Context. The Gaia-ESO Survey (GES) is a large public spectroscopic survey at the European Southern Observatory Very Large Telescope.udAims. A key aim is to provide precise radial velocities (RVs) and projected equatorial velocities (v sin i) for representative samples of Galactic stars, that will complement information obtained by the Gaia astrometry satellite.udMethods. We present an analysis to empirically quantify the size and distribution of uncertainties in RV and v sin i using spectra from repeated exposures of the same stars.udResults. We show that the uncertainties vary as simple scaling functions of signal-to-noise ratio (S/N) and v sin i, that the uncertainties become larger with increasing photospheric temperature, but that the dependence on stellar gravity, metallicity and age is weak. The underlying uncertainty distributions have extended tails that are better represented by Student’s t-distributions than by normal distributions.udConclusions. Parametrised results are provided, that enable estimates of the RV precision for almost all GES measurements, and estimates of the v sin i precision for stars in young clusters, as a function of S/N, v sin i and stellar temperature. The precision of individual high S/N GES RV measurements is 0.22-0.26 km/s, dependent on instrumental configuration.
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机译：上下文。盖亚ESO调查（GES）是欧洲南方天文台甚大型望远镜的大型公共光谱调查。 udAims。一个主要目的是为银河星的代表性样本提供精确的径向速度（RVs）和预计的赤道速度（v sin i），这将补充盖亚天文卫星获得的信息。 udMethods。我们提出了一项分析，以便使用重复暴露于同一颗恒星的光谱从经验上量化RV和v sin i中不确定性的大小和分布。 udResults。我们显示不确定性随信噪比（S / N）和v sin i的简单缩放函数而变化，不确定性随着光球温度的升高而变大，但对恒星重力，金属性和年龄的依赖性较弱。潜在的不确定性分布具有延伸的尾巴，用学生的t分布比正态分布可以更好地表示。 ud结论。提供了参数化结果，可以估算几乎所有GES测量值的RV精度，并估算年轻星团中恒星的v sin i精度，作为S / N，v sin i和恒星温度的函数。各个高S / N GES RV测量的精度为0.22-0.26 km / s，具体取决于仪器配置。
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