H2 active jets in the near IR as a probe of protostellar evolution

Details H2 active jets in the near IR as a probe of protostellar evolution H2 active jets in the near IR as a probe of protostellar evolution

Apr 2006

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2006a%26a...449.1077c&link_type=abstract

Astronomy and Astrophysics, Volume 449, Issue 3, April III 2006, pp.1077-1088

Astronomy and Astrophysics

Astrophysics

55

Stars: Circumstellar Matter, Ism: Jets And Outflows, Ism: Kinematics And Dynamics, Ism: Lines And Bands

Scientific paper

We present an in-depth near-IR analysis of a sample of H2 outflows from young embedded sources to compare the physical properties and cooling mechanisms of the different flows. The sample comprises 23 outflows driven by Class 0 and I sources having low-intermediate luminosity. We have obtained narrow band images in H2 2.12 μm and [Fe II] 1.64 μm and spectroscopic observations in the range 1-2.5 μm. From [Fe II] images we detected spots of ionized gas in ~74% of the outflows which in some cases indicate the presence of embedded HH-like objects. H2 line ratios have been used to estimate the visual extinction and average temperature of the molecular gas. Av values range from ~2 to ~15 mag; average temperatures range between ~2000 and ~4000 K. In several knots, however, a stratification of temperatures is found with maximum values up to 5000 K. Such a stratification is more commonly observed in those knots which also show [Fe II] emission, while a thermalized gas at a single temperature is generally found in knots emitting only in molecular lines. Combining narrow band imaging (H2, 2.12 μm and [Fe II], 1.64 μm) with the parameters derived from the spectroscopic analysis, we are able to measure the total luminosity of the H2 and [Fe II}] shocked regions (L_H2 and L[Fe II]) in each flow. H2 is the major NIR coolant with an average L_H_2/L[Fe II] ratio of ~102. We find that ~83% of the sources have a L_H_2/L_bol ratio ~0.04, irrespective of the Class of the driving source, while a smaller group of sources (mostly Class I) have L_H_2/L_bol an order of magnitude smaller. Such a separation reveals the non-homogeneous behaviour of Class I, where sources with very different outflow activity can be found. This is consistent with other studies showing that among Class I one can find objects with different accretion properties, and it demonstrates that the H2 power in the jet can be a powerful tool to identify the most active sources among the objects of this class.

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