RU2178899C1 - Method for measurement of magnetic field strength of self-luminous objects - Google Patents

Abstract

FIELD: astrophysical measurements, applicable for research of the structure and dynamics of magnetic fields in the solar atmosphere. SUBSTANCE: the intensity of luminous radiation is measured simultaneously in the section of superposition of spectral component φ $\genfrac{}{}{0ex}{}{\text{rb}}{\text{l}}$ in blue Ф $\genfrac{}{}{0ex}{}{\text{b}}{\text{l}}$ and red Ф $\genfrac{}{}{0ex}{}{\text{r}}{\text{l}}$ wings of the spectral line, as well as in the section of continuous spectrum Ф_c that is closest to the line. The magnetic field strength is calculated by formula:

, where k_H-calibration factor. EFFECT: provided simultaneous measurement of the longitudinal magnetic field strength and the beam velocity only per exposition, which considerably weakens the action of atmospheric instabilities and reduces the time of observations. 2 dwg

Description

 The invention relates to the field of technical physics and is intended to measure the magnetic field in a solar plasma.

 The known method [1] has a number of errors due to fundamental shortcomings of the photometer and modulation scheme.

 The closest technical solution is a method of measuring the magnetic field strength [2], based on measuring the Zeeman splitting of the spectral line by transforming the type of polarization with subsequent bifurcation of the spectrum along the dispersion direction of the spectrograph. In this method, the spatial position of the spectral components is modulated, while the amplitude of the signal at the modulation frequency is proportional to the magnetic field strength in that part of the solar surface from which light passes through the entrance slit of the spectrograph.

 The disadvantages of the prototype include significant light losses on the elements of the electro-optical modulator, which leads to a decrease in sensitivity, and the inability to simultaneously measure radial velocity. In addition, the known method is difficult to apply to work with modern multi-channel photodetectors. Due to the low reading speed (about 20-30 Hz), the modulation frequency will be too low. As a result, the internal noise of the spectrograph and atmospheric instabilities will create false signals that completely distort the measurement result.

 The proposed technical solution is aimed at eliminating the listed disadvantages of the prototype when achieving new qualities (reduction of observation time, simultaneous measurement of radial velocity).

где Ф_l ^rb - интенсивность светового излучения на участке переналожения спектральных компонент;
Ф_l ^r, Ф_l ^b, Ф_c - интенсивности светового излучения в красном, синем крыльях спектральной линии и непрерывном спектре соответственно;
k_H - калибровочный коэффициент.According to the proposed method, the circular polarization of the Zeeman spectral line components is transformed into a linear one, differently polarized spectral components are spread along the spectrograph dispersion direction by an amount equal to the half-width of the working spectral line, the light radiation intensity is measured at the reposition area of the spectral components, as well as the violet and red wings of the spectral line and in the adjacent to the line section of the continuous spectrum, and the magnetic field strength is calculated by the formula

where Ф _l ^rb is the intensity of light radiation in the area of re-arrangement of spectral components;
Ф _l ^r , Ф _l ^b , Ф _c - the intensities of light radiation in the red, blue wings of the spectral line and the continuous spectrum, respectively;
k _H is the calibration factor.

The calibration coefficient can be determined experimentally using one of the known methods (for example, according to the USSR author's certificate 1245895 "Method for calibrating measurements of magnetic field strength and differential radial velocity", 1986, Bull. Inventory 27). In this calibration method [3], the Zeeman splitting of the spectral line Δλ _H due to the action of a magnetic field of known magnitude H _{k is} simulated artificially, while the corresponding calibration signal S _k is recorded. The ratio H _k / s _k in the future and is used as a calibration factor. Such a calibration is based on the well-known formula Δλ _H = ± 4.67 × 10 ^-13 λ ² gH, where g is the Landé factor characterizing the magnetic sensitivity of the spectral line) and is suitable for any method of measuring the longitudinal component of the magnetic field strength. The cited formula is well known and can be found in the following publications: 1) Space Physics, edited by R. A. Syunyaev. M., 1986, publishing house "Soviet Encyclopedia", p. 270, left column. 2) V. M. Grigoriev, N. I. Kobanov "Solar magnetographs", collection of articles "Research on geomagnetism, aeronomy and physics of the Sun", 1980, no. 52, 155, publishing house "Science", on p. 157.

The idea of the proposed measurement method is based on the fact that with a change in the magnetic field intensity, the intensity Ф _l ^rb and the sum Ф _l ^b + Ф _l ^r change in antiphase. An increase in Ф _l ^{rb is} accompanied by a decrease in Ф _l ^b + Ф _l ^r and vice versa, thus increasing the sensitivity to a change in the magnetic field strength.

The need to measure Ф _с is due to the fact that half the intensity of the continuous spectrum is implicit in the measurements of Ф _l ^b and Ф _l ^r . If this contribution is not decompensated, then there will be problems with determining the zero of the measuring scale.

In FIG. 1 presents a simplified optical scheme that implements the proposed method, where
1 - telescope lens;
2 - input slit of the spectrograph;
3 - quarter-wave phase-shifting plate;
4 - polarizing prism;
5 - spectrograph;
6 - multi-channel photodetector (CCD - line, CCD - matrix).

The lens of the telescope 1 builds an image of the Sun in the plane of the entrance slit of the spectrograph 2, through which light from the studied area of the solar surface passes into the spectrograph. Polarizing prism 4 provides the separation of light rays in the direction of dispersion by an amount equivalent to the half-width of the working spectral line. The separation of the spectral components into the half-width of the line is ensured by using the most steep and linear sections of the line profile for measurements, which, on the one hand, guarantees maximum sensitivity to changes in the measured magnetic field strength, and, on the other hand, the signal is independent of any joint component displacements within the linear section. In this case, in the focal plane of the spectrograph, two images of the spectrum are obtained, shifted one relative to the other by an amount determined by prism 4 and the linear dispersion of the spectrograph in this spectral order. Since this is a small shift, the spectral line images will be transferred onto the photosensitive surface of a multichannel photodetector, for example, a CCD line or a matrix. The four groups of pixels of the line, which fall on the area of the reassignment of the spectral components, the red and blue wings of the spectral line, and the continuous spectrum section form four "electronic gaps". The “electronic gaps” in the wings are removed from the central “gap” in the transfer zone by a distance equal to the half-width of the working spectral line. With this arrangement, the signal calculated by formula (1) is equal to zero at zero magnetic field strength. The total charges in each of these slots are proportional to the integral light fluxes "cut out" by them. Thus, the measurement of f _l ^rb , f _l ^r , f _l ^b and f _c . In the case of the matrix, in the vertical direction, i.e., along the matrix column is an extended section of the solar image, cut out by the entrance slit of the spectrograph.

где K_v - калибровочный коэффициент, определяемый экспериментально по известной скорости вращения Солнца или рассчитываемый по справочным данным для рабочей спектральной линии. Из фиг. 2 видно, что при смещении спектральной линии в красную сторону (лучевая скорость направлена от наблюдателя), Ф_l ^b по величине превышает Ф_l ^r и знак измеряемой скорости будет положительным. При обратном смещении соответственно сменится и знак измеряемой скорости.The measurements are as follows. The investigated area of the image of the Sun is brought to the entrance slit 2, presumably without a magnetic field. If there is no magnetic field (zero intensity) in this section, then the light passing into the spectrograph will not be polarized, the Zeeman splitting of the spectral line will be absent, and the quarter-wave plate 3 will have no effect in this case, and the distance between the spectral components will be determined solely by the parameters of the polarization prism and the dispersion of the spectrograph will be Δλ _o (left position in Fig. 2). The electronic gaps in the wings of the spectral line are located symmetrically with respect to the gap in the zone of the reposition of the spectral components at a distance close to the half-width of the spectral line. Further, this distance is changed, achieving equal to zero values of the signal calculated by the formula (1). Since it is not known in advance that this is a section with a zero field, in order to avoid errors, a quarter-wave plate 3 is removed from the light beam and the operation of adjusting the position of the electronic slots is repeated, achieving a zero signal. After that, the plate 3 is returned to its original position - readiness for measurements is achieved. If the magnetic field is nonzero, the spectral line splits into two Zeeman components, the polarization of which depends on the polarity of the magnetic field. Let the polarity be such that after passing through the quarter-wave plate 3, the polarization of the left Zeeman component coincides with the polarization of the beam deflected by the prism 4 to the left, and the right to the right. In this case, the distance between the spectral components will increase by Δλ _H and become equal to Δλ _o + Δλ _H Accordingly, the intensity Ф _l ^{rb will} increase, and Ф _l ^r and Ф _l ^b will decrease and the numerator in formula (1) will take some positive value. If the magnetic field polarity is opposite, then with a prism 4 the Zeeman components are shifted towards each other, the distance between the spectral components will decrease by Δλ _H and become equal to Δλ _o - Δλ _H. In this case, the intensity Ф _l ^rb will decrease, and Ф _l ^r and Ф _l ^{b will} increase and the numerator in formula (1) will become negative, reflecting the fact of a change in the sign of the field. Radial velocity is found by the formula

where K _v is the calibration coefficient determined experimentally from the known rotation speed of the Sun or calculated from the reference data for the working spectral line. From FIG. 2 shows that when the spectral line is shifted to the red side (radial velocity is directed away from the observer), Ф _l ^b exceeds Ф _l ^r in magnitude and the sign of the measured velocity will be positive. With a reverse bias, the sign of the measured speed will change accordingly.

 Thus, the values of the magnetic field strength and radial velocity are measured in just one exposure, without changing the state of polarization to the opposite, which removes the fundamental limitation on the use of modern multi-element photodetectors for measuring magnetic field strength. This reduces the effect of atmospheric distortion and at least halves the time of observation.

Sources of information taken into account
1) Kuznetsov D.A., Kuklin G.V., Stepanov V.E. Results of observations and studies during the MGSS, 1966, no. 1.M .: Science, 80.

 2) Lebedev N.N., Klochek N.V., Grigoryev V.M., Kobanov N.I. Copyright certificate of the USSR 335652, cl. G 01 J 3/06, 1972, BI 13.

 3) Grigoriev V.M., Demidov M.L., Kobanov N.I. Copyright certificate of the USSR 1245895, cl. G 01 J 3/04, 1986, BI 27.

Claims (1)

A method of measuring the magnetic field strength of self-luminous objects, based on measuring the Zeeman splitting of the spectral line by converting circularly polarized spectral components into linearly polarized ones with their subsequent dilution along the spectrograph dispersion, characterized in that the light intensity is measured simultaneously at the reposition area of the spectral components Ф _l ^rb, _l ^b blue F and F _l ^r red spectral line wings, as well as the line closest to the site of a continuous spectrum F _s, and magnetic field strength calculated by the formula:

where k _N is the calibration coefficient.

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