On the nature of the unidentified solar emission near 117 nm

Wilhelm, K.; Schühle, U.; Curdt, W.; Hilchenbach, M.; Marsch, E.; Lemaire, Philippe; Bertaux, J.; Jordan, S. D.; Feldman, U.

doi:10.1051/0004-6361:20042580

Cited by 9 publications

(6 citation statements)

References 54 publications

(53 reference statements)

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“…1 below). Observed temporal variations are often smaller than these spatial variations, typically around 40% (Wilhelm et al 2005;Wilhelm & Kalkofen 2003). Larger temporal variations were reported by (factors of 2 as shocks pass, sometimes a factor of 3 within about 30 s).…”

Section: Introductionmentioning

confidence: 86%

Models of the Solar Chromosphere and Transition Region from SUMER and HRTS Observations: Formation of the Extreme‐Ultraviolet Spectrum of Hydrogen, Carbon, and Oxygen

Avrett

Loeser

2008

ASTROPHYS J SUPPL S

357

234

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We present the results of optically thick non-LTE radiative transfer calculations of lines and continua of H, C iYiv, and O iYvi and other elements using a new one-dimensional, time-independent model corresponding to the average quiet-Sun chromosphere and transition region. The model is based principally on the Curdt et al. SUMER atlas of the extreme ultraviolet spectrum. Our model of the chromosphere is a semiempirical one, with the temperature distribution adjusted to obtain optimum agreement between calculated and observed continuum intensities, line intensities, and line profiles. Our model of the transition region is determined theoretically from a balance between (a) radiative losses and (b) the downward energy flow from the corona due to thermal conduction and particle diffusion, and using boundary conditions at the base of the transition region established at the top of the chromosphere from the semiempirical model. The quiet-Sun model presented here should be considered as a replacement of the earlier model C of Vernazza et al., since our new model is based on an energy-balance transition region, a better underlying photospheric model, a more extensive set of chromospheric observations, and improved calculations. The photospheric structure of the model given here is the same as in Table 3 of Fontenla, Avrett, Thuiller, & Harder. We show comparisons between calculated and observed continua, and between the calculated and observed profiles of all significant lines of H, C iYiv, and O iYvi in the wavelength range 67Y173 nm. While some of the calculated lines are not in emission as observed, we find reasonable general agreement, given the uncertainties in atomic rates and cross sections, and we document the sources of the rates and cross sections used in the calculation. We anticipate that future improvements in the atomic data will give improved agreement with the observations.

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Section: Introductionmentioning

confidence: 86%

Models of the Solar Chromosphere and Transition Region from SUMER and HRTS Observations: Formation of the Extreme‐Ultraviolet Spectrum of Hydrogen, Carbon, and Oxygen

Avrett

Loeser

2008

ASTROPHYS J SUPPL S

357

234

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“…Consequently empirically derived temperature amplitudes bear the danger of being systematically too low. An example might be the low values suggested by Avrett et al (2006) and Avrett (2007), which rely on SUMER observations (Wilhelm et al 2005) with limited spatial resolution.…”

Section: Gas Temperature and Emergent Intensity -A Few Words Of Cautionmentioning

confidence: 99%

Small-scale structure and dynamics of the lower solar atmosphere

Wedemeyer

Wöger

2007

Proc. IAU

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Abstract. The chromosphere of the quiet Sun is a highly intermittent and dynamic phenomenon. Three-dimensional radiation (magneto-)hydrodynamic simulations exhibit a meshlike pattern of hot shock fronts and cool expanding post-shock regions in the sub-canopy part of the inter-network. This domain might be called "fluctosphere". The pattern is produced by propagating shock waves, which are excited at the top of the convection zone and in the photospheric overshoot layer. New high-resolution observations reveal a ubiquitous small-scale pattern of bright structures and dark regions in-between. Although it qualitatively resembles the picture seen in models, more observations -e.g. with the future ALMA -are needed for thorough comparisons with present and future models. Quantitative comparisons demand for synthetic intensity maps and spectra for the three-dimensional (magneto-)hydrodynamic simulations. The necessary radiative transfer calculations, which have to take into account deviations from local thermodynamic equilibrium, are computationally very involved so that no reliable results have been produced so far. Until this task becomes feasible, we have to rely on careful qualitative comparisons of simulations and observations. Here we discuss what effects have to be considered for such a comparison. Nevertheless we are now on the verge of assembling a comprehensive picture of the solar chromosphere in inter-network regions as dynamic interplay of shock waves and structuring and guiding magnetic fields.

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“…This Paper is in response to the recent discussion by Wilhelm et al (2005) of emission features near 117 nm in the solar spectrum that are much broader than observed emission lines in this wavelength range. These authors rule out a number of possible explanations, such as groups of emission lines blended together, but they show that the center-to-limb behavior of these features has a greater similarity to that of emission lines rather than to that of a background continuum, and the results in their Fig.…”

Section: Introductionmentioning

confidence: 92%

Identification of the broad solar emission features near 117 nm

Avrett

Kurucz

Loeser

2006

A&A

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Wilhelm et al. have recently called attention to the unidentified broad emission features near 117 nm in the solar spectrum. They discuss the observed properties of these features in detail but do not identify the source of this emission. We show that the broad autoionizing transitions of neutral sulfur are responsible for these emission features. Autoionizing lines of S i occur throughout the spectrum between Lyman alpha and the Lyman limit. Sulfur is a normal contributor to stellar spectra. We use non-LTE chromospheric model calculations with line data from the Kurucz 2004 S i line list to simulate the solar spectrum in the range 116 to 118 nm.We compare the results with SUMER disk-center observations from Curdt et al. and limb observations from Wilhelm et al. Our calculations generally agree with the SUMER observations of the broad autoionizing S i emission features, the narrow S i emission lines, and the continuum in this wavelength region, and agree with basic characteristics of the center-to-limb observations. In addition to modeling the average spectrum, we show that a change of ±200 K in the temperature distribution causes the intensity to change by a factor of 4. This exceeds the observed intensity variations 1) with time in quiet regions at these wavelengths, and 2) with position from cell centers to bright network. These results do not seem compatible with current dynamical models that have temporal variations of 1000 K or more in the low chromosphere.

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On the nature of the unidentified solar emission near 117 nm

Cited by 9 publications

References 54 publications

Models of the Solar Chromosphere and Transition Region from SUMER and HRTS Observations: Formation of the Extreme‐Ultraviolet Spectrum of Hydrogen, Carbon, and Oxygen

Models of the Solar Chromosphere and Transition Region from SUMER and HRTS Observations: Formation of the Extreme‐Ultraviolet Spectrum of Hydrogen, Carbon, and Oxygen

Small-scale structure and dynamics of the lower solar atmosphere

Identification of the broad solar emission features near 117 nm

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