|Solving the puzzle of water excitation in shocks
|Water is a highly complementary diagnostic to the commonly used CO molecule. It has a central role in protostellar environments and in outflow shocks, being one of the main coolants and the most sensitive to local conditions. As part of the WISH key program, a survey of several H2O lines at different excitation has been performed with HIFI at two selected shock spots in the bright L1448 and L1157 outflows. These observations and their analysis have given unexpected results, that contrast with current models of water emission in shocks. However, the validity of these results needs to be checked with suited high S-N observations, allowing to remove some of the free-parameters of the line excitation modeling and to derive water abundance. The goal of this proposal is to clarify the controversial issues raised by these previous observations by mapping with HIFI a 40 arcsec area covering two shock positions along the NGC1333-IRAS4A outflow, identified as very bright in H2O from our PACS map at 1670 GHz, in key spectral transitions of H2O and CO. These observations will provide unprecedented constraints on the physical and chemical properties of the gas associated with the water emission, as a function of velocity, and on the properties of the shock at the origin of the emission. In particular, mapping the H2O lines will allow us to remove the uncertainty originated by the largely different beams of the observed transitions. The CO(16-15) will be also observed: this line comes from the same high excitation gas as that traced by H2O and thus will provide a tool to derive an H2O-CO abundance ratio much more reliable than what is obtained with the low-J CO transitions observed from ground. We point out that it is crucial to solve the issue of water excitation in shocks before the end of the Herschel mission, in order to correctly interpret all the data acquired on H2O in outflows by Herschel and provide r...eliable constraints on water abundances and shock dynamics.
|Oxygen budget in low-mass protostars: the NGC 1333-IRAS4A R1 shock observed in [O I] at 63 μm with SOFIA-GREAT . Kristensen L. E. et al. . Astronomy & Astrophysics, Volume 601, id.L4, 5 pp. . 601 . 10.1051/0004-6361/201630310 . 2017A&A...601L...4K ,
Water distribution in shocked regions of the NGC 1333-IRAS 4A protostellar outflow . Santangelo G. et al. . Astronomy & Astrophysics, Volume 568, id.A125, 12 pp. . 568 . 10.1051/0004-6361/201424034 . 2014A&A...568A.125S ,
|Herschel was launched on 14 May 2009! It is the fourth 'cornerstone' mission in the ESA science programme. With a 3.5 m Cassegrain telescope it is the largest space telescope ever launched. It is performing photometry and spectroscopy in approximately the 55-671 µm range, bridging the gap between earlier infrared space missions and groundbased facilities.
|Publisher And Registrant
|European Space Agency
|European Space Agency, 2013, OT2_gsantang_1, SPG v14.1.0. https://doi.org/10.5270/esa-rh0fmqt