COLD DUST AROUND HERBIG-HARO ENERGY-SOURCES - A 1300 MU-M SURVEY

We have observed 59 young stars associated with Herbig-Haro objects in the continuum at 1300 mum, and detected 5 3 of them, corresponding to the very high detection rate of 90%. The signals are generally large, of the order of several hundred milliJansky. High extinction sources have on average more than twice as large a flux as low extinction sour ces. Translating the 1300 mum measurements into total gas and dust mas ses, under appropriate assumptions, we find that Herbig-Haro energy so urces are surrounded by considerable amounts of cold circumstellar mat erial, typically in the range from a few tenths to several solar masse s. We have additionally observed 14 sources at 870 mum, and derive a s pectral index m = 1.0 +/- 0.4, assuming a typical dust temperature of 36K, determined by additionally employing IRAS data. Such a spectral i ndex suggests either the presence of grains larger than in the interst ellar medium and/or material with large optical depth. A comparison wi th 1300 mum fluxes of T Tauri stars from the literature shows that T T auri stars and Herbig-Haro energy sources have very different distribu tions in a histogram of fluxes scaled to a given distance: the Herbig- Haro energy sources have fluxes more than an order of magnitude larger than the T Tauri stars. From their IRAS energy distributions it follo ws that almost all Herbig-Haro energy sources are class I sources. The large difference observed between Herbig-Haro energy sources and T Ta uri stars thus suggests that the major changes in the circumstellar en vironment of a young low mass star occurs within its first few hundred thousand years, which is a likely upper limit for the age of class I sources. We observe a clear relation between bolometric luminosity and 1300 mum flux for our objects, suggesting that the more massive a cir cumstellar environment is, the larger is the accretion rate towards th e star likely to be.