≤ b ≤-3.4° and-10° ≤ l ≤ +10°, were obtained within the GIRAFFE Inner Bulge Survey (GIBS) project. To this sample we added another ∼400 stars in Baade's Window at (l,b) = (1°,-4°), observed with the identical instrumental configuration: FLAMES GIRAFFE in Medusa mode with HR13 setup. All target stars lie within the red clump of the bulge colour-magnitude diagram, thus minimising contamination from the disc or halo stars. The spectroscopic stellar surface parameters were derived with an automatic method based on the GALA code, while the [Ca/Fe] and [Mg/Fe] abundances as a function of [Fe/H] were derived through a comparison with the synthetic spectra using MOOG. We constructed the metallicity distributions for the entire sample, and for each field individually, in order to investigate the presence of gradients or field-to-field variations in the shape of the distributions. Results. The metallicity distributions in the five fields are consistent with being drawn from a single parent population, indicating the absence of a gradient along the major axis of the Galactic bar. The global metallicity distribution is nicely fitted by two Gaussians. The metal-poor component is rather broad, with a mean at [Fe/H] =-0.31 dex and σ = 0.31 dex. The metal-rich component is narrower, with mean [Fe/H] = + 0.26 and σ = 0.2 dex. The [Mg/Fe] ratio follows a tight trend with [Fe/H], with enhancement with respect to solar in the metal-poor regime similar to the value observed for giant stars in the local thick disc. [Ca/Fe] abundances follow a similar trend, but with a considerably larger scatter than [Mg/Fe]. A decrease in [Mg/Fe] is observed at [Fe/H] =-0.44 dex. This knee is in agreement with our previous bulge study of K-giants along the minor axis, but is 0.1 dex lower in metallicity than the value reported for the microlensed dwarf and subgiant stars in the bulge. We found no variation in α-element abundance distributions between different fields.

AB - Aims. We investigate metallicity and α-element abundance gradients along a Galactic longitude strip, at latitude b -4°, with the aim of providing observational constraints for the structure and origin of the Milky Way bulge. Methods. High-resolution (R ∼ 22 500) spectra for 400 K giants, in four fields within-4.8° ≤ b ≤-3.4° and-10° ≤ l ≤ +10°, were obtained within the GIRAFFE Inner Bulge Survey (GIBS) project. To this sample we added another ∼400 stars in Baade's Window at (l,b) = (1°,-4°), observed with the identical instrumental configuration: FLAMES GIRAFFE in Medusa mode with HR13 setup. All target stars lie within the red clump of the bulge colour-magnitude diagram, thus minimising contamination from the disc or halo stars. The spectroscopic stellar surface parameters were derived with an automatic method based on the GALA code, while the [Ca/Fe] and [Mg/Fe] abundances as a function of [Fe/H] were derived through a comparison with the synthetic spectra using MOOG. We constructed the metallicity distributions for the entire sample, and for each field individually, in order to investigate the presence of gradients or field-to-field variations in the shape of the distributions. Results. The metallicity distributions in the five fields are consistent with being drawn from a single parent population, indicating the absence of a gradient along the major axis of the Galactic bar. The global metallicity distribution is nicely fitted by two Gaussians. The metal-poor component is rather broad, with a mean at [Fe/H] =-0.31 dex and σ = 0.31 dex. The metal-rich component is narrower, with mean [Fe/H] = + 0.26 and σ = 0.2 dex. The [Mg/Fe] ratio follows a tight trend with [Fe/H], with enhancement with respect to solar in the metal-poor regime similar to the value observed for giant stars in the local thick disc. [Ca/Fe] abundances follow a similar trend, but with a considerably larger scatter than [Mg/Fe]. A decrease in [Mg/Fe] is observed at [Fe/H] =-0.44 dex. This knee is in agreement with our previous bulge study of K-giants along the minor axis, but is 0.1 dex lower in metallicity than the value reported for the microlensed dwarf and subgiant stars in the bulge. We found no variation in α-element abundance distributions between different fields.

KW - Galaxy: abundances

KW - Galaxy: bulge

KW - Galaxy: evolution

KW - Galaxy: formation

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U2 - 10.1051/0004-6361/201526737

DO - 10.1051/0004-6361/201526737

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JF - Astronomy and Astrophysics

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