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| themis:science:history [2024/11/26 15:35] – created etienne | themis:science:history [2024/12/19 14:02] (current) – admin |
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| - Simultaneous observations in several spectral lines | - Simultaneous observations in several spectral lines |
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| - The first condition comes from the fact that the largest part of the photospheric magnetic field is concentrated in very small structures. | * The first condition comes from the fact that the largest part of the photospheric magnetic field is concentrated in very small structures. |
| - The second one is obvious: an accurate determination of the vector magnetic field, using the Zeeman effect requires a precise measurement of the four Stokes parameters. This means a polarimetric accuracy of 10<sup>-3</sup> for precise determination of the direction of strong magnetic fields. Observations of weak magnetic fields (like intra-network fields in the photosphere) will require a polarimetric sensitivity of at least 10<sup>-4</sup> | * The second one is obvious: an accurate determination of the vector magnetic field, using the Zeeman effect requires a precise measurement of the four Stokes parameters. This means a polarimetric accuracy of 10<sup>-3</sup> for precise determination of the direction of strong magnetic fields. Observations of weak magnetic fields (like intra-network fields in the photosphere) will require a polarimetric sensitivity of at least 10<sup>-4</sup> |
| - The third condition comes from several considerations: | * The third condition comes from several considerations: |
| * Local physical parameters, like temperature and density, do affect the linear polarization. To separate those effects from the one of the magnetic field (and determine the vector magnetic field as well as the other parameters), one needs to observe several spectral lines with different sensitivities to the physical conditions. | * Local physical parameters, like temperature and density, do affect the linear polarization. To separate those effects from the one of the magnetic field (and determine the vector magnetic field as well as the other parameters), one needs to observe several spectral lines with different sensitivities to the physical conditions. |
| * A realistic determination of the variation with height of the physical parameters, as well as of the magnetic field flux tubes, requires the measurement of several sets of lines, properly chosen to scan different levels in the sun atmosphere | * A realistic determination of the variation with height of the physical parameters, as well as of the magnetic field flux tubes, requires the measurement of several sets of lines, properly chosen to scan different levels in the sun atmosphere |
| * It will always remain magnetic elements of size beyond the attainable spatial resolution. For them, multilines Stokes polarimetry allows to get, in addition with the magnetic flux, the field strength and the magnetic field filling factor. | * It will always remain magnetic elements of size beyond the attainable spatial resolution. For them, multilines Stokes polarimetry allows to get, in addition with the magnetic flux, the field strength and the magnetic field filling factor. |
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| THEMIS is the first solar telescope to fill those three conditions.\\ | THEMIS is the first solar telescope to fill those three conditions.\\ |
