A Search for Chemical Stratification and Magnetic Fields in Eight Field Blue Horizontal-branch Stars*

Abstract In this article, we present the results of an analysis of chemical abundances and a search for magnetic fields in eight field blue horizontal-branch (BHB) stars: BD +01°0548, HD 74721, HD 86986, HD 87112, HD 93329, HD 109995, HD 161817, and HD 167105. This study is based on high-resolution optical spectra obtained with ESPaDOnS at the Canada–France–Hawaii Telescope. We first calculated the average chemical element abundance, the rotational velocity, and the radial velocity of the stars using the ZEEMAN2 spectrum synthesis code with the PHOENIX model atmospheres. We then studied the abundances of titanium and iron inferred from individual lines in the spectra of each star and their variations with their predicted formation depths τ 5000 . Similarly to the BHB stars cooler than 11,500 K observed in globular clusters, no clear observational evidence of vertical stratification is detected in the atmosphere of these stars. In the second part of this project, we searched for the presence of a magnetic field in the stars, applying the least-squares deconvolution technique on the Stokes I and V spectra. The measured mean longitudinal magnetic field uncertainties, ranging from 8 to 30 G, effectively rule out the presence of an organized magnetic field in these targets with a strength larger than a few 100 G.