Studies of the Peculiar a Stars.IV. The Relative Abundances of Four Iron-Peak Elements
Abstract
Equivalent widths are given for twenty-nine u?blended lines of Fe Ir, Cr ii, Mn ii, and Ti ii measured in the wavelength interval XX 3200-3520 on 10 A/mm spectrograms of each of twenty-one normal and peculiar A and B stars. These include four X 4200 Si stars, seven Mn stars, five Eu-Cr-Sr stars, one Am star, and four normal stars. The relative strengths of the measured lines of these four elements are very insensitive to changing excitation conditions and are used to determine relative abundances by coarse curve-of-growth techniques. The main results of the analyses are as follows: (a) The excitation temperatures obtained for the peculiar stars are similar to those of normal stars of the same color. (b) All the Ap stars, with the exception of the Mn stars, have abnormally high microturbulent velocities. (c) The Mn stars have an abnormal distribution of abundances among the four elements studied. The Mn stars have a ratio of Mn: Fe which is from 6 to 60 times higher than normal. In the Mn stars the ratios Cr: Fe and Ti: Fe are also abnormal, but these ratios differ from star to star. (d) In the case of the Si-rich and 0-poor varieties of Ap stars the relative abundances of the four elements studied are entirely normal. In particular, the Cr/Fe abundance ratio is normal in Ap stars of the Eu-Cr and Sr-Eu-Cr types. In these stars the enhancement of the Cr lines seen at low dispersion is real, but the lines of Fe, Ti, and Mn are also enhanced.
- Publication:
-
The Astrophysical Journal
- Pub Date:
- July 1966
- DOI:
- 10.1086/148750
- Bibcode:
- 1966ApJ...145..141S