The crucial role of surface magnetic fields for stellar dynamos: <i>ϵ</i> Eridani, 61 Cygni A, and the Sun

Jeffers, S. V.; Cameron, R. H.; Marsden, S. C.; Saikia, S. Boro; Folsom, C. P.; Jardine, M.; Morin, J.; Petit, P.; See, Victor; Vidotto, A. A.; Wolter, Uwe; Mittag, M.

doi:10.1051/0004-6361/202142202

Cited by 19 publications

(11 citation statements)

References 43 publications

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“…Coffaro et al (2020) found that ò Eri displays an X-ray activity cycle in sync with its known 2.92 ± 0.02 yr chromospheric activity cycle. In chromospheric emission, there is evidence for a ≈ 13 yr cycle as well (Metcalfe et al 2013;Jeffers et al 2022). The observations described in Section 4 coincide with minima in the activity cycle of ò Eri.…”

Section: ò Erisupporting

confidence: 53%

Constraining the Physical Properties of Stellar Coronal Mass Ejections with Coronal Dimming: Application to Far-ultraviolet Data of ϵ Eridani

Loyd

Mason

Jin

et al. 2022

ApJ

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Coronal mass ejections (CMEs) are a prominent contributor to solar system space weather and might have impacted the Sun’s early angular momentum evolution. A signal diagnostic of CMEs on the Sun is coronal dimming: a drop in coronal emission, tied to the mass of the CME, that is the direct result of removing emitting plasma from the corona. We present the results of a coronal dimming analysis of Fe xii 1349 Å and Fe xxi 1354 Å emission from ϵ Eridani (ϵ Eri), a young K2 dwarf, with archival far-ultraviolet observations by the Hubble Space Telescope’s Cosmic Origins Spectrograph. Following a flare in 2015 February, ϵ Eri’s Fe xxi emission declined by 81 ± 5%. Although enticing, a scant 3.8 minutes of preflare observations allows for the possibility that the Fe xxi decline was the decay of an earlier, unseen flare. Dimming nondetections following each of three prominent flares constrain the possible mass of ejected Fe xii-emitting (1 MK) plasma to less than a few × 1015 g. This implies that CMEs ejecting this much or more 1 MK plasma occur less than a few times per day on ϵ Eri. On the Sun, 1015 g CMEs occur once every few days. For ϵ Eri, the mass-loss rate due to CME-ejected 1 MK plasma could be < 0.6 M ̇ ⊙ , well below the star’s estimated 30 M ̇ ⊙ mass-loss rate (wind + CMEs). The order-of-magnitude formalism we developed for these mass estimates can be broadly applied to coronal dimming observations of any star.

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Section: ò Erisupporting

confidence: 53%

Constraining the Physical Properties of Stellar Coronal Mass Ejections with Coronal Dimming: Application to Far-ultraviolet Data of ϵ Eridani

Loyd

Mason

Jin

et al. 2022

ApJ

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“…Short and long cycles have been found for several stars (Brandenburg et al 2017), starting with the Sun, which exhibits the approximately 80-year-long Gleissberg cycle (Gleissberg 1945) and the 11-year-long Schwabe cycle (Richards et al 2009), although it also shows a transient periodic behaviour of about one-half to two years (Ballester et al 2002;Mursula et al 2003). Multiple cycles have also been found in other stars, such as in Eridani, which displays two distinct cycles at about three and twelve years (Brandenburg et al 2017;Jeffers et al 2022b). In addition to these decade-long cycles, F-type stars with activity cycles shorter than one year have been revealed (Jeffers et al 2018;Mittag et al 2019).…”

Section: Introductionmentioning

confidence: 96%

The CARMENES search for exoplanets around M dwarfs

Fuhrmeister¹,

Czesla²,

Perdelwitz³

et al. 2023

A&A

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It is clearly established that the Sun has an 11-year cycle that is caused by its internal magnetic field. This cycle is also observed in a sample of M dwarfs. In the framework of exoplanet detection or atmospheric characterisation of exoplanets, the activity status of the host star plays a crucial role, and inactive states are preferable for such studies. This means that it is important to know the activity cycles of these stars. We study systematic long-term variability in a sample of 211 M dwarfs observed with CARMENES, the high-resolution optical and near-infrared spectrograph at Calar Alto Observatory. In an automatic search using time series of different activity indicators, we identified 26 stars with linear or quadratic trends or with potentially cyclic behaviour. Additionally, we performed an independent search in archival R HK data collected from different instruments whose time baselines were usually much longer. These data are available for a subset of 186 of our sample stars. Our search revealed 22 cycle candidates in the data. We found that the percentage of stars showing long-term variations drops dramatically to the latest M dwarfs. Moreover, we found that the pseudo-equivalent width (pEW) of the Hα and Ca ii infrared triplet more often triggers automatic detections of long-term variations than the TiO index, differential line width, chromatic index, or radial velocity. This is in line with our comparison of the median relative amplitudes of the different indicators. For stars that trigger our automatic detection, this leads to the highest amplitude variation in R HK , followed by pEW(Hα), pEW(Ca ii IRT), and the TiO index.

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“…We mention in this context the case of ǫ Eri where the cycle was not seen in Baliunas et al (1995); Baum et al (2022) however Jeffers et al (2022) using long-term ZDI and HK data report two cycles 12.7 yr and 2.95 yr. The latter agrees with Coffaro et al (2020) while the two are identical with cycles isolated by Metcalfe et al (2013).…”

Section: Conclusion and Discussionmentioning

confidence: 94%

Solar and stellar activity cycles – no synchronization with exoplanets

Обридко

Katsova

Sokoloff

2022

Monthly Notices of the Royal Astronomical Society

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Cyclic activity on the Sun and stars is primarily explained by generation of the magnetic field by a dynamo mechanism, which converts the energy of the poloidal field into the energy of the toroidal component due to differential rotation. There is, however, an alternative point of view, which explains the field generation by gravitational influence of the planetary system and, first of all, Jupiter. This hypothesis can be verified by comparing the characteristics of exoplanets with the activity variations on their associated stars. We have performed such a comparison and have drawn a negative conclusion. No relationship between the gravitational influence of the exoplanets and cycle of the host star could be found in any of the cases considered. Moreover, there are reasons to believe that a strong gravitational influence may completely eliminate cyclic variation in stellar activity.

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The crucial role of surface magnetic fields for stellar dynamos: ϵ Eridani, 61 Cygni A, and the Sun

Cited by 19 publications

References 43 publications

Constraining the Physical Properties of Stellar Coronal Mass Ejections with Coronal Dimming: Application to Far-ultraviolet Data of ϵ Eridani

Constraining the Physical Properties of Stellar Coronal Mass Ejections with Coronal Dimming: Application to Far-ultraviolet Data of ϵ Eridani

The CARMENES search for exoplanets around M dwarfs

Solar and stellar activity cycles – no synchronization with exoplanets

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