Comparison of Solar Magnetic Fields Measured at Different Observatories: Peculiar Strength Ratio Distributions Across the Disk

Demidov, M. L.; Golubeva, E. M.; Balthasar, H.; Staude, J.; Grigoryev, V. M.

doi:10.1007/s11207-008-9225-5

Cited by 26 publications

(25 citation statements)

References 40 publications

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“…As before, the red line ratio is much more separated from the weak-field ratio as a consequence of the contamination from thermodynamic effects. This type of behavior (decrease of the line ratio with increasing of flux density) has also been noticed in observations with other instruments (Demidov et al 2008;Stenflo 2010). Line ratio 1-sigma spread …”

Section: Dependence Of the Line Ratio On Flux Densitysupporting

confidence: 80%

Calibration of the 6302/6301 StokesVline ratio in terms of the 5250/5247 ratio

Stenflo

Demidov

Bianda

et al. 2013

A&A

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Four decades ago the Stokes V line ratio in the Fe i 5247.06 and 5250.22 Å lines was introduced as a powerful means of exploring the intrinsic field strengths at sub-pixel scales, which led to the discovery that most of the photospheric flux is in intermittent kG form. The "green" 5247-5250 line pair is unique because it allows the magnetic-field effects to be isolated from the thermodynamic effects. No other line pair with this property has since been identified. In recent years much of the magnetic-field diagnostics has been based on the "red" Fe i 6301.5 and 6302.5 Å line pair, since it was chosen in the design of the Hinode space observatory. Although thermodynamic effects severely contaminate the magnetic-field signatures for this line ratio, it is still possible to use it to extract information on intrinsic magnetic fields, but only after it has been "renormalized", since otherwise it produces fictitious, superstrong fields everywhere. In the present work we explore the joint behavior of these two line ratios to determine how the "contaminated" red line ratio can be translated into the corresponding green line ratio, which then allows for a direct interpretation in terms of intrinsic magnetic fields. Our observations are mainly based on recordings with the ZIMPOL-3 spectro-polarimeter at IRSOL in Locarno, Switzerland, complemented by data from the STOP telescope at the Sayan solar observatory (Irkutsk, Russia). The IRSOL observations are unique by allowing both the green and red line pairs to be recorded simultaneously on the same CCD sensor. We show how the line ratios depend on both the measured flux densities and on the heliocentric distance (the μ value on the solar disk), and finally derive the calibration function that enables the red line ratio to be translated to the green ratio for each μ value.

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Section: Dependence Of the Line Ratio On Flux Densitysupporting

confidence: 80%

Calibration of the 6302/6301 StokesVline ratio in terms of the 5250/5247 ratio

Stenflo

Demidov

Bianda

et al. 2013

A&A

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“…The reliability of STOP's data has been shown in some previous studies, where e.g. large-scale magnetic fields (LSMF) (see Demidov et al 2008) or SMMF (Demidov et al 2002) observations are presented. With appearence of the new data sets provided by SDO/HMI it is interesting to compare STOP obseravtions with them.…”

Section: Introductionsupporting

confidence: 52%

On the peculiarities of manifestation of kG magnetic elements in observations of the Sun with low spatial resolution

Demidov¹,

Veretsky²,

Kiselev³

2014

Proc. IAU

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Abstract. On the agenda of modern astrophysics is the exploration of not only disk-integrated stellar magnetic fields but surface mapping of them. However, it is hardly possible to expect that spatial resolution better than some dozens or hundreds pixels over stellar disk will be achieved for this goal in the foreseeable future. Among other reasons this fact makes very important observations of the average and large-scale magnetic fields of the Sun, which can be naturally used for testing polarimetric measurements on other stars, especially on solar-type stars. In this study we explore different aspects of observations of solar magnetic fields (SMF) with low spatial resolution, including Sun-as-a-star observations, which are characterized by extremely low magnetic flux densities. Comparison of disk-integrated and spatially resolved Stokes observations of the Sun allow us to demonstrate how Stokes V profiles depend on the distribution of large-scale magnetic fields in the disk center. It is shown that center-to-limb variations of magnetic strength ratios (MSR) and area asymetries, most likely could be interpreted as the manifestation of kG magnetic flux tubes. We have made cross-calibration of the full-disk magnetograms obtained by space-borned SDO/HMI and by the ground-based STOP telescope, and pretty good agreement is found. Finally, the absence of significant systematic time variations of MSRs with solar cycle is demonstrated.

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“…There are some results concerning the dependence of MSR for several cases on filling factor, amount of flux, or center-to-limb angle. Complicated and sometimes rather unexpected character of spatial distribution of MSR across the solar disk when different combinations of spectral lines and observatories are used, is shown in the recent paper (Demidov et al, 2008). The main objective of this study is to explore the possible dependence of MSR on time and spatial resolution in application to the large-scale (LSMF) and solar mean (SMMF) magnetic fields.…”

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confidence: 96%

“…1 There are some indications that MSR could depend on spatial resolution used in observations (Ulrich, 1992;Demidov et al, 2008). According to Ulrich (1992), the reduction factor (by which the MWO magnetic fields observed in the Fe i λ525.02 nm spectral line should be multiplied in comparison to observations in the Fe i λ523.29 nm) is increasing with decreasing of spatial resolution: R = 4.5 for the disk center for the resolution of 20 arc seconds, and R = 3.5 for the case of 5 arc seconds.…”

mentioning

confidence: 99%

“…Numerous LSMF and SMMF observations on the STOP telescope give the following MSR numbers for the Fe i λ524.70 nm -Fe i λ525.02 nm combination: R = 0.83 for the LSMF, and R = 0.93 for the SMMF. In the paper (Demidov et al, 2008) the possibility is suggested that the dependence of MSR on spatial resolution is the consequence of non-linearity of regression coefficients on magnetic field strength (filling factor).…”

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confidence: 99%

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On the dependence of magnetic line ratios on time and spatial scales

Demidov¹

2008

Proc. IAU

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Abstract.Comparison of magnetic fields measurements made in different spectral lines and observatories is an important tool for diagnostics of magnetohydrodynamic conditions in the solar atmosphere. But there is a deficit of information about the dependence of results on detailed position on the solar disk, spatial resolution and time. In this study these issues are discussed in application to the solar large-scale and Sun-as-a-star magnetic fields observations.

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Comparison of Solar Magnetic Fields Measured at Different Observatories: Peculiar Strength Ratio Distributions Across the Disk

Cited by 26 publications

References 40 publications

Calibration of the 6302/6301 StokesVline ratio in terms of the 5250/5247 ratio

Calibration of the 6302/6301 StokesVline ratio in terms of the 5250/5247 ratio

On the peculiarities of manifestation of kG magnetic elements in observations of the Sun with low spatial resolution

On the dependence of magnetic line ratios on time and spatial scales

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