Study of FK Comae Berenices

Oláh, K.; Korhonen, H.; Kővári, Zs.; Forgács‐Dajka, E.; Strassmeier, K. G.

doi:10.1051/0004-6361:20054539

Cited by 40 publications

(63 citation statements)

References 18 publications

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“…One dominant cycle is present in the record changing smoothly between 4.5 and 6.1-yr. This is consistent with the earlier result by Oláh et al (2006), who found quasiperiods of about 5.2 and 5.8-yr in the longitudes of starspots, based on a record of 18 years, between JD 2 446 800-53 200 (1987-2004).…”

Section: Figsupporting

confidence: 93%

Multiple and changing cycles of active stars

Oláh¹,

Kollath²,

Granzer

et al. 2009

A&A

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Aims. We study the time variations in the cycles of 20 active stars based on decade-long photometric or spectroscopic observations. Methods. A method of time-frequency analysis, as discussed in a companion paper, is applied to the data. Results. Fifteen stars definitely show multiple cycles, but the records of the rest are too short to verify a timescale for a second cycle. The cycles typically show systematic changes. For three stars, we found two cycles in each of them that are not harmonics and vary in parallel, indicating a common physical mechanism arising from a dynamo construct. The positive relation between the rotational and cycle periods is confirmed for the inhomogeneous set of active stars. Conclusions. Stellar activity cycles are generally multiple and variable.

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Section: Figsupporting

confidence: 93%

Multiple and changing cycles of active stars

Oláh¹,

Kollath²,

Granzer

et al. 2009

A&A

Self Cite

194

216

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show abstract

“…It is not clear whether or not these different types of events are caused by the same phenomenon or not. A similar type of two-fold behaviour of ab-and gr-events has been reported in FK Com, by Oláh et al (2006) and Hackman et al (2013), for instance.…”

Section: Active Longitudes and Flip-flop Eventssupporting

confidence: 80%

“…The appearance of spots between the active longitudes resembles what Oláh et al (2006) found in photometry of FK Com and called phase-jumps. In a phase-jump, old active areas disappear and then new ones emerge, with an offset of roughly 90…”

Section: Active Longitudes and Flip-flop Eventssupporting

confidence: 70%

Spot activity of the RS Canum Venaticorum starσGeminorum

Kajatkari¹,

Hackman²,

Jetsu³

et al. 2014

A&A

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Aims. We model the photometry of RS CVn star σ Geminorum to obtain new information on the changes of the surface starspot distribution, that is, activity cycles, differential rotation, and active longitudes. Methods. We used the previously published continuous period search (CPS) method to analyse V-band differential photometry obtained between the years 1987 and 2010 with the T3 0.4 m Automated Telescope at the Fairborn Observatory. The CPS method divides data into short subsets and then models the light-curves with Fourier-models of variable orders and provides estimates of the mean magnitude, amplitude, period, and light-curve minima. These light-curve parameters are then analysed for signs of activity cycles, differential rotation and active longitudes. Results. We confirm the presence of two previously found stable active longitudes, synchronised with the orbital period P orb = 19. d 60, and found eight events where the active longitudes are disrupted. The epochs of the primary light-curve minima rotate with a shorter period P min,1 = 19.d 47 than the orbital motion. If the variations in the photometric rotation period were to be caused by differential rotation, this would give a differential rotation coefficient of α ≥ 0.103. Conclusions. The presence of two slightly different periods of active regions may indicate a superposition of two dynamo modes, one stationary in the orbital frame and the other one propagating in the azimuthal direction. Our estimate of the differential rotation is much higher than previous results. However, simulations show that this may be caused by insufficient sampling in our data.

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“…Oláh et al (2006) find that both flip-flops and phase jumps can be found on FK Com. They conclude that these are two different, although possibly connected phenomena.…”

Section: Introductionmentioning

confidence: 81%

Study of FK Comae Berenices

Vida

Korhonen

Ilyin

et al. 2015

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Aims. We study the connection between the chromospheric and photospheric behaviour of the active late-type star FK Comae. Methods. We use spot temperature modelling, light curve inversion based on narrow-and wide-band photometric measurements, Hα observations from 1997−2010, and Doppler maps from 2004−2010 to compare the behaviour of chromospheric and photospheric features. Results. Investigating low-resolution Hα spectra, we find that the changes in the chromosphere seem to happen mainly on a time scale longer than a few hours, but shorter variations are also observed. According to the Hα measurements, prominences are often found in the chromosphere that reach to more than a stellar radius and are stable for weeks, and they seem to be often, but not always connected to dark photospheric spots. The rotational modulation of the Hα emission typically seems to be anticorrelated with the light curve, but we did not find convincing evidence of a clear connection in the long-term trends of the Hα emission and the brightness of the star. In addition, FK Com seems to be in an unusually quiet state in 2009−2010 with very little chromospheric activity and low spot contrast, which might indicate the long-term decrease in activity.

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Study of FK Comae Berenices

Cited by 40 publications

References 18 publications

Multiple and changing cycles of active stars

Multiple and changing cycles of active stars

Spot activity of the RS Canum Venaticorum starσGeminorum

Study of FK Comae Berenices

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