Understanding Radial Velocity Jitter: Benchmark Observations of the Sun

通过径向速度技术或多普勒方法，可以通过测量多普勒频移来发现系外行星，多普勒频移是由绕轨道运行的行星的引力引起的恒星运动引起的。现有和未来的光谱仪达到0.1-1m/s水平的多普勒精度。在这样的测量中，观测到的径向速度散射不再受摄谱仪稳定性或光子噪声的支配，而是恒星本身表现出1-10m/s量级的内在变化，而不是由行星引起的。造成这种变化的主要机制是磁场活动对对流蓝移的影响。太阳为理解恒星表面速度场和活动区域的影响提供了宝贵的参考，因为它可以将精确的径向速度观测与空间分辨的太阳表面信息联系起来。我们的项目旨在通过对太阳的高精度观测，为理解对流蓝移提供必要的关键信息。我们的设施可以提供独特的数据质量，结合空间分辨太阳表面观测，太阳as-a -恒星观测，以及前所未有的波长精度，在宽波长覆盖范围和超高光谱分辨率。我们计划开展两种类型的观测：(1)高保真光谱观测整个太阳盘的太阳强度，即获得太阳表面安静区和活跃区的光谱作为恒星翼角的函数；(2)在天气允许的情况下，每隔3-10分钟拍摄太阳恒星的光谱学。第二部分提供了Göttingen太阳径向速度计划的定期观测；光谱和径向速度将免费提供给太阳系和系外行星社区。

With the radial velocity technique, or the Doppler method, extrasolar planets can be discovered from measuring the Doppler shift caused by the motion of a star induced by the gravitational pull of an orbiting planet. Exisiting and future spectrographs reach Doppler precisions on the 0.1-1m/s level. In such measurements, the observed scatter in radial velocity is no longer dominated by spectrograph stability or photon noise, but the stars themselves show intrinsic variations that are on the order of 1-10m/s and not caused by planets. The main mechanism causing this variability is the effect of magnetic activity on convective blueshift. The Sun provides an invaluable reference for understanding the influence of stellar surface velocity fields and active regions because it is possible to relate precision radial velocity observations to spatially resolved solar surface information. Our project aims to provide the key information necessary to understand convective blueshift from very-high-precision observations of the Sun. Our facilities can provide unique data quality by combining spatially resolved solar surface observations, Sun-as-a star observations, and unprecedented wavelength accuracy at wide wavelength coverage and ultra-high spectral resolution. We plan to carry out two types of observations: (1) high-fidelity spectroscopy observing solar intensity across the solar disk, i.e., obtaining spectra of the solar surface in quiet and active regions as a function of stellar limb angle; and (2) spectroscopy of the Sun as a star at 3-10min cadence during every time weather permits. The second part provides regular observations for the Göttingen Solar Radial Velocity Project; the spectra and radial velocities shall be made freely available for solar and exoplanet community.