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arXiv 2010.13992astro-ph.IMastro-ph.SR
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中国空间站望远镜(CSST)恒星径向速度精度

Precision of The Chinese Space Station Telescope (CSST) Stellar Radial Velocities

Yang Sun, Dingshan Deng, Haibo Yuan

摘要:

中国空间站望远镜(CSST)光谱巡天计划为数亿个目标提供高质量的低分辨率($R > 200$)无狭缝光谱,这些目标的极限星等约为21等,覆盖大的巡天区域(17500 deg $^2$)和宽的波长范围(255-1000 nm,3个波段GU,GV和GI)。在这项工作中,我们使用下一代光谱库的经验光谱模拟CSST恒星光谱在$R = 250$,并调查他们的能力,在测量径向速度。我们发现,速度的不确定性强烈地依赖于有效温度,弱的金属丰度只有FGK星,几乎没有表面重力。在信噪比为100的条件下,可以将AFGKM星的恒星径向速度精确到$3 \,\mathrm{km}\,\mathrm{s}^{-1}$,将OB星的径向速度精确到$10 \,\mathrm{km}\,\mathrm{s}^{-1}$。速度不确定性使用单一GU/GV/GI带谱也进行了探讨。给定相同的SNR,GU频带性能最好,GV频带第二好,然后是GI频带。频谱归一化和不完善的模板速度测量的影响进行了研究,发现是非常微弱的。波长校准引起的不确定性被认为是温和的。考虑到径向速度的可能精度,CSST光谱调查可以实现有趣的科学,例如寻找超高速恒星。我们的结果的局限性进行了讨论。

英文摘要:

The Chinese Space Station Telescope (CSST) spectroscopic survey plans to deliver high-quality low-resolution ($R > 200$) slitless spectra for hundreds of millions of targets down to a limiting magnitude of about 21 mag, covering a large survey area (17500 deg$^2$) and a wide wavelength range (255-1000 nm by 3 bands GU, GV, and GI). In this work, we use empirical spectra of the Next Generation Spectral Library to simulate the CSST stellar spectra at $R = 250$, and investigate their capabilities in measuring radial velocities. We find that velocity uncertainties depend strongly on effective temperature, weakly on metallicity for only FGK stars, and hardly on surface gravity. It is possible to deliver stellar radial velocities to a precision of about $3 \,\mathrm{km}\,\mathrm{s}^{-1}$ for AFGKM stars, and about $10 \,\mathrm{km}\,\mathrm{s}^{-1}$ for OB stars, at signal-to-noise ratio (SNR) of 100. Velocity uncertainties using single GU/GV/GI band spectra are also explored. Given the same SNR, the GU band performs best, the GV band the second best, and then the GI band. The effects of spectral normalization and imperfect template on velocity measurements are investigated and found to be very weak. The uncertainties caused by wavelength calibration are considered and found to be moderate. Given the possible precision of radial velocities, the CSST spectroscopic survey can enable interesting science such as searching for hyper-velocity stars. Limitations of our results are also discussed.

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