Zeeman‐Doppler imaging of late‐type stars: The surface magnetic field of II Peg

Carroll, T. A.; Kopf, M.; Ilyin, I.; Strassmeier, K. G.

doi:10.1002/asna.200710884

Cited by 48 publications

(60 citation statements)

References 6 publications

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“…Clearly, its emergence, structure, and decay must be addressed on a global scale. Figure 18 shows a Zeeman -Doppler image of the active spotted star II Pegasi (Carroll et al, 2007) combined with a numerical simulation of a non-axisymmetric dynamo. Although it is just a demonstration example, it nonetheless highlights the expected global starspot -dynamo connection.…”

Section: The Starspot Connectionmentioning

confidence: 99%

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Modeling the Subsurface Structure of Sunspots

et al. 2010

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While sunspots are easily observed at the solar surface, determining their subsurface structure is not trivial. There are two main hypotheses for the subsurface structure of sunspots: the monolithic model and the cluster model. Local helioseismology is the only means by which we can investigate subphotospheric structure. However, as current linear inversion techniques do not yet allow helioseismology to probe the internal structure with sufficient confidence to distinguish between the monolith and cluster models, the development of physically realistic sunspot models are a priority for helioseismologists. This is because they are not only important indicators of the variety of physical effects that may influence helioseismic inferences in active regions, but they also enable detailed assessments of the validity of helioseismic interpretations through numerical forward modeling. In this article, we provide a critical review of the existing sunspot models and an overview of numerical methods employed to model wave propagation through model sunspots. We then carry out a helioseismic analysis of the sunspot in Active Region 9787 and address the serious inconsistencies uncovered by Gizon et al. (2009aGizon et al. ( , 2009b. We find that this sunspot is most probably associated with a shallow, positive wave-speed perturbation (unlike the traditional two-layer model) and that travel-time measurements are consistent with a horizontal outflow in the surrounding moat.

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Section: The Starspot Connectionmentioning

confidence: 99%

“…On the surface, red means a field strength of up to 800 G according to the color bar while blue means basically no detection. In the interior, red means the field is pointing outward, blue means the field points inward (Carroll et al, 2007). Gizon et al (2009aGizon et al ( , 2009b.…”

Section: Conflicting Helioseismic Observationsmentioning

confidence: 99%

Modeling the Subsurface Structure of Sunspots

et al. 2010

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“…The observations are compared to a grid of local line profiles calculated using SPECTRUM spectral synthesis code (Gray & Corbally 1994) and Kurucz model atmospheres (Kurucz 1993). Before inversions the STELLA data were de-noised using 15 of 401 components of a PCA analysis using 747 spectral lines (Carroll et al 2007). In the inversion results shown here only the Fe I 6430Å line has been used.…”

Section: Spots and Surface Flowsmentioning

confidence: 99%

RS CVn binary IM Peg – investigation of stellar activity and surface flows

et al. 2009

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Abstract. We have obtained high resolution, high S/N spectra of the RS CVn binary IM Peg using UVES spectrograph at Kueyen 8.2m telescope of ESO VLT. We use Doppler imaging techniques to obtain stellar surface temperature maps from the UVES data. The TempMap code allows us to use surface differential rotation as an input parameter and thus to try to construct the rotation pattern on the stellar surface as part of the inversion process. The UVES observations are combined with spectroscopic observations from another time period obtained at the STELLA observatory. We obtain stellar surface temperature maps also from these spectra. These Doppler images are used to study the magnetic activity and surface differential rotation on IM Peg.

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“…Since the PCA multi-line method now allows the reconstruction of individual line profiles, all the known line parameters of a particular spectral line can be used in a subsequent DI and ZDI inversion. See Carroll et al (2007); Martínez González et al (2008) for a more detailed description of the method.…”

Section: Multi-line Pca Reconstructionmentioning

confidence: 99%

Zeeman-Doppler imaging: old problems and new methods

et al. 2008

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Abstract. Zeeman-Doppler Imaging (ZDI) is a powerful inversion method to reconstruct stellar magnetic surface fields. The reconstruction process is usually solved by translating the inverse problem into a regularized least-square or optimization problem. In this contribution we will emphasize that ZDI is an inherent non-linear problem and the corresponding regularized optimization is, like many non-linear problems, potentially prone to local minima. We show how this problem will be exacerbated by using an inadequate forward model. To facilitate a more consistent full radiative transfer driven approach to ZDI we describe a two-stage strategy that consist of a principal component analysis (PCA) based line profile reconstruction and a fast approximate polarized radiative transfer method to synthesize local Stokes profiles. Moreover, we introduce a novel statistical inversion method based on artificial neural networks (ANN) which provide a fast calculation of a first guess model and allows to incorporate better physical constraints into the inversion process.

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Zeeman‐Doppler imaging of late‐type stars: The surface magnetic field of II Peg

Cited by 48 publications

References 6 publications

Modeling the Subsurface Structure of Sunspots

Modeling the Subsurface Structure of Sunspots

RS CVn binary IM Peg – investigation of stellar activity and surface flows

Zeeman-Doppler imaging: old problems and new methods

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