A study of twenty-one sharp-lined cool peculiar A stars.

Abstract

view Abstract Citations (139) References (109) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS A study of twenty-one sharp-lined cool peculiar A stars. Adelman, S. J. Abstract Elemental abundance analyses have been performed for 21 cool Ap stars, also known as Sr- Cr-Eu stars, which are not known to be spectrum variables, and whose projected rotational velocities are not greater than 10 km s . Zeeman and thermal Doppler broadening are the basic line- intensification mechanisms considered. Effective temperatures estimated initially from UBVphotoelectric data are modified by requiring that the Fe abundances derived from both Fe I and Fe II lines be equal. Log g has been assumed to be 4.0. In addition, this study includes two normal stars for comparison. The cool Ap stars, in general, have normal abundances or overabundances with respect to hydrogen, for every element studied. The Fe abundance is found to increase with effective temperature. Similar dependences are found for Cr, Mn, Nd, Gd, and perhaps several other elements. The abundances are not dependent on the apparent rotational velocity or magnetic-field strength. All cool Ap stars show the same characteristic abundance anomalies, but not all to the same degree. Substantial differences in certain abundance ratios are found which distinguish Am and cool Ap stars. The elemental abundances of the cool Ap stars are similar to those of Sr-Cr-Eu spectrum variables and agree reasonably well with the results of other studies of cool Ap stars. Several stars have properties similar to those of the Si stars studied by Sargent, Searle, and Lungershausen, and support the suggestion that the Si stars and the cool Ap stars are closely related. All theories which purport to account for the elemental abundances of Ap stars have difficulties in explaining the results of this study. Some features of the abundance anomalies are similar to those produced by r- and s-processing. Theories which require mixing of the Ap star or binary companions are excluded. The magnetic-accretion hypothesis of Havnes and Conti is, nevertheless, more in agreement with observation than the other theories of Ap stars. Subject headings: abundances, stellar - atmospheres, stellar - peculiar A stars - spectrum variables - magnetic stars Publication: The Astrophysical Journal Pub Date: July 1973 DOI: 10.1086/152212 Bibcode: 1973ApJ...183...95A full text sources ADS | data products SIMBAD (32)