Solar EUV emission line profiles of Si ii and Si iii and their center to limb variations

Nicolas, K. R.; Brueckner, G. E.; Tousey, R.; Tripp, D. A.; White, O. R.; Athay, R. G.

doi:10.1007/bf00152575

Cited by 26 publications

(18 citation statements)

References 19 publications

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“…One of them is a quiet Sun region close to the solar limb, one of the few where the 1312.59 Å line was visible. We have chosen this region because the calibrated radiances of the nearby stronger lines were similar to those reported by Nicolas et al (1977).…”

Section: Skylab Atm Observationsmentioning

confidence: 99%

“…The ratios (in energy units) are relative to the 1298.9 Å self-blend. The Skylab observed ratios are from Nicolas et al (1977) [N77] and Nicolas et al (1979) [N79].…”

Section: Comparison With Observationsmentioning

confidence: 99%

“…The observations were performed with the Naval Research Laboratory (NRL) EUV spectrograph on the Skylab Apollo Telescope Mount (ATM) and were reported by Nicolas et al (1977). The slit was positioned at various locations.…”

Section: Skylab Atm Observationsmentioning

confidence: 99%

“…In these and other subsequent observations, Si iii lines are rather weak, unless the observations are close to the solar limb, so we have chosen the observation that was 4 inside the limb, although we note that the resonance line at 1206 Å has a large optical depth (see, e.g. Burton et al 1971;Nicolas et al 1977;Sandlin et al 1986) at the limb.…”

Section: Skylab Atm Observationsmentioning

confidence: 99%

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Benchmarking atomic data for astrophysics: Si iii

Zanna

2015

A&A

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We investigate the main spectral diagnostics for Si iii UV lines, which have been previously used to measure electron densities, temperatures, and to suggest that non-Maxwellian electron distributions might be present in the low transition region of the solar atmosphere. Previous atomic calculations and observations are reviewed. We benchmark the observations using a new large-scale R-matrix scattering calculation for electron collisional excitation of Si iii, carried out with the intermediate-coupling frame transformation (ICFT) method. We find generally good agreement between predicted and observed line intensities, if one takes into account the different temperature sensitivity of the lines, and the structure of the solar transition region. We find no conclusive evidence for the presence of non-Maxwellian electron distributions.

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Section: Skylab Atm Observationsmentioning

confidence: 99%

“…The ratios (in energy units) are relative to the 1298.9 Å self-blend. The Skylab observed ratios are from Nicolas et al (1977) [N77] and Nicolas et al (1979) [N79].…”

Section: Comparison With Observationsmentioning

confidence: 99%

Section: Skylab Atm Observationsmentioning

confidence: 99%

Section: Skylab Atm Observationsmentioning

confidence: 99%

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Benchmarking atomic data for astrophysics: Si iii

Zanna

2015

A&A

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“…These doublepeaked profiles correspond to a self-reversal caused by the high optical thickness of the spectral line in these areas. The selfreversed profiles of the Si ii 1533 Å line have been observed with Skylab at the limb (Nicolas et al 1977) and studied with radiative transfer calculations (Lanzafame 1994). Other Si ii spectral profiles as in Fig.…”

Section: Si II and Ne Viii Spectramentioning

confidence: 99%

Spectral diagnostic of a microflare. Evidences of resonant scattering in C IV 1548 Å, 1550 Å lines

Gontikakis

Winebarger

Patsourakos

2013

A&A

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Aims. We study a microflare, classified as a GOES-A1 after background subtraction, which was observed in active region NOAA 8541 on May 15, 1999. Methods. We used TRACE filtergrams to study the morphology and time evolution. SUMER spectral lines were used to diagnose the chromospheric plasma (Si ii 1533 Å), transition region plasma (C iv 1548, 1550 Å), and coronal plasma (Ne viii 770 Å).Results. In the 171 Å and 195 Å filtergrams, we measure apparent mass motions along two small loops that compose the microflare from the eastern toward the western footpoints. In SUMER, the microflare is detected as a small (47 Mm 2 ), bright area at the western footpoints of the TRACE loops. The spectral profiles recorded over the bright area are complex. The Si ii 1533 Å line is self-reversed owing to opacity, and the coronal Ne viii line profile is composed of two Gaussian components, one of them systematically redshifted. The C iv 1548 Å and 1550 Å profiles are badly distorted because of the temporary depression of the detector local gain caused by the very high count rates reached in the flaring region and we can only confirm the presence of strong blueshifts of -200 km s −1 .Few, unaffected C iv profiles show two spectral components. In the northern part of the bright area, all SUMER spectral lines have at least one blueshifted spectral component. In the southern region of the bright area the spectral lines are redshifted. Adjacent to the microflare we measure, for the first time on the solar disk, an intensity ratio of the 1548 Å line to 1550 Å line with values of three to four, indicating that resonance scattering prevails in the lines formation. Moreover, the scattering region is found to be cospatial to a solar pore. Conclusions. The blueshifts in the footpoints of the microflare and the apparent mass motions observed with TRACE can be explained by a gentle chromospheric evaporation triggered by the microflare. The redshifted spectral components can be explained as cooling material that is falling back on the solar surface. The presence of resonant scattering can be explained by the low electron density expected in the transition region of a solar pore, combined with the high photon flux coming from the nearby microflare. We estimate that the lower limit of the electron density in the pore lies in the range 10 8 cm −3 to 10 9 cm −3 .

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3.1.1.3 Solar energy spectrum

Durrant¹

Landolt-Börnstein - Group VI Astronomy and Astrophysics

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Solar EUV emission line profiles of Si ii and Si iii and their center to limb variations

Cited by 26 publications

References 19 publications

Benchmarking atomic data for astrophysics: Si iii

Benchmarking atomic data for astrophysics: Si iii

Spectral diagnostic of a microflare. Evidences of resonant scattering in C IV 1548 Å, 1550 Å lines

3.1.1.3 Solar energy spectrum

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