Every day space telescopes provide amazing images of solar activity. However, their instruments are blind to the main driver: the magnetic field in the outer layers of the solar atmosphere, where the explosive events that sometimes affect the Earth occur. The remarkable observations of the polarization of solar ultraviolet light achieved by the CLASP2 mission make it possible to map the magnetic field across the entire solar atmosphere, from the photosphere to the base of the extremely hot corona. This study, published today in the journal Advances in science, conducted by the international team responsible for this suborbital experiment, which includes several scientists of the POLMAG group of the Instituto de Astrofísica de Canarias (IAC).
The chromosphere is a very important area of the solar atmosphere spanning a few thousand kilometers between the relatively thin and cool photosphere (with a temperature of a few thousand degrees) and the hottest and most extensive corona (with temperatures above a million degrees). Although the temperature of the chromosphere is about one hundred times lower than the temperature of the corona, the chromosphere has a much higher density, so much more energy is needed to maintain it. In addition, the mechanical energy required to heat the corona must transcend the chromosphere, making it a critical interface region for solving many of the major problems in solar and stellar physics. One of the current scientific challenges is to understand the origin of the brutal activity of the solar atmosphere, which at times disrupts the Earth’s magnetosphere with a detrimental effect on the technological world that is today.
“It is impossible to understand the feeling of the sun if we cannot determine the magnetic fields of the chromosphere, especially in its outer layers where the plasma temperature is around ten thousand degrees and the magnetic forces gaining control over the structure and dynamics of the plasma. ” , says Javier Trujillo Bueno, CSIC Professor at the IAC and chief scientist of the POLMAG group of the IAC (see http: // research.
As the Earth’s atmosphere absorbs the sun’s ultraviolet radiation strongly, it must be observed at altitudes above 100 kilometers. An international consortium was established with this goal, led by NASA’s Marshall Space Flight Center (NASA / MSFC), Japan National Astronomical Observatory (NAOJ), French Institute of Space Astrophysics (IAS) and Instituto de Astrofísica de Canarias na Spain. (IAC). This international team designed a series of space experiments selected through competitive missions within NASA’s Rocket Sounding Program. These space tests are called CLASP, the “Chromospheric Lyman-Alpha Spectro-Polarimeter” (CLASP1, launched on September 3, 2015) and the “Chromospheric LAyer Spectro-Polarimeter” (CLASP2, which was launched launched on April 11, 2019). Both experiments were very successful (see POLMAG project webpage http: // research.
The research paper recently published in the prestigious journal “Advances in science“based on a small part of the unprecedented data obtained by CLASP2. The team analyzed the intensity and circular polarization of the ultraviolet radiation emitted by an active area of the solar atmosphere in the spectral range in which the lines h & k of Mg II (ionized magnesium) about 2800 Å (see figure 1) Within this spectral region there are two celestial lines formed by Mn I (neutral manganese) atoms.
The circular polarization observed by CLASP2 arises from a physical device called the Zeeman effect, through which the radiation emitted by atoms in the presence of a magnetic field is polarized. “The circular polarization signals of the magnesium (Mg II) lines are sensitive to the magnetic fields in the central and outer regions of the solar chromosphere, but the circular polarization of the manganese (Mn I) lines corresponds to it. the magnetic fields in the depths. regions of the chromosphere “, explains Tanausú del Pino Alemán, one of the scientists of the POLMAG group and the international team.
While CLASP2 was making its observations, the Hinode space telescope was simultaneously pointing at the same active region on the solar disk. “This made it possible to obtain information about the magnetic field in the photosphere through the polarization observed in neutral iron (Fe I) celestial lines of the visible range of the spectrum”, notes Andrés Asensio Ramos, person Another IAC researcher who took part in the project … The team also conducted a simultaneous observation with the IRIS space telescope, measuring the intensity of ultraviolet radiation with higher spatial resolution (IRIS was not designed to polarize to measure).
The team’s study, led by Dr. Ryohko Ishikawa (NAOJ) and Dr. Javier Trujillo Bueno (IAC), mapping for the first time the magnetic field in the active region observed CLASP2 throughout the entire atmosphere, from the photosphere to the base of the corona (see figure 2 ). “This mapping of the magnetic field at different heights in the solar atmosphere is of great scientific interest, as it will help us to determine the magnetic connection between the different regions of the solar atmosphere,” said Ernest Alsina Ballester, an researcher of the international team who just joined the IAC after his first postdoc in Switzerland.
The results achieved confirm and confirm that, in these regions of the solar atmosphere, the lines of force of the magnetic field expand and fill the entire chromosphere before reaching the base of the corona. . Another important finding of this study is that there is a strong correlation between the strength of the magnetic field in the outer layers of the chromosphere with radiation intensity at the center of the magnesium lines and with the electron pressure in the same layers, indicating the origin. the heating magnetic. in the outer regions of the solar atmosphere.
The CLASP1 and CLASP2 space experiments represent a milestone in astronomy, providing the first observation of the relatively weak polar signals produced by different physical devices in spectral lines of a spectrum. ultraviolet of the sun. Such observations have made remarkable theories of previous theoretical prediction, thus confirming the quantum theory of polar radiation generation and movement that these scientists apply in their investigations of the magnetic field in it. the solar chromosphere.
The international team has just received the good news that NASA has recently selected their proposal to conduct a new space test next year, which will allow them to map the magnetic field over larger regions of the disk. sunshine. “Of course, systematic observation of the intensity and polarization of solar ultraviolet radiation on an instrument-equipped space telescope such as those on CLASP will be required, as the few minutes of observation time allowed by a suborbital flight test are insufficient”, she said. clarified Javier Trujillo Bueno. The team is confident that, thanks to the achievements of CLASP1 and CLASP2, such space telescopes will soon be available and the physical interpretation of their spectropolarimetric observations will allow a better understanding of magnetic activity in series. outside the sun and other. reultan.
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Article: Mapping solar magnetic fields from the photosphere to the base of the corona
Authors: Ryohko Ishikawa, Javier Trujillo Bueno, Tanausú del Pino Alemán, Takenori J. Okamoto, David E. McKenzie, Frédéric Auchère, Ryouhei Kano, Donguk Song, Masaki Yoshida, Laurel A. Rachmeler, Ken Kobayashi, Masahisito Hara, Masahisito Hara Noriyuki Narukage, Taro Sakao, Toshifumi Shimizu, Yoshinori Suematsu,? Christian Bethge, Bart De Pontieu, Alberto Sainz Dalda, Genevieve D. Vigil, Amy Winebarger, Ernest Alsina Ballester, Luca Belluzzi, Jiri Stepan, Andrés Asensio Ramos, Mats Carlsson, Jats. Leenaarts
CLASP2 Space Test Lead Investigators:
David Mackenzie (NASA / MSFC, USA)
Ryohko Ishikawa (NAOJ, Japan)
Frédéric Auchère (IAS, France)
Javier Trujillo Bueno (IAC, Spain)
IAC scientists participate in CLASP2:
Ernest Alsina Ballester (IAC)
Andrés Asensio Ramos (IAC)
Tanausú del Pino Alemán (IAC)
Javier Trujillo Bueno (IAC)
CLASP2 is an international collaboration led by NASA’s Marshall Space Flight Center (USA), Japan National Astronomical Observatory (Tokyo, Japan), the Instituto de Astrofísica de Canarias (IAC, Tenerife , in Spain) and the Institut d’Astrophysique Spatiale (IAS, France). Additional members are the Istituto Ricerche Solari Locarno (Switzerland), the Astronomical Institute of the Czech Academy of Sciences, Lockheed Martin Solar & Astrophysics Laboratory (USA), Stockholm University (Sweden) and the Rosseland Center for Physics Supply (Norway).
* IAC’s participation in CLASP2 is funded by the European Research Council (ERC) under the European Union’s Horizon 2020 research and innovation program (Advanced Grant Agreement No. 742265).