Magnetic classification of HD 154228

Determine whether HD 154228 (33 Oph) hosts a weak Ap-type magnetic field, an ultra-weak magnetic field, or no magnetic field at all, using observations capable of improving upon the existing spectropolarimetric constraint.

Background

HD 154228 was not detected in the available spectropolarimetric observation, but its upper limit of approximately 210 G remains compatible with a relatively weak field within or below the typical Ap-star range. Because this limit does not decisively distinguish among a weak Ap-type field, an ultra-weak field, and no field, the star’s magnetic and chemical classification remains unresolved. The paper notes that additional observations are needed to determine whether its field lies below or above the critical thresholds relevant to enforcing rigid rotation.

References

With this single observation, it is not possible to confirm or rule out the presence of such a field; the star could host a weak Ap-type field, an ultra-weak field or no magnetic field at all.

— Search for magnetic fields in seven slowly rotating A stars  (2608.28258 - Rull et al., 28 Aug 2026) in Section 6.2, Non-detections, page 8