ALPHA ENHANCEMENT AND THE METALLICITY DISTRIBUTION FUNCTION OF PLAUT'S WINDOW

Journal Article · Tue May 10 04:00:00 EDT 2011 · Astrophysical Journal

DOI:https://doi.org/10.1088/0004-637X/732/2/108· OSTI ID:21576852

Johnson, Christian I; Michael Rich, R ^[1]; Fulbright, Jon P ^[2]; Valenti, Elena ^[3]; McWilliam, Andrew ^[4]

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1. Department of Physics and Astronomy, UCLA, 430 Portola Plaza, Box 951547, Los Angeles, CA 90095-1547 (United States)
2. Department of Physics and Astronomy, Johns Hopkins University, Baltimore, MD 21218 (United States)
3. European Southern Observatory, Karl Schwarzschild-Strasse 2, D-85748 Garching bei Muenchen (Germany)
4. Observatories of the Carnegie Institution of Washington, Pasadena, CA (United States)

We present Fe, Si, and Ca abundances for 61 giants in Plaut's window (l = -1{sup 0}, b = -8.{sup 0}5) and Fe abundances for an additional 31 giants in a second, nearby field (l = 0{sup 0}, b = -8{sup 0}) derived from high-resolution (R {approx} 25,000) spectra obtained with the Blanco 4 m telescope and Hydra multifiber spectrograph. The median metallicity of red giant branch (RGB) stars in the Plaut's field is {approx}0.4 dex lower than those in Baade's window, and confirms the presence of an iron abundance gradient along the bulge minor axis. The full metallicity range of our (biased) RGB sample spans -1.5 < [Fe/H] < +0.3, which is similar to that found in other bulge fields. We also derive a photometric metallicity distribution function for RGB stars in the (l = -1{sup 0}, b = -8{sup 0}.5) field and find very good agreement with the spectroscopic metallicity distribution. The radial velocity (RV) and dispersion data for the bulge RGB stars are in agreement with previous results of the Bulge Radial Velocity Assay survey, and we find evidence for a decreasing velocity dispersion with increasing [Fe/H]. The [{alpha}/Fe] enhancement in Plaut field stars is nearly identical to that observed in Baade's window, and suggests that an [{alpha}/Fe] gradient does not exist between b = -4{sup 0} and -8{sup 0}. Additionally, a subset of our sample (23 stars) appears to be foreground red clump stars that are very metal rich, exhibit small metallicity and RV dispersions, and are enhanced in {alpha} elements. While these stars likely belong to the Galactic inner disk population, they exhibit [{alpha}/Fe] ratios that are enhanced above the thin and thick disk.

• OSTI ID: 21576852
• Journal Information: Astrophysical Journal, Journal Name: Astrophysical Journal Journal Issue: 2 Vol. 732; ISSN ASJOAB; ISSN 0004-637X
• Country of Publication: United States
• Language: English

Related Subjects

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY
79 ASTRONOMY AND ASTROPHYSICS
ABUNDANCE
ALKALINE EARTH METALS
CALCIUM
DISTRIBUTION FUNCTIONS
ELEMENT ABUNDANCE
ELEMENTS
FUNCTIONS
GALAXIES
GIANT STARS
IRON
IRON-ALPHA
METALS
RADIAL VELOCITY
SEMIMETALS
SILICON
STARS
TRANSITION ELEMENTS
VELOCITY