Spectroscopic Evidence for Small Metallicity Variations among M92 Giants

• Published in: The Astronomical journal Vol. 115; no. 2; pp. 685 - 692
• Main Authors: Langer, G. E, Fischer, Debra, Sneden, Christopher, Bolte, Michael
• Format: Journal Article
• Language: English
• Published: IOP Publishing 01.02.1998
• ISSN: 1538-3881; 0004-6256; 1538-3881
• DOI: 10.1086/300228

We present spectroscopic evidence for small star-to-star variations in the abundance of the atoms from Ca to Ni (primarily Fe) among three bright giants in the metal-poor globular cluster M92: V-45, XI-19, and XII-8. Although all three have very similar B - V colors and visual magnitudes, weak 'iron peak' absorption lines are typically about 15 percent 30 percent stronger in the spectrum of star XI-19. A line-by-line analysis shows that the abundances of the 'iron peak' elements are very similar in stars V-45 and XII-8; the (logarithmic) mean difference is only 0.01 0.01 dex for 106 lines. The average abundance of the 'iron peak' elements is 0.18 0.01 dex larger in XI-19 (121 lines). The very small 'internal' error in the mean difference can be traced to (1) comparing the abundances one line at a time in order to avoid errors introduced by uncertain gf-values, (2) averaging equivalent widths for two spectra for both XI-19 and the comparison stars to reduce random errors in the equivalent widths, and (3) using a large number of lines to drive down the error in the mean. The 'external' errors must also be small: the very small differences in the positions of the stars in the (V, B - V) color-magnitude diagram imply such similar values of T(eff) and log g that the line-strength differences must be due to real abundance differences. (Author)