Metal Abundance Determinations for Vega and Sirius
Abstract
Some recent model atmosphere work done by the authors (Strom, S. E. and Avrett, E. H., Ann. Astrophys., in press) suggested that the anomalously small Balmer discontinuity observed in Sirius might be due to an increase in continuous metal opacities arising from a high abundance of metals, particularly Mg and Si. This hypothesis provided the motivation behind the two abundance analyses reported here. For these analyses a standard grid of nine, non- gray stellar models was constructed for the effective temperature range 9000< Teff< 10 0000K and from 3.7 to 4.3 in log g. This range of effective temperatures and surface gravities is representative of the values either known directly or deduced from comparison between stellar models and observations of hydrogen line profiles and continuous fluxes for Vega and Sirius. In addition we have constructed a set of models at Teff=95000 with a log H/metals of approximately 4, 3, and 2. The equivalent widths of several representative metal lines were calculated from those models and the results are compared with the observed equivalent widths. The abundances we have obtained are as follows: LogA GMA Element a Lyr a CMa Log A Nai . -5.70 -5.70 Mgi -4.50 -4.50 -4.60 Ain . -4.70 -5.80 Sin -4.50 -3.50 -4.50 Cai . -6.00 -5.85 Scn -9.00 -10.0 -9.18 Tii . -5.75 -7.32 Tin -7.20 -6.25 Cri -6.70 -6.25 -6.64 Crn -7.00 -6.5 Mni -6.2 -6.2 -7.10 Fei -5.4 -5.0 -5.43 However, estimates of microturbulent velocities in the atmospheres of both stars are critical in these abundance determinations, particularly since most of the Mg and Si lines observed fall on the flat portion of the curve of growth. Further observations will be necessary to determine these microturbulent velocities.
- Publication:
-
The Astronomical Journal
- Pub Date:
- 1965
- DOI:
- 10.1086/109588
- Bibcode:
- 1965AJ.....70R.148S