Variation of the profiles of medium-strong photospheric lines with heliographic latitude

Caccin, B.; Falciani, R.; Falchi, A.

doi:10.1007/bf00152039

Cited by 2 publications

(2 citation statements)

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“…Here, it may be worth paying attention to the spectroscopic method for diagnosing the surface temperature variation, which makes use of the fact that the strengths of spectral lines more or less change in response to temperature differences. Actually, not a few investigators had tried to detect the global temperature variation in the photosphere based on this spectroscopic approach until the 1970s (see, e.g., Caccin et al, 1970;Caccin, Donati-Falchi, and Falciani, 1973;Noyes, Ayres, and Hall, 1973;Rutten, 1973;Falciani, Rigutti, and Roberti, 1974;Caccin, Falciani, and Donati-Falchi, 1976;Caccin, Falciani, and Donati Falchi, 1978; and the references therein) but none of them could show concrete evidence of a poleequator temperature difference. Thereafter, studies in this line seem to have gone rather out of vogue among solar physicists and have barely been conducted so far.…”

Section: Introductionmentioning

confidence: 99%

Toward Spectroscopically Detecting the Global Latitudinal Temperature Variation on the Solar Surface

Takeda

Ueno

2017

Sol Phys

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A very slight rotation-induced latitudinal temperature variation (presumably on the order of several Kelvin) on the solar surface is theoretically expected. While recent high-precision solar brightness observations reported its detection, confirmation by an alternative approach using the strengths of spectral lines is desirable, for which reducing the noise due to random fluctuation caused by atmospheric inhomogeneity is critical. Towards this difficult task, we carried out a pilot study of spectroscopically investigating the relative variation of temperature (T ) at a number of points in the solar circumference region near to the limb (where latitude dependence should show up if any exists) based on the equivalent widths (W ) of 28 selected lines in the 5367-5393Å and 6075-6100Å regions. Our special attention was paid to i) clarifying which kind of lines should be employed and ii) how much precision would be accomplished in practice. We found that lines with strong T -sensitivity (| log W/ log T |) should be used and that very weak lines should be avoided because they inevitably suffer large relative fluctuations (∆W/W ). Our analysis revealed that a precision of ∆T /T ≈ 0.003 (corresponding to ≈ 15 K) can be achieved at best by a spectral line with comparatively large | log W/ log T |, though this can possibly be further improved if other more suitable lines are used. Accordingly, if many such favorable lines could be measured with sub-% precision of ∆W/W and by averaging the resulting ∆T /T from each line, the random noise would eventually be reduced down to 1 K and detection of very subtle amount of global T -gradient might be possible.

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Section: Introductionmentioning

confidence: 99%

Toward Spectroscopically Detecting the Global Latitudinal Temperature Variation on the Solar Surface

Takeda

Ueno

2017

Sol Phys

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“…These studies have mostly been concentrated towards variations in line shifts and line shapes (bisectors) (e.g. Caccin et al 1976Caccin et al , 1978Beckers & Taylor 1980;Brandt & Schroeter 1982;Andersen 1984), variations that have generally been inter-preted as variations in the photospheric velocity fields with latitude. There are few studies of the variations, or constancy, in the line strengths (equivalent widths).…”

Section: Introductionmentioning

confidence: 99%

Is the solar spectrum latitude-dependent?

Kiselman

Pereira

Gustafsson

et al. 2011

A&A

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Context. In studies of the solar spectrum relative to spectra of solar twin stars, it has been found that the chemical composition of the Sun seems to depart systematically from those of the twins. One possible explanation could be that the effect is due to the special aspect angle of the Sun when observed from Earth, as compared with the aspect angles of the twins. Thus, a latitude dependence of the solar spectrum, even with the heliocentric angle constant, could lead to effects of the type observed. Aims. We explore a possible variation in the strength of certain spectral lines, used in the comparisons between the composition of the Sun and the twins, at loci on the solar disk with different latitudes but at constant heliocentric angle. Methods. We use the TRIPPEL spectrograph at the Swedish 1-m Solar Telescope on La Palma to record spectra in five spectral regions in order to compare different locations on the solar disk at a heliocentric angle of 45 • . Equivalent widths and other parameters are measured for fifteen different lines representing nine atomic species. Spectra acquired at different times are used in averaging the line parameters for each line and observing position. Results. The relative variations in equivalent widths at the equator and at solar latitude ∼ 45 • are found to be less than 1.5% for all spectral lines studied. Translated to elemental abundances as they would be measured from a terrestrial and a hypothetical pole-on observer, the difference is estimated to be within 0.005 dex in all cases. Conclusions. It is very unlikely that latitude effects could cause the reported abundance difference between the Sun and the solar twins. The accuracy obtainable in measurements of small differences in spectral line strengths between different solar disk positions is very high, and can be exploited in studies, e.g. of weak magnetic fields or effects of solar activity on atmospheric structure.

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Variation of the profiles of medium-strong photospheric lines with heliographic latitude

Cited by 2 publications

References 5 publications

Toward Spectroscopically Detecting the Global Latitudinal Temperature Variation on the Solar Surface

Toward Spectroscopically Detecting the Global Latitudinal Temperature Variation on the Solar Surface

Is the solar spectrum latitude-dependent?

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