Heating of the solar and stellar coronae: a review

Erdélyi, R.; Ballai, I.

doi:10.1002/asna.200710803

Cited by 88 publications

(44 citation statements)

References 57 publications

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“…Although mostly treated separately in the literature, examples of the close interplay between resonant absorption and phase mixing can be found in Ruderman et al [33,34]. Apart from resonant absorption and phase mixing, other mechanisms such as (nonlinear) mode conversion (to modes which might more readily dissipate) and ion-cyclotron resonance have also been proposed (see for example, reviews by Aschwanden [9], Goedbloed & Poedts [10], Klimchuk [11], Erdélyi & Ballai [35] and references therein).…”

Section: Acoustic and Magnetohydrodynamic Wavesmentioning

confidence: 99%

A contemporary view of coronal heating

Parnell

Moortel

2012

Phil. Trans. R. Soc. A.

210

188

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Determining the heating mechanism (or mechanisms) that causes the outer atmosphere of the Sun, and many other stars, to reach temperatures orders of magnitude higher than their surface temperatures has long been a key problem. For decades, the problem has been known as the coronal heating problem, but it is now clear that 'coronal heating' cannot be treated or explained in isolation and that the heating of the whole solar atmosphere must be studied as a highly coupled system. The magnetic field of the star is known to play a key role, but, despite significant advancements in solar telescopes, computing power and much greater understanding of theoretical mechanisms, the question of which mechanism or mechanisms are the dominant supplier of energy to the chromosphere and corona is still open. Following substantial recent progress, we consider the most likely contenders and discuss the key factors that have made, and still make, determining the actual (coronal) heating mechanism (or mechanisms) so difficult.

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Section: Acoustic and Magnetohydrodynamic Wavesmentioning

confidence: 99%

A contemporary view of coronal heating

Parnell

Moortel

2012

Phil. Trans. R. Soc. A.

210

188

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“…Another proxy for magnetic activity is the emission from the stellar corona (Stelzer & Neuhäuser 2001;Preibisch & Feigelson 2005;Erdélyi & Ballai 2007;Jackson, Davis & Wheatley 2012), which is mainly observed in the soft X-ray band (0.1-10 keV). This emission stems from the hot (several million Kelvin) plasma in the stellar corona, which is collisionally excited and cools through emission at X-ray wavelengths (Raymond & Smith 1977).…”

Section: Introductionmentioning

confidence: 99%

An improved age–activity relationship for cool stars older than a gigayear

Booth

Poppenhaeger

Watson

et al. 2017

Monthly Notices of the Royal Astronomical Society

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Stars with convective envelopes display magnetic activity, which decreases over time due to the magnetic braking of the star. This age-dependence of magnetic activity is well-studied for younger stars, but the nature of this dependence for older stars is not well understood. This is mainly because absolute stellar ages for older stars are hard to measure. However, relatively accurate stellar ages have recently come into reach through asteroseismology. In this work we present X-ray luminosities, which are a measure for magnetic activity displayed by the stellar coronae, for 24 stars with well-determined ages older than a gigayear. We find 14 stars with detectable X-ray luminosities and use these to calibrate the age-activity relationship. We find a relationship between stellar X-ray luminosity, normalized by stellar surface area, and age that is steeper than the relationships found for younger stars, with an exponent of −2.80 ± 0.72. Previous studies have found values for the exponent of the age-activity relationship ranging between −1.09 to −1.40, dependent on spectral type, for younger stars. Given that there are recent reports of a flattening relationship between age and rotational period for old cool stars, one possible explanation is that we witness a strong steepening of the relationship between activity and rotation.

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“…This is known as the the Alfvén wave heating model (Hollweg et al 1982;Kudoh & Shibata 1999). Many dissipating mechanisms for Alfvén waves have been proposed, such as mode conversion, phase mixing, or resonant absorption (see reviews by, e.g., Erdélyi 2004;Erdélyi & Ballai 2007 and further references therein). Another promising coronal heating candidate mechanism is the nanoflare reconnection heating model.…”

Section: Introductionmentioning

confidence: 99%

Predicting Observational Signatures of Coronal Heating by Alfvén Waves and Nanoflares

Antolin

Shibata

Kudoh

et al. 2008

Astrophysical Journal

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Alfvén waves can dissipate their energy by means of nonlinear mechanisms, and constitute good candidates to heat and maintain the solar corona to the observed few million degrees. Another appealing candidate is nanoflare reconnection heating, in which energy is released through many small magnetic reconnection events. Distinguishing the observational features of each mechanism is an extremely difficult task. On the other hand, observations have shown that energy release processes in the corona follow a power-law distribution in frequency whose index may tell us whether small heating events contribute substantially to the heating or not. In this work we show a link between the power-law index and the operating heating mechanism in a loop. We set up two coronal loop models: in the first model Alfvén waves created by footpoint shuffling nonlinearly convert to longitudinal modes which dissipate their energy through shocks; in the second model numerous heating events with nanoflare-like energies are input randomly along the loop, either distributed uniformly or concentrated at the footpoints. Both models are based on a 1.5-dimensional MHD code. The obtained coronae differ in many aspects; for instance, in the flow patterns along the loop and the simulated intensity profile that Hinode XRT would observe. The intensity histograms display power-law distributions whose indexes differ considerably. This number is found to be related to the distribution of the shocks along the loop. We thus test the observational signatures of the power-law index as a diagnostic tool for the above heating mechanisms and the influence of the location of nanoflares.

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Heating of the solar and stellar coronae: a review

Cited by 88 publications

References 57 publications

A contemporary view of coronal heating

A contemporary view of coronal heating

An improved age–activity relationship for cool stars older than a gigayear

Predicting Observational Signatures of Coronal Heating by Alfvén Waves and Nanoflares

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