scholarly journals EUV Emission Sources in Gas-Dynamic Models of Stellar Flares

1996 ◽  
Vol 152 ◽  
pp. 171-174
Author(s):  
M.A. Livshits ◽  
M.M. Katsova
Keyword(s):  
Energy Release ◽  
Dynamic Models ◽  
Thermal Front ◽  
Euv Emission ◽  
Stellar Flares ◽  
Single Burst ◽  
Explosive Evaporation ◽  
Impulsive Heating ◽  
Stellar Chromosphere ◽  
Flare Model

A stellar flare model in which the main energy release is located above the chromosphere based on a set of elementary acts of the electron acceleration or impulsive heating of plasma is discussed. The response of the chromosphere to impulsive heating for both a single burst and the simultaneous effect of a set of the bursts is considered.The results of numerical modeling of the process of explosive evaporation of the stellar chromosphere allow us to select 3 classes of EUV emission source: (1) the bursts of the EUV emission in the temperature range of 3 · 104 – 3 · 105 K at the beginning of each of elementary act of the energy release; (2) the bursts of the EUV emission at temperatures T ≈ 106 K, accompanied by outflow of heated plasma; (3) the EUV emission, caused by new features of the process, namely, when the maxima of the distribution of the pressure are forming in the region of the downward-moving thermal front.The properties of the EUV sources, velocities of the plasma motions therein, and possible behaviour of the light curve for an elementary burst are discussed.

scholarly journals Stellar Flares: Observations and Theory

1989 ◽  
Vol 104 (2) ◽  
pp. 49-52
Author(s):  
Suzanne L. Hawley
Keyword(s):  
Scaling Law ◽  
Dynamic Scaling ◽  
X Ray ◽  
Temperature Distributions ◽  
Photometric And Spectroscopic Observations ◽  
Stellar Flares ◽  
Consistent Model ◽  
Self Consistent ◽  
Flare Model ◽  
Large Flare

AbstractPhotometric and spectroscopic observations of a very large flare on AD Leo are presented. A self consistent model of a flare corona, transition region and chromosphere is developed; in particular the chromospheric temperature distributions resulting from X-ray and EUV irradiation by coronae of various temperatures are determined. The predicted line fluxes in Hγ are compared to the observed line fluxes to find the coronal temperature as a function of time during the flare. This run of temperature with time is then compared with the predictions of an independent theoretical flare model based on a dynamic scaling law (see paper by Fisher and Hawley, these proceedings).

scholarly journals Astrophysical explosions: from solar flares to cosmic gamma-ray bursts

2012 ◽  
Vol 370 (1960) ◽  
pp. 774-799 ◽  
Author(s):  
J. Craig Wheeler
Keyword(s):  
Neutron Stars ◽  
Energy Release ◽  
Solar Flares ◽  
Gamma Ray ◽  
Gamma Ray Bursts ◽  
Accretion Discs ◽  
Stellar Flares ◽  
Crossing Time ◽  
Dynamical Time ◽  
New Research

Astrophysical explosions result from the release of magnetic, gravitational or thermonuclear energy on dynamical time scales, typically the sound-crossing time for the system. These explosions include solar and stellar flares, eruptive phenomena in accretion discs, thermonuclear combustion on the surfaces of white dwarfs and neutron stars, violent magnetic reconnection in neutron stars, thermonuclear and gravitational collapse supernovae and cosmic gamma-ray bursts, each representing a different type and amount of energy release. This paper summarizes the properties of these explosions and describes new research on thermonuclear explosions and explosions in extended circumstellar media. Parallels are drawn between studies of terrestrial and astrophysical explosions, especially the physics of the transition from deflagration-to-detonation.

scholarly journals Magnetic reconnection and energy release on the Sun and solar-like stars

2008 ◽  
Vol 4 (S259) ◽  
pp. 191-200
Author(s):  
Lidia van Driel-Gesztelyi
Keyword(s):  
Free Energy ◽  
Magnetic Reconnection ◽  
Energy Release ◽  
Energy Content ◽  
Magnetic Flux Density ◽  
The Sun ◽  
X Rays ◽  
Stellar Flares ◽  
Wide Wavelength Range ◽  
Hot Corona

AbstractMagnetic reconnection is thought to play an important role in liberating free energy stored in stressed magnetic fields. The consequences vary from undetectable nanoflares to huge flares, which have signatures over a wide wavelength range, depending on e.g. magnetic topology, free energy content, total flux, and magnetic flux density of the structures involved. Events of small energy release, which are thought to be the most numerous, are one of the key factors in the existence of a hot corona in the Sun and solar-like stars. The majority of large flares are ejective, i.e. involve the expulsion of large quantities of mass and magnetic field from the star. Since magnetic reconnection requires small length-scales, which are well below the spatial resolution limits of even the solar observations, we cannot directly observe magnetic reconnection happening. However, there is a plethora of indirect evidences from X-rays to radio observations of magnetic reconnection. I discuss key observational signatures of flares on the Sun and solar-paradigm stellar flares and describe models emphasizing synergy between observations and theory.

scholarly journals Flare in Late-type Stars: UV

1995 ◽  
Vol 151 ◽  
pp. 136-145
Author(s):  
P. Brendan Byrne
Keyword(s):  
Continuous Monitoring ◽  
Interactive Mode ◽  
Stellar Flares ◽  
Hot Plasma ◽  
International Ultraviolet Explorer ◽  
Mode Of Operation ◽  
Optical Continuum ◽  
Stellar Chromosphere ◽  
Direct Confirmation ◽  
Limited Sensitivity

Early studies of stellar flares were made entirely in the optical regime. It was recognised that flares arose from the generation of hot plasma within the stellar chromosphere at whose temperature (indicated, for instance, by the presence of a strong, blue optical continuum) a substantial emission in the ultraviolet would be expected. It was not until the advent of space-borne instruments of adequate sensitivity, however, that direct confirmation of this prediction was forthcoming. In this review I examine some results of more than a decade of observation of stellar flares in the UV.The major source of ultraviolet data on stellar flares has been the International Ultraviolet Explorer (IUE) satellite (Boggess et al. 1979). In order to understand the limitations of our current understanding in this area it is important to appreciate some of the characteristics of its instrumentation. IUE’s telescope is of 40 cm aperture and it is equipped with a spectrograph which can operate at two resolutions, i.e. Δλ/λ ∼350 (LORES) and ∼17000 (HIRES). Its detectors are optimised for operation in two wavebands, i.e. ∼1150-1950Å (SW) and ∼1950-3200 Å (LW). IUE’s small apert ure results in a limited sensitivity, a consequence of which is a modest time resolution when studying stellar flares (a long exposure time is needed to gain adequate signal-to-noise). IUE’s elliptical 24-hour quasi-geosynchronous orbit and its resulting interactive mode of operation make continuous monitoring feasible, a feature suiting flare star work.

scholarly journals Multi-Wavelength Observations of Stellar Flares

1989 ◽  
Vol 104 (1) ◽  
pp. 61-74
Author(s):  
P. B. Byrne
Keyword(s):  
Solar Flare ◽  
Observational Data ◽  
Physical Parameters ◽  
Stellar Flares ◽  
Rs Cvn Stars ◽  
New Models ◽  
Multi Wavelength ◽  
Flare Model

AbstractWe present observational data on stellar flares from a range of wavelength regimes, many of which were obtained simultaneously. Physical parameters of these flares are derived and discussed in the framework of the general solar flare model. It is found that flares on dMe stars are solar-like, except in mean energy. The parameters of flares on RS CVn stars are more extreme, however, and may require new models for their interpretation.

scholarly journals Close-by planets and flares in their host stars

2018 ◽  
Vol 610 ◽  
pp. A81 ◽  
Author(s):  
A. F. Lanza
Keyword(s):  
Energy Release ◽  
Binary Systems ◽  
Magnetic Energy ◽  
Indirect Measurement ◽  
Conclusive Evidence ◽  
Analytical Models ◽  
Stellar Flares ◽  
Active Stars ◽  
Released Energy ◽  
Field Lines

Context. The interaction between the magnetic fields of late-type stars and their close-by planets may produce stellar flares as observed in active binary systems. However, in spite of several claims, conclusive evidence is still lacking. Aim. We estimate the magnetic energy available in the interaction using analytical models to provide an upper bound to the expected flare energy. Methods. We investigated three different mechanisms leading to magnetic energy release. The first two can release an energy up to (0.2–1.2) B02R3/μ, where B0 is the surface field of the star, R its radius, and μ the magnetic permeability of the plasma. These two mechanisms operate in young active stars whose coronae have closed magnetic field lines up to the distance of their close-by planets that can trigger the energy release. The third mechanism operates in weakly or moderately active stars with a coronal field with predominantly open field lines at the distance of their planets. The released energy is of the order of (0.002–0.1) B02R3/μ and depends on the ratio of the planetary to the stellar fields, thus allowing an indirect measurement of the former when the latter is known. Results. We compute the released energy for various separations of the planet and various stellar parameters finding the conditions for the operation of the proposed mechanisms. An application to eight selected systems is presented. Conclusions. The computed energies and dissipation timescales are in agreement with flare observations in the eccentric system HD 17156 and in the circular systems HD 189733 and HD 179949. This kind of star–planet interaction can be unambiguously identified by the higher flaring frequency expected close to periastron in eccentric systems.

Pinch mechanism of energy release of stellar flares

Astrophysics ◽  
1991 ◽  
Vol 32 (3) ◽  
pp. 230-235
Author(s):  
V. S. Airapetyan ◽  
V. V. Vikhrev ◽  
V. V. Ivanov ◽  
G. A. Rozanova
Keyword(s):  
Energy Release ◽  
Stellar Flares

Monetary policy and the effect of the transfer of oil prices to inflation

2020 ◽  
pp. 41-50
Author(s):  
Ph. S. Kartaev ◽  
I. D. Medvedev
Keyword(s):  
Monetary Policy ◽  
Inflation Targeting ◽  
Dynamic Models ◽  
Oil Prices ◽  
Oil Price ◽  
Oil Price Shocks ◽  
Negative Effects ◽  
Price Shocks ◽  
Policy Regime ◽  
The Impact

The paper examines the impact of oil price shocks on inflation, as well as the impact of the choice of the monetary policy regime on the strength of this influence. We used dynamic models on panel data for the countries of the world for the period from 2000 to 2017. It is shown that mainly the impact of changes in oil prices on inflation is carried out through the channel of exchange rate. The paper demonstrates the influence of the transition to inflation targeting on the nature of the relationship between oil price shocks and inflation. This effect is asymmetrical: during periods of rising oil prices, inflation targeting reduces the effect of the transfer of oil prices, limiting negative effects of shock. During periods of decline in oil prices, this monetary policy regime, in contrast, contributes to a stronger transfer, helping to reduce inflation.

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