Understanding Radial Velocity Jitter: Benchmark Observations of the Sun

利用径向速度技术或多普勒法，通过测量由轨道行星的引力引起的恒星运动引起的多普勒频移，可以发现太阳系外的行星。现有的和未来的光谱仪都达到了0.1-1m/S水平的多普勒精度。在这种测量中，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，但恒星本身显示出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的影响提供了宝贵的参考，因为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。我们的项目旨在提供从非常高精度的太阳观测中了解对流蓝移所需的关键信息。我们的设施可以结合空间分辨率的太阳表面观测、太阳作为恒星的观测，以及在宽波长覆盖和超高光谱分辨率下前所未有的波长精度，提供独特的数据质量。我们计划进行两种类型的观测：(1)高保真光谱观测整个太阳圆盘的太阳强度，即获得安静和活跃区域中太阳表面随恒星翼角的函数的光谱；(2)在天气允许的每个时间段，以3-10分钟的节奏观测太阳作为恒星的光谱。第二部分为Göttingen太阳径向速度项目提供定期观测；光谱和径向速度应向太阳和系外行星社区免费提供。

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.