Differential rotation on UZ Librae

Oláh, K.; Jurcsik, J.; Strassmeier, K. G.

doi:10.1051/0004-6361:20031352

Cited by 29 publications

(31 citation statements)

References 9 publications

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“…Antisolar-type differential rotation has been detected in a growing number of late-type giants (e.g., Strassmeier et al 2003;Oláh et al 2003;Weber et al 2005;Vida et al 2007;etc.). Theoretically, this kind of feature can be explained by considering a fast meridional flow (Kitchatinov & Rüdiger 2004).…”

Section: Discussionmentioning

confidence: 99%

“…On the other hand, long-term photometric observations exist for a much wider sample of spotted stars in binary systems (e.g., Strassmeier et al 1997Strassmeier et al , 2011Oláh & Strassmeier 2002;Oláh et al 2003Oláh et al , 2013Lindborg et al 2013, etc. ), which can also be used for investigating the role of binarity in the formation of magnetic activity.…”

Section: Discussionmentioning

confidence: 99%

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Antisolar differential rotation of the K1-giantσ Geminorum revisited

Kővári

Kriskovics

Künstler

et al. 2015

A&A

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Context. Surface differential rotation and other global surface flows on magnetically active stars are among the observable manifestations of the underlying stellar dynamo. Therefore, these types of observations are important for stellar dynamo theory and useful constraints for solar dynamo studies as well. Aims. We revisit the active K1-giant component of the long-period RS CVn-type binary system σ Gem and its global surface flow pattern. Methods. We refine the differential rotation law from recovering the spot migration pattern. We apply a detailed cross-correlation technique to a unique set of 34 time-series Doppler images recovered using data from 1996−97. By increasing the number of the available cross-correlation function maps, we expect a more robust determination of the differential surface rotation law. In addition, we present a new time-series Doppler imaging study of σ Gem using our advanced surface reconstruction code iMap for a data set collected in 2006−07. Results. Results from the reprocessed cross-correlation study confirm that the star performs antisolar-type differential rotation with a surface shear α of −0.04 ± 0.01, i.e., almost a factor of two larger compared to the previously claimed value. We also confirm the evidence of a global poleward spot migration, with an average velocity of 0.21 ± 0.03 km s −1 , in accordance with theoretical predictions. From the new observations, we obtain three subsequent Doppler images. The time evolution of these images confirms the antisolar-type differential rotation of the same amount.

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Section: Discussionmentioning

confidence: 99%

Section: Discussionmentioning

confidence: 99%

Antisolar differential rotation of the K1-giantσ Geminorum revisited

Kővári

Kriskovics

Künstler

et al. 2015

A&A

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“…The errors of the period determinations are estimated by increasing the residual scatter of the nonlinear least-squares solutions a certain degree, which corresponds to 10% of the accuracy of our photometric data (cf. Oláh et al 2003).…”

Section: Rotational Propertiesmentioning

confidence: 99%

Doppler imaging of stellar surface structure

Kővári¹,

Korhonen²,

Strassmeier³

et al. 2013

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Aims. We present the first Doppler imaging study of the two rapidly rotating, single K-giants DP CVn and DI Psc in order to study the surface spot configuration and to pinpoint their stellar evolutionary status. Methods. Optical spectroscopy and photometry were used to determine the fundamental astrophysical properties. Doppler imaging was applied to recover the surface temperature distribution for both stars, while photometric light-curve inversions were carried out for studying the long-term changes of the surface activity of DP CVn. Surface differential rotation of DP CVn was estimated from cross-correlating the available subsequent Doppler reconstructions separated by roughly one rotation period. Results. Both stars appear to have higher than normal lithium abundance, LTE log n of 2.28 (DP CVn) and 2.20 (DI Psc), and are supposed to be located at the end of the first Li dredge-up on the RGB. Photometric observations reveal rotational modulation with a period of 14.010 d (DP CVn) and 18.066 d (DI Psc). Doppler reconstructions from the available mapping lines well agree in the revealed spot patterns, recovering rather low latitude spots for both stars with temperature contrasts of ΔT ≈ 600−800 K below the unspotted photospheric background. Spots at higher latitudes are also found but either with less contrast (DP CVn) or with smaller extent (DI Psc). A preliminary antisolar-type differential rotation with α = −0.035 is found for DP CVn from cross-correlating the subsequent Doppler images. Long-term photometric analysis supports the existence of active longitudes, as well as the differential rotation.

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“…If either the cycle is short enough or the database of sufficiently long duration and the sampling dense enough, it allows us in principle to determine the amount of differential rotation (e.g. Oláh et al 2003).…”

Section: Rotational Parametersmentioning

confidence: 99%

Binary-induced magnetic activity?

Strassmeier

Carroll

Weber

et al. 2011

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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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Differential rotation on UZ Librae

Cited by 29 publications

References 9 publications

Antisolar differential rotation of the K1-giantσ Geminorum revisited

Antisolar differential rotation of the K1-giantσ Geminorum revisited

Doppler imaging of stellar surface structure

Binary-induced magnetic activity?

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