Solar-type activity: Epochs of cycle formation

Katsova, M. M.; Bondar, N. I.; Livshits, M. A.

doi:10.1134/s1063772915070045

Cited by 12 publications

(7 citation statements)

References 28 publications

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“…The 1.6-yr activity cycle of ι Hor was first identified by Metcalfe et al (2010) in chromospheric emission and, using additional Ca H & K data, Flores et al (2017) recently suggested the presence of a secondary ∼4.5-yr periodicity. As very young stars show erratic and non-cyclic activity (see Baliunas et al 1995, Saar & Brandenburg 1999, Katsova et al 2015, Oláh et al 2016, the magnetic and activity cycles of ι Hor could be representative of the onset of cycles during the life of a Sun-like star and provide critical information to understand the generation and evolution of magnetism in late-type stars.…”

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confidence: 99%

Far beyond the Sun – I. The beating magnetic heart in Horologium

Alvarado‐Gómez

Hussain

Drake

et al. 2017

Monthly Notices of the Royal Astronomical Society

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A former member of the Hyades cluster, ι Horologii (ι Hor) is a planet-hosting Sun-like star which displays the shortest coronal activity cycle known to date (P cyc ∼ 1.6 yr). With an age of ∼625 Myr, ι Hor is also the youngest star with a detected activity cycle. The study of its magnetic properties holds the potential to provide fundamental information to understand the origin of cyclic activity and stellar magnetism in latetype stars. In this series of articles, we present the results of a comprehensive project aimed at studying the evolving magnetic field in this star and how this evolution influences its circumstellar environment. This paper summarizes the first stage of this investigation, with results from a long-term observing campaign of ι Hor using groundbased high-resolution spectropolarimetry. The analysis includes precise measurements of the magnetic activity and radial velocity of the star, and their multiple time-scales of variability. In combination with values reported in the literature, we show that the long-term chromospheric activity evolution of ι Hor follows a beating pattern, caused by the superposition of two periodic signals of similar amplitude at P 1 1.97 ± 0.02 yr and P 2 1.41 ± 0.01 yr. Additionally, using the most recent parameters for ι Hor b in combination with our activity and radial velocity measurements, we find that stellar activity dominates the radial velocity residuals, making the detection of additional planets in this system challenging. Finally, we report here the first measurements of the surface longitudinal magnetic field strength of ι Hor, which displays varying amplitudes within ±4 G and served to estimate the rotation period of the star (P rot = 7.70 +0.18 −0.67 d).

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confidence: 99%

Far beyond the Sun – I. The beating magnetic heart in Horologium

Alvarado‐Gómez

Hussain

Drake

et al. 2017

Monthly Notices of the Royal Astronomical Society

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“…We assume that regular cycles form within this type of activity. In more detail the evolution of the activity is considered by Katsova & Livshits (2011) and Katsova et al (2015). The stars in the second group obey Skumanich law v ∼ √ t, where v is the rotation velocity, t is the age of the star.…”

Section: Introductionmentioning

confidence: 99%

Change in the activity character of the coronae of low-mass stars of various spectral types

2017

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We study the dependence of the coronal activity index on the star's rotation rate. This question was considered earlier for 824 late-type stars on the basis of a consolidated catalogue of the soft X-ray fluxes. We carry out a more refined analysis separately for G, K and M dwarfs. They distinctively exhibit two modes of activity. The first one is the saturation mode, it is characteristic of young stars and is practically not related to their rotation. The second one refers to the solar-type activity the level of which strongly depends on the rotation period. We show that the transition from one mode to another takes place at the rotation periods of 1.1, 3.3 and 7.2 days for the stars of spectral types G2, K4 and M3 respectively. In the light of the discovery of superflares on G and K stars on the Kepler spacecraft there arises a question of how these objects differ from other active late-type stars. We analyse the location of superflare stars relative to the stars observed by Kepler on the "amplitude of rotational brightness modulation (ARM) -rotation period" diagram. The value of ARM reflects the relative spots area on a star and characterises the activity level in the whole atmosphere. It is shown that G and K superflare stars are basically fast rotating young objects, but some of them belong to the stars with the solar type of activity.

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“…For a saturated mode of activity, stellar dynamo is expected to enhance a quasi-stationary magnetic field with chaotic variations, yet without a pronounced cycle (Baliunas et al 1996). A regular cycle begins when the saturated regime of activity changes to the solar-type one, in which the activity level depends on the rotation period (Katsova et al 2015). Nizamov et al (2017) showed that the activity of late spectral-type K stars transitions to exhibiting regular cycles when its rotation period is equal to 3 days.…”

Section: Discussionmentioning

confidence: 99%

Wavelet analysis of the long-term activity of V833 Tau

Stepanov,

Bondar',

Katsova

et al. 2020

Preprint

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The bulk of available stellar activity observations is frequently checked for the manifestation of signs in comparison with the known characteristic of solar magnetic modulation. The problem is that stellar activity records are usually an order of magnitude shorter than available observations of solar activity variation. Therefore, the resolved time scales of stellar activity are insufficient to decide reliably that a cyclic variation for a particular star is similar to the well-known 11-yr sunspot cycles. As a result, recent studies report several stars with double or multiple cycles which serve to challenge the underlying theoretical understanding. This is why a consistent method to separate 'true' cycles from stochastic variations is required. In this paper, we suggest that a conservative method, based on the best practice of wavelet analysis previously applied to the study of solar activity, for studying and interpreting the longest available stellar activity record -photometric monitoring of V833 Tau for more than 100 years. We find that the observed variations of V833 Tau with timescales of 2 -50 yr should be comparable with the known quasi-periodic solar mid-term variations, whereas the true cycle of V833 Tau, if it exists, should be of about a century or even longer. We argue that this conclusion does not contradict the expectations from stellar dynamo theory.

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Solar-type activity: Epochs of cycle formation

Cited by 12 publications

References 28 publications

Far beyond the Sun – I. The beating magnetic heart in Horologium

Far beyond the Sun – I. The beating magnetic heart in Horologium

Change in the activity character of the coronae of low-mass stars of various spectral types

Wavelet analysis of the long-term activity of V833 Tau

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