China's Large Sky Area Multi-Object Fiber Spectroscopic Telescope (LAMOST) completed its seventh-year spectroscopic survey in June, 2019, which was also the first year that LAMOST performs the medium-resolution spectroscopic survey.

After nine months of data reduction and quality analysis, the LAMOST DR7 dataset, including the spectra obtained from the pilot survey through the seventh-year regular survey, was officially released to domestic astronomers and international partners on March 31, 2020.

Through one-year observational test, the strategy, observational targets and data reduction capability of LAMOST medium-resolution spectroscopic survey have all been proved to meet the survey requirements.

On Oct. 5, 2018, the second phase of LAMOST medium-resolution spectroscopic survey was officially launched, and it is expected to complete in June, 2023.

In the medium-resolution spectroscopic survey, LAMOST performs the medium- and low-resolution survey alternatively, that is, the low-resolution survey is conducted in dark nights, the second-phase medium-resolution survey is performed in grey nights, and the high-resolution observation is carried out in bright nights. Therefore, the released DR7 dataset includes both the regular low-resolution spectral data and medium-resolution spectral data.

Obtained from the low-resolution observation of 4,926 plates and medium-resolution observation of 680 plates, a total of 14.48 million spectra are released in the DR7, including 10.6 million low-resolution spectra, 1.01 million medium-resolution non time-domain spectra and 2.87 million medium-resolution time-domain spectra.

The number of high-quality (S/N > 10) spectra reaches 11.43 million. Moreover, a stellar spectral parameter catalogue of 7 million stars is also released in DR7, in which the abundances of 12 elements, e.g., carbon, magnesium, calcium, and so on, are included for part of the stars for the first time. It has been currently the largest stellar spectral parameter catalogue in the world.

Scientific users can log on the website at http://dr7.lamost.org to query and download the DR7 data.

At present, 937 users from 141 scientific research institutes and universities of China, the United States, Germany, Belgium, Denmark and other countries and regions are using LAMOST data to carry out research works.

LAMOST has entered a new era of low- and medium-resolution observations. Based on LAMOST data, astronomers will continue to refresh our understanding of the universe.