Detecting and quantifying stellar magnetic fields -- Sparse Stokes profile approximation using orthogonal matching pursuit

Abstract

In the recent years, we have seen a rapidly growing number of stellar magnetic field detections for various types of stars. Many of these magnetic fields are estimated from spectropolarimetric observations (Stokes V) by using the so-called center-of-gravity (COG) method. Unfortunately, the accuracy of this method rapidly deteriorates with increasing noise and thus calls for a more robust procedure that combines signal detection and field estimation. We introduce an estimation method that provides not only the effective or mean longitudinal magnetic field from an observed Stokes V profile but also uses the net absolute polarization of the profile to obtain an estimate of the apparent (i.e., velocity resolved) absolute longitudinal magnetic field. By combining the COG method with an orthogonal-matching-pursuit (OMP) approach, we were able to decompose observed Stokes profiles with an overcomplete dictionary of wavelet-basis functions to reliably reconstruct the observed Stokes profiles in the presence of noise. The elementary wave functions of the sparse reconstruction process were utilized to estimate the effective longitudinal magnetic field and the apparent absolute longitudinal magnetic field. A multiresolution analysis complements the OMP algorithm to provide a robust detection and estimation method. An extensive Monte-Carlo simulation confirms the reliability and accuracy of the magnetic OMP approach.

A&A, in press, 15 pages, 14 figures

References in corpus (11)

• The surprising magnetic topology of tauSco: fossil remnant or dynamo output?
• Large-scale magnetic topologies of late M dwarfs
• The Magnetic Fields of Classical T Tauri Stars
• Weak magnetic fields in Ap/Bp stars: Evidence for a dipole field lower limit and a tentative interpretation of the magnetic dichotomy
• Toroidal versus poloidal magnetic fields in Sun-like stars: a rotation threshold
• Magnetic cycles of the planet-hosting star tauBootis
• Searching for links between magnetic fields and stellar evolution III. Measurement of magnetic fields in open cluster Ap stars with ESPaDOnS
• The Magnetic Topology of the Weak-Lined T Tauri Star V410 - A Simultaneous Temperature and Magnetic Field Inversion
• A search for magnetic fields in the variable HgMn star $\alpha$ Andromedae
• A fast method for Stokes profile synthesis -- Radiative transfer modeling for ZDI and Stokes profile inversion
• The Meso-Structured Magnetic Atmosphere -- A Stochastic Polarized Radiative Transfer Approach

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