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

TL;DR

This study uses TESS satellite data to analyze the rotational and pulsational variability of 64 mercury-manganese stars, revealing widespread starspots, fast rotation, and pulsations, which enhances understanding of their surface phenomena.

Contribution

First comprehensive TESS-based survey of HgMn stars, demonstrating the ubiquity of starspots and identifying various pulsation and binary interaction phenomena.

Findings

84% of HgMn stars show rotational variability indicating starspots

Discovery of ultra-fast rotator with a 0.34-day period

Detection of multi-periodic pulsations and binary interactions

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 remains unknown. Here we use 2-min cadence light curves of 64 HgMn stars observed by the TESS satellite during the first two years 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 starspots 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 multi-periodic g-mode pulsations, tidally induced variation and eclipses in binary systems.