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Oláh, K.; Strassméier, K. G.; Granzer, T.

doi:10.1002/1521-3994(200210)323:5<453::aid-asna453>3.0.co;2-y

Cited by 24 publications

(35 citation statements)

References 13 publications

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“…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%

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%

Antisolar differential rotation of the K1-giantσ Geminorum revisited

Kővári

Kriskovics

Künstler

et al. 2015

A&A

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“…The presence of the long-term cyclic variability of UZ Lib (Oláh et al 2002b) has practically no effect in the rotational regime of the Fourier spectrum. We find that using the dataset pre-whitened with the short frequencies or just as observed give the same results well within the errors.…”

Section: Data Methods and Numerical Simulationsmentioning

confidence: 98%

“…Its overall data quality is near 5 mmag in V over the course of its operation (for details of the data see Oláh et al 2002b); this V dataset was used in the present paper.…”

Section: Data Methods and Numerical Simulationsmentioning

confidence: 99%

Differential rotation on UZ Librae

Oláh¹,

Jurcsik²,

Strassmeier³

2003

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Abstract. We analysed a time series of nine consecutive years of high-precision photometry of the spotted RS CVn star UZ Lib by using a discrete Fourier-transform technique and a non-linear least-squares minimization. The main period of 4.77 days due to stellar rotation was resolved into three individual periods separated by −0.2% and +0.4% around the main period. The stability of the spot pattern over many years, as derived from our contemporaneous Doppler images, allowed us to relate the different periods to co-existing spots at different latitudes, and thus to the direct determination of the strength and the sign of the differential rotation. The main period originates from the equatorial surface regions and is practically the same as the orbital period from independent radial-velocity measurements, suggesting that the stellar equator is tidally locked to the orbital motion. The higher latitudes rotate slightly faster than the equator, suggesting non-solar differential rotation with a parameter of α = ∆Ω/Ω = −0.0026, 80 times weaker than on the solar surface, and a lap time of P equator /α ≈ −1800 days, i.e. 14 times longer than for the Sun.

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“…Such a phenomenon has been noticed using the technique of Doppler imaging on, e.g., the active giant DM UMa (Hatzes 1995), on the two mainsequence components of σ 2 CrB (Strassmeier & Rice 2003), on the two pre-main sequence components of V824 Ara and the active giant UZ Lib (Oláh & Strassmeier 2002), as well as by long-term photometric analysis on, e.g., RT Lac (Ç akırlı et al 2003), UZ Lib (Oláh et al 2002a) and on the RS CVn stars II Peg, σ Gem and HR 7275 ). Holzwarth & Schüssler (2003) presented a numerical investigation for fast-rotating solar-like binaries which showed that, although the magnitude of tidal effects is small, they nevertheless lead to the formation of clusters of flux tube eruptions at preferred longitudes on opposite hemispheres and synchronized with the orbital motion.…”

Section: Preferred Longitudesmentioning

confidence: 90%

The chromospherically active binary star EI Eridani: II. Long‐term Doppler imaging

2009

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Data from 11 years of continuous spectroscopic observations of the active RS CVn-type binary star EI Eridani -gained at NSO/McMath-Pierce, KPNO/Coudé Feed and during the MUSICOS 98 campaign -were used to obtain 34 Doppler maps in three spectroscopic lines for 32 epochs, 28 of which are independent of each other. Various parameters are extracted from our Doppler maps: average temperature, fractional spottedness, and longitudinal and latitudinal spot-occurrence functions. We find that none of these parameters show a distinct variation nor a correlation with the proposed activity cycle as seen from photometric long-term observations. This suggests that the photometric brightness cycle may not necessarily be due to just a cool spot cycle. The general morphology of the spot pattern remains persistent over the whole period of 11 years. A large cap-like polar spot was recovered from all our images. A high degree of variable activity was noticed near latitudes of ≈60-70 • where the appendages of the polar spot emerged and dissolved.

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Untitled

Cited by 24 publications

References 13 publications

Antisolar differential rotation of the K1-giantσ Geminorum revisited

Antisolar differential rotation of the K1-giantσ Geminorum revisited

Differential rotation on UZ Librae

The chromospherically active binary star EI Eridani: II. Long‐term Doppler imaging

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