Computer Science
Scientific paper
Nov 2000
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2000phdt.........5r&link_type=abstract
Thesis (PhD). THE OHIO STATE UNIVERSITY, Source DAI-B 61/05, p. 2578, Nov 2000, 104 pages.
Computer Science
Scientific paper
I present measurements of [Fe/H] for six M supergiant stars and three giant stars within 2.5 pc of the Galactic Center (GC) and one M supergiant star within 30 pc of the GC. The results are based on high-resolution (λ/Δλ = 40,000) K-band spectra, taken with CSHELL at the NASA Infrared Telescope Facility. I determine the iron abundance by detailed abundance analysis of Fe I lines, performed with the spectral synthesis program MOOG. The mean [Fe/H] of the GC stars is determined to be near solar, [Fe/H] = +0.12 +/- 0.22. The analysis is a differential analysis, as I have observed and applied the same analysis technique to eleven cool, luminous stars in the solar neighborhood with similar temperatures and luminosities as the GC stars. The mean [Fe/H] of the solar neighborhood comparison stars, [Fe/H] = +0.03 +/- 0.16, is similar to that of the GC stars. The width of the GC [Fe/H] distribution is found to be narrower than the width of the [Fe/H] distribution of Baade's Window in the bulge but consistent with the width of the [Fe/H] distribution of giant and supergiant stars in the solar neighborhood. I present moderate resolution (λ/Δλ = 1300-4800) K-band spectra of more than 110 M giants in Galactic bulge fields interior to -4 degrees (560 pc) and as close as 0.2 degrees (28 pc from the Galactic Center. From the equivalent widths of three features in these spectra, EW(Na), EW(Ca), and EW(CO), I calculate [Fe/H] for these stars. Note that EW(Na) and EW(Ca) are both blends of numerous elements (Ramírez et al., 1997), and that this technique is based on an empirical calibration derived from globular clusters (Stephens et al., 2000) rather than detailed abundance analysis. The mean [Fe/H] for each field is in good agreement with the results from Frogel et al. (1999) based on the slope of the giant branch method. I find no evidence for a metallicity gradient along the minor or major axes of the inner bulge (R < 560 pc). The lack of a metallicity gradient in the inner bulge is not predicted by a theoretical model for a bulge formed by dissipative collapse (Mollá et al., 2000). A metallicity gradient along the minor axis (Frogel et al., 1999) only arises when fields located at larger galactic radius are included. However, these more distant fields are located outside of the infrared bulge defined by the COBE/DIRBE observations. I compute the [Fe/H] distribution for the inner bulge and find a mean value of -0.21 dex with a full width dispersion of 0.30 dex, close to the values found for Baade's Window (BW) by sadler et al. (1996). Unlike the absence of a gradient, these values are close to theoretical predictions for a bulge formed by dissipative collapse (Mollá et al., 2000).
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