Second‐order error propagation in the Mueller matrix of a spectropolarimeter

Ilyin, I.

doi:10.1002/asna.201211652

Cited by 25 publications

(29 citation statements)

References 20 publications

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“…These measurements agree closely with the results obtained for the same stars at other telescopes (e.g. Ryabchikova et al 2007;Ilyin 2012). Repeated observations of a very slowly rotating Ap star γ Equ reveals no systematic differences in the Stokes V profiles during the entire period of our observations of II Peg.…”

Section: Spectropolarimetric Observationssupporting

confidence: 91%

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Magnetic field topology of the RS CVn star II Pegasi

Kochukhov

Mantere

Hackman

et al. 2013

A&A

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Context. The dynamo processes in cool active stars generate complex magnetic fields responsible for prominent surface stellar activity and variability at different time scales. For a small number of cool stars magnetic field topologies were reconstructed from the time series of spectropolarimetric observations using the Zeeman Doppler imaging (ZDI) method, often yielding surprising and controversial results. Aims. In this study we follow a long-term evolution of the magnetic field topology of the RS CVn binary star II Peg using a more self-consistent and physically more meaningful modelling approach compared to previous ZDI studies. Methods. We collected high-resolution circular polarisation observations of II Peg using the SOFIN spectropolarimeter at the Nordic Optical Telescope. These data cover 12 epochs spread over 7 years, comprising one of the most comprehensive spectropolarimetric data sets acquired for a cool active star. A multi-line diagnostic technique in combination with a new ZDI code is applied to interpret these observations. Results. We have succeeded in detecting clear magnetic field signatures in average Stokes V profiles for all 12 data sets. These profiles typically have complex shapes and amplitudes of ∼10 −3 of the unpolarised continuum, corresponding to mean longitudinal fields of 50-100 G. Magnetic inversions using these data reveals evolving magnetic fields with typical local strengths of 0.5-1.0 kG and complex topologies. Despite using a self-consistent magnetic and temperature mapping technique, we do not find a clear correlation between magnetic and temperature features in the ZDI maps. Neither do we confirm the presence of persistent azimuthal field rings found in other RS CVn stars. Reconstruction of the magnetic field topology of II Peg reveals significant evolution of both the surface magnetic field structure and the extended magnetospheric field geometry on the time scale covered by our observations. From 2004 to 2010 the total field energy drastically declined and the field became less axisymmetric. This also coincided with the transition from predominantly poloidal to mainly toroidal field topology. Conclusions. A qualitative comparison of the ZDI maps of II Peg with the prediction of dynamo theory suggests that the magnetic field in this star is produced mainly by the turbulent α 2 dynamo rather than the solar αΩ dynamo. Our results do not show a clear active longitude system, nor is there evidence of the presence of an azimuthal dynamo wave.

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Section: Spectropolarimetric Observationssupporting

confidence: 91%

“…The data were reduced with the help of the 4A software package (Ilyin 2000). Specific details of the SOFIN polarimeter design and corresponding data reduction methods are given by Ilyin (2012).…”

Section: Spectropolarimetric Observationsmentioning

confidence: 99%

Magnetic field topology of the RS CVn star II Pegasi

Kochukhov

Mantere

Hackman

et al. 2013

A&A

Self Cite

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“…Two to four sub-exposures with the quarter-wave plate angles separated by 90 • were used to derive circularly polarised spectra. A detailed description of the SOFIN spectropolarimeter and its polarimetric data reduction is given in Ilyin (2012). The spectra were reduced with the 4A software package (Ilyin 2000).…”

Section: Sofin and Harps Observationsmentioning

confidence: 99%

“…A detailed description of the SOFIN spectropolarimeter and its polarimetric data reduction is given in Ilyin (2012). The spectra were reduced with the 4A software package (Ilyin 2000). Bias subtraction, master flat-field correction, scattered light subtraction, and weighted extraction of spectral orders comprise the standard steps of spectrum processing.…”

Section: Sofin and Harps Observationsmentioning

confidence: 99%

Exploring the origin of magnetic fields in massive stars

Hubrig

Schöller

Ilyin

et al. 2013

A&A

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Context. Theories on the origin of magnetic fields in massive stars remain poorly developed, because the properties of their magnetic field as function of stellar parameters could not yet be investigated. Additional observations are of utmost importance to constrain the conditions that are conducive to magnetic fields and to determine first trends about their occurrence rate and field strength distribution. Aims. To investigate whether magnetic fields in massive stars are ubiquitous or appear only in stars with a specific spectral classification, certain ages, or in a special environment, we acquired 67 new spectropolarimetric observations for 30 massive stars. Among the observed sample, roughly one third of the stars are probable members of clusters at different ages, whereas the remaining stars are field stars not known to belong to any cluster or association. Methods. Spectropolarimetric observations were obtained during four different nights using the low-resolution spectropolarimetric mode of FOcal Reducer low dispersion Spectrograph (FORS 2) mounted on the 8-m Antu telescope of the VLT. Furthermore, we present a number of follow-up observations carried out with the high-resolution spectropolarimeters SOFIN mounted at the Nordic Optical Telescope (NOT) and HARPS mounted at the ESO 3.6 m between 2008 and 2011. To assess the membership in open clusters and associations, we used astrometric catalogues with the highest quality kinematic and photometric data currently available. Results. The presence of a magnetic field is confirmed in nine stars previously observed with FORS

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“…Its generalized second-order error propagation in the Mueller matrix and the expected error budget were given in Ilyin (2012). We refer the reader to these two papers for further details.…”

Section: Polarimetersmentioning

confidence: 99%

PEPSI: The high‐resolution échelle spectrograph and polarimeter for the Large Binocular Telescope

et al. 2015

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PEPSI is the bench-mounted, two-arm, fibre-fed and stabilized Potsdam Echelle Polarimetric and Spectroscopic Instrument for the 2×8.4 m Large Binocular Telescope (LBT). Three spectral resolutions of either 43 000, 120 000 or 270 000 can cover the entire optical/red wavelength range from 383 to 907 nm in three exposures. Two 10.3k×10.3k CCDs with 9-μm pixels and peak quantum efficiencies of 94-96 % record a total of 92échelle orders. We introduce a new variant of a wave-guide image slicer with 3, 5, and 7 slices and peak efficiencies between 92-96 %. A total of six cross dispersers cover the six wavelength settings of the spectrograph, two of them always simultaneously. These are made of a VPH-grating sandwiched by two prisms. The peak efficiency of the system, including the telescope, is 15 % at 650 nm, and still 11 % and 10 % at 390 nm and 900 nm, respectively. In combination with the 110 m 2 light-collecting capability of the LBT, we expect a limiting magnitude of ≈ 20th mag in V in the low-resolution mode. The R = 120 000 mode can also be used with two, dual-beam Stokes IQUV polarimeters. The 270 000-mode is made possible with the 7-slice image slicer and a 100-μm fibre through a projected sky aperture of 0.74 , comparable to the median seeing of the LBT site. The 43 000-mode with 12-pixel sampling per resolution element is our bad seeing or faint-object mode. Any of the three resolution modes can either be used with sky fibers for simultaneous sky exposures or with light from a stabilized Fabry-Pérotétalon for ultra-precise radial velocities. CCD-image processing is performed with the dedicated data-reduction and analysis package PEPSI-S4S. Its full error propagation through all image-processing steps allows an adaptive selection of parameters by using statistical inferences and robust estimators. A solar feed makes use of PEPSI during day time and a 500-m feed from the 1.8 m VATT can be used when the LBT is busy otherwise. In this paper, we present the basic instrument design, its realization, and its characteristics. Some pre-commissioning first-light spectra shall demonstrate the basic functionality.

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Second‐order error propagation in the Mueller matrix of a spectropolarimeter

Cited by 25 publications

References 20 publications

Magnetic field topology of the RS CVn star II Pegasi

Magnetic field topology of the RS CVn star II Pegasi

Exploring the origin of magnetic fields in massive stars

PEPSI: The high‐resolution échelle spectrograph and polarimeter for the Large Binocular Telescope

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