INFRARED-SPECTROSCOPY OF HERBIG-HARO ENERGY-SOURCES

Herbig-Haro energy sources are, as a class, among the youngest stars k nown. Based on the presence of multiple working surfaces in many HH fl ows, it has previously been argued that repetitive FU Orionis disk acc retion events power the Herbiag-Haro flows emanating from newborn star s. Since the dynamical time scales for HH flows are mostly rather long er than the expected time scales for high luminosity FU Orionis stars to decay to their low (presumably T Tauri) states, it follows that a f raction - but certainly not all - of HH energy sources might show FU O rionis characteristics. All but one of the known FU Crionis stars for which near-infrared spectroscopy is available show pronounced 2.3 mu m CO absorption bands; the one exception shows very weak CO emission. A part from FU Orionis stars, deep CO absorption is seen only in the pho tospheric spectra of late K or M type stars. We present 2.0-2.5 mu m s pectroscopy of 14 Herbig-Haro energy sources plus, for comparison, of 4 known FU Orionis stars. Of these 14 HH sources, 9 have been delibera tely selected to have luminosities equal or higher than that (28 L.) o f the lowest luminosity FU Orionis star known, L1551 IRS5. Among these 9 more luminous sources, 5 have CO absorption, 2 have CO emission, an d 2 have continuous spectra. Among the five lower luminosity sources, 1 has CO absorption, 2 have CO emission and 2 show continuous spectra. Altogether,it appears that tile majority of the high luminosity HH so urces observed are likely to be presently in elevated FU Orionis state s. (C) 1997 American Astronomical Society. [S0004-6256(97)02412-6].