The variability of magnetic activity in solar‐type stars

Fabbian, D.; Simoniello, R.; Collet, Remo; Criscuoli, S.; Korhonen, H.; Krivova, N. A.; Oláh, K.; Jouve, L.; Solanki, S. K.; Alvarado‐Gómez, Julián D.; Booth, R. S.; García, Rafael A.; Lehtinen, Jaakko; See, Victor

doi:10.1002/asna.201713403

Cited by 31 publications

(20 citation statements)

References 219 publications

(258 reference statements)

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“…The first asteroseismic evidence of variations in stellar activity were found in an F5 V star observed by CoRoT [7,8], HD 49933. For this star García et al [9] found that not only did the frequencies vary Stellar magnetic activity also manifests in variability of stellar luminosity [see, e.g., 31, and references therein]. Over the solar cycle the total irradiance is found to change by about 0.1% in temporal correlation with solar activity [32].…”

Section: Introductionmentioning

confidence: 91%

Seismic Signatures of Stellar Magnetic Activity—What Can We Expect From TESS?

Kiefer

Broomhall

Ball

2019

Front. Astron. Space Sci.

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Asteroseismic methods offer a means to investigate stellar activity and activity cycles as well as to identify those properties of stars which are crucial for the operation of stellar dynamos. With data from CoRoT and Kepler, signatures of magnetic activity have been found in the seismic properties of a few dozen stars. Now, NASA's Transiting Exoplanet Survey Satellite (TESS) mission offers the possibility to expand this, so far, rather exclusive group of stars. This promises to deliver new insight into the parameters that govern stellar magnetic activity as a function of stellar mass, age, and rotation rate. We derive a new scaling relation for the amplitude of the activity-related acoustic (p-mode) frequency shifts that can be expected over a full stellar cycle. Building on a catalogue of synthetic TESS time series, we use the shifts obtained from this relation and simulate the yield of detectable frequency shifts in an extended TESS mission. We find that, according to our scaling relation, we can expect to find significant p-mode frequency shifts for a couple hundred main-sequence and early subgiant stars and for a few thousand late subgiant and low-luminosity red giant stars.

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Section: Introductionmentioning

confidence: 91%

Seismic Signatures of Stellar Magnetic Activity—What Can We Expect From TESS?

Kiefer

Broomhall

Ball

2019

Front. Astron. Space Sci.

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“…Therefore, strictly speaking, the value of B s is obtained from the average value of the radial magnetic field B c at the corona boundary r = R c , recalculated by considering the conservation of the magnetic flux by the star radius, B s R 2 s = B c R 2 c . On the other hand, it is known that the magnetic fields of solar-type stars can lie in the range from about 0.1 to several Gauss [63,64]. In addition, the host stars for hot Jupiters can be not only of the solar type, since their spectral classes lie in the wide range from class F to class M. In addition to the radial component, the azimuthal component of the magnetic field is also present in the stellar wind, which is due to the star proper rotation.…”

Section: Calculation Examplementioning

confidence: 99%

Multi-Component MHD Model of Hot Jupiter Envelopes

Жилкин

Bisikalo

2021

Universe

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A numerical model description of a hot Jupiter extended envelope based on the approximation of multi-component magnetic hydrodynamics is presented. The main attention is focused on the problem of implementing the completed MHD stellar wind model. As a result, the numerical model becomes applicable for calculating the structure of the extended envelope of hot Jupiters not only in the super-Alfvén and sub-Alfvén regimes of the stellar wind flow around and in the trans-Alfvén regime. The multi-component MHD approximation allows the consideration of changes in the chemical composition of hydrogen–helium envelopes of hot Jupiters. The results of calculations show that, in the case of a super-Alfvén flow regime, all the previously discovered types of extended gas-dynamic envelopes are realized in the new numerical model. With an increase in magnitude of the wind magnetic field, the extended envelope tends to become more closed. Under the influence of a strong magnetic field of the stellar wind, the envelope matter does not move along the ballistic trajectory but along the magnetic field lines of the wind toward the host star. This corresponds to an additional (sub-Alfvénic) envelope type of hot Jupiters, which has specific observational features. In the transient (trans-Alfvén) mode, a bow shock wave has a fragmentary nature. In the fully sub-Alfvén regime, the bow shock wave is not formed, and the flow structure is shock-less.

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“…These variations are an important forcing term for the evolution of the climate on Earth (e.g., Lean 2017). In recent years, solar irradiance variability studies have also been motivated by the necessity for achieving an understanding of and modeling stellar variability (Fabbian et al 2017;Faurobert 2019) which, in turn, may hamper exoplanet detectability (e.g., Cegla 2019) and affect both the determination of the physical properties of exoplanet atmospheres (e.g., Kowalski et al 2019) and the abundance of biomarkers (e.g., Grenfell 2017).…”

Section: Introductionmentioning

confidence: 99%

A new spectroscopic method for measuring the temperature gradient in the solar photosphere

Faurobert

Criscuoli

Carbillet

et al. 2020

A&A

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Context. The contribution of quiet-Sun regions to the solar irradiance variability is currently unclear. Certain solar-cycle variations of the quiet-Sun’s physical structure, such as the temperature gradient, might affect the irradiance. Accurate measurements of this quantity over the course of the activity cycle would improve our understanding of long-term irradiance variations. Aims. In a previous work, we introduced and successfully tested a new spectroscopic method for measuring the photospheric temperature gradient directly on a geometric scale in the case of non-magnetic regions. In this paper, we generalize this method for moderately magnetized regions that may be encountered in the quiet solar photosphere. Methods. To simulate spectroscopic observations, we used synthetic Stokes profiles I and V of the magnetic FeI 630.15 nm line and intensity profiles of the non-magnetic FeI 709 nm line computed from realistic three-dimensional magneto-hydrodynamical simulations of the photospheric granulation and line radiative transfer under local thermodynamical equilibrium conditions. We then obtained maps at different levels in the line-wings by convolution with the instrumental point spread function (PSF) under various conditions of atmospheric turbulence – with and without correction by an adaptive optics (AO) system. The PSF were obtained with the PAOLA software and the AO performance is inspired by the system that will be operating on the Daniel K. Inouye Solar Telescope. Results. We considered different conditions of atmospheric turbulence and photospheric regions with different mean magnetic strengths of 100 G and 200 G. As in non-magnetic cases studied in our previous work, the image correction by the AO system is mandatory for obtaining accurate measurements of the temperature gradient. We show that the non-magnetic line at 709 nm may be safely used in all the cases we have investigated. However, the intensity profile of the magnetic-sensitive line is broadened by the Zeeman effect, which would bias our temperature-gradient measurement. We thus implemented a correction procedure of the line profile for this magnetic broadening in the case of weakly magnetized regions. In doing so, we remarked that in the weak-field regime, the right- and left-hand (I + V and I − V) components have similar shapes, however, they are shifted in opposite directions due to the Zeeman effect. We thus reconstructed the intensity profile by shifting back the I + V and I − V profiles and by adding the re-centered profiles. The measurement then proceeds as in the non-magnetic case. We find that this correction procedure is efficient in regions where the mean magnetic strength is smaller or on the order of 100 G. Conclusions. The new method we implement here may be used to measure the temperature gradient in the quiet Sun from ground-based telescopes equipped with an efficient AO system. We stress that we derive the gradient on a geometrical scale and not on an optical-depth scale as we would do with other standard methods. This allows us to avoid any confusion due to the effect of temperature variations on the continuum opacity in the solar photosphere.

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The variability of magnetic activity in solar‐type stars

Cited by 31 publications

References 219 publications

Seismic Signatures of Stellar Magnetic Activity—What Can We Expect From TESS?

Seismic Signatures of Stellar Magnetic Activity—What Can We Expect From TESS?

Multi-Component MHD Model of Hot Jupiter Envelopes

A new spectroscopic method for measuring the temperature gradient in the solar photosphere

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