Spot activity of II Peg

Hackman, T.; Mantere, M. J.; Jetsu, L.; Ilyin, I.; Kajatkari, P.; Kochukhov, Oleg; Lehtinen, Jaakko; Lindborg, M.; Piskunov, Nikolai; Tuominen, I.

doi:10.1002/asna.201111616

Cited by 14 publications

(28 citation statements)

References 17 publications

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“…The photometric minima from our analysis, over plotted on the DI results with black crosses, closely coincide with the DI minima for the years with pronounced spot activity, while the differences are greater for the other epochs. Compared with the previous investigation of Hackman et al (2011), who used a different time-series analysis method for the photometric data, we find the results to agree fairly well. Therefore we conclude that the linear drift pattern is an authentic A97, page 7 of 10 1988.7 1988.75 1988.8 1988.85 1988.9 1988.95 1989 1989 1985.45 1985.5 1985.55 1985.6 1985.65 1985.7 1985.75 1985.8 Phase…”

Section: Comparison With Recent Temperature Mapssupporting

confidence: 70%

“…In this section we compare the temperature minima obtained from Doppler imaging (DI) by Hackman et al (2011) to the photometric results; in all, 28 surface temperature maps of the object were derived for the years 1994-2010. For comparison purposes, we plot in Fig.…”

Section: Comparison With Recent Temperature Mapsmentioning

confidence: 99%

“…7 the latitudinally averaged temperature profiles of the DI maps as a function of time, but in contrast to previous studies (see e.g. Hackman et al 2011), we wrapped the phases with the P spot that was found to describe the linear drift of the photometric minima. As evident from this figure, one large primary spot, seen as extensive dark patches in the color contour, was seen on the object during 1997-2002.…”

Section: Comparison With Recent Temperature Mapsmentioning

confidence: 99%

“…This figure is otherwise identical to Fig. 5 of Hackman et al (2011), but here we normalized each stripe with its own extrema (equivalent to the CF normalization scheme) instead of a global value, enabling us to better see the seasonal variations of the spot latitudes. From this figure it is evident that during the most persistent drift, the spot latitudes show less variation than during the epoch when distrubances in the drift were detected.…”

Section: Comparison With Recent Temperature Mapsmentioning

confidence: 99%

“…The star's photometric light curves have also been intensively studied with time-series analysis and spot-modeling methods (see e.g. Henry et al 1995;Rodonò et al 2000;Siwak et al 2010;Hackman et al 2011;Roettenbacher et al 2011). All longerterm light curve variations are commonly interpreted as being due to starspots (see e.g.…”

Section: Introductionmentioning

confidence: 99%

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Multiperiodicity, modulations and flip-flops in variable star light curves

Lindborg

Mantere

Olspert

et al. 2013

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Aims. According to previously published Doppler images of the magnetically active primary giant component of the RS CVn binary II Peg, the surface of the star was dominated by one single active longitude that was clearly drifting in the rotational frame of the binary system during 1994-2002; later imaging for 2004-2010, however, showed decreased and chaotic spot activity, with no signs of the drift pattern. Here we set out to investigate from a more extensive photometric dataset whether this drift is a persistent phenomenon, in which case it could be caused either by an azimuthal dynamo wave or be an indication that the binary system's orbital synchronization is still incomplete. On a differentially rotating stellar surface, spot structures preferentially on a certain latitude band could also cause such a drift, the disruption of which could arise from the change of the preferred spot latitude. Methods. We analyzed the datasets using the carrier fit (CF) method, which is especially suitable for analyzing time series in which a fast clocking frequency (such as the rotation of the star) is modulated with a slower process (such as the stellar activity cycle).Results. We combined all collected photometric data into one single data set and analyzed it with the CF method. We confirm the previously published results that the spot activity has been dominated by one primary spotted region almost through the entire data set and also confirm a persistent, nearly linear drift. Disruptions of the linear trend and complicated phase behavior are also seen, but the period analysis reveals a rather stable periodicity with P spot = 6. d 71054 ± 0. d 00005. After removing the linear trend from the data, we identified several abrupt phase jumps, three of which are analyzed in more detail with the CF method. These phase jumps closely resemble what is called a flip-flop event, but the new spot configurations do not persist for longer than a few months in most cases. Conclusions. There is some evidence that the regular drift without phase jumps is related to the high state, while the complex phase behavior and disrupted drift pattern are related to the low state of magnetic activity. The most natural explanation of the drift is weak anti-solar (pole rotating faster than the equator) differential rotation with a coefficient k ≈ 0.002 combined with the preferred latitude of the spot structure.

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Section: Comparison With Recent Temperature Mapssupporting

confidence: 70%

Section: Comparison With Recent Temperature Mapsmentioning

confidence: 99%

Section: Comparison With Recent Temperature Mapsmentioning

confidence: 99%

Section: Comparison With Recent Temperature Mapsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

See 3 more Smart Citations

Multiperiodicity, modulations and flip-flops in variable star light curves

Lindborg

Mantere

Olspert

et al. 2013

A&A

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Time‐series analysis of long‐term photometry of BM Canum Venaticorum

et al. 2017

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† The analyzed photometry and numerical results of the analysis are both published electronically at the CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/yyy/ Axxx.Long-term photometry is commonly used to monitor chromospheric activity of late-type stars. We study standard Johnson differential V photometry of the RS CVn binary BM Canum Venaticorum (BM CVn) spanning over a quarter of a century. Our main aims are to determine the activity cycles, the rate of surface differential rotation, and the rotation period of the active longitudes of BM CVn. The continuous period search (CPS) algorithm is applied to the photometry. The changes of the mean and amplitude of the light curves are used to search for activity cycles. The rotation period changes give an estimate of the rate of surface differential rotation. The Kuiper method is applied to the epochs of the primary and secondary minima to search for active longitudes. The photometry reveals the presence of a stable mean light curve (MLC) connected to the orbital period P orb = 20. d 6252 of this binary. We remove this MLC from the original V magnitudes, which gives us the corrected V ′ magnitudes. These two samples of V and V ′ data are analyzed separately with CPS. The fraction of unreliable CPS models decreases when the MLC is removed. The same significant activity cycle of approximately 12.5 years is detected in both V and V ′ samples. The estimate for the surface differential rotation coefficient, k ≥ 0.10, is the same for both samples, but the number of unrealistic period estimates decreases after removing the MLC. The same active longitude period of P al = 20. d 511 ± 0. d 005 is detected in the V and V ′ magnitudes. This long-term regularity in the epochs of primary and secondary minima of the light curves is not caused by the MLC. On the contrary, the MLC hampers the detection of active longitudes.

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The variability of magnetic activity in solar‐type stars

et al. 2017

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This article reviews the current knowledge and status of investigations on the variable magnetic activity of cool stars. We discuss the Sun in the context of solar-type stars, highlighting peculiarities and common features in terms of its magnetic activity and variability over different time scales. We examine how both theory and observations are providing new clues about the main physical processes that generate magnetic fields in the interior of cool stars, as well as about those that lead to evolving stellar surface magnetism and varying chromospheric and coronal phenomena. We then proceed to discuss the relations between stellar age, rotation, and activity throughout the evolution of cool stars. Finally, we touch upon the importance of understanding stellar magnetism also in view of its effect on planetary environments.

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Spot activity of II Peg

Cited by 14 publications

References 17 publications

Multiperiodicity, modulations and flip-flops in variable star light curves

Multiperiodicity, modulations and flip-flops in variable star light curves

Time‐series analysis of long‐term photometry of BM Canum Venaticorum

The variability of magnetic activity in solar‐type stars

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