Shultz, M. E.
[4, 5, 6]
Owocki, S. P.
Total Authors: 5
 Univ Delaware, Dept Phys & Astron, 217 Sharp Lab, Newark, DE 19716 - USA
 Uppsala Univ, Dept Phys & Astron, Box 516, SE-75120 Uppsala - Sweden
 Univ Sao Paulo, Inst Astron Geofis & Ciencias Atmosfer, Rua Matao 1226, Cidade Univ, BR-05508900 Sao Paulo, SP - Brazil
 Howard Univ, Dept Phys & Astron, Washington, DC 20059 - USA
 NASA GSFC, Ctr Res & Explorat Space Sci & Technol, Greenbelt, MD 20771 - USA
 NASA GSFC, Xray Astrophys Lab, Greenbelt, MD 20771 - USA
Total Affiliations: 6
Monthly Notices of the Royal Astronomical Society;
Web of Science Citations:
HD 144941 is an extreme He (EHe) star, a rare class of subdwarf OB star formed from the merger of two white dwarf (WD) stars. Uniquely amongst EHe stars, its light curve has been reported to be modulated entirely by rotation, suggesting the presence of a magnetic field. Here, we report the first high-resolution spectropolarimetric observations of HD 144941, in which we detect an extremely strong magnetic field both in circular polarization (with a line-of-sight magnetic field averaged over the stellar disc < B-z > similar to -8 kG) and in Zeeman splitting of spectral lines (yielding a magnetic modulus of < B > similar to 17 kG). We also report for the first time weak H alpha emission consistent with an origin and a centrifugal magnetosphere. HD 144941's atmospheric parameters could be consistent with either a subdwarf or a main-sequence (MS) star, and its surface abundances are neither similar to other EHe stars nor to He-strong magnetic stars. However, its H alpha emission properties can only be reproduced if its mass is around 1 M-circle dot, indicating that it must be a post-MS object. Since there is no indication of binarity, it is unlikely to be a stripped star, and was therefore most likely produced in a WD merger. HD 144941 is therefore further evidence that mergers are a viable pathway for the generation of fossil magnetic fields. (AU)