Inhomogeneous distribution of mercury on the surfaces of rapidly rotating HgMn stars

Abstract

Abstract. Starspots are usually associated with the action of magnetic fields at stellar surfaces. However, an inhomogeneous chemical distribution of mercury was found recently for the mercury-manganese (HgMn) star α And -a well-established member of a non-magnetic subclass of the chemically peculiar stars of the upper main sequence. In this study we present first results of the high-resolution survey of the Hg  3984 Å resonance line in the spectra of rapidly rotating HgMn stars with atmospheric parameters similar to those of α And. We use spectrum synthesis modelling and take advantage of the Doppler resolution of stellar surfaces to probe the horizontal structure of mercury distribution. Clear signatures of spots are found in the Hg  3984 Å line profiles of HR 1185 and HR 8723. Two observations of the latter star separated by two days give evidence for line profile variability. We conclude that inhomogeneous distribution of Hg is a common phenomenon for the rapidly rotating HgMn stars in the 13 000-13 800 K effective temperature range independent of the stellar evolutionary stage. These results establish the existence of a new class of spectrum variable spotted B-type stars. It is suggested that the observed Hg inhomogeneities arise from dynamical instabilities in the chemical diffusion processes and are unrelated to magnetic phenomena.

Dynamical evolution of titanium, strontium, and yttrium spots on the surface of the HgMn star HD 11753

“…Recently, Kochukhov et al (2005) found clear signatures of surface mercury spots in two rapidly rotating HgMn stars by analysing the Hg ii 3984 Å line profiles. Variability of spectral lines associated to larger number of chemical elements were discovered for the first time by Hubrig et al (2006a) for the primary component of the eclipsing binary AR Aur.…”

Elemental abundance analyses with DAO spectrograms

“…Recently Kockukhov et al (2005) found that HR 1185 and HR 8723, two HgMn stars with some rotation and effective temperatures between 13 000 and 13 800 K showed inhomogeneous distributions of Hg. Differences between two observations of HR 8723 suggest variability of λ3984.…”

“…For example, exploratory calculations by Seaton (1996) using Opacity Project data suggest that their manganese rich atmospheres are a time variable surface result of radiatively-driven diffusion deep in the stellar envelope. Adelman et al (2002) reported the first spectrum variability in Tables 4-8 are only available in electronic form at the CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or via http://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/447/685 this stellar class of Hg II λ3984 in α And A, a discovery whose implications are still just being explored (see, e.g., Kockukhov et al 2005). With results from many stars one can look at the dependences on stellar parameters and make comparisons with theoretical predictions (see, e.g., Adelman et al 2001).…”

A search for pulsations in the HgMn star HD 45975 with CoRoT photometry and ground-based spectroscopy

“…Among the processes invoked by these authors to explain these observations, they considered the time-dependent atomic diffusion scenario proposed by Alecian (1998). Line-profile variations have been detected during the last decade in several HgMn stars and interpreted in terms of abundance spots in the photosphere (e.g., Adelman et al 2002;Kochukhov et al 2005;Hubrig et al 2006;Briquet et al 2010). These kinds of patches generally concern elements that have low abundances in normal stars (Sr, Y, Pt, Zr, and Hg) and which are suspected of being concentrated in high-altitude (above log τ = -4) clouds.…”