Activity trends in young solar-type stars

Lehtinen, Jaakko; Jetsu, L.; Hackman, T.; Kajatkari, P.; Henry, Gregory W.

doi:10.1051/0004-6361/201527420

Cited by 88 publications

(175 citation statements)

References 115 publications

(234 reference statements)

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“…The sample of Saar & Brandenburg (1999) contains another 30 active and inactive stars from Baliunas et al (1995) and one more photometric variable, as well as 28 superactive stars with periods up to 60 yr. Lehtinen et al (2016) discovered secondary periods in some superactive stars in his sample of 21 additional stars. In the following, however, we restrict ourselves to the reduced sample of active and inactive stars, including those with short periods in the 1-3 yr range.…”

Section: Analysis Of Cycle Periodsmentioning

confidence: 99%

Evolution of Co-existing Long and Short Period Stellar Activity Cycles

Brandenburg

Mathur

Metcalfe

2017

ApJ

118

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The magnetic activity of the Sun becomes stronger and weaker over roughly an 11 year cycle, modulating the radiation and charged particle environment experienced by the Earth as "space weather." Decades of observations from the Mount Wilson Observatory have revealed that other stars also show regular activity cycles in their Ca II H+K line emission, and identified two different relationships between the length of the cycle and the rotation rate of the star. Recent observations at higher cadence have allowed the discovery of shorter cycles with periods between 1-3 yr. Some of these shorter cycles coexist with longer cycle periods, suggesting that two underlying dynamos can operate simultaneously. We combine these new observations with previous data, and we show that the longer and shorter cycle periods agree remarkably well with those expected from an earlier analysis based on the mean activity level and the rotation period. The relative turbulent length scales associated with the two branches of cyclic behavior suggest that a near-surface dynamo may be the dominant mechanism that drives cycles in more active stars, whereas a dynamo operating in deeper layers may dominate in less active stars. However, several examples of equally prominent long and short cycles have been found at all levels of activity of stars younger than 2.3 Gyr. Deviations from the expected cycle periods show no dependence on the depth of the convection zone or on the metallicity. For some stars that exhibit longer cycles, we compute the periods of shorter cycles that might be detected with future high-cadence observations.

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Section: Analysis Of Cycle Periodsmentioning

confidence: 99%

Evolution of Co-existing Long and Short Period Stellar Activity Cycles

Brandenburg

Mathur

Metcalfe

2017

ApJ

118

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“…This is one of the most used activity index to investigate activity cycles (see e.g. Rodonò et al 2000;Messina & Guinan 2002;Lehtinen et al 2016) The IQR index is proportional to the stellar variability amplitude. The variability amplitude is also an index widely used to study activity cycles (see e.g.…”

Section: Magnetic Activity Indexesmentioning

confidence: 99%

“…Other works (Saar & Brandenburg 1999;Lehtinen et al 2016) use the definition given by Brandenburg et al (1998):…”

Section: Computation Of the Global Parameters For The Target Starsmentioning

confidence: 99%

“…Oláh et al (2009) analyzed long-term spectroscopic and photometric observations to study the activity cycles in a sample of 20 late type-stars. Lehtinen et al (2016) studied activity trends in a sample of 21 young solar-type stars by analyzing long-term photometry collected in Johnson B and V bands. Suárez Mascareño et al (2016) detected long-term activity cycles in a sample of 49 nearby main-sequence stars by analyzing the V-band time-series collected by the ASAS survey (All Sky Automatic Survey, Pojmanski 1997).…”

Section: Introductionmentioning

confidence: 99%

“…Brandenburg et al 1998;Lehtinen et al 2016) possibly connected to different kinds of dynamos. Böhm-Vitense (2007) remarked that the Sun has an anomalous position with respect to these branches.…”

Section: Introductionmentioning

confidence: 99%

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Activity cycles in members of young loose stellar associations

Distefano

Lanzafame

Lanza

et al. 2017

A&A

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Context. Magnetic cycles analogous to the solar one have been detected in tens of solar-like stars by analyzing long-term time-series of different magnetic activity indexes. The relationship between the cycle properties and global stellar parameters is not fully understood yet. One reason for this is the sparseness of the data. Aims. In the present paper we searched for activity cycles in a sample of 90 young solar-like stars with ages between 4 and 95 Myr with the aim to investigate the properties of activity cycles in this age range. Methods. We measured the length P cyc of a given cycle by analyzing the long-term time-series of three different activity indexes: the period of rotational modulation, the amplitude of the rotational modulation and the median magnitude in the V band. For each star, we computed also the global magnetic activity index that is proportional to the amplitude of the rotational modulation and can be regarded as a proxy of the mean level of the surface magnetic activity. Results. We detected activity cycles in 67 stars. Secondary cycles were also detected in 32 stars of the sample. The lack of correlation between P cyc and P rot and the position of our targets in the P cyc /P rot − Ro −1 diagram suggest that these stars belong to the so-called Transitional Branch and that the dynamo acting in these stars is different from the solar one and from that acting in the older Mt. Wilson stars. This statement is also supported by the analysis of the butterfly diagrams whose patterns are very different from those seen in the solar case. We computed the Spearman correlation coefficient r S between P cyc , and different stellar parameters. We found that P cyc in our sample is uncorrelated with all the investigated parameters. The index is positively correlated with the convective turn-over time-scale, the magnetic diffusivity time-scale τ diff , and the dynamo number D N , whereas it is anti-correlated with the effective temperature T eff , the photometric shear ∆Ω phot and the radius R C at which the convective zone is located. We investigated how P cyc and evolve with the stellar age. We found that P cyc is about constant and that decreases with the stellare age in the range 4-95 Myr. Finally we investigated the magnetic activity of the star AB Dor A by merging ASAS time-series with previous long-term photometric data. We estimated the length of the AB Dor A primary cycle as P cyc = 16.78 ± 2yr and we found also shorter secondary cycles with lengths of 400 d, 190 d and 90 d respectively.

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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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Activity trends in young solar-type stars

Cited by 88 publications

References 115 publications

Evolution of Co-existing Long and Short Period Stellar Activity Cycles

Evolution of Co-existing Long and Short Period Stellar Activity Cycles

Activity cycles in members of young loose stellar associations

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

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