|Peering into the protostellar shocks: NH3 emission at high-velocities
|Ammonia and water are key molecules for determining the physical and chemical structure of star forming regions because of their large abundance variations. In shocked regions where jets driven by low-mass protostars impact the surrounding medium, the NH3 and H2O abundances undergo a dramatic enhancement due to ice grain mantle sublimation. Thanks to the very recent HIFI (CHESS KPs) observations performed towards the prototype L1157 outflow, we compared the line profiles due to the NH3(1_0-0_0) and H2O(1_10-1_01) transitions in the HIFI-band 1b. The high-spectral resolution provided by HIFI allowed us to observe a striking difference in profile between water and ammonia, with H2O emitting at definitely higher velocities. In Codella et al. (2010) we propose that such difference reflects different formation mechanisms: while NH3 is believed to be a direct product of grain surface reactions, water is enhanced by the release of the icy mantles as well as by endothermic reactions occurring in the warm (&amp;gt; 220 K) shocked gas, which convert all gaseous atomic oxygen into water. We propose here the obvious next step, i.e. to observe the NH3(1_0-0_0) line at 572.5 GHz in a sample of 8 bright low-mass outflow spots already observed in the H2O(1_10-1_01) line within the WISH KP. The analysis of the profiles in such sample will allow us to: (i) determine whether the difference in profiles is unique to L1157 or a common characteristic of chemically rich outflows; (ii) provide clues to the physical characteristics of the shock and of the pre-existing material. Such analysis will be performed by using a suite of chemical, PDR, radiative transfer and shocks models which our team has developed. The present proposal can be considered as a WISH+CHESS KPs synergy and indeed it gathers components of the teams leading the investigations of protostellar outflows in both CHESS and WISH Herschel GT-KPs.
|Diagnosing shock temperature with NH3 and H2O profiles . Gómez-Ruiz A. I. et al. . Monthly Notices of the Royal Astronomical Society, Volume 462, Issue 2, p.2203-2217 . 462 . 10.1093/mnras/stw1811 . 2016MNRAS.462.2203G ,
|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.
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|European Space Agency
|European Space Agency, 2012, OT1_ccodella_1, SPG v14.1.0. https://doi.org/10.5270/esa-wp83fib