追踪DG Tau B喷流的运动学和物理不对称性
Tracing kinematical and physical asymmetries in the jet from DG Tau B
摘要：
恒星喷流可以是高度不对称的，并且具有多个速度分量。为了澄清射流不对称性的起源并限制其发射机制，我们研究了DG Tau B发射的气流的物理和运动学结构。在KECK望远镜采取的深光谱的分析，使我们能够推断的物理性质（电子和总密度，NE和NH，电离分数，Xe和温度，TE）和空间分布的速度分量在两个喷射叶。尘埃颗粒在射流的存在下进行了研究，估计相对于其太阳值的气相丰度的钙。在喷流的底部，谱线很宽（约100 km/s），最多可检测到三个速度分量。然而，在距离源5 "处，只有密度更大、更受激发的高速分量存在，谱线更窄（约10 - 30 km/s）。射流在速度和物理结构上都是强烈不对称的。红色瓣，较慢（~140 km/s）和更准直，呈现低电离分数（xe~0.1 - 0.4）和温度（te <5e3 K），而总密度高达~2.5e4 ccm。蓝色波瓣，速度更快（~-320 km/s），准直度更低，密度也较低（nh~1e4 ccm），但高度激发（te高达~5e4 K，xe高达0.9）。估计的质量损失率是相似的两个叶（~6 - 8e-9 Msol/yr），这表明喷射功率是可比的两侧的系统，从磁离心喷射机制，以及所观察到的不对称性是由于不同的质量负载和传播特性在一个不均匀的环境。钙强烈耗尽，表明喷流包含尘埃颗粒，因此，应该起源于磁盘的区域延伸到尘埃升华半径之外。速度越高，损耗越低，这与冲击造成的尘埃破坏相一致。
英文摘要：
Stellar jets can be highly asymmetric and have multiple velocity components. To clarify the origin of jet asymmetries and constrain their launch mechanism we study the physical and kinematical structure of the flow emitted by DG Tau B. The analysis of deep spectra taken at the KECK telescope allows us to infer the physical properties (the electron and total density, ne and nh, the ionisation fraction, xe, and the temperature, te) and the spatial distribution of the velocity components in the two jet lobes. The presence of dust grains in the jet is investigated by estimating the gas-phase abundance of calcium with respect to its solar value. At the base of the jet the lines are broad (~100 km/s) and up to three velocity components are detected. At 5" from the source, however, only the denser and more excited high velocity components survive and the lines are narrower (~10-30 km/s). The jet is strongly asymmetric both in velocity and in its physical structure. The red lobe, slower (~140 km/s) and more collimated, presents low ionisation fractions (xe~0.1-0.4) and temperatures (te<5e3 K), while the total density is up to ~2.5e4 ccm. The blue lobe, faster (~-320 km/s) and less collimated, is also less dense (nh~1e4 ccm) but highly excited (te up to ~5e4 K and xe up to 0.9). The estimated mass loss rate is similar in the two lobes (~6-8e-9 Msol/yr), suggesting that the ejection power is comparable on the two sides of the system, as expected from a magneto-centrifugal ejection mechanism, and that the observed asymmetries are due to different mass load and propagation properties in an inhomogeneous environment. Calcium is strongly depleted, indicating that the jet contains dust grains and, therefore, should originate from a region of the disk extending beyond the dust sublimation radius. The depletion is lower for higher velocities, consistent with dust destruction by shocks.
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