Magnetic field topology and chemical spot distributions of the Ap star HD 119419

Abstract

Context. Analysis of high-resolution spectropolarimetric time-series observations of early-type magnetic stars is currently the most advanced method of obtaining detailed information on their surface magnetic field topologies and horizontal spot distributions. Aims. In this study we analyse a new set of high-quality four Stokes parameter observations of the magnetic Ap star HD 119419a member of the 14 Myr old Lower Cen-Cru association -for the purpose of studying the surface field topology and mapping the chemical abundance spots. Methods. We made use of the circular and linear polarisation data collected for HD 119419 with the HARPSpol instrument at the ESO 3.6-m telescope. These observations were analysed with a multi-line magnetic diagnostic technique and modelled in detail with a Magnetic Doppler imaging code. Results. We present a new set of high-precision mean longitudinal magnetic field measurements and derive a revised stellar rotational period by comparing our measurements with the literature data. We also redetermine the basic stellar atmospheric parameters. Our four Stokes parameter magnetic inversions reveal a moderately complex surface field topology with a mean field strength of 18 kG and a maximum local strength of 24 kG. A poloidal dipolar component dominates the magnetic energy spectrum of the surface field in HD 119419. However, significant contributions of the higher-order spherical harmonic components are also present. We show that the dipole plus quadrupole part of the reconstructed field geometry is incapable of reproducing the observed amplitudes and shapes of the Stokes Q and U profiles. The chemical abundance distributions of Fe, Cr, Ti, and Nd, derived self-consistently with the magnetic field geometry, are characterised by large abundance gradients and a lack of clear correlation with the magnetic field structure. Conclusions. This full Stokes vector analysis of HD 119419 extends the modern hot-star magnetic mapping investigations to an open cluster Ap star with a well-determined age. Further Magnetic Doppler imaging studies of cluster members will allow us to study the field topologies and chemical abundance spots as a function of stellar age.

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

“…These diverse chemical surface structures modulate circular and linear polarisation profiles, which can exhibit substantially different amplitudes and shapes depending on the element considered (e.g. Kochukhov et al 2014;Silvester et al 2014;Yakunin et al 2015;Rusomarov et al 2018). For this reason, a detailed, quantitative modelling of magnetic field topologies of MCP stars normally requires using element-specific LSD profiles.…”

“…The vast majority of recent ZDI studies of MCP stars also tend to be biased towards narrow-line stars with stronger than average magnetic fields (e.g. Kochukhov et al 2015;Rusomarov et al 2016Rusomarov et al , 2018Silvester et al 2014Silvester et al , 2015Silvester et al , 2017Yakunin et al 2015). Relatively little information is available about the structure of the weak magnetic fields of fast-rotating MCP stars, in spite of the fact that these objects include some of the brightest MCP stars with the most complete constraints on fundamental parameters, rotational variability, and surface chemistry.…”

Magnetic field topologies of the bright, weak-field Ap stars theta Aurigae and epsilon Ursae Majoris

“…These diverse chemical surface structures modulate circular and linear polarisation profiles, which can exhibit substantially different amplitudes and shapes depending on the element considered (e.g. Kochukhov et al, 2014;Silvester et al, 2014;Yakunin et al, 2015;Rusomarov et al, 2018). For this reason, a detailed, quantitative modelling of magnetic field topologies of MCP stars normally requires using element-specific LSD profiles.…”

Stellar Magnetic Fields

“…The presence of small-scale deviations from canonical oblique dipolar topologies was firmly established in some magnetic stars (Kochukhov & Wade, 2010;Silvester et al, 2014;Rusomarov et al, 2018), but not all of them (Rusomarov et al, 2015). When available, linear polarisation spectra typically suggested a larger deviation from dipolar fields than can be inferred from circular polarisation data alone (Kochukhov & Wade, 2010;Rusomarov et al, 2018). However, this gain of spatial resolution brought by (still very challenging and time-consuming) full Stokes vector magnetometry is mostly noticeable for slow rotators (v e sin i ≤ 20 km s −1 ), but vanishes for stars with v e sin i exceeding ∼ 30 km s −1 (Kochukhov et al, 2019).…”

“…Figure 1 shows an example, taken from Kochukhov et al (2019), of typical stellar magnetic field geometry of this kind. Another interesting finding of ZDI investigations is evidence of non-negligible and, in some cases, very large contributions of toroidal magnetic field at the stellar surface (Kochukhov & Wade, 2016;Oksala et al, 2018;Rusomarov et al, 2018). Possibility of such magnetic field structures was disregarded by all previous loworder multipolar modelling studies.…”