ULTRAVIOLET SPECTROSCOPY OF HERBIG-HARO OBJECTS - SPATIAL STRUCTURE, SPECTROSCOPIC DIAGNOSTICS, AND VARIABILITY

Using new long-exposure (two-shift) SWP IUE spectra of HH 2G, (HH 2H HH 2A'), and HH 1F and archival spectra of (HH 2H + HH 2A') and of HH 1 we have obtained the following results: 1. For the first time we ha ve determined a separate UV spectrum of the high-excitation condensati on HH 2G. The spectrum shows similarity to that of HH 2H. However, the emission lines are fainter with respect to the continuum than in HH 2 H. The H-2 line 1505 angstrom (which is the strongest of the fluoresce nt H-2 lines, that are usually typical of low-excitation objects) seem s to be present. 2. The continuous energy distributions of HH 1F, of ( HH 2H + HH 2A') and of HH 2G are all surprisingly similar and all show in addition to a two-photon continuum a rather strong continuous emis sion in the range 1400 angstrom less than or similar to lambda less th an or similar to 1600 angstrom which is probably due to a fluorescent H-2, continuum. 3. The spatial distribution of the line emission shows separate maxima for the condensations HH 2H and HH 2A' (which are abo ut 5'' apart). The spatial distribution of the continuum emission show s, however, no maximum at HH 2A', indicating that (relative to the lin e emission) the continuum emission of this recently developed high-exc itation condensation must be weak. 4. We have attempted to separate th e partially blended Si III] 1883 and 1892 lines and to use their ratio for a determination of the electron density in the ''Si III zones'' o f the shock waves of the HH objects. We get values about 2.5-7 times l arger than those determined from the [S II] lines. 5. The time variati on of the C IV 1550 and the C III] 1909 lines has been determined for HH 1 and for (HH 2H + HH 2A') during the time interval 1980-1991. In g eneral the C IV 1550 line shows a larger variation than the C III] 190 9 line. Between 1980 and 1983 there has been a rather rapid flux incre ase for both lines in (HH 2H+HH 2A'). We ascribe this to the rapid dev elopment of the high-excitation condensation HH 2A' during these years .