Accretion and ejection properties of embedded protostars: the case of HH26, HH34 and HH46 IRS

Abstract

We present the results of a near-IR spectroscopic analysis on 3 young embedded sources (HH26IRS, HH34IRS and HH46IRS) belonging to different star-forming regions and displaying well developed jet structures. The aim is to investigate the source accretion and ejection properties and their connection. We used VLT-ISAAC spectra (R~9000, H and K bands) to derive in a self-consistent way parameters like the star luminosity, the accretion luminosity and the mass accretion rate. Mass loss rates have also been estimated from the analysis of different emission features. The spectra present several emission lines but no photospheric features in absorption, indicating a large veiling in H and K. We detected features commonly observed in jet-driving sources (HI,[FeII],H_2,CO) and also a number of emission lines due to permitted atomic transitions, like NaI and TiI. The NaI 2.2um doublet is observed along with CO(2-0) band-head emission, indicating a common origin in an inner gaseous disc heated by accretion. We find that accretion provides ~50% and ~80% of the bolometric luminosity in HH26IRS and HH34IRS, as expected for accreting young objects.Mass accretion and loss rates spanning 10^-8 - 10^-6 Msun/yr have been measured. The derived Mloss/Macc is ~0.01 for HH26IRS and HH34IRS, and >0.1 for HH46IRS, numbers that are in the range of values predicted by MHD jet-launching models and found in the most active classical T Tauri stars. Comparison with other similar studies seems to indicate that Class Is actually having accretion- dominated luminosities are a limited number. Although the analysed sample is small, we tentatively present some criteria to characterise such sources. Studies like the one presented here but on larger samples of candidates should be performed in order to test and refine these criteria.