Introduction to the Chinese Hα Solar Explorer(CHASE)Mission

The Chinese HαSolar Explorer(CHASE)mission,dubbed as“Xihe”——Goddess of the Sun,was launched on 14 October 2021 as the first solar space mission of China National Space Administration(CNSA).The CHASE mission aims to test an ultra-high precision and stability platform,and to acquire solar HαSpectroscopic observations with high temporal and spectral resolutions.Since its launch,the in-orbit performance of the scientific payload——HαImaging Spectrograph(HIS)has been excellent.The first set of data has been calibrated and analyzed recently.The CHASE science data are expected to advance our understanding of the plasma dynamics in the solar lower atmosphere,and to investigate the Sun as a star for stellar physics.

LUT:A Lunar-based Ultraviolet Telescope

The Lunar-based Ultraviolet Telescope （LUT） is a funded lunar-based ultraviolet telescope dedicated to continuously monitor- ing variable stars for as long as dozens of days and performing low Galactic latitude sky surveys. The slow and smooth spin of the Moon makes its step by step pointing strategy possible. A flat mirror mounted on a gimbal mount is configured to enlarge the sky coverage of the LUT. A Ritehey-Chretien telescope with a Nasmyth focus configuration is adopted to reduce the total length of the system. A UV enhanced back illuminated AIMO CCD 47-20 chip together with the low noise electric design will minimize the instrumental influence on the system. The preliminary proposal for astrometric calibration and photometric cali- bration are also presented.

High power optics and its new manifestations

The advent of the laser has placed stringent requirements on the fabrication, performance and quality of optical elements employed within systems for most practical applications. Their high power performance is generally governed by three distinct steps, firstly the absorption of incident optical radiation (governed primarily by various absorption mechanisms);secondly, followed by a temperature increase and response governed primarily by thermal properties and finally the elements thermo-optical and thermomechanical response, e.g., distortion, stress birefringenous fracture, etc. All of which needs to be understood in the design as efficient, compact, reliable and useful for many applications high power systems, under a variety of operating conditions, pulsed and continuous wave, rep-rated or burst mode of varying duty cycles.

Forecasting supernova observations with the CSST:I.Photometric samples

The China Space Station Telescope(CSST,also known as Xuntian)is a serviceable two-meter-aperture wide-field telescope operating in the same orbit as the China Space Station.The CSST plans to survey a sky area of 17,500 deg^(2)of the medium-to-high Galactic latitude to a depth of 25-26 AB mag in at least 6 photometric bands over 255-1,000 nm.Within such a large sky area,slitless spectra will also be taken over the same wavelength range as the imaging survey.Even though the CSST survey is not dedicated to time-domain studies,it would still detect a large number of transients,such as supernovae(SNe).In this paper,we simulate photometric SN observations based on a strawman survey plan using the Sncosmo package.During its 10-year survey,the CSST is expected to observe about 5 million SNe of various types.With quality cuts,we obtain a“gold”sample that comprises roughly 7,400 SNe Ia,2,200 SNe Ibc,and 6,500 SNeⅡcandidates with correctly classified percentages reaching 91%,63%,and 93%(formally defined as classification precision),respectively.The same survey can also trigger alerts for the detection of about 15,500 SNe Ia(precision 61%)and 2,100 SNeⅡ(precision 49%)candidates at least two days before the light maxima.Moreover,the near-ultraviolet observations of the CSST will be able to catch hundreds of shock-cooling events serendipitously every year.These results demonstrate that the CSST can make a potentially significant contribution to SN studies.

The Chinese Hα Solar Explorer(CHASE) mission: An overview

The Chinese Hα Solar Explorer(CHASE), dubbed “Xihe”—Goddess of the Sun, was launched on October 14, 2021 as the first solar space mission of China National Space Administration(CNSA). The CHASE mission is designed to test a newly developed satellite platform and to acquire the spectroscopic observations in the Hα waveband. The Hα Imaging Spectrograph(HIS)is the scientific payload of the CHASE satellite. It consists of two observational modes: raster scanning mode and continuum imaging mode. The raster scanning mode obtains full-Sun or region-of-interest spectral images from 6559.7 to 6565.9 ? and from 6567.8 to 6570.6 ? with 0.024 ? pixel spectral resolution and 1 min temporal resolution. The continuum imaging mode obtains photospheric images in continuum around 6689 ? with the full width at half maximum of 13.4 ?. The CHASE mission will advance our understanding of the dynamics of solar activity in the photosphere and chromosphere. In this paper, we present an overview of the CHASE mission including the scientific objectives, HIS instrument overview, data calibration flow, and first results of on-orbit observations.

Calibration procedures for the CHASE/HIS science data

The Hα line is an important optical line in solar observations containing the information from the photosphere to the chromosphere. To study the mechanisms of solar eruptions and the plasma dynamics in the lower atmosphere, the Chinese Hα Solar Explorer(CHASE) was launched into a Sun-synchronous orbit on October 14, 2021. The scientific payload of the CHASE satellite is the Hα Imaging Spectrograph(HIS). The CHASE/HIS acquires, for the first time, seeing-free Hα spectroscopic observations with high spectral and temporal resolutions. It consists of two observational modes. The raster scanning mode provides full-Sun or region-of-interest spectra at Hα(6559.7-6565.9 ?) and Fe I(6567.8-6570.6 ?) wavebands. The continuum imaging mode obtains full-Sun photospheric images at around 6689 ?. In this paper, we present detailed calibration procedures for the CHASE/HIS science data, including the dark-field and flat-field correction, slit image curvature correction, wavelength and intensity calibration, and coordinate transformation. The higher-level data products can be directly used for scientific research.

On the technologies of Hα imaging spectrograph for the CHASE mission

The Hα imaging spectrograph(HIS) is the scientific payload of the first solar space mission, the Chinese Hα solar explorer(CHASE), supported by the China National Space Administration(CNSA). The CHASE/HIS achieves, for the first time in space, Hα spectroscopic observations with high spectral and temporal resolutions. Separate channels for the raster scanning mode(RSM) and continuum imaging mode(CIM) are integrated into one, and a highly integrated design is achieved through multiple folding of the optical path and ultra-light miniaturized components. The design of HIS implements a number of key technologies such as high-precision scanning of the optical field of view(FOV), high-precision integrated manufacturing inspection, a large-tolerance pre-filter window, and full-link solar radiation calibration. The HIS instrument has a pixel spectral resolution of 0.024 ? and can complete a full-Sun scanning within 46 s.