Comparison of direct magnetic field measurements in a sunspot by ten spectral lines of Fe I, Fe II, Ti I and Ti II

Heading: 
Solar Physics
Lozitska, NI, Yakovkin, II, Lozitsky, VG, Hromov, MA
Kinemat. fiz. nebesnyh tel (Online) 2024, 40(6):59-72
https://doi.org/10.15407/kfnt2024.06.059
Language: Ukrainian
Abstract: 

Direct magnetic field measurements in sunspots by many spectral lines are important for elucidating the true magnitude and structure of the magnetic field at different levels of the solar atmosphere. Currently, magnetographic measurements are the most widespread, but such measurements mainly represent the longitudinal component of the magnetic field. In the sunspot umbra, such measurements give unreliable information and do not allow determining the actual value of the module (absolute value) of the magnetic field. Such data can be obtained from spectral-polarization observations, thanks to which the magnetic field can be determined directly from Zeeman splitting, rather than as calibrated polarization in line profiles. The presented work presents the results of the study of the magnetic field in the sunspot on July 17, 2023, which was observed on the Echelle spectrograph of the horizontal solar telescope of the Astronomical Observatory of Taras Shevchenko Kyiv National University. The I ± V profiles of ten photospheric lines of Fe I, Fe II, Ti I, and Ti II were analyzed in detail. The strongest magnetic field measured by the Fe I lines reaches 2600 G, and the difference in the measured intensities by these lines is sometimes at the level of 50—80%. The umbral lines of Ti I show, in general, the same magnetic fields as Fe I lines, while the lines of Fe II and Ti II show significantly weaker fields. Although the lateral field profile in the spot by most of the Fe I lines is smooth, quasi-Gaussian, one of the lines, namely Fe I 629.10 nm, shows a «dip» at 400—600 G in the sunspot umbra, which, most likely, is real. Probably, the obtained data indicate a combination of at least two effects: the dependence of measurements on the height of line formation in the solar atmosphere and the manifestation of Zeeman “saturation” in lines with different Lande factors. It also turned out that the shadow line of Ti I 630.38 нм shows significantly stronger magnetic fields compared to non-shadow lines. The obtained data are planned to be used to clarify the general picture of the magnetic field in the spot by means of simulation.
Keywords: magnetic fields, solar activity, spectropolarimetry, Sun, sunspots

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References: 

1. Venglinsky E. R., Lozitsky V. G. (2012) Direct magnetic field measurements in the sunspot umbra and penumbra using 146 spectral lines. Bull. Kyiv Astron. Obs., 49, 25-27.

2. Gurtovenko E. A., Kostik R. I. (1989) Fraunhofer spectrum and the system of solar power oscillators. Kyiv: Nauk. Dumka. 200.

3. Zemanek E. N., Stefanov A. P. (1976) Splitting of some spectral lines of Fe I in a magnetic field. Vestnik Kiev University, Seria Astronomii, 18,20-36.

4. Kurochka V. V., Kurochka L. N., Lozitsky V. G., Lozitska N. I., et al. (1980) Horizontal solar telescope of Astronomical Observatory of Kyiv University. Vestnik Kiev. Univ. Astronomija, 22, 48-56.

5. Lozitsky V. G., Klyueva A. I. (2011) Peculiarities of the Zeeman splitting in lines with small Lande factors in a sunspot spectrum. Astron. School's Rep., 7, 63-69.
https://doi.org/10.18372/2411-6602.07.1063

6. Severny A. B. (1967) Calibration of magnetic field signals of solar magnetograph. Bull. Crimea Astrophys. Obs., 36, 22-50.

7. Babcock H. W. (1953). The solar magnetograph. Astrophys. J., 118, 387-396. https://articles.adsabs.harvard.edu/pdf/1953ApJ...118..387B
https://doi.org/10.1086/145767

8. Durn C. J. S., Lagg A., Solanki S. K., van Noort M. (2020) Detection of the strongest magnetic field in a sunspot light bridge. Astrophys. J., 895,129-146.
https://doi.org/10.3847/1538-4357/ab83f1

9. Frish S. E. Optical atom spectra. (2010) St.-Peterburg. Moscow. Krasnodar. 656 p.

10. Khomenko E., Collados M. (2007) On the Stokes V amplitude ratio as an indicator of the field strength in the solar internetwork. Astrophys. J., 659, 1726-1735.
https://doi.org/10.1086/512098

11. Livingston W., Harvey J. W., Malanushenko O. V. (2006) Sunspots with the strongest magnetic fields. Solar Phys., 239, 41-68.
https://doi.org/10.1007/s11207-006-0265-4

12. Lozitsky V. G. (2016) Indications of 8-kilogauss magnetic field existence in the sunspot umbra. Advances in Space Res., 57, 398-407.
https://doi.org/10.1016/j.asr.2015.08.032

13. Lozitsky V. G., Osipov S. M., Stodilka M. I. (2022) Comparative study of spectral lines with different Lande factors observed in sunspots. J. Phys. Studies, 26(4), 4902, 14 p.
https://doi.org/10.30970/jps.26.4902

14. Moore Ch. E., Minnaert M. G. J., Houtgast J. (1966) The spectrum 2935  to 8770 . Second revision of Rowland's Table of solar spectrum wave lengths. Nat. Bureau Stand., Monogr., 61. 349 р.
https://doi.org/10.6028/NBS.MONO.61

15. Priest E. R. (2014) Magnetohydrodynamics of the Sun. Cambridge University Press.
https://doi.org/10.1017/CBO9781139020732

16. Scherrer P. H., Bogart R. S., Bush R. I., et al. (1995) The solar oscillations investigation - Michelson Doppler Imager. Solar Phys., 162, 129-188.
https://doi.org/10.1007/BF00733429

17. Semel M. (1980) A precise optical polarization analyzer. Astron. and Astrophys., 91, 369-371.

18. Semel M. (1981) Magnetic fields observed in a sunspot and faculae using 12 lines simultaneously. Astron. and Astrophys., 97, 75-78.

19. Solanki S. K. (2003) Sunspots: An overview. Astron. and Astrophys. Rev., 11, 153-286.
https://doi.org/10.1007/s00159-003-0018-4

20. Stenflo J. O. (1973) Magnetic-field structure of the photospheric network. Solar Phys., 32(1), 41-63.
https://doi.org/10.1007/BF00152728

21. Stenflo J. O. (2011) Collapsed, uncollapsed, and hidden magnetic flux on the quiet Sun. Astron. and Astrophys., 529, id. A42, 20.
https://doi.org/10.1051/0004-6361/201016275

22. Unno W. (1956) Line formation of a normal Zeeman triplet. Publ. Astron. Soc. Jap., 8, 108-125. https://articles.adsabs.harvard.edu/full/1956PASJ....8..108U

23. Van Noort M., Lagg A., Tiwari S. K., Solanki S. K. (2013) Peripheral downflows in sunspot penumbrae. Astron. and Astrophys., 557, id. A24, 14 р.
https://doi.org/10.1051/0004-6361/201321073