Detection of weak magnetic fields in two HgMn stars

Abstract

The main-sequence mercury-manganese (HgMn) stars are known to exhibit large overabundances of exotic elements and, similar to magnetic Ap/Bp stars, are spectrum variables, implying the presence of an inhomogeneous element distribution over the stellar surface. A number of magnetic field studies have been attempted in the last decades, indicating that magnetic fields in HgMn stars, if they exist, should be rather weak. The presence of tangled magnetic fields was suggested by several authors who detected quadratic magnetic fields using the moment technique. We employ the least-squares deconvolution technique to carry out a sensitive search for weak magnetic fields in spectropolarimetric observations of three HgMn stars, HD221507, HD65949, and HD101189, which have different fundamental parameters and spectral characteristics. A definite weak longitudinal field is discovered in HD221507 and HD65949 on single epochs, while only marginal field detections were achieved for HD101189. The new measurements indicate that the structure of the magnetic fields is probably rather complex: our analysis reveals the presence of reversed Stokes V profiles at the same observational epoch if individual elements are used in the measurements. This is the first observational evidence that individual elements sample distinct local magnetic fields of different polarity across the stellar surface.

arXiv comment5 pages, 1 table, 3 figures, accepted for publication as MNRAS Letter

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• TESS survey of rotational and pulsational variability of mercury-manganese stars
• The SDSS/APOGEE Catalog of HgMn Stars
• New mercury-manganese stars and candidates from LAMOST DR4
• Photometric variability of the LAMOST sample of magnetic chemically peculiar stars as seen by TESS
• Analysis of high-resolution FEROS spectroscopy for a sample of variable B-type stars assembled from TESS photometry
• V680 Mon -- a young mercury-manganese star in an eclipsing heartbeat system
• The evolutionary state of the chemically peculiar members of the open cluster NGC2516