Magnetic topology and surface differential rotation on the K1 subgiant of the RS CVn system HR 1099

Petit, P.; Donati, J.‐F.; Wade, G. A.; Landstreet, J. D.; Bagnulo, S.; Lüftinger, T.; Sigut, T. A. A.; Shorlin, S. L. S.; Strasser, S.; Aurière, M.; Oliveira, J. M.

doi:10.1111/j.1365-2966.2004.07420.x

Cited by 66 publications

(73 citation statements)

References 23 publications

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“…Petit et al 2004). An alternative would be to treat the LSD profiles as a single line with average parameters or derive the local LSD profile from the full spectrum synthesis.…”

Section: Zeeman-doppler Imagingmentioning

confidence: 99%

Zeeman-Doppler imaging of active young solar-type stars

Hackman

Lehtinen

Rosén

et al. 2016

A&A

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Context. By studying young magnetically active late-type stars, i.e. analogues to the young Sun, we can draw conclusions on the evolution of the solar dynamo. Aims. We determine the topology of the surface magnetic field and study the relation between the magnetic field and cool photospheric spots in three young late-type stars. Methods. High-resolution spectropolarimetry of the targets was obtained with the HARPSpol instrument mounted at the ESO 3.6 m telescope. The signal-to-noise ratios of the Stokes IV measurements were boosted by combining the signal from a large number of spectroscopic absorption lines through the least squares deconvolution technique. Surface brightness and magnetic field maps were calculated using the Zeeman-Doppler imaging technique.Results. All three targets show clear signs of magnetic fields and cool spots. Only one of the targets, V1358 Ori, shows evidence of the dominance of non-axisymmetric modes. In two of the targets, the poloidal field is significantly stronger than the toroidal one, indicative of an α 2 -type dynamo, in which convective turbulence effects dominate over the weak differential rotation. In two of the cases there is a slight anti-correlation between the cool spots and the strength of the radial magnetic field. However, even in these cases the correlation is much weaker than in the case of sunspots. Conclusions. The weak correlation between the measured radial magnetic field and cool spots may indicate a more complex magnetic field structure in the spots or spot groups involving mixed magnetic polarities. Comparison with a previously published magnetic field map shows that on one of the stars, HD 29615, the underlying magnetic field changed its polarity between 2009 and 2013.

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“…Petit et al 2004). An alternative would be to treat the LSD profiles as a single line with average parameters or derive the local LSD profile from the full spectrum synthesis.…”

Section: Zeeman-doppler Imagingmentioning

confidence: 99%

Zeeman-Doppler imaging of active young solar-type stars

Hackman

Lehtinen

Rosén

et al. 2016

A&A

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“…Nowadays ZDI is a widely used technique (Donati et al 2003;Petit et al 2004;Catala et al 2007), applied to many different types of hot and cool magnetic stars. This widespread usage requires testing validity of the method.…”

Section: Introductionmentioning

confidence: 99%

How reliable is Zeeman Doppler imaging without simultaneous temperature reconstruction?

Rosén

Kochukhov

2012

A&A

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Aims. The goal of this study is to perform numerical tests of Zeeman Doppler imaging (ZDI) to asses whether correct reconstruction of magnetic fields is at all possible without taking temperature into account for stars in which magnetic and temperature inhomogeneities are spatially correlated. Methods. We used a modern ZDI code employing a physically realistic treatment of the polarized radiative transfer in all four Stokes parameters. We generated artificial observations of isolated magnetic spots and of magnetic features coinciding with cool temperature spots and then reconstructed magnetic and temperature distributions from these data. Results. Using Stokes I and V for simultaneous magnetic and temperature mapping for the star with a homogeneous temperature distribution yields magnetic field strengths underestimated by typically 10-15% relative to their true values. When temperature is kept constant and Stokes I is not used for magnetic mapping, the underestimation is 30-60%. At the same time, the strength of magnetic field inside cool spots is underestimated by as much as 80-95% and the spot geometry is also poorly reconstructed when temperature variations are ignored. On the other hand, the inversion quality is greatly improved when temperature variations are accounted for in magnetic mapping. The field strength is underestimated by 40-70% for the radial and azimuthal spots and by 70-80% for the meridional spots. Inversions still suffer from significant crosstalk between radial and meridional fields at low latitudes. The azimuthal field component proves to be most robust since it suffers the least from crosstalk. When using all four Stokes parameters crosstalk is removed. In that case, the reconstructed field strength inside cool spots is underestimated by 30-40% but the spot geometry can be recovered very accurately compared to the experiments with circular polarization alone. Conclusions. Reliable magnetic field reconstruction for a star with high-contrast temperature spots is essentially impossible if temperature inhomogeneities are ignored. A physically realistic line profile modeling method, which simultaneously accounts for both types of inhomogeneities, is required for meaningful ZDI of cool active stars.

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“…So far τ Boo is the only star to have shown a complete cycle of polarity reversals, apart from the Sun. A long-term monitoring of the highly active K1IV component of the RS CVn system HR 1099 did not show such a phenomenon, although the observations cover almost 15 years (Donati et al 2003;Petit et al 2004).…”

Section: New Perspectives Opened By the Latest And Forthcoming Observmentioning

confidence: 99%

Stellar magnetic cycles

Lanza

2009

Proc. IAU

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Abstract. The solar activity cycle is a manifestation of the hydromagnetic dynamo working inside our star. The detection of activity cycles in solar-like stars and the study of their properties allow us to put the solar dynamo in perspective, investigating how dynamo action depends on stellar parameters and stellar structure. Nevertheless, the lack of spatial resolution and the limited time extension of stellar data pose limitations to our understanding of stellar cycles and the possibility to constrain dynamo models. I briefly review some results obtained from disc-integrated proxies of stellar magnetic fields and discuss the new opportunities opened by space-borne photometry made available by MOST, CoRoT, Kepler, and GAIA, and by new ground-based spectroscopic or spectropolarimetric observations. Stellar cycles have a significant impact on the energetic output and circumstellar magnetic fields of late-type active stars which affects the interaction between stars and their planets. On the other hand, a close-in massive planet could affect the activity of its host star. Recent observations provide circumstantial evidence of such an interaction with possible consequences for stellar activity cycles.

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Magnetic topology and surface differential rotation on the K1 subgiant of the RS CVn system HR 1099

Cited by 66 publications

References 23 publications

Zeeman-Doppler imaging of active young solar-type stars

Zeeman-Doppler imaging of active young solar-type stars

How reliable is Zeeman Doppler imaging without simultaneous temperature reconstruction?

Stellar magnetic cycles

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