SUMER-Hinode observations of microflares: excitation   of molecular hydrogen

Innes, D. E.

doi:10.1051/0004-6361:20078977

Cited by 7 publications

(6 citation statements)

References 7 publications

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“…The H 2 emission is extremely weak in the quiet Sun (Sandlin et al, 1986). It was also observed in flares (Bartoe et al, 1979) and microflares in the active region plage (Innes, 2008). In sunspot regions, the H 2 emission is distinctive and relatively strong (Jordan et al, 1978;Schühle et al, 1999;Curdt et al, 2001).…”

Section: Peculiar Lines In the Sunspotmentioning

confidence: 96%

Solar transition region above sunspots

Curdt

Teriaca

Landi

et al. 2009

A&A

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Aims. We study the transition region (TR) properties above sunspots and the surrounding plage regions, by analyzing several sunspot reference spectra obtained by the SUMER (Solar Ultraviolet Measurements of Emitted Radiation) instrument in March 1999 and November 2006. Methods. We compare the SUMER spectra observed in the umbra, penumbra, plage, and sunspot plume regions. The hydrogen Lyman line profiles averaged in each of the four regions are presented. For the sunspot observed in 2006, the electron densities, differential emission measure (DEM), and filling factors of the TR plasma in the four regions are also investigated.Results. The self-reversals of the hydrogen Lyman line profiles are almost absent in sunspots at different locations (at heliocentric angles of up to 49 • ) on the solar disk. In the sunspot plume, the Lyman lines are also not reversed, whilst the lower Lyman line profiles observed in the plage region are obviously reversed, a phenomenon found also in the normal quiet Sun. The TR densities of the umbra and plume are similar and one order of magnitude lower than those of the plage and penumbra. The DEM curve of the sunspot plume exhibits a peak centered at log(T/K) ∼ 5.45, which exceeds the DEM of other regions by one to two orders of magnitude at these temperatures. We also find that more than 100 lines, which are very weak or not observed anywhere else on the Sun, are well observed by SUMER in the sunspot, especially in the sunspot plume. Conclusions. We suggest that the TR above sunspots is higher and probably more extended, and that the opacity of the hydrogen lines is much lower above sunspots, compared to the TR above plage regions. Our result indicates that the enhanced TR emission of the sunspot plume is probably caused by a large filling factor. The strongly enhanced emission at TR temperatures and the reduced continuum ensure that many normally weak TR lines are clearly distinctive in the spectra of sunspot plumes.

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Section: Peculiar Lines In the Sunspotmentioning

confidence: 96%

Solar transition region above sunspots

Curdt

Teriaca

Landi

et al. 2009

A&A

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“…However, in the umbra the atmosphere is very cool, making it possible to form a substantial fraction of H 2 . Observations of the fluorescent H 2 lines in the ultraviolet have confirmed its presence in the chromosphere above sunspots (Jordan et al 1978;Bartoe et al 1979;Innes 2008), while atmospheric models of the sunspot umbra predict a molecular hydrogen population of up to 10%, peaking near the height of continuum formation (Maltby et al 1986).…”

Section: The Magnetohydrostatic Equilibrium Of Sunspots and The Role mentioning

confidence: 98%

On Molecular Hydrogen Formation and the Magnetohydrostatic Equilibrium of Sunspots

Jaeggli¹,

Lin²,

Uitenbroek³

2012

ApJ

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We have investigated the problem of sunspot magnetohydrostatic equilibrium with comprehensive IR sunspot magnetic field survey observations of the highly sensitive Fe i lines at 15650 Å and nearby OH lines. We have found that some sunspots show isothermal increases in umbral magnetic field strength which cannot be explained by the simplified sunspot model with a single-component ideal gas atmosphere assumed in previous investigations. Large sunspots universally display nonlinear increases in magnetic pressure over temperature, while small sunspots and pores display linear behavior. The formation of molecules provides a mechanism for isothermal concentration of the umbral magnetic field, and we propose that this may explain the observed rapid increase in umbral magnetic field strength relative to temperature. Existing multi-component sunspot atmospheric models predict that a significant amount of molecular hydrogen (H 2 ) exists in the sunspot umbra. The formation of H 2 can significantly alter the thermodynamic properties of the sunspot atmosphere and may play a significant role in sunspot evolution. In addition to the survey observations, we have performed detailed chemical equilibrium calculations with full consideration of radiative transfer effects to establish OH as a proxy for H 2 , and demonstrate that a significant population of H 2 exists in the coolest regions of large sunspots.

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“…The authors provided a list of wavelengths in transitions (in the v � -v �� = 1-0 to 1-7 bands) which were later found to be in good agreement with the lines observed in a sunspot (Schüehle et al 1999) recorded by the Solar Ultraviolet Measurements of Emitted Radiation (SUMER; Wilhelm et al 1995) instrument. H 2 emission has also been observed in the quiet sun (Sandlin et al 1986) and by Innes (2008) in active region plage associated with the footpoints of X-ray microflares, near the footpoint of a brightening X-ray loop and at the location of strong transition region outflow.…”

Section: Introductionmentioning

confidence: 86%

“…However, depending on optical conditions, high-energy photons can. In this paper, we present observations made during a flare of enhanced line emission from molecular hydrogen, H 2 which has a formation temperature of 4200 K (Innes 2008) corresponding to the TMR. H 2 line emission is thought to be formed by photo-excitation (fluorescence) by ultraviolet (UV) radiation from the transition region, and a recent theoretical study by Jaeggli et al (2018) put the location in a narrow range around 650 km above the photosphere for a range of temperature stratifications and radiation conditions, including corresponding to a flare.…”

Section: Introductionmentioning

confidence: 99%

Evidence of chromospheric molecular hydrogen emission in a solar flare observed by the IRIS satellite

Mulay

Fletcher

2021

Monthly Notices of the Royal Astronomical Society

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We have carried out the first comprehensive investigation of enhanced line emission from molecular hydrogen, H2 at 1333.79 Å, observed at flare ribbons in SOL2014-04-18T13:03. The cool H2 emission is known to be fluorescently excited by Si iv 1402.77 Å UV radiation and provides a unique view of the temperature minimum region (TMR). Strong H2 emission was observed when the Si iv 1402.77 Å emission was bright during the flare impulsive phase and gradual decay phase, but it dimmed during the GOES peak. H2 line broadening showed non-thermal speeds in the range 7-18 $\rm {km~s}^{-1}$, possibly corresponding to turbulent plasma flows. Small red (blue) shifts, up to 1.8 (4.9) $\rm {km~s}^{-1}$ were measured. The intensity ratio of Si iv 1393.76 Å and Si iv 1402.77 Å confirmed that plasma was optically thin to Si iv (where the ratio = 2) during the impulsive phase of the flare in locations where strong H2 emission was observed. In contrast, the ratio differs from optically thin value of 2 in parts of ribbons, indicating a role for opacity effects. A strong spatial and temporal correlation between H2 and Si iv emission was evident supporting the notion that fluorescent excitation is responsible.

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SUMER-Hinode observations of microflares: excitation of molecular hydrogen

Cited by 7 publications

References 7 publications

Solar transition region above sunspots

Solar transition region above sunspots

On Molecular Hydrogen Formation and the Magnetohydrostatic Equilibrium of Sunspots

Evidence of chromospheric molecular hydrogen emission in a solar flare observed by the IRIS satellite

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