Scaling Laws and Temperature Profiles for Solar and Stellar Coronal Loops With Non-Uniform Heating

Martens, P. C. H.

doi:10.1088/0004-637x/714/2/1290

Cited by 47 publications

(78 citation statements)

References 73 publications

(95 reference statements)

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“…This is consistent with the Rosner-Tucker-Vaiana (RTV) loop scaling (Rosner et al 1978), which derives that the loop's maximum temperature, T max , scales as a positive power of the loop's length if all other parameters are roughly the same. In particular, for a same or weaker footpoint field strength (e.g., Aschwanden et al 2008;Cranmer 2009;Martens 2010;Bourdin et al 2016). Figure 3 shows synthetic X-ray images of the two solutions.…”

Section: Synthetic X-ray Emissionsmentioning

confidence: 99%

Giant Coronal Loops Dominate the Quiescent X-Ray Emission in Rapidly Rotating M Stars

Cohen

Yadav

Garraffo

et al. 2016

ApJ

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Observations indicate that magnetic fields in rapidly rotating stars are very strong, on both small and large scales. What is the nature of the resulting corona? Here we seek to shed some light on this question. We use the results of an anelastic dynamo simulation of a rapidly rotating fully-convective M-star to drive a physics-based model for the stellar corona. We find that due to the several kilo Gauss large-scale magnetic fields at high latitudes, the corona and its X-ray emission are dominated by star-size large hot loops, while the smaller, underlying colder loops are not visible much in the X-ray. Based on this result we propose that, in rapidly rotating stars, emission from such coronal structures dominates the quiescent, cooler but saturated X-ray emission.

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Section: Synthetic X-ray Emissionsmentioning

confidence: 99%

Giant Coronal Loops Dominate the Quiescent X-Ray Emission in Rapidly Rotating M Stars

Cohen

Yadav

Garraffo

et al. 2016

ApJ

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“…In general these phenomena are characterized by probability density functions with power law form (Aschwanden 2004 presents a summary of scaling exponents). Since we are dealing with nonsteady processes we cannot directly relate observed intensity changes to inputs of dissipated energy (Martens 2010).…”

Section: Loop Heating Processmentioning

confidence: 99%

HEATING MECHANISMS FOR INTERMITTENT LOOPS IN ACTIVE REGION CORES FROM AIA/SDOEUV OBSERVATIONS

Cadavid

Lawrence

Christian

et al. 2014

ApJ

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We investigate intensity variations and energy deposition in five coronal loops in active region cores. These were selected for their strong variability in the AIA/SDO 94 Å intensity channel. We isolate the hot Fe xviii and Fe xxi components of the 94 Å and 131 Å by modeling and subtracting the "warm" contributions to the emission. HMI/SDO data allow us to focus on "inter-moss" regions in the loops. The detailed evolution of the inter-moss intensity time series reveals loops that are impulsively heated in a mode compatible with a nanoflare storm, with a spike in the hot 131 Å signals leading and the other five EUV emission channels following in progressive cooling order. A sharp increase in electron temperature tends to follow closely after the hot 131 Å signal confirming the impulsive nature of the process. A cooler process of growing emission measure follows more slowly. The Fourier power spectra of the hot 131 Å signals, when averaged over the five loops, present three scaling regimes with break frequencies near 0.1 min −1 and 0.7 min −1 . The low frequency regime corresponds to 1/f noise; the intermediate indicates a persistent scaling process and the high frequencies show white noise. Very similar results are found for the energy dissipation in a 2D "hybrid" shell model of loop magneto-turbulence, based on reduced magnetohydrodynamics, that is compatible with nanoflare statistics. We suggest that such turbulent dissipation is the energy source for our loops.

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“…It could also explain why the 171 and X-ray observations are often "complementary" (e.g., Reale et al 2007;Martens 2010), i.e., the signals in 171 and X-ray filters are observed at different locations. According to Fig.…”

Section: Role Of the S H In The Structure Of The Active Region Coronamentioning

confidence: 99%

Is it possible to model observed active region coronal emission simultaneously in EUV and X-ray filters?

Dudík

Dzifčáková

Karlický

et al. 2011

A&A

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Aims. We investigate the possibility of modeling the active region coronal emission in the EUV and X-ray filters using one, universal, steady heating function, tied to the properties of the magnetic field. Methods. We employ a simple, static model to compute the temperature and density distributions in the active region corona. The model allows us to explore a wide range of parameters of the heating function. The predicted EUV and X-ray emission in the filters of EIT/SOHO and XRT/Hinode are calculated and compared with observations. Using the combined improved filter-ratio (CIFR) method, a temperature diagnostic is employed to compare the modeled temperature structure of the active region with the temperature structure derived from the observations. Results. The global properties of the observations are most closely matched for heating functions scaling as B 0.7−0.8 0 /L 0.5 0 that depend on the spatially variable heating scale-length. The modeled X-ray emission originates from locations where large heating scale-lengths are found. However, the majority of the loops observed in the 171 and 195 filters can be modeled only by loops with very short heating scale-lengths. These loops are known to be thermally unstable. We are unable to find a model that both matches the observations in all EUV and X-ray filters, and contains only stable loops. As a result, although our model with a steady heating function can explain some of the emission properties of the 171 and 195 loops, it cannot explain their observed lifetimes. Thus, the model does not lead to a self-consistent solution. The performance of the CIFR method is evaluated and we find that the diagnosed temperature can be approximated with a geometric mean of the emission-measure weighted and maximum temperature along the line of sight. Conclusions. We conclude that if one universal heating function exists, it should be at least partially time-dependent.

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Scaling Laws and Temperature Profiles for Solar and Stellar Coronal Loops With Non-Uniform Heating

Cited by 47 publications

References 73 publications

Giant Coronal Loops Dominate the Quiescent X-Ray Emission in Rapidly Rotating M Stars

Giant Coronal Loops Dominate the Quiescent X-Ray Emission in Rapidly Rotating M Stars

HEATING MECHANISMS FOR INTERMITTENT LOOPS IN ACTIVE REGION CORES FROM AIA/SDOEUV OBSERVATIONS

Is it possible to model observed active region coronal emission simultaneously in EUV and X-ray filters?

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