7 research outputs found
Oxygen Abundances in Two Metal-Poor Subgiants from the Analysis of the 6300 A Forbidden O I Line
Recent LTE analyses (Israelian et al. 1998 and Bosegaard et al. 1999) of the
OH bands in the optical-ultraviolet spectra of nearby metal-poor subdwarfs
indicate that oxygen abundances are generally higher than those previously
determined. The difference increases with decreasing metallicity and reaches
delta([O/Fe]) ~ +0.6 dex as [Fe/H] approaches -3.0.
Employing high resolution (R = 50000), high S/N (~ 250) echelle spectra of
the two stars found by Israelian et al. (1998) to have the highest
[O/Fe]-ratios, viz, BD +23 3130 and BD +37 1458, we conducted abundance
analyses based on about 60 Fe I and 7-9 Fe II lines. We determined from Kurucz
LTE models the values of the stellar parameters, as well as abundances of Na,
Ni, and the traditional alpha-elements, independent of the calibration of color
vs scales. We determined oxygen abundances from spectral synthesis of
the stronger line (6300 A) of the [O I] doublet.
The syntheses of the [O I] line lead to smaller values of [O/Fe], consistent
with those found earlier among halo field and globular cluster giants. We
obtain [O/Fe] = +0.35 +/- 0.2 for BD +23 3130 and +0.50 +/- 0.2 for BD +37
1458. In the former, the [O I] line is very weak (~ 1 mA), so that the quoted
[O/Fe] value may in reality be an upper limit.
Therefore in these two stars a discrepancy exists between the [O/Fe]- ratios
derived from [O I] and the OH feature, and the origin of this difference
remains unclear. Until the matter is clarified, we suggest it is premature to
conclude that the ab initio oxygen abundances of old, metal-poor stars need to
be revised drastically upward.Comment: 38 pages, 5 tables, 14 figures To appear in July 1999 AJ Updated
April 16, 1999. Fixed typo
EDUCATIONAL SOFTWARE IN TEACHING
This paper stands as an argument for employing educational software in teaching and evaluating skills and knowledge in higher education. The authors’ main goal is to pinpoint and focus on strategies of teaching through the use of modern means, namely educational software