X-ray-heated models of stellar flare atmospheres - Theory and comparison with observations

Hawley, Suzanne L.; Fisher, G. H.

doi:10.1086/191640

Cited by 144 publications

(210 citation statements)

References 46 publications

(71 reference statements)

Supporting

Mentioning

194

Contrasting

Order By: Relevance

“…Instead of computing this loss term using an equilibrium solution (Cargill et al 2012a), we scale this term as being proportional to the mean coronal pressure P á ñ by a scaling constant η. Such proportionality is observed in the decay phase of solar and stellar flares as well as predicted in coronal heating models (Hawley & Fisher 1992;Qiu et al 2013, and references therein). We set η by matching low-temperature emission in AIA 171 channel between model and observation.…”

Section: D Modeling Of 12500 Loopssupporting

confidence: 69%

Long Duration Flare Emission: Impulsive Heating or Gradual Heating?

Qiu

Longcope

2016

ApJ

View full text Add to dashboard Cite

Flare emissions in X-ray and EUV wavelengths have previously been modeled as the plasma response to impulsive heating from magnetic reconnection. Some flares exhibit gradually evolving X-ray and EUV light curves, which are believed to result from superposition of an extended sequence of impulsive heating events occurring in different adjacent loops or even unresolved threads within each loop. In this paper, we apply this approach to a long duration two-ribbon flare SOL2011-09-13T22 observed by the Atmosphere Imaging Assembly (AIA). We find that to reconcile with observed signatures of flare emission in multiple EUV wavelengths, each thread should be heated in two phases, an intense impulsive heating followed by a gradual, low-rate heating tail that is attenuated over 20-30 minutes. Each AIA resolved single loop may be composed of several such threads. The two-phase heating scenario is supported by modeling with both a zero-dimensional and a 1D hydrodynamic code. We discuss viable physical mechanisms for the two-phase heating in a post-reconnection thread.

show abstract

Section: D Modeling Of 12500 Loopssupporting

confidence: 69%

Long Duration Flare Emission: Impulsive Heating or Gradual Heating?

Qiu

Longcope

2016

ApJ

View full text Add to dashboard Cite

show abstract

“…Hawley & Fisher (1992) calculated the spectra resulting from X-ray backwarming, for a series of 5 models. Their models can reproduce Balmer line fluxes.…”

Section: Figmentioning

confidence: 99%

Dynamics of flares on late type dMe stars

Houdebine

2003

A&A

View full text Add to dashboard Cite

Abstract.We investigate the spectral signatures of stellar flares in the wavelength range 3600 Å to 4500 Å and in broad band photometry. We study the phenomenology of the spectral signatures and we found that flares are best described by two main phases; an impulsive phase and a gradual phase, for which the physical properties are different. Important spectral differences between flares lead us to distinguish four main classes: (i) solar-like chromospheric or two-ribbon flares, (ii) white-light flares, (iii) combined white-light flares with distinct impulsive and gradual phases, and (iv) non solar-like flares (usually occuring on RS CVn type stars). We show how this classification corresponds to substantial differences in the physical properties of the flare components. We compiled all available spectroscopic data for stellar flares. We found several new empirical correlations between the time lags in the spectral lines (rise and decay times). We found for instance that during the gradual phase, the rise time in the H γ line is well correlated to the rise time in the Ca  K line, and that the Ca  K line is 1.63 times slower to rise than the H γ line. Similar correlations were found between the rise and decay times in these lines. These correlations are evidence that there is a dominant mechanism commanding the temporal flux evolutions during the gradual phase of flares. This mechanism applies on time scales ranging from one minute to more than a hundred minutes. We found correlations between the time lags and the maximum fluxes in the Johnson U-band and the spectral lines. These correlations show that the larger the flare the longer it takes to evolve. We show that the maximum flux in the Johnson U-band correlates well, but not linearly with the maximum flux in the H γ line during the impulsive phase, and over five orders of magnitude. We argue how this correlation can provide constraints on the currently available models. The spectral line maximum fluxes during the gradual phase also correlate with the Johnson U-band flux, which demonstrates that somehow the impulsive and gradual phases are physically linked. The correlation between the H γ and Ca K line fluxes during the gradual phase and the lack of dependence of the flux ratio of those lines on flare magnitude reveal that larger flares are not "hotter" than smaller flares during the gradual phase. We examine the behaviour of the spectral line widths: While the Ca  K line width shows essentially no detectable variation, the Balmer line widths show a complex dependency on the white light intensity. We distinguish three energy domains where the Balmer line widths exhibit a different behaviour: (i) for small flares, the widths remain rather constant as a function of white light intensity, which suggests that in this energy range the U-band is not a good diagnostic of the total energy release and that dense "kernels" do not dominate the Balmer emission, (ii) for medium size flares, the widths rapidly increase with the U-band flux up to about 15 Å, which in...

show abstract

“…Chromospheric evaporation then brings "fresh material", emitting soft thermal X-ray emission, into the corona. The strong X-ray and UV radiation field finally induces further chromospheric emission (Hawley & Fisher 1992).…”

Section: Introductionmentioning

confidence: 99%

Multiwavelength observations of a giant flare on CN Leonis

Liefke¹,

Fuhrmeister²,

Schmitt³

2010

A&A

View full text Add to dashboard Cite

Context. Stellar flares affect all atmospheric layers from the photosphere over chromosphere and transition region up into the corona. Simultaneous observations in different spectral bands allow to obtain a comprehensive picture of the environmental conditions and the physical processes going on during different phases of the flare. Aims. We investigate the properties of the coronal plasma during a giant flare on the active M dwarf CN Leo observed simultaneously with the UVES spectrograph at the VLT and XMM-Newton. Methods. From the X-ray data, we analyze the temporal evolution of the coronal temperature and emission measure, and investigate variations in electron density and coronal abundances during the flare. Optical Fe xiii line emission traces the cooler quiescent corona.Results. Although of rather short duration (exponential decay time τ LC < 5 min), the X-ray flux at flare peak exceeds the quiescent level by a factor of ≈100. The electron density averaged over the whole flare is greater than 5 × 10 11 cm −3 . The flare plasma shows an enhancement of iron by a factor of ≈2 during the rise and peak phase of the flare. We derive a size of <9000 km for the flaring structure from the evolution of the the emitting plasma during flare rise, peak, and decay. Conclusions. The characteristics of the flare plasma suggest that the flare originates from a compact arcade instead of a single loop. The combined results from X-ray and optical data further confine the plasma properties and the geometry of the flaring structure in different atmospheric layers.

show abstract

X-ray-heated models of stellar flare atmospheres - Theory and comparison with observations

Cited by 144 publications

References 46 publications

Long Duration Flare Emission: Impulsive Heating or Gradual Heating?

Long Duration Flare Emission: Impulsive Heating or Gradual Heating?

Dynamics of flares on late type dMe stars

Multiwavelength observations of a giant flare on CN Leonis

Contact Info

Product

Resources

About