From solar nanoflares to stellar giant flares: Scaling laws and non-implications for coronal heating

Aschwanden, Markus J.

doi:10.1016/j.asr.2007.03.050

Cited by 12 publications

(8 citation statements)

References 39 publications

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“…At peak temperature, the loop goes from being heated to cooling, so the left hand side of Eq. ( 4) is zero instantaneously (Aschwanden 2007). Ignoring the expansion term (which is safe when flow speeds are subsonic) and assuming that there is no external heating, the right-hand side implies that conduction balances radiation instantaneously at the temperature peak, i.e.,…”

Section: Discussionmentioning

confidence: 99%

ESTIMATES OF DENSITIES AND FILLING FACTORS FROM A COOLING TIME ANALYSIS OF SOLAR MICROFLARES OBSERVED WITHRHESSI

Baylor

Cassak

Christe

et al. 2011

ApJ

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We use more than 4,500 microflares from the Reuven Ramaty High Energy Solar Spectroscopic Imager (RHESSI) microflare data set , Ap. J., 677, 1385 to estimate electron densities and volumetric filling factors of microflare loops using a cooling time analysis. We show that if the filling factor is assumed to be unity, the calculated conductive cooling times are much shorter than the observed flare decay times, which in turn are much shorter than the calculated radiative cooling times. This is likely unphysical, but the contradiction can be resolved by assuming the radiative and conductive cooling times are comparable, which is valid when the flare loop temperature is a maximum and when external heating can be ignored. We find that resultant radiative and conductive cooling times are comparable to observed decay times, which has been used as an assumption in some previous studies. The inferred electron densities have a mean value of 10 11.6 cm −3 and filling factors have a mean of 10 −3.7 . The filling factors are lower and densities are higher than previous estimates for large flares, but are similar to those found for two microflares by Moore et al. (Ap. J., 526, 505, 1999).

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Section: Discussionmentioning

confidence: 99%

ESTIMATES OF DENSITIES AND FILLING FACTORS FROM A COOLING TIME ANALYSIS OF SOLAR MICROFLARES OBSERVED WITHRHESSI

Baylor

Cassak

Christe

et al. 2011

ApJ

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“…In the future, more observational and statistical studies are desirable for comparing the similarities and differences between small-and large-scale EUV waves about their driving source, excitation mechanism, and physical properties. In addition, since small-scale EUV waves often associate with micro-flares in the quiet Sun, resembling the size distribution of flares (e.g., Hudson 1991;Aschwanden 2007), small-scale EUV waves are probably also important in the full spectrum of EUV waves of hierarchic sizes.…”

Section: Conclusion and Discussionmentioning

confidence: 99%

On a Small-scale EUV Wave: The Driving Mechanism and the Associated Oscillating Filament

Shen

Liu

Tian

et al. 2017

ApJ

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We present observations of a small-scale Extreme-ultraviolet (EUV) wave that was associated with a mini-filament eruption and a GOES B1.9 micro-flare in the quiet Sun region. The initiation of the event was due to the photospheric magnetic emergence and cancellation in the eruption source region, which first caused the ejection of a small plasma ejecta, then the ejecta impacted on a nearby mini-filament and thereby led to the filament's eruption and the associated flare. During the filament eruption, an EUV wave at a speed of 182 -317 km s −1 was formed ahead of an expanding coronal loop, which propagated faster than the expanding loop and showed obvious deceleration and reflection during the propagation. In addition, the EUV wave further resulted in the transverse oscillation of a remote filament whose period and damping time are 15 and 60 minutes, respectively. Based on the observational results, we propose that the small-scale EUV wave should be a fast-mode magnetosonic wave that was driven by the the expanding coronal loop. Moreover, with the application of filament seismology, it is estimated that the radial magnetic field strength is about 7 Gauss. The observations also suggest that small-scale EUV waves associated with miniature solar eruptions share similar driving mechanism and observational characteristics with their large-scale counterparts.

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“…This raises the question of the maximum possible flare energy which a star can produce. This quantity can be es- (Aschwanden 2007;Shibata et al 2013), where f is the fraction of the free magnetic energy E mag that can be converted into heating (about 10 per cent), B is the magnetic field strength of the active region producing the flare, and L and A are the active region size and area. The maximum flare energy of the Sun is estimated to be about 6 × 10 33 erg, but it may be in the order of 10 36 erg for the most active stars (Aulanier et al 2013).…”

Section: Maximum Flare Energymentioning

confidence: 99%

Stellar coronal mass ejections – I. Estimating occurrence frequencies and mass-loss rates

Odert

Leitzinger

Hanslmeier

et al. 2017

Monthly Notices of the Royal Astronomical Society

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Stellar coronal mass ejections (CMEs) may play an important role in mass-and angular momentum loss of young Sun-like stars. If occurring frequently, they may also have a strong effect on planetary evolution by increasing atmospheric erosion. So far it has not been possible to infer the occurrence frequency of stellar CMEs from observations. Based on their close relation with flares on the Sun, we develop an empirical model combining solar flare-CME relationships with stellar flare rates to estimate the CME activity of young Sun-like and late-type main-sequence stars. By comparison of the obtained CME mass-loss rates with observations of total mass-loss rates, we find that our modeled rates may exceed those from observations by orders of magnitude for the most active stars. This reveals a possible limit to the extrapolation of such models to the youngest stars. We find that the most uncertain component in the model is the flare-CME association rate adopted from the Sun, which does not properly account for the likely stronger coronal confinement in active stars. Simple estimates of this effect reveal a possible suppression of CME rates by several orders of magnitude for young stars, indicating that this issue should be addressed in more detail in the future.

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From solar nanoflares to stellar giant flares: Scaling laws and non-implications for coronal heating

Cited by 12 publications

References 39 publications

ESTIMATES OF DENSITIES AND FILLING FACTORS FROM A COOLING TIME ANALYSIS OF SOLAR MICROFLARES OBSERVED WITHRHESSI

ESTIMATES OF DENSITIES AND FILLING FACTORS FROM A COOLING TIME ANALYSIS OF SOLAR MICROFLARES OBSERVED WITHRHESSI

On a Small-scale EUV Wave: The Driving Mechanism and the Associated Oscillating Filament

Stellar coronal mass ejections – I. Estimating occurrence frequencies and mass-loss rates

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