TESS survey of rotational and pulsational variability of mercury–manganese stars

O Kochukhov,E Paunzen,O Kobzar,V Khalack,J Labadie-Bartz,C Neiner,A David-Uraz

doi:10.1093/mnras/stab2107

Abstract

ABSTRACT Mercury–manganese (HgMn) stars are late-B upper main sequence chemically peculiar stars distinguished by large overabundances of heavy elements, slow rotation, and frequent membership in close binary systems. These stars lack strong magnetic fields typical of magnetic Bp stars but occasionally exhibit non-uniform surface distributions of chemical elements. The physical origin and the extent of this spot formation phenomenon remain unknown. Here, we use 2-min cadence light curves of 64 HgMn stars observed by the Transiting Exoplanet Survey Satellite (TESS) during the first 2 yr of its operation to investigate the incidence of rotational modulation and pulsations among HgMn stars. We found rotational variability with amplitudes of 0.1–3 mmag in 84 per cent of the targets, indicating ubiquitous presence of star-spots on HgMn-star surfaces. Rotational period measurements reveal six fast-rotating stars with periods below 1.2 d, including one ultra-fast rotator (HD 14228) with a 0.34-d period. We also identify several HgMn stars showing multiperiodic g-mode pulsations, tidally induced variation and eclipses in binary systems.

Highlights

Mercury–manganese (HgMn) stars correspond to one of the subclasses of the heterogeneous group of chemically peculiar (CP) stars, found on the upper main sequence
Given the typical 27.4-d length of most Transiting Exoplanet Survey Satellite (TESS) data sets and the methodology of the time series analysis adopted in our study, in particular the independent treatment of slow drifts within individual 13.7 d light-curve segments, we are not sensitive to rotational modulation exceeding periods of ≈ 13 d
We have carried out a systematic search of photometric variability among HgMn stars observed by the TESS satellite at 2-min cadence

Summary

Introduction

Mercury–manganese (HgMn) stars correspond to one of the subclasses of the heterogeneous group of chemically peculiar (CP) stars, found on the upper main sequence. HgMn stars have spectral types from B6 to A0, corresponding to the effective temperature range from 16 000 to 10 000 K, and are distinguished by strong lines of ionized Hg and/or Mn, discernible in low-resolution classification spectra (e.g. Paunzen, Hummerich & Bernhard 2021b). These line strength anomalies indicate an overabundance of these chemical elements by up to 6 orders of magnitude relative to their solar abundances. HgMn stars are frequently found in spectroscopic binaries (Gerbaldi, Floquet & Hauck 1985) and rotate slower than normal stars of the same temperature (Abt, Levato & Grosso 2002)

Objectives

Results

Conclusion