Zeeman Effect in Sun-Spots. by Tutomn TANAKA and Yutaka TAKAGI.

Transcription

1 Zeeman Effect in Sun-Spots. by Tutomn TANAKA and Yutaka TAKAGI.

2 422 Tutomu TANAKA and Yutaka TAKAGI. [Vol. 21 It amounts to about 60. It is a matter of course, since the magnetic fields in sun-spots are not very intense and the absorption lines are always " winged." But the separated lines are fairly sharp (see Fig. 1), especially when their Zeeman patterns are simple. This points to the fact that there is, for every line, an effective magnetic field of which the range of magnitude is not very wide. Fig. 1 Fig. 2 Fig 3 Fig 4 The effective magnetic field is theoretically given by in gauss where ƒ v is the Zeeman separation (double resolution) expressed by wave-number per cm, and f the number found in the tables of Zeeman patterns(1). The patterns of some lines are very simple and the effective fields can be determined quite accurately. For example, and for 5F1-5F01 line the field gives no affection. (1) C. C. Kiess and W. F. Meggers, Bureau (of Standards, J. of Research 1 (1928), 641.

3 1939] Zeeman Effect in Sun-Spots. 423 The Fe-lines of , , and A are typical examples. These are shown in Figs In the present case the effective fields have often been calculated by measuring the separations of the centres of intensity of unresolved (perpendicular) component lines. With respect to the positions of these centres the results obtained by Shenstone and Blair(1) can be used. But sometimes each resolved part of the pattern is to be considered to be a mixture of a components and or (parallel) components. It occurs as a rule when J=0 and the angle between the magnetic field and the line of sight ( ) is large. In such a case the theoretical intensities of these components are to be considered(2). These intensities are to be reduced, when they are observed, by a factor of sin2 for components and of 1/ 2 (1+cos2 ) for components. Thus the centre of intensity of such a mixture can be found. The fields calculated bythis process are marked by in Table II. Our spectrograms were photographed during several days. But iron and calcium lines, which are found in nearly all plates and with different intensities, show nearly equal effective fields (see Fig. 5). Therefore it is quite improbable that the effective field in the spot Fig. 5 considered has changed meanwhile beyond the range of experimental errors. 3. The Effective Field for a Multiplet. From the investigation of the flash spectra in solar eclipses, Mitchell(3) has concluded that the height in which the light in question seems to be emitted is widely different even in the same multiplet of an element. It depends chiefly on the intensity of The line and in (1) Phil. Mag. 8 (1929), 765. (2) H. Honl-Zeits. f. Physik 31 (1925), 340. The formulae for intensities of Zeeman components in the case of J=0 are : (3) Astrophys. J. 72 (1930), 146.

4 424 Tutomu TANAKA and Yutaka TAKAGI. [Vol. 21 some degree on its excitation voltage. On the other hand, King(1) has concluded as the result of his investigations of sun-spots that the errors due to blending may be present, and therefore the question of correlation between true field-strength and line intensity must remain open. To determine whether Mitchell's conclusion is valid in our case too, we measured in the first place the effective fields for the lines composing a multiplet. Some results have been tabulated as follows:- Table 1. (1) Loc. cit.

5 1939] Zecman Effect in Sun-Spots. 425 It is quite evident that the effective magnetic field for each line composing a multiplet coincides with each other within the range of experimental errors. But the effective magnetic fields for different elements are quite different. 4. Effective Fields for Lines of Different Intensities. In the second place, the dependence of the effective magnetic field on the intensity of each spectral line has been investigated. A typical example of it will be given :- This result is represented in Fig. 6. The intensity of each line is taken from Rowland's Tables. The dependence of the field on the intensity can hardly be found. The results as regards other vapours are shown in Figs. 7 and 8. The variation of the effective field with varying intensity of the line considered is quite small, if any. It is almost within the range of experimental errors. Chromium affords the only exception. The values of the effective magnetic fields are rather inconsistent, though their mean is definitely large. This is shown in Fig. 9. Such a discordance might be due to the abnormality of g Fig. 7

6 426 Tutomu TANAKA and Yutaka TAKAGI. [Vol. 21 Fig. 8 Fig. 9 values or the obscureness of the patterns due to other lines (especially in the case of ). But we cannot say definitely for the present. The magnetic separations measured and the effective fields computed by them are shown in the following table:- Table II.

7 19393 Zeeman Effect in Sun-Spots. 427 Table II. (Continued)

8 428 Tutomn TANAKA and Yutaka TAKAGI. [Vol. 21 * Not evident. ** In most cases a disk line is broader than a resolved spot line corresponding to it. Therefore in an unresolved spot line the width of the corresponding disk line gives an upper limit of its magnetic separation if the central component is not too intense, while the difference of the widths of a disk line and the corresponding spot line gives a lower limit of the same, and so on. This method of determination proved to give rational results in all cases examined by us. Underlined) intensity is for the disk line. The field marked with this has been calculated considering each resolved part of the pattern to be a mixture of components and components; otherwise, the same is considered to be resolved or unresolved components. 5. Effective Fields for Different Elements. The effective field acting on each element differs from each other to an extent that is much larger than the order of magnitude of experimental errors. The mean value of the field intensities for each element is shown in Fig. 10 in relation to the atomic number of the Fig. 10 element. Here the points corresponding to Ni were deduced from the field of the spot appeared in the December of 1938, by reducing the magnetic fields acting on the same Fe line to an equal value. Meanwhile the point corresponding to Zn was obtained from the mean of the upper and lower limits, these limits being rather near. It can be seen front the figure that there exists some regularity, though its detailed discussions are reserved for the present. Neverthelese, the following points are noticeable:- (a) There seems to exist a maximum of the effective field in the level of chromium. Probably the heavier elements are arranged in the lower levels, but in a space of weaker field. The element, which is

9 1939] Zeeman Effect in Sun-Spots. 429 situated in the maximum part of the field, might not be strictly definite. King(1) seems to have found that vanadium showed the maximum Zeeman separation in the spots observed by him. (b) Most of the elements, of which the spectral lines show measurable Zeeman separations, are paramagnetic ones which have atomic weights within some range. This shows that the magnetic force, besides the gravitation, is effective in some degree to the formation of the levels of various elements. 6. Comparasion of Different Spots. Some comparison was made between a big spot appeared in Febr., 1939 and the one considered above. The ratios of the separations are given in the following table:- The magnetic separations seem to show tolerable similarity in the two cases. For the further investigation of this matter we expect another opportunity. 7. Meaning of the Effective Magnetic Field(2). In the lower level, the radiation pressure acting on an atom is much larger than the gravitation and the magnetic force acting on the same atone. Thus the atom is accelerated towards the upper level. There the gravitation does not decrease much, while the radiation pressure decreases remarkably owing to the decrease of the radiation intensity due to selective absorption and weaker reemission. So the atom ceases to be accelerated. Consequently above some level the gas (1) Loc. eit. (2) The former part of this idea is similar to that expressed by A. Unsold in Zeits. f. Physik 44 (1927), 793.

10 8 430 Tutomu TANAKA and Yutaka TAKAGI. [Vol. 21 pressure decreases rapidly and the percentage of the ionized atom in. creases rapidly according to Saha's theory. A wave-number of enhanced line series is expressed by in neutral elements. Therefore the whole spectrum is displaced towards the region of much higher wave-number. Hence each impulse transferred to an atone (hv/c) by each absorbed light quantum increases. But the density of radiation (pv) in the ultraviolet or Millikan region decreases considerably, and consequently the radiation pressure acting on the ionized atom considerably decreases. Thus the ionized atom begins to descend. Going downwards, the ionized atom becomes recombined by impinging on free electrons, and again begins to ascend. Thus the process is repeated, so the atom is kept in some level. Such atoms tend to make a region with comparatively large density in some height in which the gravitation, magnetic field and radiation pressure are in equilibrium. This height might be different for each gas. These layers might not be very thin owing to diffusion, but can be sufficiently thin to build up effective layers of different gases. Each effective layer corresponds to each effective magnetic field. This explains the existence of quite sharp Zeeman patterns. A report in greater detail will soon appear in the Annals of the Tokyo Astronomical Observatory. (1) For every spectral line there seems to exist an effective magnetic field of which the range of magnitude is not very wide. (2) The effective magnetic field for each of the components forming a multiplet coincides with each other. (3) The dependence, for each element, of the effective field on the intensity of a spectral line is small. It is almost within the range of experimental errors. (4) The effective magnetic fields of different elements are quite different from each other and seem to be able to be arranged with some regularity in the order of their atomic numbers. (5) An explanation can be given for the existence of the effective

11 t magnetic field, layers of different elements being considered. Tokyo Astronomical Observatory. P.S. Recently J. Evershed mentions in his report (M. N. 99 (1939), 219) that the relative magnetic separations of the five iron lines in his spot spectra agree well with those observed by King in the laboratory under a definite magnetic field. For these lines the following table can be obtained :- This shows that Zeeman separations of these lines in a sun-spot are due to the same effective magnetic field, and that this field is independent of the intensities and excitation potentials of the spectral lines. This result coincides exactly with that obtained by us. (Received June. 17, 1939).