标题： 围绕巴纳德星运行的亚地球质量行星 显示英文标题

标题： A sub-Earth-mass planet orbiting Barnard's star

摘要： 巴纳德星是ESPRESSO保证时间观测（GTO）的主要目标之一，因为它是我们太阳系第二近的邻居，仅次于半人马座$\alpha$星际系统。 我们在此展示了一组由ESPRESSO在四年间进行的156次巴纳德星观测数据，目的是探索短于50天周期的现象，从而包括宜居带（HZ）。 通过使用高斯过程（GP）来建模恒星活动，我们的ESPRESSO数据分析表明存在一个长期活动周期为3200天，并确认了由自转引起的140天周期作为径向速度（RV）变化的主要来源。 这些结果与基于公开可用的HARPS、HARPS-N和CARMENES数据的研究结果一致。 ESPRESSO径向速度（RVs）并不支持之前报道的233天候选行星的存在。 在减去GP模型后，ESPRESSO RVs揭示了几个短周期的候选行星信号，周期分别为3.15天、4.12天、2.34天和6.74天。 我们确认了3.15天的信号为一颗亚地球质量的行星，其半振幅为$55 \pm 7$厘米/秒，导致行星最小质量为$m_p \sin i$约为$0.37 \pm 0.05$倍地球质量，相当于火星质量的三倍左右。 ESPRESSO RVs提示可能存在一个由四颗亚地球质量行星组成的候选系统，这些行星以圆形轨道运行，半振幅在20到47厘米/秒之间，对应最小质量范围为0.17至0.32倍地球质量。 位于$3.1533 \pm 0.0006$天的亚地球质量行星处于接近圆形的轨道上，半长轴为$0.0229 \pm 0.0003$天文单位，因此位于巴纳德星宜居带内侧，平衡温度为400K。 需要更多的ESPRESSO观测数据来确认其他三个候选信号是否来自一个紧凑的短周期行星系统，该系统在巴纳德星的宜居带内侧绕其运行。 显示英文摘要

摘要： Barnard's star is a primary target within the ESPRESSO guaranteed time observations (GTO) as it is the second closest neighbour to our Sun after the $\alpha$ Centauri stellar system. We present here a large set of 156 ESPRESSO observations of Barnard's star carried out over four years with the goal of exploring periods of shorter than 50 days, thus including the habitable zone (HZ). Our analysis of ESPRESSO data using Gaussian process (GP) to model stellar activity suggests a long-term activity cycle at 3200d and confirms stellar activity due to rotation at 140d as the dominant source of radial velocity (RV) variations. These results are in agreement with findings based on publicly available HARPS, HARPS-N, and CARMENES data. ESPRESSO RVs do not support the existence of the previously reported candidate planet at 233d. After subtracting the GP model, ESPRESSO RVs reveal several short-period candidate planet signals at periods of 3.15d, 4.12d, 2.34d, and 6.74d. We confirm the 3.15d signal as a sub-Earth mass planet, with a semi-amplitude of $55 \pm 7$cm/s, leading to a planet minimum mass $m_p \sin i$ of $0.37 \pm 0.05$Mearth, which is about three times the mass of Mars. ESPRESSO RVs suggest the possible existence of a candidate system with four sub-Earth mass planets in circular orbits with semi-amplitudes from 20 to 47cm/s, thus corresponding to minimum masses in the range of 0.17-0.32Mearth. The sub-Earth mass planet at $3.1533 \pm 0.0006$d is in a close-to circular orbit with a semi-major axis of $0.0229 \pm 0.0003$AU, thus located inwards from the HZ of Barnard's star, with an equilibrium temperature of 400K. Additional ESPRESSO observations would be required to confirm that the other three candidate signals originate from a compact short-period planet system orbiting Barnard's star inwards from its HZ.