Measurement of magnetic field of AR 3053 and 3055 through Zeeman effect

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fulvio.mete
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Measurement of magnetic field of AR 3053 and 3055 through Zeeman effect

Post by fulvio.mete »

Solarscan photo2.jpg
Solarscan photo2.jpg (979.28 KiB) Viewed 604 times
Solarscan photo1.jpg
Solarscan photo1.jpg (989.57 KiB) Viewed 604 times
Zeeman 11_07_22.jpg
Zeeman 11_07_22.jpg (1.49 MiB) Viewed 604 times
Zeeman 11_07_22 B.jpg
Zeeman 11_07_22 B.jpg (183.67 KiB) Viewed 604 times
Fe6173 Spc profile AR 3053.jpg
Fe6173 Spc profile AR 3053.jpg (504.6 KiB) Viewed 604 times
Fe6173 Spc profile_AR 3055.JPG
Fe6173 Spc profile_AR 3055.JPG (452.92 KiB) Viewed 604 times
Not only spectroheliography and solar imaging: a high resolution spectrograph such as my VHIRSS, POSS2 and Solarscan can allow detections of scientific value, such as the measurement of the magnetic fields of sunspots (in not polarized light), an exclusive activity of observatories and solar satellites, or instruments of the value hundreds of thousands if not millions of €, inaccessible to amateurs. The instrument I dedicated to this activity was SOLARSCAN, which has been performing it perfectly for some years. The physical limit of the instrument's spatial and spectroscopic resolution is to be able to measure medium-large spots with Zeeman splitting while for the small ones the line thickening method could be used, which I believe however much less reliable of the former, unless you use it in polarized light.
The transit on the disk of two active regions of considerable extension allowed me yesterday morning to repeat once again the exciting (at least for me) experiment, for which I adopt a strict program, of a military type, under penalty of unsuccessful work, considering that the solar disk is visible from my house for no more than 1h and 15 min, in this period between 9 and 10.15 a.m. Then wake up at 7.30, preparation and control of the instrument, connection of cables to the PC and then the unpleasant positioning of the spectrograph on the Losmandy mount (which means keeping a weight of 15 kg perfectly still for the insertion of its Losmandy dovetail bar into the mount plate (for my age it is not a trifle). At the start of the management program a moment of panic: it did not respond, it was impossible to focus the spectrograph,then attempt to restart the PC, nothing: in the end, I remembered that the program was started only with a given USB port, and I solved it. In the meantime it was 9.30, and the clock ticked mercilessly. In the end I extracted 8 videos, in which the splitting of the iron line at 6173 Å was clearly visible.The dispersion of the spectra, with 4.65 micron of ,my DMK 51, was 0.01 A7pixel, R = 77000 (the seeing was not good,weather windy, focus not perfect).
This morning I calculated the magnetic field in Gauss of the two sunspots.
The procedure (in short) is as follows, using Valerie Desnoux's Visual Spec program:

1- I import the spectrum into the program, calibrating it in wavelength and flux
2- I measure the centers of the right and left cusps of the Iron line at 6173 A, make the difference in Å and divide the result by two
I then apply the following formula, where:

B is the magnetic field in gauss
λ is the wavelenght
g is the Landè factor (for Fe1 at 6173 is 2.5)


B = Δλ / 4.67 x 10^13 x λ^2 x g

In our case is:

1-For the 3053= Δλ = 0.216/2 =0.108

B = 0.108 x 10 ^13/ 444935733 = 2427.31 G

2- For the 3055: Δλ = 0.2089/2 =0.104

B = 0.104 x 10 ^13/ 444935733 = 2337.41 G




Probably the value of AR 3055 is underestimated due to its horizontal extension respect to the position of the slit.
This values are not too high for sunspots, but huge when compared with that of the earth (0.5 G).

The attached images show Solarscan on the Losmandy G11 mount, the two multipolar active Regions 3053 and 3055 (solar image Soho source) with the relative spectra , the images of the splitting of the iron line at 6173.34 Å due to the effect of the magnetic field generated by the spots, the spectral profiles of the two spectra, for the 3053 and 3055 with the center of the cusps in Å.


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Re: Measurement of magnetic field of AR 3053 and 3055 through Zeeman effect

Post by thesmiths »

Hi Fulvio, your lines are very sharp and the splitting is very clear. You mention polarising filters. Under what circumstances would linear and circular polarisers be used? Is it for different spectral lines with different angular momentum?


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Re: Measurement of magnetic field of AR 3053 and 3055 through Zeeman effect

Post by fulvio.mete »

Hi, Douglas: as I know Zeeman effect is most sensitive to circular polarization, so the measurements could be more precise.A friend of mine, solar physicist say up to 10%.In every case you need a spectropolarimeter, formed by a 1/4 wave retarder and a circular polarizer to place in front of the slit.The rotation of the retarder select the right or left polarization.Unfortunately the retarder is expensive, and , for now, i'll continue to use my system.


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Re: Measurement of magnetic field of AR 3053 and 3055 through Zeeman effect

Post by p_zetner »

Beautiful work, Fulvio (in spite of your “rocky” start)!

The splitting of the Fe 6173 line is so sharp. You can clearly see the pi and both sigma components. In fact, the pi components in the two sunspots have different intensities relative to the sigma components which, I believe, gives you some information about the inclination of the magnetic field lines relative to the line of sight. What kind of grating and collimating lens do you use? Do you fit the triplet with line profiles or simply measure peak locations?

Your splitting is clear enough that I don’t believe a circular polarizer will make any difference to your measurements. The only additional information you’d collect with the circular polarizer in a polarimeter configuration is the polarity of the magnetic field (as well as discrimination against the pi component).

Cheers.
Peter


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Re: Measurement of magnetic field of AR 3053 and 3055 through Zeeman effect

Post by fulvio.mete »

Thanks for comment Peter:I've been using Solarscan (originally developed for spectroheliography in remote) exclusively for this job since some years, considering its perfomances. The grating is a 2400 g/mm holo grating in an adjustable cell: the collimator is a SW 80/600 ED lens in a Littrow design, and the telescope a Takahashi 60/355 Fluorite refractor.All adjustaments are remote controlled from a PC with a dedicated software.Only the slit aperture isn't for i changed the initial remote controlled sophisticated slit with a simple (but effective) Edmund 5 micron air slit.About the polarimeter, I agree with you In my work of 2017 my results are quite in the median of those professional, and this is enough for me.


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Re: Measurement of magnetic field of AR 3053 and 3055 through Zeeman effect

Post by Montana »

Well done!! fascinating :bow

Alexandra


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