Width of emission cores of the line K Ca ii in sunspots

Teplitskaja, R. B.; Efendieva, S. A.

doi:10.1007/bf00152307

Cited by 4 publications

(3 citation statements)

References 8 publications

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“…This finally gives a FWHM at disk center of 53 pm, corresponding to 40 km s −1 (logarithmic value of 1.6). Wilson & Vainu Bappu (1957) give a range of 33-39 km s −1 for Ca spectra in plage where the emission core is more pronounced and can be separated from the wing contribution (see also Teplitskaja & Efendieva 1973;Jebsen & Mitchell 1978;Oranje 1983;Sivaraman et al 1996). The prediction of Wilson & Vainu Bappu (1957) …”

Section: Average Off-limb Spectramentioning

confidence: 95%

Spectroscopy at the solar limb

Beck

Rezaei²

2011

A&A

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Aims. We present constraints on the thermodynamical structure of the chromosphere from ground-based observations of the Ca ii H line profile near and off the solar limb. Methods. We obtained a slit-spectrograph data set of the Ca ii H line with a high signal-to-noise ratio in a field of view extending 20 across the limb. We analyzed the spectra for the characteristic properties of average and individual off-limb spectra. We used various tracers of the Doppler shifts, such as the location of the absorption core, the ratio of the two emission peaks H 2V and H 2R , and intensity images at a fixed wavelength. Results. The average off-limb profiles show a smooth variation with increasing limb distance. The line width increases up to a height of about 2 Mm above the limb. The profile shape is fairly symmetric with nearly identical H 2V and H 2R intensities; at a height of 5 Mm, it changes into a single Gaussian without emission peaks. We find that all off-limb spectra show large Doppler shifts that fluctuate on the smallest resolved spatial scales. The variation is more prominent in cuts parallel to the solar limb than on those perpendicular to it. As far as individual structures can be unequivocally identified at our spatial resolution, we find a specific relation between intensity enhancements and Doppler shifts: elongated brightenings are often flanked all along their extension by velocities in opposite directions. Conclusions. The average off-limb spectra of Ca ii H present a good opportunity to test static chromospheric atmosphere models because they lack the photospheric contribution that is present in disk-center spectra. We suggest that the observed relation between intensity enhancements and Doppler shifts could be caused by waves propagating along the surfaces of flux tubes: an intrinsic twist of the flux tubes or a wave propagation inclined to the tube axis would cause a helical shape of the Doppler excursions, visible as opposite velocity at the sides of the flux tube. Spectroscopic data allow one to distinguish this from a sausage-mode oscillation where the maximum Doppler shift and the tube axis would coincide.

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Section: Average Off-limb Spectramentioning

confidence: 95%

Spectroscopy at the solar limb

Beck

Rezaei²

2011

A&A

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“…This finally gives a FWHM at disk center of 53 pm, corresponding to 40 kms −1 (logarithmic value of 1.6). Wilson & Vainu Bappu (1957) give a range of 33-39 kms −1 for Ca spectra in plage where the emission core is more pronounced and can be separated from the wing contribution (see also Teplitskaja & Efendieva 1973;Jebsen & Mitchell 1978;Oranje 1983;Sivaraman et al 1996). The prediction of Wilson & Vainu Bappu (1957) for the Sun as a star line width of Ca ii H or K is 1.56, derived from their curve of what later was termed the Wilson-Bappu effect (cf.…”

Section: Average Off-limb Spectramentioning

confidence: 99%

Spectroscopy at the solar limb: I. Average off-limb profiles and Doppler shifts of Ca II H

Beck,

Rezaei

2011

Preprint

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Aims. We present constraints on the thermodynamical structure of the chromosphere from ground-based observations of the Ca ii H line profile near and off the solar limb. Methods. We obtained a slit-spectrograph data set of the Ca ii H line with a high signal-to-noise ratio in a field of view extending 20 ′′ across the limb. We analyzed the spectra for the characteristic properties of average and individual off-limb spectra. We used various tracers of the Doppler shifts, such as the location of the absorption core, the ratio of the two emission peaks H 2V and H 2R , and intensity images at a fixed wavelength. Results. The average off-limb profiles show a smooth variation with increasing limb distance. The line width increases up to a height of about 2 Mm above the limb. The profile shape is fairly symmetric with nearly identical H 2V and H 2R intensities; at a height of 5 Mm, it changes into a single Gaussian without emission peaks. We find that all off-limb spectra show large Doppler shifts that fluctuate on the smallest resolved spatial scales. The variation is more prominent in cuts parallel to the solar limb than on those perpendicular to it. As far as individual structures can be unequivocally identified at our spatial resolution, we find a specific relation between intensity enhancements and Doppler shifts: elongated brightenings are often flanked all along their extension by velocities in opposite directions. Conclusions. The average off-limb spectra of Ca ii H present a good opportunity to test static chromospheric atmosphere models because they lack the photospheric contribution that is present in disk-center spectra. We suggest that the observed relation between intensity enhancements and Doppler shifts could be caused by waves propagating along the surfaces of flux tubes: an intrinsic twist of the flux tubes or a wave propagation inclined to the tube axis would cause a helical shape of the Doppler excursion, visible as opposite velocity at the sides of the flux tube. Spectroscopic data allow one to distinguish this from a sausage-mode oscillation where the maximum Doppler shift and the tube axis would coincide.

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“…Twelve spectrograms obtained at the disk centre have been described by Teplitskaja and Efendieva (1973). The dispersion is 3.60 mm/A and fine-grained emulsion ORWO Blau Hard have been used.…”

Section: Observed Profilesmentioning

confidence: 99%

Shapes and centre-to-limb variation of the H and K lines in sunspot umbrae

Teplitskaja

Firstova

1976

Sol Phys

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The shapes of the Ca ii H and K lines in sunspot umbral spectra vary from single asymmetric peaks near the centre of the disk to almost symmetric double peaks at the limb. In addition, there are other differences in the behaviour of both H and K lines in sunspots compared to the quiet Sun. The whole complex of the phenomena observed can not be explained by large scale chromosphere motions. Instead, a satisfactory model reproducing in detail peculiarities of the umbral emission reversals contains a cloud of emitting and absorbing gas located above the chromosphere, which flows into the sunspot. The radiation field parameters in such a cloud are consistent with the concept of weak quiescent prominences above the umbra.

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Width of emission cores of the line K Ca ii in sunspots

Cited by 4 publications

References 8 publications

Spectroscopy at the solar limb

Spectroscopy at the solar limb

Spectroscopy at the solar limb: I. Average off-limb profiles and Doppler shifts of Ca II H

Shapes and centre-to-limb variation of the H and K lines in sunspot umbrae

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