标题： 高分辨率 ALMA 观测得到的 S255IR NIRS3 周围喷流和盘中电离和分子气体的精细结构与动力学特性 显示英文标题

标题： Fine structure and kinematics of the ionized and molecular gas in the jet and disk around S255IR NIRS3 from high resolution ALMA observations

摘要： We present observations of the high-mass star-forming region S255IR, which harbors the $\sim$20 M$_\odot$ protostar NIRS3, where a disk-mediated accretion burst was recorded several years ago, with the angular resolution of $\sim$15 mas, which corresponds to $\sim$25 au and is almost an order of magnitude better than in the previous studies of this object. The observations were performed with ALMA at a wavelength of 0.9 mm in continuum and in several molecular lines. In the continuum we detected the central bright source (brightness temperature $\sim$850 K) elongated along the jet direction and two pairs of bright knots in the jet lobes. These pairs of knots imply a double ejection from NIRS3 with the time interval of $\sim$1.5 years. 喷流的方向与较大尺度上的方向相差$\sim$20$^\circ$，这一点也在一些其他近期研究中提到。 中心源的0.9毫米连续谱辐射代表了尘埃热辐射和电离气体的自由自由辐射的混合。 自由自由辐射的性质与超紧致H II区典型。 在喷流结的连续谱辐射中，自由自由分量显然占主导地位。 在分子线中，观察到围绕NIRS3的一个直径约400天文单位的次开普勒盘。 朝向中心亮源的分子线吸收特征可能指示塌缩。 分子线发射在小尺度上显得非常不均匀，这可能表明盘内的小尺度团块状结构。 显示英文摘要

摘要： We present observations of the high-mass star-forming region S255IR, which harbors the $\sim$20 M$_\odot$ protostar NIRS3, where a disk-mediated accretion burst was recorded several years ago, with the angular resolution of $\sim$15 mas, which corresponds to $\sim$25 au and is almost an order of magnitude better than in the previous studies of this object. The observations were performed with ALMA at a wavelength of 0.9 mm in continuum and in several molecular lines. In the continuum we detected the central bright source (brightness temperature $\sim$850 K) elongated along the jet direction and two pairs of bright knots in the jet lobes. These pairs of knots imply a double ejection from NIRS3 with the time interval of $\sim$1.5 years. The orientation of the jet differs by $\sim$20$^\circ$ from that on larger scales, as mentioned also in some other recent works. The 0.9 mm continuum emission of the central source represents a mixture of the dust thermal emission and free-free emission of the ionized gas. Properties of the free-free emission are typical for hypercompact H II regions. In the continuum emission of the knots in the jet the free-free component apparently dominates. In the molecular lines a sub-Keplerian disk around NIRS3 about 400 au in diameter is observed. The absorption features in the molecular lines towards the central bright source may indicate an infall. The molecular line emission appears very inhomogeneous at small scales, which may indicate a small-scale clumpiness in the disk.