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Home ＞ Solutions ＞ Radioastronomy ＞ Overview of China's 40th Antarctic expedition on astronomy

Overview of China's 40th Antarctic expedition on astronomy

Exploring the Antarctic sky: Dome A’s astronomical endeavors in 2024 and beyond

Zhengyang Li1,2,3 ∙ Yun Li1,2 ∙ Peng Jiang3,4 jiangpeng@pric.org.cn

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Overview of China's 40th Antarctic expedition on astronomy

On February 17, 2024, four astronomers from the Chinese 40th Antarctic Scientific Research Expedition (CHINARE) team returned to China via Antarctic aviation after successfully completing a 100-day scientific expedition. This is the 12th expedition to Dome A since the team’s decision to conduct astronomical observations on the Antarctic Plateau in 2005. Located at the summit of the Antarctic continent, Dome A is regarded as Earth’s premier astronomical site. During this expedition, the team installed an infrared telescope, a low-frequency radio detector, and a terahertz antenna. They also conducted repairs on the previously installed optical telescope (the second Antarctic Survey Telescope AST3-2). The successful operation of these advanced instruments marked a significant milestone for Chinese Antarctic astronomy, symbolizing the commencement of the next exploration phase (Figure 1).

Figure 1 Astronomical instruments at Dome A

Exceptional ground conditions of Dome A for astronomical observation

The atmosphere at Dome A is characterized by extreme cold and aridity. Temperatures during the polar night often drop below −70°C, accompanied by negligible wind speeds. Stable atmospheric conditions ensured continuous sky observations for 3 months.

The astronomical seeing parameter refers to the blurring of stellar images caused by the Earth’s atmospheric turbulence. The typical values at the best mid-latitude sites, such as Mauna Kea, Hawaii, are around 0.6–0.8". Dome A exhibits a minimum seeing value of 0.13" at an elevation of 8 m above ice-cold ground, with a median value of 0.31". When positioned at a height of 14 m above the ice ground, values of less than 0.3" were observed approximately 49% of the time. Moreover, Dome A offers stable atmospheric inversions and prolonged clear polar nights that persist up to 83% of the time, accompanied by low average wind speeds measuring just 3.8 m/s.1 These characteristics collectively indicate that Dome A offers exceptional observing conditions within the optical band called "quasi-space." This can be attributed to its frozen tenuous atmosphere and tranquil polar nights.

Water vapor renders the terrestrial atmosphere opaque within frequency bands in the range 0.3–15 THz. The global average precipitable water vapor (PWV) value is approximately 25 mm; however, in Dome A, during winter months, this value plummets to a mere 0.1 mm, with potential daily averages dropping as low as 0.025 mm—one-fifth the typical winter PWV observed at the Atacama Large Millimeter/Submillimeter Array site.2 Consequently, Dome A presents an exceptional opportunity for conducting conventional terahertz far-infrared astronomical and atmospheric observations on Earth.

The average annual temperature of Dome A is −56°C, which significantly reduces the atmospheric background heat radiation and enhances the detection depth of astronomical observations in the infrared band. The sky-brightness measurements in J, H, and Ks bands at Dome A are 600–1,100, 1,100 and 2,600, and 200–900 μJy arcsec−2, respectively.3 Compared to other observation stations in low-latitude and high-altitude areas, the sky brightness at Dome A exhibits a significant reduction in the Ks band. This finding suggests that Dome A is an exceptional site for conducting Ks-band astronomical observations.

On polar days, the atmosphere in this region is tenuous and pristine, with a dim daylight background luminosity. Utilizing a newly installed J-band infrared telescope, we quantified that the zenith noontime J-band background brightness decreased below six magnitudes per square arcsecond in January. This enabled us to observe bright targets even during polar days.

Distinctiveness of astronomical research in Dome A

Astronomical research conducted at the Kunlun Station in inland Antarctica exhibits distinctive characteristics. Located within Dome A approximately 1,260 km away from the coastline, this unattended facility requires an annual expedition team to spend a limited period of 20 days conducting on-site work. The harsh environmental conditions at the Antarctic Kunlun Station, including extremely low temperatures and pressures, present considerable challenges in ensuring dependable equipment functionality. After enduring an arduous 2-week, 1,260-km journey, the CHINARE team reached Kunlun Station. They were faced with demanding schedules and a substantial workload. Presently devoid of human presence, Kunlun Station relies on remote control mechanisms to conduct astronomical observations using telescopes and other scientific instruments.

Astronomical instrumentation deployed at Dome A

Antarctica survey telescope (AST3-2)

AST3-2, which was installed in 2014, currently holds the distinction of being the largest optical telescope located in Dome A. With a 0.5-m aperture and a designed field of view of 4.14°, it shows exceptional pointing and tracking capabilities. Notably, its tracking error root-mean-square value remains below 0.2". Meticulously designed to endure extremely low temperatures, all electronic, mechanical, and optical components underwent rigorous testing for several months under such conditions prior to transportation to Antarctica. AST3, another instrument installed in the facility, is a catadioptric optical telescope equipped with a wide field of view, flat image plane, aberration elimination capability, compact mirror tube design, and atmospheric dispersion correction functionality. It can remotely track, automatically observe, and process with an autofocus capability. On August 18, 2017, AST3-2 took part in the internationally coordinated observation campaign for the gravitational wave event GW 170817, effectively monitoring its initial optical emission.4 Significantly, the telescope has achieved a pioneering breakthrough by detecting 116 potential exoplanets,5 representing a remarkable milestone in China’s pursuit of exoplanetary research.

Near-infrared telescope

The 40th CHINARE team successfully installed a J-band near-infrared telescope with a 150-mm aperture and a 1° field of view in Dome A, Kunlun Station, Antarctica. This device effectively fills the observational gap of 1.1–1.4 μm in the waveband range. The team conducted near-infrared astronomical observations during polar days and continuously monitored the near-Earth space environment at the Kunlun Station. They collected J-band sky background data across the entire celestial sphere, providing a solid foundation for year-round observations at this location. The telescope employs low-temperature-resistant optical lens barrels and fully sealed direct-drive motors. During the upcoming polar nights, a remote-controlled collaboration between the near-infrared telescope and AST3-2 will facilitate time-domain astronomical observations.

KL-DIMM

The Kunlun differential image motion monitors (KL-DIMMs) were installed on an 8-m-high tower in January 2019. They were specifically designed to operate automatically at temperatures as low as −80°C and provide a continuous measurement of the seeing parameter every minute. The results obtained from the KL-DIMMs unequivocally established Dome A as a preeminent astronomical observation site.

KLAWS-2G

The Kunlun automatic weather station-2 generation (KLAWS-2G) meteorological station, installed in 2015, facilitates the collection of comprehensive meteorological data, including temperature, wind speed and direction, air pressure, and humidity, within Dome A. Equipped with a 15-m-high mast, this station incorporates 10 temperature sensors, 7 wind speed and direction sensors, one air pressure sensor, and one relative humidity sensor.

PLATO-A

Plateau Observatory for Dome A (PLATO-A) serves as the primary energy and communication platform for the astronomical equipment at Kunlun Station, offering essential support for the overwintering operations of Dome A’s astronomical instruments. It features unmanned remote control capabilities and has undergone extensive reliability testing for several years.

Antarctic terahertz antenna (ATE30)

The 40th CHINARE team deployed a 30-cm wide-band THz antenna and a high-sensitivity receiver system. It conducted astronomical observations in the frequency bands of 462 and 493 GHz at Dome A during polar days. This study accomplished the first observation and mapping of CO molecular spectral lines and CI neutral carbon atomic spectral lines, providing novel insights for a deeper understanding of the structure, evolution, and formation of molecular clouds in the universe.

Development and summary

Dome A in Antarctica is an exceptional astronomical observatory location on Earth, providing a unique and invaluable resource for long-term astronomical research. It offers an ideal site for, but is not limited to, time-domain surveys for searching for extra-solar planetary systems and extreme transit events in the universe. Additionally, it supports high-resolution wide-field surveys for investigating the structure and evolution of the universe, as well as terahertz/submillimeter observations for uncovering star and galaxy formations deeply embedded in the dust. Over the years, 2-m-sized optical/infrared telescopes and 10-m-sized terahertz telescopes have been proposed. To promote the development of Antarctic astronomy in China, it is crucial to leverage its robust ice transportation capabilities and material security advantages, along with international polar cooperation. Moreover, the challenges related to wintering stations, energy supply, communication infrastructure, and equipment reliability in extreme environments should be addressed gradually.

Acknowledgments

We gratefully acknowledge the invaluable assistance provided by the CHINARE teams. This research was financially supported by the National Key R&D Program of China (grant no. 2022YFC2807300).