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26 April 2024 |
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Article overview
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Metallicity Distribution Functions, Radial Velocities, and Alpha Element Abundances in Three Off-Axis Bulge Fields | | Christian I. Johnson
; R. Michael Rich
; Chiaki Kobayashi
; Andrea Kunder
; Catherine A. Pilachowski
; Andreas Koch
; Roberto De Propris
; | | Date: |
15 Feb 2013 | | Abstract: | We present radial velocities and chemical abundance ratios of [Fe/H], [O/Fe],
[Si/Fe], and [Ca/Fe] for 264 red giant branch (RGB) stars in three Galactic
bulge off-axis fields located near (l,b)=(-5.5,-7), (-4,-9), and (+8.5,+9). The
results are based on equivalent width and spectrum synthesis analyses of
moderate resolution (R~18,000), high signal-to-noise ratio (S/N~75-300) spectra
obtained with the Hydra spectrographs on the Blanco 4m and WIYN 3.5m
telescopes. The targets were selected from the blue side of the giant branch to
avoid cool stars that would be strongly affected by CN and TiO; however, a
comparison of the color-metallicity distribution in literature samples suggests
our selection of bluer targets should not present a significant bias against
metal-rich stars. We find a full range in metallicity that spans
[Fe/H]approx-1.5 to +0.5, and that, in accordance with the previously observed
minor-axis vertical metallicity gradient, the median [Fe/H] also declines with
increasing Galactic latitude in off-axis fields. The off-axis vertical [Fe/H]
gradient in the southern bulge is estimated to be ~0.4 dex/kpc. The (+8.5,+9)
field exhibits a higher than expected metallicity, with a median [Fe/H]=-0.23,
that might be related to a stronger presence of the X--shaped bulge structure
along that line-of-sight. All fields exhibit an identical, strong decrease in
velocity dispersion with increasing metallicity that is consistent with
observations in similar minor-axis outer bulge fields. Additionally, the
[O/Fe], [Si/Fe], and [Ca/Fe] versus [Fe/H] trends are identical among our three
fields, and are in good agreement with past bulge studies. [abridged] | | Source: | arXiv, 1302.3679 | | Services: | Forum | Review | PDF | Favorites | |
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