[论文解读] Jet multiplicity in the proto-binary system NGC1333-IRAS4A. The detailed CALYPSO IRAM-PdBI view

G. Santangelo, C. Codella+11 more|arXiv (Cornell University)|Nov 4, 2015

Astrophysics and Star Formation Studies参考文献 56被引用 24

一句话总结

本研究利用CALYPSO巡天提供的高分辨率ALMA类亚角秒毫米波观测，分离了NGC1333-IRAS4A双星系统中两颗原恒星的喷流。结果表明，A1喷流速度高、结构紧凑且年轻（动力学 timescale ≤1000 yr），具有高速冲击发光，但无热托洛伊诺化学特征；而A2喷流速度较慢、发生进动，且与复杂有机分子相关，表明其处于更成熟的演化阶段。结果表明A1比A2更年轻，为原双星系统中差异演化提供了直接证据。

ABSTRACT

Owing to the paucity of sub-arcsecond (sub)mm observations required to probe the innermost regions of newly forming protostars, several fundamental questions are still being debated, such as the existence and coevality of close multiple systems. We study the physical and chemical properties of the jets and protostellar sources in the NGC1333-IRAS4A proto-binary system using continuum emission and molecular tracers of shocked gas. We observed NGC1333-IRAS4A in the SiO(6-5), SO(6_5-5_4), and CO(2-1) lines and the continuum emission at 1.3, 1.4, and 3 mm using the IRAM Plateau de Bure Interferometer in the framework of the CALYPSO large program. We clearly disentangle for the first time the outflow emission from the two sources A1 and A2. The two protostellar jets have very different properties: the A1 jet is faster, has a short dynamical timescale (<10^3 yr), and is associated with H2 shocked emission, whereas the A2 jet, which dominates the large-scale emission, is associated with diffuse emission, bends, and emits at slower velocities. The observed bending of the A2 jet is consistent with the change of propagation direction observed at large scale and suggests jet precession on very short timescales (~200-600 yr). In addition, a chemically rich spectrum with emission from several COMs (e.g. HCOOH, CH3OCHO, CH3OCH3) is only detected towards A2. Finally, very high-velocity shocked emission (~50 km s^-1) is observed along the A1 jet. An LTE analysis shows that SiO, SO, and H2CO abundances in the gas phase are enhanced up to (3-4)x10^{-7}, (1.4-1.7)x10^{-6}, and (3-7.9)x10^{-7}, respectively. The intrinsic different properties of the jets and driving sources in NGC1333-IRAS4A suggest different evolutionary stages for the two protostars, with A1 being younger than A2, in a very early stage of star formation previous to the hot-corino phase.

研究动机与目标

• 在亚角秒分辨率下解析NGC1333-IRAS4A原双星系统的最内层喷流结构。
• 利用分子示踪剂和连续谱发射，分离两颗原恒星A1与A2的喷流发射。
• 研究喷流与原恒星之间的物理与化学差异，以推断其演化阶段。
• 检验观测到的喷流特性是否可由年龄、质量或倾角差异来解释。
• 确定系统中是否存在热托洛伊诺化学特征，特别是A2周围的情况。

提出的方法

• 观测使用IRAM高原博尔干涉仪在1.3、1.4和3毫米波段进行，达到亚角秒角分辨率。
• 获取SiO(6–5)、SO(6 5–5 4)和CO(2–1)的谱线数据，以追踪激波气体和喷流动力学。
• 利用1.3和1.4毫米的连续谱发射识别并表征原恒星源A1与A2。
• 应用LTE分析推导激波区域中SiO、SO和H2CO的气相丰度。
• 利用空间与速度分辨的发射图分析喷流形态、动力学 timescale 和进动。
• 利用复杂有机分子（如HCOOH、CH3OCHO、CH3OCH3）的化学诊断工具评估热托洛伊诺化学的存在。

实验结果

研究问题

• RQ1 NGC1333-IRAS4A中两颗原恒星的喷流在物理上是否独立，其发射能否在亚角秒分辨率下被分离？
• RQ2 A1与A2喷流的动力学 timescale 和速度分别是多少，它们对年龄有何暗示？
• RQ3 为何仅在A2方向检测到复杂有机分子发射，而A1方向未检测到？
• RQ4 A2喷流的弯曲是否与喷流进动一致，其发生的时间尺度是多少？
• RQ5 喷流特性的差异是否可由原恒星质量、倾角或演化阶段解释？

主要发现

• A1喷流速度高、结构紧凑，动力学 timescale ≤1000 yr，表明其处于极早期演化阶段。
• A2喷流速度较慢，空间范围广（延伸超过4′），其弯曲形态与200–600 yr时间尺度的进动一致。
• 仅在A1喷流方向检测到高速激波发射（~50 km s⁻¹），表明存在强烈且近期的激波激发。
• A1喷流中SiO、SO和H2CO的气相丰度分别增强3–4 × 10⁻⁷、1.4–1.7 × 10⁻⁶和3–7.9 × 10⁻⁷。
• 仅在A2方向检测到复杂有机分子（如HCOOH、CH3OCHO、CH3OCH3），表明存在化学丰富的热托洛伊诺环境。
• A1方向未检测到可分辨的热托洛伊诺化学特征，表明其内部光度较低，演化阶段更早，支持A1比A2更年轻的假设。