THE ULTRAVIOLET SPECTRUM OF HH 24A AND ITS RELATION TO OPTICAL SPECTRA

Abstract

ABSTRACT We have studied the spectrum of the brightest part (HH 24A) of the complex Herbig-Haro object HH 24 in the short wavelength (1300 A The ultraviolet spectrum is definitely detected in three observations with exposure times of 560 to 680 min. It is, however, sufficiently faint that corrections for the IUE "artifact spectrum" (as described by Crenshaw et al.) have to be applied. The spectrum shows only a continuum or a quasi-continuum and is not comparable not to that of the typical high excitation object like HH1 or HH2 nor to that of a low excitation object like HH 43 or HH 47. The HH 24A spectrum does not resemble the spectra of the T Tauri stars observed with the IUE. It is therefore not probable that, as in the optical range, we are seeing dust scattered light from a T Tauri or similar star. Two of the three spectra show a suprisingly similar detailed wavelength structure. If we assume that this means that these structures are real then no convincing explanation of the spectrum seems yet to be available. If, on the other hand, we are satisfied with a crude interpretation of the average wavelength dependence (ignoring detailed structures of the spectrum) the interpretation as a collisionally enhanced two-photon continuum may be acceptable. A study of the spatial_ distribution of the ultraviolet continuum emission shows that this distribution is considerably wider than that of the optical forbidden line emission, e.g., the [S II]6716/6731 lines.