On detectability of Zeeman broadening in optical spectra of F- and G-dwarfs

Anderson, Richard I.; Reiners, A.; Solanki, S. K.

doi:10.1051/0004-6361/201014769

Cited by 34 publications

(39 citation statements)

References 51 publications

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“…5.5). All lines are magnetically sensitive and are suitable for measuring stellar magnetic fields (Anderson et al 2010;Johns-Krull et al 2004, and several follow-up papers). This will become relevant in the third paper of this series, in which the impact of the magnetic field on convection and spectral lines will be discussed.…”

Section: Line Synthesis and Stellar Disc Integrationmentioning

confidence: 99%

Three-dimensional simulations of near-surface convection in main-sequence stars

Beeck

Cameron

Reiners

et al. 2013

A&A

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Context. The atmospheres of cool main-sequence stars are structured by convective flows from the convective envelope that penetrate the optically thin layers and lead to structuring of the stellar atmospheres analogous to solar granulation. The flows have considerable influence on the 3D structure of temperature and pressure and affect the profiles of spectral lines formed in the photosphere. Aims. For the set of six 3D radiative (M)HD simulations of cool main-sequence stars described in the first paper of this series, we analyse the near-surface layers. We aim at describing the properties of granulation of different stars and at quantifying the effects on spectral lines of the thermodynamic structure and flows of 3D convective atmospheres. Methods. We detected and tracked granules in brightness images from the simulations to analyse their statistical properties, as well as their evolution and lifetime. We calculated spatially resolved spectral line profiles using the line synthesis code SPINOR. To enable a comparison to stellar observations, we implemented a numerical disc-integration, which includes (differential) rotation. Results. Although the stellar parameters change considerably along the model sequence, the properties of the granules are very similar. The impact of the 3D structure of the atmospheres on line profiles is measurable in disc-integrated spectra. Line asymmetries caused by convection are modulated by stellar rotation. Conclusions. The 3D structure of cool stellar atmospheres as shaped by convective flows has to be taken into account when using photospheric lines to determine stellar parameters.

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Section: Line Synthesis and Stellar Disc Integrationmentioning

confidence: 99%

Three-dimensional simulations of near-surface convection in main-sequence stars

Beeck

Cameron

Reiners

et al. 2013

A&A

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“…of the oscillator strengths, we need to use a sophisticated line-profile inversion technique. Examples of this method that is based on radiative transfer in magnetic atmospheres has for a long time been applied to various active cool stars (e.g., Saar et al 1986;Valenti et al 1995;Ruedi et al 1997;Anderson et al 2010). …”

Section: Magnetic Analysismentioning

confidence: 99%

Binary-induced magnetic activity?

Strassmeier

Carroll

Weber

et al. 2011

A&A

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Context. Multi-wavelength time-series observations with high cadence and long duration are needed to resolve and understand the many variations of magnetically active late-type stars, which is an approach often used to observe the Sun. Aims. We present a first and detailed study of the bright and active K0IV-III star HD 123351. Methods. We acquired a total of 955 high-resolution STELLA echelle spectra during the years 2006-2010 and a total of 2260 photometric VI C data points during 1998-2010. These data are complemented by some spectra from CFHT and KPNO. Results. The star is found to be a single-lined spectroscopic binary with a period of 147.8919 ± 0.0003 days and a large eccentricity of e = 0.8086 ± 0.0001. The rms of the orbital solution is just 47 m s −1 , making it the most precise orbit ever obtained for an active binary system. The rotation period is constrained from long-term photometry to be 58.32 ± 0.01 days. It shows that HD 123351 is a very asynchronous rotator, rotating five times slower than the expected pseudo-synchronous value. Two spotted regions persisted throughout the 12 years of our observations. We interpret them as active longitudes on a differentially rotating surface with a ΔP/P of 0.076. Four years of Hα, Ca ii H&K and He i D3 monitoring identifies the same main periodicity as the photometry but dynamic spectra also indicate that there is an intermittent dependence on the orbital period, in particular for Ca ii H&K in 2008. Line-profile inversions of a pair of Zeeman sensitive/insensitive iron lines yield an average surface magnetic-flux density of 542 ± 72 G. The time series for 2008 is modulated by the stellar rotation as well as the orbital motion, such that the magnetic flux is generally weaker during times of periastron and that the chromospheric emissions vary in anti-phase with the magnetic flux. We also identify a broad and asymmetric lithium line profile and measure an abundance of log n(Li) = 1.70 ± 0.05. The star's position in the H-R diagram indicates a mass of 1.2 ± 0.1 M and an age of 6-7 Gyr. Conclusions. We interpret the anti-phase relation of the magnetic flux with the chromospheric emissions as evidence that there are two magnetic fields present at the same time, a localized surface magnetic field associated with spots and a global field that is oriented towards the (low-mass) secondary component. We suggest that the inter-binary field is responsible for the magnetic-flux dilution at periastron. It is also likely to be responsible for the unexpected slow and asynchronous rotation of the primary star.

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“…Top: Model with identical temperature for magnetic and non-magnetic regions; best-fit: Bf = 500 G (solid blue), comparison: Bf = 0 G (dash-dotted red). Bottom: Best fit for model with different temperatures for magnetic and non-magnetic regions; Bf = 120 G (blue solid), comparison: solution from upper panel (Bf = 500 G, same temperatures, red dashed line) (fromAnderson et al, 2010). χ 2 -maps for 59 Vir solutions (seeFigure 12).…”

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Observations of Cool-Star Magnetic Fields

Reiners

2012

Living Rev. Solar Phys.

255

225

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Cool stars like the Sun harbor convection zones capable of producing substantial surface magnetic fields leading to stellar magnetic activity. The influence of stellar parameters like rotation, radius, and age on cool-star magnetism, and the importance of the shear layer between a radiative core and the convective envelope for the generation of magnetic fields are keys for our understanding of low-mass stellar dynamos, the solar dynamo, and also for other large-scale and planetary dynamos. Our observational picture of cool-star magnetic fields has improved tremendously over the last years. Sophisticated methods were developed to search for the subtle effects of magnetism, which are difficult to detect particularly in cool stars. With an emphasis on the assumptions and capabilities of modern methods used to measure magnetism in cool stars, I review the different techniques available for magnetic field measurements. I collect the analyses on cool-star magnetic fields and try to compare results from different methods, and I review empirical evidence that led to our current picture of magnetic fields and their generation in cool stars and brown dwarfs.

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On detectability of Zeeman broadening in optical spectra of F- and G-dwarfs

Cited by 34 publications

References 51 publications

Three-dimensional simulations of near-surface convection in main-sequence stars

Three-dimensional simulations of near-surface convection in main-sequence stars

Binary-induced magnetic activity?

Observations of Cool-Star Magnetic Fields

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