The undergraduate team examines and corrects the two-dimensional extinction map of the Milky Way

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(Figure 1) Comparison of E(B-V) LAMOST extinction plot (left) and the corresponding sky area primitive extinction map (right) based on LAMOST and Gaia data. From top to bottom, SFD, Planck2014-R, Planck2014-Tau and Planck2019-Tau extinction maps. (Courtesy of the interviewee)

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(Figure 2) The spatial distribution of the difference between the LAMOST extinction plot and the original extinction plot (left) and the ratio (right). From top to bottom, they correspond to SFD, Planck2014-R, Planck2014-Tau and Planck2019-tau extinction diagrams. (Courtesy of the interviewee)

Recently, using LAMOST DR5 spectral data (the fifth batch of data released by Guo Shoujing Telescope) and Gaia DR2 metering data (the second batch of scientific data released by ESA’s Gaia Space Astrometry Satellite Project), Sun Yang, an undergraduate student at Beijing Normal University, Yuan Haibo, an associate professor, and Chen Bingqiu, an associate professor at Yunnan University, collaborated to obtain high-precision extinction information on millions of stars, and the relevant research results were published in The Astrophysical on May 13 Journal Supplement Series)。

Yuan Haibo introduced to China Science News that in view of the most widely used two-dimensional extinction map of the Milky Way (SFD extinction map) in the field of astronomy in the past 20 years and based on Planck satellite (Planck) data in recent years, researchers have used different methods to construct three all-day two-dimensional extinction maps of the Milky Way, and carried out the system inspection and calibration with the largest area and the highest accuracy, which has made a driving work for the further improvement of the all-day extinction map of the Milky Way dust. It also laid an important foundation for the correction of precision extinction in the era of precision astronomy.

“There is a lot of gas and dust in the Milky Way, and in many shocking and beautiful pictures of the Milky Way, we often see black areas, which are the dark clouds rich in dust in the Milky Way.” Yuan Haibo said that the existence of interstellar dust in the Milky Way makes the brightness and color of the observed celestial bodies change, so the precise correction of the extinction of dust in the Milky Way is the basis for obtaining the nature of the celestial bodies inside and outside the Milky Way and carrying out astrophysical research, and it is also an important topic for the study of the nature of the Milky Way itself.

In 1998, Schlegel et al. constructed an SFD extinction map based on the dust radiation results of the Milky Way measured by infrared satellites, which is currently the most widely used all-day two-dimensional extinction map of the Milky Way. Yuan Haibo pointed out: “The existing research work shows that there is a systematic error in the SFD extinction map, some research results believe that the system overestimated the extinction, and some results believe that the system underestimates the extinction, and even there is a nonlinear phenomenon, which may be related to the dust temperature.” ”

In recent years, researchers have combined data from the European Space Agency’s Planck satellite using different methods to construct new all-day two-dimensional extinction maps of the Milky Way, including Planck2014-R based on dust thermal radiation, Planck2014-Tau based on 353GHz dust optical thickness, and Planck2019-Tau extinction maps.

In order to determine the accuracy of the above extinction map, Yuan Haibo et al. combined LAMOST DR5 spectral data and Gaia DR2 metering data to obtain high-precision extinction information in the BP-RP band of millions of stars.

Yuan Haibo introduced: “On this basis, we considered the influence of star temperature and extinction size into B-V band extinction, and constructed a LAMOST two-dimensional extinction map. Finally, by comparing the differences with the LAMOST extinction map, we systematically tested and corrected the most commonly used SFD extinction map and the three Planck extinction maps in the high-silver latitude region of the Milky Way. ”

The results of the related studies found that the four extinction maps and the LAMOST extinction map as a whole coincided well, and the accuracy of the extinction correction was comparable (Figure 1); all four extinction maps had significant systematic deviations with spatial changes, among which the SFD extinction map was similar to the structure of the Planck2014-R extinction map, and the structure of Planck2014-Tau and Planck2019-Tau was similar (Figure 2). The deviation of the SFD extinction map and the Planck2014-R extinction map depends on the dust temperature and extinction size, and the deviation of the Planck2014-Tau and Planck2019-Tau extinction maps depends more on the dust emission spectral index.

These results provide important clues for further improvements to the Milky Way’s all-day extinction map. The reviewers believe that the results provide the latest high-precision correction results of the galaxy’s two-dimensional extinction, which has very important application value for related scientific research. (Source: China Science Daily Shen Chunlei)

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