Doppler speeds of the hydrogen Lyman lines in solar flares from EVE

Brown, Stephen; Fletcher, L.; Labrosse, Nicolas

doi:10.1051/0004-6361/201628390

Cited by 19 publications

(34 citation statements)

References 32 publications

(48 reference statements)

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“…There is a general ordering to the derived velocities throughout the simulation, with lower-order lines suggesting higher speeds. This is particularly interesting because the opposite effect was observed by Brown et al (2016) in velocity profiles with no preflare-subtraction when ordering was present, although this could have been due to the variability in the measured velocities of the higher-order EVE lines also being greater due to their weaker irradiances.…”

Section: Velocities From Radynmentioning

confidence: 89%

“…This allows us to emulate the EVE instrumental profile (Crotser et al 2007) and compare the simulated velocities-as they would be observed by EVE-to those reported in Brown et al (2016). Examples of degraded line profiles for Ly-α are shown in Figure 4; they clearly display a stark reduction in detail, compared to the raw data.…”

Section: The F10d3 Simulationmentioning

confidence: 90%

“…The final step in analyzing the output line profiles from RADYN and RH is to simulate instrumental effects and measure the Doppler shifts that an instrument like EVE would observe (Brown et al 2016). This is done by first rebinning the non-constant RH data (between 30 and 130 nm) to a constant wavelength spacing of 0.005 nm, before convolving the RADYN and RH profiles with the instrumental profile of EVE, given by a Gaussian of FWHM 0.085 nm (see Crotser et al 2007), and then resampling the data to replicate EVEʼs wavelength bin size of 0.02 nm.…”

Section: Description Of Simulations and Methodsmentioning

confidence: 99%

“…Velocity profiles for Ly-α through Ly-δ are plotted as a function of time in Figure 6(a). We also include a panel of velocities calculated on the time-integrated line profiles (for 10 s) in order to facilitate a comparison to EVE observations (Brown et al 2016). The time-integrated velocities demonstrate an additional loss of information due to the instrumentation when compared to the results with high temporal resolution.…”

Section: Velocities From Radynmentioning

confidence: 99%

“…Unfortunately, MEGS-A is no longer operational as of May 2014, and MEGS-B functions on a reduced duty cycle of 3 hr per day. (Woods et al 2012;Brown et al 2016) Emission line spectroscopy of the hydrogen Lyman lines, which are well-observed in the MEGS-B spectrum (91.2 nm <λ<121.6 nm), was performed by Brown et al (2016). In a sample of six M and X class flares, they found red-and blueshifted Lyman lines, suggesting plasma flows on the order of several tens of km s −1 , but with some flares showing upflows and others showing downflows.…”

Section: Introductionmentioning

confidence: 99%

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Modeling of the Hydrogen Lyman Lines in Solar Flares

Brown

Fletcher

Kerr

et al. 2018

ApJ

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The hydrogen Lyman lines (91.2 nm < λ<121.6 nm) are significant contributors to the radiative losses of the solar chromosphere, and they are enhanced during flares. We have shown previously that the Lyman lines observed by the Extreme Ultraviolet Variability instrument onboard the Solar Dynamics Observatory exhibit Doppler motions equivalent to speeds on the order of 30 km s −1 . However, contrary to expectations, both redshifts and blueshifts were present and no dominant flow direction was observed. To understand the formation of the Lyman lines, particularly their Doppler motions, we have used the radiative hydrodynamic code, RADYN, along with the radiative transfer code, RH, to simulate the evolution of the flaring chromosphere and the response of the Lyman lines during solar flares. We find that upflows in the simulated atmospheres lead to blueshifts in the line cores, which exhibit central reversals. We then model the effects of the instrument on the profiles, using the Extreme Ultraviolet Variability Experiment (EVE) instrumentʼs properties. What may be interpreted as downflows (redshifted emission) in the lines, after they have been convolved with the instrumental line profile, may not necessarily correspond to actual downflows. Dynamic features in the atmosphere can introduce complex features in the line profiles that will not be detected by instruments with the spectral resolution of EVE, but which leave more of a signature at the resolution of the Spectral Investigation of the Coronal Environment instrument onboard the Solar Orbiter.

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Section: Velocities From Radynmentioning

confidence: 89%

Section: The F10d3 Simulationmentioning

confidence: 90%

Section: Description Of Simulations and Methodsmentioning

confidence: 99%

Section: Velocities From Radynmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Modeling of the Hydrogen Lyman Lines in Solar Flares

Brown

Fletcher

Kerr

et al. 2018

ApJ

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The high-energy Sun - probing the origins of particle acceleration on our nearest star

Matthews¹,

Reid²,

Baker³

et al. 2021

Exp Astron

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As a frequent and energetic particle accelerator, our Sun provides us with an excellent astrophysical laboratory for understanding the fundamental process of particle acceleration. The exploitation of radiative diagnostics from electrons has shown that acceleration operates on sub-second time scales in a complex magnetic environment, where direct electric fields, wave turbulence, and shock waves all must contribute, although precise details are severely lacking. Ions were assumed to be accelerated in a similar manner to electrons, but γ-ray imaging confirmed that emission sources are spatially separated from X-ray sources, suggesting distinctly different acceleration mechanisms. Current X-ray and γ-ray spectroscopy provides only a basic understanding of accelerated particle spectra and the total energy budgets are therefore poorly constrained. Additionally, the recent detection of relativistic ion signatures lasting many hours, without an electron counterpart, is an enigma. We propose a single platform to directly measure the physical conditions present in the energy release sites and the environment in which the particles propagate and deposit their energy. To address this fundamental issue, we set out a suite of dedicated instruments that will probe both electrons and ions simultaneously to observe; high (seconds) temporal resolution photon spectra (4 keV – 150 MeV) with simultaneous imaging (1 keV – 30 MeV), polarization measurements (5–1000 keV) and high spatial and temporal resolution imaging spectroscopy in the UV/EUV/SXR (soft X-ray) regimes. These instruments will observe the broad range of radiative signatures produced in the solar atmosphere by accelerated particles.

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The Temperature Dependence of Hot Prograde Flows in Solar Active Regions

Fitzpatrick

Hudson

2023

Sol Phys

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Using simultaneous observations from the EUV Variability Experiment (EVE) and imaging from the Atmospheric Imaging Assembly (AIA), we characterise the temperature dependence of apparent hot flows in solar active regions. The EVE instrument performs Sun-as-a-star spectroscopy and is composed of two spectrographs: MEGS-A and MEGS-B (Multiple EUV Grating Spectrograph-A, -B). It is known that EVE can measure wavelength shifts and thus can observe relative Doppler velocities in solar atmospheric plasmas over an extended temperature range. However, MEGS-A is affected by a known astigmatism effect (Chamberlin: Solar Phys.291, 1665, 2016); inhomogeneities in EUV brightness on the solar surface result in purely instrumental wavelength errors. We validate our methods by independently quantifying this effect and comparing to Chamberlin’s results, and we explore the wavelength dependence as an extension of his formula as derived for He ii 304 Å. MEGS-B is unaffected by this instrumental effect in any case, and this has allowed us to find evidence of hot prograde flows in active regions. Using our image-based models for the astigmatism and flows, we independently confirm our original MEGS-B result. We now extend our knowledge of the temperature dependence of these flows via the additional Fe emission lines available in MEGS-A. We find a monotonic increase of apparent flow speed with temperature up through lines of Fe xvi, nominally formed at about 6.4 MK.

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Doppler speeds of the hydrogen Lyman lines in solar flares from EVE

Cited by 19 publications

References 32 publications

Modeling of the Hydrogen Lyman Lines in Solar Flares

Modeling of the Hydrogen Lyman Lines in Solar Flares

The high-energy Sun - probing the origins of particle acceleration on our nearest star

The Temperature Dependence of Hot Prograde Flows in Solar Active Regions

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