Abnormal lithium abundance in several Ap-Bp stars

TL;DR

This study investigates abnormal lithium abundance in Ap-Bp stars, revealing lithium spots linked to magnetic poles and suggesting magnetic field complexity or surface reactions as possible causes.

Contribution

The paper presents the first detection of lithium spots on the surface of a roAp star and analyzes their relation to magnetic field structures using synthetic spectrum modeling.

Findings

Lithium spots are located near magnetic poles.

Lithium abundance exceeds cosmic levels in these spots.

Enhanced lithium is also found in other Ap stars.

Abstract

Using observations of rapidly rotating roAp star HD 12098, obtained with 6m telescope of SAO RAS in 2005-2008 in nine rotational phases (0.001-0.817), and code V. Tsymbal ROTATE we identified 3 lithium spots on the surface of star, one of them coincided with the position of one magnetic pole and two others are located near the other pole, symmetrically with respect to it. Perhaps magnetic field of the star has a more complex structure than the dipole (Shavrina 2008). Lithium abundance in the spots is greater than cosmic one. It can be explained by diffusion of lithium in the presence of a magnetic field or by production of lithium in the reactions of "spallation" on the surface of star near the magnetic poles (see, for example, Goriely 2007). Enhanced lithium abundances was also determined for other two slowly rotating Ap stars HR 465 and HD 965. The analysis is performed using a synthetic spectrum method taking into account magnetic splitting of lines by the SYNTHM code of Khan (2004).