Day by day for more than half a year, what secrets have you brought back?
"Xihe" obtained three solar spectrum line profiles for the first time
◎Our reporter Jin Feng
"After the launch of 'Xihe', for the first time in space, the fine structure and spectral imaging of the Hα, Si I and Fe I lines of the sun's full heliosphere, as well as data on dozens of solar flares, have been obtained simultaneously."7 On March 19, in the press release of the scientific and technological innovation reform and development achievements of colleges and universities in the "1+1" series of "Education This Decade" and "1+1" series conferences of the Ministry of Education, the academician of the Chinese Academy of Sciences, the general scientific advisor of "Xihe", and the professor of Nanjing University Fang Cheng is pleased to reveal this latest development.
The full name of "Xihe" is "Solar Hα Spectral Detection and Double Super Platform Science and Technology Experiment Satellite", and it was launched on October 14, 2021.
The launch of "Xihe" broke the history of my country's lack of dedicated satellites for solar exploration.
"We have also started planning the three-dimensional detection of the sun, looking at the sun from different angles. For example, the pre-research of 'Xihe-2' has been launched, and it is ready to be launched to the Lagrange in 5 years. Point L5, where the gravitational force of the sun and the earth is equivalent, the satellite can observe the sun from the side. In addition, the domestic heliophysics community also plans to launch the 'Xihe-3' in less than 5 years. Make observations." Fang Cheng said.
For the first time, the complete outline of the Si I spectral line has been observed in space
Fang Cheng introduced that the "Xihe" observation with high spectral resolution and high temporal resolution can perform deep "CT" scanning for the solar photosphere and chromosphere.
As the main scientific payload of the satellite, the Hα Spectral Imager is the exclusive "photographer" of the sun.
It can complete more than 4,600 steps of all-solar scans in 46 seconds, obtain spectral information of more than 16 million points, and obtain solar images of more than 300 wavelength points.
These spectra hide atmospheric information at different levels of the solar photosphere and the chromosphere.
At 0:52 on October 24, 2021, the "Xihe" officially "opened its eyes" and realized the first light observation.
"It is worth mentioning that the pixel spectral resolution of the Hα spectral imager reaches 0.024 angstroms, which is about 10 times higher than the resolution of the ground filter, and can obtain more accurate spectral line information." "Xihe No. "Li Chuan, chief designer of science and application systems and professor of the School of Astronomy and Space Science of Nanjing University, told Science and Technology Daily reporters.
During the observation, "Xihe" obtained the spectral line profiles of the solar Hα spectral line, Si I spectral line and Fe I spectral line for the first time.
Fang Cheng introduced that the solar Hα spectral line, Si I spectral line and Fe I spectral line are generated at different heights of the solar atmosphere.
Among them, the Hα spectral line is the spectral line with the strongest response of solar activity in the lower atmosphere of the sun. The center of the Hα spectral line is formed at about 1300 kilometers to 1500 kilometers away from the bottom of the photosphere, which can reflect the information of the solar chromosphere. It reflects the information of the solar photosphere; the Si I line is formed at a distance of about 50 to 60 kilometers from the bottom of the solar photosphere; the Fe I line is formed at a distance of 200 to 300 kilometers from the bottom of the photosphere.
"Analyzing the information of the three spectral lines can reveal the distribution of physical quantities of the solar atmosphere at different heights." Fang Cheng said.
What is different is that in the past, when observing on the ground, the Si I spectral line was concealed by the water molecular spectral line of the earth's atmosphere, so it was difficult to capture.
The spatial spectral line information is not affected by the earth's atmosphere, and the "Xihe" has achieved the first direct observation of the complete spectral line profile of Si I in the world.
"Once the Si I spectral line is obtained, it can be combined with other spectral lines to invert and calculate the temperature and density of the solar atmosphere, thereby helping us study the structure of the sun's atmosphere." Fang Cheng said.
The high accuracy of the full-solar Doppler velocity field is equivalent to viewing the solar activity with a magnifying glass
In addition to full-day spectral imaging, "Xihe" can also perform local solar spectral imaging and fixed-point spectral observations based on solar activity.
Fang Cheng introduced that the "Xihe" can obtain the fine contour of the Hα spectral line at any point on the sun surface, so it can invert a high-precision all-solar chromosphere Doppler velocity field, which has never been achieved by previous observations.
At the same time, the "Xihe" also obtained a high-precision full-helios photospheric Doppler velocity field.
Through pixel spectral resolution and spectral line profile fitting analysis, the accuracy of the velocity field is better than 0.06 km/s.
What does this number mean?
Li Chuan explained that the sun's influence on humans is particularly manifested in the occasional flares and coronal mass ejections.
Flares are bursts of sudden local brightening of the Sun.
A moderate-intensity flare can emit powerful radiation ranging from gamma rays to radio waves, with a total energy equivalent to about 1 billion to 10 billion atomic bombs.
A coronal mass ejection (CME) is a large-scale explosion of matter on the sun. An explosion can eject about 100 million to 1 billion tons of matter into interplanetary space.
"The material ejected by the sun's eruption moves very fast in space, often hundreds of kilometers to one or two thousand kilometers per second, and the speed also reflects the kinetic energy and force of the material. The accuracy of 0.06 kilometers per second is equivalent to Look at the process of solar activity with a magnifying glass, and then understand the cause and transmission process of these eruptive activities." Li Chuan said.
At present, the "Xihe" will generate about 1.2Tb of raw data every day, and the scientific research team will generate it into scientific data that can be directly used by scientists after preliminary analysis.