赫比格-哈罗天体(HH天体)包含了有关原恒星吸积和抛射过程的许多重要信息。HH天体高分辨观测研究取得了一系列新进展：分辨出激波峰面、马赫盘和辐射冷却区；分辨出喷流节点的结构，发现它们大多是内工作面，而不是由Kelvin-Helmholtz不稳定性所产生的斜激波；发现喷流宽度随到激发源距离的减小仅缓慢减小，对喷流的准直和加速模型提供了限制条件；HH天体在小尺度上尚有复杂的激发结构。对这些进展进行了评述。%Herbig-Haro objects and jets contain a lot of information concerning the accretion and ejection processes of protostars. The observational results fostered from the unprecedentedly high spatial resolution of Hubble Space Telescope (HST) are briefly reviewed. Bow shocks and Mach disks within the working surfaces of HH objects are fully resolved for the first time. The bright[S Ⅱ]knots on the working surfaces are found to be displaced from the bright Ha arcs located at the leading edges of bow shocks and the distances between them are identified as the "cooling distances", which in the HH 111V case is≈0.5"(230AU). The structures of the internal working surfaces within the jet bodies are also resolved. The three extended HH jets observed by HST, HH 34, HH 46/47, and HH 111, all display evidences of variations in jet velocity and direction, which supports the scenario that the knots within HH jets are the internal working surfaces driven by the time-variable eruptions of the exciting sources. Measurements of jet width at distance as close as 0.25"(35AU)to the sources reveal that the opening angles of jets decrease as the distances to the sources increase, which puts a strong constraint on models of jet collimation and acceleration. With HST observations of XZ Tau in two epochs we are witnessing the initial formation of a cooling zone in the front of an extremely young bubble with a dynamic age of≈23 yr. The discovery of complex excitation structures of a typical scale of 0.15"in HH 2A and 2H has important implications for the shock wave interpretation of HH objects.
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