Differential rotation and meridional flow of Arcturus

Küker, M.; Rüdiger, G.

doi:10.1002/asna.201011483

Cited by 32 publications

(67 citation statements)

References 16 publications

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“…Figure 9 displays the behavior of H versus ∆P/P , from which one observes a strong trend of increasing ∆P/P towards longer H-index, paralleling the background found by different studies. This outcome is in agreement with the results found by Reinhold et al (2013), where the relative differential rotation shear increases with longer rotation periods, as well as previous observations shown by Barnes et al (2005) and theoretical approaches (e.g., Kuker & Rudiger 2011). Finally, the comparison of the distribution of H for active stars with one rotation period identified and active stars with two rotation periods identified using the Kolmogorov-Smirnov test, as shown above, reveals that a correlation between ∆P/P and H can be claimed.…”

Section: Resultssupporting

confidence: 93%

New Suns in the Cosmos. V. Stellar Rotation and Multifractality in Active Kepler Stars

Freitas

Nepomuceno

Rios

et al. 2019

ApJ

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In the present study, high-precision time series photometry for the active Kepler stars is described in the language of multifractals. We explore the potential of using the rescaled range analysis (R/S) and multifractal detrended moving average analysis (MFDMA) methods to characterize the multiscale structure of the observed time series from a sample of ∼40 000 active stars. Among these stars, 6486 have surface differential rotation measurement, whereas 1846 have no signature of differential rotation. As a result, the Hurst exponent (H) derived from both methods shows a strong correlation with the period derived from rotational modulation. In addition, the variability range R var reveals how this correlation follows a high activity "line". We also verify that the H-index is an able parameter for distinguishing the different signs of stellar rotation that can exist between the stars with and without differential rotation. In summary, the results indicate that the Hurst exponent is a promising index for estimating photometric magnetic activity.

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Section: Resultssupporting

confidence: 93%

New Suns in the Cosmos. V. Stellar Rotation and Multifractality in Active Kepler Stars

Freitas

Nepomuceno

Rios

et al. 2019

ApJ

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“…The error bars on each individual measurement are 1-σ errors in the paraboloid fit. Küker & Rüdiger (2011). Alternatively, if a spot group disappeared and was replaced by another emerging at the surface our maps could signify intrinsic spot evolution on a timescale less than the year between the 2007 and 2008 observations, so the present data cannot be used to decide between spot migration and evolution.…”

Section: Brightness Mapsmentioning

confidence: 90%

Magnetic fields on young, moderately rotating Sun-like stars – II. EK Draconis (HD 129333)

Waite

Marsden

Carter

et al. 2016

Mon. Not. R. Astron. Soc.

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The magnetic fields, activity and dynamos of young solar-type stars can be empirically studied using time-series of spectropolarimetric observations and tomographic imaging techniques such as Doppler imaging and Zeeman Doppler imaging. In this paper we use these techniques to study the young Sun-like star EK Draconis (SpType: G1.5V, HD 129333) using ESPaDOnS at the Canada-France-Hawaii Telescope and NARVAL at the Télescope Bernard Lyot. This multi-epoch study runs from late 2006 until early 2012. We measure high levels of chromospheric activity indicating an active, and varying, chromosphere. Surface brightness features were constructed for all available epochs. The 2006/7 and 2008 data show large spot features appearing at intermediate-latitudes. However, the 2012 data indicate a distinctive polar spot. We observe a strong, almost unipolar, azimuthal field during all epochs that is similar to that observed on other Sun-like stars. Using magnetic features, we determined an average equatorial rotational velocity, Ω eq , of ∼2.50 ± 0.08 rad d −1 . High levels of surface differential rotation were measured with an average rotational shear, ∆Ω, of ∼0.27 +0.24 −0.26 rad d −1 . During an intensively observed 3-month period from December 2006 until February 2007, the magnetic field went from predominantly toroidal (∼80%) to a more balanced poloidal-toroidal (∼40-60%) field. Although the large-scale magnetic field evolved over the epochs of our observations, no polarity reversals were found in our data.

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“…Secondly, rapidly rotating stars should not have such a strong differential rotation (see e.g. Küker & Rüdiger 2011;Reinhold & Gizon 2015). However, HD 199178 differs significantly from most rapidly rotating late-type stars in that it has likely undergone a merger in the transit from a W Uma-type binary to a FK Comae-type star (see e.g.…”

Section: Spectral and Stellar Parametersmentioning

confidence: 99%

Starspot activity of HD 199178

Hackman

Ilyin

Lehtinen

et al. 2019

A&A

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Context. Studying the spots of late-type stars is crucial for distinguishing between the various proposed dynamo mechanisms believed to be the main cause of starspot activity. For this research it is important to collect observation time series that are long enough to unravel both long-and short-term spot evolution. Doppler imaging is a very efficient method for studying spots of stars that cannot be angularly resolved. Aims. High-resolution spectral observations during 1994-2017 are analysed in order to reveal long-and short-term changes in the spot activity of the FK Comae-type subgiant HD 199178.Methods. Most of the observations were collected with the Nordic Optical Telescope. The Doppler imaging temperature maps were calculated using an inversion technique based on Tikhonov regularisation and utilising multiple spectral lines. Results. We present a unique series of 41 temperature maps spanning more than 23 years. All reliable images show a large cool spot region centred near the visible rotation pole. Some lower latitude cool features are also recovered, although the reliability of these is questionable. There is an expected anti-correlation between the mean surface temperature and the spot coverage. Using the Doppler images, we construct the equivalent of a solar butterfly diagram for HD 199178. Conclusions. HD 199178 clearly has a long-term large and cool spot structure at the rotational pole. This spot structure dominated the spot activity during the years 1994-2017. The size and position of the structure has evolved with time, with a gradual increase during the last years. The lack of lower latitude features prevents the determination of a possible differential rotation.

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Differential rotation and meridional flow of Arcturus

Cited by 32 publications

References 16 publications

New Suns in the Cosmos. V. Stellar Rotation and Multifractality in Active Kepler Stars

New Suns in the Cosmos. V. Stellar Rotation and Multifractality in Active Kepler Stars

Magnetic fields on young, moderately rotating Sun-like stars – II. EK Draconis (HD 129333)

Starspot activity of HD 199178

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