uu.seUppsala University Publications
Change search
ReferencesLink to record
Permanent link

Direct link
Three-dimensional magnetic and abundance mapping of the cool Ap star HD 24712: III.  Three-dimensional abundance distribution of iron and calcium
Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy.ORCID iD: 0000-0001-6231-4628
Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy.
2016 (English)In: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746Article in journal (Other academic) Submitted
Abstract [en]

Context. The presence of abundance inhomogeneities in the atmospheres of chemically peculiar Ap stars presents us with an outstand- ing opportunity to investigate three-dimensional abundance distributions of chemical elements with Doppler imaging techniques, and confront these observations with the theory of atomic diffusion in the presence of a magnetic field. Aims. In this paper we present the first three-dimensional abundance distribution of Fe and Ca in the atmosphere of the cool, magnetic, chemically peculiar star HD 24712.

Methods. We used a modified version of the magnetic Doppler imaging code invers10 to derive the abundance distribution of Fe and Ca in three directions in a self-consistent way without any simplifying assumptions about the magnetic field structure of HD 24712. The analysis was performed on the basis of phase-resolved observations obtained with the HARPSpol instrument at the 3.6 m ESO telescope.

Results. The resulting three-dimensional abundance distributions of Fe and Ca successfully reproduce the observed line profiles of all spectral lines used in the inversion. We reveal a strong correlation between the horizontal and vertical abundance distribution of Fe derived from two and three-dimensional magnetic Doppler imaging, higher effective local abundance corresponds to the stratification profiles in which the transition region is shifted higher in the atmosphere. However, we could not confirm the presence of a similar correlation for Ca. 

Place, publisher, year, edition, pages
Keyword [en]
chemically peculiar stars, stellar atmospheres, abundances, HD 24712, magnetic field
National Category
Astronomy, Astrophysics and Cosmology
Research subject
URN: urn:nbn:se:uu:diva-278534OAI: oai:DiVA.org:uu-278534DiVA: diva2:906627
Available from: 2016-02-24 Created: 2016-02-24 Last updated: 2016-03-22Bibliographically approved
In thesis
1. Magnetic fields and chemical maps of Ap stars from four Stokes parameter observations
Open this publication in new window or tab >>Magnetic fields and chemical maps of Ap stars from four Stokes parameter observations
2016 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Our knowledge of stellar magnetic fields relies almost entirely on circular polarization observations, which has historically limited our understanding of the stellar magnetic field topologies. Recently, it has become possible to obtain phase-resolved high-resolution spectropolarimetric observations in all four Stokes parameters for early-type magnetic stars. Interpretation of such observations with the Magnetic Doppler imaging technique has uncovered a new, previously unknown, level of complexity of surface stellar magnetic fields. This new insight is critical for understanding the origin, evolution and structure of magnetic fields in early-type stars.

In this study we observed the magnetic, chemically peculiar Ap stars HD 24712 (DO Eri, HR 1217) and HD 125248 (CS Vir, HR 5355) in all four Stokes parameters with the HARPSpol spectropolarimeter at the ESO 3.6-m telescope. The resulting spectra have high signal-to-noise ratio and superb resolving power, by far surpassing the quality of any existing stellar Stokes parameter observations.

We studied variation of the spectrum and magnetic observables of HD 24712 as a function of rotational phase (paper I). In the subsequent magnetic Doppler imaging investigation of this star, we interpreted the phase-resolved Stokes line profile observations (paper II). This analysis showed that HD 24712, unlike more massive Ap stars studied in all four Stokes parameters, has a dominant dipolar field component with a negligible contribution of small-scale magnetic structures. Simultaneously with magnetic mapping we derived surface abundance distributions of Fe, Nd, Na, and Ca.

Building upon the technique of Magnetic Doppler imaging, we developed the first three-dimensional abundance inversion code and applied it to reconstruct the abundance distributions of Fe and Ca in three dimensions in the atmosphere of HD 24712 (paper III).

We also performed Magnetic Doppler imaging analysis of the spectropolarimetric observations of HD 125248 (paper IV). The reconstructed detailed maps of the surface abundance distribution and magnetic field topology of HD 125248 revealed a magnetic field with significant deviations from the canonical dipolar field geometry, and strong surface abundance inhomogeneities for Cr and several rare earth elements.

We assessed our inversion results in the context of magnetic Doppler imaging studies of other magnetic, chemically peculiar Ap stars and latest theoretical research on the evolution and stability of magnetic fields in radiative stellar interiors. Our analysis suggests that old or less massive Ap stars have predominantly dipolar magnetic fields while more massive or younger stars exhibit more complicated field topologies. We also compared our three-dimensional chemical abundance maps of HD 24712 to the predictions of theoretical atomic diffusion calculations in magnetized stellar atmospheres, generally finding a lack of agreement between theory and observations.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2016. 39 p.
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 1349
chemically peculiar stars, magnetic fields, spectropolarimetry, Doppler imaging, stellar atmospheres
National Category
Astronomy, Astrophysics and Cosmology
Research subject
Astronomy with specialization in Astrophysics; Astronomy
urn:nbn:se:uu:diva-278535 (URN)978-91-554-9492-6 (ISBN)
Public defence
2016-04-15, Polhemsalen, Ångströmlaboratoriet, Lägerhyddsvägen 1, Uppsala, 13:15 (English)
Available from: 2016-03-21 Created: 2016-02-24 Last updated: 2016-04-04

Open Access in DiVA

No full text

Search in DiVA

By author/editor
Rusomarov, NaumKochukhov, Oleg
By organisation
Department of Physics and Astronomy
In the same journal
Astronomy and Astrophysics
Astronomy, Astrophysics and Cosmology

Search outside of DiVA

GoogleGoogle Scholar

Total: 33 hits
ReferencesLink to record
Permanent link

Direct link