Magnetic field topology and chemical abundance distributions of the young, rapidly rotating, chemically peculiar star HR 5624

Abstract

Context. The young, rapidly rotating Bp star HR 5624 (HD 133880) shows an unusually strong non-sinusoidal variability of its longitudinal magnetic field. This behaviour was previously interpreted as the signature of an exceptionally strong, quadrupole-dominated surface magnetic field geometry. Aims. We studied the magnetic field structure and chemical abundance distributions of HR 5624 with the aim to verify the unusual quadrupolar nature of its magnetic field and to investigate correlations between the field topology and chemical spots. Methods. We analysed high resolution, time series Stokes parameter spectra of HR 5624 with the help of a magnetic Doppler imaging inversion code based on detailed polarised radiative transfer modelling of the line profiles. Results. We refined the stellar parameters, revised the rotational period, and obtained new longitudinal magnetic field measurements. Our magnetic Doppler inversions reveal that the field structure of HR 5624 is considerably simpler and the field strength is much lower than proposed by previous studies. We find a maximum local field strength of 12 kG and a mean field strength of 4 kG, which is about a factor of three weaker than predicted by quadrupolar field models. Our model implies that overall large-scale field topology of HR 5624 is better described as a distorted, asymmetric dipole rather than an axisymmetric quadrupole. The chemical abundance maps of Mg, Si, Ti, Cr, Fe, and Nd obtained in our study are characterised by large-scale, high-contrast abundance patterns. These structures correlate weakly with the magnetic field geometry and, in particular, show no distinct element concentrations in the horizontal field regions predicted by theoretical atomic diffusion calculations. Conclusions. We conclude that the surface magnetic field topology of HR 5624 is not as unusual as previously proposed. Considering these results together with other recent magnetic mapping analyses of early-type stars suggests that predominantly quadrupolar magnetic field topologies, invoked to be present in a significant number of stars, probably do not exist in real stars. This finding agrees with an outcome of the MHD simulations of fossil field evolution in stably stratified stellar interiors.

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

“…Our assessment shows that these deviations are statistically significant. The distorted dipolar field topologies of θ Aur and ε UMa are qualitatively similar to the surface field structures found by ZDI studies of MCP stars with stronger fields (Kochukhov et al, 2014(Kochukhov et al, , 2015(Kochukhov et al, , 2017Oksala et al, 2015;Silvester et al, 2015Silvester et al, , 2017. This result suggests that there is no obvious trend of the degree of field complexity with its mean intensity.…”

“…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), andOksala 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.…”

Putting atomic diffusion theory of magnetic ApBp stars to the test: evaluation of the predictions of time-dependent diffusion models

“…As noted by many observational studies (e.g. Kochukhov et al 2004Kochukhov et al , 2017Nesvacil et al 2012;Silvester et al 2014Silvester et al , 2015, such equatorial overabundance rings are exceedingly rare in real ApBp stars. The only well-established examples of such surface structures are the O map of ε UMa (Rice, Wehlau & Holmgren 1997) as well as the C and O distributions of HR 3831 (Kochukhov et al 2004).…”

Ultra-Wideband, Multi-epoch Radio Study of the First Discovered `Main sequence Radio Pulse emitter' CU Vir

“…Leto et al 2019). This explanation is unsatisfactory in one aspect, which is that the star HD 133880 has an even higher difference between the maximum strength of its two magnetic hemispheres (Kochukhov et al 2017), but the upper cut-off frequencies of RCP and LCP pulses differ by a factor smaller than that observed in CU Vir. It is however to be noted that the upper cut-off frequencies for both stars are smaller than the electrongyrofrequencies corresponding to the maximum stellar magnetic fields, and hence the premature cut-off has been hypothesized to be produced due to the presence of very high density plasma close to the stellar surface (Leto et al 2019).…”