Released about 17 million spectra and 7.75 million sets of stellar parameters
Why does LAMOST do a "census" for "stars"?
Trainee reporter Yu Ziyue
Before the completion of LAMOST, the number of celestial bodies observed by humans through photographs reached tens of billions, but the celestial bodies that have undergone spectral observation accounted for only one in ten thousand.
LAMOST pioneered large-scale spectral surveys in the international astronomy field.
Since then, the spectral data of celestial bodies has grown exponentially.
Zhao Yongheng
Executive Deputy Director of LAMOST Operation and Development Center
As night falls, everything is silent.
On the top of the quiet Yanshan Mountain, a "giant eye" slowly opened, looking at the vast starry sky and searching for the mysteries of the universe.
This "eye" is the Guo Shoujing Telescope (LAMOST), a major national scientific project of the National Astronomical Observatory of the Chinese Academy of Sciences.
Recently, LAMOST’s 1-year pilot survey and 8-year official survey data sets were released to domestic astronomers and international collaborators.
It contains about 17 million spectra and 7.75 million sets of stellar parameters, and the accuracy of data products has reached the international advanced level.
What are the characteristics of the data released this time?
What great feats did LAMOST, the "leader" of the Spectroscopic Telescope, have made?
What is its next observation plan?
With a series of questions, a reporter from Science and Technology Daily interviewed Zhao Yongheng, Executive Deputy Director of LAMOST Operation and Development Center.
Create a basic database of the Milky Way galaxy
LAMOST is the English abbreviation of "Large Sky Area Multi-Object Fiber Spectroscopic Astronomical Telescope".
Soon after passing the national inspection, it was officially named "Guo Shoujing Telescope".
Guo Shoujing is an astronomer in the Yuan Dynasty who invented various observation instruments.
What does LAMOST "look at"?
star.
Unlike traditional "photographic" astronomical telescopes, LAMOST does not take a group photo of the stars in a certain area of the sky, but obtains the spectral information of each star it wants to observe.
In 1825, French philosopher Comte asserted: "The chemical composition of stars is knowledge that humans can never obtain." However, this judgment was ruthlessly overturned shortly after.
At that time, spectroscopy was born, and astrophysics has since officially become an important branch of astronomy.
Scientists have discovered that each chemical element has its own unique spectral curve, which is as recognizable as an ID card.
Since then, people have realized that the original distant and mysterious starlight has gone through long interstellar travels and stumbled into the arms of the earth, bringing not only the news that it is there, but also that it is Many secrets about what form is there.
Based on spectral analysis, from this cluster of starlight, we can not only discover the chemical composition and element abundance of the star, but also deduce many of its properties, such as the type of celestial body, distance, apparent speed, physical conditions (temperature, density, pressure, etc.) ), the age of celestial bodies, etc. Many special celestial bodies and astronomical phenomena can be found from the spectrum observation of a large number of celestial bodies.
For this reason, Zhao Yongheng compared the work of the Spectroscopic Telescope LAMOST to a "census" of stars.
All of these will serve the three major scientific goals at the beginning of the establishment of LAMOST: studying the structure and evolution of the Milky Way, galaxies and cosmology, and multi-band target verification.
Since the completion of the pilot survey in 2011-2012, LAMOST began its official survey in September 2012. As of June 2020, 8 years have passed.
"This time, we updated the data processing system. It took 9 months to reprocess all the data from the 1-year pilot survey and the 8-year official survey to ensure the system, consistency and integrity of the survey data. It is convenient for researchers to use." Zhao Yongheng said.
After processing and quality analysis of the massive and complex spectral survey data, they will be categorized with corresponding "labels" and classified into the database, becoming an important cornerstone of the construction of a "digital galaxy", waiting for scientists to retrieve and study.
It is reported that the National Astronomical Data Center has built a special data release platform for this data release, and scientific users can log in to the website for data query and download.
See clearly and create a precedent for large-scale spectral surveys
Openness and sharing are the fine traditions of the astronomy community, and they are consistently adopted by LAMOST.
Every year, LAMOST publishes its latest data.
These data were first made available to domestic astronomers and international collaborators, and will be made available to the whole society in a year and a half.
The research value created by these data open to the whole society is amazing.
"We have done a survey and retrieved papers that published research results using LAMOST data, and found that about 1/3 of the results were researched using all of its open data." Zhao Yongheng introduced.
The same universe, the same starry sky.
This survey result once again validates the importance of sharing observational data for promoting the cognition of the universe. On the other hand, it also shows that the basic LAMOST database is like a rich mine, waiting for gold-mining adventurers to continue to dig.
So here comes the problem.
What method does LAMOST have to obtain a lot of high-value data?
Zhao Yongheng pointed out that LAMOST has two innovative technologies: active optical technology and parallel controllable fiber positioning technology.
The ancients said that fish and bear's paw cannot have both.
For a telescope, a large aperture means "see clearly", and a large field of view will "see much". The two are a contradiction between a pair of fish and a bear's paw.
The above two technologies make LAMOST see more clearly.
Active optical technology is to actively change the shape of the lens, and "auto focus" makes the image clearer.
LAMOST creatively applied this technology to break through the bottleneck of the large aperture and large field of view of the telescope, making it the world's largest telescope with large field of view, large aperture and highest spectral acquisition rate.
Earlier, a spectroscopic telescope could only observe one celestial body at a time.
Later, with the development of science and technology, the number of simultaneous observations by the spectroscopic telescope gradually increased.
Until the eve of LAMOST, similar equipment in the world can observe up to 640 celestial bodies at a time.
What about LAMOST?
The answer is 4000.
4000 optical fibers are densely inserted on the 1.75-meter focal panel. The LAMOST automatic optical fiber positioning system can accurately locate the optical fiber according to the position of the star catalog within a few minutes, and then start the observation.
Previously, methods such as manual placement of optical fibers were commonly used internationally, which took several hours at every turn.
Moreover, before changing the observation area, the position of the optical fiber must be adjusted to the position of the star table, which not only consumes time and effort, but also has poor positioning accuracy.
The positioning error of LAMOST fiber does not exceed 40 microns, which is thinner than a single hair.
"The complex design and manufacture of LAMOST were all completed by Chinese scientists. Before it was built, humans had taken tens of billions of celestial bodies to observe, but only one out of ten thousand celestial bodies had been observed by spectroscopy." Zhao Yongheng pointed out , LAMOST pioneered large-scale spectral surveys in the international astronomy field.
Since then, the spectral data of celestial bodies has grown exponentially.
Achievements in many fields, the second phase of the sky survey, detailed drawing of the bright star map
From the rich mines of the LAMOST database, scientists have found many treasures.
In the field of research on the structure of the Milky Way, based on LAMOST data, scientists have rewritten the previous academic understanding of the size of the Milky Way, and found that the Milky Way is twice as large as previously thought.
Another representative achievement is that LAMOST re-established a new image of the halo structure.
Researchers analyzed the distribution of stars and found that the inside of the halo is oblate, while the outside gradually becomes spherical. The number density of stars decreases from the inside to the outside according to a new law.
This clear observational evidence overturns previous speculations that a star halo is an oblate spheroid with a constant axial ratio.
In the field of the evolution of the Milky Way, the research that can be done based on LAMOST data is varied.
Such as the analysis of the type of stars in the galactic disk, how the stars evolve, the analysis of the process of merging galaxies, the confirmation of whether a certain star is an "indigenous inhabitant" or an "intergalactic migration", etc.
For the research of special celestial bodies, LAMOST is also very powerful.
For example, with the advantage of the LAMOST sky survey, researchers discovered a black hole with a constant star.
This result has overturned people's cognition of the formation of black holes with constant stars, and is expected to promote the innovation of stellar evolution and black hole formation theories.
LAMOST also discovered the star with the highest lithium content, known as the "largest power bank" in the universe.
Found tens of thousands of lithium-rich superstar candidates, and constructed the largest lithium-rich superstar sample in the world.
"There are countless research results based on LAMOST data, and the above are only a few representative examples." Zhao Yongheng introduced that the LAMOST observation is a stage every 5 years, and corresponding goals are set.
2012-2017 is a phase of low-resolution spectral survey.
The period from 2018 to 2023 is the second phase of the mid-resolution spectral survey phase, which adopts the mid- and low-resolution spectral survey mode alternately.
Observation tasks are also different. The first phase aims to "sweep" and roughly draw a star map of the observing sky; the second phase focuses on "watching", focusing on observation of areas of interest.
Zhao Yongheng said that the second phase of the LAMOST sky survey is currently in progress, and 2 to 3 million spectral data will be output every year. It is estimated that by 2022, the number of spectra released by the telescope is expected to exceed 20 million.