Research Information System
The Molecular Universe, Posters from the proceedings of the 280th Symposium of the International Astronomical Union, Toledo, Spain, 30 May - 03 June 2011, pp.195, (Full Text)
During the embedded phase of pre-main sequence stellar evolution, a disk forms from the dense envelope while an accretion-driven outflow carves out a cavity within the envelope. Warm water emission in Spitzer IRS spectra of a prototypical Class 0 object, NGC 1333 IRAS 4B, has previously been linked to the envelope-disk accretion shock, with implications for how the disk forms from the envelope. However, the interpretation of unresolved emission from Class 0 objects is often complicated because both the disk/envelope and outflow/envelope interfaces can be heated by shocks and energetic photons from the central star. As part of the WISH Herschel Key Program, we obtained low-resolution Herschel/PACS far-IR spectra to assess the origin of warm H_2O emission from NGC 1333 IRAS 4B. The H_2O emission is spatially offset by ∼ 2.5%B rime%B rime (600 AU) in the direction of the blueshifted outflow from the location of the far-IR continuum emission. The spatial offset confirms that warm H_2O emission is predominantly produced in shocks and not the UV-heated cavity walls. The outflow origin is also consistent with the interpretation from high-resolution Herschel/HIFI spectra that spectrally-broad emission in lower-excitation H_2O lines is produced in shocks along the cavity walls. In contrast, high angular resolution millimeter interferometric observations of the H_218O isotopologue have indicated that the inner 50-100 AU may contribute to some of the warm H_2O emission seen with PACS. We also discuss the presence of warm H_2O emission detected from other YSOs.