Mixed poloidal–toroidal magnetic configuration and surface abundance distributions of the Bp star 36 Lyn★

Abstract

Previous studies of the chemically peculiar Bp star 36 Lyn revealed a moderately strong magnetic field, circumstellar material and inhomogeneous surface abundance distributions of certain elements. We present in this paper an analysis of 33 high signal-to-noise ratio, high-resolution Stokes IV observations of 36 Lyn obtained with the Narval spectropolarimeter at the Bernard Lyot Telescope at Pic du Midi Observatory. From these data, we compute new measurements of the mean longitudinal magnetic field, Bℓ, using the multiline least-squares deconvolution (LSD) technique. A rotationally phased Bℓ curve reveals a strong magnetic field, with indications for deviation from a pure dipole field. We derive magnetic maps and chemical abundance distributions from the LSD profiles, produced using the Zeeman–Doppler imaging code InversLSD. Using a spherical harmonic expansion to characterize the magnetic field, we find that the harmonic energy is concentrated predominantly in the dipole mode (ℓ = 1), with significant contribution from both the poloidal and toroidal components. This toroidal field component is predicted theoretically, but not typically observed for Ap/Bp stars. Chemical abundance maps reveal a helium enhancement in a distinct region where the radial magnetic field is strong. Silicon enhancements are located in two regions, also where the radial field is stronger. Titanium and iron enhancements are slightly offset from the helium enhancements, and are located in areas where the radial field is weak, close to the magnetic equator.

The magnetic early B-type stars – III. A main-sequence magnetic, rotational, and magnetospheric biography

“…36 Lyn's rotational and stellar parameters were provided by Wade et al (2006), from which we can determine RK= 4.4 R * . Using Vink et al (2001) mass-loss rates determined from the stellar parameters, and adopting B d ∼ 3 kG from the ZDI map presented by Oksala et al (2018), we find RA = 31 R * and log (RA/RK) = 0.84. 36 Lyn is therefore in the same magnetospheric regime as the emission-line stars examined here, strongly suggesting that its eclipses are a consequence of a CM.…”

Magnetic field topologies of the bright, weak-field Ap stars θ Aurigae andεUrsae Majoris

“…The Doppler imaging reconstruction of the magnetic field geometries and chemical abundance distributions of θ Aur and ε UMa was carried out using the INVERSLSD magnetic inversion code. This mapping software, developed by Kochukhov et al (2014) and subsequently used by Rosén et al (2015), Kochukhov et al (2017), and Oksala et al (2018), is specially designed for accurate, self-consistent modelling of the LSD Stokes parameter profiles of different types of magnetic stars. INVERSLSD allows one to use detailed polarised radiative transfer calculations with realistic model atmospheres and a full line list as an approximation of the local LSD profiles.…”

Global simulations of Tayler instability in stellar interiors: the stabilizing effect of gravity

“…Having in hand more realistic models, we will be able to evaluate the surface poloidal-to-toroidal field ratio as well as other diagnostics which could be directly compared to spectropolarimetric observations (e.g. Oksala et al 2018).…”